[
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "• holistic battery metric analysis correlating sei kinetics and storage mechanisms in ether and carbonate ester electrolytes. • intercalation mechanism dominates in ether electrolyte beneficial for high rate performance and high cycle stability. • pore-filling mechanism is dominant for carbonate ester leading to poor rate performance and cycle stability. • hard carbon shows a reversible capacity of 352 mah g⁻1 with 91 % retention after 1000 cycles at 1c in ether electrolyte. • high-rate performa"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "high rate capability for sodium-ion batteries (sibs). however, higher first-cycle efficiency and cycling stability are needed to realize the full commercial potential of hc. herein, the battery metrics and the na+ storage mechanism of hard carbon in ether and carbonate electrolytes are explored using ex-situ microscopic, spectroscopic, and electrochemical techniques. the commercial hc shows an excellent first-cycle efficiency of 79 % and capacity retention of 91 % after 1000 cycles at 1c in ethe"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "ether-based electrolyte. a full cell demonstrates the high-rate performance of ether electrolytes for sibs, delivering a high energy density of 265 wh kg− 1 at an average operating potential of ~3.36 v in ether electrolytes. 1. introduction producing less costly and more efficient energy storage systems is crucial for using renewable energy sources [1]. the abundance and affordability of sodium are leading researchers to investigate sibs as a potential long-term solution for intelligent electric"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "that hinder their widespread commercial prospects. while efforts to optimize intrinsic properties by micro-structure design or heteroatom doping have been made, they alone cannot sufficiently enhance hc anode performance [5]. establishing a robust interface between hc and the electrolyte, sei layer, is crucial for improving hc anode performance, and carbonate electrolytes are found wanting in forming a stable sei layer. the carbonate electrolytes dimethyl carbonate (dmc), propylene carbonate (pc"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "sei layer has limited rate capacity because of its inhomogeneous inorganic-organic hybrid structure, which inhibits na+ transport at the interface, leading to unstable cycling performance and poor ice [13,14]. however, the sei layer formed by ethers is more homogeneous, robust, and thin, leading to improved ice [15,16]. the inorganic-rich structure of ether-sei allows for efficient na+ transfer, enhancing rate performance and providing better stability for hc anodes during cycling [17]. sei-comp"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "al. studied the na- storage mechanism in hc in carbonate and ether electrolytes [20], revealing a three-stage mechanism for both the system and a better ice in ether-based electrolytes (81.14 % at 0.1c). liu et al. revealed that the hc follows the adsorption-insertion-pore-filling mechanism in ether-based electrolytes with an ice of 77.3 % at 20 ma g− 1, and only the adsorption-pore-filling mechanism is observed for the carbonate electrolytes [21]. along with the ambiguity in the storage mechani"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "structure and morphology of the sei layers formed by both the electrolyte systems were established using xps, xps-depth profiling, hr-tem, hr-sem, and afm. in addition, we focused on the different stages of the charge- discharge process to investigate the reason behind the differential kinetics found between ether- and carbonate ester-based electrolytes in hc electrodes. ex-situ studies using xps, xrd, hr-tem, epr, hr-sem, multiphysics simulations, and electrochemical techniques holistically exa"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 0,
    "chunk_index": 7,
    "text": "0.6 ma. raman spectra were acquired with a horiba t6400 spectrometer with an ar-krypton mixed ion gas * corresponding author. e-mail address: sreeraj@iitkgp.ac.in (s. puravankara). https://doi.org/10.1016/j.jpowsour.2025.236234 received 22 november 2024; received in revised form 4 january 2025; accepted 12 january 2025 available online 22 january 2025 0378-7753/© 2025 elsevier b.v. all rights are reserved, including those for text and data mining, ai training, and similar technologies."
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 2 laser (wavelength 532 nm in the range 1000–2000 cm− 1). thermo fisher scientific instruments were used to record ft-ir (fourier transform infrared spectrometer) spectra. using a bruker elexsys e580 spectrometer, electron paramagnetic resonance (epr) spectra were acquired at room temperature with a microwave power of 15 mw and modulation amplitude of 5 g. hr-tem (tem, jeol jem 2100) with saed, fe-sem with (merlin, zeiss gemini 2), and a"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "prepared by mixing hard carbon (80 %), super-p black carbon (10 %), polyvinylidene difluoride (pvdf) (10 %), and n-methyl-2-pyrrolidone (nmp) solvent uniformly. after that, this mixture was spread out over a thin layer of aluminum (al) foil and dried in a vacuum oven at 90 ◦c for 12 h. the resultant coated electrode had a mass loading of around ~2.2 mg cm− 2. the half-cells (cr2032 coin cell) were assembled in an argon-filled glovebox (m-braun, h2o < 0.5 ppm; o2 < 0.5 ppm), with sodium metal ser"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "(cv) were performed in the voltage range of 1.5 v–0.005 v. full cell was made using commercial o3-type nani0.4fe0.2mn0.4o2 (nfm) as cathode and hc as anode in the same electrolyte in 4.0–2.0 v range. the gitt (galvanostatic intermittent titration technique) was carried out in half- cell, giving a pulse current of 30 ma g− 1 for 20 min and a 1h resting period. eis (electrochemical impedance spectroscopy measurements) were performed (frequency range was 100 mhz − 10 khz) using a bio- logic (bcs 81"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "hr-sem and tem images (fig. 1a and fig. s1) revealed that the commercial hard carbon (hc_c) (haycarb) displayed irregular- shaped particles. from the hr-tem image (fig. 1b), the graphite layer spacing of hc_c was found to be ~0.387 nm (inset of fig. 1b). large interlayer spacing is beneficial for containing more na-ion and higher capacity [22,23]. hc_c composed a bet surface area of 127.5 m2/g as obtained from the n2 adsorption-desorption isotherm (fig. s2a), showing dominant mesoporosity in the"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 3 the saxs (small angle x-ray scattering) results provide valuable insights into the porosity of hard carbon materials, crucial for their application in batteries (fig. 1c). saxs profile at the lower scattering vector reveals the presence of larger closed pores within the hard carbon structure. also, the missing plateau in the saxs pattern indicates the existence of a mesoporous structure. the mesoporous structure facilitates electrolyte"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "peaks at 23.06◦ ((002) plane) and 43.56◦ ((100) plane) (fig. 1d). the calculated interlayer spacing from xrd is ~0.385 nm, which matches tem results. raman spectroscopy of hc_c indicated d1 and g peaks at 1343 and 1581 cm− 1, respectively (fig. 1e). the id1/ig ratio of hc_c is 1.14, implying a higher degree of defects associated with sodium adsorption [27]. fig. 1f shows high-resolution c-1s xps spectra of hc_c containing c=c/c-c, c-o, and c=o groups [28]. the hc_c structure is well-suited for i"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "446 mah g− 1 and 352.3 mah g− 1 in the ether electrolyte and 500 mah g− 1and 327 mah g− 1 in the carbonate electrolyte, respectively, at 30 ma g− 1. table s1 compares the electrochemical performance of different reported hard carbon with this work. however, the two electrolytes had noticeable differences in ice and plateau capacity contributions. ether electrolytes demonstrated higher ice fig. 1. (a) fe-sem image, (b) hr-tem image of hc_c, inset of (b) shows the intensity profile generated from "
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 4 values (79 %) than carbonate electrolytes (65 %) associated with the formation of a more stable sei layer on the surface of hc in ether electrolytes, suppressing side reactions such as electrolyte decomposition during the initial cycle, as discussed later [30]. the superior ice in ether electrolyte is critical for reducing the irreversibility in the first cycle in full cells for commercial applications of sibs. as shown in fig. 2c, the"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "at the same current densities. the rate performance of the hc_c anode with other carbonate and ether electrolytes using the napf6 salt is shown in fig. s4. up to 1c, the slope and plateau capacity contribution from the two electrolytes were the same; above 1c, the plateau capacity decreases drastically in carbonate electrolytes than ether electrolytes (figs. s5a and s5b). the reversible capacity of the hard carbon is higher in ether electrolytes than carbonate electrolytes at all c-rates, and th"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "region, even under high current densities. the plateau capacity is higher in carbonate electrolytes at a low rate (<1c), and the slope capacity increases for higher c-rates (>1c). the low intercalation capacity of hc_c in ether electrolytes is evident from the c-rate studies. fig. s5c quantifies the slope and plateau capacity contribution of hc_c in ether and carbonate electrolytes at different rates. the plateau capacity contribution to the total capacity is higher in ether than in carbonate el"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "in (a) ether (1m napf6 in degdme) and (b) carbonate (1m napf6 in ec:dec) electrolytes. (c) rate performance of hc_c at different c- rates (d) comparing the sloping (capacity >0.1 v) and plateau (capacity <0.1 v) capacity regions of hc_c in both electrolytes at different current densities. cyclic stability of hc_c anode for (e) 120 cycles at 0.1c, and (f) 1000 cycles at 1c rate for both the electrolytes."
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 5 electrode exhibited a capacity of 244.8 mah g− 1 (91 % retention) and 131 mah g− 1 (86 % retention) in the ether and carbonate electrolytes, respectively (fig. 2f). ether electrolytes exhibited better capacity retention over extended cycling than carbonate electrolytes in sibs from reduced electrolyte decomposition and sei growth in ether electrolytes, leading to lower irreversible capacity loss and improved electrode stability over ti"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "from the sei formation due to the electrolyte reduction. the carbonate-ester electrolyte decomposition is more substantial than the ether counterpart, as evidenced by the ice values. the ether-based electrolyte shows higher peak currents due to the enhanced ionic conductivity [30]. a dominant capacitive storage mechanism for ether electrolytes and a diffusion-controlled mechanism for carbonate are evident from the profile shapes of the cv curves. the cv curves were recorded at various scan rates"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "a and b. the ideal b values are 1 for solely capacitive processes and 0.5 for the systems under diffusion control. according to fig. s6 (c), hc_c, the computed b-values for ether and carbonate are 0.63 and 0.54, respectively, suggesting pseudo-capacitive electrochemical activity in both systems with a dominant capacitive and diffusion-controlled contribution for ether and carbonate, respectively [30]. the capacitive contribution increases as the scan rate increases, and for a lower scan rate, di"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 6 electrolytes [21] (figs. s7c and s7d). randles sevcik’s equation [31,32] was used to calculate the diffusion coefficients (dna+ ) of sodium –ions in both electrolytes at different potentials [33]. the obtained diffusion coefficient for ether and carbonate electrolyte at a scan rate of 0.1 mv s− 1 were 9.09 × 10− 10 and 10.23 × 10− 11 cm2 s− 1, respectively, which complements the diffusion coefficient values using gitt measurements. the"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "the area of the electrodes, and δeτ represents the potentials difference, δes represents the voltage difference. the vm value was 1.94 g cm− 3 for the hc [34]. in this study, gitt data highlights a significant contrast in na+ ion diffusion coefficients between the plateau and sloping regions. this discrepancy underscores the influence of electrode/electrolyte affinity and sei (solid-electrolyte interface) resistance on sodium-storage kinetics. for instance, this study observed that the na+-diffu"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "adsorption, where ions diffuse faster than intercalation. in contrast, a lower dna + value suggests diffusion-limited insertion in the plateau region. to differentiate the insertion and pore-filling mechanism, further sodiation was done at low potentials. after the u-turn point, the dna + value remains stable, indicating a pore-filling mechanism similar to the previous observation [34]. the established three storage mechanisms are consistent for both electrolyte systems. in the case of ether ele"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "electrolyte, where diffusion is limited to 2.5 μm, at t = 30 min, na-ions reach a concentration of 0.5 m up to 7.5 μm (fig. 3e). as observed at t = 120 min, ether electrolytes have a larger capacity due to the enhanced na-ion concentration. within 120 min of discharge, the na-ion concentration in ether approaches a steady state, and in 50 % of the electrode depth, a concentration of 0.5 m is reached. even at higher c-rates, na-ion concentration remained higher in the ether electrolyte, facilitat"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "showed, including a semicircle in the high- frequency region and a finite warburg diffusion in the low-frequency region. an equivalent circuit (inset of fig. s8a) was used to represent the physical electrochemical processes in the hc_c in both electrolyte systems. w1 is due to the warburg diffusion of na + ions in the bulk hc, and ra is the ohmic resistance of the cell. rb and rc are the sei layer and charge-transfer resistances in hc electrodes parallel with the interfacial capacitance. ether-b"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 5,
    "text": "275 ω after ten cycles, suggesting a continuously growing and unstable sei layer after the first cycle. in contrast, the ether-based electrolyte exhibited a relatively stable semicircle diameter over multiple cycles, with an initial rb + rc value of approximately 45 ω that increased slightly to 73 ω after ten cycles. this stability suggests that the sei formed in the ether-based electrolyte is more robust and consistent, contributing to steady ionic conductivity and charge transfer at the electr"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 6,
    "text": "of fig. 2a and b. the hc_c anode in ether electrolytes contributes less adsorption capacity of 32 % to sibs in the 1.5–0.14 v voltage range, but it dominates the (de)intercalation capacity in the 0.14–0.05 v (44 %) and pore (de)filling capacity was 24 % in 0.05–0.005 v. on the other hand, in carbonate electrolytes, the (de) adsorption capacity contribution was 34 % (1.5–0.14 v), (de)intercalation capacity in the 0.14–0.04 v (32 %) and pore (de)filling capacity was 34 % in 0.04–0.005 v. the inves"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 7,
    "text": "of hc_c, including its ice and cycle stability, is closely linked to the properties of the sei films. the xps analysis of the electrode films provided valuable insights into their composition. the discharged hc_c electrodes exhibited c1s, f1s, and o1s peaks in both ether and carbonate electrolytes. the deconvoluted c1s spectrum exhibits three peaks located at 284.62 ev (c-c/c-h), 285.86 ev (c-o), and 288.82 ev (o-c=o) in ether electrolytes (fig. 4a) [37]. on the other hand, in the case of carbon"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 5,
    "chunk_index": 8,
    "text": "electrochemical conditions. during cycling, the solid electrolyte interphase (sei) formed in ether electrolytes is primarily composed of inorganic components (e.g., naf, na2co3, and na3po4), with significantly lower contributions from organic decomposition products that typically contain c=o bonds. previous studies have observed ether electrolytes generating thinner and uniform seis, which are predominantly inorganic in nature [20]. f-1s spectra can be fitted into two peaks for both the electrol"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 7 (1st cycle, discharged state). sample showed a higher ratio of na-f components compared to the carbonate-ester sample (fig. 4c and d). na-f plays a crucial role in the stability of the sei layer and the decomposition of electrolytes. there is a peak shift in the higher binding energy in carbonate electrolytes for c1s, o1s, and f1s spectra, which could be assigned to the more complex environment than carbonate electrolytes. in the xps r"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "of the sei layer is lower for the ether- based electrolyte. fig. s10a also reveals that the ratio of na-f components in the sei was more prominent in the ether-based sample, rendering a more stable sei layer. fig. s10b shows the valence band xps spectra of the hc_c sample in carbonate and ether electrolytes. taking into account the location of ef at zero binding energy, the valence band edges (evb) of the ether electrode were found to be 2.42 ev, whereas that of the carbonate electrode was 1.06 "
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 8 below 10 nm of the surface, naf is increasing in ether electrolytes, indicating a robust and uniform sei layer and improved cycle stability (fig. 5c–f). in carbonate electrolytes, the intensity of c-o, o-c=o, and roco2na peaks are comparatively higher than ether electrolytes, giving rise to inhomogeneous organic and inorganic components distribution at greater depth from the surface (fig. 5g, j, 5h, 5k). the proportion of organic compo"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "than the carbonate-ester electrolyte, contributing to the enhanced stability and lower impedance observed in the eis results. hr-tem and afm techniques were also used to characterize the sei morphology. hr-tem images in fig. 6a, b revealed that hc_c in the ether electrolyte had a much thinner sei film (about 14.3 nm) compared to the carbonate electrolyte (about 29.5 nm). the ether-based system reduces electrolyte consumption at the hc interface, which improves ice and makes na+ transport across "
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "xps depth-profiling: high-resolution xps spectra at different etching depths of 0 and 10 nm for c 1s (a and d), o 1s (b and e), and f 1s (c and f) of sei components on the hc_c anode after second discharge in ether electrolytes at 0.1c. high-resolution xps spectra at different etching depths of 0 and 10 nm for c 1s (g and j), o 1s (h and k), and f 1s (i and l) of sei components on the hc_c anode after second discharge in carbonate electrolytes at 0.1c. fig. 6. hr-tem images of hc_c electrodes af"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 9 ether and (d) carbonate electrolytes. this uniform sei morphology likely contributes to the enhanced performance of the hc anode, including improved cycling durability and rate capability [21]. 3.4. revealing the storage mechanism to further confirm the charge storage mechanism in commercial hard carbon (hc_c) using two different electrolytes, we conducted ex- situ raman spectroscopy to detect changes caused by na-insertion throughout "
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "electrode was discharged up to 0.005 v, but the intensity of those two bands changed. id/ig increases up to 0.1 v discharge state (1.012), indicating that the c─c stretching mode was somewhat unaffected by the sloping region’s adsorption-dominated sodiation process [35,41–44]. further insertion results in a decreased id/ig value (1.005), implying insertion-assisted pore-filling. the unstable na graphite intercalation compound (na-gic’s) formation could be the reason for the non- shifting g-bands"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "(averaging different regions of the tem image as shown by the dotted red box) following the insertion of na+ into graphitic layers for both electrolytes [45,46]. the mechanisms involving na-intercalation were further clarified using ftir spectroscopy (fig. s13). we examined the electrode in its raw and fully discharged states by ftir, with additional characterization of the ether-based electrolyte for comparison. the c-o-c ether bond peak in the electrode after it was fully discharged suggested "
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 10 the formation of metallic clusters was further supported by applying ex- situ epr, a powerful technique for locating unpaired electrons (fig. 7c and d). ex-situ epr revealed more about the broadening of the spectra and formation of na metal clusters from pore-filling. the pristine electrode (pe) has a distinct symmetric epr spectrum. the symmetric epr signal broadens and intensifies when the electrode is discharged to 0.1v because the"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "results in a dysonian asymmetric epr line. the metal cluster formation through pore filling results in a very narrow dysonian epr peak of the 0.005v discharged electrode [47]. the a/b ratio (peak intensity ratio) is higher in carbonate electrolytes (1.14) (fig. 7d) compared to ether electrolytes (1.09) (fig. 7c), indicating more pore-filling in carbonate electrolytes [48]. the linewidth narrows when the electrode is charged, and the intensity of the peaks decreases, as observed for the pristine "
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "higher binding energy in carbonate electrolytes (δeb.e. = 0.98 ev) (fig. 7f) than ether electrolytes (δeb.e. = 0.75 ev) (fig. 7e) concerning the 0.1 v discharged state, validating the more pore-filling for carbonate electrolytes in concurrence with the experimental epr results. the epr, xps, gitt, and charge-discharge profile data indicate more insertion in ether and more pore- filling in carbonate electrolytes of na+-ions in hc_c. ex-situ xrd was employed to analyze the structural changes of ha"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 11 xrd patterns revealed a broadening and shifting of (002) diffraction peak at a lower angle, indicating the amorphization of the hard carbon structure upon sodiation in both the electrolyte systems. upon desodiation, the (002) peak shifts back to higher angles, showing the reversibility of na-ion insertion/deinsertion. this shift is higher in ether electrolytes (fig. s14a) than in carbonate electrolytes (fig. s14b), indicating more int"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "b) than carbonate electrolytes (fig. 8c and d), and the clumped particles do not alter even after repeated charging and discharging cycles and are more compact in the case of the ether system [53]. 3.5. full cell a full cell was fabricated by combining the commercial o3- nani0.4fe0.2mn0.4o2 (nfm) cathode with the hc_c anode to produce full cells employing both electrolytes. the electrochemical performance of the cathode in the half-cell with ether electrolyte and the carbonate system is shown in"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "s. manna et al. journal of power sources 631 (2025) 236234 12 ether electrolytes at a current rate of 0.1c is shown in fig. 8a. based on the cathode mass with ice 63 %, the cell has a specific 79 mah g− 1 capacity for the initial cycle and shows an energy density of 265 wh kg− 1 (the full cell operates at 3.36 v). the charge-discharge curve of a full cell utilizing carbonate electrolytes at a current rate of 0.1c is depicted in fig. 8b. based on the cathode mass and an ice 55 %, the specific cap"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "48 mah g− 1, and the carbonate system delivers only 39 mah g− 1 of reversible capacity. the ether-based system outperforms the carbonate- ester electrolyte at all c-rates. the full cell delivers 63 mah g− 1 and 58 mah g− 1 capacity with ether and carbonate electrolyte at 0.1c (fig. 8d) and at 1c rate, and the ether electrolyte outperforms the carbonate system with improved retention for the ether-based electrolyte especially at 1c rate for the initial cycles (fig. 8e). 4. conclusions in conclusi"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "sei formation in ether electrolytes contribute to their superior electrochemical performance and cyclability. xps-depth profiling shows that the sei contains more inorganic components in the inner layer of ether electrolyte, resulting in a robust, favorable, and highly conducting sei layer. combining electrochemistry with the other ex-situ techniques once could reaffirm the storage process for both the ether and carbonate electrolyte involving the adsorption of na+ ions in the slope region of hc"
  },
  {
    "source_pdf": "Correlating_storage_mechanism_and_solid_electrolyte_interphase_kinetics_for_high_rate_performance_of_hard_carbon_anode_in_ether_electrolytes_for_sodium_ion_batteries_Sanchita_Manna_Prakhar_Verma.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "at an average operating potential of ~3.36 v in ether electrolyte, outperforming the carbonate electrolyte system with high-rate capabilities and capacity retentions. the study underscores the importance of electrolyte selection in optimizing the performance of hard carbon-based sibs and provides valuable insights for developing next- generation energy storage devices with improved battery metrics."
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 1 the rise in environmental pollution originated from the burning of fossil fuels, and concerns about depleting these non-durable energy resources have recently prompted scientists to quest for clean and sustainable energy resources. among the encouraging candidates, renewable energy resources, for instance, solar energy, wind energy, and hydroelectric power, have drawn considerable attention [1–4]. indeed, the trans"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "barriers have hampered the application of libs in large-scale grid storage. first of all, lithium sources are limited to a few countries, giving rise to concerns about the lithium supply due to its low abundance in the earth's crust [3,8]. secondly, libs encounter high costs, sustainability concerns, and safety issues [9–11]. much effort has been made to explore alternatives to libs like sodium-ion batteries [12], lithium-sulfur batteries [13], metal-air batteries [14], redox flow batteries [15]"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "its affordable cost and ability to hinder alloy formation with sodium [3]. the higher reduction potential of sodium (e0 = −2.714 v) compared to the lithium (e0 = −3.045 v) allows sibs to operate at lower voltages, which subsequently enables the usage of electrolytes with lower decomposition potentials [8,9,18,19]. another advantage of sibs is their capability to discharge to zero volts since they have no over-discharge characteristics [9,18]. as the number of publications on sibs from 2000 to 20"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "with sibs shows an exponential growth (see fig. 1b). the years of uncertainty ranging from 2018 to 2020 are taking for the patenting process to be completed. because of some restrictions on publishing facing the owners, patent filing applications per year may be published two years after the first patent application is filed. it is worth mentioning that 33.44% of the filed patents were granted by at least one organization, indicating these patents' reliability and validity. according to fig. 1c,"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 2 like libs, sodium-ion configurations are composed of anode and cathode, soaked in an electrolyte and disconnected by a separator. moreover, their performance is similar to libs, but instead of li+ ions, na+ ions participate in charging and discharging processes. a positive electrode (cathode) undergoes oxidation during charging, by which na+ ions and electrons are produced. in this process, na+ ions move towards th"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "[21]. on the other hand, hard carbon (hc) and na3v2(po4)3 (nvp) are respectively highly-used anode and cathode in sibs [22,23]. microporous membrane separators made of polyethylene (pe), polypropylene (pp), or their combinations are widely adopted in libs. glass fibers (gfs) are the most common separator in sibs [24,25]. unlike in sibs where al foils are used as current collector for both anode and cathode, copper (cu) and al foils are respectively adopted as current collector for anode and cath"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "of an additive does not exceed 5% either by weight or by volume. at the same time, its presence can substantially improve the cyclability and cycle life of libs [28,29]. based on their function, additives in libs are classified into two main groups, including function- improving additives and safety protection additives [29–31]. similarly, the cycling deterioration and safety concerns in sibs can be diminished by adding small amounts of additives to the electrolyte [32,33]. despite a host of com"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "used in sibs. 1. function-improving additives solid electrolyte interphase (sei) and cathode electrolyte interphase (cei) are two main types of function-improving additives [30]. both of them are responsible for stabilizing the electrode-electrolyte interfaces [34,35]. for this purpose, the electrochemical stability window (eg) of the additives should be within the highest occupied molecular orbital (homo)-the lowest unoccupied molecular orbital (lumo) gap of the electrolyte components. sei addi"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 3 would avoid the further degradation of the solvent and salt [39,40]. the higher homo energy levels (or correspondingly lower oxidation potentials) of additives with respect to the electrolyte solvents (fig. 4) is an integral factor for forming the cei layer at the cathode [41,42]. in the following sections, the most critical function-improving additives used in sibs are listed and investigated. 1.1. fluoroethylene "
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "of 5 vol % fec to the electrolyte enabled the nfp/c electrode to have a good performance at the 1100th cycle at a discharge rate of 5 c. the nfp/c electrodes with and without fec showed capacity retentions of 89.6% and 82.8%, respectively, highlighting the fec additive's importance for the battery's long-life cycling [45]. esters (carbonates), as commonplace solvents in sibs, suffer from the formation of thicker sei layers compared to other solvents, bringing about the low initial coulombic effi"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "schematic illustration of surface morphology of hc particles without and with sei layer formed at different charging rates in ester and ether-based electrolytes, respectively. (c, d) cycling stability of the hc-cnt electrodes in ester and ether-based electrolytes, respectively at current density of 100 a/g. reproduced with permission of ref. [46], copyright 2019 american chemical society. (e) tem images of fesb-tic-c composite anodes before and after 100 cycles. the red regions show the particle"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 4 mission electron microscopy (hrtem) images of the rigid carbon-carbon nanotubes (hc-cnts) electrodes cycled in 1 m naclo4 ec: pc solution (1:1, volume ratio) containing 0.3 wt% fec at different charging rates, including 1 a/g and 100 a/g. the formed sei layer at a high charging rate is thinner and more uniform than a low charging rate, similar to those formed at 1 a/g and 100 a/g charging rates in the ether-based e"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "to protect the electrodes from further electrolyte degradation [46]. the electrolyte and the sic-sb-c electrode structure's reductive decomposition can be ameliorated through fec's addition to the electrolyte [48]. the reversible capacity of the sic-sb-c electrode with no fec (1 m naclo4 in ec: dimethyl carbonate (dmc) (1:1, volume ratio) was used as blank electrolyte) increased gradually during the initial cycles and then declined in subsequent cycles. the electrode cycled in the electrolyte wi"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "electrode cycled in fec-containing electrolyte shifted to higher binding energy than its counterpart in the electrode before cycling. conversely, the sb 3d5/2 peak in the electrode cycled in the electrolyte with no fec illustrated the same position as the electrode before cycling. the results showed that fec takes part in the sei formation, evidenced by the position of the sb 3d5/2 peak. thus, it modifies the film's chemical composition, which resulted in an improvement in the electrode's electr"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "resistance (rct) after 100 cycles compared to the electrode with no additive. it is worth noting that the fec-free electrode at the 100th cycle demonstrated a considerable increment in particle size and also major particle agglomerations over a large area compared to the electrode before cycling. the introduction of fec into the electrolyte significantly decreased the particle agglomerations. the electrode showed a smaller particle size increase, which positively affected the electrode's electro"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "to its counterpart with no fec and the other two electrolytes containing naclo4 salt. concerning the electrolytes' impact on the electrode's performance, gas chromatography-flame ionization detector (gc-fid) measurements were carried out. the fec peak intensity in gc-fid chromatograms of four electrolytes decreased with the increasing cycle number attributed to fec consumption due to sei formation at the sodium metal. the fec peak in naclo4-based electrolyte vanished after 500 cycles while found"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 5,
    "text": "mol dm−3 naclo4 + 2 vol% fec electrolyte presented the best performance compared to the electrolytes with no fec and 10 vol% fec. in terms of vc, es, and dfec, their addition to the electrolyte led to detrimental effects on the hc electrode's performance. for further investigation, the na/hc half-cell and hc/nani1/2mn1/2o2 full-cell were dissembled after the first galvanostatic cycle to observe the color changes separators. before the electrochemical tests, the pc-based solutions without additiv"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 6,
    "text": "and 133 processes were not colored in yellow (fig. 6e, f). the fec is the most effective electrolyte additive for the na cells among the case-study additives [52]. many studies have been conducted to probe the chemistry and nature of the fec-derived sei layer to find a clue for this additive's extraordinary performance [53,54]. fondard et al. [53] studied the hc/na half-cell containing 1 m napf6 dissolved in a mixture of ec and dmc with equal proportions. it showed better performance at the 135t"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 7,
    "text": "3% fec delivered the best performance, comprised mostly of sodium ethylene dicarbonate (nedc) and naf. on the other hand, the half-cells whose sei layers were mainly composed of na2co3 and naf represented more unsatisfactory electrochemical performances, in which fec was used with natfsi salt, or dmcf was hired with both napf6 and natfsi salts. consequently, the presence of nedc in the composition of the sei layer had an advantageous effect on the coating's physical and chemical properties. nota"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 3,
    "chunk_index": 8,
    "text": "to the same condition, in which naclo4 is employed instead of napf6 [55]. fig. 7 shows the hard x-ray photoelectron spectra of the hc electrodes cycled in different electrolytes. the constituents containing carbons bonded to three oxygen atoms like na2co3 shown in the c 1s and o 1s spectra are ascribed to the products formed by the solvent's electrochemical decomposition. higher intensities of the peaks mentioned earlier in naclo4- based electrolyte signify the remarkable accumulation associated"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 5 which is not found in f 1s and p 1s spectra of naclo4-based electrolyte. the f 1s spectrum of naclo4-based electrolyte peaks is assigned to the pvdf binder since there is no fluorine source except for pvdf [55]. the addition of 2 wt% fec to the electrolyte decreased the peaks' intensities in the p 1s spectrum, which originated from residual napf6 and its decomposed products, including naxpfy, and naxpoyfz. higher i"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "composition of the fec additive's sei layer [56,57]. takenaka and co-workers [56] theoretically investigated the role of fec in the improvement of the sei formation in sibs using the hybrid monte carlo (mc)/molecular dynamics (md) reaction method. the hybrid mc/md reaction simulations were performed at a carbon anode in 1.1 m napf6 pc-based electrolyte without 10 vol % fec based on the experimental conditions. moreover, the decline in the irreversible capacity and thinner sei film forming in the"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "of fec reduction reaction is attributed to the strong electronegativity of fluorine atoms in fec molecules. it enabled them to enhance the network formation of organic salts and consequently suppress their diffusion into the bulk electrolyte. hence, the development of such an effective network by intact fec molecules would lead to the preclusion of the sei film's negative growth at the carbon electrode. on the contrary, the increase in naf complexes' production due to fec's reduction reaction wo"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "vc solution after the first galvanostatic cycle. (d) photographs of the used glass-separators in coin-type cells of na/hc cell with 1 mol dm−3 naclo4 in pc after 5 cycles, (e) and (f) pc:fec (98:2, volume ratio) after 5 cycles and 133 cycles, respectively. reproduced with permission of ref. [52], copyright 2011 american chemical society."
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 6 recent and rapid development and progress in spectroscopic, microscopic, and scattering techniques have provided researchers with wide opportunities to study the structurally growth, morphologically changes, and the contents of the sei and cei layers [58]. in this regard, shu-wei et al. [59] investigated the morphologically evolution of the sei layers during the first cyclic voltammetry (cv) on highly oriented pyro"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "the electrodes, and more nano- meter particles accumulate at these places. unlike thinner films observed on the basal plane, dense and thicker films were formed at the step edges of the hopg electrodes in ec-based electrolyte. conversely, in fec-based electrolyte, sei films having double-layer structure were detected on hopg electrodes, made up of an upper layer composed of large particles and a lower layer made of dense small particles. worth mentioning that the main components in chemical comp"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "in the tmp + 10 vol% fec became a little dim after 45 days; however, the electrolyte solution remained as clear as the fresh one, testifying to the excellent compatibility of the tmp-based electrolyte with na metal. a direct igniting experiment verified the non-flammability of the case-study electrolyte. the tmp-containing electrolyte did not ultimately ignite on fire. on the other hand, the carbonate electrolyte ignited immediately, implying the excellent capability of tmp in the retardancy of "
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "coating (fig. 8e). the capacity of the sb/nani0.35mn0.35fe0.3o2 full-cell containing tmp + 10 vol% fec electrolyte showed a slow decline at the initial cycles and then remained stable at a constant current of 50 ma g−1. furthermore, the full-cell ce increased from 58% at the first cycle to 98% after several processes, confirming that both the sb anode and nani0.35mn0.35fe0.3o2 cathode were performed perfectly in the tmp + 10 vol% fec electrolyte [60]. similarly, liu and co-workers [61] investiga"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 7 sodium metal is found in the tep after 5 days, and it is completely dissolved. moreover, the solution's color is changed from colorless to yellowish, testifying na's incompatibility with tep. the addition of 5 vol% fec to build a protective sei layer on the na metal surface enhanced the compatibility between na metal and tep. the transparent color of tep solution after 9 months manifests the compatibility of na met"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "˃99.5%. furthermore, the half-cell in which nvp was designated as anode delivered a charge capacity of 45.5 mah g−1 after 1000 cycles at the rate of 2 c, exhibiting capacity retention of 95.4% and a high ce of >99.5%. the outstanding cycling performance of nvp as both anode and cathode was ascribed to the wide electrochemical window of the tep-based electrolyte, which was stable up to 5 v (fig. 8h) [61]. the full-cell cycling performance using nvp as both anode and cathode delivered a discharge "
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "a potential higher than 1 v to lithium [30]. vc has also been adopted to improve the electrochemical performance of sibs. bai et al. [81] introduced an avenue to build a sustainable sei film at the hc electrode through vc's addition to an ether-based electrolyte. besides, they found that additive amount can have substantial impact on the sodium storage performance of hc anodes. in this regard, the influences of ethylene glycol dimethyl ether (dme)-based electrolytes without and with various amou"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "on the hc anodes, formation of thicker sei films, and subsequently increment in the impedance. electrolyte with 0.5 vol% vc fig. 8. a) room temperature storage of na metal in the tmp + 10 vol% fec electrolyte. b) combustion behaviors of the tmp + 10 vol% fec electrolyte and carbonate-based electrolyte. sem images of the sb-sic-c electrode (c) before and (d) after 10 cycles at 100 ma/g in fec-free and (e) fec-containing napf6/tmp electrolytes. reproduced with permission of ref. [60], copyright 20"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 8 delivered more reversible capacity and capacity retention than that of the one with 1 vol% vc [81]. the hc/na half-cell's capacity retention containing 1 m napf6 dissolved in vc-free dme solvent dramatically declined to 72.3% after 2000 cycles. however, the addition of 0.5 vol% vc to the electrolyte increased the capacity retention up to 95.6% with an impressive rever- sible capacity (211 mah g−1). the sei layer bu"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "that the sei layer was plentiful of organic polymeric species derived from vc reduction and less inorganic naf compared to one cycled in the vcfree electrolyte. fig. 9c, d shows young's module distribution images of the hc electrodes in vc-free and vc-containing electrolytes at 10th cycle, analyzed by using atomic force microscope (afm) technique to investigate the mechanical properties of the electrodes. a high modulus of 14149 mpa was achieved for the vc-free electrolyte, which can be deducted"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "with appropriate mechanical flexibility, leading to a prolonged lifespan of the electrode during the charge-discharge process with an excellent electrochemical performance [81]. three primary allotropes of phosphorus, including white, red, and black p, have drawn particular attention as negative electrode materials in sibs. but, phosphorus suffers from a volume expansion during sodiation-desodiation reactions, contributing to the electrolyte decomposition. the vc and fec additives were investiga"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "napf6 in ec:diethyl carbonate (dec) (1:1, volume ratio) + 5% fec sp/cnt@tio2 – n/a 585 (2 a g−1) (1000) n/a [63] xiao et al. (2019) 1 m naclo4 in ec:dec (1:1, volume ratio) + 10 wt% fec phosphorus/c – 0.001–2 1070 (400 ma g−1) (200) 78 [64] nagulapati et al. (2019) 1 m naclo4 in ec: pc (1:1, volume ratio) + 5% fec sbte-c – 0–3 421 (100 ma g−1) (200) 96 [65] li et al. (2018) 1 m naclo4 in ec:pc (1:1, volume ratio) + 5% fec tio2 coated with al2o3 – 0.01–2.5 <186.8 (0.1 c) (50) n/a [66] sadan et al"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "(2017) 1 m naclo4 in ec:dmc(1:1, volume ratio) + 5 wt% fec carbon coated bimetallic sulfide hollow nanocubes – 0.01–3 87 (500 ma g−1) (150) n/a [68] huang et al. (2017) 1 m napf6 in ec:dec (1:1, volume ratio) + 5 vol% fec – border-rich sodium iron hexacyanoferrate (br- fehcf) 2–4.2 n/a (n/a) (500) 79 [69] mogensen et al. (2017) 1 m sodium bis(fluorosulfonyl)imide nafsi in ec:dec (1:1, volume ratio) + 5 vol% fec sn4p3 – 0.01–2.5 ∼400 (50 ma g−1) (50) n/a [70] wen et al. (2016) 1 m naclo4 in pc + "
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 7,
    "chunk_index": 5,
    "text": "fec sn@casac – 0.01–2 415 (100 ma g−1) (50) ∼95 [73] lee et al. (2016) 0.5 m naclo4 in ec:pc:dec (5:3:2, volume ratio) + 5 wt% fec – na4fe3(po4)2(p2o7) 1.7–4.2 90.5 (c/2) (300) 97.5 [74] song et al. (2016) 1 m napf6 in ec:dec:pc (1:1:2, volume ratio) + 5 vol% fec hc na0.76ni0.3fe0.4mn0.3o2 2–4.2 n/a (1 c) (40) 80 [75] tran et al. (2015) 1 m naclo4 in pc:ec (1:1, weight ratio) + 5 wt% fec fe1.18sb1.82 – n/a 100 (c/20) (20) n/a [76] hur et al. (2015) 1 m naclo4 in ec:pc (1:1, volume ratio) + 2 vol"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 9 the electrode cycled in 1 mol dm−3 napf6 dissolved in ec: dec mixture (1:1, volume ratio) without additive delivered the specific capacities of 1479, 1453, and 957 mah g−1 at 1st, 2nd, and 23rd cycle, respectively. the decline observed in the capacity was attributed to unstable electrode-electrolyte interphase by the additive-free electrolyte. like phosphorous, silicon (si) as an anodic active material in libs unde"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "stability made by additives, which sem further analyzed. a thick and non-homogenous layer is formed on the surface of the electrode cycled in the free-additive electrolyte (fig. 9e). on the other hand, both electrolytes containing vc and fec were capable of forming thin and homogeneous layers at the electrode's surface (fig. 9f, g), resulting in relatively good cycle stability [82]. 1.3. sulfur-containing additives the application of electrolytes, in which multiple electrolyte additives holding "
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "m napf6 dissolved in a mixture of ec and pc was used as an electrolyte, in which four additives in proper quantities were adopted, including 3% vc, 3% ps, 1% succinic anhydride (sa), and 0.5% sodium difluoro(oxalato)borate (naodfb). the right choice of each additive based on its function and amount is a critical issue. for example, vc was considered an sei builder at the negative electrode. fig. 9. (a, b) tem images of the hc anodes after 2000 cycles in the dme-based and dme containing 0.5 vol% "
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 10 still, high amounts of this additive would contribute to side products at the positive electrode due to its oxidative decomposition. moreover, amounts of naodfb of more than 3% resulted in a severe increase in the cell impedance because parasitic decomposition reactions assisted the growth of thick deposits at the positive electrode. the ps additive was adopted to enrich the sei layer with sulfur-containing specie"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "vol% sulfolane (tms) were adopted as additives. among the case-study solvents, pc as a carbonate-based solvent demonstrated the best performance. it is realized that some additives consisting of fec, vc, and nabob possess the capability to work as stand-alone sei formers. on the other hand, there are additives which should be used as complementary additives, including tms and tmsp [87]. che et al. [88] examined the effect of an electrolyte using a triple blend of electrolyte additives on the per"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "the 1000th cycle. the highest cycling was achieved for the cell using a triple blend of electrolyte additives comprising of 2 wt% fec, 1 wt% pes, and 1 wt % ethylene sulfate (dtd) (denoted as “fpd”), delivering capacity retention of 92.2% at the 1000th cycle. fpd electrolyte's excellent performance was attributed to its capability to form protective passivation layers at both anode and cathode surfaces. the amount of deposited transition metal ions at the hc anode was measured with inductively c"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 9,
    "chunk_index": 3,
    "text": "grey color matters specified with the yellow circles were a mixture of the dead sodium and its products due to the electrolyte's reaction, whose color was turned to white after exposure to air (see fig. 10a). the fp and fpd showed fewer side products among the case-study electrolytes (fig. 10b, c). the migration and afterward precipitation of transition metal ions at the hc anode led to further solvent decomposition and sodium deposition [88]. the sei layer in sibs is primarily tied with the cap"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 9,
    "chunk_index": 4,
    "text": "lead to organic sei components, including (ch2ch2co3na)2, (ch3ch2ch2co3na)2, and (chchco3na)2. the two-electron reduction reaction of ec, pc, and vc would result in the production of inorganic sei components of na2co3. as mentioned earlier, among the three carbonate esters, vc and ec are highly liable to produce the organic and inorganic ingredients in the sei layer, respectively. it is worth noting that the two-electron reduction of sulfites to make inorganic na2so3 is more rigid than that of c"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 11 in which fluoride ions react directly with na ions to produce naf. among the case-study additives, vc, es, and ps tend to make organic components in the sei layer rather than inorganic products. on the contrary, fec yields mostly inorganic naf during reductive decomposition [89]. 1.4. tris(trimethylsilyl) phosphite (tmsp) the excellent capabilities of tris(trimethylsilyl) phosphite (tmsp) in scavenging the hf acid"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "by eliminating hf from the fec additive. the intensity of the peak assigned to naf in xps f 1s spectrum of the sn4p3 anode cycled in fec + tmsp-added electrolyte dramatically decreased compared to one in the absence of the tmsp manifesting the fact that tmsp has the potential to restrain the formation of large amounts of naf caused by fec decomposition. the data obtained from electrochemical impedance spectroscopy (eis) measurements of the sn4p3 anode after full sodiation showed that addition of"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "from 49 ω to 14 ω. [90]. 2. additives for safety improvement 2.1. flame retardant additives due to their self-extinguishing properties, phosphorus-containing organic compounds like phosphates, phosphites, and phosphines are widely hired as flame retardant additives in libs [91,92]. flame retardant additives play their role by scavenging the active free radicals, contributing to the combustion chain reaction [34,92]. feng et al. [93] formulated a non-flammable electrolyte for sibs, in which ethox"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 3,
    "text": "with efpn was not burned. the electrolyte containing efpn presented notable compatibility with sodium metal and no evident side reaction observed between them. the cycling performance experiments of acetylene black (ab) anode and na0.44mno2 cathode configured separately with na metal as half-cells with efpncontaining electrolyte delivered higher capacities compared to those in the electrolyte with no efpn at 200th and 50th cycle, respectively [93]. the enhanced electrochemical performance of bot"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 4,
    "text": "efpn (700 and 6000 ω) [93]. 2.2. additives for overcharge protection in response to the risk of explosion ensuing from overcharging of libs, overcharge protection additives are successfully developed as an efficient remedy to address this issue [31,94]. as a classification of overcharge protection additives, redox shuttle additives are obliged to undergo a reversible oxidation reaction at slightly higher potentials than the positive electrode's average end- of-charge potential [29]. when overcha"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 5,
    "text": "additives' reverse redox potential until the end of overcharging [29,34]. similar to libs, sibs are also vulnerable to overcharging. qu's group reported recently [95], trisaminocyclopropenium perchlorate (tac•clo4) compound is eligible to be adopted as a novel redox shuttle additive for overcharge protection in sibs. during the overcharging, the tac molecule could lock the nvp cathode's potential at 3.75 v (vs. na+/na). it happens by reversibly shuttling between cationic and dicationic forms wit"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 6,
    "text": "of the overcharged cathode in the electrolyte containing tac starts at 180 °c, higher than that in the electrolyte with no additive (171 °c). also, the introduction of tac into the electrolyte led to a 20% decline in heat generation during the overcharge. due to its high ability to procrastinate the starting temperature of thermal runaway and reduce the cathode's heat generation, the tac additive could significantly improve battery safety during overcharge. the addition of tac to the electrolyte"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 10,
    "chunk_index": 7,
    "text": "cathodes in libs, several alternative electrolytes taking advantage of high anodic stability have been probed to tackle this problem [96]. among the offered electrolytes, nitriles, for instance, adiponitrile (adn), exhibit high anodic stability towards the high voltage cathodes, adopted as either solvent or additive [97,98]. following the findings unveiled by song and his co-workers [99], the addition of 3% adn and fec to the pouch cell made up of hc anode and na0.76ni0.3fe0.4mn0.3o2 cathode ena"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 12 the practical application of high-performance cathode materials in sibs [99]. succinic anhydride (sa) is another well-known additive in libs. the incorporation of species originated from reduction of sa into the sei layer can enhance the layer's thermal stability. thus, it would aid the battery to operate at elevated temperatures [100]. such a favorable attribute motivates researchers to examine the effect of sa o"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "upon storage of symmetric cells at 60 °c for 550 h, the open- circuit voltage (ocv) of the cells with no additive and with fec showed a rapid rise from 0.9 v to above 2.0 v just within 200 h. the increase in the ocv during storage at 60 °c was ascribed to the hc anodes' thermal degradation, leading to an increment in the potential of the anode due to the loss of stored na ions (desodiation). by adding sa, the increase in ocv observed for the cells mentioned above was mitigated from 0.9 to 1.7 v "
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "salt's thermal decomposition because of the fec-derived sei layer's relatively poor thermal stability [101]. the hydrofluoric acid (hf) originated from the hydrolysis of lithium hexafluorophosphate (lipf6) salt, resulting from trace moisture and can result in adverse and destructive outcomes in libs. the usage of organophosphorus compounds as hf scavengers is highly proposed [102,103]. analogously, napf6 salt is liable to undergo degradation in water and form hf acid, which affects the electroly"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "diglyme + 5% vc fes@c na3v2(po4)3@c 1–3 49.5 (0.5 c) (1000) 67 [105] mogensen et al. (2020) 1 m napf6 in tmp + 10 vol% vc hc prussian white cathode 1–3.8 ∼115 (30 ma g−1) (50) n/a [106] fang et al. (2020) 4 m nafsi in1,2-dimethoxyethane (dme) + 1% sbf3 – nvp 2–4 ∼90 (2 c) (1400) 82.5 [107] zhang et al. (2020) 1 m naclo4 in pc + 2 wt% vc moo2 – 0.01–3 ∼100 (300 ma g−1) (1000) 96.5 [108] cometto et al. (2019) 1 m napf6 in ec:dmc (1:1, volume ratio) + 3% vc + 0.5% sodium (oxalate) difluoro borate ("
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 11,
    "chunk_index": 4,
    "text": "in tmp with the molar ratio of 1:3 + 5 vol% fec hc – 0–2 ∼75 (200 ma g−1) (1500) 84 [111] che et al. (2017) 0.8 m napf6 in pc:ec (4:1, volume ration) + 0.05 m rbpf6 or 0.05 m cspf6 hc – 0.01–2 ∼293 (30 ma g−1) (100) for cs+, ∼283 (30 ma g−1) (100) for rb+ 97.1 for cs+, 95.3 for rb+ [112] kumar et al. (2016) 10 m naclo4 in aqueous electrolyte + 2 vol% vc – na3v2o2x(po4)2f32x- mwcnt 0–0.9 45 (1 c) (1400) 93 [113] feng et al. (2015) 1 m napf6 in ec:dec (1:1, volume ratio) + 3% biphenyl – na0.44mno2"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "b. mosallanejad et al. journal of electroanalytical chemistry 895 (2021) 115505 13 phosphazene is recognized as an hf scavenger in sibs, which plays an essential role in stabilizing electrolytes' shelf life containing water or becoming exposed to it [104]. table 2 provides a summary of the research done on using different electrolyte additives in sibs. 4. conclusions and outlook as the number of articles and patents dealing with sibs attested, a substantial attempt has been made in the last deca"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "problems, the addition of a small dose of electrolyte additives can be a practical and cost-effective avenue. in this review, the detailed literature survey substantiated that fec is the most effective electrolyte additive for sibs among the functionimproving additives due to its extraordinary capability to form robust and efficient passivation layers surfaces of both anode and cathode. however, the fec reduction can bring about the formation of a considerable amount of naf inorganic species. be"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "of organic species. on the other hand, fec usage and other salts like naclo4 or natfsi would contribute to high amounts of resistive inorganic species. secondly, fec's application in multiple blends of electrolyte additives is more applicable than when used alone. tmsp additive is the right choice for reducing the high amounts of resistive naf species by eliminating hf from the fec additive. organic electrolytes' flammability can be diminished by introducing flame retardant additives into the el"
  },
  {
    "source_pdf": "Cycling_degradation_and_safety_issues_in_sodium_ion_batteries_Promises_of_electrolyte_additives_Behrooz_Mosallanejad_Shaghayegh_Sadeghi_Male_Mahshid_Ershadi_Ahmad_Ahmadi_Daryakenari_Qi_Cao_F.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "electrolyte formulation is a critical parameter enabling highperformance sibs. disparate electrolyte formulations have been tested in the vicinity of different anode and cathode materials. a negligible modification in every component of electrolyte, in particular additives, can directly affect the electrochemical performance of sibs ensuing from an alteration in the sei layer composition. thus, the optimization of electrolyte formulation can be one of the main bottlenecks in developing sibs. to "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 1 secondary batteries degrade over time due to many factors, see e.g. [1,2], which means that their capacity to deliver energy and power deteriorates over time. state of health (soh) is a measure that can be related to either capacity fade, internal resistance increase or both. it is important to accurately monitor the state of health of maritime (soh) battery systems used for propulsion and maneuvering. together with state of charge (soc), t"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "things, continuously estimates soh. however, it is acknowledged that soh estimates from the bms may not be accurate or reliable. therefore, for ships relying on battery power for propulsion, classification societies require the soh estimates from the bms to be verified by independent tests [3,4]. it is not specifically prescribed how this independent verification should be carried out, but this can normally be done by an annual capacity test where the vessel is taken temporarily out of service t"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "can be collected continuously from the ship and fed into appropriate algorithms to predict soh. these models obviously need to be different and independent from the algorithms running on the bms, and the need to be reliable and accurate enough to yield equally robust estimates of soh as one would have achieved by a physical test. data-driven approaches to soh estimation for maritime battery systems were thoroughly investigated in a recent research project. a literature review identified a number"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "and main results will be given below. however, only one particular type of lithium-ion nmc (nickel manganese cobalt) cells were investigated. it is known that different battery types degrade differently, and the objective of this paper is to discuss data-driven soh estimation for alternative battery chemistries. this includes lithium-ion batteries with different composition as well as non-lithium types of batteries, and the main focus will be on lfp-type (lithium iron phosphate) lithium-ion and "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "and cost of lithium. it is worth mentioning that other types of batteries such as solid-state and zinc-ion batteries also show great promise but their current development is not mature enough to be applied for nearterm maritime applications due to high production costs and limited scalability, and therefore is not included in the scope of this work. moreover, existing work [8,9] also indicated that existing methods such as data-driven methods were mainly developed to estimate the soc of solid st"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "charging protocols [10–13], see also the review in [14]. hence, it is possible that models and algorithms developed for a specific type of nmc cells can be transferred to apply to other lithium-ion chemistries and non-lithium batteries. however, this would require a pre-trained base model, possibly trained on a vast amount of publicly available battery data, and additional representative training data for the target battery type. note also that transfer learning has been suggested as a way to ac"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "how shipspecific conditions influence the degradation of batteries. for example, energy storage systems onboard ships in operation might experience different vibration conditions and more movements compared to other applications [20], and previous studies have indicated that vibration may significantly accelerate battery aging [21,22]. battery systems onboard ships may also be exposed to larger temperature variations than other applications [20], although battery rooms onboard ships should, in p"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 7,
    "text": "and discuss definitions and methods for determining the state of safety (sos) of batteries, with a focus on lithium-ion lfp types of batteries and sodium-ion batteries. the state of safety is a relatively new measure that has not previously been much used in maritime applications. it is noted that several other measures are used for describing the states of batteries [23]. for example, state of power (sop) describes the maximum charge and discharge power that a battery can support [24], the stat"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 0,
    "chunk_index": 8,
    "text": "and devices [27– 29]. for instance, the study in [27] addressed the challenges of lithium–sulfur (li–s) batteries, such as lithium polysulfide dissolution and low conversion efficiency, by designing homonuclear transition-metal dimers embedded in monolayer c2n. through firstprinciples calculations. the work demonstrated that these materials can enhance the anchoring of lithium polysulfides, suppress shuttle effects, and improve catalytic conversion efficiency, offering insights into dual-atom ca"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 2 data decomposition, and an enhanced informer algorithm. by clustering data by weather conditions and employing precise data reconstruction methods, the model achieved improved accuracy and stability, validated through experiments with real-world pv plant data. the review [29] explored the development and potential of liquid–liquid triboelectric nanogenerator mechanisms and applications, which converts mechanical and tidal energy into electr"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "lack comprehensive review for investigating and assessing critical performance metrics like state of health (soh) and the emerging state of safety (sos), which are essential for ensuring reliability and safety in demanding maritime environments. the paper aims to bridge this gap by reviewing the existing soh estimation methodologies to the alternative chemistries and exploring the integration of sos into realtime monitoring systems. ultimately, the key contributions of this work include: (1) enh"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "energy density and extended cycle life; see e.g. [30,31] for a thorough introduction to lithium-ion batteries, and see [32] for an overview of important aspects of maritime battery systems. more recently, other types of chemistries, utilizing nonlithium charge carriers, e.g. sodium-ion (na-ion), zinc-ion (zn-ion) or fig. 1. comparison of lithium-ion and sodium-ion battery cells within six dimensions. magnesium-ion (mg-ion) have emerged as alternatives to lithium-ion. in this subsection, a very b"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "c-rate and cell impedance are comparable for sodium-ion and lithium-ion cells, and that the tested sodium-ion cells had a higher gravimetric energy density than tested lfp cells. a comparison of typical soc-ocv curves for different chemistries is also presented in [33] (ocv = open circuit voltage; the terminal voltage without any load). one striking difference that is observed is that the ocv-curve is almost flat for lithium-ion lfp cells, a fact that is generally well acknowledged; see also [35"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "the main function of a secondary battery is to convert electrical energy into chemical energy for storage and then to release the energy by converting it back to electrical energy when needed. a secondary battery cell typically consist of a few main components: positive and negative electrodes (often referred to as cathode and anode), the electrolyte, a separator and current collectors. the cell’s active materials reside in the electrodes where oxidation (loss of electrons) and reduction (gain o"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "most common batteries use liquid electrolyte solutions, but solid state batteries are battery cells with solid electrolyte. in lithium-ion battery cells, the electrical charge are carried by lithium ions (li+). in sodium-ion batteries, the charge carriers are sodium ions (na+), but the cell components and the electrochemical reaction mechanisms are similar to that of lithiumion batteries. however, since na+ is larger and heavier than li+, a sodium-ion battery will typically have lower energy den"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 6,
    "text": "ranges and the need for scarce materials. they also respond differently to various stress factors with respect to aging, as presented in [38]. in addition to the large number of different lithium-ion types of cells, other types of batteries uses non-lithium material as charge carriers. some examples of these are sodium-ion, zinc-ion and magnesiumion, where sodium, zinc and magnesium, respectively, are used as charge carriers between the electrodes. these alternative chemistries will have differe"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 1,
    "chunk_index": 7,
    "text": "differently to various abuse factors. in fact, it is noted in [39] that operating performance may differ significantly even for cells with the same underlying chemistries but from different manufacturer. a review and comparison of thermal behavior, degradation and safety between lithium-ion and sodium- ion batteries are presented in [40]. it is stated that very little is published on the degradation of sodium-ion batteries at cell level. at any rate, for different types of battery cells, one can"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 3 in this paper, an investigation into data-driven approaches to soh estimation for the types of batteries will be presented. that is, the focus will be on estimating soh for lfp lithium-ion and sodium-ion types of batteries. since actual data from such types of batteries are scarce, this investigation is initially based on a review of the scientific literature on the topic. previous research on nmc lithium-ion batteries previous research has"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "ranging from direct measurement techniques to simple semi-empirical and statistical models to more advanced machine learning techniques. methods were further classified into cumulative and snapshot methods. an illustration of the categorization of different methods is shown in fig. 2 (from [5]). some of these approaches were further explored and tried out on various battery datasets. the battery ai tool [41], which is a cumulative model combining a semi- empirical model with machine learning was"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "but another more fundamental problem with cumulative methods was source: from [5]. revealed: cumulative methods need the complete data history in order to estimate current capacity and state of health. however, the maritime battery datasets available for the study contained several long gaps in the data, and this might be difficult to avoid for maritime battery systems. this could possibly be improved by better and more reliable ship-to-shore connectivity, but it was deemed difficult to guarante"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "not recommended for maritime battery systems. also, the multivariable fractional polynomial regression models presented in [45] are cumulative in the sense that they estimate the change in capacity rather than actual capacity from the selected features. realizing that cumulative models would be associated with practical challenges, different snapshot methods were explored. various snapshot features were extracted from charge and discharge curves and used to establish simple statistical regressio"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "this might be difficult to guarantee. typically, models that needs to be trained require laboratory cycling data, which are expensive and time consuming to generate, and it will be difficult to design experiments that ensure that every imaginable loading conditions will be well represented. more complicated machine learning techniques were used to establish snapshot methods in [48], that was found to perform reasonably on laboratory cycling data. however, the models were not applied to actual op"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 2,
    "chunk_index": 5,
    "text": "data for this method to yield sufficiently good results. obtaining sufficient relevant training data from laboratory tests is expensive and time-consuming, and the resulting data might not be representative of actual operational conditions. hence, it was investigated whether operational data from existing battery installations could be used for training. however, one problem with this approach is that operational data contains very few labels or actual measurements of battery capacity. typically"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 2,
    "chunk_index": 6,
    "text": "vessels with batteries that have reached end of life would be required. moreover, operational conditions not experienced in the training data would be difficult to predict. hence, also this approach has limitations. due to several challenges with purely data-driven approaches to soh estimation, it was concluded in previous research that this might not be enough without incorporating some physics-based elements in the modeling. hence, simple linear models based on coulomb counting were explored i"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 4 somewhat by data filtering and pre-processing and by applying an ensemble of such linear models for different subsets of the data, as described in [54]. however, results were still not entirely satisfying. one of the reasons for this is probably that the coulomb method depends heavily on the state of charge (soc), which is a derived quantity and not directly measured. although it is assumed that estimating soc is less challenging than soh, "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "voltage measurements. then, the open circuit voltage is mapped to soc using a known cell-specific ocv- soc curve. this can e.g. be established by specific characterization tests. results from this approach can be found in [55], which unfortunately still display some lack in precision. one of the main reasons that was identified for the lack of precision might be the failure to accurately account for variations in operational conditions. for example, temperature effects and hysteresis were not we"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "laboratory and field data, indicates that is can provide reliable and accurate estimation of soh from operational data, conditional on the battery system having experienced sufficiently deep cycles. further validation of this method is ongoing, and the required deepness of the operational cycles will presumably be battery-type specific. notwithstanding, with this approach, data-driven verification of soh as an alternative to annual capacity tests has been made possible. the methods that were pre"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "have flat charge/discharge curves compared to nmc. while this might gives some advantages such as the ability to deliver constant power over an extended period of time, it also makes it more challenging to determine soc based on voltage level. in particular, this means that methods that are found to work well for nmc lithium-ion battery cells that relies on soc (directly, or indirectly via an soc-ocv curve), may not work as well for lfp cells. this may rise the need for completely different type"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "focus on lfp li-ion and na-ion batteries. data requirements relevant data is obviously needed for data-driven methods. if the aim is to establish data-driven methods and algorithms to predict battery degradation and estimate state of health, then obviously data measuring battery degradation over time is needed. the specific data requirements will depend on the actual methods and algorithms one wants to develop, but obviously data from cells that have experienced notable degradation are needed to"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 5,
    "text": "important to have training data from identical, or at least similar, battery cells to the cells one wants to apply the data-driven methods to. generic cycling data may not be representative for cells even with similar chemistries and compositions. hence, not only is there a need for long time series, but the data need to be specifically for the type of cells in question. even with techniques such as transfer learning which could exploit more generic battery data, there would need to be some amou"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 6,
    "text": "features at certain intervals might suffice [47]. moreover, purely data-driven models typically extrapolate poorly, so data might need to be combined with physics-based models, or data need to be covering all realistic combinations of operating conditions. hence, the data requirements need to be assessed carefully considering the types of models that are to be used. one way of obtaining relevant training data is to perform laboratory cycling tests. however, this is expensive and time consuming a"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 7,
    "text": "not for novel systems with alternative battery chemistries. it is also challenging to combine data from different battery systems that have experienced very different usage patterns [57]. for the purpose of testing out different data-driven methods within a research environment, publicly available datasets represent a possible source of training data. hence, in the following, a review of some publicly available battery dataset will be given, with a focus on cycling data from lfp and na- ion cell"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 3,
    "chunk_index": 8,
    "text": "lfp types of batteries are presented, e.g. from toyota research institute (https://data.matr.io/ 1 ), from sandia national laboratories (https:// www.batteryarchive.org/snl_study.html), from mendeley data (https: //data.mendeley.com/datasets/r4n22f4jfk/1 [59]; https://data.mende ley.com/datasets/bs2j56pn7y/1 [60,61]; https://data.mendeley.com/ datasets/6s6ph9n8zg/1 [61,62]) and from the university of science and technology of china [63]. another review of lithium- ion datasets is presented in [6"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 5 tools.html); see [58] for the full list. battery data from nasa have been thoroughly analyzed by several authors, see [65], and data from accelerated life testing described in [66] can also be found here. some additional battery data repositories not mentioned in [58] include the automated battery database (https://aging.battronics.com/ database/0), the data used in [67] (https://data.matr.io/1/projects/ 5c48dd2bc625d700019f3204) and the da"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "might be expected to become available as the technology mature and become more widely used. commercially available models some battery degradation models are commercially available for various types of battery cells. it is not the aim of this paper to provide a comprehensive overview and assessment of these, and the models have not been tested, but it should be mentioned that such products exist. one example is the suite of twaice battery aging models for lithiumion batteries [70], which are bas"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "on a combination of a semi-empirical model and a machine-learning model for predicting battery degradation [41]. it is essentially a cumulative model that adds the degradation contribution from repeated cycles under varying conditions. it has been tested on maritime battery data in [42]. it has been trained on various lithium-ion types of batteries (including both nmc and lfp), but not yet on sodium-ion batteries, as far as the author of this paper is aware. mathworks offers battery simulation m"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "library includes a wide range of physics-based models including various electrochemical lithium-ion models and equivalent circuit models. an extension of this for simulating lithium-ion battery packs is available in the liionpack package [74]. pybamm is also used to build the model in [75] that couples several degradation mechanisms. parasweeper is a python script based on pybamm for high-throughput computing of complex physics based degradation models for lithium-ion batteries [76]. the battery"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 4,
    "text": "aging of rechargeable batteries remains challenging, and countless of scientific papers have been published addressing this, even though commercial software is available. data-driven state of health monitoring previous research explored a number of different data-driven approaches for soh monitoring of lithium-ion batteries, i.e. for particular types of nmc li-ion cells. in addition to this, there are a lot of literature on the degradation of batteries, but most focuses on lithium-ion batteries;"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 5,
    "text": "that sodium-ion batteries are less prone to plating and dendrite formation during fast charging [82]. cycling tests reported in [83] confirm that there are no strong effects of high charge currents on capacity fade of sodium-ion batteries. however, it is noted in [40] that very little literature is available on cell-level comparison of lithiumand sodium-ion degradation and aging, and that more investigations are necessary to understand the aging mechanisms in na-ion batteries under normal operat"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 6,
    "text": "soh estimation for li-ion lfp lfp is an established technology which has been used in many applications, including stationary storage and electric vehicles [39]. results of some cycling tests with both lfp and nmc types of cells are presented in [39], indicating that the capacity degradation of different lfp cells might be quite variable even for the same cycling conditions. however, results were less variable when cycled with reduced c-rates. with regards to the effect of temperature on capacit"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 7,
    "text": "be emphasized that these are observations from a limited number of tests only, and one should be careful with basing general conclusions based on this. it is stated in [39] that even though it may be possible to draw some general conclusions regarding degradation for a given chemistries, this will not tell the full story for a specific cell model, and laboratory testing for specific cells may be important. the relatively flat ocv curve of lfp cells, corresponding to a wide constant potential pla"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 4,
    "chunk_index": 8,
    "text": "accurate enough for lfp cells. on the other hand, the method proposed in [86] utilizes the length of the voltage plateaus in order to estimate capacity, and claims that this contains sufficient information, without the need to fully discharge the battery. hysteresis effects can also be notable for lfp batteries and are affecting the open circuit voltage. empirical and semi-empirical models are often used for battery degradation. however, a serious challenge with such approaches is that battery d"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 6 conditions, is applied to both nmc and lfp lithium-ion cells in [87]. results demonstrate that such a model yields reasonable results for both nmc and lfp chemistries. however, it is based on infinitesimal changes over time, and hence suffers the problems of any cumulative damage models. it requires complete operating histories to obtain estimates of the capacity. numerous other semiempirical models for aging of lfp cells are proposed in th"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "resistance-capacitance (rc) equivalent circuit model is proposed to co-estimate soc and soh in [94], and is reported to perform better than conventional ocv-based methods. the effect of soh, soc and temperature on the model parameters for lfp cells was investigated in [95], and an empirical model was developed to account for this. a third-order rc model integrated with a hysteresis model is proposed for lfp batteries in [96], with a focus of estimating soc. this highlights the need for accountin"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "capacity fade simulations, see also [98,99] for other coupled electrochemical– thermal models. a comparison of electrochemical–thermal models for describing lithium-ion batteries is presented in [100], suggesting that 3d models perform best. however, a drawback with electrochemical models is that they are computationally costly, and increasingly so for more complex models. a comparison of equivalent circuit models and physics based models for lfp batteries is presented in [101]; ecms are typical"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "logic or other data- driven approaches has been proposed. in principle, adaptive models may be accurate, but they do require extensive training data to estimate the correlation between model parameters and cell degradation, and they might be very computationally intensive. an alternative approach is proposed in [102], which identifies some features of interest from incremental capacity analysis relating the cell voltage-response to degradation and generate a multi-dimensional lookup table based "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "based on cell inconsistencies and lorenz plots, where the average lorenz radius of a module is used to estimate module soh is presented in [103] and applied to lfp-type batteries. a linear relationship between soh and the average lorenz radius was found, and the algorithm shows good goodness-of-fit for lfp cells connected in series and parallel. a number of data-driven approaches relies on machine learning techniques for soh estimation. these would typically extract features from the data and mo"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 5,
    "text": "improvement in accuracy of soh estimation up to 71.1% is reported. it is also reported to work well on features extracted from partial voltage ranges. a different approach to feature extraction for estimation of soh is proposed in [105], where features are selected theoretically based on their relationship with soh. features extracting from charging curves and temperatures are selected and validated based on grey relational analysis theory and used to generate training data for data-driven metho"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 6,
    "text": "kolmogorov–arnold representation theorem, kan decomposes multivariate functions into sums of univariate functions, facilitating accurate approximation of battery degradation behaviors. recent advancements in kan frameworks have improved their scalability and computational efficiency, enabling real-time soh predictions under dynamic operational conditions. for instance, a soh estimation method combining kolmogorov–arnold networks (kan) and long short-term memory (lstm) networks was proposed in [1"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 7,
    "text": "cycled at various power levels. the hybrid deep learning framework presented in [110] combines both convolutional neural networks and recurrent neural networks to estimate soh. neural ordinary differential equations based machine learning models are used to predict state of health in [111] and compared to some standard recurrent neural networks. a deep neural network is suggested in [112], which was found to outperform an alternative model based on a feedforward neural network. deep learning is "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 8,
    "text": "the review in [122]. it is out of scope of this paper to review these in detail, but suffice to say that a large number of machine learning models have been suggested for data-driven capacity estimation of batteries, including lfp. soh estimation for na-ion sodium-ion batteries are, similarly to lithium-ion batteries, relying on intercalation and deintercalation of the charge-carrying ions at the electrodes. hence, in many ways, the fundamental principles are similar for na- and li- ion cells, a"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 5,
    "chunk_index": 9,
    "text": "adaptation and fine tuning, even though the underlying degradation mechanisms might be very different. that is, it can be expected that empirical/semi-empirical models, ecm and electrochemical-based models and machine-learning based data driven models for capacity estimation should work equally well for na-ion cells as for li-ion cells, but obviously adapted to the particular cell. it is also stated in [83] that the transferability of diagnostic algorithms from lithium-ion to sodium-ion batterie"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 7 data-driven methods depend on data, for training, calibration and fine-tuning, and there might be less available data on sodium-ion batteries for training and calibrating models. one possible way to handle this could be to exploit transfer learning and use models trained with large amounts of lithium-ion battery data and only relatively small amounts of sodium-ion and cell-specific data, as suggested in e.g. [10,14,19]. however, in the foll"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "little literature on the degradation of sodium-ion batteries. hence, there are insufficient information on cell-level to compare the performance and aging of lithium-ion and sodium-ion batteries. one of the differences mentioned is that the solid electrolyte interface (sei) might be less stable for sodium-ion batteries compared to li-ion cells, which is a critical factor for battery degradation since it consumes cyclable na+ ions. one of the first studies on na-ion cell degradation is presented "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "alternatives for applications requiring fast-charging. it is reported in [56] that the cyclability of sodium-ion batteries are comparable or better than lithium-ion batteries, and that the cyclability is good over a wide range of ambient conditions; specific sodium-ion cells tested under specific conditions were reported to last twice as many cycles compared to lfp cells cycled at similar conditions. moreover, it was suggested that na-ion batteries might not experience a knee-point in the degrad"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "in principle make soc estimation easier, and requiring much less data and less complicated models [125]. equivalent circuit models (ecm) can be used for sodium-ion batteries, as for lithium-ion. ecms for sodium-ion batteries with different numbers of rc- elements are investigated in [126]. it is concluded that a third-order model is sufficient to describe the dynamic nonlinear voltage response of the sodium- ion cell, and that this works better than lower-order alternatives. however, the ecm was"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 4,
    "text": "are constant current charging time, constant voltage charging time and constant current discharging time. these indicators may be extracted from testing data, where particular cccv (constant current constant voltage) charging schemes are employed, but it is noted that they are not likely to be found in real operating data from batteries during variable loading. moreover, the effect of e.g. temperature is not accounted for. notwithstanding, it is reported that the methods achieve good results for"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 5,
    "text": "machine learning have also been used for capacity prediction of sodium- ion batteries. the performance analysis presented in [130] applied machine learning to a large dataset constructed from the literature, and reported that random forest models are reasonably good in obtaining crude predictions for discharge capacity. several other machine learning techniques were explored, but the scope of this study is somewhat different from on-line monitoring of capacity and state of health. rather, averag"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 6,
    "text": "models. input data are current, voltage and temperature, and a lowcomplexity model is found sufficient due to the absence of voltage plateaus such as the ones observed for a typical lfp ell. a fusion of deep learning models is used in [131] to improve the modeling of state of charge for na-ion batteries, and is reported to perform well under various operation conditions. although these models are used for state of charge rather than state of health, it is acknowledged that soc and soh are depend"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 7,
    "text": "cycling conditions, and it is demonstrated to perform also for sodium-ion batteries. it is designed to be applied to raw data without the need for prior feature engineering and includes an encoder–decoder framework based on lstm. two variants of this model is adapted and fine-tuned for na-ion cells in order to predict battery degradation and monitor soh. a recurrent neural network architecture is utilized to predict state of health in [10] lithium-ion and sodium-ion batteries. then renormalizati"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 8,
    "text": "on na-ion data performs better on the liion data than a reference model trained on li-ion applied to na-ion data. however, this was thought to be due to differences in charging protocols rather than differences in chemistries. the literature on data-driven state of health monitoring specifically for sodium-ion batteries is relatively scarce and the technology is still immature. nevertheless, the literature survey suggests that there should be no fundamental differences between lithium-ion and so"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 6,
    "chunk_index": 9,
    "text": "batteries. moreover, some studies that have investigated transfer learning methods suggest that it can be possible to transfer data-driven models trained on one type of batteries (e.g. a type of lithium-ion) to other types (e.g. sodium-ion). data-driven state of safety monitoring the concept of a measure for the state of safety (sos) is relatively novel and not well established. in particular, it is not widely used in the maritime industries. however, as the safety of maritime battery systems is"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 8 the concept of state of safety (sos) for batteries and battery systems, and a preliminary assessment of the feasibility of introducing data-driven state of safety for all-electric maritime vessels. it includes a literature survey on scientific literature on battery state of safety, which is currently scarce. it is noted that the discussions in this section is chemistries-agnostic, although applications reported in the literature are mostly "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "requirements for lithium- ion energy storage systems on board ships [132]. fire safety and the safety of electrical installations are main focus areas of these guidelines, which are developed based on imo guidelines for developing goal-based standards. several recommendations relating to the design and arrangements of the energy storage system is made, and means to detect, contain and suppress/extinguish fires both inside and outside of the battery room are suggested. some explicit goal is that "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "detection systems should initiate an alarm. other goals and requirements are related to e.g. ventilation, electrical arrangements and temperature control. it is further required that alerts and indicators should be raise alarms at a manned control position in case of e.g. earth fault detection, high or low battery voltage, high or low temperature, high charge current, and failure of the bms or any sensors. however, there is no mention of a metric such as the state of safety (although it is menti"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "a probabilistic approach to safer operating areas (soa) is proposed in [134] based on abuses, failure mechanisms, electrochemical parameters and various health indicators. large amounts of data and machine learning are used in [135] to define a safety envelope of mechanical loading conditions for lithiumion batteries. naturally, battery aging affects the safety limits of a battery, and this should be reflected in how the batteries are operated when the batteries age and approach end of life, see"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "thermal runaway [137]. under certain conditions, external or internal, the energy stored in the batteries might be released at a rate faster than it can be absorbed and cause an uncontrolled temperature rise and subsequent fire. it is therefore of paramount importance to understand what these conditions are and to prevent them from occurring. typically, abuse conditions can be categorized into three types, i.e. mechanical abuse (e.g. cell penetration), electrical abuse (e.g. overcharge) and ther"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 5,
    "text": "to avoid unsafe conditions (external or internal) or to provide adequate cooling systems to be able to dissipate excess energy in case of an imminent thermal runaway event. typically, the battery management system (bms) monitors the cell voltage, current and possibly also the temperature to ensure proper control. this is an area of active research, and there are rapid developments in battery safety management [138]. it is noted in [139], that most fires and safety incidents with electrical vehic"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 6,
    "text": "and that therefore cascading heat propagation is more likely for lithium-ion systems. another aspect of maritime battery safety is the ability of the battery system to deliver the required energy and power at any time during operation. failure to do so might cause loss of propulsion and maneuverability which might again lead to serious accidents such as collision and grounding. this safety aspect is typically monitored by combining state of charge and state of health of the battery. these two ty"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 7,
    "text": "the battery’s ability to deliver the required energy and power is reduced over time. another effect is that the battery internal resistance and impedance might increase, and this may increase the risk of thermal runaway and fire. it is generally assumed that degradation in terms of capacity loss and impedance increase is highly correlated, but this may not necessarily be the case for all battery chemistries. other degradation mechanisms such as lithium plating may also affect a battery’s thermal"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 8,
    "text": "safety, related to fire safety, state of safety might be an interesting metric to monitor in a condition monitoring system. it has been suggested that ultrasonic monitoring can be used to detect physical changes in batteries and provide a means for early warning of thermal runaway without relying on the electrical measurements [142,143]. according to [142] it is possible to detect the start of overcharge in order to trigger an emergency stop and take the battery out of service before a catastrop"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 7,
    "chunk_index": 9,
    "text": "conventional bms systems. however, more research is needed for such systems to be used under real world operating conditions. a comprehensive review of early warning methods for thermal runaway of lithium-ion batteries is presented in [144], including early warning based on monitoring of internal electrical characteristics, temperature, force or gas generation, as well as ultrasound detection. alternative approaches to monitor and classify thermal safety status of batteries are explored in e.g. "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 9 machine learning is used to develop an online safety classification method for lithium-ion batteries during charging and discharging in [146]. four representative safety levels are defined and the model only needs a short period of current and voltage signals as input. however, it is noted that capacity loss is not considered, and this is a limitation of the current model. a simulation study analyzing the safety state based on characteristi"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "state of charge and state of health to consider the battery’s state of x (sox), where sox is formulated as a uniform indicator of the overall health conditions for battery cell, modules, packs and even large- scale battery systems. more data-driven approaches to early warning for thermal runaway in batteries are also suggested in the literature. warning methods for overcharge-thermal runaway for lithium-ion batteries based on features extracted from measurements of voltage, temperature and press"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "the focus on this literature is on the state of safety metric for monitoring the safety of batteries. an sos metric could integrate both aspects of battery systems into one, monitoring both conditions that might increase the risk of fire events and accounting for the effect of the gradual degradation. this is suggested in [139] as an important direction for future research. however, as discussed in [57] this may be very challenging, since two identical cells might respond differently to identica"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "cited several times in the literature, only one additional reference, i.e. the master thesis presented in [153] has been found that really focuses on the sos of batteries. hence, the state of safety concept does not seem to have been widely implemented or further developed. in particular, no applications of the concept of state of safety have been identified for maritime battery systems. however, some related concepts, such as the overcharge safety status (ocss) proposed in [154] and the safety "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 4,
    "text": "of safety function is composed of sub-functions corresponding to various forms of abuse, e.g. related to voltage, temperature or mechanical deformation. the formulation is open for additional sub-functions to be added in order to generalize the concept of state of safety to cover other abuse conditions. mathematically, the state of safety function is defined as follows: 𝑓𝑠𝑎𝑓 𝑒𝑡𝑦(𝒙) = 𝑓𝑎𝑏𝑢𝑠𝑒1 (𝒙) = 𝑔(𝒙)1 + 1 (1) where 𝑓𝑎𝑏𝑢𝑠𝑒(𝒙) denotes the state of abuse, 𝑓𝑠𝑎𝑓 𝑒𝑡𝑦(𝒙) is the state of safety and 𝒙 "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 5,
    "text": "function is suggested, to arrive at the following form 𝑓𝑠𝑎𝑓 𝑒𝑡𝑦(𝒙) = ( 1 )[ ℎ(𝒙1)−ℎ(𝒙100) ]2 , (2) − 1 + 1 𝜁 ℎ(𝒙𝜁−ℎ(𝒙100)) where 𝒙100 represents the combination of battery variables corresponding to 100% safety and 𝒙𝜁 corresponds to the variables describing the limit of acceptable safety, i.e. 𝑓𝑠𝑎𝑓 𝑒𝑡𝑦(𝒙100) = 1 and 𝑓𝑠𝑎𝑓 𝑒𝑡𝑦(𝒙𝜁) = 𝜁∕100, see [152] for details. it is observed that eq. (2) takes the form of a cauchy distribution. it is further suggested that such state of safety can be formulated "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 6,
    "text": "each sub-function, then one would have some important values sos = 1.0: completely safe sos = 𝜁: warning (one sub-function may be at 𝜁) sos = 𝜁𝑛: minimum safety (all sub-functions might be 𝜁) sos < 𝜁𝑛: unsafe (all sub-functions might be below 𝜁) that can be used to trigger warnings and alarms. note however, that it could be possible with this construction that all but one sub-functions are equal to 1.0 even if 𝑆 𝑜𝑆 < 𝜁𝑛, indicating an unsafe condition in only one of the variables, so how to use "
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 7,
    "text": "are discussed in [152] are temperature (over- and under-temperature), current (overcurrent), voltage (over- and under-voltage), state of charge (higher soc means more energy stored in the battery and hence less safety) and state of health. with regards to the latter, is suggested that soh may have two opposite effects on safety; lower soh means less energy stored even at maximum soc and hence less fire potential and that an older battery (lower soh) might be more prone to unsafe behavior and pos"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 8,
    "chunk_index": 8,
    "text": "functions are defined for the battery system in question. it is noted in [156] that the fidelity and practicability of such an sos implementation is difficult to guarantee, and that the accuracy will depend on the selected sub-functions. this definition of state of safety is further investigated in [153]. the variables current, rack voltage, maximum and minimum cell voltage, cell imbalance and maximum and minimum cell temperature were used, and state of safety was monitored based on the followin"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "e. vanem and s. wang future batteries 5 (2025) 100033 10 classifies operations into safe, warning and critical conditions, and results are reported in terms of time spent in each of the warning/critical conditions for each of the sub-functions. it is reported that one or more abuses are identified for about 13% of the days (12 955 out of 97 182 rack days). critical abuses are identified much less frequent than warning conditions, which is to be expected, except for cell imbalance. it is noted th"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "safety as suggested in [152]. another shortcoming of this application is that no sub-function was introduced to relate the state of safety to battery degradation and aging. hence, an old battery would be regarded at 100% state of safety after experiencing abuse if the corresponding variables return within operational limits. it seems counterintuitive to allow the state of safety to return back to 100% when it is approaching end of life, so adding such a sub-function is believed to be important t"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "this metric in detail, i.e. the master thesis in [153]. this study indicates that the state of safety, as defined in [152] is a feasible measure that can be used to monitor the safety level of a battery with respect to thermal runaway and fire. however, the various safety sub-functions and the various threshold levels need to be determined and further research is recommended to further develop and validate the sos as a reliable measure for safety monitoring. it is believed to be important to inc"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 3,
    "text": "for these. in addition, it is believed to be interesting to investigate how to build in some kind of memory into the state of safety measure, assuming that a battery that has experienced abuse might be less safe than an equally old battery (with the same soh) that has never experienced abuse. it is not obvious how this should best be incorporated in a state of safety measure, and more research is recommended to further develop these aspects of battery state of safety. based on the above discussi"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 4,
    "text": "or electrical faults. however, the effective implementation of sos also faces several obstacles such as the lack of standardized safety protocols across diverse battery technologies, the complexity of integrating state-of- safety assessments with existing ship systems, and the high cost of advanced monitoring and control systems. addressing these challenges requires industrywide collaboration, regulatory support, and advancements in robust and cost-effective safety technologies. conclusions impl"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 5,
    "text": "the standardization of monitoring frameworks. economically, the high initial investment in advanced sensors, data analytics platforms, and integration with existing ship systems can be a barrier, particularly for smaller operators. furthermore, ongoing costs for calibration, maintenance, and potential retrofitting add to the financial burden. operationally, integrating soh and sos monitoring into the workflows of maritime personnel requires adequate training and user-friendly interfaces to avoid"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 6,
    "text": "lithium-ion and sodium -ion batteries, and how these differ from methods applied to nmc type of lithium ion batteries. based on the literature review, there are no reason to believe that data-driven approaches to state of health estimation should be fundamentally different for these alternative chemistries compared to nmc- type of batteries. hence, approaches such as empirical and semi-empirical methods, physicsbased models and purely data-driven machine learning techniques are believed to be ap"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 7,
    "text": "poorly on lfp-type of batteries. this is not the case for sodium-ion batteries, which are associated with comparable large voltage drops during discharge. the concept of a measure for the state of safety of batteries is relatively novel and is not yet well established in the industry. the most common definition is that the state of safety can be regarded as the reciprocal of the state of abuse, and various safety sub-functions can be defined based on different abuse conditions, e.g. thermal, vol"
  },
  {
    "source_pdf": "Data_driven_state_of_health_and_state_of_safety_estimation_for_alternative_battery_chemistries_A_comparative_review_focusing_on_sodium_ion_and_LFP_lithium_ion_batteries_Erik_Vanem_Shuai_Wang.pdf",
    "page": 9,
    "chunk_index": 8,
    "text": "all in maritime applications, this measure seems highly relevant for maritime battery systems. if successfully implemented, it is believed that it may provide a means for monitoring when the battery experiences abusive conditions and hence provide a means for early warning of impeding safety events and possible thermal runaway. this is deemed particularly important for very large onboard battery systems, with large fire potential. nevertheless, the maturity of this measure is low, and further in"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "r t i c l e i n f o a b s t r a c t keywords: sodium-ion batteries aging mechanism electrochemical impedance spectroscopy state of health support vector regression as sodium-ion batteries (sibs) increasingly penetrate the electrochemical energy storage market, elucidating their degradation mechanisms and precisely assessing the state of health (soh) become critical to ensure the efficient management and operational safety of sib systems. this study aims to investigate the aging mechanisms of sib"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "and construction of aging features from the eis resistant to temperature disturbances. finally, leveraging the proposed temperature-resistant eis health factor, high-precision estimation of battery soh over a wide temperature range is realized by only using eis data from a single temperature to train a support vector regression (svr) model, and there is no need to rely on temperature sensors for correction. results show that the gaussian- kernel svr model has an average root-mean- square error ("
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "this situation is reflected in the extreme price volatility of lithium carbonate. in the long term, the high abundance of sodium resources, in contrast to the scarce, uneven distribution of lithium elements in the earth’s crust, makes sodium-ion batteries (sibs), which operate on principles similar to those of lithium-ion batteries (libs), an attractive strategic alternative [3–5]. currently, the main cathode materials used in the development of sibs are layered oxides [6], polyanions [7], and p"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "the aging mechanisms of sibs is limited, and aging data during long-term cycling are scarce, making the similarities and differences in the degradation mechanisms of sibs and libs unclear. therefore, conducting aging tests on sibs and analyzing the degradation mechanisms are crucial for optimizing the performance of sibs and extending their service life. battery performance degradation affects the reliability of equipment operation. real-time understanding of the state of health (soh) of batteri"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "coulomb counting, open-circuit voltage (ocv) measurement, and internal resistance measurement [14]. these methods are straightforward and easy to implement but incompatible with online applications. they are mainly used in offline scenarios, such as estimating the capacity of used batteries. the cumulative retired capacity of power batteries in china has exceeded 25 gwh, and it is expected to surpass 100 gwh by 2025. with the anticipated large-scale retirement of power batteries and the widespre"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "decay. they provide a detailed description of the internal electrochemical mechanisms and different aging processes of batteries. however, the complex modeling and solving process of electrochemical models requires high computational resources, making these models impractical for large-scale application in actual battery operations. ecms typically incorporate parameter identification algorithms, such as kalman filters, particle filters, or their variants, to identify parameters, including intern"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "aging mechanisms of the battery no longer need to be assessed. however, the predictive performance of data-driven models is highly dependent on data quality. in practical applications, battery charging conditions are sometimes incomplete. although some studies have proposed the use of fragmented voltage and current data for modeling [20,21], achieving online application under complex environmental conditions and variable operating scenarios remains difficult. in summary, the reliance of traditio"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 0,
    "chunk_index": 7,
    "text": "(eis) measurements into the engineering application of batteries as a new feature for battery soh estimation was proposed. eis, a noninvasive in- situ characterization technique, can acquire extensive internal information on batteries [22], thereby providing a detailed description of the battery aging state. numerous studies have used eis testing technology for the rapid assessment of retired battery soh in offline scenarios. for example, faraji et * corresponding author. e-mail address: yljcqu@"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 - 2 al. [23] developed a gaussian-process regression model for soh estimation by using 325 lithium battery eis samples collected under varying aging, soc, and temperature conditions. cross-validation results demonstrated that the model’s soh estimation error for batteries with unknown historical information is only 1.1 %. with the continuous advancement of eis online measurement technologies, several researchers have proposed advanced and practical onboard "
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "as an example, an integrated eis testing platform can provide an alternating current excitation signal that enables bms to capture the response voltage signals from each cell. subsequent discrete fourier transform of these response voltages yields impedance data. author’s team has also proposed a passive eis measurement technique for online applications. this approach replaces the alternating current source in traditional eis testing platforms with an electronically programmable load. perturbati"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "of batteries in complex environments is difficult to determine, which can lead to degradation information being compromised under temperature interference. some studies that utilized eis for battery soh estimation have overlooked this critical issue. fu et al. [24] performed online rapid eis through improved fast fourier transform; they selected six eis features to characterize battery degradation and established an extreme learning machine model for soh estimation. however, all eis samples in t"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "included in the training samples remains to be validated. recognizing the seriousness of temperature interference, some researchers have corrected their models by inputting the collected battery temperatures. for example, zhang et al. [27] identified mapping relationships among solid electrolyte interface resistance, charge transfer resistance, and soh under different temperatures and states of charge (soc). they established a probabilistic model for lithium battery soh estimation with charge tr"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "methodology centered on temperature-resistant impedance feature extraction and construction, effectively mitigating thermal disturbances in battery soh estimation. firstly, cyclic aging experiments were conducted on commercially available sibs, and the aging mechanism of sibs was analyzed using eis, incremental capacity analysis (ica), and scanning electron microscopy (sem) techniques. secondly, temperature- resistant battery impedance features were extracted and constructed by studying the agin"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 3 fig. 2. overall roadmap of this study. were identified as the crucial factors that accelerated the per formance degradation of commercial sibs. (2) a novel method that extracts and constructs temperature- resistant health factors, rather than relying on temperature correction and compensation, was proposed for the first time to address the issue of temperature interference in eis-based battery soh estimation. by using eis data obtained at a single tempera"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "v, the discharge cutoff voltage was 1.5 v, the nominal capacity was 3.3 ah, and the maximum continuous charging rate was 1 c. cyclic aging and eis testing experiments were conducted with the test platform shown in fig. 3(a) by following the battery test scheme illustrated in fig. 3(b). first, fresh sibs were subjected to eis tests prior to cyclic aging by using current excitation provided by the multifrequency sinusoidal mode of an electrochemical workstation (solartron, echemlab xm), with an ex"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "at 10 ◦c, 25 ◦c, and 30 ◦c in a fully charged state. the batteries were left in a thermal chamber for over 3 h prior to each eis test to ensure that a steady state was reached. finally, end-of-life cells were disassembled in a glovebox under an inert atmosphere, and sem (thermo fisher scientific, quattro s) was employed to characterize the electrodes and separator morphology. 2.2. aging mechanism of sibs on the basis of the experiments, the aging condition and eis data of 12 sibs were obtained a"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "corresponds to solid electrolyte interface (sei) impedance (zsei), which expresses the resistance to sodium ions through the sei layer on the surface of the anode material. the second semicircle in the middle- and low-frequency bands refers to charge- transfer impedance (zct), which describes the resistance to adsorption of sodium ions at the interface of the battery and the ability of transferred sodium ions to resist entering the interface and undergoing electrochemical reactions. the diagonal"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 - 4 the ohmic impedance (rs) of the battery. the total impedance of ecm can be expressed as: ztotal =zrs + zsei + zct + zw (1) where zsei and zct consist of a constant phase element (cpe) in parallel with a resistive element and zw is described by series-connected cpe. further expansion of each component leads to: z(jω)=rs + rseiy1r(jseiω)n1 + 1 + rcty2(rjωct)n2 + 1 + y3(j1ω)n3 (2) where y is the equivalent capacitance and n is the index in the range of [-1"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "as the battery underwent aging, the impedance spectrum developed two distinct semicircles, indicating a progressive increase in rct during the subsequent cycles. the data in table 1 show that rct increased by more than 300 times after 180 cycles. the causes of the increase in rct were further analyzed by comparing sem images of the cathode before and after aging, as shown in fig. 5(a) and (b). initially, the fresh sib cathode material was characterized by well-defined spherical particles with a "
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 5 table 1 ecm parameters for aging sib. cycle number rs (mω) rsei (mω) y1 (snω− 1) n1 rct (mω) y2 (snω− 1) n2 y3 (snω− 1) n3 0 14.35 19.54 1.27 0.73 0.16 59.46 0.98 1083 0.78 20 14.54 19.28 1.29 0.71 0.21 51.19 0.96 1328 0.84 40 14.91 18.60 1.42 0.69 0.24 42.24 0.89 1323 0.84 60 15.29 21.11 1.46 0.69 3.88 33.94 0.94 1104 0.81 80 15.77 20.60 1.30 0.70 5.52 29.22 0.97 1016 0.80 100 15.82 21.73 1.27 0.70 9.99 27.35 1.00 1056 0.82 120 15.94 20.81 1.23 0.70 15.4"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "and (d) aged cathodes, and (e) healthy and (f) aged diaphragms of sibs. cathode material led to pulverization and agglomeration [30]. in addi tion, unlike the surface of the fresh cathode, that of the aged cathode material was covered with a thin film probably because of the thermal instability of the electrolyte during cycling, resulting in the accumulation of by-products on the cathode surface [31]. furthermore, the loss of the active material in the electrode hindered the electrochemical reac"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 - 6 the sei film increasingly difficult. moreover, the rightward shift of the eis curve indicated that the ohmic resistance of sib increased by approximately 12.5 % during cycling because of the degradation of the electrode material and electrolyte, the increased interface resistance, and some physical damage to the battery components. the aging process of sibs was further analyzed from the perspective of internal phase transitions by using the ica method. "
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "is shown in red. three distinct peaks were observed in the charging ic curve of sib. the first peak was in the low-voltage range, the second peak was around 3.3 v and attributed to the main voltage platform, and the third peak was near 3.6 v and associated with the high-voltage platform. the two voltage plateaus were attributed to the redox couples [33] involved in the two-stage phase transition of the sib cathode material. the aging patterns of sib were qualitatively assessed by analyzing the v"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "this degradation reduces the available active hard carbon, the utilization of the high-voltage plateau capacity in hard carbon is enhanced due to the redundant capacity design of the negative electrode [34]. this results in the increased third peak amplitude alongside reductions in other peaks. in addition, the second peak gradually widened, and the peak slope decreased when the number of cycles increased, indicating that the path length of the phase transition reaction and resistance increased "
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "carbon particles, with numerous small black carbon particles embedded in the edges and gaps of these particles. by contrast, the surface of the aged hard carbon electrode contained a large amount of deposited sodium dendrites, which were sharp and needle-like in appearance. the sem images in fig. 5(f) reveal extensive damage to the battery separator caused by the sodium dendrites. this observation indicates that the sodium deposition side reactions that reduced the active sodium ion quantity wer"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "in this study is much faster than that of libs under similar conditions [27]. this difference may be attributed to the large radius of sodium ions that causes substantial volume changes in layered oxide cathode materials during charge and discharge cycles. the highly pronounced particle degradation during prolonged cycling leads to a severe decline in sodium ion diffusion kinetics. therefore, controlling the volume changes associated with phase transitions in layered oxide cathode materials duri"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 5,
    "text": "platform working potential (<0.1 v) of the hard carbon anode used in sibs [38] is lower than that (0.01–0.2 v) of the graphite anode employed in libs; the latter is closer to the sodium metal deposition potential (0 v) than the former is. previous research on hard carbon anodes primarily focused on increasing their low platform working potential to achieve high energy density [39,40], which further increases the risk of sodium deposition during charging. therefore, increasing the platform workin"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 6,
    "text": "soc at 10 ◦c, 25 ◦c, and 30 ◦c, respectively. overall, the eis curves were considerably affected by temperature. in particular, the semicircle representing sei impedance decreased markedly with increasing temperature. according to the arrhenius equation [41], an increase in temperature enhances ion transport properties and chemical reaction rates. consequently, the resistance to sodium ion migration across the battery interfaces and electrolyte is reduced, and this reduction is reflected as a de"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 5,
    "chunk_index": 7,
    "text": "the charge transfer impedance of the fresh sibs was low, so the variations in charge transfer impedance with soc did not substantially affect the overall eis curve. considerable changes in the eis curve were observed only when soc was extremely low and when charge transfer impedance increased dramatically. in conclusion, temperature and soc variations have a considerable effect on the impedance of sibs, with temperature fluctuation being more pronounced than soc variation. although bms can estim"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 7 (f) 30 ◦c. developed. 3. extraction and construction of health indicators with temperature interference resistance 3.1. extraction of health indicators the considerable effect of temperature fluctuations on impedance measurements renders the implementation of methods reliant on the extraction of health indicators through ecm a challenging endeavor. single- frequency impedance, which is minimally sensitive to temperature, should be extracted as an aging fe"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "features will exhibit weak correlations with battery soh, whereas others will be substantially affected by temperature. therefore, the variation of each impedance feature with fig. 7. (a) real part, (b) imaginary part, (c) magnitude, and (d) phase of impedance at different temperatures for sib. (e) real part, (f) imaginary part, (g) magnitude, and (h) phase of impedance at different soh for sib."
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 8 temperature must be analyzed at different frequencies to identify the features that effectively characterize battery aging while exhibiting minimal fluctuations with temperature changes. these features can then be employed as indicators of battery health. fig. 7 presents the variations in the real part, imaginary part, magnitude, and phase of sib impedance with temperature and battery aging at different frequencies. as shown in fig. 7(e), the real part of"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "errors. by contrast, the real part of impedance at 1000 hz from the eis spectrum can be directly regarded as ohmic resistance. this ac impedance method is the measurement principle employed by many commercial battery internal resistance analyzers. with regard to the effect of temperature on ohmic resistance, previous engineering experience and studies revealed that temperature affects the ohmic resistance of batteries. fig. 8(a) illustrates the observed growth trend of the ohmic resistance of si"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "the given temperature interval. this finding shows that even in the absence of temperature data, the ohmic resistance of sibs is still a valuable health indicator. the remarkable variations in the imaginary part and magnitude of impedance with battery aging, as shown in fig. 7(f) and (h), revealed a strong correlation between the two impedance characteristics and battery soh across most of the studied frequencies. however, fig. 7(b) and (c) indicate that the imaginary part and magnitude of imped"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "principal component analysis (pca) [42] is a commonly used method of dimensionality reduction in high-dimensional data sets. this method involves the decomposition of the data’s covariance matrix to identify principal components, which are the directions of maximum variance, thereby defining the principal axes of the data. through coordinate transformation, pca projects the data into a new coordinate system that captures abundant information in certain dimensions, as shown in eq. (4): zproj =xw "
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "data under varying temperatures and soh conditions in fig. 8(b), the feature after dimension reduction demonstrates strong correlations with battery soh while exhibiting acceptable temperature-induced interference. consequently, the first principal components of the impedance imaginary part and magnitude data were retained after dimensionality reduction and served as extracted health factors for battery soh regression prediction. as illustrated in fig. 7(d), the phase of impedance demonstrates c"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 7,
    "chunk_index": 5,
    "text": "found that among all the impedance values, the phase impedance at 0.065 hz was the most resistant to temperature interference. hence, it can be used as another health indicator for battery aging. 3.2. constructed of health indicators four sib health indicators, namely, ohmic impedance (zre1000), dimensionality-reduced high-frequency imaginary impedance (zimpca), dimensionality-reduced high-frequency magnitude impedance (zpca), and the phase at 0.065 hz (zp0.065), were extracted from the original"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 9 p/zim: although impedance in the mid-frequency range is affected by temperature, different impedance characteristics exhibit similar trends under the effect of temperature variations. therefore, adopting the ratio of the two characteristics at specific frequencies can partially mitigate the influence of temperature interference. fig. 7(h) indicates that the impedance phase angle at 10 hz did not exhibit dramatic changes during battery aging, but its varia"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "made to identify the impedance feature in the imaginary part that could be used as the denominator of the ratio. fig. 9(a) illustrates how the ratio between the phase at 10 hz and the imaginary part at various frequencies changed with temperature. the ratio of the 10 hz phase to the 22 hz imaginary part (p/zim) exhibited the least fluctuation with temperature changes. the reliability of the p/zim feature across a wide temperature range was further assessed. fig. 9(b) shows the distribution of th"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "at 25 ◦c, indicating a strong correlation between p/zim and soh of sib. this decrease trend was similar to the variation observed in the reciprocal of the 22 hz imaginary parts. second, as the cycle count increased, the red region, which represents the standard deviation range of the feature collected within the 10 ◦c-30 ◦c range during battery aging, showed a consistent rise-and-fall pattern around the standard temperature curve, suggesting that the temperature variations caused some interferen"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "changing of the shape of the impedance spectrum from one semicircle to two semicircles. as illustrated in fig. 10(a) and (b), the second semicircle in the eis curve, which characterizes the rct of sib, gradually grew as soh decreased. however, fig. 10 demonstrates that the effect of temperature on rct was more pronounced than that of battery aging. consequently, rct measurements obtained under dynamic temperature conditions are not a reliable indicator of sib aging. to address this issue, a new "
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 8,
    "chunk_index": 4,
    "text": "good resistance to temperature perturbations. aging information on charge transfer impedance over a wide temperature range can be obtained by extracting the aging feature from the shape changes of the eis curve. in the fresh batteries used in this study, rct was small, and eis had a semicircle shape. as the number of cycles increased, rct continuously increased, causing a second semicircle to gradually emerge and eventually exceed the first semicircle as the battery continued to age. the most in"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 8,
    "chunk_index": 5,
    "text": "study, two characteristic frequency points within the sei and charge transfer impedance frequency ranges were selected for analysis, and the ratio of their imaginary part was employed to reflect the changes in the sizes of the two semicircles on the eis curve. the selection of the two characteristic frequency points followed the rule that when the capacity degradation of sib reaches half of the retirement standard, the frequencies corresponding to the peaks of the two semicircles in the eis spec"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 8,
    "chunk_index": 6,
    "text": "not affect the correlation of the features. the ratio of the imaginary impedance at 0.26 hz to that at 8.5 hz (zim0.26/8.5) was employed as a constructed health factor for sibs in this study. fig. 10(d) illustrates the variation in the zim0.26/8.5 characteristic during the cycle process and its resilience to temperature-related fluctuations. zim0.26/8.5 increased with battery aging, an observation that is consistent with the gradual enlargement of the second semicircle on the eis curve. furtherm"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 10 fig. 10. eis at 10 ◦c, 25 ◦c, and 30 ◦c for sibs under (a) 93 %, (b) 92 %, and (c) 90 % soh. (d) zim0.26/8.5 and its fluctuation with temperature disturbance during the cyclic aging of sibs."
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 11 temperature-related influences because the temperature response patterns of sei film impedance and charge transfer impedance were disparate. nevertheless, the discrepancy was relatively small and acceptable throughout the entirety of the battery’s aging cycle. hence, the zim0.26/8.5 characteristic proposed in this study is an effective aging feature that is resistant to temperature interference. 4. soh estimation model and results 4.1. soh estimation bas"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "the original nonstationary sequence and utilizes a residual stripping technique to decompose the original signal into a series of stable intrinsic mode functions (imfs) and a residual model (res), as shown in eq. (5): ∑n x(t)= imfi(t) + rn (5) i=1 where x(t) is the original capacity sequence, imfi(t) is the ith imf component, n is the number of imfs, and c is a residual term that reflects the long-term trend of the original signal sequence. as shown in fig. 11, the original signal was decomposed"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "and the nominal capacity, respectively. fig. 12 presents the pearson correlation coefficients between six battery health indicators and soh measured at different temperatures. the correlation coefficients of the health indicators varied at different temperatures, but they were all greater than 0.6. this result indicates that although temperature slightly affected the correlation of some health indicators, they still exhibited a strong correlation with soh across all temperatures. subsequently, a"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 10,
    "chunk_index": 3,
    "text": "the prediction samples spanned multiple measurement temperatures. specifically, 10 out of the 12 sibs were designated as the training set, and the 2 remaining sibs served as an independent test set. eis samples for training were collected only at 25 ◦c, resulting in 80 samples, and the test set samples were collected at 10 ◦c, 25 ◦c, and 30 ◦c. a five-fold cross-validation [46] framework was applied to train the svr model to prevent overfitting while maintaining computational tractability. the i"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 10,
    "chunk_index": 4,
    "text": "and epsilon parameter (log-uniform distribution over [0.001, 0.1])—were optimized in combination. the optimization process was limited to 200 iterations. 4.2. soh prediction results and analysis 4.2.1. soh estimation results based on svr the comparison of the optimized estimation results for svr models with linear, polynomial, and gaussian kernels is presented in table 2. among the models, the svr model utilizing a gaussian kernel achieved the best estimation performance, with an r2 of 0.90, a r"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 10,
    "chunk_index": 5,
    "text": "function r2 rmse (%) mae (%) linear kernel 0.81 1.68 1.06 polynomial kernel 0.86 1.47 0.98 gaussian kernel 0.90 1.26 0.89 with that of the actual values for all samples, and fig. 13(b) depicts the discrepancies between the observed values and predictions at various stages of aging. overall, the model exhibited high estimation accuracy, with the majority of predictions aligning closely with the corresponding measured values. fig. 13(c) shows the estimation residuals, which represent the differenc"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 12 model at temperatures of 10 ◦c, 25 ◦c, and 30 ◦c. as the number of cycles increased, the soh of the three batteries exhibited considerable degradation. throughout the entire cycling process, the average soh values estimated by the model on the basis of impedance data collected at different temperatures consistently maintained a small error relative to the measured values, with an mae of approximately 1 %. moreover, the pink shading represents the standar"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "plots and error data of the gaussian-kernel svr model at various temperatures to further demonstrate the stability of the proposed soh estimation method across a wide temperature range. the box plots indicate that the absolute values of the observed errors at each temperature were less than 2.5 %, with no outliers, demonstrating that the model maintained high accuracy and stability in its estimates across the different temperatures. the median of the errors at different temperatures indicates th"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "constructed sodium-ion battery health indicators at (a) 10 ◦c, (b) 25 ◦c, and (c) 30 ◦c with soh. fig. 13. (a) response distribution plot, (b) true value-predicted value distribution plot, and (c) residual plot for model cross validation. fig. 14. soh estimation results for (a) test set #1, (b) test set #2 and (c) test set #3 at multiple temperatures based on svr."
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 13 fig. 15. box plots of prediction errors at different temperatures. three batteries at all temperatures were below 1.5 %, further confirming that the proposed temperature-resistant health indicators, combined with the svr model, exhibited good adaptability across the wide temperature range. to further analyze the importance of the proposed features and test the model’s robustness, we employed a model perturbation-based approach for feature sensitivity ana"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "1.33 1.17 0.54 0.47 30 1.12 1.04 1.47 1.33 0.56 0.50 sequentially removed to retrain the model and record its performance, thereby quantifying the impact of feature removal on prediction outcomes. the sensitivity of each feature is reflected by the ratio of the error increase after feature removal to the baseline error: sensitivityi =rmseremovermsei − basermsebase (7) where rmseremovei denotes the estimated error when the i-th feature is removed, and rmsebase represents the baseline error. based"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "than zero. this indicates that all features positively contribute to the model performance, with each feature providing irreplaceable information. notably, the p/zim feature showed the highest sensitivity, suggesting that the charge impedance growth exerted the strongest influence on the model, whereas the zimpca feature displayed the lowest sensitivity, reflecting its relatively minor importance and confirming the model’s robustness to the absence of this non- critical feature. 4.2.2. compariso"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "cross-validation protocols, while employing a consistently optimized svr model as the unified estimation framework. the comparative soh estimation results obtained from the different feature extraction strategies are systematically presented in fig. 16. as shown in fig. 16, the mae of soh estimation using full-frequency- point features and equivalent ecm features reached 2.93 % and 3.83 %, respectively, with a substantial proportion of residuals exceeding 5 %, where some estimated values even su"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 12,
    "chunk_index": 4,
    "text": "a single temperature condition without temperature labels, these temperature- induced feature variations in the test set were misinterpreted by the model as soh changes. comparative results demonstrate that our proposed temperature interference-resistance features exhibit superior performance over traditional approaches when processing wide- temperature-range impedance data. 4.2.3. comparison of different data-driven models to comprehensively evaluate the performance of the proposed model, this "
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 14 fig. 16. (a) response distribution comparison plot of different features, (b) residuals comparison plot of different features, true value versus predicted value distribution plot of (c) temperature interference-resistance features, (d) full-frequency-point features and (e) ecm features."
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 14,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 15 fig. 17. (a) response distribution comparison plot of different models, (b) residuals comparison plot of different models, true value versus predicted value dis- tribution plot of (c) svr (d) gpr and (e) mlp. models, the svr framework achieved superior performance with a mae of 0.755 %, outperforming both the gpr (0.790 %) and mlp (0.833 %) approaches."
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 15,
    "chunk_index": 0,
    "text": "y. liu et al. energy 332 (2025) 137064 16 in addition, in terms of residual distribution, the svr model maintained all residuals below 2 %, while the gpr and mlp models exhibited peak residuals exceeding 2 % and 5 %, respectively. these comparative results conclusively demonstrate the enhanced precision and reliability of our proposed svr- based estimation framework. 5. conclusions this study conducted cyclic life tests using a commercially available sib to investigate the aging mechanisms and p"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 15,
    "chunk_index": 1,
    "text": "battery life degradation. additionally, the manufacturers’ strategies of extending the low-potential plateau to achieve high energy density lead to a low operating potential of hard carbon anodes and a high risk of sodium deposition. the formation of sharp sodium dendrites could pierce the separator and trigger thermal runaway in sibs. (2) four features reflecting the changes in ohmic resistance, sei impedance, and sodium ion diffusion impedance of sibs were extracted, namely, zre1000, zimpca, z"
  },
  {
    "source_pdf": "Degradation Mechanism of Sodium-Ion Batteries and State of Health Estimation Via Electrochemical Impedance Spectroscopy under Temperature Disturbances, Yupeng Liu, Lijun Yang, Ruijin Liao.pdf",
    "page": 15,
    "chunk_index": 2,
    "text": "◦c, 25 ◦c, and 30 ◦c, the average rmse was 1.14 %, and the average mae was 0.96 %. all rmse and mae values were below 1.5 % at each temperature. these results indicate that the model maintained stable performance despite the temperature variations. in future studies, we will further validate the proposed method using battery datasets from diverse operating conditions and engineering applications, while also enhancing the scientific validity of feature extraction and improving the robustness and "
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 1 1. introduction as renewable energy gains wider adoption and the promotion of new energy vehicles is accelerated, the realm of electrochemical energy storage devices has witnessed remarkable growth and research activity. at the forefront, lithium-ion batteries have commanded significant attention [1–5]. however, the escalating production costs stemming from uneven distributions of valuable metals like lithium (li) and co"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "cathode materials in sibs. to further improve their viability, current research endeavors have concentrated on expanding the discharge range and boosting the capacity of ptype layered oxide materials [15]. a noteworthy example is na0.67ni0.3mn0.7o2 (nnm), which leverages a fabrication process reminiscent of ternary materials in lithium-ion batteries [3]. operating within a lower voltage range, this material displays excellent stability and reduced production costs [16]. however, its constrained "
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "and na+ vacancy ordering are frequently employed [20,21]. introducing metal ions with closely matched ionic radii at transition metal sites can induce a controlled structural distortion, effectively suppressing phase transitions and yielding smoother charge- discharge curves [14,15,22,23]. besides, the strategy of mg doping has previously exhibited its efficacy in fine-tuning phase transitions within p-type materials, especially under high voltage conditions, resulting in a transition from p2-o2"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "of the transition metal layer along the (002) plane led to a marked reduction in active sites, translating to significant capacity decay. the introduction of mg proved instrumental in enhancing structural resilience under high voltages, effectively suppressing anion redox reactions and inhibiting layer detachment. the ensuing structural degradation pathway shifted from the outer to inner regions along the (002) plane, elevating cycling stability at elevated voltages. this research comprehensivel"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "mg:ni: mn = x: (0.3 x): 0.7. concurrently, a suitable amount of naoh solution (5 mol l1) and nh3h2o solution (2 mol l1) were added to the reactor. the precursor was formed at ph = 11.1–11.5 and nh3h2o concentration of 3–4 g l1 until the particle size reached approximately 10 lm. the resulting mgxni0.3xmn0.7(oh)2 particles were obtained after washing, filtration, and vacuum drying at 110 c overnight. subsequently, the mgxni0.3xmn0.70(oh)2 particles were mixed with na2co3 in a molar ratio of 0.7:1"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "evolution of synthesized products was investigated with x- ray diffraction (xrd) spectroscopy. refined fitting was performed to extract specific structural information using the gsas software. the microstructure and elemental distribution of the materials were examined using scanning electron microscopy (sem), transmission electron microscopy (tem), and energy-dispersive x-ray spectroscopy (eds). to obtain crosssectional profiles, an ion milling system (im4000, hitachi) was employed. the chemica"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "in-situ xrd measurements were conducted at a current of 0.1 c within the 2.0–4.0 v voltage range. the scan rate was set at 5 min1, and diffraction patterns were acquired every 10 min. 2.3. electrochemical characterization all electrochemical analyses were conducted using 2023-type coin cells. the cathode was composed of active material, carbon black, conductive graphite, and polyvinylidene difluoride (pvdf) in a ratio of 90:6:1:3, respectively. the electrolyte comprised 1 m naclo4 dissolved in a"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 2 intermittent titration technique (gitt) test involved resting the coin cells for 1 h after charging/discharging at 0.05 ma for ten min within the voltage range of 2– 4.3 v. 2.4. calculation method the computational investigations were conducted employing the first- principles calculation framework of castep. for the exchange-correlation potential, the generalized gradient approximation (gga) was employed using the perdew"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "wave functions was established at 450 ev [26–28]. 3. results and discussion xrd tests were conducted on samples with varying doping ratios to validate the homogeneity of mg doping and its impact on the material structure (fig. s1a–d). the positions of characteristic peaks in the xrd spectra of these samples aligned consistently with the standard peak at pdf#54-0894 [29]. the xrd refinement patterns of nmnm-5 establish the p2-type layered structure of material without distinct characteristic peak"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "primary flake-like particles. similar results are observed in the series samples, indicating the successful doping of mg (fig. s3a–l). to further ascertain the distribution of mg elements, particles were dissected and subjected to sem-based eds mapping. this analysis revealed the uniform distribution of mg elements across the entire particle cross-section without surface enrichment, affirming the effectiveness of the doping process (fig. 1b– d). additionally, tem was employed to validate the mic"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "material elements, xps was employed to analyze the surface elemental species and their oxidation states in the nmnm-5 material. the high-resolution xps spectra of ni 2p were resolved into ni 2p3/2 and ni 2p1/2 components. by deconvolution, peaks at 854.7/872.2 ev and 856.0/873.9 ev were discerned, corresponding to the oxidation states of ni2+ and ni3+ (fig. 2a) [31,32]. the mn 2p peak comprised features positioned at 641.8 and 653.6 ev, attributing to the mn4+ oxidation state (fig. 2b) [33]. the"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "of the high-resolution ni 2p, mg 2p, c 1s, and o 1s xps spectra were conducted for the nnm material. it was observed that the oxidation states of ni and mn remained consistent (fig. 2e and f). notably, the peak area ratio of o 1s deconvolution peaks corresponding to tm– o and na2co3 for nmnm and nmnm-5 was 1: 2.44 and 1: 2.17, respectively, indicating the reduction in the proportion of surface carbon attributable to na2co3 after mg doping (fig. 2g). this decrease implies that the introduction of"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "materials. nnm exhibits five pairs of redox peaks (3.90/3.88 v, 3.71/3.64 v, 3.63/3.56 v, 3.38/3.29 v, and 3.18/2.97 v), whereas doped nmnm-5 material shows four pairs of redox peaks (3.89/3.86 v, 3.61/3.55 v, 3.41/3.34 v, and 3.27/2.97 v) (fig. 3a) [37]. this arises from mg doping, which suppresses the formation of intermediate phases and optimizes the thermodynamics of sodium ion fig. 1. (a) the xrd refinement patterns of nmnm-5; (b) sem image of nmnm-5; (c) the cross-section sem of nmnm-5; (d"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 3 extraction (as cited in references) [22,23,38]. this phenomenon is also reflected in the smoother charge-discharge curves of nmnm-5 compared to nnm, with fewer electrochemical plateaus (fig. 3b). the 3.18/2.97 and 3.63/3.56 v peaks of the cv curve of nnm are related to the continuous reversible transition of ni2+/ni3+/ni4+ [39–41]. two pairs of reversible redox peaks are located at 3.38/3.29 and 3.71/3.64 v, which corres"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "of 86.7, 82.8, 77.4, 73.2, 68.6, and 64.3 ma h g1 at the corresponding current rates (fig. 3c). moreover, after 100 cycles at 10 c, nmnm-5 demonstrated a reversible capacity of 62.8 ma h g1, achieving the retention of 97.6%, surpassing nmnm-10 and nmnm-15. long-term cycling performance at 1 c rate was also assessed. while nnm possessed the highest initial capacity of 82.2 ma h g1, its capacity retention (82.9% after 300 cycles) was inferior to nmnm-5 (93.7% after 300 cycles, fig. 3d). upon eleva"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 4 fig. 3. (a) cv curves of nnm and nmnm-5 at a scan rate of 0.1 mv s1 within the voltage range of 2.0 to 4.0 v; (b) the charge-discharge curves of nnm and nmnm-5 at 0.1 c within the voltage range of 2.0 to 4.0 v; (c) the rate performances of samples under different current densities at 2.0–4.0 v; (d) the cycle performance of series samples under 1 c at 2.0–4.0 v; (e) cv curves of nnm and nmnm-5 at a scan rate of 0.1 mv s1 "
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "and nmnm-15 under 10 c at 2.0–4.3 v. ni3+/ni4+ and anion redox processes [15]. however, nmnm-5 displays only one pair of oxidation-reduction peaks (4.27/4.04 v) pertaining to ni3+/ni4+, indicating that mg doping partially suppresses the anion redox reaction, which is consistent with the charge/discharge curves (fig. s4). rate performance within the 2.0–4.3 v range is presented in fig. 3(f), where nmnm-5 attains capacities of 132.1, 130.2, 125.3, 117.8, 107.6, and 100.7 ma h g1 at 0.1, 0.5, 1, 2,"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "1 c after 100 cycles. the retention rate of 100 cycles at 10 c is 72.0%, much higher than that of undoped nnm materials (fig. 3g and h). the comparison of the discharge capacity retention ratio and residual capacity at constant current density of various p-type layered cathodes was conducted and nmnm-5 materials demonstrate a high level of capacity and rate performance (table s3). besides, as the doping ratio increases, the material capacity exhibits a decreasing trend. this is because, in the n"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "reversibility; thus, mg doping does not confer a capacity advantage. conversely, within the 2–4.3 v voltage range, the undoped material experiences irreversible structural delamination. this phenomenon leads to a significant reduction in active sites available for sodium ion extraction, consequently resulting in a substantial capacity loss. in this context, mg doping plays a beneficial role in enhancing capacity retention at high voltages. to elucidate the enhancement of electrochemical performa"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "ni3+/ni4+ in the high-voltage range, explaining the elevated capacity of material. subsequent gitt testing was conducted on nnm and nmnm-5 materials, revealing slightly higher diffusion coefficients in the doped system (fig. 4b–d). to further analyze the impact of interfacial resistance on the material, we conducted eis tests on materials under different discharge voltages (fig. 4e–g). by comparing the interfacial charge transfer resistance and coating resistance at different discharge voltages,"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 5 5 material remained consistent, while the interfacial transfer resistance was lower than that of nnm material. we characterized the structural changes of the materials after 100 cycles at a high voltage of 1 c using sem, tem, and other techniques. fig. 5(a) reveals that the material retained its secondary particle morphology composed of aggregated primary layered particles. tem images confirmed the dense block- like natu"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "the material undergoes irregular structural degradation from the outer to the inner along the (002) crystal plane. this process is likely a crucial factor contributing to the decrease in material stability. in contrast, severe delamination occurred in the nnm material after cycling. sem and tem images revealed the delaminated layered morphology, with hrtem images showcasing lattice fringes corresponding to the (002) crystal plane (fig. 5f–i). based on these results, a schematic of the structural"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "v under 1 c at a scan rate of 0.1 mv s1; (b) gitt curves of nnm and nmnm-5 after 100 cycles at 2.0– 4.3 v under 1 c; (c) the calculated sodium ion diffusion coefficient of nnm and nmnm-5 in the charging process; (d) the calculated sodium ion diffusion coefficient of nnm and nmnm-5 in the discharging process; the eis curves of nnm (e) and nmnm-5 (f) at different discharge potentials (4.3 v, 4.0 v, 3.5 v, and 2.9 v) under 1 c; (g) the fitted rs, rct, and rcoating of nnm and nmnm-5 at different pot"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 6 fig. 5. sem (a), tem (b), and hrtem (c, d) of nmnm-5 after 100 cycles at 2.0–4.3 v under 1 c; (e) schematic diagram of structure degradation in schematic diagram cycled at 2.0–4.3 v; sem (f), tem (g), and hrtem (h, i) of nnm after 100 cycles at 2.0–4.3 v under 1 c; (j) schematic diagram of structure degradation in the schematic diagram cycled at 2.0–4.3 v. fig. 6(a and b) shows in-situ xrd spectra for nmnm-5 and nnm in t"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "of a structural transition from the p2 phase to the op4 phase [22,23]. during the early stages of the discharge process, nmnm-5 still maintains the op4 structure, albeit with a gradual shift towards lower angles of the (002) diffraction peak. upon reducing the voltage below 4.0 v, the material reverts to the p2 structure without significant alterations in peak intensity, thereby affirming the structural reversibility (fig. 6c). in contrast, the undoped nnm material retains the p2 structure withi"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "and tem. subsequent xrd testing of the materials after cycling in the 2.0–4.3 v range (fig. s5) reveals the persistent presence of the (002) peak in nmnm-5 material, while the (002) peak in nnm material is nearly absent. this confirms a severe disruption of the layered structure in the undoped material. to further analyze the effects of mg doping on reaction mechanisms and structural stability, xps tests were performed on the electrode after 100 cycles at a high voltage (fig. 7 and fig. s6). at "
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 7 this implies that the reversibility of the oxidation reaction of nickel during cycling is weaker in nnm, aligning with the weakening of oxidation-reduction peaks above 4.0 v in the post-cycle cv. the variations in the mn peaks were negligible for both materials at 4.3 v, indicating the absence of significant oxidation reactions (fig. 7b). in nmnm-5 material charged to 4.3 v, the o 1s peak exhibited five sub-peaks corresp"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "peaks in nmnm-5 material (fig. 7d). xps confirmed that mg doping enhances the reversibility of the ni3+/ni4+ reaction at high voltages. theoretical calculations were conducted using first-principles methods to analyze the effects of mg doping on the nmnm-5 material (fig. s7). the three- dimensional difference maps showed that most of the electron-deficient regions around sodium became more symmetric after doping, suggesting an improvement in interlayer sodium stability (fig. 8a and b). moreover,"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "this cross-section, it can be seen that after doping, there are three subregions within the red regions fig. 6. (a) the in-situ xrd patterns of nmnm-5 in the first cycle at 2.0–4.3 v; (b) the in-situ xrd patterns of nnm in the first cycle at 2.0–4.3 v; (c) relevant peak shifts of (002), (004), (100), and (012) crystal planes in the first cycle of nmnm-5 at 2.0–4.3 v; (d) relevant peak shifts of (002), (004), (100), and (012) crystal planes in the first cycle of nnm at 2.0–4.3 v. fig. 7. the high"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "within the voltage range of 2.0–4.3 v. fig. 8. three-dimensional charge distribution mapping of nmnm-5 (a) and nnm (b); two-dimensional charge distribution mapping of nmnm-5 (c) and nnm (d); twodimensional charge distribution mapping of nmnm-5 (e) and nnm (f) after rotation about the ni–o axis; the cohp and pdos curves of nmnm-5 (g) and nnm (h) materials."
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "b. zhang, y. zhao, m. li et al. journal of energy chemistry 89 (2024) 1–9 8 associated with the upper and lower o atoms bonded to the ni atom. one of them aligns directly with the ni–o bond axis, providing evidence of enhanced covalent bonding (circled with a dotted line). however, this trend could not be quantified from the map alone and require further analysis through the partial density of states (pdos) and crystal orbital hamilton population (cohp) analyses. post-doping, the peak around the"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "intensity and a substantial weakening of antibonding components. this effectively enhances the stability of the ni–o bond [3,9,18,30,44–47]. the introduction of mg enhances the stability of ni–o bonds and the overall material stability, which likely accounts for the suppression of o oxidation and structural delamination. 4. conclusions in conclusion, a series of na0.67mgxni0.3xmn0.7o2 (x = 0.05, 0.1, 0.15) materials were synthesized through co-precipitation. xrd and morphological characterizatio"
  },
  {
    "source_pdf": "Degradation_analysis_and_doping_modification_optimization_for_high_voltage_P_type_layered_cathode_in_sodium_ion_batteries_Bao_Zhang_Yi_Zhao_Minghuang_Li_Qi_Wang_Lei_Cheng_Lei_Ming_Xing_Ou_Xi.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "h g1 at 0.1, 0.5, 1, 2, 5, and 10 c, respectively, with a capacity recovery to 132.2 ma h g1 at 0.1 c. in contrast, although nnm exhibited a higher initial capacity (145.7 ma h g1), it suffered severe degradation, retaining only 54.4 ma h g1 at 10 c. characterization of post-cycling materials confirmed severe delamination in the non-doped material, leading to a significant capacity decrease during cycling. mg doping could suppress the anion oxidation-reduction reactions in the 4.0– 4.3 v voltage"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "1. introduction lithium-ion batteries (libs) have become the industry standard due to their superior performance, which includes high energy density, extended cycle life, no memory effect, and low environmental pollution [1–6]. under conditions of mechanical, thermal, or electrical abuse [7–15], the battery produces excessive heat within a confined space, resulting in thermal runaway (tr) and potentially severe thermal disasters. extensive research has been conducted on the thermal safety issues"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "investigated the thermally induced tr process at varying current rates, demonstrating that the cell exhibited higher tr onset and peak temperatures as the current rates increased. wang et al. [21] employed varying charging rates to induce tr in lib through overcharging. the study revealed that nomenclature sibs sodium-ion batteries libs lithium-ion batteries soc state of charge tr thermal runaway nb normal battery ob overcharged battery arc acceleration rate calorimeter sem scanning electron mic"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "of the battery, demonstrating that an elevated charging rate is associated with a higher peak tr temperature. liu et al. [23] analyzed the thermal stability of libs under conditions of minor overcharging, demonstrating that the increase in heat generation following overcharging is primarily due to a rise in the battery’s internal. kong et al. [24] investigated the impact of operating temperature on the tr and combustion characteristics of libs. the experimental results demonstrated that a decrea"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "to ncm batteries. huang et al. [26] conducted a comparative analysis of the tr propagation characteristics between ncm and lfp modules. the results indicated that ncm modules displayed intense ejection ignition and combustion behavior, while lfp modules generated only a significant volume of white smoke. mao et al. [27] employed an acceleration rate calorimeter (arc) to investigate the self-heating reactions of libs at various socs. they discovered that fully charged libs are capable of self-ign"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "soc is associated with an increased average heating rate of the battery. when the soc exceeds 60 %, the battery is prone to severe tr events, such as explosion and fire emission, subsequent to the bending test. research on the thermal safety of libs is extensive, encompassing performance evaluations across multiple dimensions, such as varying charge and discharge rates, operating temperatures, battery chemistries, socs, and temperature rise rates [30]. the thermal safety assessment of sibs, an e"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "comparison to libs, research on the thermal safety of sibs remains relatively limited. significant attention and enhanced research efforts are required to comprehensively address the thermal safety challenges associated with sibs. yue et al. [38] conducted a comprehensive investigation into the tr characteristics and associated hazards of sibs utilizing ntm (naxtmo2) as the cathode material, compared to libs employing lfp and ncm as cathode materials, respectively. their findings revealed that t"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "(t2) of 243.4 ◦c, followed by a rapid and abrupt surge, reaching a peak temperature (t3) of 312.24 ◦c within seconds. according to zhou et al. [40], tr study was conducted on high-power 26,650 cylindrical sibs, revealing that the sibs exhibited greater thermal stability than libs, with initial decomposition temperatures exceeding 110 ◦c and maximum thermal runaway temperatures below 350 ◦c. a. bordes et al. [41] investigated the gas production characteristics of 18650 cylindrical sibs (na₃v₂(po₄"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 0,
    "chunk_index": 7,
    "text": "study systematically compares the fundamental thermoelectrochemical * corresponding author. e-mail address: roseyyun@163.com (j. zhang). https://doi.org/10.1016/j.ijoes.2025.101027 received 3 march 2025; received in revised form 26 march 2025; accepted 10 april 2025 available online 11 april 2025 1452-3981/© 2025 the author(s). published by elsevier b.v. on behalf of esg. this is an open access article under the cc by-nc-nd license ( http://creativecommons.org/licenses/by-nc-nd/4.0/) ."
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 2 characteristics of 18650-type sibs and libs under both normal operating conditions and abuse conditions. initially, under normal operating conditions, the effects of ambient temperature and discharge rates on the capacity and exothermic behavior of both libs and sibs were systematically investigated. subsequently, under overcharge abuse conditions, the electro-thermal characteristics of the two battery types, includ"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "employed 18650-type sibs (procured from jiangsu transimage sodium-ion battery technology co., ltd.) and libs (procured from guangzhou jieli new energy co., ltd.) with closely matched nominal capacities as experimental subjects. the physical appearance and technical specifications of the two battery types are illustrated in fig. 1 and table 1, respectively. the procedure for assessing the initial capacity consistency of the cells was as follows: three cells were randomly selected for each type an"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "10–45 discharging: − 30–60 charging: 0–45 discharging: − 20–60 storage temperature interval, ◦c − 20–40 − 20–25 cell weight, g 30 g 40 g cell size, mm height: 65.3 ± 0.1 diameter: 18.4 ± 0.1 height: 65.0 ± 0.5 diameter: ≤ 18.6 and serial number. for the sibs, a standard cc-cv charging protocol was applied, wherein the cells were charged at a constant current of 0.5 c to a cutoff voltage of 3.95 v, followed by constant-voltage charging until the current dropped to 65 ma. after a 30-min rest perio"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "ma. after a 30-min rest, the cells were discharged at a constant current of 0.5 c to a cutoff voltage of 2.0 v, with the cycle also repeated three times. ultimately, cells with capacity variations within ± 1 % were selected for the experiments. 2.2. experimental test system fig. 2 illustrates the experimental testbed. in the experimental part of this study, a high-precision battery performance test system (neware technology limited, bts-60v100a-ntf) was employed to conduct charge/discharge exper"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "methodology was employed for testing, utilizing a silicone rubber heating pad powered by a dedicated heating supply. the heating pad primarily consists of a nickel-chromium alloy heating wire encapsulated within a high-temperature-resistant silicone rubber insulating layer, with a thickness of 1.5 mm, a power rating of 20 w at 24 v, and a heating area of 19 mm × 59 mm. a uni-t (utp1310) dc regulated power supply, capable of delivering 32 v/10 a, was employed to energize the heating pad. temperat"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 3 2.3. electrochemical performance testing 2.3.1. impact of ambient temperature on battery capacity the ambient temperature was set at 0 ◦c, 10 ◦c, 25 ◦c, and 45 ◦c. prior to testing, the batteries were placed in a controlled temperature environment for 3 h to ensure uniform internal and external temperatures of battery. a constant temperature chamber with a fluctuation range of ± 1 ◦c was used to maintain the desired"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "a total of 200 cycles. the ambient temperature was meticulously regulated using an indoor air conditioning system, with fluctuations confined to a narrow range of ± 1◦c. 2.3.3. impact of overcharging on battery performance three distinct levels of overcharging were applied to the batteries (ob, overcharged battery), exceeding the standard charging cutoff voltage by 5 %, 10 %, and 15 %. these results were then compared to those of batteries operating under normal conditions (nb, normal battery). "
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "spectroscopy (eis) testing the pristine battery, which had not been subjected to any cycling tests, and the battery cycled at the maximum discharge rate (3 c) were stored in a fully discharged state (0 % state of charge, soc) for over 3 hours under controlled ambient conditions at 25 ◦c. eis measurements were subsequently conducted on both batteries, covering a frequency range from 0.01 hz to 1000 hz. 2.4. heat generation characteristic testing heat generation tests were incorporated into both t"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "at intervals of one second. 2.5. battery thermal runaway test thermal runaway (tr) experiments were performed on batteries that had undergone maximum overcharging (15 %-ob) and nb, as outlined in section 2.3. to achieve a soc of 100 %, the batteries were fully charged at a controlled ambient temperature of 25 ◦c in accordance with a standardized charging protocol. as illustrated in fig. 4(b), the battery was heated in an open environment using a silicone rubber heating pad affixed to one side. a"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "following thermal runaway (tr), with data recording continued for an additional 5 min before cessation. 2.6. battery microstructural characterization disassemble the overcharged batteries within a glove box, ensuring that the batteries are fully discharged to 0 % soc prior to disassembly. begin by fig. 2. experimental platforms built: (a) electrochemical and heat production test and (b) tr test."
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 4 making several small incisions around the outer ring of the battery’s positive terminal, followed by the careful removal of the aluminum casing using sharp- nosed pliers. meticulously cut through the securing tape to access the internal components. subsequently, separate the positive and negative electrodes and place them into individual, lidded containers. add an adequate volume of dimethyl carbonate (dmc) to fully"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "analysis was performed using a hitachi field emission scanning electron microscope (model su8010). disassemble the overcharged batteries in the glove compartment, ensuring the batteries are at 0 % state of charge prior to disassembly. initially, create several small incisions in the outer ring of the battery’s positive terminal, then utilize sharp-nosed pliers to remove the aluminum casing and meticulously cut through the securing tape. next, separate the positive and negative electrodes and put"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "sheet was extracted for surface and cross-sectional microscopic analysis. the sem characterization instrument used in this paper is a hitachi field emission scanning electron microscope (su8010). 3. results and discussions 3.1. comparative study of electrochemical performance of sibs and libs 3.1.1. impact of ambient temperature on the performance of sibs and libs fig. 5(a) and (b) illustrate the discharge plateau curves of the batteries under varying ambient temperature conditions. as depicted,"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 5 fig. 6. voltage curve over time of (a) sibs and (b) libs; capacity retention rate changes of (c) sibs and (d) libs. retention rates further decline to 90.20 % for sibs and 76.26 % for libs. the discharge plateau progressively diminishes with decreasing ambient temperature, suggesting an increase in the batteries’ internal polarization and internal resistance. although sibs and libs exhibit similar trends, sibs displ"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "45 ◦c, the electrochemical reactions within the battery become more pronounced, facilitating the release of a greater amount of energy. when the ambient temperature is reduced to 10 ◦c, the capacity retention rates of sodium- ion batteries (sibs) and lithium-ion batteries (libs) decrease by 8.47 % and 9.17 %, respectively, relative to their performance at 25 ◦c. this reduction is primarily caused by the diminished reversibility of active materials, reduced electrolyte activity, and inferior comp"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "superior low-temperature properties of the electrolyte employed in sibs. specifically, the electrolyte in sodium-ion batteries exhibits better fluidity at low temperatures compared to that in lithium-ion batteries, thereby promoting faster diffusion of sodium ions within the electrolyte [43]. 3.1.2. impact of different discharge rates on the performance of sibs and libs the discharge characteristics of batteries under varying discharge rates at an ambient temperature of 25 ◦c are illustrated in "
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 6 attributable to intensified polarization effects. at this stage, the polarization within the battery increases substantially, resulting in a marked rise in internal resistance and a consequent rapid decrease in voltage. additionally, higher discharge currents exacerbate the voltage drop across the internal resistance, leading to lower terminal voltages [44]. furthermore, as depicted in fig. 6(c) and (d), the dischar"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "materials in electrochemical reactions before the cutoff voltage is reached, thereby reducing the overall discharge capacity. moreover, the joule heat generated during high-rate discharge induces a temperature rise within the battery, potentially initiating side reactions or accelerating material degradation, which further compromises capacity retention [45]. 3.1.3. impact of cycle number on the capacity retention of sibs and libs the capacity retention rates of batteries under varying discharge"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "this phenomenon is primarily attributed to the substantial increase in current density at higher discharge rates, which induces excessive heat generation, thereby triggering electrolyte decomposition, electrode material degradation, and ultimately a progressive decline in battery capacity. moreover, sibs display a more pronounced degradation rate compared to libs. this disparity arises from the larger ionic radius of na⁺ relative to li⁺, which imposes greater mechanical strain during the interca"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "the capacity decay of batteries tends to decelerate in the later stages when cycled at higher charge/discharge rates, a phenomenon that is corroborated by the current experimental results. 3.1.4. comparison of ac impedance between sibs and libs fig. 8 displays the eis curves for both the pristine battery and the battery cycled at a 3 c rate. as illustrated in the figure, the impedance of the battery following 3 c cycling is markedly higher than that of the pristine battery, suggesting that a sig"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "resistance (roh), determined by the intersection of the curve with the real axis, exhibits a noticeable increase for sib, rising from 0.1286 ω to 0.1578 ω, while the change in ohmic resistance for lib remains minimal. the charge transfer resistance (rct), represented by the diameter of the semicircle in the medium-to-high frequency region, corresponds to the resistance associated with electrochemical reactions during charge transfer. both lib and sib demonstrate a substantial rise in rct, with l"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 7 line after 3 c cycling indicates an incremental rise in solid-phase diffusion resistance during battery cycling. detailed quantitative data are summarized in table 2. 3.1.5. the impact of overcharge level on the performance of sibs and libs the overcharging levels were set at 5 %, 10 %, and 15 %. for libs, the nb voltage was 3.65 v, with overcharging voltages of 3.8 v (5 %), 4.0 v (10 %), and 4.2 v (15 %). for sibs,"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "batteries showed premature degradation compared to the nb. for libs, the residual capacities of the nb and ob at 5 %, 10 %, and 15 % overcharging were 98.97 %, 98.89 %, 98.86 %, and 99.07 %, respectively. for sibs, the residual capacities of the nb and ob at 5 %, 10 %, and 15 % overcharging were 99.70 %, 97.65 %, 92.08 %, and 67.72 %, respectively. the data indicate that as the degree of overcharging increases, the capacity retention rates of both sibs and libs progressively decrease, with the r"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "differences in residual capacities between the overcharged batteries table 2 impedance fitting results. items roh/ω rct/ω sib-fresh 0.1286 0.1511 sib-3c 0.1578 0.6180 lib-fresh 0.0180 0.0042 lib-3c 0.0176 0.1238 and the nb are 0.09 %, 0.11 %, and 0.10 %, respectively, indicating minimal variations. this suggests that the overcharge cycles in this study had a negligible impact on the performance of libs. in contrast, for sibs, the differences in residual capacities between the overcharged batteri"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "materials for charge/discharge processes. these findings demonstrate that libs exhibit superior cycle stability compared to sibs under mild overcharging conditions. 3.2. heat generation characteristics of sibs and libs 3.2.1. comparison of heat generation in batteries at different discharge rates the batteries were discharged at rates of 0.5 c, 1 c, 1.5 c, 2 c, and 3 c in a constant temperature chamber maintained at 25 ◦c. during the discharge process, the surface temperatures of the batteries w"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 6,
    "chunk_index": 4,
    "text": "differentials between the discharge temperature and the initial temperature. for libs, these differentials were 1.56 ◦c, 3.81 ◦c, 5.50 ◦c, 7.02 ◦c, and 10.29 ◦c, while for sibs, they were 1.94 ◦c, 3.42 ◦c, 4.83 ◦c, 4.68 ◦c, and 7.61 ◦c. the analysis reveals that at a discharge rate of 0.5 c, libs exhibited a slightly lower peak surface temperature than sibs. however, at higher discharge rates (1 c, 1.5 c, 2 c, and 3 c), libs consistently demonstrated higher peak surface temperatures compared to "
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 6,
    "chunk_index": 5,
    "text": "trend is particularly pronounced at a discharge rate of 0.5 c. this phenomenon is primarily attributed to the following underlying mechanisms: during the initial phase of discharge, the rapid escalation in battery temperature is predominantly driven by two critical factors. firstly, the minimal thermal gradient between the battery fig. 9. battery capacity degradation curves: (a) sibs, (b) libs and (c) comparing capacity retention after overcharging between sibs and libs. fig. 10. variation of ce"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 8 various multiplicities. and its ambient environment results in diminished heat exchange efficiency, thereby impeding the rate of thermal dissipation. secondly, the elevated activation energy required for internal electrochemical reactions, combined with the pronounced joule heating effect induced by ohmic resistance and electrochemical polarization, culminates in a heat generation rate that surpasses the rate of hea"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "deceleration in the rate of temperature rise. in the terminal phase of discharge, the rate of temperature increase undergoes a pronounced acceleration, a consequence of the synergistic interplay of multiple contributing factors. primarily, the substantial reduction in electrolyte concentration within the battery augments ionic migration resistance, leading to intensified ohmic polarization. additionally, the precipitous decline in the concentration of active materials at the electrode surfaces e"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "15 %), with the resulting temperature profiles depicted in fig. 11. the data reveal that the peak surface temperature of the batteries increases with the degree of overcharging. for libs, under normal charging conditions, the peak surface temperature was recorded at 26.36 ◦c. in contrast, under overcharging conditions of 5 %, 10 %, and 15 %, the peak temperatures were 26.34 ◦c, 26.56 ◦c, and 26.58 ◦c, respectively. on the other hand, sibs exhibited a peak surface temperature of 26.54 ◦c under no"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "well as the temperature rise caused by various levels of overcharging. during the initial stage of constant-current charging, the rapid extraction of ions from the cathode and their subsequent insertion into the anode, coupled with the combined effects of reaction heat, ohmic heat, and polarization heat, results in a significant temperature rise due to the relatively high internal resistance of the battery. in the intermediate charging phase, as the extraction and insertion of ions in the cathod"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "temperature. when the voltage exceeds the standard cut-off voltage, all batteries with varying degrees of overcharge reach their maximum temperature. however, if charging continues beyond this point, the battery’s surface temperature slightly decreases. this phenomenon occurs because, when a battery is fully charged, the internal electrochemical reactions become saturated, leading to minimal heat generation. according to existing literature, the entropy heat coefficient of a battery initially in"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 9 battery exhibited a decline due to the thermal inertia of the constant temperature chamber, which led to an unstable initial temperature. subsequently, the temperature increased as the heat generated by the charging process accumulated. therefore, in practical applications, the surface temperature of the battery can only serve as one of the monitoring parameters and is insufficient as a standalone indicator to deter"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 10 fig. 13. libs charging voltage and surface temperature variation curves: (a) nb, (b) ob-3.8 v, (c) ob-4.0 v, and (d) ob-4.2 v. fig. 14. (a) temperature at different regions on the surface of sibs and libs; (b) voltage variations of sibs and libs. voltage of the sib abruptly dropped to 0.53 v when the temperature at monitoring point t2 reached 81.6 ◦c, and it remained at this level for approximately 135 s. when t2 f"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "voltage remaining stable around 3.3 v without significant fluctuations. as discussed in section 3.1.5, the soc of the sib at the maximum overcharge level (15 %) was 67 %, significantly lower than the 80 % threshold, whereas the lib maintained a healthy soc of 98.79 %. additionally, as highlighted in section 3.2.2, under overcharge abuse conditions, the surface temperature of sibs was higher than that of libs, indicating an increase in internal resistance and polarization within the sibs. this in"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 11 discussed above. the surface of the sib exhibited clear signs of combustion, with visible damage to both the cathode and anode. in contrast, the lib did not undergo thermal runaway, and its surface remained intact without any noticeable deterioration. these observations align with the experimental data presented earlier. 3.4. macrostructure of battery anode and cathode the batteries subjected to varying degrees of "
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "generation was observed, accompanied by significant delamination of the active material. the surface appeared whitened and became soft and fragile, a phenomenon likely attributed to sodium deposition reactions occurring on the negative electrodes. sodium deposition reactions typically occur at the negative electrode of sibs. upon disassembly of the battery, it was observed that no significant alterations had occurred in the cathodes. consequently, sem analysis was exclusively conducted on the an"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "with ob-10 %, cross-sectional delamination worsens, accompanied by mild shedding and collapse of the active material. at ob-15 %, delamination is most severe, with active materials spread unevenly, significant powder loss, and structural collapse. fig. 17(e) to (h) illustrate the surface morphologies of the libs anode electrodes. the nb exhibits a smooth and homogeneous surface, as indicated in the images. cracks form in the surface active materials of ob-5 % and ob- 10 %. when the battery is ob"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 10,
    "chunk_index": 3,
    "text": "can increase the internal resistance of the battery or potentially cause battery damage, posing a safety risk. fig. 17(m)–(p) show the surface morphologies of the sibs anode electrodes. as illustrated in the images, the nb’s surface material is densely packed and homogeneous, with distinct boundaries between material particles. in overcharged batteries with ob-5 %, ob-10 %, and ob-15 %, the boundaries of the active components become increasingly blurred and fused. the microscopic morphologies of"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 10,
    "chunk_index": 4,
    "text": "and blurred, disordered particle gaps. in the battery with ob-15 %, agglomeration and fractured anode active material particles are evident. overcharging cycles lead to excessive lithium intercalation in the anode material over time, resulting in volume expansion and increased interlayer gaps. when the internal stress within the anode active material exceeds its mechanical stability limit, it causes structural breakage, agglomeration, and material shedding [46]. fig. 18(e) to (h) illustrate the "
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 12 fig. 17. cross-sectional sem morphology of negative electrode sheet of overcharged battery: lib-nb~ob-15 %: (a)–(d)；sib-nb~ob-15 %:(i)–(l)；sem morphology of negative"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 13 electrode surface of overcharged batteries: lib-nb~ob-15 %: (e)–(h)；sib-nb~ob-15 %: (m)–(p)；. fig. 18. sem of the anode material: (a) lib-nb, (b) lib-ob-5 %, (c) lib-ob-10 % and (d) lib-ob-15 %; (e) sib-nb, (f) sib-ob-5 %, (g) sib-ob-10 % and (h) sib- ob-15 %. sodium clusters form, followed by the deposition of sodium dendrites [47,48]. for ob-10 % and ob-15 %, the sodium clusters on the surface dissolve, and bulk "
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "help explain the significant capacity fading observed in the sib- ob-15 % scenario described in section 3.1.5. 4. conclusion and outlook 4.1. conclusion comparative studies were conducted between libs and sibs by varying ambient temperature, charge/discharge rates, and overcharging levels to systematically evaluate and analyze their electrochemical performance and thermal behavior. the fundamental causes of the observed performance degradation were elucidated from a microscopic perspective. the "
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "of sibs is 15.81 % lower than that of libs. (2) sibs exhibit greater safety under normal operating conditions but demonstrate inferior thermal stability under abusive conditions. under normal working conditions at the maximum discharge rate (3 c), sibs generate less surface heat than libs, with a difference of 2.683 ◦c. however, under the maximum overcharging level (15 %) in abusive conditions, sibs produce more surface heat than libs, with a difference of 1.53 ◦c. additionally, sibs are more pr"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "generation due to elevated internal resistance. 4.2. outlook this thesis investigates the fundamental thermal-electrical characteristics of sibs and libs at both macro and micro levels, including their thermal runaway behavior and the underlying mechanisms of performance degradation under overcharge abuse. however, significant work remains to be addressed in future studies, as outlined below: (1) the research in this thesis focuses on 18650 cylindrical cells, without addressing large-capacity so"
  },
  {
    "source_pdf": "electrochemical_comparison_Na_vs_Li_Han_Xu_Guoqing_Zhang_Jiantao_Zhang_Jiangyun_Zhang_Hongwei_Wu_Liqin_Jiang_Wenzha.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "h. xu et al. international journal of electrochemical science 20 (2025) 101027 14 (2) the performance of sibs and libs can be improved by optimizing electrode materials, enhancing the stability of cell interfaces through surface modification, interfacial coating, or interfacial modulation, and optimizing current collectors and binders. this includes selecting more compatible current collector materials and binders with higher bond strength and stability. (3) while this thesis employs experimenta"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "1. introduction large-scale energy storage is essential for transitioning towards a more sustainable and resilient energy future, as it enables improved integration of renewable energy for reliable and cost-effective power supply [1,2]. lithium- ion batteries (libs), featuring the outstanding energy density and exceptional cycling lifetime, are applicable to contemporary portable applications involving electronics and electric vehicles [3,4]. unfortunately, due to their prohibitive expense, rest"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "etc. ; x = p, s, si, etc.) possess the benefit of a rigid framework structure attributing to outstanding stability [10,11]. the richer electronegativity of the x in the anion produces a stronger induced effect conducing to a higher redox potential, thus the sulfate cathode presents a considerable competitive advantage as a consequence of the impressive electronegativity of so2-4 [12,13]. na2+2xfe2-x(so4)3 reported by yamada in 2014 exhibited a higher redox potential of 3.8 v (versus na+/na), pro"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "j. wu et al. chemical engineering journal 512 (2025) 162535 2 stringently controlled during material storage and battery cell preparation, leading to significantly increased costs. therefore, it is a critical issue for practical applications to elucidate the moisture degradation mechanism and achieve capacity rehealing after degradation of materials. the phenomenon of moisture degradation in sulfate-based cathodes has been reported in libs. chen et al. demonstrated that tavorite- type lifeso4f u"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "with regard to na2+2xfe2- x(so4)3, reports indicated that a hydrated phase, na2fe(so4)2⋅4h2o, was inclined to develop upon moisture, but its intrinsic causes and corresponding changes in electrochemical performance have not yet to be elucidated [21–23]. more importantly, the restoration of capacity in degraded materials has yet to be resolved. fig. 1. a) rietveld refinement xrd pattern and b) crystal structure of nfs. c) enlarged sem image of nfs sphere. d) tem image of cnts network around the n"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "j. wu et al. chemical engineering journal 512 (2025) 162535 3 here, na2.67fe1.67(so4)3 (nfs) with an outstanding electrochemical performance of 103 mah/g is used as the model to investigate its degradation process upon certain humidity conditions. experimental results indicate that at 50 % humidity, alluaudite-type na2+2xfe2- x(so4)3 gradually transforms into bloedite-type na2fe(so4)2⋅4h2o, and feso4⋅7h2o appears at 80 % humidity. thermodynamic cycle calculations show that the enthalpy change fo"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "refinement and electrochemical performance test results indicate that the content of the hydrated phase increases linearly to 31.7 % after 48 h of storage at 50 % humidity and the discharge capacity correspondingly degrades to approximately 83.5 %, which is caused by the poor sodium storage capability of the hydrated phase and decreased conductivity. since alluaudite and bloedite undergo reverse reactions, a simple strategy is proposed to restore the initial crystal structure of the completely d"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "is determined to be optimal for further investigation based on xrd and electrochemical performance tests results (fig. s2a-c). to obtain finer structural information, rietveld refinement is performed and the results confirm that the as- synthesized nfs exhibits outstanding purity, belonging to the c2/c space group with a monoclinic crystal system (fig. 1a). the refined lattice parameters are a = 12.6592 å, b = 12.7792 å, c = 6.51907 å, β = 115.545◦, and v = 951.5038 å3, which are in agreement wi"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "analysis reveals a carbon content of 2.05 wt% in nfs, which enable the confirmation of the material chemical composition. sem and tem reveal the nfs particles are spherical with an average diameter of 3–5 μm (fig. 1c and fig. s3a- c). high-resolution tem (hrtem) image shown in fig. 1d indicates a well-defined cnts visible around the nfs material, forming a long- range conductive network on the surface, significantly improving the electronic conductivity. the lattice fringe of 0.299 nm observed i"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "the features observed in the cv curves (fig. s4a), which is resulted from the structural rearrangement during the first charging process [27]. significantly, nfs exhibits a superior long-cycling performance, with a capacity retention of 77.8 % after 6000 cycles at a rate of 10 c and the exceptional rate performance with 71.36 mah/g at 20 c (fig. 1g and fig. s4b). due to the long-range conductive network provided by cnts, the nfs with cnts exhibits an increased specific capacity of 103 mah/g, wit"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 5,
    "text": "charge–discharge cycle (fig. 1h-i). all characteristic peaks show reversible shifts during the charge–discharge process, indicating that the material maintains a stable structural framework. despite the high electronegativity of so2-4 in nfs initiates high voltage activity, the lewis basicity of the oxygen atoms in so2-4 is equivalent to that in water, which makes sulfates intrinsically hypersensitive to moisture [29]. therefore, it is imperative to investigate the air stability and deterioratio"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 6,
    "text": "progressively intensifies (fig. s5). this indicates a proclivity of nfs from the alluaudite-type na2+2xfe2-x(so4)3 to bloedite-type na2fe (so4)2⋅4h2o upon the moisture. in order to accelerate the study of the moisture-induced phase transition, a high-humidity environment is employed to store nfs for expedited deterioration (80 % humidity). a complete conversion occurs in the refined xrd patterns into a mixture of na2fe(so4)2⋅4h2o and feso4⋅7h2o, with phase proportions of 86.34 % and 13.66 %, res"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 7,
    "text": "[feo6] octahedra connected to two [so4] tetrahedra and four h2o. fig. 2c-f illustrate the xrd rietveld refinement of nfs after various storage time, all yielding satisfactory fits. the xrd refinement results indicate that with increasing storage time, the fe-fe bond distance increases, suggesting the decoupling of the [fe2o10] dimer structure (fig. s7). through xrd refinement, specific variations in the lattice parameters and phase content of nfs with storage time can be ascertained (table s5-s1"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 2,
    "chunk_index": 8,
    "text": "the time-dependent changes in the phase content of the two phases. by fitting the phase content to storage time, we observe an ideal primary linear correlation, which is instrumental in predicting the air stability and lifespan of nfs over storage time at 50 % humidity. to further investigate the intrinsic causes for moisture-induced degradation of nfs material, δg for the reaction of nfs with water is calculated using density functional theory (dft). the optimized structure of the nfs model is "
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "j. wu et al. chemical engineering journal 512 (2025) 162535 4 structural stability to the material (fig. 3c). the δg for the reaction between nfs and h2o is calculated to be − 0.91 ev, indicating that the process is spontaneous reaction. the results of the above calculations consistently illustrate that nfs exhibits a strong affinity for water and is more likely to form the hydrate. in addition, the enthalpies of formation for nfs and degraded nfs are experimentally measured using isothermal aci"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "na2+2xfe2-x(so4)3 and na2fe(so4)2⋅4h2o are shown in table 1. the power changes of the reactants and products dissolved in 5 m hcl are recorded (fig. s9a-d), and the dissolution enthalpies (δhds) obtained from the integration of power are listed in table 1. the dissolution enthalpy of na2+2xfe2-x(so4)3 is 2.633 kj/mol, while that of na2fe(so4)2⋅4h2o is 31.87 kj/mol. using the thermodynamic cycle in table s13, we calculate the enthalpies of formation (δhf) for these two products using the na2so4-f"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "that na2+2xfe2- x(so4)3 undergoes a moisture-induced phase transition spontaneously. the ft-ir, raman, and sem characterizations are performed to investigate the degradation process of nfs. after 48 h storage, a significant hydroxyl peak at about 3450 cm− 1 associated with water is prominently observed in the ft-ir spectrum (fig. 4a) [32]. a variation at a lower wavenumber of 594 cm− 1 assigned to the fe-o peak in the ft- ir spectra is noticeable from a split peak to a single peak of nfs stored "
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "j. wu et al. chemical engineering journal 512 (2025) 162535 5 table 1 calorimetric data for na2+2xfe2-x(so4)3 and na2fe(so4)2⋅4h2o. substance δhds (kj/mol) δhf (kj/mol) na2so4 12.27 feso4 − 9.316 h2o − 0.54 na2+2xfe2-x(so4)3 2.633 − 8.997 na2fe(so4)2⋅4h2o 31.87 − 31.08 na2fe2(so4)3 + 4h2o → na2fe(so4)2⋅4h2o + feso4 δh = –22.083 ig ratio over time, indicating a decrease in the degree of graphitization (fig. 4b and s10b) [36,37]. the phenomenon arises from the formation of hydrates on the surface "
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "to rough structures owing to volume expansion caused by water adsorption (fig. 4c). as the content of impurities ascents, the likelihood of impurity particles coming into contact and fusion significantly rises, leading to the agglomeration of material particles (fig. s10d), which reflects in a notable drop in specific surface area from 7.06 m2/g to 1.15 m2/g (fig. s10c). characterization results show that water accumulation on the nfs surface leads to a decrease in the material electronic conduc"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "transfer resistance (rct) demonstrates a significant increase from 1020 ω to 1291 ω. this is ascribed to the deterioration in the electronic conductivity of the active fig. 3. a) schematic diagram of water adsorption on nfs and the variation of gibbs free energy. b) schematic diagram of the electronic coupling mechanism between fe in nfs and o in water. c) schematic diagram of the stable hydrogen bond network in na2fe(so4)2⋅4h2o. d) principle of instrument testing for the μrc micro-response calo"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "j. wu et al. chemical engineering journal 512 (2025) 162535 6 stored in the dry room (humidity:1%). particles, which impairs the charge transfer capability and hinders the reversible storage of na+. after the entire moisture-induced transformation, the nfs exhibits a discharge specific capacity of only 61.2 mah/g (fig. s11b) and a redox peak at probable 3.3 v (fig. s11c) consistent with the na2fe(so4)2⋅4h2o reported in the literature [38]. the degradation in electrochemical performance is primar"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "apparent difference in the xrd patterns or electrochemical performance of nfs, confirming that moisture is the determining factor in inducing material deterioration. the xrd pattern indicates that the precursor obtained via spray drying consists of na2fe(so4)2⋅4h2o, na2fe(so4)2⋅h2o and feso4⋅h2o and the target product is formed after annealing (fig. s13a-b), suggesting that alluaudite na2+2xfe2-x(so4)3 and bloedite na2fe (so4)2⋅4h2o materials undergo reversible reactions. therefore, a simple sec"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "to inferior electrochemical performance (fig. s14b-c). thus, 350 ◦c is selected as the optimal heating temperature. fig. 5a demonstrates the comparison of nfs-pristine, nfs- wet, and nfs-heat in xrd patterns, indicating the nfs-heat reconstructs to alluaudite-type crystal structure with acceptable purity. after heating, the surface becomes relatively smooth and porous as the escape of internal crystalline water (fig. 5b), resulting in an improvement in the specific surface area to 15.8 m2/g (fig"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "performance test results and h) eis test results. i) cycle stability tests at 1c of nfs after 1–10 days fig. 5. a) comparison of xrd spectra of nfs-pristine, nfs-wet, and nfs-heat. b) sem image of nfs-heat. xps spectra of nfs-pristine, nfs-wet, and nfs-heat c) s 2p, d) fe 2p, e) c 1 s. f) cycling stability tests of nfs-pristine and nfs-heat. g) diagram of the process for moisture-induced degradation of na2+2xfe2-x(so4)3 to"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "j. wu et al. chemical engineering journal 512 (2025) 162535 7 na2fe(so4)2⋅4h2o. group, and the s content shows an upward trend of nfs-wet, attributed to the surface precipitation of feso4⋅7h2o impurities (fig. 5c) [39,40]. the intensity of the o-h peak at 535.9 ev in the o 1 s spectra of nfs-wet is significantly enhanced, indicating the material’s water adsorption (fig. s16a). in nfs- pristine, the valence of fe is confirmed to be + 2 by the peaks at 710.5 ev (fe 2p3/2) and 724.2 ev (fe 2p1/2) i"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "(fig. 5d). the loss of this electrochemically active redox pair explains the decline in electrochemical performance after hydration. the c spectra of the nfs at 284.4, 286.0, and 288.3 ev correspond to c–c, c– o, and c=o, representing typical functional groups of conductive carbon, which are intimately associated with the charge transfer processes and electronic conductivity (fig. 5e) [44]. the peak intensity weakens after hydration and enhances after heating, correlating exactly with the declin"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "is because the incremental specific surface area enhances ion adsorption and diffusion on the material surface. subsequently, the electrochemical performance of the nfs-heat is evaluated, showing a discharge capacity of 85.7 mah/g at 1c and 97 mah/g at 0.1c recovered 94 % of nfs-pristine (fig. 5f and fig. s17d-e). this irreversible capacity loss results from the incomplete phase transformation, partial damage of the electrochemically active redox pair and diminishing electronic conductivity. nfs"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "j. wu et al. chemical engineering journal 512 (2025) 162535 8 new hydrated phase na2fe (so4)2⋅4h2o. this transformation is thermodynamically driven, meaning that the hydration process lowers the system energy and forms a more stable phase. in high-humidity environments, the hydration process intensifies, further promoting the formation of feso4⋅7h2o. the material undergoes a phase transition, accompanied by a decrease in conductivity and changes in morphology, which significantly degrades the el"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "instability and systematically evaluate the changes in crystal structure, system energy, chemical composition, and electrochemical performance. in detail, after the nfs material is exposed to 50 % humidity for 2 days, the 31.7 % na2fe(so4)2⋅4h2o impurity formation is detected. upon exposure to moisture, water adsorbs around the fe atoms and forms hydrogen-bonding network with the oxygen atoms in the lattice, thereby enhancing the structural stability. additionally, the strong coulombic repulsion"
  },
  {
    "source_pdf": "Elucidating_of_moisture_induced_degradation_and_rehealing_of_alluaudite_Na2_2xFe2_x_SO4_3_cathode_for_Sodium_Ion_batteries_Jiayue_Wu_Xing_Chen_Jing_Zeng_Jinbao_Zhao.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "the morphology of nfs transforms from smooth spheres to a rough structure, with visible impurities clearly appearing on the surface. (iii) fe2+ is oxidized to fe3+ causing the loss of active electrochemical pairs. (iv) electronic conductivity declines significantly, all of which ultimately lead to deterioration of electrochemical performance. after full hydration, the discharge capacity of nfs decreases to 61.2 mah/g and then following secondary heating, the capacity can be recovered to 97 mah/g"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "a r t i c l e i n f o a b s t r a c t keywords: thermal stability degradation characteristic nani1/3fe1/3mn1/3o2 high potential sodium-ion battery sodium-ion batteries (sibs) have developed into prospective contenders in energy storage systems because of their significant superiority in abundant resources and low cost. the cycling performance and thermal stability at high potential hinder the commercial application of sibs. the electrochemical performance is comprehensively investigated and degr"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "the uneven cathode electrolyte interphase (cei) due to the cathode/electrolyte interfacial side reactions simultaneously affect the cycling performance. in addition, it revealed that high potential weakens the thermal stability of nfm and the oxygen released from pyrolysis of nfm impacts the thermal stability of nfm/electrolyte system. these findings provide valuable insights for nfm material optimization in cycling stability and inspire concern about the material-level thermal safety design at "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "properties and working principles with libs, which can greatly expedite the deployment of sibs [2,3]. layered transition-metal oxides (naxtmo2, tm = transition metals) of sibs have aroused considerable notice because of their advantages in high theoretical capacity, good cycling performance, and eco- friendliness [4,5]. delmas et al. [6,7] initially classified layered transition oxides into four types: p2, o3, p3, o2, and others. among these, the o3-type is regarded to be a potential cathode due"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "utilized the ta5+ ions doping modification strategy to enhance the crystal structure and phase transition reversibility of the nfm, leading to a pronounced improvement in electronic conductivity and rate performance for nfm. kim et al. [11] significantly improved the electrochemical performances of the nfm and simultaneously suppressed the instability in moisture air by coating na2moo4 (nmo) onto the surface of the nfm. in summary, ion doping, surface covering, and tuning chemical composition ha"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "the cathode can provide higher capacity when charging with high potential, presenting a promising prospect for meeting the demands of booming development for the electric vehicles market [15–17]. nevertheless, the capacity of nfm exhibits more severe decay and complex phase transformation when cycling with high potential. at present, the capacity degradation behaviors are systematically investigated by multiple electrochemical tests and material characterization methods [18–20]. xu et al. [21] e"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "2.0–4.3 v. prior efforts had confirmed that the poor cycling stability of nfm was mainly impacted by particle failures, bulk structure instability and surface chemical reactions [24–26]. however, there is still a dearth of adequate understanding and thorough investigation of the capacity degradation mechanisms of nfm upon higher potential cycling. aside from capacity fading, the thermal stability of the cathode is another critical factor that should be considered before sibs are sized up for com"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "compatibility, while the flammable organic solvents that exist in the electrolyte increase its safety risk [28]. thermal runaway risk also exists in sibs, three stages can be summarized in the thermal runaway process: pre- stage, heat-gathering stage, and thermal abuse stage provided by robinson et al. [29]. in the heat-gathering stage, exothermic chemical chain reactions are the pivotal cause of the increase in battery temperature. it's worth mentioning that the strong heat generation and oxyge"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 0,
    "chunk_index": 7,
    "text": "the battery [30]. however, comprehensive * corresponding author. e-mail address: gaoweidlut@dlut.edu.cn (w. gao). https://doi.org/10.1016/j.est.2025.115776 received 28 november 2024; received in revised form 2 february 2025; accepted 5 february 2025 available online 10 february 2025 2352-152x/© 2025 elsevier ltd. all rights are reserved, including those for text and data mining, ai training, and similar technologies."
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 2 research for the thermal stability of nfm cathode at high potential still remains lacking. in this work, we focus on the degradation behaviors and thermal stability of nfm cathode at high potential. a series of degradation characteristics of nfm cathode with various charge termination voltages are systematically investigated by electrochemical performance tests combined with x-ray photoelectron spectroscopy (xps), scanning electron micr"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "mechanisms of nfm cathode at high potential, also it gives guidance for designing a better nfm with excellent cycling stability and superior thermal stability upon higher charge potential. 2. experimental 2.1. cathode preparation and electrochemical performance tests the cathode active material nani1/3fe1/3mn1/3o2 (nfm) was pur- chased from haian zhichuan battery material technology co., ltd. (jiangsu, china). for the cathode preparation, the compound nani1/ 3fe1/3mn1/3o2 (nfm) was composed of t"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "m napf6 in ec: pc (1:1 v/v) with 2 % fec electrolyte. to investigate the electrochemical performance of nfm with different charge termination voltages, the cr- 2032 coin cells were carried out with specific capacity, rate performance, and cycling performance measurements using a multichannel galvanostatic system (ct3002a, lanhe). as the carbonate-based electrolytes become thermodynamically unstable when the charge voltage is higher than 4.2 v, thus we selected three different charge cut-off volt"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "% soh and 0 % soh were seen as the end of life and failure of batteries, respectively [31]. the soh of batteries was calculated by eq. (1), where qcurrent was the current capacity and qinitial was the initial capacity. soh = qqcurrentinitial ×100% (1) to qualitatively reveal the degradation modes, we utilize the ic-dv curves analysis. the ic curve is derived by calculating the derivative of the capacity relative to the open circuit voltage (ocv), whereas the dv curve represents the inverse of th"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "of 5 k/min under the 50 ml/min nitrogen flow rate. the mass loss of the sample was measured by the initial mass minus the residual mass, the mass loss derivative (dtg) curve characterized the rate of mass loss rate of the sample at each temperature, the position of the peak in the dtg curve corresponded to the stage of mass loss on the tg curve. in addition, to simulate the exothermic reaction of cells in practical application environments, the nfm/electrolyte system (the mass ratio of cathode a"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "post-mortem characterization tests were used to reveal the degradation mechanisms. the scanning electron microscopy (jsm-7900f, jeol) was used to investigate the morphology of nfm cycled with various charge termination voltages. the transmission electron microscopy (tecnai g2 f30 s-twin, fei) was used to investigate the evolution of cei and crystal structure of nfm. the x-ray diffractometer (bruker d8 advance) was implemented to investigate the structure evolution and phase identification of nfm"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 6,
    "text": "various charge termination voltages, we used a 20 ◦c/min heating rate analyze samples from 30 ◦c to 600 ◦c under argon atmosphere. the technical route of this work is illustrated in fig. 1). 3. results and discussion 3.1. electrochemical degradation characteristic to comprehensively explore the effect of the electrochemical characteristic of nfm during cycling with high potential, half-cells in the coin-cell configuration of nfm with various charge termination voltages were assembled and tested."
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 1,
    "chunk_index": 7,
    "text": "the charge curves and further extension of the slope at higher potential (> 4.4 v), the reversible specific capacity of nfm increases from 120.17 to 162.66 mah g− 1 when the potential raising from 4 v to 4.7 v. with the increasing of charge termination voltage, more sodium ions extracted, thus the capacity proceeding increases. the increasing capacity for nfm can be mainly attributed to the new potential platform occurring at higher charge potential regions, whereas the higher dv = docvdq≈ d(ocv"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 3 reversible capacity of nfm only maintains the first few cycles of cycling, and a significant capacity fading occurs during subsequent long cycling, as exhibited in fig. 2(c). the rate performance of nfm/na half-cells at different current rates (0.1, 0.5, 1, 1.5, and 2 c) with various charge termination voltages has also been explored. fig. 2(b) shows the samples with various charge termination voltages display a progressive diminish in "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "the cells with various charge termination voltages, the rapid specific capacity degradation occurs as cycling proceeds and the increased charge termination voltages accelerate the influence of capacity degradation. the capacity of cells presents a linear decay during the cycling process, the cycled nfm/na at 4.7 v delivers 58.6 mah g− 1 corresponding to 35.5 % capacity retention at 0.5 c (100th-cycle), which is lower than at 4, 4.4 and 4.6 v at 0.5 c 100th-cycle (78.9 %, 57.3 % and 53.4 %). mean"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "it can be calculated that the batteries charged with 4, 4.4, 4.6, and 4.7 v reach 80 % soh after 87, 30, 24 and 17 cycles, respectively, indicating that nfm is not stable upon cycling and the degradation becomes severe, especially in high-voltage charging. these results confirm that the capacity degradation exacerbates at high potential, and a decay in electrochemical kinetics may be responsible for it. given the significant capacity degradation of nfm owing to cycling with high potential, it is"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 4 fig. 2. electrochemical performance of nfm/na half-cells with various charge termination voltages: (a) the charge/discharge profiles of the initial cycle. (b) rate performance at different current rates. (c) cycling performance and coulombic efficiency at 0.5 c current rate. (d) capacity retention curves. cycled with 4.0, 4.4, 4.6 and 4.7 v voltage is depicted in fig. 3(a, b, c, d), respectively. they all possess similar charge/discharg"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "voltage displays a high initial specific capacity compared with 4 v normal charge potential, a rapid decrease from the 1st cycle to the 100th cycle is observed along with increasing charge termination voltage. fig. 3(e, f, g, h) show the changes in the electrochemical impedance spectroscopy (eis) profiles of the cell with various charge termination voltages after 1, 5, 20, and 30 cycles, individually. fig. s1 displays the equivalent circuit model and the calculated value of resistance is exhibit"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "furthermore, incremental capacity (ic) - differential voltage (dv) curve method is employed to qualitatively investigate cycling with various charge termination voltages affecting the battery degradation behavior, as depicted in fig. 4. ic-dv analysis is a useful non-destructive method for exploring degradation mechanisms of cells by analyzing the shift and change of valleys and peaks of ic-dv curves [34,35]. by utilizing the ic-dv analysis method, it's clear to reveal the degradation modes duri"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "during the charge/discharge process [37,38]. lam usually has a direct correlation with the structure transformation, cathode surface degradation, and electrolyte oxidative decomposition [39]. the methodology mentioned above can also be applied to the investigation of sibs. in this study, we proposed three degradation modes to describe degradation behaviors for sibs: the loss of conductivity (loc), the loss of sodium inventory (lsi), and the loss of active material (lam). for the cell charged to "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "decreases, which means a slight loc happens. the lam primarily causes the reduction of the magnitude of two valleys. it can be found that lam is more prominent than loc, particularly at 80 % soh, which indicates that the degradation impact of the cathode structure and the loss of active material are more severe than the loss of electronic connection. comparing the various charge termination voltages (4.0, 4.4, 4.6, and 4.7 v), it is worth noting that the valley ① has a greater leftward shift ten"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 5,
    "text": "exacerbates, causing an excessive extraction of sodium ions from the cathode. this results in severe degradation of the host structure, ultimately leading to the disordering of the internal structure and bulk degradation. furthermore, the same conclusion can be obtained from the dv curves, it can be observed that the magnification of dv curves near 0.7 mah shows a significant increase in the intensity of the peak, suggesting that lam occurs. it also can be found that the dv curves show a low cap"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 6,
    "text": "damage to the inherent electrochemical properties of the cell. herein, from an electrochemical perspective, the loc and lam degradation modes have a significant influence on cycling performance, leading to the capacity fading and the decline of the voltage plateau of the battery. 3.2. thermal stability analysis of nfm the individual evolution of thermal stability for nfm material cycling with high potential was investigated. the tg-dtg profiles of nfm with various charge termination voltages (4."
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 3,
    "chunk_index": 7,
    "text": "the tg curves between 300 and 600 ◦c are considered as stage ii, a series of complex pyrolysis processes, including the main decomposition of nani1/3fe1/3mn1/3o2, besides, pvdf and nmp involved in the synthesis of nfm fig. 3. degradation profiles of nfm cathode with various charge termination voltages vary with cycle numbers: (a) 4.0 v; (b) 4.4 v; (c) 4.6 v; (d) 4.7 v; nyquist plots of nfm cathode with various charge termination voltages during different cycles: (e) 1st cycle; (f) 5th cycle; (g)"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 5 also decompose. to better analyze the changes of nfm with different charge voltages. the 4.4 v nfm sample is used as an example which is exhibited in fig. 5(b), the weight loss of the two stages is 2.18 % and 11.92 %, respectively. therefore, stage ii can be defined as the dominant weight loss stage in the whole thermal decomposition process. although the figure of the weight loss curve is similar among different samples, comparing the "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "termination voltage and high potential weakens the thermal stability of nfm. based on the above results, it clarifies that nfm experiences a greater degree of de- embedded sodium at high potential, thus the original layered structure becomes unstable, resulting in worse thermal stability. 3.3. pyrolysis process analysis of nfm to further elucidate the pyrolysis process of nfm with various charge termination voltages, the ftir spectrum is employed to qualitatively investigate the gas component ge"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 6 pyrolysis process. the evolution of the gas infrared absorption spectrum of nfm with various charge termination voltages during the 100–600 ◦c heating process is shown in fig. 6. it can be observed that the gas products of nfm with various charge termination voltages are similar, which mainly consist of co2, and h2o, the peak at wavenumber 3950–3500 cm− 1 is gaseous h2o, and the peak at wavenumber 2359 cm− 1 represents co2, respectively"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "the gaseous h2o is generated by the combination of hf and naoh or -oh groups. the hf is produced by the thermal decomposition of binding agent pvdf, while naoh or -oh groups are released from the oxide surface of nfm which thermal decomposes at about 300 ◦c [41,42]. therefore, it can be speculated that in the two stages of the nfm cathode in the pyrolysis process, the release of o2 is relatively low not enough to reach the reaction condition with conductive carbon black before 300 ◦c, while in t"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "(7) in addition, the ms data of co2 (m/z = 44) and gaseous h2o (m/z = 18) of diverse samples during the heating process is compared in fig. 6 (e, f). the intensity of the gas signal peak can reveal the relationship between the amount of gas generated from the nfm pyrolysis process and the charge termination voltage. there is no obvious variation in the intensity of the gaseous h2o signal peak, while it's noteworthy to mention that the intensity of the co2 signal peak increases as charge voltage "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "then subsequently reacts with conductive carbon black at high temperature, thus the total weight loss increases. hence, from the tg- ftir- ms analysis, it can be inferred that the thermal stability of the nfm is highly related to the charge termination voltage, the higher the charge voltage, the lower thermal stability presents. it is demonstrated that the nfm cathode has a higher desodium state at high potential, which weakens its thermal stability and increases the amount of o2 release. to ver"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "a sharp main exothermic peak beginning at about 203.17 ◦c, which is considered as the initial thermal decomposition of nfm. the small exothermic peak following the first peak should be prone to the products from nfm thermal decomposition at high temperatures and further redox exothermic reactions with the electrolyte. these reactions overlap each other and generate heat violently, the significant overlapping exothermic peaks between 205 ◦c–300 ◦c most likely be the consequence of the exothermic "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 7 pc [43,44]. it can be seen clearly that o2 plays a pivotal role in the exothermic reaction process, while o2 is mainly released from the thermal decomposition of nfm. from the conclusion of tg analysis, it can be found that the excessive desodium of nfm cycling at high potential will enhance its oxidation, thus more o2 will be released, then o2 further reacts with the electrolyte. it can be noted that the exothermic behavior of samples "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "surface degradation of nfm is characterized by sem. as exhibited in fig. 8, the morphology evolution of nfm cycling with various charge termination voltages is thoroughly investigated. fig. 8(a, b, c) show the sem images of pristine nfm powder material, the secondary particles are composed of large amounts of tightly agglomerated flake-shaped primary grains, presenting a spherical morphology with an approximate size of 5 μm. fig. 8(d, e, f) show the morphology of fresh nfm cathode, it can be obs"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "cathode is revealed both at the particle surface and inner fig. 7. thermal stability of nfm/electrolyte system with various charge termination voltage: (a) heat flow curves; (b) the magnification of peak heat flow curves; (c) the onset temperature and peak temperature; (d) total heat release. bulk. it can be demonstrated that cycling with high potential exacerbates bulk degradation. as illustrated in fig. 8(g, h, i), the bulk defects are observed in diverse samples. fig. 8(g, h) show the evoluti"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "of the nfm cathode after prolonged 4.7 v cycling. therefore, high potential cycling drives more sodium ions out of the bulk lattice and destabilizes the original layered structure, consequently resulting in the degradation of the capacity and thermal stability of nfm. except for the morphology change of nfm, the gradual fading of capacity cycling at high potential is likely attributed to the inevitable side reactions of the cathode/electrolyte interface. when cycling at high potential, the react"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 8 magnification figure of (104) peak. 1s peak at 535.4 ev and 530.2 ev can be assigned to na auger and lattice oxgen [45,46]. fig. 9(a) reveals the difference in naf content for different samples, which is produced by fec and pf6− . it can be observed that the intensity and area of naf peak increases as the charge termination voltage rises, indicating that the decomposition of electrolyte accelerates, thus more pf6− anion generated. to fu"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "lattice oxygen peaks diminishes on the cei film with the charging voltage increasing, which suggests the degradation of cei film at high potential, resulting in the reduction of the o 1s content. meanwhile, the increased cathode/electrolyte interfacial side reactions at high potential make the cei film nonuniform as shown in fig. s4, thus leading to the electrochemical performance unstable, finally leading to severe capacity degradation. moreover, to fully elucidate the correlation resulting fro"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "y. gan et al. journal of energy storage 114 (2025) 115776 9 termination voltages and the 4.0 v nfm material was used as a compared sample. as is shown in fig. 9(d), for the 4.0 v nfm, all the diffraction peaks can be assigned to the space group r-3m with α-nafeo2 hexagonal layered structure. when charging proceeds, the (003) and (104) diffraction peaks associated with the o3 phase start to change after cycling with various charge termination voltages. compared with the 4.0 v nfm, the (003) peak "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "c decreases as the charge termination voltage rises. it is proved that redox reactions of the tm ions (tm = ni, fe, and mn) have a vital influence on the lattice parameter a. when the cell is cycled at high potential, the tm cations undergo severe redox reactions, the active cations ni and fe experience ni2+/ni3+/ni4+and fe3+/fe4+, respectively, while mn4+ cations are known to be electrochemically inactive [47,48]. thus, after the completion of the high potential discharging process, the tm ions"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "as evident in fig. 9(e, f). it's worth noticing that high potential accelerates the evolution of crystal structure, which may be attributed to the more complex phase transformation of the nfm [23]. additionally, the tem images and saed patterns of the cycled nfm cathode with different termination voltages are shown in fig. s5. it can be observed that the nfm cathode still maintains the layered structure after cycling with different charge termination voltages, whereas the lattice spacing of the "
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "breakdown failure, which can be contributed to deep dissociation process and severe crystal structure change due to complex phase transformation. additionally, the continuous cei reformation introduced by particle breakdown makes the cei film unstable, also accelerating capacity fading. moreover, cathode/ electrolyte interfacial side reactions are more prone to occur at high potential, resulting in the side products adhering to the surface of the cathode, impeding the na+ transfer and introducin"
  },
  {
    "source_pdf": "Exploring_the_degradation_characteristics_and_thermal_stability_of_NaNi13Fe13Mn13O2_cathode_for_sodium_ion_battery_cycling_with_high_potential_Yixiu_Gan.pdf",
    "page": 8,
    "chunk_index": 4,
    "text": "of high potential on the capacity degradation characteristics and thermal stability of the nfm cathode. based on ic-dv analysis, the dominant degradation modes are loc and lam. as the rise of charge termination voltage, bulk degradation, and internal structure evolution are exacerbated, which progressively impacts the morphology and crystal structure stability of nfm. furthermore, the interfacial side reactions between the cathode and electrolyte also aggravate at high potential. the oxygen rele"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "adv. energy sustainability res. 2022, 3, 2200009 2200009 (1 of 23) © 2022 the authors. advanced energy and sustainability research published by wiley-vch gmbh 1. introduction energy is the driving force for promoting the continuous growth of social development and economy. and developing renewable energy and broadening its application in human life and industry production are strongly necessary to meet the demand for energy. [1] among the energy storage systems, the electrochemical energy storag"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "reach 1.24 million w. shao, x. jian, f. hu state key laboratory of fine chemicals department of polymer materials & engineering school of materials science and engineering key laboratory of energy materials and devices (liaoning province) dalian university of technology dalian 116024, china e-mail: hufangyuan@dlut.edu.cn h. shi, z.-s. wu state key laboratory of catalysis dalian national laboratory for clean energy dalian institute of chemical physics chinese academy of sciences 457 zhongshan roa"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "and the estimated supply of lithium carbonate is only 1.08 million tons in the same year. [4] a large supply gap will occur at that time. thus, developing non-lithium energy storage technologies that can replace the application of libs in certain fields is urgent. [4–6] sodium (na) and lithium (li) are alkali metals with similar electronegativity values, both of which are next to each other in the periodic table, resulting in their similar physical and chemical properties. different from lithium"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "principle of sibs is similar to that of libs. [5] with the straightforward producing equipment of libs, the fabrication progress of sibs is relatively fast. to date, many companies have been established to verify the technical feasibility and marketability of sibs, including hina battery company (china), natron energy and sharp (usa), and altris (sweden). [7] in this case, the electrode material is one of the key factors to obtain sibs with high performance and cycling stability. for the cathode"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "sn,[12] sb,[13] and p,[14] among which the theoretical specific capacity of element p can reach 2596 mah g1. [15,16] these alloy-type anodes can provide high theoretical capacity due to the existence of multiple electron exchange reactions during the process of forming a binary alloy with sodium. however, this process is accompanied by serious electrode structure changes, and the volume expansion rates of sn, sb, and p are as high as 420%, 390%, and 440%, respectively. [15] the volume expansion "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "distance, alleviate the volume change, and result in longer cycling stability. what's more, sodium-ion batteries (sibs) hold great potential in the application of large-scale energy storage. with the coming commercialization of sibs, developing advanced anode of particularly hard carbon is becoming increasingly urgent yet challenging. hard carbon still suffers from unclear sodium storage mechanism, unsatisfactory performance, and low initial coulombic efficiency (ice). herein, the current stateo"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "designing surface coatings or constructing composite materials can further improve the stability of the electrode. [18] engineering the defect of alloy anodes can provide additional reactive sites and accelerate charge transfer kinetics. thus, defect engineering is widely used to adjust the performance of alloy anodes. [15,19] transition metal compounds are another type of high-capacity anode materials, including transition-metal oxides, sulfides, and selenides, because transition metals usually"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "bi, ge, sn, and pb. [24,25] however, similar to that of alloy materials, these compounds still suffer from low conductivity, limited ionic diffusion rate, serious particle aggregation, and volume expansion. although their performance can be improved through methods similar to that of alloy materials, their practical application value is still limited. [15,20] benefiting from their merits of abundant resources, low cost, easy preparation, and environmental protection, carbonaceous materials are c"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "practical application. [28] in this review, the current state-of-the-art advances in designing hard carbon anodes for high-performance sibs are summarized. we begin with a demonstration of the microstructure formation process of hard carbon, and the key structural features of hard carbon are discussed in detail. according to different sodium storage behaviors, several modified sodium storage mechanisms are illustrated, including the models of “insertion–adsorption,” “adsorption–insertion,” “adso"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "2. importance of hard carbon for sibs graphite and amorphous carbon are commonly used carbonaceous materials. [35] amorphous carbon can be divided into soft carbon and hard carbon according to the graphitization ability of carbon materials. in general, soft carbon is considered to be the type of carbon material that can be completely graphitized at 3000 c. hard carbon cannot be completely graphitized even at 3000 c.[35] the disordered degree and layer spacing of the materials increase from graph"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "copyright 2018, wiley-vch gmbh. the precursors, heating rate, target temperature, and posttreatment condition. as shown in figure 2a, during the pyrolysis below 700 c, the precursor is gradually decomposed, accompanied by the release of small molecules, including h2o, co2, co, ch4, and h2. [11] the precursors are usually considered to be carbonized above 700 c. the precursors of soft carbon, such as pitch, coal tar, and ethylene polymers, can convert into a fluid-phase at the pyrolysis temperatu"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "precursors of hard carbon are either highly cross-linked or can react to be crosslinked during the first pyrolysis stage, including biomass and synthetic resins, e.g., polyaniline (pani), polyacrylonitrile (pan), phenolic resin, epoxy resin. [26,35] as shown in x-ray diffraction (xrd) patterns (figure 2b), graphite has an obvious crystallization peak, while the reduced graphene oxide (rgo) and soft carbon exhibit slightly wider peaks at around 25. [11] for hard carbon, two obvious wide diffracti"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "reversible capacity with an obvious plateau region below 0.1 v (figure 2c). [26,35] the small layer spacing of graphite and soft carbon is unsuitable for sodium storage, resulting in low capacity. as reported previously, the sodium storage performance of graphite can be improved by optimizing the electrolyte or modifying the graphite. [27,37,38] for instance, adelhelm et al. [27] suggested that naþ ions cannot form stable binary intercalation compounds in graphite, which was the main limitation "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "ordered structure of graphite, which could be seen in the high-resolution transmission electron microscopy (hrtem) images. [39] the expanded graphite was beneficial for sodium storage (figure 3c–f). the interlayer spacing can be adjusted by tuning the reduction time. as a result, the optimized carbon showed a layer spacing of 0.43 nm and a capacity of 284 mah g1 at a current density of 20 ma g1 (figure 3g,h). similar to graphite, soft carbon exhibits a highly ordered microstructure. although its"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "800 c by lowing target carbonization temperatures of pitch (figure 4a). at a current density of 0.15 c, the reversible capacity was 263 mah g1 (figure 4b). the carbon anode showed slope-dominated sodium storage behavior, endowing it good rate performance. furthermore, they proposed an in situ mg(no3)2 curing strategy to restrain the graphitization of pitch (figure 4c). [36] oxygen and solid products produced during the pyrolysis of mg(no3)2 can consume the hydrogen components inside the pitch, t"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "figure 3. a) charge–discharge profiles of lithium-ion batteries (libs) and sibs with graphite anode in 1 m mþ (pf6) in ethylene carbonate (ec): dimethyl carbonate (dmc), and b) charge–discharge profiles of sibs with graphite anode in 1m naotf in diglyme. reproduced with permission. [27] copyright 2014, wiley-vch. c–f) high-resolution transmission electron microscopy (hrtem) images of pristine graphite, go, thermal reduced graphite oxide with 1 h (eg-"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "1 h), and thermal reduced graphite oxide with 5 h (eg-5 h). g, h) electrochemical performance of pristine graphite, go, eg-1 h, and eg-5 h at a current density of 20 ma g1. reproduced with permission. [39] copyright 2013, nature publishing group. figure 4. a) schematic of the carbonizing pitch with low-temperature and high-temperature methods, b) charge–discharge profiles of pitch-derived carbon under 800 and 1550 c. reproduced with permission. [43] copyright 2019, wiley-vch gmbh. c) hrtem image"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "as o released from mg(no3)2 during the pre-oxidation process (figure 4e). during pretreatment, sodium storage performance can be optimized by adjusting the temperature and time of the pre-oxidation process. an optimized anode with an ice of 88.6% and a specific capacity of 300.6 mah g1 was obtained (figure 4f,g). in addition, liu et al. [44] regulated the microstructure of pitch by the ti3c2tx mxene terminations, which could also consume the intrinsic hydrogen of pitch, leading to a disordered c"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "increasing studies have been conducted on the sodium storage mechanism of hard carbon. [46–49] however, certain challenges still remain in obtaining a clear sodium storage mechanism. the heterogeneity of amorphous hard carbon materials may lead to a contradiction between the results from local testing technologies (such as hrtem) and average testing technologies (such as xrd patterns). [50,51] whether the electrolyte can enter the micropores in the material is difficult to identify, and the effe"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "techniques. the process of sodium storage in hard carbon can be derived into three parts, including: i) adsorption near the surface, defects, and heteroatoms; ii) insertion into carbon layers; and iii) nanopore filling. at present, four models, namely, “insertion– adsorption” model,[46] “adsorption–insertion” model,[55] “adsorption–pore filling” model,[50] and “adsorption– insertion–pore filling” model,[56] have been proposed to explain the sodium storage behavior in hard carbon. [7,11,57] among"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "in the nanopores, resulting in a long plateau of sodium storage at the potential close to sodium deposition(figure 5b). [46] further, dahn et al. [46] used in situ xrd measurement to analyze the sodium storage behavior of soft carbon. it was found a significant left shift of the (002) peak during discharge in the “slope” region, indicating the carbon layers were increased at this stage. however, the shift of (002) peak for hard carbon was unremarkable because it was extremely wide to determine i"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "using ex situ xrd and raman techniques. the interlay spacing changed more obviously in the “slope” region than that of the “plateau” region. thus, they proposed sodium intercalation mainly occurred at the “slope” region (figure 5d). 3.2. “adsorption–insertion” model although the “insertion–adsorption” model fits several kinds of hard carbon materials, some important experimental observations still cannot be explained well. [60,61] in particular, most of the porous carbon materials only show slop"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "proposed an “adsorption– insertion” model for sodium storage. it was proposed that the mechanism of sodium storage in hard carbon was similar to that of lithium in graphite. the naþ ions were adsorbed on the surface, defects, and pores in the slope region, and naþ ions intercalated into carbon layers in the plateau region. after simulating the reaction energy barrier of the compound formation between naþ ions and carbon, it was pointed out that the minimum interlayer spacing for naþ ions interca"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "carbon at different charging and discharging states. reproduced with permission. [45] copyright 2000, electrochemical society. d) ex situ xrd patterns of electrode tested at different charging and discharging states, i)–vi) refers to pristine electrode and electrode discharging to 0.4, 0.2, 0.1, 0 v, and charging to 2.0 v, respectively. reproduced with permission. [59] copyright 2011, wiley-vch gmbh. figure 6. a) theoretical energy cost for naþ and liþ ions to insert into carbon interlayer. repr"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "of chemistry. f) in situ xrd patterns of hc-1300 anode during the initial cycle. reproduced with permission. [55] copyright 2017, wiley-vch gmbh. carbon showed no obvious change under high potential, whereas it gradually separated into two diffraction peaks with the decreased potential. it was suggested that only part of the graphite microcrystals was suitable for naþ ions intercalation, and the other parts with smaller interlayer spacing remain unchanged during the charge and discharge process."
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "and naþ ions inserted into graphite crystallites at the potential below 0.1 v by using the ex situ 23 na nmr technique (figure 6c). the characteristic peak of sodium metal disappeared during the whole process, indicating that sodium mainly existed inside the hard carbon as ions. later, ghimbeu et al. [47] proposed the positive correlation between porous structure and slope capacity by analyzing the porous structure of cellulose- derived carbon with different pyrolysis temperatures through gas (n"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "storage mechanism (figure 6e). a new diffraction peak at around 28 appeared in the plateau region, which was likely associated with the intercalation compound, clearly indicative of sodium intercalation. [64] to explain the sodium storage mechanism, joaquin et al. [65] presented a comprehensive approach of synchrotron x-ray total scattering experiments to observe the structure information of hard carbon at the nanoscale. specifically, carbon materials may undergo an atomic rearrangement at the t"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "the defects and disordered structure of carbon could be adjusted by tuning the post- treatment time. smaller microcrystalline and higher content of disorder structure were related to less plateau capacity, thereby confirming the “insertion– adsorption” model well. for further development of the “insertion–adsorption” model, xu et al. [51] proposed an extended “insertion–adsorption” mechanism on the basis of correlation between microstructure and sodium storage behavior of hard carbons synthesize"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "storage behavior for the plateau capacity remains inconclusive because the testing results from electrochemical ex situ xrd and operando xrd patterns are difficult to unify with carbon materials derived from different precursors. thus, the controversy remains over the storage mechanism at low potential. [55,67] in 2016, hu et al. [50] prepared uniform microtubular-shaped carbon materials from renewable biomass under 1300 c (hct1300) to explore the sodium storage mechanism. ex situ hrtem images s"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "filling” model (figure 7c). to eliminate the influence of inevitable factors during ex situ testing, grey et al. [68] conducted the operando 23na solid-state nmr and probability density function analysis experiments to provide insights into the sodium storage mechanism (figure 7d). significantly, operando 23na solid-state nmr spectra showed a single resonance initially, which shifted to positive frequencies later, indicating a two-stage mechanism. ionic naþ was detected in the sloping region, na"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "this case, an increased metallic nature of carbon materials with higher pore size was proposed after sodiation. this original quasi-metallic phase only existed in the carbon materials with a low potential plateau. carbon materials obtained under high pyrolysis temperature showed low plateau capacity, owing to the reduced graphite interlayers and accessible pores (figure 7f). thus, the “adsorption–pore filling” model was well proven (figure 7g). therefore, balancing the interlayer spacing, the nu"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 7,
    "chunk_index": 5,
    "text": "the plateau capacity increased continuously with the increase in shell numbers because increasing the number of shells can promote the formation of closed pores inside the materials. thus, a high reversible capacity of 360 mah g1 at a current density of 30 ma g1 was achieved by the optimized electrode. the testing results verified the “adsorption– pore filling” mechanism. later, wu et al. [53] probed the quasi-ionic bonds and quasi-metallic sodium between carbon and sodium with the assistance of"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 7,
    "chunk_index": 6,
    "text": "estimated to be nac6.7, corresponding to a theoretical capacity of 334 mah g1. 3.4. “adsorption–insertion–pore filling” model as shown in the above-mentioned models of sodium storage mechanism, the recognition of sodium storage behavior changes over time. more and more advanced techniques have been applied to detect such a process. [68,70,71] the experimental methods transitioned to direct proof gradually, avoiding the errors from"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "indirect speculation. however, whether the process of sodium storage in the plateau region is the insertion or pore filling remains controversial. [29] whether both the insertion and the pore-filling processes will occur in the plateau region, while only one of them is the main process. in particular, neither the “adsorption–insertion” model nor the “adsorption–pore filling” model can explain the increased diffusion coefficient of naþ ions near the cutoff potential during galvanostatic intermitt"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "insertion–pore filling” model (figure 8b). combined with ex situ saxs and ex situ xrd techniques, kim et al. [73] determined the significantly changed interlayer spacing of hard carbon at the potential range of 0.03–0.1 v. the peak intensity from saxs tests decreased obviously below 0.1 v, indicating that the insertion and the pore filling process occurred in the plateau region (figure 8c). besides above, some studies suggested that the process of sodium insertion was not limited to the potentia"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "insertion in hard carbon with density functional theory calculation to yield a clear picture of sodium storage mechanism. it was concluded that naþ ions intercalated into carbon to form nac24 after the surface and defects were occupied at high figure 7. a) ex situ hrtem images of hct1300 anodes before and after discharging. b) ex situ na 1s x-ray photoelectron spectra (xps) spectra of hct1300 at different charging and discharging states. c) schematic of the “adsorption–pore filling” mechanism fo"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "potential. naþ ions filling reaction occurred in the plateau region to form quasi-metallic sodium. recently, yamada et al. [29] explored the sodium storage mechanism of hc-1400 (source-derived hard- carbon pyrolysis under 1400 c) by combining ex situ saxs and wide-angle x-ray scattering (waxs). the graphite interlayer started to expand when the content of sodium inside the carbon reached 50–60% (figure 8d). the metal sodium peak can be obviously observed in the overcharged sample at the voltage "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "a large scale, which is considered to be the preferred material for practical application of sibs, the capacity and rate capability of hard carbon still need to be further improved. as sodium storage capacity is mainly contributed by defect/pore adsorption, interlayer intercalation, and pore filling, the key strategies including morphological engineering, heteroatom doping, and graphitic structure regulation are the most commonly used approaches in enhancing the performance of hard carbon. [26] "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "unique hollow structure, which can provide a large active surface area, facilitate the mass transfer, and reduce ion diffusion distance. [83] using the same strategy, maier et al. [84] fabricated hollow carbon spheres with thin amorphous carbon walls by using a polystyrene (ps) latex template. glucose was hydrothermally polymerized on the surface of the ps template to form carbonaceous spheres, and the ps template was further eliminated during the pyrolysis process under 1000 c, resulting in the"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 9,
    "chunk_index": 3,
    "text": "thiourea-modified phenolic resin on the surface of pmma (figure 9b). such n, s co-doped hollow nanospheres showed the specific capacity of up to 110 mah g1 at a current density of 10 a g1. [85] on the basis of hollow carbon spheres, hu et al. [69] prepared multi- shelled hollow carbon nanospheres through a repeating etching and growing process with the precursor of phenolic resin (figure 9c), and hollow carbon nanospheres with different shell numbers from one to four were successfully fabricated"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 9,
    "chunk_index": 4,
    "text": "showed a superior sodium storage capacity of 310.5 mah g1. besides, figure 8. a) naþ ions diffusion coefficients of hard carbon calculated from galvanostatic intermittent titration technique (gitt) curves. b) schematic of “adsorption–insertion–pore filling” model. reproduced with permission. [56] copyright 2018, elsevier. c) ex situ saxs patterns of c-1300 during sodiation at 50 ma g1. reproduced with permission. [73] copyright 2019, elsevier. d) ex situ waxs patterns of hc-1400 at different dis"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "polydopamine, polypyrrole, polythiophene, and other precursors that can be attached to the surface of templates are widely explored to prepare hollow carbon spheres with high performance. [81,86] as the same with carbon spheres, 1d carbon nanofibers are also widely used as anodes for sibs. they can be fabricated as self- supporting films, which can be directly applied as electrodes after pyrolysis. it is well known that the removal of binders and conductive agents can greatly reduce the invalid "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "and showed excellent prospects for flexible energy storage devices (figure 10b–d). when used as a self- supporting electrode for sib, it exhibited the specific capacity of 303 mah g1 at a current density of 0.2 a g1 (figure 10e). as another example, wu et al. [89] prepared a type of flexible carbon paper possessed of self-interlacing carbon microstrips by carboning plant tissues through a two-step annealing process. such carbon paper owned high conductivity and ultrafast ion transport kinetics, "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "particular, hollow carbon nanofibers with multichannels were obtained by adding a ps template during the electrospinning. this multichannel structure was beneficial for loading other materials to prepare highperformance composite electrodes. as a result, the figure 9. a) rate capability of carbon spheres and hollow carbon spheres. reproduced with permission. [84] copyright 2012, wiley-vch gmbh. b) schematic of the procedures for the synthesis of hollow carbon. reproduced with permission. [85] co"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "sulfur-rich carbon nanofiber films prepared exhibited a specific capacity of 187 mah g1 at a current density of 2 a g1. [91] in addition to the 0d carbon spheres and 1d carbon nanofibers, 2d layered materials and 3d porous materials with abundant pore structures can be synthesized by adjusting the morphologies of polymers or the proportion of template agents. [94] it is recognized that covalent organic framework-derived carbon are typical 2d carbon materials. besides, it is well accepted that 2d"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "through the same method, 3d porous carbon materials were fabricated by reducing the proportion of nacl (figure 10n). the electrode of 3d porous carbon delivered the capacity of 280.1 mah g1 at 0.03 a g1 (figure 10o), and showed a better rate capability than that of the bulk electrode (figure 10p). [93,95] as another example, cellular porous carbon can be attained after spray drying and further pyrolysis of the mixture of the nacl template and precursors (figure 10q–s). [32] without using the tem"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "a g1. 4.2. heteroatom doping heteroatom doping is another feasible method used to improve the electrochemical performance of hard carbon. [96] hard carbon doped with one or multiple types of heteroatoms, including b, n, o, f, s, and p have been reported previously. [26] in general, heteroatom doping can change the structural characteristics of hard carbon systematically, which will greatly affect the performance of sibs. for instance, ji et al. [97] prepared b-, s-, and p-doped carbon from sourc"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "bacterial cellulose at different rates. reproduced with permission. [87] copyright 2019, elsevier. f) schematic of the fabrication procedure of carbon nanofiber films. reproduced with permission. [30] copyright 2015, wiley-vch gmbh. g–i) sem images, j) atomic force microscope (afm) image, and k–m) hrtem images of f127 derived 2d nanosheets. reproduced with permission. [92] copyright 2017, royal society of chemistry. n) schematic of the fabrication procedure of pitch and phenolic resin derived 3d"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "of the plateau region by combining the experimental data and first- principle calculation (figure 11a). however, the binging energy between b and na was extremely large to release the na during the desodiation process, leading to a large irreversible capacity (figure 11b). [97] further, b, n co-doped carbon networks were prepared by freeze-drying the mixture solution of bacterial cellulose and ammonium borate solution, and exhibited a reversible specific capacity of 691 mah g1 at 0.1 a g1. [98] "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "cof-derived porous carbon showed a capacity of 88.8 mah g1 at 2.5 a g1. further, 2-methylimidazole can chelate with polyvalent metal ions to prepare zif-type covalent metal–organic frameworks (mofs) because it contains two n atoms, these mofs have a regular 3d structure and can be used to prepare n-doped porous carbon with specific morphologies. [104] as another example, mitlin et al. [105] used poly (acrylamide-acrylic acid) and sulfur as the precursors to manufacture n, s co-doped porous carbo"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "side chains can be used to fabricate o-doped carbon materials. [106,107] what's more, the oxygen in the air may affect the oxygen content of carbon materials. [37,106,108,109] however, the influence of o doping on electrode performance has not been clarified in a long time. the functional groups of c ¼ o and cooh are the most electrochemically active forms among all the existing o forms by summarizing the results of experiments and theoretical calculations. [110–112] to identify the correlation "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "reaction process, thereby improving the reversible capacity. [113,116] the doped s atoms can enlarge the layer spacing and shorten the ion diffusion distance, resulting in fast reaction kinetics for sibs. [117] the strategies to fabricate s-doped carbon include synthesizing figure 11. a) xrd patterns and b) charge/discharge profiles of undoped and b, s, p-doped hard carbons. reproduced with permission. [97] copyright 2017, wiley-vch gmbh. c) major synthesis route of hypercrosslinked microporous "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "precursors with thiophene and –sh,[118–120] carbonizing sulfur powder or thiourea with precursors,[116,121–123] and activating precursors with sulfuric acid or h2s. [124] representatively, wang et al. [113] accurately adjusted the composition and structure of n, s co- doped porous carbon by carbonizing the designed pyrrole/thiophene hypercrosslinked microporous polymers (figure 11c), where its capacity reached 521 mah g1 at a current density of 0.1 a g1 (figure 11d), accompanied by a capacity of"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 13,
    "chunk_index": 1,
    "text": "attain sulfur- rich carbon materials (figure 11f). [114] recently, ji et al. [125] proposed a new strategy for s-doping. they prepared a covalent sulfur–carbon complex with high covalent sulfur contents by applying the –so3h and so42 as sulfur sources. the content of long- chain sulfur and short-chain sulfur in the complex was precisely controlled. the reversible transformation of long-chain sulfur to short-chain sulfur and na2s during cycling was well evidenced. doping hard carbon with p can gr"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 13,
    "chunk_index": 2,
    "text": "the surface of the carbon layer in the form of “protrusions” rather than “holes.” such “protrusions” can promote the migration of naþ ions without causing excessive irreversible capacity, thereby effectively improving the capacity and rate performance of the electrodes. [134] in particular, zhao et al. [115] prepared a phosphoric-acid-doped pan through amidoxime and phosphorylation reactions to fabricate n, p co-doped carbon materials with the p content of 6.19% (figure 11g). p─c bonds can impro"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 13,
    "chunk_index": 3,
    "text": "naþ ions. in addition, n-related functional groups can enhance the capacity through pseudocapacitive behavior, while c ¼ o can electrostatically adsorb naþ ions and redox reactions would happen. s-related active sites may transform into mercaptan anions and react with naþ ions during sodiation. and p doping can improve the electronic conductivity and greatly improve the specific capacity through a multi-electron redox reaction. 4.3. graphitic structure regulation the purpose of regulating the 3d"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 13,
    "chunk_index": 4,
    "text": "to the graphitic structure of materials. [48,53] carbonization temperature is one of the key factors affecting the degree of graphitization for hard carbon. obvious differences are found in the optimum carbonization temperature of various precursors. the carbon materials with the highest plateau capacity were prepared under 1200–1600 c.[65] lower pyrolysis temperature results in a low graphitization degree and negligible plateau capacity, and the graphitization degree is extremely high under hig"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 13,
    "chunk_index": 5,
    "text": "proper pyrolysis temperature should be explored to fabricate carbon materials with abundant pseudo-graphite phases. to obtain hard carbon with an appropriate graphitic structure at low temperature, shen et al. [138] utilized graphite powder and graphite blocks to assist the carbonization of egg films and hydrothermal polymerized glucose (figure 12b). the introduced graphite powder can promote the formation of pseudo-graphite phases, reduce the defects, improve the ice, and enhance the plateau ca"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 13,
    "chunk_index": 6,
    "text": "capacities, and their capacity can reach 340 mah g1 at a current density of 0.1 a g1 (figure 12g). moreover, kaskel et al. [140] prepared a cross-linked ps network by coupling benzene rings of ps through the scholl reaction (figure 12h). the coupled benzene rings can promote the aromatization of the polymer during pyrolysis, which was helpful for the growth of pseudo-graphite phases. in addition, taking polymers with significantly different aromatic structures as precursors can obtain hard carbo"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 14,
    "chunk_index": 0,
    "text": "with a higher degree of order (figure 12i). the polyethylene terephthalatederived carbon delivered a high capacity of 342 mah g1 at a current density of 20 ma g1, with a remarkable ice of 86.1% (figure 12j). [141] after exploring several precursors, hu et al. [54] suggested that the pyrolysis process of precursors was accompanied by the change in graphite microcrystals and the transformation of open pores to closed pores (figure 13a). the closed pores don't directly contact with the electrolyte,"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 14,
    "chunk_index": 1,
    "text": "mah g1. similarly, komaba et al. [143] fabricated hard carbon with abundant closed pores successfully by pyrolyzing the freezedried mixture of glucose and magnesium gluconate (figure 13c). during the pyrolysis process, magnesium gluconate decomposed to form mgo nano-templates, which generated the pores in the composites after the removal of mgo before high-temperature carbonization. as a result, the reversible capacity of carbon materials synthesized under 1500 c was as high as 478 mah g1. in ad"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 14,
    "chunk_index": 2,
    "text": "sodium storage performance in comparison with that of the single component, which are promising candidates for practical materials in large-scale sibs technology. [144] therefore, improving the graphitic structure of hard carbon can be realized by regulating the precursors, pyrolysis process, and target temperature. from the aspect of precursors, selecting polymers with optimized aromatic structure and cross-linked network, or constructing a heterostructure of two carbon precursors can obtain ha"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 14,
    "chunk_index": 3,
    "text": "copyright 2019, wiley-vch gmbh. d) schematic of cellulose nanocrystals extracted from wood. hrtem images of cellulose nanocrystals e) before and f) after carbonization. g) charge/discharge profiles of cellulose nanocrystals derived carbon at different rates. reproduced with permission. [139] copyright 2017, elsevier. h) schematic of the synthesis process of cross-linked ps networks. reproduced with permission. [140] copyright 2020, elsevier. i) schematic of the carbonization process of polycarbo"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 15,
    "chunk_index": 0,
    "text": "effectively. finally, controlling the carbonization temperature has always been used to adjust the graphitization degree of hard carbon, while proper pyrolysis temperature should be explored for different precursors with different pyrolysis mechanisms. 5. initial coulombic efficiency apart from the low reversible capacity and large volume changes of anode materials, some other key issues, e.g., low ice, still reproduced with permission. [143] copyright 2020, wiley-vch gmbh. must be addressed bef"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 15,
    "chunk_index": 1,
    "text": "is low. once the anode materials are used in a full battery system, many naþ ions from the electrolyte and cathode are consumed irreversibly for the formation of solid electrolyte interphase (sei) and side products during the initial cycle. [147] the quality of the cathode reported in many studies is higher than that of the anode to supplement this consumption. [50,56] however, the energy density of the whole system decreases in this process. therefore, high ice is an extremely important paramet"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 15,
    "chunk_index": 2,
    "text": "[59,148] however, the formation of a stable sei film always results in a large irreversible capacity because many electrolytes are decomposed at the corresponding potential. [149] the stable potential window for most of the electrolyte is 1.0–4.5 v vs naþ/na, and most of the anodes for sibs are tested at the potential window of 0–3 v vs naþ/na, which leads to the decomposition of electrolyte during cycling. [147] in accordance with the mechanism of sodium storage in hard carbon, increasing the c"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 15,
    "chunk_index": 3,
    "text": "ice of anode materials. figure 13. a) true density and the corresponding closed pore volume of carbon obtained under different temperatures. reproduced with permission. [54] copyright 2019, wiley-vch gmbh. b) hrtem images of hard carbon with different contents of closed pores. reproduced with permission. [142] copyright 2019, american chemical society. c) schematic for preparation of the mixtures of glucose and magnesium gluconate and their pyrolysis process."
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 16,
    "chunk_index": 0,
    "text": "5.2. electrolyte optimization the reason for low ice can be attributed to the issues from the interfacial reactions between electrode and electrolyte. to improve the ice, we should focus on several factors that can influence the phase interface, including the composition of the electrolyte, the structure of the electrode, and the existing electrode–electrolyte interface. [28] the majority of the irreversible capacity is caused by the decomposition of the electrolyte. thus, optimizing the electro"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 16,
    "chunk_index": 1,
    "text": "pc, and bc solutions. it was disclosed that hard carbon showed a stable capacity in ec and pc solutions. in terms of the mixture solution, the solution of ec:dec can enable the hard carbon for a high capacity. it was demonstrated that organic compounds, such as – ch2, –co–o–, and inorganic compounds, such as alkali carbonate and alkyl carbonate, were the main compounds of the sei film. however, it is problematic for electrolytes with solely solvent to form a stable sei film, so a small number of"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 16,
    "chunk_index": 2,
    "text": "improve the ice of hard carbon significantly. [155] typically, yang et al. [150] introduced ether- based electrolyte of diglyme to sodium half cells with the anode of rgo. it was suggested that a thin, stable, uniform, and ion- conducting sei film was formed in the ether-based electrolyte (figure 14a), and compared with the ester-based electrolyte of ec/dec, the ice of the cells with ether-based electrolyte showed an intense improvement from 39 to 74.6% (figure 14b). the ether- based electrolyte"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 16,
    "chunk_index": 3,
    "text": "general, naclo4-based electrolytes have been praised for high capacity and good cycling performance, but they are unsafety in the case of thermal runaway, which will cause fire and explosion. [26,156] electrolytes with napf6 are more secure, while they are more sensitive to moisture in comparison with naclo4. [157] alternatively, natfsi and nafsi show good physical and chemical stability, yet they will react with the al foils at high voltages in the concentration of 1.0 m.[158] fortunately, this"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 16,
    "chunk_index": 4,
    "text": "d) schematic for engineering the defects of hard carbon and e) its charge– discharge profiles. reproduced with permission. [168] copyright 2019, elsevier. f) schematic for the preparation of acm coated hard carbon and g) its charge– discharge profiles. reproduced with permission. [152] copyright 2018, elsevier. h) schematic for preparation of ald for depositing al2o3 on hard carbon and i) its charge–discharge profiles. reproduced with permission. [169] copyright 2019, elsevier."
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 0,
    "text": "of electrolytes with two salts, napf6 and natfsi, in the concentration of 0.1, 1.0, and 3.0 m, respectively. it was found that electrolytes with 3.0 m natfsi can passivate the al foil, which was able to avoid al corrosion. in contrast, patra et al. [160] proposed that ec and pc can promote the formation of ion aggregates between fsi and naþ. at the concentration of 3.0 m, nafsi in ec:pc electrolyte exhibited reasonable viscosity and conductivity, leading to a robust organic–inorganic sei film. t"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 1,
    "text": "the result showed that organic species were the main components for the outermost sei layer upon sodiation, of which content increased in the order: nafsi < naftfsi< natfsinaclo4 < napf6. moreover, nabf4 has been always used to fabricate non-flammable electrolytes. du et al. [162] proved that hard-carbon anode exhibited a better electrochemical performance when using the electrolyte of 1m nabf4 in tetraglyme in comparison to 1m naclo4 in ec and pc. what's more, nabf4-based ionogel electrolyte ha"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 2,
    "text": "electrolyte and electrode. [156] meanwhile, the negative effect of additives on the electrode and electrolyte system should be as low as possible. fec and vinyl carbonate (vc) are widely used electrolyte additives for hard carbon anode in libs and sibs. komaba et al. [163,164] have demonstrated that fec can effectively improve the reversibility of sodium insertion for hard carbon. the reason was that an improved passivation was generated and the side reactions between hard carbon and electrolyte"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 3,
    "text": "fec, vc is another most used electrolyte additive. it can help induce thermal-resistant organophosphates on the surface of hard carbon, thereby improving the thermal stability of the whole system. [26] however, the electrochemical performance of electrolyte with the additive of vc is not as good as that with fec when used for hard carbon in sibs. [164] 5.3. defect engineering and surface adjustment it is well demonstrated that higher content of defects can provide extra sodium storage sites for "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 4,
    "text": "for a high ice. [167,169] as reported previously, lower pyrolysis temperature results in a large number of defects and functional groups in hard carbon. these defects will disappear when increasing the pyrolysis temperature, but high pyrolysis temperature may lead to a low interlayer spacing of carbon materials, which is undesirable for naþ ions insertion. [65] to engineer defects, liu et al. [167] adjusted the heating rate of the precursors to control the porosity and defect concentration of ha"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 5,
    "text": "external graphite can act as a crystal template for the development of graphite crystals. the asobtained sucrose- derived carbon exhibited a high ice of 91% with a capacity of 301 mah g1. similarly, sun et al. [168] reported an in-situ engineering method to tune the defects and oxygen functional groups of hard carbon by introducing an external carbon source into the pyrolysis atmosphere (figure 14d). the hard carbon with reduced defects can achieve a high ice of 85%, which was higher than that o"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 6,
    "text": "m2 g1 for the product. compared with hard carbon obtained without graphene oxide, the carbon with a low specific surface area exhibited an improved ice of 83%. apart from graphene oxide, phenolic resin, epoxy, and many other precursors that could react with sucrose during pyrolysis could be used to prevent the foaming of sucrose for obtaining hard carbon with low surface area. [28,151] typically, li et al. [152] reported a facile-tailored strategy to obtain carbon with low surface area. the surf"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 17,
    "chunk_index": 7,
    "text": "by soft carbon, resulting in the low surface area of hard carbon. [171] to prevent the direct contact between hard carbon and electrolyte, lu et al. [169] deposited an ultrathin al2o3 coating to hard carbon by direct atomic-layer deposition (ald) (figure 14h). the deposited al2o3 coating can act as an “artificial sei film” and suppress the decomposition of electrolyte, resulting in the ice of 75% for the modified hard carbon (figure 14i). in addition, designing a"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 18,
    "chunk_index": 0,
    "text": "functional binder is a promising method to improve the ice of the anode. for instance, xia et al. [172] successfully designed and synthesized a trifunctional sa/polyethylene oxide (peo) binder through an esterification reaction. this original binder can form a passivation film on hard carbon and suppress the decomposition of the electrolyte, resulting in the ice of 87% for the anode (figure 15a). the introduced peo can provide ionic transfer channels to improve the kinetics of naþ ions conductio"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 18,
    "chunk_index": 1,
    "text": "agents or sacrificial additives has been developed. [173] as a typical example, liu et al. [174] designed a sodiation agent of sodium biphenyl (na-bp) to improve the ice of hard carbon (figure 15c). during the reaction between hard carbon and na-bp, bp transferred an electron to form the biphenyl, and hard carbon accepted electrons to form a sodiated host. the sodiated host can further react with electrolyte for the formation of a stable sei film. thus, the presodiated hard carbon anode showed a"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 18,
    "chunk_index": 2,
    "text": "schematic of the preparation for original cross-linked sa/ polyethylene oxide (peo) binder, and b) the charging–discharging profiles of the electrode with the synthesized binder. reproduced with permission. [172] copyright 2021, wiley-vch gmbh. c) schematic of chemical presodiation of hard carbon, and d) the charging–discharging profiles of modified carbon. reproduced with permission. [174] copyright 2020, american chemical society charging–discharging profiles of e) na2c2o4 and f–g) half-cells "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 19,
    "chunk_index": 0,
    "text": "sibs. na-containing salts, such as na2nio2,[176] na2co3,[177] na2c2o4,[178] na2c4o4,[179] na2c6o6,[180] and sodium citrate,[181] have been explored as sacrificial additives for sibs. these additives can deliver a high initial charge capacity, and the discharge capacity is extremely low (figure 15e). no capacity contribution occurs in the following charge and discharge process. the released naþ ions during the initial charge process can compensate for the irreversible naþ ions loss at the anode. "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 19,
    "chunk_index": 1,
    "text": "further application. 6. sodium-ion full batteries up to now, most of the carbon anodes are evaluated in half cells with the counter electrode of na metal, which are certainly different from full cells with limited na sources. therefore, evaluating the performance of carbon anode in full cells is more convincing for the practical application of carbon materials. [183] in addition to adjusting the structure and optimizing the ice of anodes, rationally matching the anodes with appropriate cathodes "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 19,
    "chunk_index": 2,
    "text": "obtained full cell exhibited a high capacity of 290 mah g1 at a current density of 60 ma g1, corresponding to an energy density of 207 wh kg1 (based on the total mass of active materials of anode and cathode). for the same purpose, na3v2(po4)3 (nvp) and its derivations were also used to match up with hard carbon for fabricating full cells (figure 16a). [32,56] it was reported that full cells composed of na3v2(po4)2f3 and rice-husk-derived carbon delivered a reversible capacity of 258 mah g1 with"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 19,
    "chunk_index": 3,
    "text": "cycling performance of full cells at different being states. f) the demonstration application of full cells on the wearable egion. reproduced with permission. [187] copyright 2021, springer nature. g) self-charging profile of serially connected devices and the application of driving the led light, smartwatch, electric calculator, and humidity indicator. reproduced with permission. [188] copyright 2020, royal society of chemistry. h) schematic of tube-type sib. reproduced with permission. [33] co"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 20,
    "chunk_index": 0,
    "text": "to further promote the application fields of sibs, many works have adjusted the electrode–electrolyte interphase by optimizing the electrolytes to build full cells with unique characters. [186,189] for instance, to enhance the low-temperature properties of na3v2(po4)2f3|| hard-carbon full cell, deng et al. [185] introduced a low-concentration electrolyte (0.3 m naclo4 in ec: pc ¼ 1:1 v v1 with 5% fec) to construct a weakly solvating structure, which endowed the cell a lower activation energy bar"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 20,
    "chunk_index": 1,
    "text": "m sodium bis(fluorosulfonyl)imide dissolved in trimethyl phosphate: bis(2,2,2-trifluoroethyl) ether: vinylene carbonate¼1:1.5:0.15 to construct nvp|| hard carbon cells with stable cycling and nonflammable property simultaneously. the electrode/electrolyte interphases of the cell were well optimized by adjusting the solvation structure of the electrolyte through an intermolecular h─bond. the obtained nvp|| hard carbon cells can light the bulb even under a flame test, and no smoke was emitted (fig"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 20,
    "chunk_index": 2,
    "text": "challenging. to fabricate flexible sibs, zhao et al. [187] have matched the flexible electrodes prepared by using cotton cloth derived carbon as anode and na3v2(po4)2o2f modified carbon cloth as cathode with the gel-polymer electrolyte of p(vdf-hfp)-naclo4 (figure 16e). the resulting cells exhibited impressive mechanical flexibility, and no obvious capacity fade was observed after bending the cells in different angels. they wore the cell onto the arm of a model, and a series of lamps can be well"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 20,
    "chunk_index": 3,
    "text": "2d in-plane sib[34] (figure 16i) with excellent mechanical flexibility have also been designed, showing a bright foreseeable future of flexible sibs. 7. conclusion and outlook in summary, hard carbon is considered to be the most potential anode for the coming commercialization of sibs due to its merits of abundant resources, easy preparation, and environmental protection. in this review, we have summarized the current state-of-the-art development of high-performance hard-carbon anodes for sibs f"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 20,
    "chunk_index": 4,
    "text": "of hard carbon are presented, which can be classified into morphological engineering, heteroatom doping, and graphitic structure regulation. to improve the unsatisfactory ice, the approaches like electrolyte optimization, defect and surface engineering, and presodiation are discussed in detail. subsequently, several functional sodium ion full cells based on hard carbon are presented. however, despite considerable progress has been achieved, to realize high performance and practically applicable "
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 20,
    "chunk_index": 5,
    "text": "evaluate which of the appropriate pseudo-graphite phases or closed pores is better. nowadays, plenty of in situ or ex situ characterization techniques, such as xrd, raman, saxs, tem, xps, nmr, have been applied to detect the sodiation and desodiation process. these researches can help probe fundamental understanding of the sodium storage process, but testing results from different techniques sometimes are hard to unify. thus, more advanced and intuitive techniques should be applied to directly d"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 20,
    "chunk_index": 6,
    "text": "also quite necessary to the sodium storage process. designing and implementing advanced techniques with supplemental density functional theory (dft) calculations will help to reveal the surface chemical and dynamic evolution of hard carbons at the atomic scale. [26] in addition, combining theoretical calculations with experiments is efficient in deciphering the sodium storage behavior on the electrode/electrolyte interface, thereby guiding the design of optimized electrodes/ electrolytes and red"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 21,
    "chunk_index": 0,
    "text": "perspective of the precursor, the application of synthetic polymers to prepare hard carbon may be an effective way to accomplish this goal. [113,115] by adjusting the molecular structure and cross-linking degree of polymer, the a)htt: high temperature treatment; b)rev. q: reversible specific capacity. microstructure and composition of hard carbon can be finely tuned. ordinary polymers, such as epoxy, phenolic, pan, and ppy, have already been tested, but many other synthetic polymers or the polym"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 21,
    "chunk_index": 1,
    "text": "on the chains of polymers can be regulated to control the interactions between the precursors. in addition, morphological engineering and heteroatom doping have been instrumental in capacity enhancements. hollow carbon spheres, 1d carbon nanofibers, 2d layered materials, and 3d porous materials with abundant pore structures and large surface areas can accelerate the transport of na ions. heteroatoms, such as b, n, o, s, and p can increase the wettability of electrodes, provide active sites, enha"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 21,
    "chunk_index": 2,
    "text": "carbon – 218 (50 ma g1) 75 na0.44mno2 313 2016[194] corn cobs 1300 300 (30 ma g1) 86 na0.9[cu0.22fe0.30mn0.48]o2 207 2016[195] source@ phenolic resin 1400 319 (30 ma g1) 87 na0.9[cu0.22fe0.30mn0.48]o2 256 2017[151] macadamia shell 1400 300.9 (30 ma g1) – na[cu1/9ni2/9fe1/3mn1/3]o2 215 2017[196] commercial hard carbon – 320 (20 ma g1) 86 na[ni0.6co0.2mn0.2]o2 130 2017[197] pvp – 225 (100 ma g1) 54 nafepo4 168 2018[198] rice husk 1300 372 (25 ma g1) 66 na3v2(po4)2f3/c 185 2018[56] pitch 750 272 (1"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 21,
    "chunk_index": 3,
    "text": "225 2019[202] phenolic resin 1100 300 (20 ma g1) 70 na3v2(po4)3 218 2020[174] bacterial cellulose 800 223 (50 ma g1) 76.1 na3v2(po4)3 156 2020[203] commercial hard carbon – 260 (30 ma g1) 72.8 na4v2(po4)3 265 2020[204] glucose 800 350 (50 ma g1) 86.1 na3v2(po4)3f2 259 2020[205] commercial hard carbon – 220 (50 ma g1) 66 na2/3ni1/3mn2/3o2 212.5 2020[206] mushroom spores 1400 305.8 (20 ma g1) 68 na3v2(po4)3 199.2 2021[207] phenolic resin 1300 325 (20 ma g1) 88.6 nani1/3fe1/3mn1/3o2 239 2021[208] p"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 22,
    "chunk_index": 0,
    "text": "the conductivity, and enlarge the interlayer spacing of hard carbon. the specific capacity related to the capacitive storage process will be improved, which shows a fast sodium storage kinetic, leading to impressive rate capability. consequently, these strategies are attractive in optimizing carbon materials, but there are still substantial challenges that demanded to be solved. for instance, higher average oxidation voltage will appear, which may lead to a lower energy density than those of tra"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 22,
    "chunk_index": 1,
    "text": "and electrolytes. the low ice is resulting from three main factors, namely, irreversible electrolyte decomposition, limitation effects of defects and surface functional groups, and other side reactions. [28] to tackle these issues, the strategies like adjusting the electrolyte system, engineering defects, reducing the specific surface area, and presodiation demonstrate great potential for improving the ice. [145,173] regardless of which method is elected, we should keep in mind that the key to i"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 22,
    "chunk_index": 2,
    "text": "with ether-based electrolytes. [150] in addition to changing the electrolyte systems, regulating the defects and surface area of carbon materials can help settle the limitation effects of defects and surface functional groups and decrease the amount of irreversible trapped na ions. [167] meanwhile, another method to enhance the ice is to compensate for the irreversible na loss through presodiation. [178,182] presodiation of carbon anode through chemical sodiation agents, sodium-rich cathode, and"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 22,
    "chunk_index": 3,
    "text": "compensate the na ions loss at the anode during sei film formation, which is proved to be effective in improving the ice of anodes. although numerous efforts have been paid to solve the irreversible loss of na ions, shortcomings and challenges still exist. all individual strategy has its limitation, which must be considered before commercial application. for example, most ether-based electrolytes reported are unstable and easy to be decomposed under high potential, which is inapplicable in going"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 22,
    "chunk_index": 4,
    "text": "conducted to address these shortcomings, including designing original ether-based electrolytes that can be used under high potential, engineering defects and surface area to balance the ice and specific capacity, and exploring more appropriate sacrificial additives that are acceptable for commercialization. furthermore, a combination of the abovementioned approaches should be considered to work together. finally, to meet the demand of practical and functional sodium ion full cells, particular at"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 22,
    "chunk_index": 5,
    "text": "used electrolyte are liquid electrolytes, they show the merits of high ionic conductivity and low resistance for high energy cells, but the potential risks of electrolyte leakage and flammability can't be ignored during application. [186] to solve these challenges and further improve the energy density of full cells, more and more attention has been paid to constructing solid- state electrolytes, especially the polymer gel electrolyte composed of liquid electrolyte and the hosting polymer networ"
  },
  {
    "source_pdf": "Hard_Carbon_Anodes_for_Sodium_Ion_Batteries_Recent_Status_and_Challenging_Perspectives_Wenlong_Shao_Haodong_Shi_Xigao_Jian_Zhong_Shuai_Wu_Fangyuan_Hu.pdf",
    "page": 22,
    "chunk_index": 6,
    "text": "efforts from academic level to applied research, and pushing the practical cell/pack level testing of sibs are essential. at the same time, sustainable recyclability and safety hazards of sibs are also fundamental obstacles, which cannot be ignored. therefore, more research efforts on hard carbon still need to be performed to promote the development of high rate, long lifespan, and high safety sibs. therefore, we do hope this review will provide our comprehensive insights and potential solutions"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "1. introduction with increasing research investment in sodium-ion batteries (sibs), they have gradually come into maturity and entered the arena competing with lithium-ion batteries (libs).1 hard carbon possesses many advantages,1–4 such as high initial coulombic efficiency (ice),1 decent gravimetric specific capacity (roughly more than 2× that of well-known cathodes such as layered oxides5 and polyanionic compounds2,6,7), as well as stable cycling capacity,4 and thus is regarded as a star class"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "assembly have been made.1,8,9 zheng et al.1 obtained a very competitive sodium-matched fullcell based on the hard carbon anode, which delivered a high a school of materials science and engineering, tongji university, shanghai 201804, china. e-mail: lisa@tongji.edu.cn b institute of new energy for vehicles, tongji university, shanghai 201804, china c department of nuclear science and engineering and department of materials science and engineering, massachusetts institute of technology, cambridge,"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "impedance, which often leads to an overly pessimistic indication of half-cell performance, underutilizing the low-lying plateau part of hard carbon’s capacity. it is important to point out that hard carbon is not a specific material, but a class of carbonaceous materials with a quite wide variation in micro-structures and consequently different electrochemical behaviors in sibs.9,12 the term “hard” in hard carbon points to its mechanically harder characteristic than graphite or “soft carbon”, wh"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "without complete graphitization. soft carbon also has sp2- nanodomains and disorder in between, but in contrast, it is more compact due to the higher content of hydrogen in the precursors which makes the carbon atoms more mobile at the earlier stage of carbonization, such that the orientational disorder between the nanodomains is not locked in so strongly that they can be eliminated and can finally coarsen to large graphite crystals around 3000 °c.13 practically speaking, one can distinguish “ha"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "does not have a black-and-white definition, similar to the “microcrystalnanocrystal-glass” continuum in metallurgical definitions. indeed, when one produces a carbonaceous electrode material by heating, say some biological matter to 1200 °c in a reducing atmosphere, the resulting product could be a heterogeneous mixture of hard carbon and soft carbon. in this review, as long as the mechanically hard, lower-density and “non- graphitizable” component is the majority, we will accept such a heteroge"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "applied to sibs. then the reason for the pessimistic indication of half-cell results is revealed and a revised half- cell test (rht) method is introduced to provide a useful reference capacity (but not cycle life) before designing the full-cell match-up. finally, based on this full cell perspective, we review rational design of the hard carbon material and electrolyte selection. 2. developing promising full-cell metrics of sibs while tremendous effort has been spent on sib research, it is frustr"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "and anode must be matched based on the half-cell nameplate specific capacities and initial coulombic efficiency (ice), with a little capacity redundancy on the anode side (5%–10% in the lib industry) to avoid local sodium– metal deposition caused by heterogeneous current density. some materials researchers may complain about the availability of appropriate sib cathodes with matching areal capacity and the complexities of designing a well-matched full-cell battery and stop their research at the l"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "2 | nanoscale, 2019, 11, 22196–22205 this journal is © the royal society of chemistry 2019 100× in excess). however, the presence of a superabundant nabcc metal chip counter electrode with a lot of electrolyte can hide potential problems of the material being tested, which will show up in an unpleasant way when finally adopted in practical full cells (“overly optimistic” half-cell prediction). nabcc is also highly reactive with liquid electrolytes (much more so than libcc) and the resultant larg"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "all the sibs are cheaper than libs. a useful full- cell metric should fully consider its application scenario, and a crude p metric to estimate the economic competitiveness of a sib full-cell is p ¼ c=ðe lþ; ð1þ where c, e, and l represent the total cost (unit $), discharge energy (unit kw h) per cycle, and cycle life of the battery (defined as dropping to 80% of the initial discharge energy), respectively. to improve the p value, researchers should pay attention to lowering the total cost per k"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "function of the depth of discharge (dod),20,21 which affects e, the optimization of p as well as the down payment (capex) c/e may lead to an optimal solution with the dod significantly less than 1. this in turn means that the anode and cathode may be operated in restricted voltage/capacity regimes that do not span the full range, respectively. the full-cell voltage cutoffs [vlower, vupper] in charging and discharging are also design parameters that affect e and l and may be optimized to improve "
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "measurement.22 besides, even if ce can be recorded without any error, ci may still be overly pessimistic in evaluating how quickly the cyclable alkali ions are trapped and turn non-cyclable. as one cannot directly follow and count ions moving inside the cell and can only count electrons moving in the outer circuit, one have to infer what happens inside the cell based on some assumptions about what can and cannot move in the electrolyte and what can or cannot be accepted/generated at the electrol"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "the anode to the cathode side continuously which leads to a leaked capacity in discharge (qld) and charge (qlc), respectively. thus, there will always be ce ; qed=qec ¼ ðqid qldþ=ðqic þ qlcþ < qid=qic ð2þ and ci > (qic − qid)/qic. for example, co2 solvated in the liquid electrolyte could cause a shuttling or self-discharge effect in libs.24 in our previous report on a sodium-ion full-cell which exhibits a much greater shuttling effect than libs, the cycle life is ∼5× better than what the ci cumu"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "areal capacities to avoid the unnecessary redundancy of the electrode mass, increasing e and reducing c. the areal capacities are usually estimated from traditional half-cell tests (thts), on the anode and on the cathode separately. (we have already mentioned that tht can be an overly pessimistic indicator of cycle life, but here we are just talking about first-10-cycle capacity.) but surprisingly, when running tht with voltage cutoffs [vlower, vupper] = [0 v, 2.0 v], it was found that such tht "
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 1,
    "chunk_index": 6,
    "text": "full-cell in cyclability and capacity, since the counter electrode nabcc metal provides almost endless na inventory, which is expected to be consumed continuously at the anode/electrolyte interface for parasitic reactions. but actually it was reported1 that in a traditional halfcell test, the sodium-matched full- cell based on the hard carbon anode could survive for 1300 cycles at 1c with a capacity retention of 70%, while the sodium–metal redundant half-cell possessed only ∼1/6 of the capacity "
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "respect to the current density q˙ in dynamic charging tests. the tht 0 v cutoff, a convenient and often-taken operational measure, often corresponds to the plateau part of the open-circuit voltage (ocv) profile of hard carbon uocvanode(q), where q is the areal capacity and the subscript “anode” here just stands for hard carbon. how this truncation is actually triggered is shockingly sensitive to the current density q˙: uanode(q˙, q) ≠ uocvanode(q), unabcc(q˙, q) ≠ uocvnabcc(q) ≡ 0. in other word"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "with respect to q, the sodiation process of hard carbon is likely truncated at a sloping part of full-cell vocv(q) in charging, which is much more tolerant to polarization, as shown in fig. 1(a and b).1 premature truncation due to high q˙ tends not to occur in the full-cell test since we rely more on ucathode↑ to trigger the full-cell voltage cutoff, if we design the anode to be slightly capacity-excess than the cathode (of course, this relies on knowing what the reversible capacity of the anode"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "the three-electrode testing method and the results are shown in fig. 1(c). due to polarization, the cutoff of 0 v in v ≡ uhard carbon − unabcc in tht will indeed result in the premature ending of “plateau part” of uocvhardcarbon (even though the open-circuit voltage is still above 0 v versus na+/nabcc and also nabcc does not actually precipitate out in these tht half-cell tests) and it gets much more obvious at a higher current density, which leads to the undervalued rate capacity of hard carbon"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "undervalued half-cell results, is not just specific to sibs, but is a common issue in all alkali ion batteries. the only difference might lie in the degree of impact, and actually the nabcc metal is more severe than the libcc metal25 as shown in fig. 1(d). larger electrochemical polarization of sib half-cells results from the higher parasitic reactions of the na metal with the liquid electrolyte, which introduces larger impedance related to the sei layer,25,26 compared to lib half-cells. for the"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "nabcc even at quite small current densities. 3.2. a revised half-cell test (rht) method traditionally, the tht half-cell test is an essential step to examine the specific capacity, rate performance and cyclability of a newly designed electrode material. however, without using the nabcc metal anode, the capacity-balanced full-cell with a transition-metal–oxide cathode and a hard carbon anode can actually exhibit much better specific capacity, rate capability and cycle life as discussed previously"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 2,
    "chunk_index": 5,
    "text": "still be better assessed by the fullcell test, not with tht or rht. considering that in practical usage scenarios, all the capacity before nucleation of nabcc on the surface of hard carbon is actually acceptable, we define reversible anode capacity as the maximum capacity right before nucleation of nabcc at a certain current density/rate and cathode capacity could be defined as the capacity within a certain voltage range at a certain current density/rate. a three- electrode setup might be an acc"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "4 | nanoscale, 2019, 11, 22196–22205 this journal is © the royal society of chemistry 2019 copyright 2017. elsevier. and sibs, caused by the nucleation energy barrier27 of the bodycentered cubic (bcc) li/na metal. this v-shaped cusp indicates the end of reversible capacity precisely even if the half-cell voltage is a little negative. in their work, the half-cell delivers a specific capacity of 314 ma h g−1 in rht, which is in excellent agreement with the full- cell test in long-term cycling. thu"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "kw h and a long cycle life. high specific capacity (low c/e) and high ce (long l) are essential for hard carbon to reduce the cost of the full-cell according to the model.10 the cycling capability of hard carbon is acceptable since the sodium-matched full-cells could survive for more than 1000 cycles.1,8 however, due to the lack of explicit knowledge of the sodium storage mechanism, it becomes quite a tough mission to carry out rational design of the hard carbon material. most of the material ex"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "liquid electrolyte on the surface of the anode will affect l in eqn (1), we will discuss electrolyte optimization for sibs with a hard carbon anode. 4.1. sodium storage mechanism in hard carbon many researchers have tried to obtain reasonable proof of the sodium storage mechanism. since the intercalation/nanoporefilling mechanism28 was proposed by stevens and dahn et al. in 2000 as shown in fig. 3(a), the debate around the mechanism has never stopped. generally, the primary debate is on the deta"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "hand, as higher pyrolysis temperature induces a smaller interlayer distance of nanocrystals of graphite in hard carbon and consequently lowers formation energy for the layer-intercalated nacx when the distance is less than 0.47 nm (most of the hard carbons present an interlayer distance between 0.37 nm and 0.42 nm), corresponding to the lower plateau voltage.4 however, it was reported by tarascon’s group33 that no obvious interlayer expansion can be observed using in situ xrd detection and the p"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "of hard carbon still remains uncertain. in 1951, rosalind franklin13 described the non-graphitizing carbon as randomly oriented crystallites with strong cross-linking and offered a vivid 2d schematic (fig. 4(a)) of the structure. however, hard carbon is not a specific structure but an extensive span of carbonaceous materials, whose structures are extremely complex and are usually correlated closely with the precursors and synthesis process. structural models3,30,35,36 on hard carbon are continuo"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "fig. 4 the proposed structural model of hard carbon. (a) proposed by franklin in 1951.3,13 reproduced with permission from ref. 13. copyright 2018. elsevier. (b) proposed by shinn in 1984.3,36 reproduced with permission from ref. 3. copyright 2018. elsevier. (c) proposed by harris in 1997.32,35 reproduced with permission from ref. 32. copyright 2001. elsevier. (d) proposed by dahn in 2000 (known as the “house of cards” model).28 reproduced with permission from ref. 28. copyright 2000, ecs-the el"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "sodiation processes much effort1,8,9,37–39 has been continuously made. xiao et al.38 obtained a hard carbon anode with a low defect and low porosity, which delivered a high reversible capacity of 361 ma h g−1 and an excellent capacity retention of 93.4% after 100 cycles. lu’s group37 utilized electrospinning to synthesize a phosphorus-functionalized hard carbon anode which exhibited 393.4 ma h g−1 with the capacity retention up to 98.2% over 100 cycles. hu and coworkers9 reported a novel carbon "
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "peels,44 tea leaves,45 cellulose41 and even cotton,43 and the different precursors usually exhibit different chemical components and microstructures and consequently result in hard carbon with different nano- and micro-structures. the cost of raw materials and yield should also be taken into consideration. li et al.48 obtained a hc anode from the cheap anthracite in an environmentally friendly way and the yield is as high as 90%, which is now being industrialized for its low cost. the pyrolysis "
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "evaluation of the full-cell, ice is as important as the specific capacity of hard carbon, as both of them impact c/e of the full-cell, and evaluation of one newly designed hard carbon needs to focus on p, not just specific capacity. as for heteroatom doping, the mechanism is quite complex because the outcome highly depends on the dopant type and a commonly accepted sodium storage mechanism picture is still absent even for pure hard carbon itself. it was reported that certain doping such as s50 a"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 4,
    "chunk_index": 4,
    "text": "behavior such as lower plateau capacity.46 it is also worth mentioning again that heteroatom doping usually brings a lower ice compared to the original hard carbon,38 which may sometimes bring a pyrrhic victory and cause higher c/e of the fullcell.46 therefore, researchers have to evaluate the practicability of heteroatom doping under the consideration of p. 4.3. electrolyte optimization for sibs with a hard carbon anode electrolytes are hugely important for the total price and cyclability of th"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 4,
    "chunk_index": 5,
    "text": "the relationship between these issues should fully consider the full-cell perspective mentioned above. it is wise to compromise and develop a moderately concentrated electrolyte, and it is reported that an appropriate salt concentration of electrolyte,53,54 for example, 3 m nafsi in pc : ec, can also improve the flame-retardant properties, which are important for industrial applications. besides, an appropriate electrolyte content in sibs should be taken into consideration. for graphite//nmc532 "
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 4,
    "chunk_index": 6,
    "text": "sibs, the electrolyte should be essential for forming contiguous and stable sei, which is closely related to solvents, additives, salt concentration and binder. solvent is usually made of polar molecules like ec or pc to achieve high solubility for salts, with chain molecules like dmc or dec for viscosity reduction. it is worth mentioning that ec is essential in graphite-based libs because it can help in forming stable seis.56 in contrast, the relatively higher absolute potential of hard carbon "
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "6 | nanoscale, 2019, 11, 22196–22205 this journal is © the royal society of chemistry 2019 at the end of the charging process may prevent ec or other esters from forming a stable organic layer.57,58 instead, long-neglected ether-based electrolytes56,59–62 in libs are continuously reported to exhibit excellent properties when pairing hard carbon with nabcc metal counter, such as the long cycle life,61 high capacity,60 and excellent rate performance.62 however, whether these improvements can reeme"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "on electrolyte optimization for sibs are carried out in a half-cell system and the conclusion might be unsuitable for the sodium-matched full- cell, due to the huge difference between the nabcc-metal counter electrode and a real cathode51,57,63,64 as discussed previously. fec and other additives must be reconsidered for their compatibility with the hard carbon anode in well matched full-cell sibs. meanwhile, it is worth mentioning that the binder can assist in forming a protective layer on the e"
  },
  {
    "source_pdf": "High_performance_sodium_ion_batteries_with_a_hard_carbon_anode_transition_from_the_half_cell_to_full_cell_perspective_Xinlong_Chen_Yuheng_Zheng_Wenjian_Liu_Can_Zhang_Sa_Li_Ju_Li.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "sib half-cell test results, due to the extraordinary reactivity and excessive impedance brought by the nabcc metal counter-electrode, which is much more extreme than the libcc metal counter-electrode. a revised half-cell test method that can measure ice and real capacity of hard carbon more precisely is introduced to lay the foundation for full-cell design. the full-cell configuration is always recommended to assess the true cycle life, due to the soluble redox mediators brought by the reaction "
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "abstract the accurate state-of-charge (soc) estimation of sodium-ion batteries is the basis for their efficient application. in this paper, a new soc estimation method suitable for sodium-ion batteries and their application conditions is proposed, which considers the combination of open circuit voltage (ocv) and internal resistance correction. first, the optimal order of equivalent circuit model is analyzed and selected, and the monotonic and stable mapping relationships between ocv and soc, as "
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "not more than 2.6%. eveloping electrochemical energy storage is an important way to address the high proportion of renewable energy consumption. at present, electrochemical energy storage has been widely used in fields such as electrified transportation, wind power generation, and photovoltaic power generation[1]. among them, lithium-ion battery has become the mainstream electrochemical energy storage method due to its advantages of high specific energy and long service life[2]. however, the rap"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "its current remaining electric quantity, which is used as a necessary input for other functions[6]. however, the internal electrochemical mechanism of batteries is complex, and the external measurability is limited, making accurate soc estimation extremely difficult. owing to the widespread use of lithium-ion batteries, many soc estimation methods have been proposed. the model- based soc estimation method has become mainstream[7,8]. in this method, a battery model is established to map the termi"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "feedback to correct the aforementioned soc error, with the correction magnitude determined by the selected filtering algorithm[10]. the performance of this process depends on three aspects: model precision, the monotonicity of the ocv–soc curve, and the performance of the selected filtering algorithm[11]. model precision further depends on both the model structure and model parameter identifi- cation[12]. for sodium-ion batteries, there are few studies on soc estimation. owing to the difference "
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "feng et al. [14] compared the application effects of four commonly used model structures for lithium- ion batteries on sodium-ion batteries and selected the third- order rc model with the smallest terminal voltage error as the final model. in addition to the voltage error, the computational complexity is another important indicator for determining the model structure in practical applications[15,16]. the balance between model precision and the complexity of sodium-ion batteries still requires ca"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "correction relationship, such as internal resistance, no discussion has been conducted so far. finally, most of the foreseeable application scenarios of sodiumion batteries are energy storage power stations, two- wheeled vehicles, tricycles, etc. in these applications, the battery current is relatively stable and often exhibits multiple constant current conditions, which directly affect the process of model parameter identification[18] and further cause the failure of existing methods. there are"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "ienergy | vol 3 | september 2024 | 128–134 129 affected by the soc, temperature and other factors, many battery tests are needed to construct an offline mapping relationship between the parameters and each influencing factor, which will lead to a long development period and high development costs[21]. online identification uses real-time collected data to directly calculate model parameters based on recursive least squares (rls)[22], extended kalman filter (ekf)[23], unscented kalman filter[24],"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "of this work are as follows: (1) a first-order rc model suitable for practical applications ofsodium-ion batteries was selected and built, and its parameters were identified via a genetic algorithm. the model parameters of sodium-ion batteries and their mapping relationships with the soc are compared with those of lithium-ion batteries. (2) according to the correlation between model parametersand soc of sodium-ion batteries, a joint estimation method of model parameters and soc for sodium-ion ba"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "in figure 1. in this model, a voltage source uoc, which represents the static ocv of the battery, is employed. additionally, a resistance r0 alongside several rc networks are used to describe the dynamic rp1 rpn r0 t uoc figure 1 battery nth-order rc model. polarization behaviors, specifically encompassing ohmic, electrochemical and concentration polarization[25]. the state space equation of the model can be expressed as ik + 1rp1 t u = e(up2,k ) ik + 1rp2 (1) where i is the input current (disch"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "improves, the complexity of the model also increases, and overfitting occurs. selecting the appropriate model order is the first step in building the battery model. in this work, based on the experimental data from sodium- ion batteries, offline parameter identification for models with different orders is carried out via a genetic algorithm. the root mean square error (rmse) and the maximum absolute error (mae) of each model in different soc intervals are analyzed, as shown in figure 2. 0 0.2 0."
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "letter soc estimation of sodium-ion battery 130 ienergy | vol 3 | september 2024 | 128–134 accuracy of the second-order and third-order models is improved to a very limited extent, and the increased number of rc networks may lead to more calculations and easier fitting. considering the factors of model precision and computational complexity, the best model order for sodium-ion batteries in this paper is first-order, and then the first-order rc model is selected for model parameter identification"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "the parameters of various batteries are shown in table 1. as shown in figure 3, similar to those of the ternary lithiumion batteries in table 1, the ocv–soc curve of the sodium-ion battery is monotonic and has a large slope, which means that this curve can be used to correct the soc of the sodium-ion battery, similar to the traditional soc estimation methods of lithium-ion batteries. unlike those of the lithium- ion batteries, as shown in figure 3(b), the internal resistance r0 of the sodium-ion"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "figure 4 shows that in addition to the stable ocv‒soc mapping relationship, the r0‒soc mapping relationship of sodium-ion batteries is also relatively stable and meets the requirement for soc correction. whether the monotonic and stable r0‒soc mapping relationship needs to be used for real- time soc correction will be discussed in detail in the following text. for rp and τ, their mapping relationships with the soc are significantly affected by operating conditions and do not exhibit monotonic re"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "forgetting factor (ffrls) is utilized to identify the model parameters. suppose that the following systems are provided: yk = φkθk +εk (2) where y is the system output, ε is the random noise, φ is the data matrix composed of input and output data, and θ is the parameter matrix to be identified. therefore, the identification process of the system is as follows: (3) = μ [ φ k] where kls is the gain matrix; pls is the error covariance matrix of the state; δt is the identification time step; and μ i"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "ienergy | vol 3 | september 2024 | 128–134 131 w and ν are process noise and measurement noise, respectively. the specific implementation process of the ekf includes two steps: state prior estimation and posterior estimation, as shown in eqs. (5) and (6). x−k = axk−1 +t buk−1 (5) p−k = apka +q where p and q are the covariance matrices of the process noise and the measurement noise, respectively; the superscript “−” represents the state prior estimation. {"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "letter soc estimation of sodium-ion battery 132 ienergy | vol 3 | september 2024 | 128–134 1 sodium-ion battery (sodium nickel ferrite/hard carbon) 2.5 na 2 ternary (nickel cobalt manganese) lithium-ion battery 2.5 li-1 θ0 = [θ0(1),θ0(2),θ0(3),θ0(4)]t x0 = [up,0,z0] current for a constant time. ii) recursive operation: k = 1, 2,... a) build the data matrix: b) update the gain matrix kls and the error: d) the model parameters are reversed via eq. (10): { ["
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "ienergy | vol 3 | september 2024 | 128–134 133 figure 4 comparison of model parameters of sodium-ion (na-ion) and lithium-ion (li-ion) batteries under different operating conditions: (a) ocv, (b) ohmic internal resistance, (c) polarization internal resistance, and (d) time constant. kkk = pk−k c[cpk [−kkck−t +rk ]]−1 x = x−+k y cx− (6) pk = [i−kkc]p− where k represents the kalman gain, r is the covariance matrix of the model error, and i is the unit matrix. 2.3 applied to the sodium-ion battery "
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "sumk ⩽ β and then perform posterior estimation, as shown in eq. (6); otherwise, the soc is not updated. i) determine whether sumk-1 > β and sumk = 0; then, execute eq. (13); otherwise, return to a). this step is employed to capture the moments of current jumps during multiple constant current conditions and then correct the soc via the r0–soc mapping relationship. notably, the abrupt change in current does not necessarily result in the instant mutation of r0 identified by ffrls, and a delay can "
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "necessary parameter information and validate the performance of the proposed method. the test platform is composed of charging and discharging test equipment, a temperature box, an upper computer and batteries. the sodium-ion batteries used in the experiments are shown in table 1. battery capacity calibration experiments and small current ocv experiments were first performed to obtain the necessary battery parameters, such as the battery capacity and ocv–soc curve. then, dynamic working conditio"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "multiple constant current conditions, named conditions 1, 2, and 3, are designed. their constant current time lengths are set to 30, 30, and 1800 s, respectively; their standing times are set to 30, 600, and 30 s, respectively; their multiple constant current rates are set in the order of 1c, 1.5c, 0.5c, −1c, −0.5c, 0.5c and 1c. 3.2 validation of the method via simulation data the simulation data is used to verify the soc correction mechanism based on the ocv or ohmic internal resistance when th"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "soc is directly calculated via interpolation of the model parameter−soc mapping relationships rather than via the ekf. (1) working conditions with a short standing time the performance of the method when the model polarization voltage is large (short standing time, 30 s) is discussed, as shown in figure 7. soc estimation of sodium-ion battery letter table 1 parameters and specifications of various batteries number type rated capacity (ah) abbreviation"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "letter soc estimation of sodium-ion battery 134 ienergy | vol 3 | september 2024 | 128–134 0 50 100 150 200 250 300 time (min) 0 50 100 150 200 250 300 0 200 400 600 800 1,000 1,200 1,400 time (s) 0 500 1,000 1,500 2,000 time (s) figure 5 battery current curves used in the experiments: (a) wltc and (b) ctcdc. 0 200 400 600 800 1,000 time (min) figure 6 battery voltage curves from the model simulation. 0 50 100 150 200 250 300 time (min) figure 7 parameter identification and soc estimation result"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "resistance is accurately identified and can be used to correct the soc accurately, with an mae of 2.2% after convergence. (2) working conditions with long standing times the performance of the method when the model polarization voltage is small (long standing time, 600 s) is discussed, as shown in figure 8. the parameter identification method can accurately identify the ocv and ohmic internal resistance. in this case, both the ocvbased correction method and the ohmic internal resistance-based co"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "ienergy | vol 3 | september 2024 | 128–134 135 soc estimation of sodium-ion battery letter 0 200 400 600 800 1,000 0 200 400 600 800 1,000 time (min) figure 8 model parameter identification and soc estimation results under condition 2: (a) ocv and ohmic internal resistance and (b) soc error. 0 50 100 150 200 250 time (min) 0 50 100 150 200 250 time (min) figure 9 parameter identification and soc estimation results under working condition 3: (a) ocv and ohmic internal resistance and (b) soc error"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "of the current fluctuation is significant (the green point in figure 9(a)), which can further be used to correct the soc. the estimation results of the proposed method are shown by the green line in figure 9(b), and the battery capacity in the method is set to 90% of its true value. the method can accurately estimate the soc even under long-term multiple constant current conditions. in general, from the point of view of the online identification reliability of model parameters, when the battery "
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "the proposed method was validated with wltc experimental data. the errors of the initial soc and capacity were set to 10% and 10%, respectively. the estimated results are shown in figure 10. as shown in figure 10, under dynamic working conditions, the proposed method can also accurately estimate the battery soc, with an mae of 2.6% after convergence. 0 100 200 300 400 time (min) 0 100 200 300 400 time (min) figure 10 results of model parameter identification and soc estimation under wltc working"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "for the measured data, there are errors in the model, and these errors are introduced into the identified ohmic internal resistance. this phenomenon can also be explained by figures 4(a) and 4(b); that is, although the internal resistance of the model is stable under experimental dynamic conditions, it is still less stable than the ocv, and this fluctuation is directly reflected in the soc correction results. to avoid the large deviation of the soc by directly correcting the ohmic internal resis"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "letter soc estimation of sodium-ion battery 136 ienergy | vol 3 | september 2024 | 128–134 (1) in this work, a nth-order rc equivalent circuit model was established. combined with the charging and discharging data of sodium-ion batteries, the model parameters were identified via a genetic algorithm, and the accuracy and complexity of the models were compared at different orders. finally, the first-order rc model was selected as the basic model structure for subsequent soc estimation of batteries"
  },
  {
    "source_pdf": "improved_state_of_charge_estimation_method_for_sodium_ion_battery_based_on_combined_correction_of_voltage_and_internal_resistance.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "with different working conditions are generated. the performance of the joint estimation method is discussed under both energy storage conditions and vehicle dynamic conditions. the results show that the proposed method is suitable for the above application conditions, and the maximum absolute error is 2.6% under dynamic working conditions. compared with traditional methods for lithium- ion batteries, the proposed method demonstrates superior accuracy and applicability to sodium-ion batteries an"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "w. li et al. journal of power sources 639 (2025) 236635 1 h i g h l i g h t s • the chemical and electrochemical degradation mechanisms of sibs were revealed. • multi-level analysis methods are used to uncover the failure mechanism of sibs. • the contribution capacity loss of sibs has been successfully decomposed. a r t i c l e i n f o keywords: sodium ion battery battery safety capacity degradation post-mortem analysis * corresponding author. g r a p h i c a l a b s t r a c t sodium ion batteri"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "(nfpp) and hard carbon (hc) as cathode and anode are taken as the research objects. the capacity degradation experiment of sibs is conducted under different aging modes. subsequently, comprehensive non-destructive and post-mortem analyses are combined to explore the failure mechanism of sibs. this study indicates that the loss of active sodium and the increase of interface impedance are the main reasons for the capacity decay of sibs. in particular, during the room temperature cycling, sodium pl"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "reason. surprisingly, throughout the entire aging test, the structures of nfpp and hc do not show significant deterioration, indicating that sibs also have great potential for application in high-temperature scenarios. this study reveals the failure mechanism of sibs, which provides reference for battery design and material research. 1. introduction over the past decades, the requirement for low-cost, long-life, and high- safety energy storage technologies has been continuously increasing in ord"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "however, in reality, this performance is closely related to the cathode and anode materials and battery design [7–9]. in long-term research, both cathode and anode materials of sibs have shown excellent electrochemical performance. for cathodes, layered oxide cathode with high theoretical specific capacity and polyanion cathode materials with stable structure have become the focus of research [7,10]. among these materials, iron-based mixed polyanionic material stands out due to its low cost, hig"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "carbon (hc) materials have shown stable high capacity of >300 mah g− 1, which have an absolute advantage among various anode materials of sibs and can meet the application requirements of commercial anode of sibs [14–16]. therefore, the sibs using nfpp and hc as cathode and anode are considered as one of the most promising sibs. in addition, these sibs have also been proven to have excellent cycling stability and low- temperature discharge capability. mai et al. assembled full sibs based on modi"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "w. li et al. journal of power sources 639 (2025) 236635 2 as well as the design and development of the batteries, especially in failure analysis under important application conditions, which is more conducive to leveraging the characteristics of sibs [20–22]. additionally, the capacity degradation of batteries is often accompanied by safety issues, which makes the battery failure analysis more important for the large-scale application of sibs [23–25]. herein, the 7.3 ah cylindrical sibs (diamete"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "both cathode and anode materials maintain excellent structural stability. during the high- temperature cycle/calendar aging process, the conductivity of electrolyte is increased, and the solid-phase diffusion of sodium ions is accelerated, avoiding sodium plating. however, interface side reactions lead to continuous thickening of solid electrolyte interface (sei) and solid electrolyte interface (cei), which increases battery polarization and ultimately results in capacity loss. during the room-t"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "study reveals the degradation mechanism of sibs under different temperatures and aging modes, which is expected to provide reference for battery design and management. 2. experimental 2.1. battery safety test the nfpp materials from anhui huana new materials technology co., ltd, are selected as cathodes of sibs. the hc materials are commercial materials. the electrode design parameters of sibs are shown in table s1. these sibs are filled with ester electrolyte, consisting of 1 m napf6 in ethylen"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "the battery overcharging test, the battery was charged at a rate of 1.0 c–1.5 times the charging cutoff voltage. in the forced discharge test, the battery was discharged at a rate of 1.0 c for 90 min. arc (hel btc 130) was used to evaluate the safety performance of the sibs. the initial temperature of the test was 50 ◦c, under the adiabatic condition, each step was heated by 5 ◦c, and the self-generated heat rate detection threshold was 0.02 ◦c min− 1. all the above tests were conducted in an ex"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "determined by using x-ray diffraction (xrd) analysis (rigaku miniflex 600 instrument), with a scan rate of 5◦ min− 1 and employing cu kα radiation. the surface morphologies of the cathode, anode and separator were characterized by scanning electron microscopy (sem, hitachi/ zeiss). raman spectroscopy data of hc were obtained by raman spectrometer (horiba xplora). solid-state nuclear magnetic resonance (ssnmr) was carried out on bruker avance neo 600 mhz. 2.3. electrochemical measurements the cyl"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "w. li et al. journal of power sources 639 (2025) 236635 3 thermal runaway). (cccv) charging and discharging steps between 1.5 and 3.5 v. and the coin cells used cccv charging and discharging steps between 1.5 and 3.5 v (nfpp||na) or 0.01–2.0 v (hc||na). and all coin cells were assembled using the 2016-type coin cell. in addition, glass fibers (gf/d, whatman), a counter electrode (na metal sheet), and electrolyte (hunan fenlanite new energy technology co., ltd.) were also used for coin cell assem"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "and the mass and volume energy density are 89.69 wh/kg and 181.33 wh/l, respectively. the batteries have excellent consistency and moderate energy density (fig. 1(a), figure s1, table s2). the sibs exhibit great potential in rate discharge, with no significant capacity and voltage reduction observed as the rate increases from 1.0 c to 4.0 c (fig. 1(b), figure s2). meanwhile, sibs also demonstrate excellent rate performance, the charge-discharge capacity at 4 c can reach 6.10 ah (fig. s3). moreov"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "the full-charged fresh sibs underwent safety testing that met international standards. in the tests of overheating, overcharging and over-discharging, the sibs did not ignite or explode (fig. 1(d–f)), which exhibited excellent safety. during the sibs overcharge test, the highest temperature of the battery only reached 79.9 ◦c, and the battery did not experience thermal runaway even after internal-short circuit. in the overheat and over-discharging tests, there was no significant temperature rise"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "been significantly improved [26–28]. and before the thermal runaway occurs, the safety value opens in advance, releasing some combustible gases and electrolytes, which effectively reduces the severity of the thermal runaway. in summary, all of these indicate that the cylindrical sibs with nfpp and hc as cathode and anode exhibit excellent electrochemical performance and safety, which is basically in line with practical applications. thereafter, this battery will be used for research on capacity "
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "w. li et al. journal of power sources 639 (2025) 236635 4 during the energy storage process, sibs will experience complex and extremely harsh external environments. in addition, high-safety sibs are expected to be applied in high-temperature scenarios, therefore, it is particularly important to study the capacity degradation mechanism under extreme conditions. in this study, sibs were used to investigate the capacity degradation mechanism in high temperature and room temperature scenarios. herei"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "ah, respectively (fig. 2(c)). this indicates that capacity decay also occurs during the aging process of the fully charged calendar, especially in high-temperature environments. during the cycle process, the capacity retention rate of sibs is 96.43 % and 92.43 % after 400 cycles at temperatures of 25 ◦c and 80 ◦c, respectively (figure s6, fig. 2(d–f)). the reasons for the capacity degradation that occurred during these processes are further investigated. non-destructive characterization methods "
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "(six coordination), na4 (six coordination), and na2 (seven coordination) sites [32]. three sodium sites can be reversibly extracted or inserted into the crystal, while na2 is electrochemically inert. the sodium extraction sequence is as follows: first, na3 and na1 are extracted, and then na4 is extracted. the insertion order is reversed [33]. the multiple oxidation/reduction peaks (observed in fig. s7) indicate the insertion/extraction of sodium ions into different sites within the structure. du"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "the high-temperature cycle process. this phenomenon may be due to the degradation of the cathode structure, which leads to the decrease in the activity of the na3 site, or the loss of active sodium causing sodium ions to be unable to fully occupy the sites. for this speculation, further verification will be conducted through post-mortem analysis. 3.2. post-mortem analysis through an analysis of capacity, voltage and ic curves of the sibs above, a preliminary understanding of the capacity degrada"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "w. li et al. journal of power sources 639 (2025) 236635 5 optical images of the separator, cathode, and anode after battery disassembly are shown in fig. 3. except for sibs that have undergone room temperature cycle, there are little differences in the appearance of the cathode, anode and separator between the pristine and degraded battery. obviously, the anode of sibs undergoing room-temperature cycle has severe sodium plating, and the by-products of the reaction between sodium metal and electr"
  },
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    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "different aging modes: (a) pristine; (b) cycle at 25 ◦c; (c) calendar aging at 25 ◦c; (d) cycle at 80 ◦c; (e) calendar aging at 80 ◦c. sem images of anodes under different aging modes: (f) pristine; (g) cycle at 25 ◦c; (h) calendar aging at 25 ◦c; (i) cycle at 80 ◦c; (j) calendar aging at 80 ◦c. sem images of separator under different aging modes: (k) pristine; (l) cycle at 25 ◦c; (m) calendar aging at 25 ◦c; (n) cycle at 80 ◦c; (o) calendar aging at 80 ◦c. fig. 5. capacity degradation mechanism"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "w. li et al. journal of power sources 639 (2025) 236635 6 (h) schematic diagram of cathode failure. low. therefore, the design of electrodes is crucial for the construction of safe sibs [34,35]. further, sem images of pristine and degraded cathode were used to analyze the degradation of nfpp particles and surfaces (fig. 4(a–e)). the cathodes after calendar aging at 25 ◦c and 80 ◦c exhibited the same morphology as that of the fresh cathode with the particles remaining intact. however, particle mi"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "the particle microcracks were structural degradation caused by electrochemical reactions, rather than erosion of the electrolyte at high temperatures. the sodium plating and structural degradation behavior of hc under multiple conditions were observed by sem (fig. 4(f–j)). after room-temperature cycle, there is a large- area moss-like sodium plating on hc anode and by-products on separator, while those under other aging modes do not exhibit sodium plating or other obvious phenomena. we analyzed "
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "the hc surface are metallic sodium (fig. s10). in summary, we have confirmed that the deposits on the surface of hc are sodium plating. sem is used to further characterize the microstructure of by-products. it can be observed that the ceramic particles of the ceramic separator have been detached, and at the same time, some ceramic particles adhere to the cathode electrode. the position of by-products is very consistent with that of sodium plating, indicating that the by-products are generated by"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "of structural degradation, polarization, and other aspects, the disassembled cathode and anode were separately reassembled with sodium metal to form a coin type half-cell. the nfpp||na half-cells were charged to 3.5 v with a current of 1.1 ma, to calibrate the residual capacity of the cathode materials (fig. 5(a)). then, through discharging to 1.5 v, sodium ions insert back into the cathode material to eliminate capacity degradation caused by loss of active sodium (fig. 5(b)). after testing, it "
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "in high- temperature cycling is more severe than the sodium plating during fig. 6. capacity degradation mechanism analysis of anode materials. (a) discharge curve of hc||na coin cells (the hc electrodes were obtained from disassembled batteries). (b) capacity statistics of different coin cells. (c) xrd patterns of anode materials under different aging modes. (d) raman spectrum of anode materials under different aging modes. (e) eis curve of hc||na coin cells (inset is the equivalent circuit to f"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "w. li et al. journal of power sources 639 (2025) 236635 7 anode failure. room temperature cycling. when sodium ions embed back into cathode, the active sites of nfpp can be almost completely inserted by sodium ions, and there is no significant difference between the aged cathode material and the pristine sample (fig. 5(c)). the specific capacity loss of active sodium after cycle (25 ◦c and 80 ◦c) is slightly higher than calendar aging (fig. 5(c and d)). it is worth noting that the loss of active"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "peak did not show significant changes compared to the fresh cathode (fig. 5(e)). especially, the peak below 3.0 v reappeared in the high-temperature aged cathode material, indicating that the na3 sites still have electrochemical activity. in the sibs, the loss of active sodium is the main reason for the disappearance of the na3 sites peak below 3.0 v, and the structure of nfpp does not significantly deteriorate during the aging process. significantly, the polarization of the aged cathode materia"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "degraded batteries exhibit increased impedance (fig. 5(g), figure s12). at the same time, the rct of the batteries after high temperature aging also significantly increases (compared to room temperature aging). impedance data and polarization data have also confirmed each other. the hc anode is also used to reassemble coin cells for further measurement of sodium storage capacity (hc has selected areas without sodium plating). from the discharge program of constant current and constant voltage (c"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "stacking distance of hc have not undergone significant changes (fig. 6(c)). raman spectroscopy (fig. 1(f)) is further conducted to assess the microstructure of hc. the peak positions of the d and g peaks of hc before and after aging are around 1353 cm− 1 and 1594 cm− 1, with no significant shift observed, and the id/ig ratio remains unchanged. this indicates that the edge defects and microcrystals of hc are not damaged. overall, the structure of hc did not show significant deterioration during t"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 6,
    "chunk_index": 4,
    "text": "during the cycling process, and the increase in interfacial impedance is the significant reason for the degradation of battery capacity, especially for batteries aging at high-temperature. during the cycling process at room temperature, the battery exhibits sodium plating, resulting in loss of active sodium and safety hazards (fig. 6(f)). 4. conclusion in this work, nfpp||hc cylindrical battery has been proven to have excellent safety and electrochemical performance. and based on this battery, t"
  },
  {
    "source_pdf": "Insights on the degradation mechanism of 7 Ah sodium ion batteries at different aging modes, Wei Li , Honghao Xie , Shini Lin, Yuan Qin , Jing Zeng , Peng Zhang, Jinbao Zhao.pdf",
    "page": 6,
    "chunk_index": 5,
    "text": "of active sodium, but also sharply increase interface impedance, leading to degradation of battery capacity. in addition, the main reason for capacity degradation at room-temperature cycling batteries is the sodium plating on the surface of anode, which further leads to the sei regeneration and increased interfacial impedance. fortunately, the structures of nfpp and hc remain stable under different aging modes, demonstrating the promising application prospects of sibs with nfpp and hc as cathode"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "due to the sodium abundance and availability, sodium-ion batteries (sibs) have the potential to meet the worldwide growing demand of electrical energy storage. p2-type sodium transition-metal layer oxides with a high energy density are considered as the most promising cathode materials for sibs. we present here a detailed study of the enhanced rate capability and cyclic stability of the ti-doped na0.67ni0.33mn0.67o2 cathode material. the combined analysis of ex-situ x-ray absorption fine structu"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "better understanding in optimization of the design of high-energy cathode materials based on titanium doped layered oxides for sibs. © 2021 published by elsevier ltd on behalf of the editorial office of journal of materials science & technology. 1. introduction large scale electric energy storage (ees) represents the key issue in development of sustainable new energy technologies, such as electric vehicles (evs) and renewable power stations (rps) [1,2]. lithium-ion batteries (libs) with high ene"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "to enable the technology. ∗ corresponding authors. e-mail addresses: taoshi@cslg.edu.cn (s. tao), chuws@ustc.edu.cn (w. chu), marcelli@lnf.infn.it (a. marcelli). https://doi.org/10.1016/j.jmst.2020.06.055 recently, cathode materials are vigorously studied to satisfied performance, such as layered oxides, polyanionic compounds and prussian blue [5,6]. among them, because of the simple synthesis process, layered oxides are excellent candidates for sodium-based cathode materials with a high capacit"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "(> 4.0 v). this is due to the transformation of p2-o2 phase with a large volume change [12–14]. in this regard, cation doping can be considered as an effective way to overcome this drawback and enhance the electrochemical performance. the introduction of additional doping ions inside the nnmo material have been proven to improve the cyclability in a widened voltage range [15–23]. guo et al. reported that the replacement of ni with mg in na0.67mn0.67ni0.33o2 effectively inhibits the p2-o2 phase t"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "s. tao et al. journal of materials science & technology 74 (2021) 230–236 231 fig. 2. the morphology characterizations of na0.67ni0.33mn0.52ti0.15o2 sample. (a, b) sem images at different magnification. (c) tem image. (d) hrtem image. (e) eds mapping images."
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "s. tao et al. journal of materials science & technology 74 (2021) 230–236 232 fig. 3. the electrochemical performance of as-prepared na0.67ni0.33mn0.67o2 and na0.67ni0.33mn0.52ti0.15o2 samples. (a) cyclic voltammetry curves at 0.2 mv s− . (b) 1 galvanostatic charge/discharge curves at 0.1 c. (c) comparison of rate capabilities at different current densites. (d) cycle performances at 0.5 c after 200 cycles. in this work, we prepared the ti-substituted p2-type na0.67ni0.33mn0.52ti0.15o2 (nnmto) as"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "and lead to the good cyclability. 2. experimental 2.1. material synthesis stoichiometric amount of naco3, nio, mno2 and tio2 were mixed by wet ball- milled with acetone addition for 6 h. the obtained mixture was dried in oven at 60◦c and then pressed into pellets. the latter were calcined at 900◦c for 12 h and naturally cooled down room temperature. the final products were obtained by grinding the pellets in a agate mortar. 2.2. material characterization powder x-ray diffraction (xrd) patterns w"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "spectrometry (icpaes, varian 725-es). ni and mn k-edge xafs spectra of the samples were collected at the 1w2b beamline of beijing synchrotron radiation facility (bsrf). the desired electrodes were washed with dimethyl carbonate (dmc) in the argon-filled glove box, and then sealed by 3 m selloptape. 2.3. electrochemical tests for the preparation of electrodes, the active material (nnmto or nnmo), acetylene black and poly (vinyl difluoride) binder were mixed in the weight ratio of 80:10:10, using "
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "were performed on a land ct 2001a tester. 3. results and discussion the crystal structure of the obtained na0.67ni0.33mn0.67o2 and na0.67ni0.33mn0.51ti0.15o2 samples were characterized by x-ray diffraction (xrd) technique it can be seen that all samples crystallize in a hexagonal p2-type phase with space group p63/mmc, indicating that the ti-doping maintains the rhombohedral symmetry (fig. s1 in supporting information). the xrd rietveld refinement diffraction patterns are presented in fig. 1(a) "
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "s. tao et al. journal of materials science & technology 74 (2021) 230–236 233 pointing out that the ti4+ ions are located in the transition-metal layer. according to the refined crystallographic data listed in tables s1 and s2, the lattice parameters of na0.67ni0.33mn0.52ti0.15o2 increase upon ti substitution compare to the na0.67ni0.33mn0.67o2, owning to the distinction in the ionic radii between mn4+ (53pm) and ti4+ (60.5pm). the sem images of the na0.67ni0.33mn0.67o2 samples are shown in fig."
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "uniformly distributed in the particle. the atomic ratios of na0.67ni0.33mn0.67o2 and na0.67ni0.33mn0.52ti0.15o2 samples are further confirmed by means of icp-aes analysis, as shown in table s3. x-ray photoelectron spectroscopy (xps) was carried out to study the chemical state and composition of as-prepared samples (fig. s3). from the survey spectrum, we identify the ti 2p peaks confirming the ti doping of the na0.67ni0.33mn0.67o2. from high-resolution spectra we determined the valences of ni, mn"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "with oxygen redox reactions [31]. while for the na0.67ni0.33mn0.52ti0.15o2 electrode, the reversible oxidation/reduction peaks become broad, indicating that the multiphase transformation is suppressed and restrain tmo2 gliding during the charge- discharge process after ti-doping [20,32]. fig. 3(b) presents the charge-discharge curves of na0.67ni0.33mn0.67o2 and na0.67ni0.33mn0.52ti0.15o2 in the first cycle at 0.1 c (1 c = 150 ma g−1). ti-free na ni mn o delivers several voltage plateaus, 0.67 0."
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "s. tao et al. journal of materials science & technology 74 (2021) 230–236 234 3.0, and 5.0 c, respectively. furthermore, when the current density recovers back to 0.1 c, the capacity can returns to 133.2mah g−1, which are much higher than the undoped na0.67ni0.33mn0.67o2, suggesting the ti- doping retains the expansion and gliding of the tm layer. the cycling performance of na0.67ni0.33mn0.67o2 and na0.67ni0.33mn0.52ti0.15o2 at 0.5 c are compared in the fig. 3(d), the na0.67ni0.33mn0.52ti0.15o2 "
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "the electrochemical properties of the ti-doping are further examined by the electrochemical impedance spectra (eis). as shown in fig. s4, all the nyquist plots of both electrodes are characterized by semicircles in the high frequency domain and straight lines in the low frequency region. the curves are also fitted by equivalent circuit model and the impedance parameters are listed in table s4, na0.67ni0.33mn0.51ti0.15o2 presents smaller interfacial resistance (rct + rint) than the na0.67ni0.33mn"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "s. tao et al. journal of materials science & technology 74 (2021) 230–236 235 barrier derived from the biphasic reaction. this observation indicates that ti-doping enlarge the interslab distance and reduces the barrier for na+-ions transfer in the charge/discharge process, leading to better cell performance. the ti-doped effect of the local structure changes and redox reactions are tested by x-ray absorption fine structure (xafs) spectra under different charge/discharge states. the ni and mn k-e"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "no change, a clear indication that mn4+ are electrochemically inactive in the range of 2.5–4.5 v. the measured capacities for two electrodes only originate from ni2+/ni3+/4+ redox couples, which are consistent with the cv test. the corresponding extended x- ray absorption fine structure (exafs) spectra of na0.67ni0.33mn0.51ti0.15o2 at different charge/discharge states are shown in fig. 4(c) and (d). in general, the peaks in the range of 1−2 å and 2−3 å can be assigned to the tm o and tm tm bonds"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "changes induced by the phase transition maintaining the local structure during the electrochemical process [37–39]. the structure evolution of na0.67ni0.33mn0.67o2 and na0.67ni0.33mn0.52ti0.15o2 electrodes is also investigated by the ex-situ xrd (fig. 5(a) and fig. s6). after the charging process, the (002) peak shifts to lower angles due to the increased electrostatic repulsion among neighboring tmo2 slabs, and a new (002’) peak located at about 20◦ can be observed at the end 4.5 v for na0.67ni"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "used to analyze the microstructure changes after cycling. fig. 6(a) shows the ab-hrtem image of na0.67ni0.33mn0.67o2 electrode after 10 cycles, it is clearly observed that the well- defined fringes of the two phases (p2 + o2) coexist in the electrode. in addition, the o2 phase with an obvious adjacent layer distance reduction is observed. while for the ti-doped electrode only presents the p2 phase (fig. 6(b)), which is identical to the ex-situ xrd data. again data confirm that the ti-doping supp"
  },
  {
    "source_pdf": "Insights_into_the_Ti4_doping_in_P2_type_Na0_67Ni0_33Mn0_52Ti0_15O2_for_enhanced_performance_of_sodium_ion_batteries_Shi_Tao_Wei_Zhou_Dajun_Wu_Zhicheng_Wang_Bin_Qian_Wangsheng_Chu_Augusto_Mar.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "octahedra during cycling, as evidenced by xafs. (3) ti in tm layers stabilizes the p2 structure over a wide range of voltage can effectively eliminate na+/vacancy ordering. 4. conclusion in summary, the ti-doped na0.67ni0.33mn0.52ti0.15o2 cathode was successfully synthesized by a convetional solid phase method. ex-situ xafs, xrd and hrtem were applied to monitor the short and long range structural changes during the charge/discharge process, showing that a partial ti substitution affects the na+"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "mg-doping as strategy for improving the electrochemical behaviour of p-type oxides. synthesis of naxmg0.11mn0.89o2 via co-precipitation method and solid state reaction. naxmg0.11mn0.89o2 has p2-type structure and consists of m-sized particles. promising long-term cycling performance for 200 cycles. 125 mah g1 delivered capacity and 93.8% capacity retention (10the100th cycle). a r t i c l e i n f o a b s t r a c t article history: received 16 december 2014 received in revised form 5 february 2015"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "to provide a complementary rather than competing battery technology other than lithium-ion. with the same scope in mind, herein we present the structural and electrochemical characterization of p2-type naxmg0.11mn0.89o2 material to demonstrate the effectiveness of mg-doping for the development of future layered cathode materials. of particular interest is the effect on the long-term cyclability (200 cycles), which has not been reported, yet. as shown in the manuscript, a mg content as low as 11%"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 0,
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    "text": "high potential and enables large low-cost advantages, such as the use of aluminium (instead of pricey copper) as anode current collector [1,2]. moreover, superior electrochemical performance to other * corresponding author. helmholtz institute ulm (hiu), helmholtzstrasse 11, 89081 ulm, germany. e-mail address: stefano.passerini@kit.edu (s. passerini). http://dx.doi.org/10.1016/j.jpowsour.2015.02.069 0378-7753/© 2015 elsevier b.v. all rights reserved. secondary batteries (with the exception of th"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "decades. in the past, the main motivation behind research in the sodium-ion based chemistry was to find sodium precursors that could be used to synthesize the lithium analogues via ion- exchange reactions [4]. a great variety of materials have already been structurally but not electrochemically characterized, in terms of their sodium-ion chemistry. investigations on sodium ion battery materials started in the mid-1970s with the studies of parant et al. on the physical properties of na0.44mno2 [5"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "devices powered with lithium-ion batteries by sony in 1991, the main focus of battery research was set on the optimization of the existing lithium technology. this led to the intermixing of transition metals like cobalt, nickel and manganese, as a way to improve the poor cyclability observed for linio2 and limno2 and to reduce the content of the expensive cobalt, which finally led to the commercially famous lini1/3co1/3mn1/3o2 [8]. a similar trend of intermixing transition metals in order to com"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "metal oxides in sibs, and for this reason a series of na0.67mn1xmgxo2 (0 x 0.3) materials has already been synthesized and structurally characterized. billaud et al. reported the electrochemical properties of a series of mg-doped na0.67mn1xmgxo2 (0 x 0.2) materials [13]. the effect of quenching in the solid state synthesis and an investigation on the galvanostatic cycling and the (de-)sodiation process was performed. the doping mg content of x ¼ 0.05 led to smooth potential profiles, while highe"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "of p2-type naxmg0.11mn0.89o2 with a particular focus on the long-term cycling performance, not reported for ptype layered oxides, only containing manganese and magnesium in the mo2-layer. we believe this work to provide very useful information about this material class and to highlight the importance of mg 582 d. buchholz et al. / journal of power sources 282 (2015) 581e585"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "doping for the development of next-generation layered cathode materials for sibs. 2. experimental part 2.1. synthesis of naxmg0.11mn0.89o2 the material was synthesized via a two-step solid-state reaction with sodium hydroxide (naoh, aldrich >98%) and a mixed manganeseemagnesium hydroxide precursor. the precursor was prepared by co-precipitating the aqueous solution of the two metal acetate tetrahydrate salts (mnac2$4 h2o and mgac2$4 h2o; aldrich >98%) in a stoichiometric ratio of 11:89 with sodi"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "powder, subjected to the high temperature annealing at 900 c for 6 h (heating rate: 5 c min1), using an open-air muffle oven, resulting in dark brownish powder. finally, about 1 g of the pristine material was stirred in 20 ml of distilled water at 25 c for 5 min. the suspension was then filtered, washed with 80 ml of distilled water and dried at 100 c in air for 24 h. afterwards, the material was ground, screened over a 45 mm sieve and finally stored under inert atmosphere. 2.2. material charact"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "in the 2q range from 10 to 90. lattice parameters were determined by rietveld refinement with topas software. the particle size distribution and particle morphology was evaluated with the help of a high-resolution scanning electron microscope (fe-sem, zeiss auriga). 2.3. electrode preparation & cell assembly electrodes were made from slurries, which dry composition was 85 wt.% active material, 10 wt.% carbon black super c65 (timcal), and 5 wt.% polyvinylidene fluoride (pvdf e kynar flex 761a, ar"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "into threeelectrode swagelok® cells with a glass fibre separator (whatman) soaked with 1 m napf6 (99%, alfa aesar) in propylene carbonate (pc e ube, japan) and sodium metal as counter and reference electrodes. the sodium was cut from sodium chunks (99.8%, acros organics), rolled, pressed and finally punched on the current collector. cells were cycled galvanostatically at different constant currents from 12 ma g1 to 610 ma g1 between 4.4 and 1.5 v vs. na/naþ, or 4.6e1.5 v vs. na/naþ, at 20 ± 2 c "
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "0.76 eq mol1 added during the synthesis is associated to sodium evaporation during the annealing process, sodium loss during the mixing process and the water treatment, which is leading to the dissolution of impurities (e.g. sodium carbonate) formed during the solid state synthesis in air, but also a partial chemical desodiation. although the water treatment led to an improved electrochemical performance for analogous p-type layered oxides, [9,10] it also has to be considered that a sodium conte"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "in the supplementary information (si-1). the very weak reflection at 22.1 2q originates from the ordering of the magnesium and manganese cations in the transition metal layer. the low intensity of this reflections is in accordance with billaud et al. for naxmn1xmgxo2 (0 x<¼0.2) materials, slowly cooling down to room temperature after the solid state reaction [13]. the presence of the hydrated phase is evidenced by the diffraction peaks at 12.6 and 25.4, corresponding to the (002) and (004) refle"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 6,
    "text": "information about the (de-)sodiation process and the electrochemical performance (fig. 2). four peaks, located at about 2.2 v, 3.0 v, 3.5 v and 4.2 v, are observed during charge. during the consecutive cycling the peak at 2.2 v decreases in intensity and shifts to higher potentials. in addition, also the peak at 4.2 v decreases while all other peaks remain constant (3.0 v) or even increase in intensity (3.5 v). similarly, during the sodiation four corresponding peaks at about 2.1 v, 2.9 v, 3.4 v"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 1,
    "chunk_index": 7,
    "text": "and 4.2 v/3.9 v, nicely demonstrate the sequence of the structural changes upon the (de-) sodiation process. the peak at 3.5 v is known to be caused by the phase transition from the p2 to a stacked fault op4 structure [12,13,16,17]. it is interesting to mention, that the peak related to the final o2 phase transition decreases in intensity upon cycling d. buchholz et al. / journal of power sources 282 (2015) 581e585 583"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "fig. 1. x-ray diffraction pattern, corresponding rietveld refinement and sem image of pristine naxmg0.11mn0.89o2 material. asterisks in the diffractogram mark the diffraction peaks of the hydrated phase. the reflection originating from the superlattice ordering of mg2þ/mn4þ is indicated by the dashed black box. fig. 2. differential capacity plots for the 3rd, 4th, 5th, 10th, 20th, 50th and 100th cycle of naxmg0.11mn0.89o2 galvanostatically cycled at 12 ma g1 in the potentials range of 4.4e1.5 v "
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "are present, although all sodium cations are prismatically coordinated [4]. in the energetically stabilized site the sodium cation is superimposed by additional two oxygen anions of the next coordination sphere. therefore, this site is nearly exclusively occupied at lower sodium contents [18]. instead, in the second site the sodium cation is superimposed by a metal cation (in this case manganese or magnesium) of the mo2 layer, leading to additional coulombic repulsion. therefore, the (de-)interc"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "an overview about the electrochemical performance of naxmg0.11mn0.89o2 is given in fig. 3. despite the presence of the hydrated phase, naxmg0.11mn0.89o2 reveals an overall promising electrochemical performance, additionally highlighted by the high average coulombic efficiency (99.6%) and the good long-term cycling stability. as for other p2type materials a marked initial capacity fade is observed as evidenced by the capacity decreasing from 174 mah g1 to 151 mah g1 and 129 mah g1 in the 1st, 2nd"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "capacities of 121 mah g1 and 96.8 mah g1 after 100 and 200 cycles, respectively. this corresponds to a rather high capacity retention of 93.8% and 75.0% (vs. 10th cycle), respectively, which is even more remarkable when considering the stress caused by the two intermediate current rate tests. interestingly, these latter tests reveal the material to exhibit good rate capability"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "fig. 3. a) galvanostatic cycling at 12 ma g1 for naxmg0.11mn0.89o2 material. cycles 21e45 and 65e90 illustrate the electrochemical behaviour for five cycles each at increased currents of 24 ma g1, 61 ma g1, 122 ma g1, 244 ma g1 and 610 ma g1 b) potential profile of the initial charge and discharge process at 12 ma g1. cut-off limits: 4.4e1.5 v vs. na/naþ. counter and reference electrode: na. electrolyte: 1 m napf6 in pc. temperature: 20 ± 2 c. fig. 4. a) charge and discharge potential profiles r"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "na/naþ). reference and counter electrodes: na. electrolyte: 1 m napf6 in pc. temperature: 20 ± 2 c. although the highly conductive metals like cobalt or nickel are absent. in more detail, discharge capacities of 116 mah g1, 103 mah g1, 93 mah g1, 82 mah g1 and 63 mah g1 were obtained at current rates of 24 ma g1, 61 ma g1, 122 ma g1, 244 ma g1 and 610 ma g1, respectively. the low initial charge capacity of 55 mah g1 (0.20 eq of naþ removal) is in accordance with the detected sodium content via i"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "plateau is probably related to the oxidation of oxygen anions and is essential for the access of capacities of up to 220 mah g1. the observed lower initial discharge capacity of 174 mah g1 for naxmg0.11mn0.89o2, thus, is in accordance with the absence of the high potential plateau, probably only occurring at higher magnesium contents. the potential profiles of some selected cycles during the galvanostatic cycling at low currents and during the current rate test are depicted in fig. 4. interestin"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "the cell voltage would change less rapid compared to other p2-type layered oxides [13]. upon charge, only a very weak feature at about 4.0 v is observed, indicating the phase transition to o2-type to occur only in minor extent, which is in contrast to other p2-type layered oxides like naxni0.22co0.11mn0.66o2. at higher currents of about 122 ma g1, the plateau fully vanishes as the two phase reaction is kinetically slow. however, the major capacity fade is clearly related to the continuous shrink"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "active material (e.g., applying carbonaceous or metal oxide coatings) might be strategies to improve the cycling performance. to investigate if higher capacities can be obtained, the upper cut-off voltage was increased to 4.6 v (fig. 5). the comparison illustrates that, indeed, higher initial discharge capacities are accessible as the material delivers 178 mah g1 between 4.4 v and 1.5 v and 190 mah g1 between 4.6 v and 1.5 v. however, the higher initial discharge capacity is also accompanied by "
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "fig. 5. galvanostatic cycling at 12 ma g1 for naxmg0.11mn0.89o2 material. cycles 21e45 and 65e90 illustrate the electrochemical behaviour during increased currents of 24 ma g1, 61 ma g1, 122 ma g1, 244 ma g1, and 610 ma g1. cut-off limits: 4.6e1.5 v or 4.4e1.5 v vs. na/naþ. counter and reference electrode: na. electrolyte: 1 m napf6 in pc. temperature: 20 ± 2 c. material degradation process as the electrolyte was found to be rather stable in this potential range [22]. as a consequence, already a"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "more detail, a high capacity retention of 93.8% (from 10th to 100th cycle) and 75.0% (from 10th to 200th cycle) as well as very high coulombic efficiencies, exceeding 99.6%, were obtained. reversible specific capacities of about 125 mah g1 were obtained at low specific currents (12 ma g1) and, surprisingly, the material additionally exhibited good rate capability (e.g. 82 mah g1 at 244 ma g1), despite the absence of transition metals like nickel or cobalt. attempts to access higher reversible ca"
  },
  {
    "source_pdf": "Mg_doping_for_improved_long_term_cyclability_of_layered_Na_ion_cathode_materials_The_example_of_P2_type_NaxMg0_11Mn0_89O2_Daniel_Buchholz_Christoph_Vaalma_Luciana_Gomes_Chagas_Stefano_Passerini.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "material by application of coatings. the successful utilization of magnesium- doped layered oxides in na-ion batteries also necessitates an increased initial sodium content in the material and an improved average discharge potential, e.g., via the implementation of other suitable transition metals like nickel. d. buchholz et al. / journal of power sources 282 (2015) 581e585 585"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 1 1. introduction the major cause of global warming is the greenhouse effect, which is a result of the combustion of fossil fuels as primary energy sources. to mitigate the effect of climate change, partial replacement of fossil fuel source with sustainable technologies such as solar, wind or hydropower has been implemented in some parts of the world. successful adaptation of these renewable energy technologies requires a robust and safe en"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "the demand for li is continuously rising due to rapid growth of mobile and stationary energy storage applications [3,4]. li reserves apart from being limited, are accessible only at certain geographical areas of the world [5]. this geological limitation of li, when coupled with the costs of mining, transportation and import, may make it necessary to explore alternatives to libs from future supply-and-demand and cost perspectives. safety is another important factor in large-scale ess as libs in g"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "concern over the safety of grid storage systems [6]. in jecheon in south korea, an ess of 1 mwh worth of $3.3 million caught fire and caused recall of nearly 500 units [7]. more recently, an explosion in arizona public service’s (aps) energy storage facility saw four firefighters sustain severe injuries when putting off the battery fire [8]. all these incidents make us realise that highly safe and robust batteries are mandatory for large-scale ess to minimise the risk of fire and explosion. na-i"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "abundance of na resources in the earth’s crust [10], which is believed to have a colossal effect on cost of this technology. however, before reaching the commercial market, as reported by niu et al. [11], more comprehensive investigations on nib full cells are required to understand the fitness of nibs as a competitive substitute for libs. identifying appropriate anode, cathode, electrolyte, as well as the combination of these three components has always been challenging to develop a robust yet "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "over the years. the ease of synthesis and excellent safety aspect of polyanionic compounds especially phosphate systems have attracted great attention and this safety feature is caused by an inductive effect of the po3-4 anion, along with the strong phosphorus-oxygen covalent bond [31–33]. the nasicon-type na3v2(po4)3 (nvp) has a high operating potential at around 3.37 v vs. na [5,10,23,34], owing to the vanadium redox couple, making this compound a possible cathode of choice for nibs. besides, "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "nib studies, highly flammable carbonate-based compounds are used as the electrolyte solvent, e.g., ethylene carbonate (ec), propylene carbonate (pc), diethyl carbonate (dec), and dimethyl carbonate (dmc). even though these carbonate-based solvents perform well in nibs and proven to operate at high voltage to achieve high energy density; their highly flammable and volatile nature means that at elevated temperatures, a single point of leakage can trigger a catastrophic failure of the whole battery"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "the safety aspect of the battery for large-scale ess has been highlighted in recent times [6–8,38]. different approaches have been utilised by the research community to optimize electrolytes to enhance the safety of libs/nibs. one of the most prevalent approaches is using solid-state electrolytes. unlike a liquid electrolyte, a solid- state electrolyte will not suffer from evaporation or leakage issues, which makes them less hazardous to use [39]. however, the most vital drawback of solid- state"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 0,
    "chunk_index": 7,
    "text": "the electrolyte remains as a carbonate- based compound, flammability issue cannot be entirely diminished [42]. therefore, the ultimate solution could be entirely changing the carbonate solvent-based electrolyte system to a less flammable solvent-based electrolyte system. lecce et al. [43] reported 1 m licf3so3 and 1 m lino3 in tetraglyme non-flammable ether-based electrolyte for libs. the ether-based electrolytes are not only compatible with libs but also with nibs, and successfully tested in ni"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 2 present manuscript reports our effort in the development of an industry- standard nib technology, which is not only non-flammable, but safe enough and ready for commercialisation. the first half of this report focuses on the hc anode tested in two different types of electrolytes, namely a carbonate-based (1 m naclo4 in ec:pc (v:v ¼ 1:1)) and an ether-based (1 m nabf4 in tetraglyme) electrolyte [45,46], where the latter has a non-flammable"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "flammable ether-based electrolyte, 1 m nabf4 in tetraglyme and the conventional carbonate-based electrolyte, 1 m naclo4 in ec:pc before considering the cathode for designing the full cell. the second half of this article dwells on the discussion of two different nvp cathodes (pristine and modified), where sodium storage performances are analysed and compared systematically using various characterisation techniques. subsequently, full cells (in both coin cell and 18650 formats) comprising the pri"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "substituted na3v2(po4)3, the addition of (ch3coo)2zn (alfa aesar, 98.0–101.0%) is considered. all chemicals are used as received without any further purification unless stated otherwise. briefly, all precursors are added in stoichiometric amount to a water-rich ethanol solution and stirred at room temperature for 24 h. the obtained homogenous mixture is then dried in a drying oven and milled to achieve powder form. the green powder is then calcined at 650 c for 6 h under constant argon flow. the"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "dissolving nabf4 (sigma aldrich, 98%) in tetraglyme (sigma aldrich, 99%) [45,46]. in order to ensure that the electrolyte is moisture-free, the salt is dried inside the antechamber at 120 c for 18 h under vacuum and the solvent is kept with dried molecular sieves (alfa aesar, 4a, 1– 2 mm) inside the ar-filled glove-box before use. after mixing the salt and solvent, the electrolyte is stirred for 24 h at 600 rpm. 2.2. material characterisations 2.2.1. hard carbon differential scanning calorimetry"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "an aluminium pan inside the glove box itself. therefore, the samples within the pan are at the exactly same conditions as they were inside the half- cells, ensuring that the dsc measurements captured thermal stabilities of the active materials in the most realistic setting possible. the dsc measurements are conducted on a ta instrument 2920 with a heating rate of 10 c min1 from room temperature to 350 c (under ar atmosphere). symmetric cells and half- cells are prepared for the electrochemical i"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "metal during eis measurements [48,49]. the eis scans are made from 1 mhz to 10 mhz with 10 points per decade and 6 measures per frequency with the sinus signal of amplitude 100 mv. the attenuated total reflection (atr) technique is adopted for fourier transform infrared spectroscopy (ftir) analyses of the electrodes (fresh, sodiated and desodiated) using agilent cary630 instrument in absorbance mode over a range of wavenumbers from 650 to 4000 cm1. for the atr-ftir measurements, the sodiated and"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 6,
    "text": "2.2.2. na3v2(po4)3 powder x-ray diffraction (pxrd) pattern is recorded using a d8 advance powder diffractometer (bruker, germany) with cu-kα radiation, operated at 40 kv and 40 ma. the 2θ range is between 10 and 120 with the total data accumulation time for one pattern set to 6 h. rietveld refinement is performed using bruker’s diffrac.suite topas v6 software. particle morphology and size are observed using field-emission scanning electron microscopy (fesem). the electron microscope (jsm7000f; j"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 1,
    "chunk_index": 7,
    "text": "dv system (perkinelmer, usa). prior to the analysis, both samples are digested with hno3/hcl and topped up to 10 ml with deionised water. the precipitate is detected before the icp-oes analysis. bet surface area and pore size distribution of the samples are obtained using brunauer-emmett-teller (bet) method. measurement has been carried out on a nova 2200e surface area analyser (quantachrome, usa). detailed experimental conditions can be found in ref. [50]. tap density is obtained by filling a g"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 3 active material (a) carbon additives (b) binder (c) ratio (a: b: c) hc nil carboxy methyl cellulose sodium salt (cmc; alfa aesar) 95:0:5 pristine nvp modified nvp carbon black super p (alfa aesar; 99þ%) equally mixed with graphite (mti corporation, usa) polyvinylidene fluoride (pvdf; kynar 2801) 80:10:10 fitting of the obtained xps spectra is made using the xpspeak 4.1 software, and the spectra are subtracted with a shirley-type backgroun"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "the binder is finally added. the anode and cathode mixtures are then stirred for 40 min and 80 min, respectively, using a planetary centrifugal mixer (kakuhunter, japan). the slurry is spread and coated on an aluminium current collector (kanematsu corp, japan) with a thickness of 15 μm using an automated, dual-zone heated coating machine (tester sangyo co. ltd., japan) with a drying temperature of 100 c for hc, and 180 c for nvp. the coating is made on one side for coin cell electrodes and both "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "slightly elevated temperature of 60 c at 9.0 kn. the pressed electrode is then stored in vacuum oven set at 100 c for later use. the typical single-side electrode loading is about 4–5 mg cm2 for hc and ~10 mg cm2 for nvp. 2.4. coin cell fabrication all hc and nvp electrodes are punched from the single-side coated electrode into circular discs with a geometrical area of 2.01 cm2, and dried again in the antechamber at 120 c for 2 h under vacuum prior to fabrication of 2016- type (mti corporation) "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "three- electrode setup (mti corporation), the counter electrode used is na metal for half-cell and hc for full cell, respectively, with nvp as the working electrode. the swageloksized electrode used here has an area of 0.95 cm2. depending on the aim of the analysis, the electrolytes used in hc cells are either 1 m nabf4 in tetraglyme or 1 m naclo4 in ec: pc. only 1 m nabf4 in tetraglyme was used as electrolyte in nvp half-cell and full-cell. 2.5. 18650-type cell fabrication in addition to the co"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "wound together with polypropylene separators (mti corporation) into cylindrical jellyroll and then dried at 100 c overnight under vacuum before fig. 1. cycling performances of hc half-cells at c/20 with (a) 1 m nabf4 in tetraglyme and (b) 1 m naclo4 in ec:pc (v:v ¼ 1:1). (c) coulombic efficiency as a function of cycle number for hc half-cell cycled in 1 m nabf4 in tetraglyme and 1 m naclo4 in ec: pc (v:v ¼ 1:1). (d) rate performance of hc half-cell cycled in 1 m nabf4 in"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 4 being sealed in 18650-cylindrical case with the electrolyte mentioned previously. the loading of the double-side coated cathodes and anodes are 16- 20 mg cm2 and 8-10 mg cm2, respectively. the assembled batteries are kept at room temperature for about 24 h and cycled between 1.0 and 4.1 v at various current densities. 2.6. electrochemical characterisation the voltage window for assembled coin-type hc half-cells is 0.001–1.5 v and for nvp "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "discussion 3.1. hard carbon anode in coin cell 3.1.1. cycling performance fig. 1 presents the galvanostatic cycling performance of hc vs. na cycled in both ether- and carbonate-based electrolytes. at a slow rate of c/20, the hc fabricated using 1 m nabf4 in tetraglyme (fig. 1a) achieves a high first cycle charge capacity of 273 mah g1, as compared to only 178 mah g1 using carbonate-based, 1 m naclo4 in ec:pc electrolyte (fig. 1b). after 50 cycles, hc in ether-based electrolyte displays an impres"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "the hc anode in ether-based electrolyte discharged at a slow c/20 rate but charged at various current rates of c/20, c/5, c/2, 1c and 2c. at a fast rate of 2c, this anode is still able to achieve a high charge capacity of 223 mah g1. rate performance of hc vs na at same charge-discharge rates is presented in fig. s2."
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 5 3.1.2. thermal stability analysis 3.1.2.1. differential scanning calorimetry. aside from the good cycling performance, safety is one of the most important aspects of a battery. differential scanning calorimetry (dsc) experiments have been performed on hc electrodes using the aforementioned electrolyte solutions at fresh, fully discharged (sodiated) and fully charged (desodiated) states and the results are presented in fig. 2a. it can be s"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "upon increase in temperature, the sei layers start to crack [51], resulting in the presence of the 1st exothermic peak. following this event, the inserted naþ further react with the electrolyte on the sei-free surface of the anode, forming a fresh sei layer. finally, the re-formed sei layer decomposes and can be seen as the 2nd exothermic peak [51]. the total area under the exothermic peaks of the hc electrodes (designated by the yellow shaded area in fig. 2a) cycled in the carbonate-based elect"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "of the unit energy released and the onset temperatures of the 1st exothermic reactions for all investigated hc samples (sodiated and desodiated) using these two electrolytes. the region where a higher onset temperature of the 1st exothermic reaction coincides with lower total unit energy released (bottom-right in fig. 2b) implies higher safety aspects of the electrolyte. from this figure, it is evident that 1 m nabf4 in tetraglyme is a much safer electrolyte compared with 1 m naclo4 in ec:pc for"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "desodiated cycled with 1 m nabf4 in tetraglyme and 1 m naclo4 in ec:pc; eis nyquist spectra of hc half-cells after 1st, 2nd, 20th and 100th sodiated, fully desodiated samples cycled with (d) 1 m nabf4 in tetraglyme and (e) 1 m naclo4 in ec:pc. (f) ir data obtained from atr-ftir measurements of electrodes at fresh, fully sodiated, fully desodiated states of hc cycled with 1 m nabf4 in tetraglyme and 1 m naclo4 in ec:pc."
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 6 3.1.3. investigations on solid electrolyte interface it is generally known that the formation of a highly insulating passivation layer (sei) on the surface of the anode can be a major contributor to the observed low coulombic efficiency, especially in the first cycle [52]. thus, higher 1st cycle coulombic efficiency would mean fewer irreversible naþ being involved in the formation of sei layers, which lead to the assumption that a lesser "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "m naclo4-ec:pc (ch2oco2na)2 882, 1074, 1243, 1342 na2co3 1441 r–oco2na 1655 it may be noticed that the unit energy released for all samples decreased in the desodiated state with respect to the sodiated samples. this observation indicates that the sei formed during sodiation process is likely to decompose partially during desodiation process for all samples tested in both the electrolyte solutions. in order to test the above hypotheses on the sei formation of hc using both type of electrolytes, "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "in the form of symmetric cells to specifically quantify the impedance corresponding to the sei. fig. 2c shows the corresponding nyquist plots of the hc electrodes. we can see that the samples cycled using 1 m naclo4 in ec:pc shows larger semicircles (multiple layers of sei may result in larger depressed semicircles) in the high-frequency region than its ether- based counterpart, indicating more resistive passivation layers, suggesting the formation of thicker sei layers in the carbonate-based el"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "it is quite clear that, in hc vs. na half-cell, the ether-based electrolyte generally favours the formation of low resistance sei layers with better stability than carbonate-based electrolyte during cycling: there is no significant growth in the size of the semicircles for the former while there is perceptible growth for the latter (compare growth of nyquist plots at the sodiated states). 3.1.3.2. attenuated total reflection-fourier-transform infrared spectroscopy. in order to further understand"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "that the electrodes cycled in 1 m naclo4 in ec:pc shows stronger absorbance than electrodes cycled in 1 m nabf4 in tetraglyme, which is consistent with our previous hypothesis that a thicker sei is formed on the electrodes cycled in 1 m naclo4 in ec:pc. it is also clear that the ir signal for desodiated electrodes is weaker than the sodiated ones, suggesting partial dissolution of the sei in the desodiation (charge) process. the"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 7 fig. 3. rietveld refinement patterns of (a) pristine and (b) modified nvp, lattice parameters and with reliability factor values. fesem images of the (c) pristine and (d) modified nvp, with inset showing at higher magnification."
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 8 fig. 4. voltage profiles of (a) pristine nvp and (b) modified nvp cycled at c/10. (c) rate performances of both the pristine nvp and modified nvp. (d) eis nyquist plots of pristine nvp and modified nvp, with inset showing the equivalent circuit model used for data fitting. (e) linear fittings between zre and ω1/2 in the low- frequency region for the pristine nvp and modified nvp. compilation of absorbance peaks obtained from the atr-ftir "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "while, r–oco2x is observed in pc-based ones [55] (x stands for li or na and r stands for hydrocarbon groups). earlier studies also reported that ec and pc share the same degradation product x2co3 [56,58,59]. consistent with these findings, the signals of (ch2oco2na)2, r–oco2na and na2co3 are observed through the atr-ftir analysis of hc electrodes harvested from the cells with 1 m naclo4 in ec:pc. however, 1 m nabf4 in tetraglyme is one of the rarely investigated ether-based electrolytes and rela"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 9 na3v2(po4)3 (hereafter known as pristine nvp) and zn-substituted na3.2v1.8zn0.2(po4)3 (hereafter known as modified nvp) have been fully resolved using slow-scan powder x-ray diffraction (pxrd) data. both the samples crystallise in a rhombohedral phase defined with the space group r-3c. please note that we have not considered sodium ordering while refining the structure [61]. fig. 3a and fig. 3b show the result of the rietveld refinement a"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "compared to v3þ (78 pm) [36,37,64]. this decrease in lattice parameter is suggested to have an effect on the crystal structure stabilisation which promotes high rate performances [62,65]. the field emission scanning electron microscopy (fesem) images depicted in fig. 3c and fig. 3d show an apparent difference in morphology between the pristine and modified nvp. in fig. 3c of the pristine nvp, the secondary particle has a wider particle size distribution range of 5–15 μm (vs. 5–10 μm, for the mod"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "refine the structure, and the results obtained for the pristine and modified nvp are summarised in table s1 and table s2, respectively, in the supplementary information. note that zn2þ is deliberately inserted into v1 site in the refinement of the pristine nvp, which serves as a comparison. the normalised occupancy of naþ, v3þand zn2þ for pristine nvp is 3.002, 2.02 and 0.00 respectively, which corresponds to the chemical formula na3v2(po4)3. on the other hand, the normalised site occupancy of n"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "pristine nvp (31.6 m2 g1) (fig. s3). interestingly the measured tap density of the modified nvp (1.24 g cm3) is also almost two times higher than the pristine nvp (0.74 g cm3). the high tap density of the modified nvp is beneficial for loading more amount of the cathode material on each side of current collector during the fabrication of 18650 cells, which will be described later. x-ray photoelectron spectroscopy (xps) analysis for v 2p of both the pristine and modified nvp is illustrated in fig"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 4,
    "text": "(icp) elemental analysis of na, v, zn, and p, presented in table s3. the modified nvp sample shows a zn amount of 0.21 mol, consistent with the refinement results. a na:v:p stoichiometric molar ratio of 3:2:3 is obtained for the pristine nvp, which matches the chemical formula na3v2(po4)3. data from elemental analysis validate the presence of 0.2 mol of zn2þ per formula unit in the modified nvp sample, and results from rietveld refinement confirm that this amount of zn2þ are located in the v sit"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 5,
    "text": "nvp (fig. 4a) when cycled between 2.3 and 4.2 v (vs. na) at c/10. lower voltage polarisation (~28 mv) is achieved in the modified nvp. one may recognise that na3.2v1.8zn0.2(po4)3 has a theoretical capacity of 127 mah g1 but we obtained only 99 mah g1. one possible explanation is that the active material loading in the modified nvp electrode being high (~10 mg cm2) generally has its own inherent issues, e.g. poor electronic conductivity hence poor electronic wiring and poor electrolyte wettabilit"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 6,
    "text": "couple, where the extraction-insertion of naþ occurs via a single phase mechanism [36]. such a high voltage plateau is absent in the pristine nvp (fig. 4a). the presence of v4þ→ v5þ redox transition is shown systematically using ex-situ xps, discussed in the later section of the manuscript. in terms of rate performance, the modified nvp displays distinct improvement of high c rate capability compared to the pristine sample (fig. 4c). at a current rate of 4c, the modified nvp retains a higher dis"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 7,
    "text": "of the depressed semicircle, where the modified nvp has a noticeably smaller size. by fitting the obtained impedance spectra with the equivalent circuit model shown in the inset to fig. 4d, various resistances are obtained and summarised in table s4. the values of the solution and contacts resistance (rs), as well as passivation film resistance (r1) are almost identical between both pristine and modified nvp. however, the value of the charge transfer resistance (r2) computed for the modified nvp"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 8,
    "chunk_index": 8,
    "text": "chemical diffusion coefficients for the pristine and modified nvp are determined using the following equation [68]: r2t2 dnaþ ¼2a2n4f4c2σ2 (1) a detailed explanation of the various terms in the equation above is presented elsewhere [50]. table s4 shows that the estimated na chemical diffusion coefficient at 25 c for the modified nvp (19.2 1016 cm2 s1) is almost one order of magnitude higher than pristine nvp (2.931016 cm2 s1). both the lower charge transfer resistance at interfaces and higher na"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 10 3.2.4. redox reaction of v3þ during electrochemical cycling as mentioned earlier, the higher voltage plateau observed in the modified nvp during cycling is associated with the role of v4þ/v5þ redox couple, activated by the substitution of zn2þ. the following reversible compositional change in modified nvp is expected during the charge- fied nvp. discharge processes: na3:2viii1:8zn0:2ðpo4þ3⇋na3:2xviii1:8xvivxzn0:2ðpo4þ3 na3:2xviii1:8xvivx"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "state- of-charge (soc) electrodes, and a fully discharged (100% dod) electrode (see fig. 5). it should be noted that all fittings of the xps spectra produced a χ2 value of 0.3 or less, which indicates a good fit. as seen in the xps spectra of the fresh electrode of the modified nvp in fig. 5b, only the presence of v3þ is detected. as the electrode is continuously charged, v3þ peak is seen to decrease in intensity, while the v4þ peak is slowly rising. at 80% soc, the emergence of v5þ peak is seen"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "in the respective v3þ and v4þ species is observed. at 100% soc, not all v3þ is utilised in the charging process. upon a full discharge (100% dod), all v4þ species are entirely reduced to v3þ for the pristine nvp. 3.2.5. sodium storage performance of na3v2(po4)3 vs. hard carbon full cell encouraged by the interesting storage performance of nvp upon zn substitution discussed above, we have assembled full cells of these two nvp samples against hc anode. however, to determine the optimum voltage win"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 11 fig. 6. (a) three-electrode voltage profiles of modified nvp vs. hc cycled between 1.0 and 4.5 v at c/10. (b) cycling profiles of nvp vs. hc full cell in 2016-type coin cell format cycled at c/10 between 1.0 and 4.1 v. fig. 7. voltage profiles at c/7 and rate performance of (a,c) pristine nvp vs. hc and (b,d) modified nvp vs. hc in 18650 format cycled between 1.0 and 4.1 v. inset to (a) and (b) depicts the respective fabricated 18650 cel"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "the voltage profile begins to flatten out, and the corresponding disturbance starts to develop in the voltage profiles of both the nvp cathode vs. ref and hc anode vs. ref (blue line). this unidentified plateau at high voltage might be ascribed to the decomposition of the ether- based electrolyte at high voltage in presence of nvp nanoparticles while that at low voltage might be associated with na metal plating at the anode, and these processes continue indefinitely until the cell fails. please "
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "that an optimised upper cut-off voltage below 4.3 v is crucial to achieve the best performance of the full cell. judging from the voltage at which the side reactions take place, and that the v4þ⇋ v5þ activity happens at the nvp vs. hc charge voltage of ~3.9 v (when the cell is believed to be fully charged), an upper cut-off voltage of 4.1 v is employed for the cycling of full cell both in coin cell and 18650 format cells. the voltage profiles of both the pristine and modified nvp coin cells galv"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "k. du et al. energy storage materials 29 (2020) 287–299 12 second cycle; the first cycle, being the formation cycle, is not shown. similar to the half-cell cycling data shown in fig. 4, the pristine nvp vs. hc cell results in a lower discharge capacity of 79.3 mah g1 with a coulombic efficiency of only 95.8%. on the other hand, modified nvp vs. hc coin cell shows improved discharge capacity, 84.5 mah g1 with an impressive coulombic efficiency of 99.4%. when the full cell is scaled up to 18650 fo"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "complete cell weight. it is found that the modified nvp vs. hc exhibits higher energy density of 60 wh kg1 (fig. 7a) compared to the pristine nvp vs. hc cells, which is only 47 wh kg1 (fig. 7b). besides the higher discharge capacity acquired, the difference in energy density in both the 18650 cells is also attributed to the maximum obtainable electrode active material loading (5.8 g in pristine nvp vs. 6.5 g in modified nvp) in both the cathodes. when the pristine nvp loading on the aluminium fo"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "for the modified nvp results in better electrode packing, and this plays a crucial role in producing good quality electrodes with high active material loading. both the 18650-type cells fabricated are tested for rate performance, and the resultant discharge profiles at various current rates are presented in fig. 7c and fig. 7d for pristine and modified nvp, respectively. the pristine nvp vs. hc delivers a discharge capacity of 474 mah at a low rate c/7 and 71.1% of this capacity is retained at a"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "to reach a fully discharged state. for a clearer explanation, a current rate of 4.93c in fig. 7d means that the cell takes 12.2 min to be fully discharged. to access the durability of the modified nvp vs. hc cell, a long-term cycling test is conducted at a rate of c/5 for both charge and discharge. fig. 7e presents the cycle life data, demonstrating reasonably good capacity retention of 90% after 200 cycles. after witnessing excellent performance in modified nvp vs. hc than pristine nvp vs. hc i"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 11,
    "chunk_index": 4,
    "text": "improved thermal stability on the hc electrode when the ether-based electrolyte is used. besides superior cycling performance and high first cycle coulombic efficiency, we also believe that a thinner and more robust sei layer is formed with the non- flammable ether-based electrolyte. on the other hand, two nvp samples, namely pristine nvp (na3v2(po4)3) and modified nvp (na3.2v1.8zn0.2(po4)3) are synthesised and their storage performances are compared. with zn being successfully substituted in th"
  },
  {
    "source_pdf": "nonflammable_sodium_ion_battery_Kang_Du_Chen_Wang_Lihil_Uthpala_Subasinghe_Satyanarayana_Reddy_Gajella_Mark.pdf",
    "page": 11,
    "chunk_index": 5,
    "text": "addition, the charge transfer resistance decreases in the zndoped nvp, thus enhancing the na chemical diffusion coefficient. this observation gives rise to a considerable improvement in high rate performance, as well as long cycle life (90% capacity retention after 200 cycles) in 18650 cell format. moreover, the 18650 cell with modified nvp cathode delivers a discharge capacity of 566 mah, resulting in an energy density of 60 wh kg1. at a discharge rate close to 5c, the modified nvp can still de"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications 1 &2015 macmillan publishers limited. all rights reserved. most p2-type layered oxides exhibit naþ/vacancy-ordered superstructures because of strong naþ–naþ interaction in the alkali metal layer and charge ordering in the transition metal layer. these superstructures evidenced by voltage plateaus in the electrochemical curves limit the naþ ion transport kinetics and cycle performance in rechargeable ba"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "a simple way to design disordered electrode materials with high power density and long cycle life. ayered oxides have attracted great attention because of their unique low-dimensional structure and physical/chemical properties. in particular, they are a class of important cathode materials for rechargeable batteries. among them, licoo2 is still the most successful high-energy-positive electrode material for lithium-ion batteries1. in sodium-ion batteries showing worldwide interest for large-scal"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "of these phenomena in turn results in rapid capacity-fading during cycling. such a common behaviour was also observed in other layered oxides with brucite-type octahedral (mo6) layers, for example, naxmno2 (ref. 12–15), naxvo2 (ref. 16), na2/3ni1/3mn2/3o2 (ref. 17), na2/3co2/3mn1/3o2 (ref. 18), and so on. the goal of this work was to understand the conditions leading to naþ/vacancy ordering and potentially find a way to prevent it. we focused on p2-type layered oxides, which are known to be espe"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "oxides6,8,9,12–35. large difference in ionic radii is favourable for forming ordered arrangement while small difference tends to form disordered arrangement. in line with the general trend well established in crystal chemistry, we found the critical difference ionic radii to be b15%. if the radii difference is higher than 15% and m1/m2 content is close to a rational ratio, then an ordered structure is expected; otherwise m1 and m2 are disordered. occurrence of charge ordering is determined by th"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "ionic radii and substantially different redox potential versus na, such as cr3 þ and ti4 þ in expectation to build the p2- layered oxide free of naþ/vacancy ordering. disordered arrangement of cr3 þ and ti4 þ in the transition metal layers prevents m3 þ /4 þ charge ordering such as observed in naxcoo2 (ref. 9) and naxvo2 (ref. 16) that in turn prevents naþ/vacancy ordering. using neutron powder diffraction (npd) we show that p2- na0.6[cr0.6ti0.4]o2 synthesized through a simple solid-state reacti"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "na0.605[cr0.6ti0.4]o2. the morphology of the sample was investigated with scanning electron microscopy (sem). as shown in the inset of supplementary fig. 1, the distribution of particle size of the as- prepared sample is in the range of 1–4 mm. sample phase purity was verified using powder x-ray diffraction. all the diffraction peaks were found in good agreement with the jcpds no. 52-537 (ref. 36) that indicated a pure p2 phase material. the crystal structure of the material was further studied "
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "article nature communications | doi: 10.1038/ncomms7954 2 nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications &2015 macmillan publishers limited. all rights reserved. trigonal prismatic interlayer space containing sodium37. there are two inequivalent trigonal prismatic positions available for na atoms: sharing faces and edges with transition metal octahedra, designated in the following text na1 and na2, respectively. for the title composition na0.6[cr0."
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "of cr and ti the contribution of transition metals to the total diffraction pattern is rather small (bcoh(cr0.6ti0.4) ¼ 0.833 fm) that makes npd more sensitive to the contribution from the sodium sublattice (bcoh(na0.6) ¼ 2.18 fm). at room temperature the high-quality npd data unambiguously revealed absence of supercell diffraction peaks and therefore a high symmetry model (space group p63/mmc no. 194) with a unit cell (ab3å, cb11å) and random distribution of cr/ti and na over a single octahedra"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "density, which could not be adequately modelled by anisotropic thermal parameters because of the point symmetry of the sites. therefore, both na1 and na2 positions were split into 6-h (x, 2x, 1/4) sites that significantly improved refinement quality. the rp and rwp reduced from 2.30% and 2.99% to 2.08% and 2.73%, respectively, with only two additional variables, which is certainly statistically significant39. such sodium site splitting was previously proposed in several structural studies of var"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "p2-na0.6[cr0.6ti0.4]o2 in sodium half cells using 0.8 m napf6 in ethylene carbonate (ec)/diethyl carbonate (dec) as the electrolyte is shown in figs 2 and 3. since the valence state of cr in this compound is 3 þ , it can be oxidized to 4 þ on na deintercalation, enabling it as a possible positive electrode. meanwhile, the valence state of ti in this compound is 4 þ ; it can be reduced to 3 þ on na intercalation, making it a possible negative electrode. figure 2 shows the typical first charge and"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "different from some other p2-type electrodes such as naxcoo2, naxvo2, where multiple plateaus were observed during sodium deintercalation/intercalation, which is related to the formation of naþ/vacancy and charge-ordered superstructures9,16. in the case of na0.6[cr0.6ti0.4]o2, the disordered distribution of cr and ti in the transition metal layer as discussed above is responsible for such sodium storage mechanism. table 1 | possible ordered combinations in p2-type layered oxides. m1/m2 charge na"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "nature communications | doi: 10.1038/ncomms7954 article nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications 3 &2015 macmillan publishers limited. all rights reserved. interestingly, the average na storage voltage for the positive electrode is ca. 3.5 v, which is much higher than that of o3-type nacro2 (ca. 3 v) with the same cr3 þ/cr4 þ redox couple43. this is likely related to the different sodium contents in na0.6[cr0.6ti0.4]o2 and nacro2 samples. the"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "against npd data collected at 300 k. the red crosses and black and green solid lines indicate the observed and calculated patterns and their difference, respectively. the tick marks indicate the position of the diffraction peaks. rp ¼ 2.08%, rwp ¼ 2.73%. (b,c) general view of the crystal structure and view along the c axis showing splitting of na1 and na2 sites from the centres of prisms. figure 2 | typical first charge/discharge profiles of p2-na0.6[cr0.6ti0.4]o2 electrodes in the napf6-based e"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "article nature communications | doi: 10.1038/ncomms7954 4 nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications &2015 macmillan publishers limited. all rights reserved. retention at 1c is 82% of the initial capacity. the long-term cyclic stability of this material is also excellent at current rates of 0.1c and 1c as shown in fig. 3a,c. the na0.6[cr0.6ti0.4]o2 electrode exhibits over 200 cycles with capacity retention of 94% at a current rate of 1c. the co"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "first cycle is b80% in the napf6- based electrolyte. this low coulombic efficiency is because of the reduction of the used electrolyte to form the solid electrolyte interphase (sei) layer on the surface of the electrode. it is noted that when a naclo4-based electrolyte was used, an even much lower coulombic efficiency of 54% was observed as shown in supplementary fig. 3, indicating a serious decomposition of the electrolyte. it was found that the thickness of the formed amorphous sei layer on th"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "that of the positive electrode as shown in fig. 3e and supplementary fig. 5. this is likely related to smaller number of available vacancies for the na content (x ¼ 0.6–1) in the nax[cr0.6ti0.4]o2 negative electrode, resulting in slower naþ ion figure 3 | sodium storage performance of p2-na0.6[cr0.6ti0.4]o2 electrodes in the napf6-based electrolyte. (a) the second, tenth and thirtieth charge/discharge profiles at a current rate of c/10 (7.6 ma g1) in the voltage range of 2.5–3.85 v versus naþ/na"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "cycling performance. the capacity and coulombic efficiency versus cycle number at a current rate of 1c. figure 4 | full-cell performance of p2-na0.6[cr0.6ti0.4]o2 as both positive and negative electrodes in the napf6-based electrolyte. (a) discharge profiles of na0.6[cr0.6ti0.4]o2/na0.6[cr0.6ti0.4]o2 sodium-ion full cell at various rates. (b) the capacity and coulombic efficiency versus cycle number of the full cell at 1c rate. the capacity was calculated based on the mass of negative electrode."
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "70 60 80 90 110 0 4080 120160 200 20 10 40 0 30 0 20 406080 100 120 0.8 1.2 1.6 2.0 2.4 0.4 0 40 80 120 160 200 240 capacity (mah g –1 ) 20 10 40 0 second tenth thirtieth 30 50 70 80 60 15 cycle number cycle number 20 30 40 25 35 10 5 0 0 20 40 60 80 c/10 c/5 c/5 c/2 1 c c 1 c 2 100 120 140 charge discharge 20 40 60 80 100 120 140 160 100 40 50 70 60 80 90 110 04080120160200 3.9 3.6 3.3 3.0 2.7 2.4 capacity (mah g –1 )"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "nature communications | doi: 10.1038/ncomms7954 article nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications 5 &2015 macmillan publishers limited. all rights reserved. diffusion because of the strong repulsive electrostatic interactions among naþ ions. again, it can be seen from fig. 3d,f that the material presents very stable cycling performance at low and high current rates. after 200 cycles at 1c rate, the capacity retention is 90.4% (also see supplem"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "show that the full cell delivers an average operating voltage plateau at b2.53 v and extraordinary rate (fig. 4a) and superior cycling performance (fig. 4b and supplementary fig. 7). even at a very high rate of 12c, the capacity retention is 75% of that at 1c rate. the energy densities of this system are calculated to be 82 and 94 wh kg 1 at current rates of 1c and c/5 based on the mass of positive and negative electrodes. this battery system shows the best performance among symmetric rechargeab"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "capability, cycle life and cost are more critical than energy density, such as large-scale electrical energy storage. discussion to elucidate the structure evolution during sodium deintercalation and intercalation, we carried out the electrochemical in situ xrd experiment and the results are displayed in fig. 5. in fig. 5a, on na deintercalation, the (002) and (004) peaks continuously shift to lower two theta angles; while (100) and (102) peaks slightly shift to higher angles, no new peaks beyon"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "structures. in addition, these peak shifts are also highly reversible when na is inserted back to the structure. a very similar behaviour but with the opposite trend is observed when the na0.6[cr0.6ti0.4]o2 electrode was first discharged and then charged as shown in fig. 5b. for both positive and negative electrodes, the na storage mechanism is through a single phase reaction, that is, a wide solid- solution exists in nax[cr0.6ti0.4]o2 in the studied range 0.33rxr1. in order to investigate the c"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 4,
    "chunk_index": 4,
    "text": "of cr-l2,3 could be assigned to the formation of cr4 þ, which is further supported by the xas results as shown in supplementary fig. 8 (refs 44,45). for the negative electrode, only the ti-l2,3 edge changes significantly, corresponding to the ti4 þ/ti3 þ reduction figure 5 | crystal and electronic structure evolution during electrochemical desodiation and sodiation. in situ xrd patterns collected during the first charge/discharge of the na/na0.6[cr0.6ti0.4]o2 cells under a current rate of c/5 at"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "article nature communications | doi: 10.1038/ncomms7954 6 nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications &2015 macmillan publishers limited. all rights reserved. whereas ti4 þ/ti3 þ is involved in the charge compensation during na insertion, which is in excellent agreement with our initial design. to confirm that the disordered cr/ti distribution in the transition metal layer prevents naþ ordering at any temperature and sodium content such as known"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "content and high temperature, the further analysis of the npd data was performed using not only the rietveld method but also the maximum entropy method. the analysis of the npd data collected for na0.6[cr0.6ti0.4]o2 on cooling down to 3 k showed no evidence of cr/ti and naþ/ vacancy ordering such as that found in na0.7coo2 (ref. 11). instead, the sodium nuclear density was found to gradually delocalize with the increase in temperature (fig. 6). at high temperature, sodium is disordered into an a"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "1,073 k na0.6[cr0.6ti0.4]o2 demonstrates normal debye-type thermal expansion without anomalies (supplementary fig. 10). as expected, the c axis expands significantly faster than the ab plane as illustrated by linear thermal expansion coefficients estimated in the high temperature range, 22.5 10 6 and 11.5 10 6 k 1, respectively. also as expected, the c axis expands mostly because of the expansion of sodium- containing interlayer space rather than that of transition metal layers (supplementary fi"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "a combination of the unit cell contraction and expansion is that the unit cell volume changes with x very slightly, within 0.5% (fig. 7a, inset). furthermore, compared with the parent material na0.6[cr0.6ti0.4]o2, sodium-rich and sodiumpoor compositions have slightly smaller and larger cell volume, respectively. this means that changes in the total volume of a symmetric battery using na0.6[cr0.6ti0.4]o2 as both negative electrode and positive electrode will be negligible. this is very different "
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "the rate performance. therefore, lowering of x in nax[cr0.6ti0.4]o2 has an effect similar to increasing temperature (fig. 6a–f). to obtain a microscopic picture of the naþ ion transport we also performed first-principles molecular dynamics (fpmd) simulations as implemented in the vasp (viena ab initio simulation package) code47. a special quasi-random structure (sqs) was constructed to simulate the disordered configuration of naþ/vacancy and cr/ti using a 108-atom supercell through the atat code"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "nature communications | doi: 10.1038/ncomms7954 article nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications 7 &2015 macmillan publishers limited. all rights reserved. figure 6 | nuclear density distribution of sodium calculated by the mem using neutron powder diffraction data. (top) section of nuclear density at z ¼ 0.25 for na0.6[cr0.6ti0.4]o2 at 3 k (a), 300 k (b) and 1,073 k (c); (bottom, d) general view of the crystal structure with nuclear density "
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "na1 and na2 sites as a function of x; (c) na1 and na2 displacement from the centres of prisms as a function of x. k 3 k 300 1 ,073k 20 10 0 40 30 50 70 60 80 0.0 relative distance between ( –2/3,–1/3,1/4) and (4/3,2/3,1/4) sites 0.20.40.60.8 0.2 0 5 10 470 k k 623 873 k 1 ,073k ideal na1 position ideal na2 position 0.4 0.6 0.8 1.0 3 k 100 k 200 k k 300 k 400 470 k 623 k k 873 1 ,073k 0.3 2.93 2.94 2.95 2.96 a c v / v x =0.6 0.4 0.50.6 x in na x cr ( 0.6 ti 0.4 o ) 2 x in na x cr ( 0.6 ti 0.4 ) o"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "0.50.60.70.8 0.91.0 20 40 30 50 70 60 80 na1 occ % na2 occ % 0.00 0.05 0.10 0.15 0.20 0.25 0.30 na1 displacement na2 displacement 0.30.4 0.50.60.70.8 0.91.0 11.35 11.30 11.25 11.20 11.15 11.10 11.05 11.00 0 20 40 60 80 100 ,700k 2 2 ,400k 1 ,800k 1 ,500k 1 ,200k 0 2 4 t (ps) 6 8 10 0.4 –11.0 –10.0 –9.0 –9.5 –8.5 ind=–4,100/t–7,075 e a ev =0.35 –10.5 0.5 0.6 1 ,000/t (k –1 ) 0.8 0.7"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "article nature communications | doi: 10.1038/ncomms7954 8 nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications &2015 macmillan publishers limited. all rights reserved. figure 8 | naþ ion transport properties of p2-na0.6[cr0.6ti0.4]o2 obtained by fpmd simulations. (a) msd at 1,200, 1,500, 1,800, 2,400 and 2,700 k. (b) arrhenius plot of diffusion coefficients, from which the naþ ion migration energy barrier of 0.35 ev is obtained. (c) trajectories (small g"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "trajectories of the naþ ions are given to illustrate the migration pathways. the positions of cr, ti and o atoms are fixed at their initial ones for clarity, since no breaking of cr–o and ti–o bonds is found in all the simulations. it is clear to see that the naþ ions migrate within two-dimensional channels, since no diffusion between the naþ layer and the transition metal layer can be found. the top view of trajectories in each naþ layer reveals similar pictures with the section of nuclear dens"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "demonstrated that this cation-disordered material can function as both positive and negative electrodes with average operation voltages of 3.5 and 0.8 v, corresponding to the redox couples of cr3 þ/cr4 þ and ti3 þ/ti4 þ, respectively. a symmetric sodium-ion battery using the same p2-na0.6[cr0.6ti0.4]o2 electrode material demonstrates charge/discharge curves free of voltage plateaus, outstanding rate performance and long cycle life. our study highlights the importance of designing a disordered tr"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "agate mortar and pressed into pellets under pressure of 20 mpa. then, the pellets were heated at 1,000 c for 15 h under ar atmosphere in an alumina crucible. characterizations. the morphologies of the materials were investigated using a scanning electron microscope (hitachi s-4800). powder x-ray diffraction was performed using a bruker d8 advance diffractometer equipped with a cu ka radiation source (l1 ¼ 1.54060 å, l2 ¼ 1.54439 å) and a lynxeye_xe detector. the xrd pattern was refined using the"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "discharge at a current rate of c/10, between 0.5b2.5 and 2.5– 3.85 v versus naþ/na. an aluminium foil was placed between the cathode electrode and the beryllium window, to prevent beryllium oxidation at high operating voltages. the na0.6[cr0.6ti0.4]o2 powder was chemically sodiated49 by chemical reduction with sodium-biphenyl-1,2-dimethoxyethane (dme) solution as sodiation reagent. in a typical process, 0.0956 g pure sodium was dissolved into 10 ml colourless 1 m biphenyl-dme solution, forming a"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 7,
    "chunk_index": 5,
    "text": "no2bf4 was dissolved in acetonitrile and na0.6[cr0.6ti0.4]o2 (molar ratio, no2bf4: na0.6[cr0.6ti0.4]o2 ¼ 0.1:1 or 0.27:1) was added to the resulting solution. the slurry was stirred overnight at room temperature, filtered under vacuum and then finally washed several times with acetonitrile. npd data were collected using the high-resolution powder diffractometer echidna at the opal research reactor (ansto, lucas heights) using wavelengths of 1.6215 å. the npd data analysis with rietveld and maxim"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 7,
    "chunk_index": 6,
    "text": "mm.the eels spectrum background was subtracted by power law fitting. the electronic states of the cr during the charge and discharge processes were probed using x-ray absorption near-edge structure spectroscopy techniques at cr k-edges. the ex situ xas data at the cr k-edge were recorded at room temperature in the transmission mode at beam line bl14w1 of the shanghai synchrotron radiation facility (ssrf), china. the station was operated with a si (111) double crystal monochromator. the photon en"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "nature communications | doi: 10.1038/ncomms7954 article nature communications | 6:6954 | doi: 10.1038/ncomms7954 | www.nature.com/naturecommunications 9 &2015 macmillan publishers limited. all rights reserved. sodium foil as the counter electrode, and a glass fibre as the separator in an argonfilled glove box. the charge and discharge measurements were carried out on a land bt2000 battery test system (wuhan, china) in voltage ranges of 0.5–2.5 and 2.5–3.85 v under room temperature. a sodium-ion "
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "through the atat code56. this structure is built from the hexagonal cell with the transformation matrix [–3,–2,0;1,–1,1;0,5,0]. the fpmd method is adopted to investigate the naþ ion transport properties in p2-na0.6[cr0.6ti0.4]o2. the simulations are performed using the density functional theory as implemented in the vasp code47,56. the present data are obtained using the generalized gradient approximation with a parameterized exchange-correlation functional according to perdew–burke–ernzerhof57."
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "and a time step of 1 fs is used to integrate the equation of motion. to keep the computational cost at a reasonable level, only the g point is used for the brillouin zone sampling in fpmd calculations. the msd can be used to characterize the diffusion behaviour of the system, msdðtþ ¼ r2ðtþ ¼ jriðtþ rið0þj2 ð1þ where ri(t) is the position of the i-th naþ ion at the time t, and the average is over the time steps and all the naþ ions. according to the einstein equation, the slope of the msd presen"
  },
  {
    "source_pdf": "P2_Na0_6_Cr0_6Ti0_4_O2_cation_disordered_electrode_for_high_rate_symmetric_rechargeable_sodium_ion_batteries_Yuesheng_Wang_Ruijuan_Xiao_Yong_Sheng_Hu_Maxim_Avdeev_Liquan_Chen.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "interests. reprints and permission information is available online at http://npg.nature.com/ reprintsandpermissions/ how to cite this article: wang, y. et al. p2-na0.6[cr0.6ti0.4]o2 cation-disordered electrode for high-rate symmetric rechargeable sodium-ion batteries. nat. commun. 6:6954 doi: 10.1038/ncomms7954 (2015). this work is licensed under a creative commons attribution 4.0 international license. the images or other third party material in this article are included in the article’s creati"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 access metrics & more article recommendations abstract: sodium-ion batteries (sibs) are seen as an emerging force for future large-scale energy storage due to their cost-effective nature and high safety. compared with lithium-ion batteries (libs), the energy density of sibs is insufficient at present. thus, the development of high-energy sibs for realizing large-scale energy storage is extremely vital. the key factor de"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "(sibs) offer safer and more environmentally sustainable solutions to lithium-ion batteries (libs) with comparable performance.1 despite great potential in applications for high-power energy storage systems, current sibs still suffer from drawbacks, such as an inferior charge and discharge rate (low power density), lower specific capacity (low energy density), and short cycle life.2−4 cathode materials play a central role in determining the electrochemical performance of sibs. however, the curren"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "compounds, and prussian blue analogs (pbas). each category of the cathode materials has their own features and inherent problems. the transition layered oxides with large spacers for na+ storage have high reversible specific capacities, high energy densities, and excellent rate capabilities combined with susceptibly convertible technologies. however, such a layered structure is prone to collapse when © 2023 the authors. published by american chemical society accommodating large-radius na+ for (d"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "and reduces the chemical stability and structural stability of the pba material.12 effective improvement strategies have been proposed to address the shortcomings of different cathode materials, such as surface modification (isolation or coating), structural design, and lattice or interlayer modulation, in order to realize the high energy density, superior rate capability, and long service lifespan of sibs (figure 1). in this outlook, we summarized the recent progress of the major cathodic mater"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2013 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 figure 1. overview of cathodic materials and their effective modification strategies. top left image reproduced with permission from ref 182. copyright 2016 american chemical society. middle left image reproduced with permission from ref 44. copyright 2018 american chemical society. bottom left image reproduced with permission from ref 138. copyright wi"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "(left) and o3 (right) crystal structures. reproduced with permission from from ref 20. copyright 2021 iop. structures, physicochemical properties, and electrochemical applications. finally, the remaining challenges in the application of these cathode materials for future large-scale energy storage sibs are discussed. we hope this outlook can make a guiding contribution to the development of cathode materials for high-energy sibs. 2. transition metal oxides the composition and structure of curren"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "2a compares the voltages, capacities, and energy densities of the layered metal oxide cathodes composed of single, binary, ternary and multicomponent metal ions. typical na-based layered transition oxides, i.e., namo2 (m = ni, co, mn, fe, cr, v, etc. ), exist in different crystal structures denoted as p2, p3, o2, and o3 according to delmas’ notation.13 o and p indicate the coordination environment of na+, in which o represents the na occupancy at the octahedron sites surrounded by six oxygens an"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2014 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 prism sites surrounded by six oxygens. among them, o3- phase and p2-phase are most widely investigated as cathodes for sibs, and their crystal structures are illustrated in figure 2b. typical examples of o3-type metal oxides include nafeo2,14 nanio2,15 and nani1/2mn1/2o2,16 and those for p2- type metal oxides include na2/3mno2,17 na0.7coo2,18 and na2/3n"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "high capacity and low cost. vo2(a) is unstable during electrochemical reactions,21 but vo2(b) is considered a more suitable cathode for sibs because its layered structure allows for rapid na ion diffusion; the corresponding theoretical capacity is as high as 322 ma h g−1, which is associated with one e− transfer during the (de)sodification process.22,23 however, vo2(b) is metastable and less conductive, so rapid capacity fading was often observed for vo2(b) because of the drastic volume expansio"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "morphology change or crystal structure collapse upon cycling, which is also known as “lattice breathing”.24 the stability of v2o5 electrodes can be enhanced by inserting larger cations (na+, nh4+) or water molecules into the crystal interlayers.25,26,27 constructing v2o5 aerogels with highly porous 3d networks has also proved to be an efficient strategy for enhancing their performance.28 apart from the crystallized structure, the amorphous v2o5 also demonstrates a na storage property.29 furtherm"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "further investigation.31 2.2. layered sodium monometallic oxides. the sodium monometallic oxides often suffer from poor stability and rapid degradation due to the continuous phase changes of the oxides, especially at high voltages. for example, α- nafeo2 is a o3-type cathode material with excellent thermal figure 3. (a) schematic illustration of the hydration and co2 uptake process when exposing layered metal oxides in air. reproduced with permission from ref 51. copyright 2023 american chemical"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2015 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 stability with an active fe3+/fe4+ redox couple. under higher voltages, their electrochemical performance degrades mainly due to the jahn−teller distortion and polarization. fe4+ is reduced to fe3+ at the charged state, and the excessive fe3+ will migrate and block the diffusion pathways of na ions, causing the degradation of performance.32 a recent fin"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "mainly affected by the na+/vacancy ordering, which can be relieved by partial substitution of the co ions with ni3+, mn2+, and ti4+.36,37,38 similar to mno2, naxmno2 suffers from severe volume change induced by the jahn−teller distortion and dissolution of mn species during the electrochemical reactions.39,40 the disproportion of mn3+ into mn4+ and mn2+ results in the dissolution of mn species into the electrolyte. high-temperature quenching can remove the mn vacancies and suppress their dissolu"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "tmo2 slabs and oxidation of the electrodes.42−44 washing with ethanol, reducing interlayer spacing, and using proper electrolyte are effective strategies to enhance their stability.45 navo2 shows a similar structure to o3 anafeo2, while the pure-phase navo2 is difficult to synthesize. navo2 can only be reversibly cycled in the narrow working window of 1.4−2.5 v.46 when a higher voltage was applied, the composition underwent continuous variation with the emergence of many potential plateaus. nacr"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2016 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 theoretical capacity of ∼250 ma h g−1, but it faces a similar issue of poor irreversibility at high voltages, just like navo2.47 it has been reported that partial substitution of cr by ru and ca ions can be effective in obtaining a more stable nacro2 electrode.48,49 the ru substitution can possibly improve the working plateau (presenting an extra high v"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "to improve the structural stability (air- stability). in this regard, some inactive elements such as ti, ru, and ca have shown effective results in improving the aforementioned effects. another challenge with the layered metal oxides is their hygroscopic nature, as they tend to uptake water and co2 from air, which results in fast capacity decay and dissolution of the electrodes (as illustrated in figure 3a).42,50,51 surface modification by coating zro2, na2tio7, or alf3 can be effective in promo"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2017 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 2.3. layered sodium multimetallic oxides. nowadays, most of the research attention has been devoted to the development of multimetallic oxide cathodes for high- performance sibs. with the cooperative benefits from different metal ions, the common issues encountered by the monometallic oxide cathodes, such as the jahn−teller distortion, undesired na+/vac"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "mixed with minor p2 phases, such as na0.66li0.18mn0.71ni0.21co0.08o2,57 na0.67mn0.55ni0.25ti0.2−xlixo2,58 and nax[ni0.2fex−0.4mn1.2−x]o2 (x = 0.7−1.0).59 these hybrid-structured electrodes generally showed smoother charge−discharge profiles, reduced polarizations, and higher capacities during the cycling process. metal substitution is effective in suppressing the phase transition during the reaction process. for example, al and fe substitution can suppress the undesired phase figure 5. (a) illus"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2018 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 transition in na0.67al0.1fe0.05mn0.9o2.41 the jahn−teller distortion in naxmno2 can be suppressed by the introduction of li+, mg2+, fe3+, ni3+, and ti4+ ions.,60,61 the reason for li+ and mg2+ substitution is that they can oxidize mn3+ into mn4+ and thus reduce the jahn−teller distortion.62,63 besides cation doping, doping with fluorine has lowered the "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "phases within the crystal structure of na0.2ni0.45zn0.05mn0.4ti0.1o2, which not only fully strengthened the potential capacity of the metal oxide electrode but also suppressed the undesired phase transition and structural degradation upon cycling.66 potassium ions were introduced into the p2−k0.5mn0.7fe0.2ti0.1o2 and served as pillar ions to expand the lattice for na ion insertion and deinsertion and stabilize the crystal structure.67 to address the irreversible structural changes or phase trans"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "structure in figure 4a, nb doping can expand the spacing between the tm layers from 0.376 to 0.389 nm and extend the na−o bond from 0.251 to 0.256 nm, endowing na+ with enhanced (de)intercalation capabilities. the in situ x-ray diffraction (xrd) spectra shown in figure 4b illustrate that all the characteristic diffraction peaks revert to their original initial positions without the appearance of any new phase after a charge/discharge cycle. the charge density distribution of the nb-doped na2/3mn"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "oxides (meos) and high- entropy oxides (heos) are novel categories of multimetallic singlephase solid solution oxides with multiple metals sharing the crystallographic sites and stabilizing the host structure through the “entropy-stabilization effect”.69 in addition, the oxygen vacancies generated among the metal ions can effectively promote the na ion diffusion. for example, the multic o m p o n e n t i n o 3 - t y p e n a - ni0.12cu0.12mg0.12fe0.15co0.15mn0.1ti0.1sn0.1sb0.04o2 results in diffe"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 6,
    "chunk_index": 4,
    "text": "0.1 c and 78.2 ma h g−1 at 10 c, demonstrating its superior rate capacity. excellent cycling stability with the retention of 63.7% after 300 cycles at a current density of 5 c was also validated. in situ high-energy xrd confirmed the o3-type structure of the original cathode, which underwent a fast o3−p3 phase transition at the initial stage of charging (figure 5b). x-ray absorption spectroscopy (xas) analysis (figure 5c, d) reveals that the ni2+/ni3+/ni4+ and fe3+/fe4+ redox couples jointly con"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 6,
    "chunk_index": 5,
    "text": "anionic redox couples that contribute to the high capacity.72,73 with proper engineering over the structure and composition, arr electrodes can be created through metal ion doping. the zn- doped p2− na2/3mn1−yznyo2 electrode showed high oxygen redox activity associated with nonbonding o(2p) orbitals.74 doping metal ions causes ionic bonding, such that the electrons fully localized on the oxygen anions and the tm deficiency were the key to activate the oxygen anion redox activity. metal ions that"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2019 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 repulsion around the empty na layer and hence stabilized the structure. besides, with the double redox reaction from both ni2+/ni4+ and o2−/on−, the higher redox potential of na[mn0.5ni0.5]o2 compared to that of namno2 with a single redox reaction was expected.76 however, it was also noticed that the arr electrodes suffer from the structural degradation"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "prepared through coprecipitation followed by milling at a rotational speed of 1000 r min−1 at 50 °c.52 its first discharge specific capacity was 168 ma h g−1 measured at 0.5 c within the voltage range of 1.5−4.0 v, and the capacity retention rate after 50 cycles was found to be 77%. ding et al. synthesized a novel ni-rich o3-type na[ni0.60fe0.25mn0.15]o2 cathode for sibs via the industrially feasible hydroxide coprecipitation method followed by high- temperature calcination.77 by reducing the ch"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "cathode materials in sibs is namx(xoy)z· nh2o, where m represents a transition mental element, such as v, fe, mn, cr, ni, ti, etc., and x is nonmetal element like p, s, si, as, mo, or w.9,10 according to the different type of polyanion, polyanionic cathode can be divided into the following categories: phosphate, sulfate, silicate, borate, and mixed-polyanion materials. the high induction effect brought by the polyanionic xo4 can effectively increase the working voltage of the cathode, and the po"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "storage mechanism, and current advances of polyanionic cathodes for sibs. figure 6. (a) crystal structure of na3v2(po4)3. reproduced with permission from ref 87. copyright 2019 royal society of chemistry. (b) crystal structure of na2fe2(so4)3. reproduced with permission from ref 88. copyright 2019 royal society of chemistry. (c) crystal structure of na2fesio4. reproduced with permission from ref 82. copyright 2016 american chemical society. (d) crystal structure of na3feb5o10. reproduced with pe"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2020 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 3.1. characteristics of polyanionic compounds. 3.1.1. phosphates. the phosphate-based materials in sibs can be divided to three categories: orthophosphate nampo4 (m = fe, mn, ni), nasicon-type naxmy(po4)3 (m = v, fe, mn, ti), and pyrophosphate na2mp2o7 (m = v, fe, co, mn).79 as a representative of nampo4, the crystal structures of nafepo4 are mainly oli"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "of m-nafepo4, methods for stimulating its electrochemical activity are being continuously studied. as shown in figure 6a, the classical nasicon-type na3v2(po4)3 belonging to naxmy(po4)3 (m = v, fe, mn) has two mo6 octahedra and three po4 tetrahedra sharing oxygen atoms for linkage, with the na+ occupying two unequal wyckoff sites, one na+ at the 6b site (m1) and the other at the 18e site (m2). the pyrophosphatetype materials are represented as na2mp2o7 (m = v, fe, co), with p2o75− having a highe"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "a suitable voltage window for the reversible extraction/insertion corresponding to one na+ with a theoretical specific capacity of 97 ma h g−1, and two clear plateaus of 2.5 and 3.0 v can be observed. 3.1.2. sulfates. the thermodynamic stability of the so42− group in sulfate polyanionic compounds na2m(so4)2·nh2o (m = fe, mn, co, ni, etc.) is inferior, and its decomposition temperature is lower than 400 °c. when exposed to temperatures above the decomposition temperature, so2 gas is easily releas"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "material high. since the charge-to-mass ratio of sulfate is significantly lower than that of phosphate, the theoretical specific capacity of sulfate materials is thus lower. although in terms of practical applications, sulfate materials can hardly be comparable to commercialized licoo2, lifepo4, ncm-811, and so on, they can unleash their own unique advantages in the field of lowcost energy storage. in 2014, yamada et al. successfully prepared na2fe2(so4)3, which belongs to monoclinic crystal sys"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2021 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 6b, the feo6 octahedra form an isolated fe2o10 dimer by coedging and bridging with the so4 tetrahedra through the vertices, thus resulting in a three-dimensional (3d) skeletal structure with large ion channels along the c-axis. more specifically, na+ occupies three different na sites in the 3d skeleton structure, where the na2 and na3 sites have 1d na+ "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "feo4 tetrahedron and sio4 tetrahedron are joined alternately to form a solid framework, while the sodium is hexacoordinated and forms a sublattice alone; na ions are in a relatively disordered state in this structure (figure 6c). due to the large ion gap in the structure framework, na+ has greater freedom of motion, leading to a high na+ diffusion coefficient. thus, high na+ diffusion in na2fesio4 can still be achieved even without the fast ion transport channels, which also applies to co-based "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "borate polyanionic electrode materials have also received some attention from researchers because of their small molar mass, abundant resources, and environmental friendliness. boron atoms can be sp2- and sp3-hybridized to form various groups, such as [bo3]3−, [bo4]5−, and [b2o4]4−, that can be condensed or polycondensed to form islands, chains, layers and skeletal groups, leading to a variety of boronate crystal structures. compared with other polyanionic compounds, borates have higher theoreti"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 9,
    "chunk_index": 3,
    "text": "interlamination positions.83 additionally, its theoretical capacity is 78 ma h g−1 based on the reversible intercalation of one na+ per formula unit. 3.1.5. mixed-polyanion materials. a series of hybrid polyanionic cathode materials with novel structures, such as a phosphate−pyrophosphate hybrid, a phosphate−carbonate hybrid, and fluorinated phosphate, can be obtained by taking advantage of their mutual compatibility. the phosphate− pyrophosphate hybrid polyanionic cathode material can be expres"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2022 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 in addition, a series of crucial fluorinated polyanionic materials with high voltages can be prepared by replacing part of the polyanion with high electronegativity fluorine, thereby developing navpo 4 f, na 3 v 2 (po 4 ) 2 f 3 (nvpf), na3v2(po4)2o2f (nvpof), nafeso4f, and other fluorinated materials. the tetragonal nvpf with a space group of p42/mnm wa"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "most widely studied polyanionic materials, na3v2(po4)3 (nvp) possesses high ionic conductivity, excellent cycling stability and great thermal stability. employed as the cathode for sibs, na3v2(po4)3 has a theoretical capacity of 117.6 ma h g−1 and a working plateau of 3.4 v, which originated from the v3+/v4+ redox couple corresponding to two na+ ionsinvolved in (de)sodiation.87,90 unfortunately, the nvp cathode material characterized by sluggish diffusion kinetics and low electronic conductivity"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2023 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 unsatisfactory specific capacity and rate capability, and effective modifications are desired. at this stage, modification methods, including surface coating, morphological construction, and lattice modulation, have been developed. recently, xiong and coworkers proposed a polymer-stabilized droplet template strategy to synthesize a novel porous single-c"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "the hp-nvp. as a consequence, an outstanding rate capability of 61 ma h g−1 at ultrahigh rate of 100 c and a prolonged lifespan of 10000 cycles at 20 c without capacity fading can be achieved (figure 7c). specially, hp-nvp was assembled to form a symmetric cell, which exhibits a specific capacity of 47 ma h g−1 at 50 c and stable cycling at 10 c for 700 cycles.91 xu et al. proposed a spray drying method for synthesizing nvp/rgo hss. owing to the unique porous hollow architecture effectively shor"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "application of nvp/rgo hs cathode, the full cells assembled with nvp-hss cathode and s-cmts anode exhibit a capacity retention of 84.2 ma h g−1 after 100 cycles at 1 c. assembling a high-performance sodium-ion full battery (sifb) requires overall matching between the cathode, anode and electrolyte. wei et al. proposed an excellent sifb integrated with an optimized nvp@c@carbon nanotube (nvp@c@cnts) cathode, a mesocarbon microbead (mcmb) anode, and a na+−diglyme electrolyte. the as-synthesized nv"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "w h kg−1 at ∼23 kw kg−1. besides, superior cyclability with 72.7% capacity retention for 5000 cycles at 5 a g−1 could be achieved (figure 7d). both the high conductivity of nvp@c@cnt cathode and the expanded ion diffusion paths at the anode resulted from the initial pseudocapacitive cointercalation, which contributed to this high rate capability and excellent cyclability.92 in addition to morphological construction and surface coating, lattice regulation is also beneficial for improving nvp perf"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 11,
    "chunk_index": 4,
    "text": "8000 cycles at 5 c. additionally, the constructed pocket-flexible sibs demonstrated a large energy density of 262.4 w h kg−1 and an ultrahigh rate capability of 77 ma h g−1 at 150 c. this is because when higher valence mo6+ was introduced into the nvp, na+ vacancies would be generated due to valence equilibrium, which enhanced the electronic conductivity and ion diffusion kinetics of the electrode due to the smaller na+ migration barrier. besides, shi et al. developed a cathode of bismuth-doped "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 11,
    "chunk_index": 5,
    "text": "rate capability and outstanding cyclability can be attributed to the doped bi3+ that acted as the pillar of nvp crystal structure, buffering crystal deformation and enhancing the structural stability. 3.2.2. na3vm(po4)3. vanadium-based materials profiting from multivalence states and rich resource of vanadium are some of the preferred electrodes for batteries, but vanadium has high toxicity. thus, cost-efficient and environment-friendly elements (e.g., fe, mn) are doped into the v-site in na3v2("
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2024 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 na3vm(po4)3 is to coat it with conductive materials. recently, zhu et al. designed a unique hierarchical bayberry- like nmvp@nc material as a cathode for sibs via facile ball- milling and subsequent calcination. even cycled at an ultrahigh rate of 100 c, the nmvp@nc cathode can still deliver a high discharge capacity of 82.4 ma h g−1 (figure 8b), which "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "and the charge process appear symmetric, confirming the high reversibility of the electrochemical reactions. the nmvp@nc cathode is unique: (i) the ultrasmall sizes of nanoparticles render a short diffusion distance for na+ and provide a larger electrode/ electrolyte contact area, (ii) the 3d n-doped carbon network availably improves the electrical conductivity of nmvp, and (iii) the robust structure suppresses the volumetric expansion during the repeated na+ insertion/extraction, giving rise to"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "which are expected to reduce the activation energy and enhance the na+ mobility.97 in addition to doping at the vanadium sites, doping at the polyanion sites has also been studied. the innovative na- deficient na3.85□0.15mnv(po3.95f0.05)3 material was fabricated by partially doping f into the nmvp. electron density differences shown in figure 8d and e prove that the change of electron density caused by the substituted f near mn or v atoms and the weak coulomb interaction induced by the na vacanc"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "a novel na4fev(po4)3@c cathode synthesized via a combined ballmilling, sol−gel, and calcination process. the as-prepared na4fev(po4)3@c exhibited specific capacities of 100 ma h g−1 at 0.1 c and 80.6 ma h g−1 at 10 c when tested at the wide voltage window of 1.3−3.8 v. in charge−discharge curves, two plateaus located at 2.5 and 3.5 v can be ascribed to fe2+/fe3+ and v3+/v4+ redox couples, respectively. besides, the cathode exhibited great cycling stability, with 96.8% capacity retention after 80"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2025 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 its stable framework structure.99 wang et al. reported a bicarbon-decorated nfvp@rgo@cnt material as the cathode for sibs. a high discharge capacity of 156 ma h g−1 at 0.1 c could be achieved in the operating window of 2.0−4.4 v. besides, a rate capacity of 60 ma h g−1 at 30 c and 71% capacity retention over 600 cycles at 2 c were realized. such great r"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 13,
    "chunk_index": 1,
    "text": "na vacancies to boost the electroconductivity. the optimized na3.9fev0.9zr0.1(po4)3/c electrode exhibited a high discharge capacity (114 ma h g−1 at 0.1 c), superior rate capability (66.7 ma h g−1 at 40 c), and remarkable cyclability of 82.4% capacity retention over 4000 cycles at 20 c (figure 9c). as illustrated in figure 9d, the nfvz0.1p/c cathode showed a smaller volume change (δv/vpristine) of ∼5.21% during electrochemical cycling compared with the undoped sample. its excellent structural st"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 13,
    "chunk_index": 2,
    "text": "and low temperatures. benefiting from the doping of high-entropy crystals, the activity of v4+/v5+ electron couples is activated, enabling a highly reversible capacity of 102 ma h g−1 at 0.1 c. besides, the nmvp half-cell also showed outstanding cyclability over 5000 cycles at 20 c. even tested at −20 °c, the nvmp cathode could still demonstrate prolonged cyclability with 94.2% capacity retention over 1000 cycles at a high rate of 5 c. for a real application, the constructed nvmp||hc full batter"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 13,
    "chunk_index": 3,
    "text": "unfavorable jahn−teller effect. to address this, additional atoms such as nonactive metal elements like al, mg, ce, and cr are introduced to suppress the adverse effects caused by mn3+.103 the introduction of fe stabilizes the lattice further, but the overall decreased voltage (∼3.0 v) limits its application in high-energy-density sibs, making it less favorable. on the other hand, the introduction of highly electronegative fluorine at polyanion sites has proven to be an effective strategy for pr"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 13,
    "chunk_index": 4,
    "text": "synthesis route for the scalable production (150 g per batch) of multishelled na3(vopo4)2f microspheres using in situ generated bubbles as soft templates at room temperature.104 in this method, raw materials were extracted from vanadium slag and nvpof microspheres were formed during the coprecipitation process with the appropriate reaction time. the large-scale prepared na3(vopo4)2f exhibited an outstanding rate capacity of 81 ma h g−1 and remarkable cycling stability, with 70% capacity remainin"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 13,
    "chunk_index": 5,
    "text": "remarkable cyclability (maintaining 98% capacity over 10 000 cycles at 20 c). to confirm the feasibility of large-scale production of sodium vanadium fluorophosphate using mechanochemical methods, a kilogram-scale preparation was executed. subsequently, the large-scale synthesized nvpof materials were matched with a hard carbon anode to fabricate a 26650 cylindrical battery, which delivered a high capacity of 1500 ma h g−1 and an energy density of ∼90 wh kg−1. the successful kilogram-scale produ"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 14,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2026 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 chemical f o r m u l a s o f p b a s c o u l d b e d e n o t e d a s naxm1[m2(cn)6]y□1−y·zh2o (0 ≤ x ≤ 2, 0 ≤ y ≤ 1), where m1 = fe, mn, ni, cu, co, zn, etc. ; m2 = fe, mn, co; and □ represents a transition metal coordinated with n and c atoms and [m2(cn)6] vacancies inside the crystal structure, respectively.108 the crystal structures of pbas can be cu"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 14,
    "chunk_index": 1,
    "text": "water.110 the specific capacities of pbas depend on chemical compositions when applied as cathode materials for sibs (e.g., 85 ma h g−1 for a single-electron redox-active site (se-pbas m1 = zn, ni) and 170 ma h g−1 for double-electron redoxactive sites (de-pbas, m1 = mn, fe, co)). taking into account the high average discharging voltage (above 3.0 v vs na+/na), the theoretical energy density of de-pbas could reach 510 wh kg−1, which is competitive with commercial lifepo4 employed in libs.111 typ"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 14,
    "chunk_index": 2,
    "text": "sites, and (iii) coordinated h2o chemically bonded with transition metals for the absence of [m2(cn)6]. the h2o/vacancies in pbas would cause lattice distortion and even structure collapse during (de)sodiation processes, leading to rapid capacity degradation.112 meanwhile, the irreversible phase transition during charging and discharging process also contributes to the short cycle lifespan. further, low electronic conductivity for poor rate performance of pbas is another obstacle should be overc"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 14,
    "chunk_index": 3,
    "text": "besides of the high content of h2o/[fe(cn)6] vacancies and low electronic conductivity, fe-based pbas also suffer from a low practical specific capacity for the irreversible electrochemical reaction of low-spin fe coordinated with c,114 and the mnbased pbas suffer from the jahn−teller effect of mn3+ and the dissolution of mn2+.115,116 crystal structure control, nonaqueous preparation/dehydration treatment, compositing with conductive carbon, surface coating, and cationic doping are effective app"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 14,
    "chunk_index": 4,
    "text": "initial charge and discharge profiles of (c) mna2−δmnhcf and (d) r-na2−δmnhcf. reproduced with permission from ref 110. copyright 2015 acs publications. (e) 2d contour map of in situ high-temperature synchrotron x-ray diffraction patterns of as-prepared na2−xfefe(cn)6 samples under ar and (f) corresponding crystal structures at 40, 270, and 320 °c. reproduced with permission from ref 112. copyright 2022 wiley-vch."
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 15,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2027 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 water and interstitial water reduce the amount of extractable sodium, hinder the migration of na+, and decrease the practical specific capacity.117,118 additionally, the crystal structure of defect-rich pbas tends to collapse during (de)insertion of na+ due to the absence of bulky [fe(cn)6], which deteriorates the electrochemical performance.15 it is do"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 15,
    "chunk_index": 1,
    "text": "temperature for fe-based pbas. our group124 found that fe-based pbas prepared below 0 °c or iced conditions exhibited fewer [fe(cn)6] vacancies than those synthesized at room or high temperature for the decreased reaction rate, which was consistent with the result of ma’s group.125 (iii) preparing a high salt concentration. guo’s group reported mn-pbas fabricated using a saturated na4fe(cn)6 solution displayed only 4% vacancies (24% at traditional condition), and vacancy-free mn-pbas could be ob"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 15,
    "chunk_index": 2,
    "text": "the ultrahigh value about 20 ppm, which was fivefold higher than those in na3v2(po4)3, and resulted in the swell of pouch cell.112 therefore, it is imperative to solve the water problem of pbas to promote their commercial application. normally, preparing pbas in a nonaqueous solution and performing a dehydration treatment after primary drying are effective methods to reduce the water content. 4.1.2.1. nonaqueous preparation. as we discussed above, pbas were prepared in an aqueous solution, makin"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 15,
    "chunk_index": 3,
    "text": "was necessary to dissolve na4fe(cn)6 precursors. to improve the solubility of the precursor and accelerate the reactions in organic solutions, he’s group developed a microwave-assisted solvothermal approach with anhydrous ethanol as the solvent. the microwave supplies external energy, and pbas could be synthesized at a slightly elevated temperature within hours.130 as a result, the content of interstitial water in obtained samples is only 4.34−5.13 wt %, and a high discharging specific capacity "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 16,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2028 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 na2−δmnhcf. meanwhile, the monoclinic na2−δmnhcf (mna2−δmnhcf) converted to the rhombohedral phase (rna2−δmnhcf) after the dehydration treatment due to lattice shrinking and distortion, as shown in figure 10a and b. the electrochemical behavior was also changed after the removal of interstitial water. the m-na2−δmnhcf electrode show two pairs redox peak"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 16,
    "chunk_index": 1,
    "text": "after dehydration.132 furthermore, the relationship between the water content and phase structure of sodiumrich na2−xfefe(cn)6 was systematically studied in our 112 group. as depicted in figure 10e and f, the pristine trigonal phase was maintained when adsorbed water was removed (<150 °c), while cubic and new high-temperature trigonal phases could be found from 220 to 300 °c; the trigonal phase dominated at 270 °c, at which the interstitial and coordinated water faded away. the cubic phase disap"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 16,
    "chunk_index": 2,
    "text": "electrochemical performance of pbas. 4.1.3. compositing with conductive carbon. although the 3d open framework inside the pbas facilitated na+ diffusion, the rate capability of pbas is below expectation for their figure 11. coating layers for pbas: (a) zno (reproduced from ref 137, copyright 2019 royal society of chemistry), (b) coxb (reproduced from ref 138, copyright 2023 wiley-vch), (c) artificial naf-rich cei (reproduced from ref 139, copyright 2022 elsevier), (d) ni-hcf (reproduced from ref"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 17,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2029 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 limited electronic conductivity. compositing pbas with conductive carbon has been considered as an effective strategy to improve their rate performance. hence, considerable research has been devoted to building mesoscopic or nanoscopic interactions between conductive carbon (carbon nanotubes (cnt),113 ketjen black (kb),133 graphene,134 ordered mesoporou"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 17,
    "chunk_index": 1,
    "text": "could be obtained at −25 °c, while it is only 2 ma h g−1 for bare pbas. after that, dou and coworkers synthesized a pb@c composition through a facile and in situ solution method, with nafehcf directly grown on kb chains.133 despite the degraded electrochemical activity of fels(c) caused by [fe(cn)6] vacancies, the perfectly shaped pb@c composition with a lower vacancy content (7% vs 15% for bare pb) and fast charge/na+ diffusion exhibited a higher reversible capacity (130 ma h g−1 vs 90 ma h g−1"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 17,
    "chunk_index": 2,
    "text": "3dnc (8.26 wt %) into nak-mnhcf, contributing to the better rate performance of the nak- mnhcf@3dnc composite compared to the bare nak- mnhcf. therefore, compositing affords a simple solution to resolve the low electrical conductivity for pbas.136 4.1.4. surface coating. it is well acknowledged that pba cathodes suffer from serious capacity fading due to the transition metal dissolution and side reactions between the electrode materials and organic electrolytes. thus, surface coating has been us"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 17,
    "chunk_index": 3,
    "text": "of naxfefe(cn)6 (pb@zno) via a thermal treatment at 200 °c under n2 (figure 11a), which helped reduce the charge-transfer resistance and prohibit the decomposition of the pb lattice.137 in order to suppress the microstructural degradation and undesirable jahn−teller effect, hu’s group recently created a magical coxb on the mnhcf surface through a facile wet-chemical coating method (figure 11b).138 owing to the whole coverage of coxb, the optimal mnhcf-5%coxb cathode displayed limited mn dissolut"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 17,
    "chunk_index": 4,
    "text": "temperature (84.3% capacity retention after 500 cycles) and 55 °c (78.8% capacity retention after 200 cycles) could be acquired at the current density of 100 ma g−1. moreover, the degradation of pbas would induce cracks and even the collapse of the cathode−electrolyte interface (cei), and the newly exposed surface could trigger new cei formation. eventually, a thick and uneven cei was formed and the electrolyte was used up, leading to the death of sibs. therefore, it is of great significance to "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 17,
    "chunk_index": 5,
    "text": "the uniformity was maintained, and the thickness of the cei was approximately 4.8 nm after cycling, which was much smaller than that of pb (∼22.6 nm). 4.1.4.2. stable se-pbas materials. although the aforementioned inorganic coating layers have been proven effective, a lattice mismatch between pbas and coating exists. coating pbas with compounds of similar lattice parameters will eliminate lattice mismatches to a greater extent. among various pbas with different transition metal ions, ni-based pb"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 18,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2030 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 hcf on the surface of pbas through coprecipitation.143,144 (ii) in situ ion exchange. given the fact that the mncnfe group has a higher solubility constant than ni-hcf, it is feasible to coat sodium nickel hexacyanoferrate (pbn) on the surface of sodium manganese hexacyanoferrate (pbm), as shown in figure 11d.115 (iii) one-pot synthesis to obtain epitax"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 18,
    "chunk_index": 1,
    "text": "of mnpb) to imbue the material with phase stability and an ultrahigh capacity retention of 96% after 500 cycles. 4.1.4.3. conductive carbon/polymers. besides inorganic materials and ni-hcf, conductive carbons/polymers, including reduced graphene oxide (rgo),146,147 polypyrrole (ppy),140,148 polydopamine (pda),149 polyaniline (pani),150 and poly(3,4-ethylene dioxythiophene) (pedot),151 could be applied as the coating layers. the conductive carbon/polymer coating has multiple merits: enhancing the"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 18,
    "chunk_index": 2,
    "text": "coordinated with a n atom (fe atom coordinated with c is fixed in most cases) or an alkali element. it is confirmed that the species or amount of doping metal has a significant influence on the structural stability and electrochemical behavior of pbas. therefore, ingenious regulation of the doping level is crucial for electrochemical performance improvement. the studies on transition metal doping are mainly focused on de-pbas (fe-hcfs and mn-hcfs) with high specific capacities but insufficient c"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 18,
    "chunk_index": 3,
    "text": "was found that 3% ni substitution in fe-hcf could increase the low spin fels capacity contribution from 28% (27 ma h g−1) to 43% (50 ma h g−1).152 meanwhile, yang’s group reported that 11% zn substitution in fezn-pb delivered a higher low spin fels capacity of 60.5 ma h g−1, which was higher than that of fe- pb (50 ma h g−1) at current density of 20 ma g−1.154 in addition, it was demonstrated in our group that a sample with 36% zn substitution shows minor lattice distortion for the simplified an"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 19,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2031 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 tetragonal.158 as for mn-hcf, a dramatic capacity decay is observed due to the jahn−teller distortion of mn3+, and a 10% decrease in mn−n distances could be detected after a full charge.159,160 the effects of doping fe, co, and ni for the cycling and rate performance of mn-hcf have been investigated in shibata’s group.161 they found that the lifespan an"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 19,
    "chunk_index": 1,
    "text": "in order to further enhance the electrochemical performance, multication lattice substitution has been employed.164,165 high quality (hq)-nixco1−x[fe(cn)6] pbas were synthesized through a chelating agent (trisodium citrate)/surfactant (polyvinylpyrrolidone, pvp) coassisted crystallization method with fewer [fe(cn)6] vacancies and water molecules in han’s group.166 as a result, the optimized sample (x = 0.3) exhibited a high specific capacity of 145 ma h g−1 and prolonged cyclability of 90% capac"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 19,
    "chunk_index": 2,
    "text": "m1 site for sib were first reported by brezesinski’s group.168 the equimolar fractions of above five metal cations increased the structural stability and configurational entropy and suppressed the degradation of pbas cathodes at high voltages. after that, a link between the high-entropy effect and the observed energy storage capabilities of mn-hcf was established for the first time. by systematic comparison of the structural and chemical properties of high-, medium-, and low-entropy mn-hcfs, bre"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 19,
    "chunk_index": 3,
    "text": "(a capacity retention of 79.2%) was achieved. owing to the large family of pbas, the reversible figure 13. figure for the development prospects of cathode materials in sibs. top left image reproduced with permission from ref180. copyright 2023 springer nature. top right (center) image reproduced with permission from ref 181. copyright 2019 wiley-vch. far right image reproduced with permission from ref 185. copyright 2021 royal society of chemistry. bottom left (center) image reproduced with perm"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 20,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2032 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 (de)insertion of an alkali ion can be allowed, and k+ insertion has been confirmed to exhibit the best reversibility with the highest potential.171 therefore, most researchers are forced on k+ doping to improve the structural and electrochemical stability.172,173 a low concentration of k+ in naxkyfehcf samples would expand the pba framework structure an"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 20,
    "chunk_index": 1,
    "text": "and nanocubic morphology compared to the sample without k-doping. a facile “potassium-ions assisted” strategy was developed by our group to prepare highly crystallized fe-based pbas by controlling the crystal phase orientation.176 the optimized product nkpb-3 (na0.28k1.55fe[fe(cn)6]·1.53h2o) displayed a stable structure-orientating (220) plane with fewer [fe(cn)6]4 vacancies and a lower water content. attributed to the highly crystal structure and pillar effect of k+, the as- obtained electrode "
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 20,
    "chunk_index": 2,
    "text": "stability. in this strategy, elements such as fe, co, ni, and sn were adopted. it was worth noting the introduction of both co and ni, as they had dual effects, while taking into account their intake/cost. furthermore, doping k+ into the alkali site is an excellent practice that greatly improves the structural and electrochemical stability. continuous regulation of the introduced solubility is necessary to achieve the best effect for future development. 4.2. scalable preparation. up to now, seve"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 20,
    "chunk_index": 3,
    "text": "= 150 ma g−1), 45 °c (83.5% capacity retention, 300 cycles, 1 c), and −20 °c (92.1% capacity retention, 700 cycles, 1 c). after that, they synthesized mn/ni binary pbas in a high precursor salt concentration of 0.5 mol l−1 (mn0.5ni0.5-0.5), resulting in a higher yield for mass production.178 the result showed that the cycling performance and discharge specific capacity were better than those of the sample prepared at a lower salt concentration. moreover, mn0.5ni0.5-0.5 displayed excellent cyclin"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 20,
    "chunk_index": 4,
    "text": "crystal growth. with the increase of the na3cit concentration, the morphology of na2−xfefe(cn)6 turned to a single microcube compared to irregular particles at low concentration. subsequently, a 5 ah pouch full cell with an asprepared na2−xfefe(cn)6 cathode and hard carbon anode has been assembled, and excellent electrochemical behavior has been achieved (figure 12c). additionally, no sodium compensation was added because the sodium atomic ration in this fe-pba cathode reached up to 1.73. as sho"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 20,
    "chunk_index": 5,
    "text": "polyanion compounds, and prussian blue (analogs), which have different physical and chemical properties and electrochemical performance due to their versatile compositions and crystal structures. the transition metal oxides can be simply prepared and demonstrate high specific capacity and good rate capability, but they are prone to collapse during repeated na insertion/ extraction owing to their fragile crystal structures, which is usually resolved by lattice regulation. polyanionic materials ha"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 21,
    "chunk_index": 0,
    "text": "acs central science http://pubs.acs.org/journal/acscii outlook 2033 https://doi.org/10.1021/acscentsci.3c01022 acs cent. sci. 2023, 9, 2012−2035 addressed before the above three categories of cathode materials showcase their grandeur in the field of large-scale energy storage, as discussed in below (figure 13). (i) developing large-scale synthesis techniques: anode materials, such as hard carbon and silicon, can be easily mass produced with high consistency due to their simple compositions and a"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 21,
    "chunk_index": 1,
    "text": "a cathode electrolyte interface (cei) film during cycling are essential to illustratethe na storage mechanism and guiding the development of the high performance cathode materials. therefore, advanced characterization techniques, such as in situ neutron diffraction, in situ xray absorption spectroscopy (xas), and in situ electrochemical monitoring, should be more intensively adopted. (iii) seeking matching anodes for full-cell study: the assemble of a na full cell must consider the matching betw"
  },
  {
    "source_pdf": "Promising_Cathode_Materials_for_Sodium_Ion_Batteries_from_Lab_to_Application_Shitan_Xu_Huanhuan_Dong_Dan_Yang_Chun_Wu_Yu_Yao_Xianhong_Rui_Shulei_Chou_Yan_Yu.pdf",
    "page": 21,
    "chunk_index": 2,
    "text": "of the na metal anode will be resolved in the near future. (iv) optimizing the construction of sibs: the bipolar electrode design using inexpensive aluminum as a shared current collector can help achieve efficient recycling of electrode materials, and the absence of alloying reaction between na and al is the foundation of this design. although the construction of sibs with a bipolar electrode may render a lot of advantages, including higher specific (volumetric) energy density, excellent high-ra"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "according to the reports of ‘‘top ten emerging technologies in chemistry 2022” released by the international union of pure and applied chemistry, sodium-ion battery (sib) technology is identified as a crucial emerging technology, indicating its promising development for future energy-storage applications [1]. in practical applications, commercialized lithium-ion batteries (libs) with lithium cobalt oxide and ternary oxide as cathode materials have assumed a dominant position [2]. however, these "
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "technologies. generally, cathode materials in sibs mostly include fe, mn, cu, and other elements due to their high reactivity and cost-effectiveness for redox reaction during charging/discharging operations and also to further eliminate the dependence on co and ni, which are less abundant and more expensive. for hard carbon, which is the common anode material for sibs, the process requirements are significantly less stringent and sufficiently competitive. however, cheaper aluminum (al) foil can "
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "include distributed grid energy storage, low-speed transportation, communication stations, and other applications where high energy density is not a primary concern. although there are multiple technological approaches for developing sibs, the business model for their technology is still in the mapping phase. developing the process and industry chain for sibs is still in its infancy, and the main challenge is the lack of supply channels for core electrode materials and electrolytes. in addition,"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "widely believed that the sib manufacturing industry will experience a rapid expansion within the next 3–5 years. the operating principle of sibs is similar to that of libs. during charging, positively charged na+ migrates from the cathode and diffuses through the electrolyte and separator before being inserted into the anode [4]. simultaneously, electrons move from the cathode to the anode through an external circuit, and the charging capacity of the battery increases as more sodium ions are ins"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "low cost, chemical and thermal stability, and safety. tmos have a structural formula of naxmeo2, where me represents one or more transition metals that include mn, fe, ni, co, fig. 1. (color online) component-built and classified materials for sibs. v, cu, and cr; tmos can be categorized as tunnel-type or layered oxides based on their crystal structure. when the sodium content is high, the layered phase is generally dominant, primarily composed of meo6 octahedra stacked in lamellae with shared e"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "phase oxides are considered the trend for future industrialization, as p2 phase oxides, which usually have large layer spacing, can provide many na+ storage sites and ensure fast na+ transport. furthermore, during charging and discharging, the structure of the p2 phase compound changes as na+ is embedded and removed. especially while charging too high voltages, the p2 structure is susceptible to a complex p2-o2/op4 transition as large amounts of na+ are removed from the layer structure, leading "
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "z.-y. gu et al. science bulletin 68 (2023) 2302–2306 2303 typically used [7]. therefore, how to maintain the structural stability of p2 during cycling becomes one of the key issues in the preparation of high- performance cathode materials for sibs. moreover, the p2 phase oxides are na- poor compounds, which limits their capacity, particularly during the first-cycle charging process, necessitating supplementary sodium sources for soft-pack battery assembly. conversely, the p2 and o3 phases contai"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "of the oxide surface are the most prevalent solutions. the problem of residual alkali issues on the surface can lead to reduced electrochemical properties and make the coating process more difficult. nevertheless, both p2 and o3 phase compounds face table 1 multidimensional intuitive comparison of p2 and o3 phase oxides. p2 o3 structure stability worse after deep sodium removal prone to phase transition air stability excellent poor sodium content lean rich capacity low high rate and cycle perfor"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "market is advancing much faster than that of the same period, and some products have already successfully entered the market. the air stability of o3-phase materials in layered-oxide systems and inhibition of phase transition during charging and discharging is a pressing issue that must be addressed in future studies. pbas are represented by the molecular formula naxma[mb (cn)6]1yhynh2o (0 x 2 and 0 y 1), where ma represents fe, mn, ni, etc. ; mb represents fe or mn; and h represents the defect "
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "addition, the crystalline water and mb(cn)6 defects in pbas may considerably affect the structural integrity, posing a critical obstacle in their industrialization [8]. there are several methods for preparing pbas, including co-precipitation, gradient substitution co-precipitation, single heat source method, and hydrothermal methods. pbas prepared by precipitation techniques are typically synthesized in an aqueous solution, leading to trace amounts of crystalline water retained in the final samp"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "and cycling stability. to achieve pbas with high energy density and long cycling stability, optimizing the synthesis process, utilizing multielement synergistic modulation of transition-metal sites, and implementing surface/ interface modification strategies are essential. during the electrode coating process, the crystalline water in pbas causes the slurry to settle, resulting in poor adhesion between the slurry and the current collector. in particular, when performing electrode sheet extrusion"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "progress of industrialization. for the future industrialization of pba materials, the main challenges are to improve the compaction density of pbas and reduce the reactive water content. pacs are represented by the general formula naxmy[(xom)n]z, where m represents transition-metal ions such as fe, v, mn, ti, and cr, and x represents p, s, si, etc. these compounds with stable polyhedral frameworks provide excellent cycling and thermal stability. in addition, the polyanion units of pacs have uniq"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 6,
    "text": "pacs include the iron-based phosphates nafepo4, na2fe2(so4)3, and na4fe3(po4)2p2o7 and the vanadium- based phosphates na3v2(po4)3, na3v2(po4)2f3, and na3v2(po4)2o2f. fe-based pacs have the advantages of environmental friendliness, low cost, and excellent cycling stability. however, the lower redox potential of iron limits the energy density of the battery, and thus fe-based pacs may be more widely used in large-scale energy-storage fields in the future [9]. among the febased pacs exemplified abo"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 7,
    "text": "density and a wider range of applications. therefore, they are considered the most promising candidates to replace lifepo4 batteries in the future. furthermore, v-based pacs are simple to prepare and exhibit excellent thermodynamic, cycling, and air stability. nevertheless, v-based pacs face the challenges of toxicity and high ingredient costs. therefore, for the large-scale application of vbased phosphates, it is imperative to establish a systematic vanadium recycling process to reduce environm"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 1,
    "chunk_index": 8,
    "text": "the technology exploration process, reduce production costs, and greatly advance the industrialization of pacs. for the future industrialization of phosphate systems, the key challenges are to improve the electronic conductivity of the material and further reduce its cost. among the current mainstream anode materials for sibs, alloys and transition-metal oxides/sulfides with high-capacity features face difficulty in achieving large-scale applications due to their high dependence on precise nanos"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "z.-y. gu et al. science bulletin 68 (2023) 2302–2306 2304 commercialization potential. the structure of soft carbon is conducive to ion intercalation and sodium storage, which can enhance the specific capacity at various rates [10]. the specific surface area and surface defects of soft carbon are relatively low, which can reduce the consumption of ester-based electrolytes and improve the ice. however, the sloping capacity accounts for most of the total sodium storage capacity, limiting its energ"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "and electrolytes during sodium storage are difficult to detect dynamically. further, it is difficult to conduct microscopic quantitative analysis of electrochemical reactions, even when combined with existing in situ techniques. the disordered structure limits the migration of sodium ions, resulting in the failure of hard carbon and difficulty in achieving the expected rate performance [11]. therefore, it is imperative to employ more advanced detection technologies in designing hard carbon mater"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "sodium storage capacity, reducing the operating voltage plateau, improving the initial coulomb efficiency, and optimizing the rate performance should be the focus. electrolyte, as the ‘‘blood” of sibs, exhibits electronic insulation and ionic conductivity characteristics and plays a crucial role in charge transfer between the cathode and anode, enabling the battery to cycle repeatedly during charge/discharge processes [12]. furthermore, electrolytes significantly affect the battery performance, "
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "electrolytes, represented by nafsi and natfsi, have garnered attention in sodium metal/ion batteries. the solvent mainly consists of carbonate esters and ether types; a mixture of carbonate esters (linear carbonate esters, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and cyclic carbonate esters, ethylene carbonate, propylene carbonate) is currently the mainstream formula because it can meet the basic requirements of most materials. ethers (ethylene glycol dimethyl ether, bis(2-m"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "interphase/cathode/electrode interphase derived on the cathode and anode surfaces affect and improve the overall electrochemical stability window. compared with liquid electrolyte, solid-state electrolyte exhibits higher safety [16], longer lifespan, and lower self-discharge, and can also work over a broader temperature range. solid-state electrolytes can effectively reduce the interface side reaction and self-discharge effect. thus, sodium metal can be used as the anode to further enhance energ"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 5,
    "text": "electrolytes, the superior interfacial stability between polyethylene oxide (peo)-based solid-state electrolytes and metal anodes may make peo-based solid-state electrolytes the most commercially promising products. current research on sibs separators is relatively limited, primarily focusing on polyolefin separators, functional polymer separators, and glass fiber separators. polyolefin separator has been mass produced on a large scale with balanced performance, but problems such as thermal stab"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 6,
    "text": "cost, thick material and low tensile strength [18]. therefore, the development of separator material has to balance cost, safety, and performance. both the current collectors for the cathode and anode of sibs can use inexpensive al foil, whose advantages, such as relatively lightweight and good electrical conductivity, are beneficial for producing high energy density sibs [19]. however, owing to highpotential operation, electrolyte erosion, and dendrite growth, present al collectors can also be "
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 7,
    "text": "to al foil; however, their high cost, poor conductivity, and heavy weight are the issues that need to be solved urgently. likewise, the structural design of the current collectors cannot be ignored. in addition to being cost-effective, sibs offer superior rate performance and can be adapted to responsive energy storage and a scale of power supply. furthermore, the operating temperature range of sibs is broader than that of libs and is generally considered more secure. despite these advantages, c"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 2,
    "chunk_index": 8,
    "text": "kg1. in addition, the optimization strategy can be performed to increase the average operating voltage and the capacity of the cathode, such as enhancing the operating voltage by selecting transition metal with high redox potential and utilizing an anionic group with strong electronegativity. the anode side can further lower the operating voltage or enhance the capacity to improve the overall energy density of sibs. with inexpensive raw materials compared to the lib technology and an abundance o"
  },
  {
    "source_pdf": "Prospects_and_perspectives_on_advanced_materials_for_sodium_ion_batteries_Zhen_Yi_Gu_Xiao_Tong_Wang_Yong_Li_Heng_Kai_Yang_Zhang_Hao_Jie_Liang_Jia_Lin_Yang_Edison_Huixiang_Ang_Peng_Fei_Wan.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "z.-y. gu et al. science bulletin 68 (2023) 2302–2306 2305 sibs will be industrialized after 2025 with production processes similar to that of libs, lower fig. 2. (color online) technology and performance advantages associated with sibs. initial research investment, similar technology in multiple manufacturing processes, and low conversion costs between production lines. furthermore, a solution is required that integrates sibs and libs in a reasonable mix of series and parallel connections and in"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "energy 261 (2022) 125151 r t i c l e i n f o a b s t r a c t keywords: 18650 sodium-ion batteries aging mechanism remaining useful life incremental capacity analysis gaussian process regression accurate prediction of remaining useful life (rul) and management for sodium-ion batteries have great significance, since they are promising for implementation as large-scale energy storage plants in renewable energy systems. in this paper, 18650 sodium-ion batteries are investigated. the observed data fr"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "corresponding to the incremental capacity peak is selected to extract six potential health indicators. to reduce redundant information among various features, the principal component analysis is utilized to obtain the syncretic health indicator. the gpr is established for reliable prediction with a 95% confidence interval. when compared to the traditional methods, the proposed method can achieve higher accuracy in rul prediction with a root mean square error below 1.16%. 1. introduction with the"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "large-scale ess [7]. compared with li, na has advantages of abundance, similar electrochemical properties, and a matured extraction process. the up-to- date commercial libs have a high energy efficiency of around 95% (e. g., lifepo4–li4ti5o12 chemistry with an efficiency of 95%) [8]. in comparison, na-ion batteries (nibs) have a slightly lower efficiency of ~90% [9], but they can remarkably outperform libs from a safety perspective. thus, nibs are being considered another potential candidate for"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "replacing the battery. to this end, it is significant to further investigate the aging mechanism of nibs, which has not been well investigated in the existing studies. considering the characteristics of nibs, we acquired accurate remaining useful life (rul) estimation for optimizing the corresponding battery management system (bms). currently, the research on the aging mechanisms of libs mainly focuses on the loss of lithium-ion and active material and has provided a useful understanding of the "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "salt layer formation affect the storage performance of o3-type layered metal oxide cathodes [14]. however, in polyanion cathode systems such as na3v2(po4)3 (nvp), the material undergoes two phase reaction during charge and discharge processes for sodium storage. no specific surface abbreviations acronyms ann artificial neural network ap area of peak bms battery management system bpnn back propagation neural network ce coulombic efficiency dc discharge capacity ess energy storage system elm extre"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "sei solid electrolyte interphase svm support vector machine phase transition is observed. considering the larger radius of sodium-ion compared with li-ion, using sodium-ion might cause huge volume expansion and sluggish reaction [15]. as a typical polyanionic compound, phosphate is not only easy to be industrially synthesized, but also able to ensure safe performance [16]. nasicon type nvp could offer a high voltage of ~3.37 v (vs. na+/na), which has been proved to be an excellent sodium storage"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "nibs (e.g., ethylene carbonate, propylene carbonate, and dimethyl carbonate). these carbonate- based electrolytes perform well in nibs and have proven to obtain high energy density at high voltage [19]. however, the decomposition of the sei layer and a heat-generating reaction may occur at high temperatures as seen in the differential scanning calorimetry experiments. the flammable and volatile properties restrict the application of carbonate-based electrolytes. to this end, the ether-based elec"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 2 nasicon-type phosphate-based cathode still exhibits significant capacity fading over cycling, and hard carbon (hc) anode also remarkably contributes to capacity fading, rul is a vital metric to evaluate the battery aging state and should be carefully monitored. due to the complex, nonlinear, high- dimensional electrochemical behaviours and various possible external stresses, an accurate rul prediction is still difficult. the rul prediction approaches can "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "and verhulst method [27]. the empirical methods have the advantages of simplicity (i.e., high computational efficiency); however, the accuracy of estimation is limited owing to the phenomenon of divergence. the model-based methods, including kalman filter, particle filter, and cubature kalman filter [28,29], effectively solve the divergence problem and improve the accuracy of rul estimation. however, the battery degradation process involves complex physical and chemical reactions, and it is diff"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "is a non-parametric regression and has been successfully used in many regression domains, owing to the advantages in probabilistic estimation and nonparametric modelling. compared with other methods, such as anns and svm, gpr has great adaptability in dealing with small samples and nonlinear problems [36,37], with a high confidence interval. therefore, the gpr is selected in this study for reliable rul prediction, which is nonlinear and generally subject to limited size of the database for train"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "effective non-destructive analysis method and can convert the voltage plateau caused by the internal electrochemical reaction to the ic peak [43]. meanwhile, the analytical ic peak is related to the phase transition of active material for nibs caused by the intercalation/de-intercalation process [44]. through the analysis of the ic curve of nibs, the height, area, slope, and width can be extracted to investigate the aging mechanism. in this study, the hc-based half-cell, nvzp-based half-cell, fu"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "six potential health indicators are selected, and principal component analysis (pca) is introduced to obtain the syncretic health indicator avoiding redundant information. (3) it is first verified that the ica-based features are also informative for the aging of nibs. in addition, the proposed method is experimentally validated to be accurate and efficient. to the best of our knowledge, this is the first attempt to analyze and predict the rul of nibs. the remainder of this paper is organized as "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "nvzp positive electrode and hc negative electrode along with non-flammable ether-based electrolyte (i.e., nabf4 in 1 m tetraglyme). the detailed synthesis conditions, characterizations, type of materials, and electrochemical performances for 18650 nibs have been illustrated in ref. [45]. specifically, the nvpz was synthesized by the soft template method and the hc was supplied by haycarb plc, sri lanka. the differential scanning calorimetry (dsc) analysis was used to show the improved thermal st"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 6,
    "text": "nvzp vs hc were fabricated in an ar-filled glove box (mbraun, germany; h2o and o2 < 5 ppm) as described in ref. [45]. the 18650 type nibs were assembled in a dry room with less than 1% relative humidity followed by electrolyte filling and crimping in the ar filled glove box. the assembled 18650 nib cells were rested at room temperature for 24 h before testing. this resting process is mainly incorporated to allow electrolyte penetration within the mesoporous positive electrode and negative electr"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 7,
    "text": "cells considered in this article. cycling experiments were performed on the batteries using an arbin bt-2000 at room temperature. specifications for the manufactured nibs and their test conditions are shown in table 1. the assembled hc half-cell was tested at 0.1c within the voltage window of 0.001–1.5 v, and the nvzp half-cell was tested within the window of 2.3–4.2 v at 0.1c. the fabricated full coin cell was charged and discharged at 0.1c in the voltage window of 4.1–1.0 v. for the 18650 cell"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 1,
    "chunk_index": 8,
    "text": "hc is selected as the negative electrode of nibs to enhance the cell capacity density owing to its higher relative capacity and lower voltage plateau. as shown in fig. 1 (a), the second cycle of the specific discharge capacity (dc) of hc half-cell is 250.0 mah/g and the coulombic efficiency (ce) is 99.5% at 0.1c. the specific dc of nvzp half-cell is 99.0 mah/g and the ce is 99.6% at 0.1c, as shown in fig. 1 (b). we found two plateaus at about 3.4 v and 3.9 v during the charging process of nvzp. "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 3 both the half cells (i.e., hc and nvzp) have shown good sodium storage performance and high ce [45]. therefore, the hc and nvzp are selected to manufacture the full coin cell. as shown in fig. 1 (c), the specific dc of the full coin cell is 84.5 mah/g and the ce is 99.4% at 0.1c. the nvzp, hc, and non- flammable electrolyte were selected for fabrication of the 18650 nibs. this paper selected two sample cells for modelling studies, which are denoted as the"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "and discharged with a constant current. as shown in fig. 1 (d), the capacity is larger than 500 mah, and the energy density is about 60 wh/kg. finally, both sample cells were cycled at 0.2c and 0.5c for a total of 200 cycles. as shown in fig. 1(e and f), the capacity retention of the no. 1 and no. 2 cells are approximately 90% and 70%, respectively, and the ce remains high after 200 cycles. 2.2. incremental capacity analysis ica, as an effective non-destructive battery analysis method, has been "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "coin coin cylindrical cylindrical anode hc na hc hc hc cathode na nvzp nvzp nvzp nvzp non-flammable electrolyte ether- based ether- based ether- based ether-based ether-based lower cutoff voltage/v 0.001 2.3 1.0 1.0 1.0 upper cutoff voltage/v 1.5 4.2 4.1 4.1 4.1 charging current/c- rate 0.1 0.1 0.1 0.2 0.5 discharging current/c-rate 0.1 0.1 0.1 0.2 0.5 discharged under unit voltage. this method is able to convert the voltage plateau to ic peak, which indirectly reflects the equilibrium process o"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 4 the ic curves of nibs are calculated based on experimental measurements (i.e., voltage and current). therefore, the shape of the ic curve is sensitive to measurement noise, especially when the derivative operator is incorporated. before analyzing, those ic curves are smoothed and filtered using the existing methods provided in ref. [46], i.e., the savitzy-golay filter. the points of the window are set as 10 and the polynomial order is set as 2. based on t"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "sodium storage at a lower voltage plateau [47]. the charging ic curve of nvzp half-cell is shown in fig. 2 (b), and there is an obvious ic peak around 3.410 v, correlated to the main voltage platform by the charging curve (v3+ → v4+) [16,45]. the main peak appears at about 3.945 v, corresponding to the high voltage platform by the charging curve [45]. as shown in fig. 2 (c–f), we can find that there are three ic peaks in the charging/discharging curves of the full cells. the peak ❶ may be inferr"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "on the right side of peak ❸, owing to the two independent sodium atoms located in the fig. 1. (a) voltage profiles of hc half-cell at 0.1c, (b) voltage profiles of nvzp half-cell at 0.1c, (c) voltage profiles of nvzp vs. hc full coin cell at 0.1c, (d) voltage profiles of 18650 full-cell at 0.2c, (e) cycle performance of no. 1 18650 full-cell at 0.2c, (f) cycle performance of no. 2 18650 full-cell at 0.5c."
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 5 framework of nvp [16,18]. note that there are similar peaks in the discharging ic curves. for the 18650 nib cell, we can find the three obvious peaks (i.e., ❶, ❷ and ❸) in the charging ic curves. at 0.5c. 2.3. aging investigation based on ica the 18650 nibs were selected for aging experiments with the constant charging/discharging current in the voltage window of 4.1–1.0 v. ica is conducted for converting the internal chemical reactions of nibs to informa"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "sei layer may be formed on the hc surface, accompanied by some losses of na-ion. from the second cycle, area of peak ❶ remains relatively constant with an increasing cycle life until 50 cycles. at 0.2c, peak ❷ has a slight decrease and the corresponding voltage does not change significantly. at 0.5c, it can be clearly seen that the ic curves are shifted to the right. it is shown that the voltage platform of redox couple from v3+ → v4+ is increased because of the internal polarization at larger r"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 6 for peak ❸, a high voltage plateau appears at around 3.9 v, which is attributed to the redox couple of v4+ → v5+ in the different cycles, (d) discharging ic curve of no. 2 cell under different cycles. modified nvp. by comparing different discharging rates (i.e., 0.2c and 0.5c) in fig. 3(b–d), two obvious peaks ② ③ can be obtained, which are similar to the charging ic curve for the same underlying mechanisms. 3. extraction of the health indicators 3.1. hea"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "the cell aging. thus, the feature parameters of ic peak ❷ can be studied to potentially indicate capacity fading, as shown in fig. 3. according to the charging ic curve, we can find that the height and area of ic peak are related to the amount of reaction sodium- ions. specifically, when the peak value and area are reduced the amount of reaction sodium-ions decreases. the correlation between the position of peak and the redox reaction voltage platform shows that the right shift of peak is accomp"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "indirect health indicators, i.e., the height of peak (hp), position of peak (pp), left slope of peak (lsp), right slope of peak (rsp), area of peak (ap), and half width of peak (hwp). the proposed health indicators under different cycles are depicted in fig. 4. 3.2. grey relational analysis the grey relational analysis (gra) is adopted to characterize the correlation between the proposed health indicators and the capacity fading of nibs [48]. the workflow of gra is given as follows: step 1. usin"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 7 step 3. the correlation coefficient ξij(t) is calculated with xi(t) and yi(t) as follows ξij(t) = (5) width of peak line. step 4. the correlation coefficient between input and output sequences is obtained by ρ. the value of identification coefficient is taken as ρ ∈ (0,∞). the identification performance is improved with a decreasing ρ, and when ρ ≤ 0.5463, the best performance of identification is achieved. generally, ρ is set as 0.5 [49]. ∑n rij = ξij(t)"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "redundant information, which may lead to over- fitting effects. therefore, the pca is selected to reduce redundant information for obtaining the syncretic health indicator by reducing the dimensionality and noise of the selected health indicators. the syncretic health indicator will determine the performance of rul prediction, and the steps of the pca algorithm are as follows. step 1. over every n cycles, the health indicators are extracted and clustered in the m − dimension feature matrix. norm"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "x2m ⎟ ⎠ ⋮ xnm (7) step 2. the covariance matrix σ is calculated as follows 1 t σ= x x (8) n step 3. the values and eigenvectors of the correlation coefficient matrix are calculated. step 4. the contribution rate ci and cumulative contribution rate c are calculated, and p is the number of loading vectors. λi ci (9) c ∑ 1,2,⋯,m) (10) i=1λi step 5. the value of p is selected based on the cumulative contribution rate higher than 85% [50]. then, the score matrix of the selected principal components i"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 8 reduces the correlation between the potential health indicators but also improves the credibility of evaluation results [51]. 4. methods 4.1. gaussian process regression the gpr is proposed for reliable and accurate rul prediction. here, the training data is defined as d = (x, y), i.e., x = [ x1 x2 ⋯ xi ] and y = [ y1 y2 ⋯ yi ], where xi represents the ith input value, and yi represents the ith output value. the probability distribution of the function f("
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "n(0,σ2n)). the prior distribution of y is shown in eq. (14), and the prior distribution of the predicted variable y* is shown in eq. (15). ) y i (14) [ ] ([ ] []) yy* ∼ n 00 kk(x*,x) in kk((xx*,,xx**)) (15) , where in is an n-dimensional identity matrix. therefore, the posterior distribution of y* is given in eq. (16). p(y*|x,y,x*) ∼ n(μ*,σ*) (16) y (17) (18) where, μ* is the mean value of test data, and σ* is variance matrix of test data, which reflects the reliability of the estimation. here, "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "each input vector, σ2f is signal variance, and σ2n is the noise variance. the hyper-parameters are optimized using the maximum likelihood estimation function as follows 1 ( ( 2 )) 1 t[ 2 ]− 1 n l=logp(y|x,θ)=2 log det k +σnin − 2y k + σnin − 2 log2π (20) here, the partial derivative of the likelihood function l is obtained for the hyper-parameters and the optimal hyper-parameters are calculated by the gradient method (see eqs. (17) and (18)) to obtain the mean value and variance of the predictio"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "and hwp) are extracted through the ic curves. then, the normalization and correlation analysis are performed on all potential health indicators. to reduce redundant information, pca is employed to obtain the syncretic health indicator. next, the syncretic health indicator and capacity retention are selected to construct training samples and test samples. the squared exponential covariance function is selected as the kernel function in gpr. the hyper-parameters in the gaussian process are obtaine"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "n rmse n (22) / n mae |y* − y| n (23) mape n |y|(24) 4.3. rul prediction results the proposed syncretic health indicator is extracted by ica and pca of nibs. specifically, the six potential health indicators (i.e., hp, pp, lsp, rsp, ap, and hwp) are extracted from the charging ic curve. due to the redundancy between the six characteristic parameters, the pca is used to obtain the syncretic health indicator to improve the accuracy. the rul prediction results for nibs are shown in fig. 6. the firs"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 9 fig. 5. the flow chart of rul prediction based on gpr. reliability. we can see that the proposed method can obtain an accurate rul prediction. although the width of the 95% confidence interval increases slightly in the later stage of rul prediction, it can be seen from fig. 7 (b) that the relative prediction error is mostly below 2%, revealing the high reliability of the proposed method. to further verify the effectiveness of the proposed method, for the "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "40% of data are used as training data, and the relative prediction error is within 3%. when the first 60% of data is used, the relative prediction error is within 2%, revealing that the prediction accuracy is improved with the increasing number of cycles involved in training because more information is available. the good robustness of the proposed method in the rul prediction of nibs is therefore demonstrated. to further show the superiority of the proposed method, the gpr method is compared wi"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "classic single feedforward hidden layer neural network, in which the loss function based on moore penrose’s generalized inverse matrix is selected and minimized to obtain the weight of the output layer [52]. compared with bpnn, the training of elm is a simple linear regression process, which has the advantages of fewer parameters and strong generalization [53]. the key advantage of gpr method is non-parametric, which exhibits good performance for modelling complex battery systems [54,55]. as sho"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "to bpnn-pso and elm (i.e., ~4%). we can see that the gpr method has the highest accuracy among the three methods, validating that the gpr method is applicable for the complex regression problem of nibs (i.e., nonlinearity, high dimension, and small sample). when compared with bpnn and elm, the proposed method has the advantages of the adaptive acquisition of hyper-parameters, ease of implementation, and robust performance. to better demonstrate the superiority of the proposed method, fig. 7 (e) "
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 8,
    "chunk_index": 4,
    "text": "2.55%, following the one of elm which is 2.42%. we can find that the mape of the proposed method is limited below 1.1%. thus, the gpr method can obtain an accurate and reliable rul prediction for nibs. fig. 6. (a) rul prediction results based on ica-gpr, (b) rul prediction error based on ica-gpr."
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "m. wei et al. energy 261 (2022) 125151 10 5. conclusion in this study, the hc half-cell, nvzp half-cell, full coin cells, and 18650 cells are manufactured and analysed with ica. the oxidation process and aging mechanism of nibs are comprehensively discussed. then, six potential health indicators are selected, and correlation analysis is introduced according to the aging mechanism analysis of nibs. in order to reduce redundant information among health indicators, this paper proposes pca to obtain"
  },
  {
    "source_pdf": "Remaining_useful_life_prediction_for_18650_sodium_ion_batteries_based_on_incremental_capacity_analysis_Meng_Wei_Palani_Balaya_Min_Ye_Ziyou_Song.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "for health indicator extraction. the height, area, slope, and width are selected as indirect health indicators. the pca is introduced to obtain the syncretic health indicator. (3) in comparison with the traditional methods, the gpr method exhibits higher accuracy with a 95% confidence interval and good robustness for rul prediction, with the rmse, mape, and mae limited below 1.16%, 1.10%, 0.83%, respectively. in the future, more experiments on nibs under various operation conditions will be cond"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "a r t i c l e i n f o a b s t r a c t keywords: p2-na0.67mn0.67ni0.33o2 na+/vacancy ordering p2-o2 phase transition optimizing components interface control structural design the p2-na0.67ni0.33mn0.67o2 material, renowned for the high sodium-ion (na+) diffusion rate and conductivity, exhibits remarkable rate capability and cycling performance, making it a promising candidate for the cathode of sibs. however, the performance of the p2-na0.67ni0.33mn0.67o2 cathode is hindered due to high-voltage ph"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "designs are reviewed comprehensively. finally, some insights on the innovative research direction, potential modification strategies, and development trends of p2- na0.67ni0.33mn0.67o2 cathode are presented. this review will supply a reference for the component regulation and structural design of the p2-na0.67ni0.33mn0.67o2 cathode, expected to facilitate the practical application of the p2-type layered oxide cathodes. 1. introduction with the rapid development of new energy vehicles, consumer e"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "wide attention [3]. compared with lithium-ion batteries, sibs have the following advantages: 1. sodium resources are evenly distributed, rich in content, and low in cost. 2. sodium and aluminum do not undergo an alloying reaction, enabling the utilization of cost-effective aluminum foil as a negative current collector, while also facilitating the design of bipolar batteries for enhancing energy density. 3. sibs have relatively stable, safe, and reliable electrochemical performance, enabling them"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "applicable in the low- speed electric vehicle market to gradually replace traditional lead-acid batteries. it can be used with lithium-ion batteries to reduce the cost of the entire battery pack, which can alleviate the limited development of energy storage batteries caused by the shortage of lithium resources to a certain extent [6]. sibs are a type of rechargeable battery that primarily operates through the movement of sodium-ions between the cathode and anode (fig. 1b). their working principl"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "include co, ni, fe, mn, cr, cu, and v, et al. [8] (fig. 1c). the structure of sibs is similar to that of lithium-ion batteries, comprising cathodes, anodes, separators, electrolytes, and current collectors. taking a full battery assembled with a layered material naxtmo2 as the cathode and hard carbon as the anode as an example, the specific charge–discharge reaction process is as follows: cathode reaction: naxtmo2 ↔ y na+ + nax-ytmo2 + y e− anode reaction: y na+ + n c + y e− ↔ nay cn overall rea"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "sibs, transition metal oxides [10], prussian blue analogues [11], and polyanionic compounds [12] are currently under extensive research. transition metal oxides (naxmeo2) can be classified into layered transition metal oxides with a higher sodium content (x > 0.5) and tunnel-type transition metal oxides with a lower sodium content (x < 0.5). various tunnel oxide materials, represented by na0.44mno2, possess mutual support from mn-o octahedra (fig. 2a). during the process of sodium ion embedding "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "and a three-dimensional porous structure (fig. 2b), which can accommodate the free and rapid insertion/extraction of sodium-ions, thereby effectively enhancing the electrochemical performance of sibs [20,21]. however, the removal of interstitial water poses significant difficulties, while the inevitable lattice distortion during charge–discharge cycles and the jahn-teller effect of mn3+ contribute to low capacity retention and compromise the cycle stability of materials [21–24]. polyanionic comp"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 2 by poor electrical conductivity. furthermore, elements like v and f exhibit high toxicity, posing potential safety hazards [26,27]. among various fig. 1. (a) price trend of sodium carbonate and lithium carbonate from 2005 to 2019. inset: percentage of price changes for both materials over the past 10 years [2]. (reproduced from ref. [2] with permission from wiley, copyright 2020). (b) illustration of a sodium-ion battery system [7]. ("
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 3 fig. 2. (a) crystal structure of na0.44mno2 [17]. (reproduced from ref. [17] with permission from nature portfolio, copyright 2015). (b) framework of prussian blue analogues [11]. (reproduced from ref. [11] with permission from royal society of chemistry, copyright 2012). (c) crystal structure of phosphate-based compounds with fe: triphylite-type na(li)fepo4 [25]. (reproduced from ref. [25] with permission from wiley, copyright 2017)."
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "of this article.) cathode candidates, layered transition metal oxides (naxmeo2, me representing co, fe, mn, cr, ti, etc.) are widely regarded as promising cathode materials due to their advantages of easy preparation, dense crystal structure, high theoretical capacity, and excellent comprehensive properties [28–32]. studies on layered transition metal oxides have been reported since the 1980s [33]. in the layered structure, oxygen atoms serve as the backbone, forming a layered framework where tr"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 4 surrounding oxygen atoms to form mo6 polyhedral layers and alkali metals are coordinated with six surrounding oxygen atoms to form nao6 alkali metal layers. the polyhedral layers and alkali metal layers alternate, resulting in a layered structure (fig. 2e). in 1980, delmas et al. [33] classified sodium-based layered oxides into o3, o2, p3, and p2 types based on the arrangement of sodium-ions within the layered metal structure and the "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "metal oxides, binary metal oxides, and ternary metal oxides. during the deintercalation/intercalation process of sodium-ions in single-metal oxides, structural changes occur, leading to rapid capacity decay. binary metal oxides exhibit synergistic effects among different metals with a focus on combinations of fe, ni, co, and mn. ternary metal oxides primarily include ni-co-mn and ni- fe-mn systems. layered oxide materials possess high sodium-ion insertion/extraction rates due to their open two-d"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "structural changes, impacting cycling performance [35,36]. 2. during charging and discharging, changes in sodium-ion concentration within the cathode material lead to structural rearrangements of sodium-ions/sodium- ion vacancies at different concentrations, causing phase transformations that affect the electrochemical performance and cycling stability of the oxide [37,38]. 3. in the process of charging and discharging, the interface between the cathode and the electrolyte is prone to side react"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "structural design, and multiphase composites to enhance battery performance [42,43]. among the three major routes for cathode materials in sibs, layered oxide cathodes of transition metal oxide materials exhibit the most outstanding comprehensive performance [28]. with the further development and design of new materials, sibs possess promising application prospects in new energy low-speed transportation, large-scale energy storage, construction machinery, and other areas. consequently, the indus"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "slippage, forming new trigonal prismatic sodium sites, and transforming into the p3 phase. conversely, when na+ is extracted from the p2 phase, the repulsive force between adjacent oxygen layers increases, leading to the slippage of the transition metal layers to form the new octahedral sodium sites and transform into the o2 phase. typically, the determination of whether an oxide is p-type or o-type can be achieved by exposing the oxide to an oxygen atmosphere under a certain pressure and measur"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 5,
    "text": "o- na-o bond angle (or equivalently, the geometric configuration parameter d). conversely, by increasing the na content, the screening effect of electrostatic repulsion between tmo2 layers is strengthened, weakening the direct interaction between layers and thereby promoting the formation of the more stable o3 crystal structure [45]. in general, when the na content ranges from 0.7 to 1.0, it tends to form the o3 phase with an abcabc stacking pattern, where na+ is located at the center of the oct"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 6,
    "text": "although the characteristic endows the material with specific electrochemical properties, it also accompanies a higher diffusion energy barrier, making the migration of na+ ions particularly challenging. the design intent behind high sodium content is to enhance the material first-charge capacity, yet it poses even more formidable challenges to the ion transport dynamics of the material. the o3-structured layered transition metal oxides incorporate abundant and cost-effective iron or manganese e"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 7,
    "text": "structural instability directly affects the cycle of the battery. furthermore, the presence of mn3+ ions can induce the jahn-teller effect, causing distortion of the crystal structure and further exacerbating performance instability. lastly, under high-voltage operating conditions, undesirable chemical reactions at the material interface occur, not only reducing the capacities of batteries but also significantly slowing down ion migration rates, and limiting the fast-charging performance of batt"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 3,
    "chunk_index": 8,
    "text": "a lower diffusion barrier, providing favorable transport channels for na+ ions, resulting in superior kinetic performance, higher ionic conductivity, and environmental friendliness. additionally, it is easily synthesized and possesses an excellent specific capacity [50,51]. compared to o3-type layered oxide materials, p2-type materials exhibit better rate performance and cycle stability. however, due to their lower initial sodium content, p2-phase materials tend to have a relatively lower availa"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 5 testing, the performance of p2-type layered structure materials in terms of operating voltage and structural stability is less than satisfactory. the main reasons include: 1. the p2-o2 phase transition during cycling at high voltages (>4.2 v) results in significant volume changes, leading to particle cracking and exfoliation. notably, the o2-type structure cannot be converted back to the p2- type, causing irreversible capacity loss [4"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "acidic environment, mn3+ undergoes a disproportionation reaction (2mn3+ → mn2+ + mn4+), and mn2+ is easily dissolved in the electrolyte. to enhance the cycle stability of the materials, doping with metal elements is commonly employed to address the issues of low operating voltage and poor structural stability at high voltages [56]. for most p2- phase layered cathode materials for sibs, the major phase transitions during charging and discharging involve the irreversible transformation from p2 to "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "delmas et al. [59] discovered through coupled electrochemical processes and in-situ x-ray diffraction (xrd) that p2-naxcoo2 has a reversible specific capacity of 110 mah g− 1 within the operating voltage range of 2–3.8 v. during charging and discharging, multiple charge/discharge platforms emerge with the na+ concentration varies, indicating the formation of na+/vacancy ordered structures. this complex phase transition process and ordered structure will affect the structural stability during the"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "coupled with a low actual capacity. the extensively studied p2-type layered transition metal oxide is primarily p2-type manganese-based transition metal oxide naxmno2. p2- na0.6mno2 demonstrates a reversible specific capacity of 150 mah g− 1 within the operating voltage range of 2–3.8 v, which is characterized by high working potential (na+/na), high capacity, low price, and simple preparation [64]. due to the low cost and abundant manganese sources, naxmno2 has been widely researched for use as"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 4,
    "chunk_index": 4,
    "text": "can further lead to the collapse of the material structure. in p2-type manganese-based layered transition metal oxides, the jahn-teller effect caused by mn3+ alters bond lengths and angles, further inducing lattice distortions, damaging the material structure, and resulting in rapid capacity decay. in acidic environments, the disproportionation reaction of mn3+ (2mn3+ → mn2+ + mn4+) generates mn2+, which is easily soluble in electrolytes. the problems mentioned above and other issues such as sid"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 6 combining the characteristics of various transition metals and learning from each other. p2-type multilayered transition metal oxide materials usually include p2-na2/3fe1/2mn1/2o2, p2-na2/3mn1/ 3co2/3o2, p2-na2/3cu1/3mn2/3o2 and p2-na2/3ni1/3mn2/3o2. p2-na2/3fe1/2mn1/2o2 material has a low cost, a theoretical specific capacity of up to 190 mah g− 1, and an average operating voltage of 2.75 v [67]. with high theoretical capacity and ec"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "irreversible transfer of fe in the charging state affects the diffusion of na+ in the lattice. consequently, these materials exhibit pronounced voltage hysteresis [75,76] and poor air stability [77]. p2-na2/3mn1/3co2/3o2 cathode material has a reversible specific capacity of 112 mah g− 1 in the voltage range of 1.5–4.0 v. it has a smoother charge and discharge curve compared with p2-naxcoo2 and naxmno2 materials and shows good stability under high voltage [78,79]. in the charging process, co cha"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "materials [78,80,81]. in addition, the limited cobalt resources and the single supply channel make its price increase, and cobalt element is toxic, which makes various cobalt-free materials show better application prospects [79,82]. p2-na2/3cu1/3mn2/3o2 is a kind of cathode material based on cu3+/ cu2+ redox pair. due to the low cost and environmental friendliness of copper, cu- based electrode materials have also been studied [83–85]. with an average working voltage of 3.7 v, p2-na2/3cu1/3mn2/3"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "fe-mn base, co-mn base, and cu-mn base oxide materials, ni-mn base oxide materials (p2-na2/3ni1/3mn2/3o2) have better comprehensive properties, which has attracted wide attention [7,86–89]. on the one hand, the ni2+/ni3+ and ni3+/ni4+ redox electron pairs not only simultaneously elevate the operating voltage and energy density of the material but also suppress the structural distortions caused by the jahn-teller effect of mn3+ [7,88,89]. on the other hand, compared with other sodium-ion battery "
  },
  {
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    "page": 5,
    "chunk_index": 4,
    "text": "close to the theoretical capacity of 173 mah g− 1, and an operating potential of 3.63 v [90]. the material boasts advantages such as high specific capacity and operating voltage, high ionic conductivity, low cost, and good air stability, making it a promising material with significant development potential. although ni-mn base materials have advantages in energy density, rate performance, safety, and low-temperature performance, in research and practical applications, they also show a tendency t"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 5,
    "chunk_index": 5,
    "text": "x < 1/3, the material exists as a coexistence of the p2 and o2 phases. liu et al. [88] synthesized the layered p2- na0.67ni0.33mn0.67o2 (fig. 3b) via the sol–gel method. their research demonstrated a strong dependence of the electrochemical performance of the material on the cutoff voltage. when the cutoff voltage was set at 4.5–1.5 v, capacity fading occurred due to the p2-o2 transition under high voltage conditions, electrolyte decomposition, and the redox reactions involving the mn4+/mn3+ ion"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 5,
    "chunk_index": 6,
    "text": "reactions and sluggish na+ diffusion kinetics exacerbate the decay of electrochemical performance, severely limiting the practical applications. 3. issues and mechanism analysis of p2-na0.67ni0.33mn0.67o2 3.1. structural phase transition in high-voltage region during the charge–discharge process of layered transition metal oxides, the transition metal layers undergo a certain degree of layer sliding as na+ ions are continuously inserted/extracted, exhibiting complex phase transitions in the mate"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 7 as observed from in-situ xrd (fig. 4b and c), the (001) and (101) peaks shifted towards lower angles during the initial charge–discharge cycle, while the (110) and (112) peaks shifted towards higher angles, indicating that the c- axis expanded while the a-axis contracted during charging [35]. before reaching a charging voltage of 3.9 v, the material retained the p2 phase structure with na+ content ranging from 0.33 to 0.67. however, w"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "was lost, leading to c-axis expansion due to electrostatic repulsion between the oxygen atoms. as the amount of extracted na+ increased, the electrostatic repulsion promoted relative sliding between adjacent layers. transition metals might slide from a-sites to b-sites or c-sites, and na+ shifted from original trigonal prismatic sites to octahedral sites (fig. 4d). due to the randomness of interlayer sliding, the p2-o2 phase transition is often accompanied by significant stacking faults, explain"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "inside the particle is not uniform, and the crack generation and further expansion are promoted. with the multiple charge and discharge cycles of the battery, the material continues to experience volume expansion and contraction, resulting in the accumulation of internal stress of the particles and eventually leading to obvious cracking and spalling of the particles, which seriously affects its cycle stability. 3.2. na+/vacancy ordering layered oxides typically exhibit three types of ordering: 1"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "[55]. when the ratio of transition metal ion radii is less than 1.15 and the substitution amount exceeds 1/6, the distribution of transition metal ions is considered disordered. in p2-na0.67ni0.33mn0.67o2, the radius of ni2+ is 0.069 nm, and that of mn2+ is 0.083 nm, suggesting that the material exhibits positional ordering of transition metals. 2. charge ordering of transition metal ions. charge ordering is determined by the redox potential (fermi level) of the transition metals. a small differ"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 6,
    "chunk_index": 4,
    "text": "is small, enabling the formation of a na+ superlattice structure. conversely, a larger potential difference favors a disordered arrangement, promoting na+/vacancy disorder. fig. 4. (a) charge-discharge curves of p2-na0.67ni0.33mn0.67o2 under a voltage range of 2.0–4.5 v. (b) in situ x-ray diffraction patterns of p2-na0.67ni0.33mn0.67o2 during the first charge– discharge process. (c) the xrd pattern of p2-na0.67ni0.33mn0.67o2. (d) schematic diagram illustrating the high-pressure phase transition "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 8 in layered oxide structures, na+/vacancy ordering often occurs due to the high diffusion rates of na+ ions and electrons. as the sodium content changes, the distribution of cations also varies, leading to structural rearrangements and the formation of new superlattice phases. additionally, in the p2 phase, na+ ions occupy two distinct sites: nae (1/ 3 2/3 1/4) and naf (0 0 1/4) (fig. 5a and b). the nae site has a lower energy and is t"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "novel na+/vacancy configurations at x = 1/3 and 1/2, where na+/vacancy ordering frequently occurs when the sodium content is 1/3, 1/2, 5/8, or 2/3. this phenomenon disappears for x < 1/3, indicating that the voltage plateau around 3.5 v corresponds to structural transitions between x = 1/3 and x = 2/3 configurations (fig. 5c-e). for instance, p2-naxcoo2 exhibits voltage jumps at sodium contents of 1/2 and 2/3, located near 3.45 v and 2.8 v, respectively. the ordered distribution of na+/vacancies"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "orderliness of transition metal layers can be effectively restrained due to the similar ionic radii and significantly different fermi levels of mn4+ and ti4+, inhibiting the formation of superlattice structures in the na+ layer and creating a disordered arrangement of na vacancies within the sodium layer. it reduces the potential energy difference between nae and naf, significantly enhances the diffusion rate of na+ between transition metal layers, and lowers the migration barrier for na+. there"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "cycling stability of the material but also potentially increase the internal resistance of the battery, adversely affecting the performance. liu et al. [39] first investigated the differences in p2- na0.67ni0.33mn0.67o2 material before and after cycling, revealing that the extraction and insertion of na+ ions in the high-voltage region are accompanied by the dissolution of transition metals, which triggers an irreversible phase transition from the p2 to o2 phase, further contributes to material "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "issue in both lithium- ion and sibs [95]. generally, transition metals such as ni and mn, which exhibit the jahn-teller effect, are more prone to dissolution compared to co. dissolved transition metal ions migrate to the anode and deposit on the side, which not only increases the thickness of the solid electrolyte interphase (sei) film on the anode side, reducing the availability of active na+ ions and increasing the internal resistance of the battery but also continuously catalyzes the decompos"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 7,
    "chunk_index": 5,
    "text": "a strong lewis acid. in an acidic environment, mn3+ undergoes a disproportionation reaction (2mn3+ → mn2+ + mn4+) [96,97], and mn2+ fig. 5. crystal structure of p2-type naxmo2. (a) view parallel to the c-axis with ab | ba stacking of the oxygen sheets. large blue (na1) and yellow (na2) spheres represent sodium-ions at different sites, while small blue (m) and red (o) spheres represent transition metal and oxygen ions, respectively. (b) view parallel to the c- axis with emphasis on the two sodium"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 9 readily dissolves in the electrolyte, leading to continuous degradation of active materials [66,94]. hf reacts with the axial oxygen at the cathode/ fig. 6. (a) schematic figure of the exfoliation during the sodiation and desodiation process of the p2-na0.67ni0.33mn0.67o2 particle [39]. (reproduced from ref. [39] with permission from elsevier, copyright 2016). (b) charge compensation mechanisms in the p2-na0.78ni0.23mn0.69o2 cathode ["
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 10 electrolyte interface, generating h2o. the actual electron count on the o in m− o is insufficient to form h-o because the covalency of the h-o bond in h2o is weaker than that of the m− o bond in the cathode, thereby needing the extraction of electrons from m, leading to an increase in the valence state of m ions. high-valence m ions return to a stable, non-jahn-teller state (e.g., mn4+ → mn2+, ni3+ → ni2+) through direct oxidation of"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "material polarization and rapid capacity decay. as the number of cycles at high voltages increases, active transition metal ions eventually migrate to the anode side, thickening the sei film, hindering na+ diffusion, and catalyzing electrolyte decomposition, further contributing to capacity decay. constructing a protective layer on the surface of electrode materials is a commonly used modification method for cathode materials, which can prevent direct contact between the material and the electro"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "layered cathode materials is achieved through the redox reactions of transition metal ions such as ni2+/ni3+/ni4+ [89,98] and mn4+/mn3+ [91]. among the rechargeable batteries, common 3d transition metal (tm) elements used as redox centers are ti, v, cr, mn, fe, co, ni, and cu [89]. the content of the variable-valence transition metal ions directly affects the energy density of the cathode material. the charge compensation mechanism in sodium-deficient p2- na0.67ni0.33mn0.67o2 is primarily domina"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 3,
    "text": "of holes above the fermi energy level (ep) and electrons below the fermi energy level. for transition metal oxides, the band structure needs to consider the overlap between the transition metal d-orbitals and the oxygen p-orbitals. the overlap results in the formation of two energy bands: a strongly ligand-bound bonding state (m− o) and an antibonding state (m− o)* with metallic characteristics. the redox process in traditional cathode materials only involves the antibonding state (m− o)* with s"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 4,
    "text": "layered oxide limo2, the o/m ratio is 2, and all three 2p orbital electrons of o participate in bonding. however, once the electrons in the antibonding state (m− o)* band are depleted, additional electrons can only come from the bonding state m− o band, and the participation of the latter can affect the structural stability of the material. ma et al. [99] found that the first charging process of na0.78ni0.23mn0.69o2 generated an unusually excessive capacity, primarily originating from the high- "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 5,
    "text": "to a gradient of transition metals from the surface to the bulk. bai et al. [101] proposed that anionic redox was due to the emergence of o(2p) non- bonding orbitals in the material, which could be generated by substituting part of the transition metal m(d) with li, na, and mg. the formation of these o(2p) non-bonding orbitals relied on strong li-o, na-o, and mg-o bonds. substituting transition metals with more electronegative and electrochemically active elements can exhibit enhanced m− o(2p) i"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 6,
    "text": "therefore, avoiding anionic oxygen redox at high voltages or improving the reversibility of oxygen redox in layered transition metal oxide cathode materials is crucial for their future applications at high voltages. 3.5. air stability the p2-na0.67ni0.33mn0.67o2 material exhibits strong hygroscopicity and is prone to chemical degradation in humid air, primarily due to reactions between the transition metal ions in the material and moisture or carbon dioxide in the air [41]. water in the air oxid"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 7,
    "text": "oxides exhibit a strong tendency for water intercalation and hydration phase formation at lower sodium content levels (fig. 6c) [91,104–106]. buchholz et al. [56] synthesized naxni0.22co0.11mn0.66o2 with a p2/p3 mixed structure and investigated the water sensitivity using xrd. they found that at lower sodium content (x <0.33), the presence of h2o significantly increases the interlayer distance, altering the material structure. in contrast, at higher sodium content (x > 0.33), the material exhibi"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 9,
    "chunk_index": 8,
    "text": "utilized neutron/xrd combined with mass spectrometry and thermal analysis to demonstrate that carbonate ions insert into vacancies in the p2- na0.67mn0.5fe0.5o2 structure, resulting in the decomposition during electrochemical charging and causing mn3+ to be oxidized to mn4+. this exacerbates polarization during charging and discharging, resulting in capacity loss. currently, layered transition metal oxides require full dew point control to prevent material transformation during production and st"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 11 between layered transition metal oxides and water/carbon dioxide in the air is critical for future developments in layered oxide cathode materials. 4. modification methods of p2-na0.67ni0.33mn0.67o2 4.1. bulk element doping or substitution the strategy of element doping and substitution can effectively slow down the phase transition process and significantly improve the structural stability of materials. meanwhile, it exhibits divers"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "the material. through the synergistic effect between different metal ions, the cycle stability of the battery can be significantly improved. substituting ni2+ sites with fe3+ can induce a new “z” phase within the high- voltage range, thereby inhibiting the irreversible p2-o2 phase transition that occurs when the material is charged to high voltages. at the same time, the high-priced substitution of fe3+ for ni2+ can make part of mn exist in the form of mn3+, so that mn shows electrochemical acti"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "charge compensation, inhibiting the orderly arrangement of na+/vacancy, and promoting the diffusion of na+. the resulting fe/ti co-doped p2- na0.67ni0.23fe0.1mn0.57ti0.1o2 cathode delivered a high specific capacity of 420 wh kg− 1 within the voltage range of 4.3–2.6 v, accompanied by excellent kinetic performance and structural stability. hasa et al. [114] prepared a p2-na0.6ni0.22fe0.11mn0.66o2 electrode using a co-precipitation method (fig. 7b and c). the full cell sb-c/ na0.6ni0.22fe0.11mn0.6"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 10,
    "chunk_index": 3,
    "text": "at high operating voltages. the formation of fe-(o- o) bonds due to fe doping significantly inhibited oxygen release, reducing the irreversible capacity loss in the first cycle from 25 % to 4 %. the material achieved a high specific energy density of 500 wh kg− 1 and excellent cycle stability, indicating that strengthening the tm-o bonds can effectively limit oxygen release and improve electrochemical performance. substituting cu2+ for ni2+ sites can effectively suppress high-voltage phase trans"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 10,
    "chunk_index": 4,
    "text": "diffax software (fig. 8a). zheng et al. [116] replaced ni2+ with cu2+ to obtain a series of na2/3ni1/ 3− xcuxmn2/3o2 (0 ≤ x ≤ 1/3) samples. in the cycling process, cu2+/ cu3+ also participates in redox reactions, enhancing the stability of the material without compromising capacity. xrd analysis showed that the ex-situ xrd patterns obtained after charging to 4.4 v did not indicate fig. 7. (a) na0.67ni0.23fe0.1mn0.57ti0.1o2 in-situ xrd results [113]. (reproduced from ref. [113] with permission fr"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 12 fig. 8. (a) ex-situ synchrotron xrd patterns of na2/3ni1/4mn2/3cu1/12o2 [111]. (reproduced from ref. [111] with permission from the electrochemical society, copyright 2017). (b) ex situ x-ray diffraction patterns of compounds in the na2/3ni1/3− xcuxmn2/3o2 series after being fully charged to 4.4 v [116]. (reproduced from ref. [116] with permission from american chemical society, copyright 2017). na0.67ni0.1cu0.2mn0.7o2 electrodes col"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "did not exhibit a na+/vacancy ordered structure (fig. 8c and d). the addition of cobalt can adjust the exposed crystal facets of p2- type cathode material, thereby mitigating the irreversible p2-o2 phase transition that occurs under high pressure and stabilizing the structure of naxmno2. the contraction of tm-o and o-o bond lengths and the shrinkage of mo6 octahedra upon co substitution stabilize the framework structure. wu et al. [118] investigated the structural evolution of p2-type manganese-"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "average spacing is 0.56 nm, which is basically the same as the (002) interplanar spacing of the material at the initial voltage. the distortion region is smaller compared to the material without co, indicating that the substitution of cobalt effectively reduces the lattice stress and has a stable layered structure. yuan et al. [119] prepared pure p2-phase na0.67mn0.65ni0.15co0.2o2 microtubes using a sol–gel method and utilized them as cathodes for na+ ion storage. the cv test results showed that"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "balanced ni, co, and mn. compared with similar materials studied previously, the material could be charged to a higher voltage of 4.25 v and exhibited more stable cycling. hou et al. [120] synthesized spherical p2-na2/3[ni0.3co0.1mn0.6]o2 using co-precipitation and solid-state reaction method (fig. 9g). ex situ x-ray diffraction tests showed that when na+ was removed from the cathode material, the peak of (002) kept moving towards the low diffraction angle (fig. 9h-j). it shows that the c-axis h"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 11,
    "chunk_index": 4,
    "text": "process continues, the (002) peaks moved to higher angles, and these shifts of the diffraction peaks are highly reversible, suggesting that active co3+ substitution effectively suppressed the p2-o2 high- pressure phase transition above 4.0 v. electrochemical test results show that the material exhibited a high specific capacity of 161.6 mah g− 1and a voltage of 3.64 v (vs. na/na+),"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 13 right 2019). resulting in an energy density as high as 590 wh kg− 1. this indicates that the p2-na2/3[ni0.3co0.1mn0.6]o2 material replaced by co3+ can exhibit high energy density and show mitigated p2-o2 transformation without reducing the capacity, which improved the structural stability of the material. furthermore, the research revealed that when subjected to a high rate of 10c, the accessible capacity attained approximately 56 % "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "doping with inert elements the introduction of non-electrochemically active elements such as mg [121–123], ti [92,124–126], zn [92,124–126], li [127,128], and al [129] can effectively widen the interlayer spacing of transition metals due to their typically larger ionic radii, which in turn inhibits the occurrence of irreversible p2-o2 phase transitions and stabilizes the p2 phase structure [51]. incorporating ions with ionic radii similar to those of metal ions that cause a decrease in electroch"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "material during charge–discharge cycles (fig. 10a). when 5 % mg is doped into the material, even at a high potential of 4.35 v during charging, the xrd pattern still fully exhibits the characteristic peaks of the p2 phase, demonstrating excellent phase stability (fig. 10b and c). g. singh et al. [131] found that mg-partially doped na0.67ni0.2mg0.1mn0.7o2 undergoes a reversible p2-op4 transition within a voltage range of 2.0–4.5 v (fig. 10d). compared to the irreversible p2-o2 phase transition, t"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "american chemical society, copyright 2021). (g) sem images of the target precursors [ni0.3co0.1mn0.6](oh)2 [120]. (reproduced from ref. [120] with permission from royal society of chemistry, copyright 2019). (h) charge/discharge curves of p2-na2/3[ni0.3co0.1mn0.6]o2 cathodes in half-cells; the dots indicate the used charge/discharge state for the ex situ x-ray diffraction measurement; (i, j) ex situ xrd analysis of p2- na2/ 3[ni0.3co0.1mn0.6]o2 cathodes at various discharge/charge states [120]. "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 14 stability and inhibiting high-voltage phase transitions. ti4+ has a similar ionic radius to mn3+ and a large difference in fermi energy levels. based on the previously mentioned na+/vacancy ordering structure mechanism, ti doping can enhance the electrochemical performance of materials by eliminating na+/vacancy ordering and resisting high-pressure deformation. shi et al. [124] conducted a comprehensive study on the effects of ti4+ i"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 13,
    "chunk_index": 1,
    "text": "the material but also disrupts the originally ordered arrangement of na+ vacancies, effectively inhibiting irreversible phase transitions that may occur during charge–discharge (insertion/extraction) processes. the experimental results are remarkable (fig. 10f-h). specifically, the na0.67ni0.33mn0.52ti0.15o2 material exhibits a reversible capacity of 89.6 mah g− 1 even at a high charge–discharge rate of 5c. moreover, under milder conditions of 0.5c, it retains a capacity of 88.78 % after 200 cyc"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 13,
    "chunk_index": 2,
    "text": "10i-k). pahari et al. [92] synthesized ti-doped nnmo materials using a solid-state method, achieving an initial discharge capacity of 125 mah g− 1. na0.67ni0.25ti0.08mn0.67o2 maintained approximately 83.5 % of its capacity (110 mah g− 1) after 50 cycles within a voltage range of 1.5 v − 4.3 v. by lowering the upper cutoff voltage to 4.1 v, additional capacity from the redox reaction in na0.67ni0.17ti0.16mn0.67o2 was utilized, demonstrating exceptional cycling stability within a narrower voltage "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 13,
    "chunk_index": 3,
    "text": "electrodes [130]. (reproduced from ref. [130] with permission from wiley, copyright 2016). (d) galvanostatic charge/discharge curves in the 2–4.5 v range at 12 ma/g showing 50 cycles for na0.67mg0.1ni0.2mn0.7o2 [131]. (reproduced from ref. [130] with permission from american chemical society, copyright 2016). the electrochemical performance of as- prepared p2-na0.67ni0.33mn0.67o2 and na0.67ni0.33mn0.52ti0.15o2 samples: (e) cyclic voltammetry curves at 0.2 mv s− 1, (f) galvanostatic charge/discha"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 14,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 15 permission from wiley, copyright 2022). performance tests revealed that the na0.66ni0.33zn0.07mn0.60o1.93 sample exhibited superior cycling stability compared to na0.66ni0.33mn0.67o2 both within voltage ranges of 2.0–4.4 v and 2.0–4.1 v. in addition, when examining the na0.66ni0.26zn0.07mn0.67o2 material, it was found that the voltage profile remained stable at voltages exceeding 4.0 v, accompanied by a significant increase in the di"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 14,
    "chunk_index": 1,
    "text": "bonds due to their significant electronegativity. these bonds stabilize structural transitions and lattice oxygen states, effectively suppressing distortions of ni-o octahedral structures during charge–discharge cycles. the enhanced stability also promotes the reversibility of octahedral distortions, conferring superior operating voltage performance and higher capacity retention on the cathode material [98,101]. furthermore, introducing zn2+ ions into the alkali metal layer and subsequently char"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 14,
    "chunk_index": 2,
    "text": "phase transitions. the optimization effect enables na0.66ni0.26zn0.07mn0.67o2 to exhibit superior capacity retention and voltage stability. peng et al. [134] found that zn doping at the alkali metal site acted as an o2− -zn2+–o2− “pillar”, enhancing electrostatic cohesion between adjacent transition metal layers, preventing cracking along the a-b plane of active materials, and inhibiting the formation of the o2 phase during deep desorption (fig. 11b-d). li doping can endow the na+ deintercalatio"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 14,
    "chunk_index": 3,
    "text": "the tm layer, the presence of monovalent li+ enabled more na+ to stably occupy prismatic interstitial sites, maintaining the overall charge balance of the compound. the characteristic was particularly pronounced during charging, as it allowed more na+ to remain within the compound, enabling the p2-type structure to remain stable under high-pressure conditions and effectively delaying phase transitions. ex-situ nmr analysis of samples at various charging/discharging stages revealed that some li+ "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 15,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 16 pillar. the interlayer spacing is ensured, and the o-o interaction is reduced, and the cycle stability is enhanced. in addition, the xps analysis results show that mn maintains the mn4+ state and stabilizes in the structure during the first cycle charging and discharging process, thus inhibiting the jahn-teller distortion of mn3+ and improving the cyclic stability of the material. furthermore, li+ doping enhances the initial sodium c"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 15,
    "chunk_index": 1,
    "text": "(102), and (103) diffraction peaks shifted to higher angles, while the (002) and (004) peaks shifted in the opposite direction during charging, indicating electrochemical oxidation-induced contraction in the a-b plane and expansion of the c-axis due to enhanced electrostatic repulsion between o layers. all shifted diffraction peaks returned to their original positions during discharge, demonstrating the excellent electrochemical reversibility of p2- na0.85li0.12ni0.22mn0.66o2. additionally, the "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 15,
    "chunk_index": 2,
    "text": "(reproduced from ref. [127] with permission from wiley, copyright 2020). magnetization and oxidation state evolution during the desodiation process of ni and o ions in intermediate phases from na10lini3mn8o24 to na3lini3mn8o24. electronic structure evolution on partial density of states (pdos) of the ni 3 deg*, mn 3d t2g, and o 2p orbitals of x = 0 (d), 5 (e), and 7 (f) in na10-xlini3mn8o24 [128]. (reproduced from ref. [128] with permission from american chemical society, copyright 2020). (g) th"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 17 na0.67ni0.33mn0.67o2 matrix to obtain a high-sodium-content p2-na45/ 54li4/54ni16/54mn34/54o2. dft calculations confirmed the magnetization intensities of ni and o ions (fig. 12d-f). upon charging to high voltages, approximately half of the o2− showed an increased magnetic moment to 0.35 μb, while ni magnetization displayed an opposite trend, indicating the reduction of ni4+ and oxidation of o2− , and demonstrating that a small amoun"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 1,
    "text": "of bulk doping and surface modification, enhancing the diffusion capability of sodium-ions and improving the kinetic properties of materials. shi et al. [129] synthesized the p2- na0.78al0.05ni0.33mn0.60o2.50 (fig. 12g). comprehensive analysis using x-ray photoelectron spectroscopy (xps) and energy dispersive spectroscopy (eds) revealed that al doping in al2o3 triggered a dual mechanism of surface coating and bulk lattice doping, which significantly suppressed the irreversibility of p2- o2 struc"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 2,
    "text": "the electrochemical performance of the na0.78al0.05ni0.33mn0.60o2 electrode relative to the undoped electrode. besides, cheng et al. [137] demonstrated that the al doping strategy in na0.6ni0.3mn0.7o2 material significantly enhanced the electrochemical performance through two primary mechanisms: first, promoting oxygen redox reactions and stimulating the oxidation–reduction activity of mn, thereby increasing specific capacity. second, effectively inhibiting undesirable p2-o2 phase transitions du"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 3,
    "text": "non-active ions play an indispensable role as “behind- the- scenes heroes” in the sophisticated construction of cathode materials though indirectly participating in significant redox reaction processes. the main contribution lies in the unique “pinning effect” akin to robust anchors in the microscopic world, deeply embedded within the material structure, and effectively reinforcing the structural stability within cathode materials. the mechanism significantly mitigates microstructural sliding an"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 4,
    "text": "and durable. consequently, the rational selection and modulation of the types and contents of non-active ions in the design and optimization of cathode materials has emerged as one of the crucial strategies to enhance the comprehensive battery performance and extend the service life. 4.1.3. dual-doping modification electrochemically active ions such as ni2+, cu2+, fe3+, and co3+ significantly contribute to the capacity of materials, whereas inert elements including mg, ti, zn, li, and al act as "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 5,
    "text": "regulation of materials science, the flexible integration of the unique advantages of various dopants has emerged as a pivotal strategy for optimizing material performance. co-doping technology, a current research hotspot, aims to explore the potential synergies between multiple ions introduced simultaneously into the same host material. the approach significantly enhances the physical, chemical, and functional properties of materials such as improving conductivity, optimizing thermal stability,"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 6,
    "text": "tm positions. however, some li ions occupy the na layer when the li doping level reaches 0.06, resulting in observable superlattice peaks in the xrd pattern. electrochemical tests (fig. 13b-e) revealed that ti doping alone improved capacity retention compared to na0.67ni0.33mn0.67o2. the introduction of li on top of ti further enhanced capacity retention with optimal doping effects observed at 0.04li and 0.10 ti contents, achieving a capacity retention of 74.2 % after 100cycles. peng et al. [134"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 16,
    "chunk_index": 7,
    "text": "phase transition under high voltage, as evidenced by the selected area electron diffraction (saed) and the corresponding fast fourier transform (fft) patterns of [na0.67zn0.05] ni0.18cu0.1mn0.67o2 (nzncmo) after deep cycling, indicating that well- preserved p2 structure without phase separation significantly improves the cycling stability (fig. 13f and g). huang et al. [140] replaced sodium with magnesium ions to reduce na-layer spacing and acted as a supporting element to prevent irreversible p"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 17,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 18 reader is referred to the web version of this article.) significantly reducing polarization, while inert ti4+ doping disrupted na+/vacancy ordering. the optimized material achieved a high capacity retention of 77.2 % after 300cycles at 2c and delivered 87.5 mah g− 1 at 6c, demonstrating excellent cycling stability and rate performance. in summary, the designed elemental combinations and multi- element doping strategies leverage the c"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 17,
    "chunk_index": 1,
    "text": "continuous improvement in doping strategies but also significantly advances the frontier of high- entropy materials research, leading to a new wave of innovation in materials science. fig. 13. (a) structural evolution of namn, namnt, and namnt-lix [139]. (reproduced from ref. [139] with permission from elsevier, copyright 2020). (b) charge and discharge curves of the first cycle of namn (black) and namnt (red). (c) first charge and discharge curves of namnt (black), namnt-li0.02 (red), namnt-li0"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 17,
    "chunk_index": 2,
    "text": "and sn anode: (h) cycling performance at 1c, (i) rate capability at rates ranging from 0.2 - 6c [140]. (reproduced from ref. [140] with permission from elsevier, copyright 2020). (j) xrd patterns and (k, l) enlarged xrd patterns of nanmof [141]. (reproduced from ref. [141] with permission from elsevier, copyright 2022). (for interpretation of the references to colour in this figure legend, the"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 18,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 19 4.1.4. entropy-tuning modification in 2015, rost et al. [142] proposed the concept of high-entropy layered oxides (heos) based on high-entropy alloys (heas) by introducing multiple different cations into a single sublattice (fig. 14a and b). as a unique design concept, heos can effectively enhance the cycling performance of cathode materials through two-dimensional ion migration channels between layers. zhang et al. [143] achieved th"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 18,
    "chunk_index": 1,
    "text": "in equal or nearly equal proportions, the multi-cation system exhibits the highest configurational entropy. typically, single-phase solid-solution oxides with five or more cations are classified as high-entropy oxides. the entropy-tuning strategy applied to layered manganese-based oxide cathode materials can yield medium-entropy oxides with four cations and high-entropy oxides with five or more cations. hu et al. [144] pioneered the field of sodium layered oxide research by introducing the conce"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 18,
    "chunk_index": 2,
    "text": "the tm layer to design a novel multi-principal component p2-structured cathode material, na0.6ti0.2mn0.2co0.2ni0.2ru0.2o2 (p2-tmcnr). they fig. 14. crystal structure of (a) high entropy alloys and (b) high entropy ceramics [146]. (reproduced from ref. [146] with permission from royal society of chemistry, copyright 2021). electrochemical properties in half cells: (c) charge-discharge curves cycled at a rate of 0.1 c (ca. 12 ma g− 1) in the voltage range of 2.0–3.9 v; (d) charge-discharge curves "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 19,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 20 summarized the effects of different transition metal elements on the na+ migration barrier by employing a site percolation model (fig. 14g and h). the material exhibited exceptional rate performance, with a capacity of 164 mah g− 1 at 0.1c and 68 mah g− 1 at an extremely high rate of 86c, surpassing most existing sodium-ion battery cathode materials. the mixing of high-entropy transition metal ions in layered p2 oxides combines the a"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 19,
    "chunk_index": 1,
    "text": "the jahn-teller effect [148], thereby enhancing structural stability during cycling. more importantly, the high- entropy structure facilitates the formation of low-diffusion-barrier domains, favoring na+ diffusion and improving the material kinetic performance [145]. furthermore, the high-entropy composition introduces greater complexity to the research. the primary challenge lies in the need for a comprehensive and in-depth understanding of the multifaceted mechanisms exhibited by each element "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 19,
    "chunk_index": 2,
    "text": "of high-entropy materials. meanwhile, the choice and fine-tuning of preparation techniques have a decisive impact on the final properties of high-entropy materials. different preparation methods can lead to significant differences in the microstructure and properties of the materials. therefore, conducting table 1 systematic comparative research on preparation techniques to reveal their underlying mechanisms affecting material properties is another critical direction for advancing the research a"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 19,
    "chunk_index": 3,
    "text": "are applied. to enhance the cycling stability of cathode materials under high- voltage conditions, constructing protective layers on the surface of electrode materials is an effective method to improve the interfacial stability of layered oxide cathode materials. the coating layers can prevent direct contact between the material and the electrolyte, thereby inhibiting the occurrence of side reactions and promoting the formation of dense and thick cei films. meanwhile, it can suppress the dissolu"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 19,
    "chunk_index": 4,
    "text": "of the electrochemical properties of doped and modified p2-na0.67ni0.33mn0.67o2. materials dopant element valence dopant site (s) voltage range (v) specific capacity (mah/g) cycle performance (%) ref p2-na0.62k0.05ni0.33mn0.67o2 p2-na0.59sr0.04ni0.33mn0.67o2 p2-na0.67ni0.33mn0.37ti0.3o2 p2-na0.67mg0.1ni0.23mn0.67o2 p2-na0.67ni0.23cu0.1mn0.67o2 p2-na2/3ni1/4cu1/12mn2/3o2 k+ sr2+ ti4+ mg2+ cu2+ cu2+ na na mn ni ni ni 2.0–4.1 2.0–4.25 2.0–4.5 2.5–4.4 2.5–4.3 1.5–3.65 80.78 (3c) 117.6 (1c) 123 (0.2c"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 19,
    "chunk_index": 5,
    "text": "1.5–4.3 2.0–4.3 2.0–4.3 2.5–4.4 100.1 (23.4 ma g− 1) 92.5 (8c) 128 (20 ma g− 1) 73 (10c) 114.3 (100 ma g− 1) 103.4 (5c) ~229 (0.1c) 136.9 (0.1c) 78 (1 a g− 1) 91.54 (10c) 91.5 (500 cycles,1.71 a g− 1) 94.44 (500 cycles,1c) 82.7 (500 cycles, 1 a g− 1) 83.4 (2000 cycles, 10c) 83 (150 cycles, 100 ma g− 1) 81.1 (200 cycles, 5c) 87.7 (50 cycles, 0.1c) 94.2 (50 cycles, 0.1c) 75 (1000 cycles, 1 a g− 1) 100 (500 cycles, 10c) [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] na0.65mn0.65cu0.2li"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 20,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 21 structural stability of the cathode material and prolonging the cycle life of the battery. it has been widely applied in the modification research of p2-type layered sodium-based oxides. recent research progress has shown that different types of metal oxide coatings, particularly al2o3 [39,177,178], zro2 [57,63], mgo [173,179], etc., have been successfully applied as protective layers on p2-type layered cathode materials, significant"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 20,
    "chunk_index": 1,
    "text": "layered metal oxide particles from damage and ensuring system stability and durability. liu et al. [39] first proposed an alumina coating method to prepare al2o3-coated p2- na0.67ni0.33mn0.67o2 material. although the coating did not inhibit the phase transition from p2 to o2 during the electrochemical reaction, it significantly improved the cycling stability of the material without affecting the initial capacity, achieving capacity retention of 73.2 % after 300 cycles, confirming that the al2o3 "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 20,
    "chunk_index": 2,
    "text": "dissolution of transition metal particles. dang et al. [175] selected cuo as the coating material, demonstrating that cuo not only stabilized the surface structure of the cathode material but also allowed some cu2+ ions to enter the crystal structure and participate in redox reactions. the doping of cu2+ in the crystal structure increased the d-spacing of the na+ diffusion layer, enhancing the diffusion coefficient of na+ ions (fig. 15d). the nnmo material co- modified with cuo coating and cu2+ "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 20,
    "chunk_index": 3,
    "text": "material exhibited a high specific capacity of up to 167 mah g− 1 in the voltage range of 2.0–4.2 v at 0.1c and a capacity retention of 60 % at 10c. in summary, metal oxide materials as cathode coatings significantly enhance battery performance from multiple dimensions. the materials construct a robust barrier on the cathode surface, effectively isolating harmful factors such as moisture and oxygen from the outside, thereby preventing erosion of the cathode material and ensuring a pure and stabl"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 20,
    "chunk_index": 4,
    "text": "their effectiveness. to overcome the challenge, researchers have turned to high-precision but costly techniques such as atomic layer deposition (ald) to achieve uniform coverage of metal oxide coatings. nevertheless, a major limitation of ald technology lies in the fine modification of electrode fig. 15. (a) cycling performance of the as-prepared na0.67ni0.33mn0.67o2 and al2o3-na0.67ni0.33mn0.67o2 [39]. (reproduced from ref. [39] with permission from elsevier, copyright 2016). tem images of the "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 21,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 22 surfaces with less impact on deep optimization of the bulk material structure, which to some extent restricts the full realization of the overall performance [177]. meanwhile, some metal oxides exhibit dual advantages, including not only serving as robust protective layers to effectively isolate the electrode material from external environmental erosion but also significantly inhibiting material phase transitions under high-voltage o"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 21,
    "chunk_index": 1,
    "text": "metal oxide, the coating of metal oxide materials can significantly hinder the smooth diffusion of sodium ions and effective electron transfer on account of the low conductivity resulting from the inorganic metal oxide materials, thereby weakening their high-rate performance and leading to the formation of discontinuous coating layers on the surface of na0.67ni0.33mn0.67o2 particles. in light of this, some researchers have shifted their focus to developing highly conductive carbon coating techno"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 21,
    "chunk_index": 2,
    "text": "a capacity of 62 mah g− 1 at a high current density of 1536 ma g− 1) (fig. 16c), and excellent cycling stability with a capacity retention of 90.7 % after 100 cycles (fig. 16d). the results strongly demonstrated that implementing appropriate surface protection strategies to reduce the generation of electrode surface byproducts was a critical approach to enhancing the comprehensive performance of p2- type cathode materials. it is evident that carbon coating modification technology significantly i"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 21,
    "chunk_index": 3,
    "text": "cathode materials, contributing to the comprehensive enhancement of the overall performance. 4.2.2.1. metal salt materials. the traditional al2o3 coating is renowned for the remarkable capability to enhance cyclic stability, while ingeniously introducing a lattice doping effect that effectively suppresses the detrimental p2-o2 phase transition process, significantly increasing the structural stability of the material. nevertheless, the relatively low ionic conductivity of the al2o3 coating hinde"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 22,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 23 fig. 17. (a) schematic illustration of the preparation process for na2ti3o7-coated na0.67ni0.33mn0.67o2 [174]. (reproduced from ref. [174] with permission from american chemical society, copyright 2019). (b) schematic of melt-impregnation of napo3 coating on na0.67ni0.33mn0.67o2 [176]. (reproduced from ref. [176] with permission from wiley, copyright 2018). (c) schematic illustration of degradation process of bare and rhenanite-coate"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 23,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 24 strategy and providing new insights and directions for the design and optimization of future cathode materials. to address the issue of residual alkalinity on the surface of layered oxide materials, nh4h2po4 [176] or cahpo4 [183] as treatment agents were innovatively employed to construct a protective layer of napo3 or nacapo4 through in-situ treatment, which not only significantly enhances the material ionic conductivity but also im"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 23,
    "chunk_index": 1,
    "text": "as a protective coating for p2- na0.67ni0.33mn0.67o2 cathode materials (fig. 17c). the coating effectively prevented the formation of hf and h2o, significantly reducing the exposure of the cathode material to acidic environments, thus avoiding metal ion dissolution and ensuring excellent capacity retention. the strategy proposal demonstrates great potential for integration with cathode materials for rechargeable sodium batteries, mitigating the adverse effects of internal acidic conditions on ba"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 23,
    "chunk_index": 2,
    "text": "layer exhibits excellent sodium-ion conductivity, facilitating smooth ion migration between the electrode and electrolyte interface, significantly reducing interface resistance, mitigating resistance during ion transport, and ultimately optimizing and enhancing the electrochemical performance of the material. in practical application deployment, it is crucial to consider the specific requirements of the application situation and the inherent properties of the material to precisely match and sele"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 23,
    "chunk_index": 3,
    "text": "cycles at a 5c rate, significantly enhancing the rate response capability and cycle durability (fig. 18b). experiments confirmed that the surface coating and doping strategy of ntp effectively suppressed the structural deformation of nmnco during alkalization/desalination cycles, [185] with permission from elsevier, copyright 2020). fig. 18. (a) schematic illustration of the fabrication of ntp surface-modified nmnco samples [112]. (reproduced from ref. [112] with permission from elsevier, copyri"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 24,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 25 ensuring a high degree of reversibility, while also defending against erosion processes and maintaining a stable phase interface effectively. li et al. [184] coated p2-na0.67ni0.33mn0.67o2 with a solid electrolyte film of ntp (fig. 18c), which not only effectively prevented the p2-o2 phase transition and dissolution of transition metal ions during cycling but also led to partial doping of ti4+ into the crystal structure, increasing i"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 24,
    "chunk_index": 1,
    "text": "interface, effectively resisting hf erosion and promoting efficient na+ migration at the cathode- electrolyte interface (fig. 18e). the dual strategy also significantly inhibited particle cracking and peeling. experiments confirmed that the modified material exhibited exceptional cycle stability with a capacity retention of up to 77.4 % at 1c and superior rate performance (reaching 106.8 mah g− 1 at 5c) (fig. 18f). therefore, the dual modification method opens up a new path and perspective for e"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 24,
    "chunk_index": 2,
    "text": "nasicon-type materials are renowned for their stable crystal structure, a crucial characteristic during charge–discharge cycles, as it effectively restrains volume fluctuations in the cathode material, ensuring stable and long-lasting battery cycle performance. furthermore, the latest research achievements in enhancing the electrochemical performance of p2-na0.67ni0.33mn0.67o2 materials through surface coating technology are systematically reviewed, and table 2 provides a detailed overview of th"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 24,
    "chunk_index": 3,
    "text": "materials science, an increasing number of novel coating materials have been developed and applied to the coating of sodium-ion battery cathode materials, including nanomaterials with unique structures and properties, organic–inorganic composites, and polymeric materials [107]. these innovative approaches, through precise control of material interfaces, effectively promote charge transport and structural stability, having demonstrated the promising effects of the coating in enhancing the perform"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 24,
    "chunk_index": 4,
    "text": "cycles, 100 ma g− 1) [186] [187] p2-na0.67ni0.33mn0.67o2@ceo2 p2-ni0.67ni0.23mn0.67v0.1o2@ thf 2.6–4.3 1.5–4.0 134 (0.5c) 150.5 (50 ma g− 1) 75.3 (100 cycles, 0.5c) 84.7 (100 cycles, 50 ma g− 1) [188] [189] p2-ni0.67ni0.23mn0.67v0.1o2@ na3v2o2(po4)2f p2- na0.67ni0.33mn0.67o2@catio3 1.5–4.1 1.5–4.5 150 (2c) ~180 (17.3 ma g− 1) 84 (100 cycles, 2c) 75.3 (200 cycles, 346 ma g− 1) [190] [191] p2-na0.67ni0.33mn0.67o2@zno2 2.5–4.15 75 (1c) 92.7 (300 cycles，1c) [192] p2-na0.67ni0.33mn0.67o2@mgfe2o4 2.0–"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 25,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 26 furthermore, enhancing battery performance by optimizing the fig. 19. xrd pattern and rietveld refinement of (a) p2-type na2/3mn0.7ni0.1fe0.1mg0.1o2 (minor impurity of an o3-type phase is marked with o), (b) o3-type na1mn0.5ni0.3fe0.1mg0.1o2 (minor cubic phase is marked with squares), and (c) p3/p2/o3-material (cubic mg1-xnixo (x ≈ 0.3) phase is marked with squares) [52]. (reproduced from ref. [52] with permission from wiley, copyrig"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 25,
    "chunk_index": 1,
    "text": "from ref. [199] with permission from american chemical society, copyright 2024). (h) charge-discharge curves of na0.8ni0.4mn0.4ti0.2o2-t electrodes at 0.1c between 2.0 and 4.2 v. (i) cyclic voltammetry (cv) profiles of na0.8ni0.4mn0.4ti0.2o2-t electrodes scanned at a rate of 0.1 mv s− 1. (j) cycling performance and (k) rate capability of na0.8ni0.4mn0.4ti0.2o2-t electrodes [200]. (reproduced from ref. [200] with permission from mdpi, copyright 2023)."
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 27 interface structure between the electrolyte and cathode material [189] offers a novel approach to cathode coating and modification research. attention should not only be focused on the coating and modification of the cathode material itself but also on the interaction and interfacial stability between the electrolyte and cathode material. by adjusting the composition, concentration, and additives of the electrolyte, it is possible to"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 1,
    "text": "rate capability due to their unique na+ sliding diffusion mechanism, maintaining high efficiency even at high charge–discharge rates. however, p-type materials suffer from relatively lower specific capacity compared to o-type materials due to being sodium-deficient inherently. in contrast, o-type materials, as representatives of sodium- rich materials, possess higher specific capacity primarily attributed to the stable presence of sodium-ions in their octahedral interstices. yet, the structural "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 2,
    "text": "adjusting the mn4+/ni2+ ratio to modify the structural properties of the composite material, the research showed that a high mn4+ content is beneficial for the p2 structure, while a high ni2+ content is beneficial for forming the o3 material. by adjusting the ni/mn ratio, it is possible to obtain composite materials with a p2/o3 dual-phase structure, thereby combining the advantages of both and enabling the material to exhibit high reversible capacity and high-rate performance. structural, morph"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 3,
    "text": "of 99.9 %, and remarkable cycling stability with a capacity retention of 90.2 % after 601 cycles, demonstrating overall excellent electrochemical performance. buchholz et al. [56] synthesized naxni0.22co0.11mn0.66o2 with a p2/p3 mixed structure. xrd analysis (fig. 19d) showed that the material synthesized at 750 ◦c possessed a mixed p2 and p3 phase structure, and further elucidated the sensitivity to water. a strong tendency for water absorption was observed at lower sodium contents (x ≤ 0.33), "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 4,
    "text": "g− 1, an initial coulombic efficiency of 94.8 %, a high operating voltage of 3.53 v (vs na+/na) based on the ni2+/ni4+ redox pair, and outstanding rate capability. precise control of the phase ratios of p2/o3composites remains a formidable challenge due to the complex and variable composition of the composites, directly impacting the precise regulation of electrochemical performance. hu et al. [199] proposed a simple and efficient method aimed at designing advanced layered oxide materials that i"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 5,
    "text": "o3 during na+ extraction/insertion (fig. 19f and g). notably, all designed p2/o3 biphasic samples exhibited exceptional electrochemical performance with capacities exceeding 120 mah g− 1 and capacity retention of over 91 % after 500 cycles, fully demonstrating the effectiveness of the approach and the superiority of the prepared materials. recent research by ma et al. [200] showed that the introduction of ti substitution and the adoption of a high- temperature synthesis strategy could effectivel"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 6,
    "text": "in contrast, when the synthesis temperature was lowered (for example, 850 ◦c) to increase the proportion of the p2 phase, the resulting na0.8ni0.4mn0.4ti0.2o2-850 sample exhibited enhanced rate performance, with capacity retention increasing to 65 % at a high rate of 5c while maintaining similar cyclic stability. the discovery provides important insights for balancing and enhancing the overall performance of p2/o3composites in energy storage applications through the adjustment of phase compositi"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 26,
    "chunk_index": 7,
    "text": "interfaces. consequently, biphasic or multiphasic composite structures open up new avenues for optimizing battery performance compared with traditional single-phase structures, fulfilling the urgent demands of modern electrochemical energy storage systems for high energy density, high power density, and long cycle life. 4.4. fabrication of hierarchical structures the electrochemical performance of sibs is primarily influenced by the cathode material, whose properties are determined by the compos"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 27,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 28 with permission from tsinghua university press, copyright 2023). outstanding performance lies in the unique hierarchical nanoarchitecture design, where the two-dimensional structure provides favorable channels for ion diffusion, effectively mitigating the pulverization process of active materials and successfully inhibiting the agglomeration of nanoparticles during frequent sodiation/desodiation cycles. xrd patterns (fig. 20c and d) "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 27,
    "chunk_index": 1,
    "text": "constructed from nanoparticles in promoting reaction kinetics and maintaining structural stability. he et al. [211] successfully synthesized high-purity and well- crystallized single-crystalline na0.44mno2 nanoplates via template- assisted sol–gel technology. the nanoplates exhibited uniform plate- like morphology with clearly visible layered structural features, ensuring uniform channel distribution within the nanoplates and achieving highly controllable morphology (fig. 20e and f). critically,"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 27,
    "chunk_index": 2,
    "text": "density and cycling durability. yin et al. [136] prepared a polyhedral hollow structure na0.67li0.1(mn0.7ni0.2cu0.1)0.9o2 by solvothermal method and high- temperature calcination. due to the presence of multiple cations, the ordering of na+/vacancy was inhibited and a honeycomb-ordered superstructure was formed. the reaction is carried out over a wide voltage range. based on sem images, the material shows a uniform polyhedral hollow structure, which table 3 summary of the electrochemical propert"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 27,
    "chunk_index": 3,
    "text": "1.5–4.2 160 (0.1c) 70 (100 cycles, 0.1c) [208] fig. 20. sem images of the (a) electrospun nanofibers and (b) resultant p2-na0.67ni0.33mn0.67o2 nanofibers [210]. (reproduced from ref. [210] with permission from wiley, copyright 2020). na-storage mechanism: (c) in situ x-ray diffraction patterns of the p2-na0.67ni0.33mn0.67o2 nanofiber electrode during the first charge/ discharge process at 25 ma/g, as well as (d) the selected (002) and (102) diffraction profiles [210]. (reproduced from ref. [210]"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 29 reduces the volume change of the material in the electrochemical reaction process and has good structural stability. the electrochemical test results show that nlmnc has almost no platform on the initial charge and discharge curve of 2.1–4.0 v. especially the high-voltage platform near 4.2 v is not obvious, which indicates that the high-voltage phase transition is effectively suppressed, and the stability of the material under high v"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 1,
    "text": "by hydroxide co-precipitation combined with a solid-phase reaction. these microspheres display a densely packed arrangement of nanoflakes. based on low-magnification sem images (fig. 20g), most of the p2-na2/3ni1/3mn2/3o2 are composed of monodisperse microspheres with a diameter of 5–8 μm. high- magnification sem images show (fig. 20h) that individual microspheres are composed of overlapping nanoplate-like particles having a diameter of 0.5–1 μm with a faceted structure. due to the structural ad"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 2,
    "text": "peak intensity has slightly decreased, indicating that the electrode has good reversibility. electrochemical tests revealed that the material, had an initial capacity of 87.8 mah g− 1 and a capacity retention of 97.5 % after 100cycles when used as a cathode for sibs. liang et al. [216] employed a self-templating technique to successfully synthesize hierarchical p2-na0.67ni0.33mn0.67o2 hollow microspheres exquisitely assembled from nanosheets (fig. 20i). the nanosheets not only existed in abundan"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 3,
    "text": "capacity retention of 83.3 % after 500cycles at a current density of 1.0c (fig. 20j). furthermore, the recent advancements in the electrochemical performance of p2-na0.67ni0.33mn0.67o2 materials after modification through structural design are systematically reviewed, which primarily concentrates on enhancing and optimizing key parameters such as average potential and specific capacity. the detailed overview of the table 4 relevant research progress is illustrated in table 4. in summary, the con"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 4,
    "text": "improve the stability of the material under high- temperature conditions, thus improving the overall safety of the battery. moreover, it enhances the charge transport pathways within the material, facilitating efficient electron and ion migration. this leads to improved conductivity and mitigates the poor electrochemical activity of materials at low temperatures [219], significantly enhancing its low- temperature electrochemical performance [220,221]. in addition, the optimized structure can als"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 5,
    "text": "battery technology, injecting new vitality into the development of the new energy equipment. 5. conclusions the p2-na0.67ni0.33mn0.67o2 material with the remarkable na+ ion diffusion rate and ionic conductivity, exhibits exceptional rate performance and cycling stability, making it a promising candidate in the field of sodium-ion battery cathodes. however, the p2- na0.67ni0.33mn0.67o2 material still confronts challenges such as high-voltage phase transitions, na+/vacancy ordering reconstruction,"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 6,
    "text": "focusing on strategies such as elemental doping, precise surface engineering, multiphasic composite structural design, and innovative material configuration design. the approaches effectively mitigate structural degradation during cycling, notably enhancing cycling durability, boosting reversible capacity, and comprehensively optimizing electrochemical performance. the innovative modification strategies for p2-na0.67ni0.33mn0.67o2 precisely target the core challenges faced by traditional cathode"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 28,
    "chunk_index": 7,
    "text": "structure banded superstructure honeycomb-ordered superstructure a single crystalline mirorods structure 2.5–4.35 2.1–4.3 2.1–4.0 0.9–1.8 111.8 (0.1c) 123.5 (10 ma g− 1) 102.1 (102.1 ma g− 1) 159.3 (0.1 a g− 1) 82.64 (1000 cycles, 5c) 94.4 (100 cycles, 500 ma g− 1) 82.5 (100 cycles, 102.1 ma g− 1) 93 (2500 cycles, 5 a g− 1) [217] [191] [136] [218] summary of the electrochemical properties of structurally modified p2-na0.67ni0.33mn0.67o2."
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 29,
    "chunk_index": 0,
    "text": "c. wu et al. chemical engineering journal 500 (2024) 157264 30 elements, not only leveraging the single positive impacts of dopant elements on cathode properties but also generating unexpected synergistic gains, and promoting the na0.67ni0.33mn0.67o2 cathode to achieve impressive improvements in the multiple key performance. furthermore, advancements in interface engineering, particularly the application of surface coating technologies, provide effective methods to stabilize the cathode-electrol"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 29,
    "chunk_index": 1,
    "text": "for the continuous innovation and development of sodium-ion battery cathode materials, demonstrating broader application prospects. to address the inherent technical bottlenecks and challenges of p2- na0.67ni0.33mn0.67o2 in the future, more delicate work needs to be explored based on the traditional modification strategies with the integration of innovative thoughts. meanwhile, the practical application should also be considered to comprehensively elevate battery performance. specifically, this "
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 29,
    "chunk_index": 2,
    "text": "design of the na0.67ni0.33mn0.67o2 cathode 2. exploring the boundaries of innovative coating materials. drawing inspiration from the abundant research achievements in lithium-ion batteries (libs), conventional frameworks should be broken and novel coating materials need to be explored urgently such as cutting- edge magnetic materials and liquid metals. the introduction of the novel materials aims to achieve multi-dimensional improvements in p2- na0.67ni0.33mn0.67o2 through the synergistic effect"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 29,
    "chunk_index": 3,
    "text": "balanced, enhancing the overall battery performance. furthermore, innovative microstructural designs such as high-sodium-content structures and composite structures can be pursued 4. refining the regulation strategies of cathode materials. by clarifying the aim of modifying cathode materials, such as inhibiting the ordered arrangement of na+/vacancies, suppressing high-pressure phase transitions, and enhancing discharge specific capacity, it is necessary to precisely design the types and valence"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 29,
    "chunk_index": 4,
    "text": "parameters represents a future research direction 6. synergistic optimization of battery material systems. the selection and matching of other crucial components in the battery system should be noticed except for cathode materials, including binders, separators, and electrolytes. the interface between the cathode and electrolyte requires more attention, and the synergistic effect achieved by modifying the separators with a coating layer and regulating the component of electrolytes demands furthe"
  },
  {
    "source_pdf": "Research_progress_on_P2_type_layered_oxide_cathode_materials_for_sodium_ion_batteries_Chen_Wu_Yuxing_Xu_Jiechen_Song_Ying_Hou_Shiyang_Jiang_Rui_He_Aijia_Wei_Qiangqiang_Tan.pdf",
    "page": 29,
    "chunk_index": 5,
    "text": "focused. on the other hand, explore the adjustment and optimization of electrolyte systems, particularly by adding specific electrolyte additives to enhance the battery’s adaptability to extreme temperature conditions while improving safety performance. the comprehensive improvement strategy will effectively enhance the reliability and stability of batteries in practical applications this study comprehensively reviews the current research status of p2-na0.67ni0.33mn0.67o2 materials for sibs. thr"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "j. am. chem. soc. abstract: layered na-based oxides with the general composition of naxtmo2 (tm: transition metal) have attracted significant attention for their high compositional diversity that provides tunable electrochemical performance for electrodes in sodium-ion batteries. the various compositions bring forward complex structural chemistry that is decisive for the layered stacking structure, na-ion conductivity, and the redox activity, potentially promising new avenues in functional mater"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "as required for cathode materials in sodium-ion batteries. it leads to excellent na-ion mobility, a large storage capacity (>100 mah g−1 between 2.0-4.0 v), yet preventing the detrimental sliding of the tmo2 layers (p2−o2 structural transition), as reflected by the ultralong cycle life (3000 (dis)charge cycles demonstrated). these findings expand the horizons of high na-content p2-type materials, providing new insights of the electronic and structural chemistry for advanced cathode materials. 1."
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "high cycle/rate capabilities. however, it is established that p2-type electrodes usually made in finding suitable electrode materials with desired ∼80 mah g−1 below 4.0 properties and the determination of structure−property deliver a low initial charge capacity of7−15 11,13,16,17 v or a low average voltage <3.2 v (figure s2a). relationships. because of the large compositional diversity of the structural chemistry, layered oxides are considered as one of the most important electrodes families for"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "in figure 1a, which compromises the cycling stability.7,9,12,13,16,18 in order to enhance the properties of p2-type materials, ionsubstitution and/or doping, with li+, mg2+, al3+, ti4+, and zn2+, having no or fully occupied d orbitals19−22 and cu2+ inducing the jahn−teller effect,13 are widely used to alleviate the structural instability. for example, it has been demon- are accommodated at the octahedral (o) sites and p denotes na ions at trigonal prismatic (p) sites; the number 2 or 3 represent"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "journal of the american chemical society pubs.acs.org/jacs article figure 1. possible advantages of the high-na p2-type na-ion cathodes and the corresponding design strategy. (a) structural evolution mechanism of high-na p2 oxides during desodiation. (b) electronic structure of the low-na and high-na p2 oxides. (c) crystal structure of p2-type oxides. the interlayer distance d(o−na−o) is the average perpendicular distance between the two oxygen sheets enclosing na ions, and the interlayer distan"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "p2type oxides with tms, such as mn3+,12 fe3+,9 and co3+,23 have been studied. however, the redox potential of these p2- type cathodes is generally lower than 3.0 v, compromising the overall energy density of the battery, and they often suffer from structural transitions in both the high-voltage (p2 to o2, op4/ ′z′) and low-voltage (p2 to p′2) regions. another disadvantage is that these materials are often sensitive to water and moisture in air.24 from the above, it is clear that it is challengin"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "stackings. therefore, if more na can be retained in the p2 host upon charging (desodiation), the structural stability can be better maintained during the charge−discharge process. in addition, by analyzing the electrochemical performance of p2 and o3 na-ion cathodes (figure s2), we find that o3-type cathodes usually show a higher na storage capacity than p2-type cathodes in a stable voltage window of 2.0−4.0 v, which is most likely related to the larger initial na composition (x = 1) of the host"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "is to develop p2 materials with high na content, so that more na+ to be retained in the nao2 slabs to prevent the structure transition, while reaching or exceeding the capacity of low na-content p2 materials (x = 2/3). to achieve high na-content p2 materials, we pursue the following rational design strategy. based on our understanding of na-ion intercalation chemistry,25 the ratio between the interlayer distances of d(o−na−o) and d(o‑tm‑o) can be used as an indicator to distinguish structural co"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "the interlayer distance of d(o−na−o) will decrease, because the increased na content will raise the electrostatic cohesion forces between na+ and o2− layers. if we assume that the interlayer distance d(o‑tm‑o) is the determining descriptor, a potential strategy is to substitute tms in naxtmo2 with cations having a smaller ion-size and higher oxidation state to reduce its value. following this strategy, we used p2-type na2/3ni1/3mn2/3o2 as a starting model, which features a large fraction of mn4+"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "such as li+, mg2+, cu2+, mn3+, fe3+, and ti4+, to substitute the mn4+/ni2+. through this approach, several high na- content materials were obtained with a na content between 42/54 to 45/54 mol per unit. 2. results 2.1. structural analysis. i n t h i s w o r k , na45/54li4/54ni16/54mn34/54o2 was prepared based on the known p2-type na2/3ni1/3mn2/3o2 through the same synthesis method (see methods in the supporting information). in this as-prepared material, 34/54 mol mn ions and 16/54 mol ni ions e"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "journal of the american chemical society pubs.acs.org/jacs article allows an increase in na composition to balance the charge. inductively coupled plasma atomic emission spectrometry (icp-aes) analysis confirms the composition of na0.85li0.08ni0.30mn0.62o2 (table s1). the morphology of this as-prepared material is characterized by scanning electron microscopy (sem) (figure s3), displaying platelike particles with a distribution of sizes in the range of 8− 12 μm. the crystal structure and phase p"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "na-content p2 type oxide. (a) rietveld refinement of x-ray diffraction (xrd) pattern of na45/54li4/54ni16/54mn34/54o2 (a = 2.89058(7) å, c = 11.07541(18) å), with the inset showing the enlarged pattern of the (002) peak. (b) atomic-resolution high-angle annular dark field (haadf) and annular bright field (abf)-scanning transmission electron microscopy (stem) images at the [010] zone axis. the scale bar is 1 nm. (c) electron energy loss spectroscopy (eels) mappings of na, mn, ni, and o elements. "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "is further investigated by high-resolution transmission electron microscopy (hrtem), where the interplanar distance between the adjacent lattice fringes corresponds to the d spacing value of the (002) planes of the obtained p2 phase (figure s4). na ions occupy two kinds of trigonal prismatic sites, amounting 0.536 mol in the 2d site and 0.313 in the 2b site. the prismatic nao6 2b site shares two faces with the lower and upper octahedral tmo6, which can be expected to be less stable than that of "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "is consistent with p2-type structure as demonstrated by the inset. the distance of the adjacent layer d(tm‑tm) in haadf-stem image is measured to be ∼0.558 nm, which corresponds to the interslab distance from the xrd refinement. atomic-scale stem image and electron energy loss spectroscopy (eels) mappings of this p2-type material were carried out to confirm the elemental distribution, and the corresponding elemental mappings of na, mn, ni, and o are exhibited in figure 2c. tm sites are occupied "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "journal of the american chemical society pubs.acs.org/jacs article stability in convex hull. (a) determination of the li/ni/mn (dis)ordering in the system of na12−xlini3mn8o24. the detailed information on determination of the ground state structure and li/ ni/mn (dis)ordering in the system of na12−xlini3mn8o24 is presented in supporting discussion s1. (b) phase stability in the na12−xlini3mn8o24−lini3mn8o24 convex hull. the formation energy was calculated considering all possible na and their va"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "with respect to the end member phases. two high na-content phases are identified, having a na composition of 9/12 and 10/12, which are larger than the well-known structure with a na composition of 8/12 per super cell. the highest na composition was further evaluated by a na−li−ni−mn−o phase diagram (in figure s5), which demonstrates an energy of ∼1.68 ev/atom lower than the combination of stable phases: namno2 + li2mno3 + na2mn3o7 + na2o2 + nanio2. the predicted stability of the p2-type phase in"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "v s n a + / n a . ( c ) r a t e c a p a b i l i t y o f na45/54li4/54ni16/54mn34/54o2 from 0.1c (16 ma g−1) to 20c (3200 ma g−1). (d) discharge capacity retention of na45/54li4/54ni16/54mn34/54o2 with the first three cycles at 0.1c (18 ma g−1) and following cycle at 3.0c (540 ma g−1). the capacity is normalized by that of 3.0c. above 70% capacity is retained up to 2500 cycles with approximate 99.9% coulombic efficiency (ce), but the ce is found to be unstable in the following cycles; after 3000 "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "below 4.0 v.32 interestingly, this high na-content p2-type material contains a smaller amount of ni2+ (16/54 mol) compared to 1/3 mol in na2/3ni1/3mn2/3o2. nevertheless, the as-prepared material exhibits a capacity that is 1.25 times higher in the same voltage range. the rate performance was also evaluated using electrodes with a relatively large mass loading of 8−10 mg cm−2 from 0.1c (16 ma g−1) to 20c (3200 ma g−1) as shown in figure 4c. when cycled at 10c, the capacity retention is ∼ 65% of i"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "journal of the american chemical society pubs.acs.org/jacs article g−1). the average capacity decay is 0.012% per cycle. more than 70% of the capacity is retained up to 2500 cycles with a coulombic efficiency (ce) that approaches 100%. clearly, the present high na-content material shows superior electrochemical properties compared to the reported low na- content materials as shown in figures s6 and s7.7−15,32 2.4. understanding the desodiation process and charge compensation. although a cutoff v"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "range of 2.0−4.60 v. (b,c) calculated formation energy of desodiation structures of the na10−xlini3mn8o24 (0 ≤ x ≤ 7) convex hull and the corresponding voltage profile during the desodiation process in na45/54li4/54ni16/54mn34/54o2. (d,e) magnetization and oxidation state evolution during the desodiation process of ni and o ions in intermediate phases from na10lini3mn8o24 to na3lini3mn8o24. electronic structure evolution on partial density of states (pdos) of the ni 3d eg*, mn 3d t2g, and o 2p o"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "n i 4 + p e r u n i t o f na45/54li4/54ni16/54mn34/54o2. to examine the origin of the charge compensation during the electrochemical desodiation, the formation energy during the charge process is evaluated as plotted in figure 5b and c. based on the calculated formation energies, the obtained voltage is in good agreement with the experimental observations. to obtain more insights into the redox activity, the magnetization of ni and o ions is determined from dft calculations, shown in figure 5d a"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "magnetization of mn ions (figure s8) indicates that mn4+ does not participate in the redox reaction. it has recently been reported that mn4+ can be oxidized to mn7+ with the migration of mn from octahedral sites to tetrahedral sites during the charge process,33 although no evidence of this was found in the current system. upon desodiation of na10−xlini3mn8o24 (0 ≤ x ≤ 5), ni magnetization first decreases from 1.78 ub (bohr magneton) to 1.077 ub at x = 3, corresponding to the oxidation from ni2+ "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 4,
    "chunk_index": 4,
    "text": "level (ef) than the mn 3d and o 2p states. with further desodiation to na5lini3mn8o24 (x = 5), the decreased ni magnetization indicates that all ni2+ ions are oxidized to ni3+ and 1/6 ni3+ is further oxidized to ni4+. meanwhile, the o ions remain in the o2− state where o magnetization retains a value between 0.002 and 0.158 ub. based on the above results, the desodiation results in partial oxidation of ni2+ to ni4+ below charging to 4.0 v. upon further desodiation from na5lini3mn8o24 (x = 5) to "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 4,
    "chunk_index": 5,
    "text": "ni4+ limits additional charge compensation and thus a higher capacity. comparing the contributions of the o 2p and ni 3deg* orbitals, it is observed that the latter still dominates the valence band immediately below the ef level as shown in figure 5g. this implies preferential electron extraction from ni during charge (na10−xlini3mn8o24, 5 ≤ x ≤ 7). on the other hand, during further desodiation, the ni 3d states and o 2p states increasingly overlap near the ef level in the valence band, as shown"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "journal of the american chemical society pubs.acs.org/jacs article features of the pristine spectrum demonstrate that ni ions are in the divalent state, consistent with previous reports.37 during the desodiation process, both ni l3- and l2-edge sxas spectra shift toward higher energies, which indicates that the ni oxidation states increases. when increasing the potential from 3.5 to 4.0 v, the l3-high and l2-high features increase further, which indicates a mixture of ni3+ and ni4+ states.37,38 "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "chemical bonding between ligand and tm atomic species. generally, the pre-edge peaks in the range of 527−535 ev are due to the electronic transitions from the o 1s state to the o(2p)-tm(3d) hybridized states, which can be further divided into a lower energy peak of the band and a higher peak of the o(2p)-tm(3d-eg*) hybridized states. the increase of the o(2p)-tm(3d-eg*) hybridized state (in figure s10a) shows that oxidization of ni creates more holes in the antibonding eg* orbital, leading to th"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "surface-sensitive total electron yield measurements (tey) demonstrate the presence of oxygen-containing decomposition products of the electrolyte and surface densification at 4.60 v. this can suppress the o(2p)-tm(3d) hybridization features for the electrodes resulting in a relative lower average valence state of ni/mn ions as shown in figures s10b and s11.40 meanwhile, the mn l-edge pfy results show negligible changes upon cycling, as demonstrated in figure s12, suggesting that the mn4+ ions do"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "slightly shift to a lower angle, while (100), (102), and (103) reflections move toward a higher angle. subsequently, the (002) and (004) reflections become asymmetric and broader, and two new p2 phases (phase 2 and 3) appear upon further charging. the (002) reflection of the pristine p2 phase (phase 1) continuously shifts to lower angles, while the (002) reflections of the new p2 phases grow gradually without shifting, even up to the end of charge at 4.60 v. the main difference between these p2 "
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 5,
    "chunk_index": 4,
    "text": "c = 11.21(13) å, a = 2.8668(4) å and c = 11.2335(15) å, and a = 2.8135(13) å and c = 11.2763(14) å, respectively. the average na content obtained from the refinement is ∼0.24 mol, in good agreement with icp results (∼0.245 mol based on the normalized value of mn). during the refinement, a relatively large 2b na+ occupation is found in the na-poor phases. this indicates that na+ at the 2d sites is preferentially deintercalated from the structure, which should be expected based on the larger energ"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 5,
    "chunk_index": 5,
    "text": "a rate of 0.05c charged to 4.60 v. the peaks marked by an asterisk originate from the casing of the in situ swagelok cell. (b) in situ xrd patterns recorded at a high rate of 0.5c in the voltage range 2.0−4.0 v. (c) na+ migration pathway in the high na-content p2-type oxide simulated at a temperature of ∼1400 k over a period of 6 ps. the detailed views of na+ layers are given in the right and lower panels, where the yellow spheres indicate the trace of the na+ positions during md simulations. (d"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "journal of the american chemical society pubs.acs.org/jacs article desodiation, new p2 phases with a large interlayer distance are formed and their phase fractions increase simultaneously. at the same time, na is mainly deintercalated from the pristine na-rich p2 phase. the formation of the new p2 phases can be held responsible for the stability of the materials, as opposed to the commonly reported o2, op4/′z′ phase transition upon desodiation. during na+ intercalation upon discharging, the coex"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "indexed with the hexagonal space group p63/mmc, and no additional diffraction peaks are detected. the lattice parameters are presented in tables s5 and s6. in contrast to the pristine p2- na45/54li4/54ni16/54mn34/54o2 material, the lattice parameter evolution is highly reversible, reflecting the excellent cycling stability. the evolution of the structure is also studied at different current rates, the results of which are presented in figure s17 and discussed in supplementary discussion s2. give"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "na+ migrates through the twodimensional planes of the nao2 layers. as compared to the low na-content material (0.667 mol), for the present high nacontent material the trajectories are more interconnected, showing many more jumps within the same simulation time.5,32 figure 6d shows the arrhenius plot of the calculated diffusion coefficient, resulting in a very low activation energy for diffusion (∼0.28 ev) and a very large room temperature diffusion coefficient (∼0.55 × 10−10 cm2 s−1) as compared"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "against water and air. nibs utilizing a hard carbon anode were assembled to investigate the full cell long-term cyclability of the high nacontent p2- type cathode, having a relatively high active mass loading of approximately 8 mg cm−2, as shown in figures s21− s23. the electrochemical results show that the reversible capacity between 1.5 and 4.0 v is above 100 mah g−1, based on the mass of the cathode at a current rate of 0.1c at a high average operation voltage of ∼3.3 v. the full cells displa"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 6,
    "chunk_index": 4,
    "text": "(e.g., ni2+) to their high-valent states even at a relatively low cutoff charge voltage. for the asprepared high na-content cathode, the ni2+/ni4+ redox couple is successfully activated to provide additional capacity below 4.0 v, which is an essential ingredient for the design of highperformance ni- based p2-type cathodes.46 generally, the redox reaction of ni2+/ni4+ occurs at voltages around or exceeding 4.2 v. such a higher redox potential introduces three issues, including structural transiti"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 6,
    "chunk_index": 5,
    "text": "contribution of low-valent cations in the valence band below the fermi level, which provides additional capacity. to rationalize this finding, dft calculations were performed, the results of which are shown in figure 7. comparing the pdos of p2-type na0.83li1/12ni1/4mn2/3o2 figure 7. illustration of the electronic evolution mechanism in the na45/54li4/54ni16/54mn34/54o2 high na-content p2-type material. the dft predicted electronic evolution during charge (desodiation). the large amount of na in"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "journal of the american chemical society pubs.acs.org/jacs article respectively, where the former displays a larger contribution near the fermi level. this implies easier participation of ni2+ in the charge compensation upon desodiation. the disadvantage of the high na-content p2 phase is that it is thermodynamically less stable compared to the low na- content material, as demonstrated in figure 3b. this is a result of the stronger na+na+ electrostatic repulsions within the nao2 slabs (which may"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "results in several advantages compared to known low na-content p2 materials. na45/54li4/54ni16/54mn34/54o2 is demonstrated to have a higher reversible capacity of >100 mah g−1 accompanied by the favorable multielectron reaction of the ni2+/ni4+ redox couple within the stability window of typical electrolytes of 2.0−4.0 v. additionally, stabilizing the p2-type structure leads to an ultralong cycle life of up to 3000 cycles in combination with good rate performance. the advantages of the presently"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "catalysts.48 1 .2. stabilizing p2-type structure to prevent degradation from structural instability. the large amount of na in a p2- type host structure can ensure a high structural stability in a large compositional range during the desodiation process, as demonstrated in figure 7. for low na-content p2-type materials, structural transitions from p2 to o2 or op4/′z′ occur for voltages below ∼4.2 v when the na content in the structural host drops below 1/3 mol. the higher na content allows the s"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "beijing 100190, china; orcid.org/0000-0002-1749-4428 ming liu − department of radiation science and technology, delft university of technology, 2629jb delft, the netherlands swapna ganapathy − department of radiation science and technology, delft university of technology, 2629jb delft, the netherlands yaxiang lu − key laboratory for renewable energy, beijing key laboratory for new energy materials and devices, beijing national laboratory for condensed matter physics, institute of physics, chines"
  },
  {
    "source_pdf": "Revealing_High_Na_Content_P2_Type_Layered_Oxides_as_Advanced_Sodium_Ion_Cathodes_Chenglong_Zhao_Zhenpeng_Yao_Qidi_Wang_Haifeng_Li_Jianlin_Wang_Ming_Liu.pdf",
    "page": 7,
    "chunk_index": 4,
    "text": "n s t r a t e t h a t , d u r i n g d e s o d i a t i o n o f na45/54li4/54ni16/54mn34/54o2, na-poor phases have a similar structure as the pristine material. these newly formed phases have a larger interlayer distance compared to that of the pristine structure, which is expected to be beneficial for na+ migration. the phase fractions of these desodiated phases increase upon charging and reversible transform back to the pristine structure upon discharging (sodiation). 2 . summary in this work, w"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "view article online chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3529 s, it is important to use a true na-ion tem, where na ions are"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "view article online review article chem soc rev 3530 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 exchanged between cathodes and anodes in a ‘rocking-chair’ format. a new type of electrolyte for sibs is needed, as the use of organic liquid electrolytes raises practicality and safety issues. the most common electrolyte formulations for sibs are naclo4 or salts in carbonate ester solvents, particularly propylene carbonate (pc). metallic sodium anodes"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "electrolytes instead of organic electrolytes could be essential to the success of sibs. recently, an aqueous rechargeable battery with na2nife(cn)6 and nati2(po4) as the cathode and anode, respectively, demonstrated a good rate and cycle life with a theoretical energy density of 42.5 w h kg1.29 thus, it is possible to achieve higher energy density by selecting the appropriate electrode material. nevertheless, an aqueous electrolyte system is more complicated than an organic system because of the"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3531 2. cathode materials similar to libs, highly reversible cathode materials based on the intercalation reaction, which involves interstitial introduction of a guest species (na+ in the present context), are needed for high capacity and good cyclability of sibs. these electrode materials are mainly categorized into oxides, polyanions such as phosphates, pyrophosphates, fluor"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "three-dimensional crystal structures. early investigation of two-dimensional layer oxides was performed by delmas and hagenmuller in the early 1980s.13,14,33 they defined the crystal structure of layered compounds depending on the stacking sequence of alkali ions between layers. sodiated transition metal oxides, na1xmo2 (m: transition metal), were representatively classified into two main groups, o3 type and p2 type (fig. 2), by delmas et al.33 those crystal structures comprise sheets of edgesha"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "review article chem soc rev 3532 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 that o03 and p03 represent monoclinic distortion of the o3 and p3 phases, respectively. the o3 type is stable when the x value is high in na1xmo2 (x is close to 0), in which the average oxidation state of m is close to 3+. electrochemical de-/sodiation of the o3 structure fig. 2 crystal structures; (a) perspective view (top) and top view of the (00l) layer of the o3 struc"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "p03. na+ ions energetically favor a prismatic environment when na+ ions are partly extracted from the crystal structure, which creates vacancies. at the same time, this extraction induces strong repulsion of oxygen in the na layers, and the interlayer distance thus expands. na+ diffusion occurs faster in the p03 phase due to the greater interlayer distance compared to o3. these transitions are followed by gliding of the mo2 slab without breakage of m–o bonds, as proposed by delmas et al.33 the p"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "na+ ions occupying prismatic (p) sites due to the large na ionic size. na+ ions occupy two different types of trigonal prismatic sites: naf (na1) contacts the two mo6 octahedra of the adjacent slabs along its face, whereas nae (na2) contacts the six surrounding mo6 octahedra along its edges. adjacent naf and nae sites are too close together (considering the na+ ionic radius) to be occupied simultaneously. the p2 phase is maintained in a wide desodiation range up to na0.46mo2. further desodiation"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "apart from phase transition, the p3 type can be produced not only via electrochemical desodiation, but also at low temperatures when synthesizing p2 type compounds; p3 and p2 are low and high temperature phases, respectively, indicating that phase transition requires breakage or reformation of m–o bonds via heat treatment. 2.1.1. na1xfeo2 and derivatives. the o3 type layers, a-, b-, and g- type lifeo2, have advantages including non-toxicity and cost effectiveness related to the abundance of fe. "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 4,
    "chunk_index": 4,
    "text": "et al.42,43 suggested the possibility of na+ deintercalation from a-nafeo2, creating na0.9feo2, using a chemical oxidizing agent (br2), while takeda et al.39 successfully performed electrochemical na+ deintercalation to na0.5feo2 with an approximate 125 ma h g1 capacity whereas lithium metal was used as the anode (fig. 3a), which accompanied phase transformation into the monoclinic p3 phase on charge. further investigation using mo¨ssbauer spectroscopy indicated that the fe3+/4+ redox reaction w"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3533 fig. 3 (a) charge and discharge curves of o3-nafeo2. (reprinted from ref. 39, copyright 1994, with permission from elsevier.) (b) charge and discharge curves of o3-na[fe1xnix]o2. (reproduced with permission from ref. 48, copyright 2014 american chemical society.) (c) clce performance for the fe3o4/na[ni0.25fe0.5mn0.25]o2 full cell. (reproduced with permission from ref. 51"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "presence of co enabled an increase in electrical conductivity, such that the electrode was active up to 30 c-rates (102 ma h g1). wang et al.48 stabilized the crystal structure of nafeo2 by forming a solid solution with nanio2, nafe1xnixo2 (0 r x r 1). the dilution of the fe concentration, nafe0.3ni0.7o2, effectively increased capacity and retention (135 ma h g1 and 74% retention after 30 cycles) via fe3+/4+ and ni3+/4+ redox couples (fig. 3b). in addition, they also recorded the 57fe mo¨ssbauer"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "coprecipitation, [ni1/3fe1/3mn1/3]c2o4, due to the difficulty of forming hydroxides when fe is involved. na[ni1/3fe1/3mn1/3]o2 could deliver a discharge capacity of 120 ma h g1 in the voltage range of 2–4 v for a half cell. they also tested the cyclability after adopting a hard carbon anode (100 ma h g1 after 150 cycles). oh et al. also synthesized spherical na[ni0.25fe0.5mn0.25]o2 using [ni0.25fe0.5mn0.25](oh)2.51 they found that the electronic states of ni, fe, and mn were 2+, 3+, and 4+, resp"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "the good reversibility of na[ni0.25fe0.5mn0.25]o2, the discharge capacity limit of 140 ma h g1 in o3 type layer materials needs to be overcome. the voltage limitation to 3.9 v prevents iron migration during charge. oh et al. suggested another approach to raise the upper voltage cutoff to 4.4 v, in order to offer more capacity in o3 type compounds using the mn3+/4+ redox, but reducing the concentration of fe3+ in na[li0.05(ni0.25fe0.25mn0.5)0.95]o2.52 as anticipated the compound was active based "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "review article chem soc rev 3534 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 structural transformation (o3 2 o03 2 p3 2 p03). further desodiation results in hexagonal p300 from p03 that shows much greater interslab distances of approximately 7 å compared to the p03 phase (5.6 å).53 this greater distance is not preferred because it induces intercalation of electrolytic molecules formed from oxidative decomposition of electrolytes at high voltage. h"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "made it possible to utilize the electrochemical oxidization of fe3+ to fe4+ reversibly, in particular in a voltage range of 3.8–4.2 v. upon desodiation, the p2 phase was maintained at 3.8 v by the oxidation of mn3+/4+, na0.42[fe0.5mn0.5]o2, after which the oxidation of fe3+/4+ led to phase transformation from p2 to op4 at 4.2 v (na0.13[fe0.5mn0.5]o2) as shown in fig. 4b. an in situ xrd study also demonstrated that p2- na2/3[fe0.5mn0.5]o2 undergoes a reversible p2–op4 phase transition at the end "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "the p2 phase, na0.62[fe0.5mn0.5]o2, was transformed into orthorhombic p02 (space group: cmcm), na0.97[fe0.5mn0.5]o2, by cooperative jahn–teller distortion at the end of discharge. in a p2 type layer structure, nae and naf sites are both simultaneously occupied at a ratio close to 2:1. this distribution results from the strong sodium– sodium repulsion interaction, which prevails over sodium–transition metal repulsion. hence, nae and naf cannot be occupied simultaneously in the p2 phase. all na+ i"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "phase, the resulting desodiation to 4.3 v leads to the formation of not op4, but also a new and unindexable ‘‘z’’ phase (nax[fe0.5mn0.5]o2, x o 0.25) with poor crystallinity (fig. 4c).55 talaie et al. revealed phase ‘‘z’’, which is a result of migration of fe3+ into tetrahedral sites in the interlayer space, showing a short range order between two adjacent layers.56 this migration is highly reversible, although it induces polarization of the cell. addition of ni instead of fe was very effective "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3535 fig. 4 (a) charge and discharge curves of p2-na2/3[fe1/2mn1/2]o2 and (b) sxrd patterns of p2-na2/3[fe1/2mn1/2]o2 samples charged to 3.8 and 4.2 v in which the p2 phase was transformed into op4 one. (reproduced by permission from ref. 46, nature publishing group, copyright 2012.) (c) operando in situ xrd patterns of the p2- nax[fe1/2mn1/2]o2 electrode. the red xrd patterns"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "review article chem soc rev 3536 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 xrd patterns of the p2-na0.7[fe0.4mn0.4co0.2]o2. (reproduced from ref. 58 with permission, copyright 2015 wiley-vch verlag gmbh & co. kgaa.) (f) first charge and discharge curves of the nax[fe1/2mn1/2]o2/nan3 composite electrode. (reprinted from ref. 60, copyright 2013, with permission from elsevier). mn4+/3+ oxidation below 3.5 v. this coincides with the results of yabuu"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "and the o2 phase was transformed into p2 upon sodiation. the p2 to o2 transition was reversibly achieved via the gliding of slabs due to prismatic site instability without na+ ions. this simple phase transition is related to the addition of co in the transition metal layers, as a result of structural stabilization. the phase transition from p2 to op4 is supposed to occur (fig. 4e); however, the added co that stabilizes the crystal structure is likely to suppress phase transition towards the op4 "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "regarding the na-deficient p2 structure is that such high capacities can be obtained only after the first cycle with a na metal counter electrode. compensation of na in the synthetic state causes formation of an o3 and/or o03 structure with a further increase in the na content of nax[fe1/2mn1/2]o2 (x z 0.8).59 therefore, the irreversible capacity of the first cycle is an intrinsic issue with p2 type materials. singh et al. suggested using a nan3 additive, sacrificial salt, which acts as follows:"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "oxidative decomposition at high potentials, an appropriate amount of nan3 is recommended because decomposition can cause swelling of cells. however, degassing is possible in pouch-type cells, such that the addition of sacrificial salts is likely to facilitate full cell configuration of the p2 cathode materials. sensitivity in air, in particular uptake of co2 in air, is a serious problem because of the formation of electrochemicalinactive mn4+ on the surface of active materials. ni-doping of the "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 8,
    "chunk_index": 4,
    "text": "revealed that direct hopping from one octahedral to an adjacent octahedral site requires high activation energy to overcome the barriers. in contrast, the p2 type framework has an open path for na+ diffusion that is expected to have a lower diffusion barrier, such that na+ diffusion occurs readily in the p2 structure relative to the o3 structure. as mentioned in section 2.1.1 and fig. 3a and b, nafeo2 exhibits poor electrochemical performance. again, nacoo2 is active in a very narrow range. howe"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 8,
    "chunk_index": 5,
    "text": "solid state reaction in the temperature range of 500– 800 1c under oxygen pressures of 0.4 r x r 0.45 (p03), 0.26 r x r 0.36 (p2), x = 0.23 (o03), and x = 0 (o3) in na1xcoo2. they suggested that oxygen-deficient naxcoo2y was a stabilized form due to the instability of co4+ when co3+ and co4+ are mixed. early work found that the p2 structure was maintained over a wide range 0.46 r x r 0.83 in naxcoo2, although two-phase domains were observed in the charge–discharge curves (fig. 5a).33 molenda et "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 8,
    "chunk_index": 6,
    "text": "na should be added to equalize the co oxidation state. this was proven experimentally by chou et al. using the oxygen nonstoichiometric single crystal na0.7coo2y (y b 0.073) in air and na0.75co2y (y b 0.08) in oxygen.70 for this reason, oxygen deficiency in na0.7coo2 induces a lower electrochemical capacity and operating voltage such that an oxygen atmosphere is required to minimize oxygen deficiency and improve electrode performance in terms of capacity and operating voltage."
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3537 delmas suggested the presence of several naxcoo2 structures and shacklette confirmed that it has four phases.71 in particular, o3, o03, and p3 layer structures were formed in a temperature range of 400– 600 1c, whereas the p2 structure was stable only when the heating temperature was 4700 1c in an oxygen atmosphere via the conversion of the p3 phase, which involved rotati"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "for the p2 and p3 phases could account for the behavior variation below 2.7 v, at which considerable na+ is included at trigonal sites. capacity retention was over 80% for 300 cycles for p2-na0.7coo2, p(eo)8nacf3so3 electrolyte at 90 1c.72 berthelot et al. revisited p2-naxcoo2 to investigate the phase diagram in a range of 0.45 r x r 0.9, in which nine potential drops were found during the second discharge (fig. 6a).62 weak polarization, which is an intrinsic property of p2-na0.7coo2 due to its "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "na0.79coo2 (no. 9), although they are present only in very narrow ranges. between the voltage plateau and the voltage drop, the diffraction peak shifts slightly with solid solution behavior. na ordering arises from two different repulsive interactions, sodium–sodium and sodium–cobalt. ions are located at the shared faces (na ). for p2-na ordered phase, half of na occupies nae appears at naf sites, which probably minimizes the repulsive"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "review article chem soc rev 3538 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 occupation of na at the shared edges (nae) for p2-na2/3coo2 was predicted by first-principles calculations63,67 and was ions in these two positions depends on the na content in the compound, which affects the na+/vacancy-ordered structure. croguennec et al. obtained t#2-li2/3[co2/3mn1/3]o2 via ionexchange from p2-na2/3[co2/3mn1/3]o2, in which the oxidation states of co an"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "in nax[co2/3mn2/3]o2 (fig. 6b). note that p2-na0.74coo2 formed nine distinct phases in a range of 0.5 r x r 0.9 in naxcoo2 (fig. 6a). however, the single phase domain for x = 0.5 in naxcoo2 is still found in na2/3[co2/3mn1/3]o2, although the voltage drop at that composition is lower than in naxcoo2. the main difference after mn substitution for co is abrupt voltage decay in a range of 0.65 r x r 0.83 in nax[co2/3mn1/3]o2. they further"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3539 revealed that co3+/2+ and mn4+/3+ reactions were involved in the low voltage plateau, as similar behavior was found when li1+x[ni1xycoxmny]o2 was overlithiated on discharge. yang et al.77 successfully stabilized the p2-na2/3[co1xmnx]o2 phase to x = 0.5, although the resulting capacity was limited to 120 ma h g1. meanwhile, co3+/2+ and mn4+/3+ reactions were more fig. 6 (a"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "review article chem soc rev 3540 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 dominant in a voltage range of 1.5–2.1 v. lowering the synthetic temperature to 700 1c resulted in p2/p3-na2/3[co0.5mn0.5]o2 compound.78 this biphasic compound greatly improved the capacity to 180 ma h g1 at a rate of 0.1c in a voltage range of 1.5–4.3 v compared with pure p2-na2/3[co0.5mn0.5]o2.77 rate cycling performance at a rate of 5c was also remarkably high, deliver"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "for cathodes. recently, matsui et al. explored the possibility of ca-doping at na sites to form na2/3xcaxcoo2.79 the similarity in the ionic radius of ca2+ (1.00 å) versus na+ (1.02 å) allows the incorporation of ca2+ into the na sites. although the delivered capacity decreased to some extent due to ca2+ in the na layers, na2/3xcaxcoo2 could suppress the multiple phase transition during charge and discharge. for example, na5/8ca1/24coo2 could be cycled even at 5 ma cm1 with very little capacity "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "na0.35coo2 decomposed to na0.7coo2 and co3o4 with oxygen release from the crystal structure. the napf6 salt rapidly reacted with na0.35coo2, and nacof3 was produced via the exothermic reaction. this reaction has not been reported in a lixcoo2 system thus far. selection of the electrolytic salt is another important issue to utilize the electrode in na cells. 2.1.5. na1xnio2 and derivatives. nanio2 is stable as two polymorphs, a low temperature type with an o3 layer structure and a high temperatur"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "o03 2 p03 2 p03 2 o03 multiple phase transition based on the ni3+/4+ redox reaction in the voltage range of 1.7–3.5 v.33 later work by vassilaras reported delivery of a high capacity of approximately 145 ma h g1 in a 2.2–4.5 v voltage range.81,82 by charging to 4.5 v, however, the capacity retention stabilized when the upper voltage cutoff was lowered to 3.75 v, with 94% of the initial capacity (115 ma h g1) after 20 cycles. the considerable coulombic efficiency was due to oxidation of the elect"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 12,
    "chunk_index": 4,
    "text": "of tetravalent mn induced the formation of ni2+ in na[ni0.5mn0.5]o2. the two-electron reaction led to a high discharge capacity of 185 ma h g1 in a voltage range of 2.5–4.5 v (fig. 7b), whereas optimization of the electrode performance limited the upper voltage cutoff to 3.8 v, resulting in a capacity above 100 ma h g1 over 20 cycles. in contrast to nanio2, the o3 2 o03 2 p3 2 p03 phase transition was highly reversible in a voltage range of 2.5–3.8 v (fig. 7c). fe-substituted na[ni0.5mn0.5]o2, h"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 12,
    "chunk_index": 5,
    "text": "capacity retention was improved in a voltage range of 2–4.3 v. in particular, a long irreversible reaction due to the formation of p300 phase transitioned to the op2 phase in a voltage range of 4–4.3 v on charge, although the length of the plateau did not appear on discharge. this peculiar behavior seems to be related to the effect of fe. recently, hwang et al. investigated the collation of ni and fe contents in na[ni0.75xfexmn0.25]o2 (x = 0.4, 0.45, 0.5, and 0.55).85 the structural and thermal "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 12,
    "chunk_index": 6,
    "text": "with increasing fe content is attributed to the improvement in electric conductivity derived from fe in the compound. also, their dsc study revealed that reactive ni4+ ions in the desodiated host material cause oxygen removal from the crystal structure, and that oxygen evolution can effectively suppress the fe increase in the crystal structure (fig. 7e). they also developed a radially-aligned hierarchical columnar structure in spherical particles with a varied chemical composition from the inner"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3541 ti-substituted o3-na[ni0.5ti0.5]o2 is also interesting due to its superior cyclability under moderate conditions, with an average operating potential of 3.1 v (vs. na+/na) and delivery of a reversible capacity of 121 ma h g1 at 20 ma g1. since the average oxidation states of ni and ti are 2+ and 4+, respectively, the ni2+/4+ redox reaction is responsible for electrochemic"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 14,
    "chunk_index": 0,
    "text": "review article chem soc rev 3542 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 fig. 7 (a) charge and discharge curves of o03-nanio2. (reproduced with permission from ref. 81, copyright 2013 the electrochemical society.) (b) the first charge and discharge curves of o3-na[ni0.5mn0.5]o2 and (c) structural evolution of na1x[ni0.5mn0.5]o2 (x = 0–1). (reproduced with permission from ref. 83, copyright 2012 american chemical society.) (d) ex situ xrd patte"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 15,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3543 ni3+/4+ contributes to high capacity delivery, while optimization of the ni content in the transition metal layer is important in ensuring capacity retention and thermal properties. 2.1.6. naxmno2 and derivatives. in comparison to the other compounds, these compounds are in particular interesting because of the cost effectiveness of the na and mn elements. naxmno2 (x = 0."
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 15,
    "chunk_index": 1,
    "text": "pmnm) is the high-temperature form. p2-na0.7mno2 is no more stable when the na layer is fully sodiated to namno2 at a low temperature. in a p2 layer structure, nae and naf sites are simultaneously occupied, due to the strong sodium–sodium repulsion interaction in the na layers (fig. 2). hence, simultaneous distribution of nae and naf is not possible in the p2 phase, but all na+ ions are located in one site to form a-namno2 (space group: c2/m, o03 structure, fig. 8a). the prime symbol is an indic"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 15,
    "chunk_index": 2,
    "text": "a rate of c/30 (fig. 8b).90 this behavior differs from an earlier report by mendiboure and hagenmuller.91 the charge and discharge curves show many plateaus and voltage drops, with eight and five charge and discharge plateaus, respectively. the hysteresis was reversible even after cycling. a long plateau observed at 2.63 v from na0.93mno2 to na0.7mno2 is associated with a two-phase reaction. their ex situ xrd investigation revealed that the second phase was na0.7mno2, although this was not consi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 15,
    "chunk_index": 3,
    "text": "active material), such that dissolution was not likely to affect electrode performance. their successive work demonstrated the readiness of the 1801 na–o– mn3+–o–na strip formation in contrast to vna–o–mn3+–o–na, albeit insufficient na+ ions in na5/8mno2, because na+ ions relax to the highly distorted octahedral sites, where they share the symmetric attraction of two neighboring jahn–teller distorted –o–mn3+–o–na configurations along the [100] axis.91 this structural imperfection may be the reas"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 15,
    "chunk_index": 4,
    "text": "is energetically more stable than orthorhombic b-namno2.93,94 b-namno2 is active in a narrow range (0.85 r x r 0.96) in naxmno2.91 in this range, a twophase domain is attributed to b-namno2 and naxmno2. phase transformation towards spinel was possible in b-limno2, because mn can migrate into tetrahedral li sites to form the spinel phase. this phase transition is unlikely to occur because tetrahedral sites rarely form in spinel with na due to the large ionic size of na+ relative to li+. reducing "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 15,
    "chunk_index": 5,
    "text": "by caballero et al. showed reversible capacity delivery of more than 150 ma h g1 in a voltage range of 2–3.8 v in na cells.98 they also suggested that intercalation of na+ ions occurred in several steps, but the resulting capacity fade progressed upon successive cycling tests. increasing the synthetic temperature to 900 1c, yabuuchi et al. could improve the capacity up to 190 ma h g1 in a voltage range of 1.5–4.3 v during several early cycles (fig. 8d).99,100 the electrode performance is similar"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 15,
    "chunk_index": 6,
    "text": "redox reaction, delivering approximately 160 ma h g1 in a voltage range of 2–4.5 v (fig. 8e). because of the similarity in the ionic size between ni2+ and mn3+, ni2+ prefers to occupy the mn3+ sites instead of mn4+ in na2/3mno2. their in situ xrd study revealed a reversible p2–o2 phase transition stemming from the oxygen shift, in which the o2 phase prevails at a voltage plateau above 4 v on charge and 3.8 v on discharge (fig. 8f). this is the main difference from p2-na0.67mno2; the absence of t"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 16,
    "chunk_index": 0,
    "text": "review article chem soc rev 3544 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 from p2 to o2 at 4.2 v.103 the long voltage plateau is the evidence of two forms of na+ ion ordering: one row of naf and two rows of nae in na1/2[ni1/3mn2/3]o2 and na orders in rows on either nae or naf order in na1/3[ni1/3mn2/3]o2, in which the latter corresponds to the region where the o2 phase is dominant. in the p2 phase, the path with the minimum energy passes throug"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 16,
    "chunk_index": 1,
    "text": "mobility in the o2 phase, as was confirmed experimentally. it is reasonable because the diffusion path of na+ ions is more spacious in the p2 phase relative to the o2 phase; this leads to a lower activation barrier (fig. 8e inset). hence, a cycling test in the voltage range of 2.3–4.1 v,"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 17,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3545 fig. 8 (a) crystal structure of monoclinic o03-na0.93mno2 projected in the a–c-plane and (b) charge and discharge curves of monoclinic o03-na0.93mno2. (reproduced with permission from ref. 90, copyright 2011 the electrochemical society.) (c) schematic illustration of orthorhombic p02-na0.7mno2. (reprinted from ref. 95, copyright 2010, with permission from elsevier.) (d) c"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 17,
    "chunk_index": 1,
    "text": "the reversible evolution of p2–o2 phase transition. (reproduced with permission from ref. 101, copyright 2001 the electrochemical society.) which is associated with the p2 phase reaction, resulted in o2 phase formation in a deeply desodiated state to retain the excellent cycling behavior retaining 96% of the initial capacity capacity for a long-term. surprisingly, li substitution in the (b80 ma h g1). they further extended their work to inhibit transition metal layer, na0.80[li0.12ni0.22mn0.66]o"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 17,
    "chunk_index": 2,
    "text": "transition.106–113 a decrease in the initial charge capacity is natural because the electro-active species ni2+ was reduced by substitution, as shown in fig. 9a, which reflects the origination of the capacity drop from the ni2+/4+ redox reaction. stepwise voltage plateaus were not dominant throughout the operation range of 2–4.5 v.106,107 compared with na2/3[ni1/3mn2/3]o2, the capacity drop in na0.67[ni0.2mg0.1mn0.7]o2 was only 6 ma h g1 for 50 cycles.107 using in situ xrd, instead of the p2 pha"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 17,
    "chunk_index": 3,
    "text": "p2 phase is retained as the major phase, though transition to op4 because deep desodiation is observed at high voltage as a minor phase. hence, the p2–o2 transition and the na+/vacancy ordering in na2/3[ni1/3xmgxmn0.7]o2 are suppressed during cycling via mg substitution. this p2–op4 phase transition is highly reversible; the cycling performance demonstrates its superiority compared to the p2– o2 phase transition.101 while zn-substituted p2- na2/3[ni1/3xznxmn2/3]o2 induces reversible phase transi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 17,
    "chunk_index": 4,
    "text": "redox has superior capacity delivery. the substituent stabilized the host structure and the resulting cyclability was significantly improved, in particular for al-doped p2-na2/3[ni1/3mn2/3]o2, which had 94.8% (from b147 ma h g1) retention over 30 cycles. replacement with a trivalent 3d transition metal element such as co and fe is also interesting because they are electrochemically active in the same operating range.114–116 yoshida et al. investigated the composition of p2-na0.7[mn0.6ni0.3co0.1]"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 17,
    "chunk_index": 5,
    "text": "redox reaction. as cycles went by, the length of the upper voltage plateau related to ni2+/4+ and the lower voltage plateaus related to mn3+/4+ 2 v decreased. this can be interpreted in two ways: (1) the progressive formation of the o2 phase at high voltage and the effect of the jahn–teller distortion in the crystal lattice. this further limited the cycling region to three parts: 1.5–4.3 v, 1.5–4.0 v, and 1.7–4.0 v. it is evident that, although the jahn– teller distortion is present in low volta"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 17,
    "chunk_index": 6,
    "text": "(p2-na0.7[mn0.65ni0.15fe0.2]o2) led to an improvement in capacity and retention: 208 ma h g1 with 71% retention over 50 cycles.115 the phase transition was p2 to op4 in this case.117 tetravalent ti-substituted p2- na2/3[ni1/3mn2/3xtix]o2 yielded a wide solid solution range of 0 r x r 2/3.118,119 due to the similarity of both mn4+ and ti4+ in the valence and ionic radius, such a solid solution can be formed readily throughout the range. the reason remains unclear, but an increase in the ti conten"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 18,
    "chunk_index": 0,
    "text": "review article chem soc rev 3546 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 g1 with an average operating voltage of approximately 3.7 v on discharge, which corresponds to 470 w h kg1. more importantly, the stepwise voltage profiles of na2/3[ni1/3mn2/3]o2 were obviously diluted by ti substitution. xrd suggested that the volume change of the fully charged state was reduced from 23.1% in ti-free compounds to 12–13% for ti-substituted compounds, conf"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 18,
    "chunk_index": 1,
    "text": "approximately 220 ma h g1 for na2/3[mg0.28mn0.72]o2 (fig. 9e) and 180 ma h g1 for na5/6[li1/4mn3/4]o2. similarly, a recent reportby slateret al.alsoshowed a largecapacity of 200mahg1 for p2-na0.85[li0.17ni0.21mn0.64]o2.7 taking themn3+/4+ redoxspecies into account, it is not possible to explain the delivery of high capacity. indeed, there is almost no delivery of capacity in the voltage cutoff up to 4 v on charge; however, those capacities are delivered above 4 v, which is related to oxidation o"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 19,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3547 fig. 9 (a) continuous charge and discharge curves of p2-na0.67[mg0.1ni0.2mn0.7]o2 and (b) in situ powder x-ray diffraction of p2-na0.67[mg0.1ni0.2mn0.7]o2 showing the reversible evolution of p2–op4 phase transition at the end of the charge and beginning of the discharge. (reproduced with permission from ref. 107, copyright 2016 american chemical society.) (c) continuous c"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 20,
    "chunk_index": 0,
    "text": "review article chem soc rev 3548 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 surface modification was performed on p2-na2/3[ni1/3mn2/3]o2 via wet milling in an al-containing aqueous solution.123 na-containing transition metals react very quickly when moisture is present. although p2-na2/3[ni1/3mn2/3]o2 is stable in air, ion exchange between na and h occurs when the reaction progresses in an aqueous medium. optimized experimental conditions facilit"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 20,
    "chunk_index": 1,
    "text": "na1xtio2 and derivatives. natio2 was first synthesized by hagenmuller et al. and maazaz et al. evaluated its potential as a na+ insertion/extraction material.124,125 this material underwent phase transformation from o3 2 o03, in which the chemical composition reaches na0.7tio2 (approximately 75 ma h g1) on desodiation, showing an average operating voltage of 1 v, which is suitable for an anode. in contrast to the other materials, the electrode exhibited a low operating voltage of b1 v, followed "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 20,
    "chunk_index": 2,
    "text": "and electrochemical methods, in which extraction facilitated the formation of na0.4cro2.127 they also confirmed the formation of cr4+ for desodiated na0.5cro2, as analyzed based on magnetic susceptibility. recently, komaba et al. revisited o3 type layer-structured nacro2, in which na ions could be inserted into/extracted from the host structure.128 in contrast to licro2 in li cells, nacro2 could deliver a capacity of approximately 110 ma h g1 in the voltage range of 2–3.6 v due to the greater in"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 20,
    "chunk_index": 3,
    "text": "fading during cycling.128,129 in consideration of synthetic conditions, nacro2 is usually produced in a reducing atmosphere to retain the oxidation state of cr at 3+. this condition enables carbon coating, which can dramatically improve electrode performance. ding et al. found that citric acid- assisted carbon coating slightly improved the cycling stability of nacro2 electrodes.130 although the cycling performance of carbon- coated nacro2 was improved compared to the bare material, operation at "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 20,
    "chunk_index": 4,
    "text": "the carbon-coated nacro2 electrode exhibited excellent cyclability and an ultrafast rate capability of up to a 150c-rate (fig. 10b). high electrical conductivity successfully promotes reversible insertion and extraction of sodium ions accompanied by a facile complementary redox reaction of the cr3+/cr4+ couple as confirmed by xanes (fig. 10c–e). the nacro2 electrode was also sufficiently stable in an intermediate temperature ionic liquid, nafsa-kfsa, at 363 k.132 excellent electrochemical perfor"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 20,
    "chunk_index": 5,
    "text": "to the formation of naoh and na2co3 on the surface of active materials. the sodium diffuses to the surface, and electrochemically inactive parts are formed within the particles. even worse, the naoh and na2co3 formed are electrical insulators. the carbon coating can prevent moisture uptake due to its hydrophobic characteristics. 2.1.9. na1xvo2 and derivatives. among several na1xvo2 compounds, only two compositions, x = 0 and x = 0.3, have been identified;133,134 the former represents o3 and the "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 20,
    "chunk_index": 6,
    "text": "transforms into the o03 structure via monoclinic distortion. na+ extraction above x = 0.5 in na1xvo2 deteriorates electrode performance, resulting from the migration of vanadium ions into interslab vacancies. this phenomenon is similar to na1xcro2.128,130 despite considerable voltage variation and oxygen sensitivity, capacity fading was negligible for 15 cycles, as reported by hamani et al.135 in p2-na0.7vo2, the resulting charge and discharge behavior is very reversible in a voltage range of 1."
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 21,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3549 based compounds presented in sections 2.1.2 and 2.1.6, the related phase transition is more or less complicated (fig. 11c and d). an abrupt voltage drop occurs due to the single phase domain and the plateaus are associated with the solid solution reaction. hence, four single phase domains and solid solutions are present between the single phase domains, which have been id"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 21,
    "chunk_index": 1,
    "text": "cubic closepacked oxygen array. na2ruo3 shows metallic conduction and is crystallized in layer structures consisting of na and na1/3ru2/3 slabs.137 the crystal structure is indexed as hexagonal r3%m without ordering of the fig. 10 (a) charge and discharge curves of o3-nacro2. (reprinted from ref. 128, copyright 2010, with permission from elsevier.) (b) rate performances of 3.4 wt% carbon- coated o3-nacro2. (c) ex situ xrd patterns obtained during charging and discharging, cr k-edge xanes spectra"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 22,
    "chunk_index": 0,
    "text": "review article chem soc rev 3550 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 superstructure, unlike li2mno3. the first discharge capacity was approximately 150 ma h g1 at the first cycle and this capacity was maintained throughout the cycling test. for na+ insertion and extraction, the electrochemical reaction proceeded via a two-phase reaction with hex-i and hex-ii phases. although further studies are needed to elucidate the structural evolution "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 23,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3551 fig. 11 voltage–composition curves of (a) o3-navo2 and (b) p2-na0.7vo2. (reprinted from ref. 135, copyright 2011, with permission from elsevier.) p2-naxvo2: (c) the limits of the biphasic domains and the solid solutions (d) in situ x-ray diffraction data recorded during the galvanostatic intermittent titration technique experiments. (reproduced by permission from ref. 136"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 24,
    "chunk_index": 0,
    "text": "review article chem soc rev 3552 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 structures, na+ ions can diffuse in x, y, and z directions; fast na+ many of these compounds are synthesized at low temperatures, migration is possible relative to two-dimensional structures. such that their large surface area with small particles contributes fig. 12 (a) the crystal structure of na0.44mno2 perpendicular to the ab–plane. (reproduced with permission from re"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 24,
    "chunk_index": 1,
    "text": "copyright 2013 the royal society of chemistry.) to unexpectedly high rate performance. since the ionic size of na+ is larger than that of li+, the host structure should be sufficiently rigid or have a large tunnel size to facilitate the entry of large ionic species. otherwise, the crystal structure could collapse upon repetitive na+ insertion and extraction. these electrodes are active compared to na metal; however, the main difficulty is that a sodiated anode is needed to construct a full cell."
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 24,
    "chunk_index": 2,
    "text": "na4mn4ti5o18, is particularly interesting because of its cycling stability with a reasonable capacity, b120 ma h g1. doeff et al. first examined the na+ insertion properties of na0.44mno2 with a solid-state polymer electrolyte at 85 1c.139,140 the crystal structure consists of four mno6 octahedral sites with mn4+ and one mno5 square-pyramidal site with a half of mn3+ (fig. 12a). these are connected by corner sharing to"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 25,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3553 form two types of tunnels. each unit cell contains a large s-shaped tunnel with four sodium sites, as well as two identical pentagonal tunnels. the na sites in the small tunnels are nearly fully occupied, while the large tunnel sites are partially occupied: na1 and 2 sites in the s-shaped tunnels, half-filled; na3 sites with an inner position in the small tunnels, fully-f"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 25,
    "chunk_index": 1,
    "text": "not generally extracted. an in situ xrd study revealed the structural evolution during the electrochemical reaction in na cells. a biphasic reaction was found upon reduction in the range of x = 0.2–0.44 in naxmno2. in a range of x = 0.44–0.612 naxmno2, not a single solid solution, but several multiphase reactions were associated with the electrochemical oxidation. unfortunately, the high rate test caused a drastic capacity drop (to b1016 s cm1) due to some kinetic limitations, as calculated by c"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 25,
    "chunk_index": 2,
    "text": "high crystallinity provided the long-term durability for na+ insertion and extraction and the reduced diffusion path also contributed to excellent capacity retention. the application of na0.44mno2 electrodes has also been highlighted in aqueous systems. whitcare et al. documented a full cell with a na0.44mno2 cathode and an activated carbon anode in a 1 m naso4 aqueous electrolyte.144 despite a smaller capacity in the aqueous solution relative to the aprotic ones, the full cell could be tested w"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 25,
    "chunk_index": 3,
    "text": "few studies have explored na-free mno2 for na+ insertion. because of the relatively large tunnel size of a- and b-mno2, na+ insertion is also possible for both a- and b-mno2. a-mno2, which is called hollandite, is composed of double chains of edge-sharing mno6 octahedra that are linked at the corners to form a 2 2 and 1 1 tunnel structure (fig. 12c). because of the large size of the 2 2 tunnel, na+ insertion into the empty tunnel is possible, as suggested by su et al.146 and islam et al.147 (fig"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 25,
    "chunk_index": 4,
    "text": "insertion of ion species, i.e., li+, is not easy due to the small size of the 1 1 tunnels.148 su et al. also tested b-mno2 in na cells, which delivers approximately 300 ma h g1 during the first cycle.146 in comparison with a-mno2, the b-mno2 nanorods exhibited a higher discharge capacity of approximately 145 ma h g1 after 100 cycles. they attributed the better electrochemical performance of b-mno2 to the large number of empty tunnels that accommodate the na+ ions. since both a- and b-mno2 have a"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 25,
    "chunk_index": 5,
    "text": "o03 namno2 via electrochemical cycling and showed stable cycling performance. 2.2.2. vanadium oxides. vanadium oxides have been intensively studied as cathode materials for lithium-ion batteries. in na cells, a-, b-naxv2o5, and na1+xv3o8 were investigated for na+ ion insertion by west et al. in the 1980s. a-v2o5 and na1+xv3o8 have layered structures, and b-naxv2o5 has a three-dimensional structure with wide channels.151 in experiments, upon na+ ion insertion, a-v2o5 underwent a phase transition "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 25,
    "chunk_index": 6,
    "text": "which the interslab distance was approximately 13.5 å, which is significantly larger than that of conventional v2o5 showing 4.4 å.152 this was possible because they used electrochemical deposition from aqueous vanadyl sulfate on a ni foil substrate followed by heat treatment at 120 1c for removal of water molecules present in the interslabs (fig. 13a). the electrode was activated by a v5+/4+ redox reaction in a voltage range of 1.5–3.8 v, but showed sloping charge– discharge curves. the electrod"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 26,
    "chunk_index": 0,
    "text": "review article chem soc rev 3554 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 was related to the electrochemical reaction. both na+ insertion into vo2(b) and pseudo-capacitive behavior were confirmed via xrd and xas studies. 2.2.3. metal fluorides. fluorine compounds have a high discharge voltage due to their ionic metal–ligand bonds. perovskite-type metal trifluorides with a corner-sharing matrix (r3%c) have large bottlenecks in diffusion pathways"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 26,
    "chunk_index": 1,
    "text": "nafef3 had a relatively a large discharge capacity (128 ma h g1) with an average cell voltage of 2.7 v (fig. 13c), while nanif3 and namnf3 suffered from capacities below 40 ma h g1 with sloppy voltage decay. even when the synthesis method was switched from mechanomilling to a solution-based method, the resulting capacity did not exceed the prior report at the same current density (0.2 ma cm1), but instead reached 180 ma h g1 at a rate of 0.01c.157 the strong ionic character of the m–f bond must "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 27,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3555 2.3. three-dimensional polyanion compounds in comparison with oxide and fluoride systems, transition metal polyanion materials have shown significant thermal stability, which is supported by the presence of covalent bonds such as p and o, in particular cathodes are in a deeply-charged prevail in li cells and also apply to na systems, since the related material chemistry d"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 27,
    "chunk_index": 1,
    "text": "na sites, (ii) partial or full replacement of fe by the other transition metals, (iii) a mixed anion system with f, oh, co2, and (iv) extension towards mixed phosphate (po4)3 and pyrophosphate (p2o7)4 ions also stabilize the crystal structure in the na system. unfortunately, because moisture absorption occurs easily in these polyanion systems, avoiding hydration and formation of naoh on the surfaces of particles can be a challenge. heterogeneous surfaces may lead to misinterpretation of the elec"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 28,
    "chunk_index": 0,
    "text": "review article chem soc rev 3556 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 with two distinct voltage plateaus, delivering over 120 ma h g1 150 olivine nafepo lifepo"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 29,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3557 4 capacity (fig. 14c).163–173 during the electrochemical reaction, 4 the oxidation state of fe is systematically altered followed by 163 3+/2+ a redox reaction of fe , as confirmed by the xas studies performed by ali et al.173 carbon coating led to excellent long6 octahedra and po4 tetrahedra. the maricite term cyclability. an interesting feature of triphylite nafepo4 fig"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 30,
    "chunk_index": 0,
    "text": "review article chem soc rev 3558 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 group, copyright 2007.) (e) charge/discharge curves of the na2fepo4f cell cycled at a rate of 6.2 ma g1. (reprinted from ref. 178, copyright 2012, with permission from elsevier.) approximately 2 orders of magnitude lower.175 recent density functional theory calculation revealed that the migration energy of na+ ions in nafepo4 is 0.05 ev higher than that of li+ ions in lif"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 30,
    "chunk_index": 1,
    "text": "of na+ ions, allowing 0.6 mol na+ into nax[fe0.5mn0.5]po4. since large na+ ions are associated with migration, minimization of the interface energy is essential to the utilization of the other transition metals such as co, mn, and ni, among others. the ionicity of fluorides over oxides and sulfides is ascribed to their higher electronegativity, which thus increases the operating voltage of the electrodes. this concept was successfully applied to the discovery of na2fepo4f, which is applicable to"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 30,
    "chunk_index": 2,
    "text": "when fe was substituted for mn greater than 25%. in the case of the tunnel structure, the na cations are located within channels.177 notwithstanding the advantages of high operating voltage relative to nafepo4, the strong ionicity lowers the intrinsic electric conductivity. hence, the bare na2fepo4f delivered almost no capacity. surprisingly, the carbon-coated na2fepo4f could deliver approximately 110 ma h g1, which corresponds to a 90% theoretical capacity.178 two voltage plateaus are evident w"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 30,
    "chunk_index": 3,
    "text": "redox is clearly greater than that of the fe2+/3+ redox, which is similar to those observed in lifepo4 and limnpo4. in place of divalent transition metal elements, a trivalent element is also available in the form of navpo4f. barker et al. first introduced the material as an electrode material for hybrid-ion cells in 2003.181 during the initial charging, na+ ions are extracted from the host material while na+ ions are plated on the surface of the li metal anode in a li cell. this process release"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 30,
    "chunk_index": 4,
    "text": "po4 tetrahedra (fig. 15a). na+ ions are present in the empty channel and diffuse along the c-axis. coupling with a hard carbon anode, navpo4f, led to two-step voltage responses (fig. 15b), while the delivered discharge declined to less than 50% of the initial capacity (approximately 82 ma h g1). zhao et al. found another crystal system in this compound: monoclinic (c2/c) as the low temperature form and tetragonal (i4/mmm) as the high temperature form.183 cr- doping into the v site of navpo4f cry"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 30,
    "chunk_index": 5,
    "text": "crystal structure of na3v2(po4)2f, which can be presented as na1.5vopo4f0.5 instead of navpo4f. in this structure, na+ ions are disordered across two sites (8h and 8j) and the oxidation state of v is 4+ (fig. 15c). the crystal structure is composed of a vo5f octahedral and po4 tetrahedra sharing o vertices parallel to the ab-plane. along the c-axis direction, vo5f octahedra are connected via f vertices located in the same ab-plane as the disordered na atoms. this structure could accommodate 0.56"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 30,
    "chunk_index": 6,
    "text": "at the lower voltage plateau. these results, including capacity and retention, agree with an earlier report by barker et al.181 the oxidation state of v was lowered to 3.8+ in na1.5vpo4.8f0.7.187 in comparison with na1.5vopo4f0.5,188 the oxygen content was reduced slightly, but the equivalent content of f increased. although structural refinement was performed based on space group p42/mnm, the xrd pattern, including the bragg peak position, is the same for both compositions. na1.5vpo4.8f0.7 is c"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 31,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3559 open framework with na+ ions located at interstitial sites (fig. 15e). na1.5vpo4.8f0.7 provided a discharge capacity of approximately 137 ma h g1 based on the v3.8+/5+ redox reaction (1.2 mol na+ per formula unit in na1.5vpo4.8f0.7) with excellent cyclability for 500 cycles (fig. 15f). to further lower the average oxidation state of v efforts were made employing na3v2(po4"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 32,
    "chunk_index": 0,
    "text": "review article chem soc rev 3560 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 fig. 15 (a) the crystal structure of a-na3al2(po4)2f3 along the a-axis. (reprinted from ref. 182, copyright 1999, with permission from elsevier.) (b) electrochemical performance data for a typical hard carbon//navpo4f cell. (reproduced with permission from ref. 181, copyright 2003 the electrochemical society.) (c) the crystal structure of na1.5vopo4f0.5 in the (ac) plane "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 33,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3561 na1.5vpo4.8f0.7 cathode (voltage window: 2.0–4.5 v vs. na+/na) appeared with the average voltage (3.8 v vs. na+/na) as a horizontal dotted line. (reproduced with permission from ref. 187, copyright 2013 american chemical society.) (g) synchrotron radiation diffraction data in the p42/mnm space group (top) and in the low- symmetry orthorhombic group amam (bottom). (reprodu"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 33,
    "chunk_index": 1,
    "text": "rhombohedral na3v2(po4)3 with space group r3%c, which will be addressed in section 2.3.4. similar to na1.5vopo4f0.5186 and na1.5vpo4.8f0.7,187 the presence of fluorine with phosphorus ions raises the operating voltage originating from the strong inductive effects of the anion group, even though the v3+/4+ redox couple is available for delivery of high capacity (approximately 120 ma h g1) in na3v2(po4)3f3 compounds, with two voltage plateaus at 3.7 and 4.2 v (fig. 15h). computational calculations"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 33,
    "chunk_index": 2,
    "text": "pnma space group, which is the same as olivine lifepo4. the presence of an empty channel enabled na+ insertion into (moo2)2p2o7, with a discharge capacity of 190 ma h g1 corresponding to 3.1 mol na+ per formula unit in (moo2)2p2o7, although the rate capability was limited due to the large ionic size of the na+ ion. in 2008, adam et al.193 introduced the crystal structure of li2mnp2o7, and it was confirmed using li+ intercalation cathode materials.194,195 recent developments in sibs have motivate"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 33,
    "chunk_index": 3,
    "text": "staggered fashion, thus creating large tunnels along the [110] direction, which accommodate na atoms at four distinct sites. however, these materials are not competitive cathode materials because of the two phosphate groups per transition metal in terms of capacity (theoretical capacity approaching 97 mah g1) even though the related material chemistries are interesting. the appearance of stepwise voltage plateaus (roughly at 2.5 and 3 v) may indicate the presence of na+/vacancy ordering in the s"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 33,
    "chunk_index": 4,
    "text": "three-dimensionality and low migration energy for na+ ion diffusion in na2fep2o7. the good electrode performances of na2fep2o7 were further evidenced in an inorganic ionic liquid nafsa-kfsa (fsa: bis(fluorosulfonyl)amide) at 363 k.200 ha et al. extended the composition to na3.32fe2.34(p2o7)2, which can be represented as na1.66fe1.17p2o7, of which the crystal structure is identical to na2fep2o7, but the new composition is able to increase the theoretical capacity to approximately 110 ma h g1.201 "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 33,
    "chunk_index": 5,
    "text": "elements to improve electric conductivity. recent work of barpanda et al. identified a new polymorph of b- na2mnp2o7, which was also stabilized into a triclinic structure, p1.% 202 the structure consists of distorted mno6 octahedral and po4 tetrahedral blocks creating tunnels accommodating na atoms along the [001] direction. the structure has corner-sharing mno6–mno6 (mn2o11) dimers, which are in turn connected by po4–po4 (p2o7) diphosphate units in a mixed-edge and corner-sharing fashion (fig. "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 33,
    "chunk_index": 6,
    "text": "they also suggest a new pyrophosphate oxyanionic framework compound, tetragonal na2(vo)p2o7 with space group p4bm.202 this material belongs to the fresnoite family consisting of a vo5 or (vo)o4 square pyramid and po4 tetrahedral units (fig. 16e). each vo5 pyramid is connected to four independent po tetrahedra in a corner-sharing fashion, thus forming [vp2o11] units. also, each po4 tetrahedron is connected to two vo5 units and one po4 unit that share corners. the delivered capacity was approximat"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 34,
    "chunk_index": 0,
    "text": "review article chem soc rev 3562 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 the theoretical capacity (93 ma h g1) (fig. 16f). the discharge curve was sloppy with the v5+/4+ redox reaction showing an average operating voltage of 3.8 v. apart from the above-mentioned compounds, the other pyrophosphates with ni(ii), cu(ii), ti(ii), co(ii) and higher transition metal oxidation states have not yet been explored as host materials for na+ insertion. 2.3"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 35,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3563 provide better na+ diffusion in comparison with a one-dimensional channel. double chains are formed from simple parallel chains along the [010] direction. kim et al. first utilized the mixed phosphate framework by introducing fe2+ in the m sites to form na4fe3(po4)2p2o7.205 their first principles calculations demonstrated a low activation barrier for na+ diffusion lower t"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 35,
    "chunk_index": 1,
    "text": "197, copyright 2012, with permission from elsevier.) (c) the crystal structure of b-na2mnp2o7 polymorph consisting of mno6 octahedra (pink), po4 tetrahedra (light purple) and na atoms (yellow) along [110] projection in which the possible sodium migration tunnels are highlighted by black dotted rectangles and (d) charge and discharge profiles of the b-na2mnp2o7 cathode at a rate of c/20. (reproduced with permission from ref. 202, copyright 2013 the royal society of chemistry.) (e) the crystal str"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 36,
    "chunk_index": 0,
    "text": "review article chem soc rev 3564 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 material could deliver a capacity of 105 ma h g1 with an average operating voltage of 3.2 v (fig. 17b). nose et al. investigated na4co3(po4)2p2o7 instead of the compound with fe to improve the energy density.206 knowledge obtained from experiments with licopo4, which exhibits a high operating voltage from the co2+/3+ redox reaction, was applied to na4co3(po4)2p2o7.207 alt"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 36,
    "chunk_index": 1,
    "text": "galvanostatic charge/discharge profiles of na4fe3(po4)2(p2o7) under a c/40 rate and the calculated average voltage at each region, where the inset shows the dq/dv curve of initial charge/discharge profiles. (reproduced with permission from ref. 205, copyright 2012 american chemical society.) (c) galvanostatic charge/discharge curves at 1st, 10th and 50th cycles of na4co3(po4)2p2o7. (reprinted from ref. 206, copyright 2012, with permission from elsevier.) (d) the projected crystal structure along"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 37,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3565 approximately 80 ma h g1 even at 25c-rates (4.25 a g1). this superior electrochemical performance was attributed to the help of the three- dimensional na+ diffusion pathways in the crystal structure. in an attempt to mitigate the multistep voltage plateaus, they synthesized na4[co2.4mn0.3ni0.3](po4)2p2o7. the material also exhibited an average operating voltage of 4.5 v, "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 38,
    "chunk_index": 0,
    "text": "review article chem soc rev 3566 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 by lim et al.208 et al. demonstrated the possibility of na+ extraction to form po po fig. 17d). based on the v fig. 17e). addition of rgo further extended its cycle life to 1000 cycles with 78% capacity retention. po electro- po"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 39,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3567 7 4 4 chemical na+ extraction was investigated by masquelier211 and 4 6 plashnitsa et al.212 7 6 2 7 4 4 3 2 4 3 + ion diffusion 4 3 3+/4+ 209 the fig. 18 (a) the crystal structure of na3v2(po4)3. (reprinted from ref. 209, copyright 2012, with permission from elsevier.) (b) tem bright-field image of carbon-coated na3v2(po4)3. (reproduced from ref. 213 with permission, cop"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 40,
    "chunk_index": 0,
    "text": "review article chem soc rev 3568 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 to 3.8 v for carbon-coated na3v2(po4)3. (reprinted from ref. 209, copyright 2012, with permission from elsevier.) (d) long term cycle life and coulombic efficiency for 30 000 cycles at a rate of 40c for carbon-coated na3v2(po4)3. (reproduced from ref. 214 with permission, copyright 2013 wiley-vch verlag gmbh & co. kgaa.) rate of 40c (4.68 a g1) with superior rate capabili"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 40,
    "chunk_index": 1,
    "text": "extraction at the m2 site, which is related to the formation of nav2(po4), in which only one na (6b, m1) resides in the crystal structure. nmr further revealed that, in na3v2(po4)3, the na atoms were not randomly distributed at m2 sites, but appeared in an ordered arrangement locally; an na+ ion at the m2 sites in na3v2(po4)3 is mobile, whereas an na+ ion at the m1 site is immobile, corresponding to 2 mol na+ per formula unit in na3v2(po4)3, while 1 mol na+ per formula unit in na3v2(po4)3 can re"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 40,
    "chunk_index": 2,
    "text": "na systems, namely, namso4f (m: fe, co, and mn), as suggested by barpanda et al.217 the compounds are crystallized in a monoclinic structure with a p21/c space group (fig. 19a). tripathi et al. calculated the activation energy for na+ diffusion. although nafeso4f has a three-dimensional structure in only one direction, [010], it has relatively low activation energy (0.6 ev).218 the measured ionic conductivity of the compound was sufficiently high at approximately 107 s cm1. notwithstanding, the "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 40,
    "chunk_index": 3,
    "text": "na2fe2(so4)3 does not contain [m2(xo4)3] units, but has a unique structure with an alluaudite type framework (fig. 19c). feo6 octahedra share edges, forming fe2o10 dimer units. these fe ions could be assigned to two distinct groups, fe(1) and fe(2), since local structures of fe(1) and fe(2) were found to have two doublets in the mo¨ssbauer spectra. the fe2o10 dimers were linked with so4 units in a corner-sharing fashion, generating a threedimensional network framework with large tunnels along th"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 40,
    "chunk_index": 4,
    "text": "a moderate rate capability (fig. 19d). the structure may be able to extend to several family compounds, adopting not only fe, but the other transition metal elements such as ni, co, v, and mn, among others. sodiated metal carbonophosphates, such as sidorenkite na3mpo4co3 (m: mg, mn, fe, co, ni, and cu), were recently introduced as a new intercalation cathode by chen et al.220,221 two different series of (po4)3- and (co2)2-ions have bonds with m in na3mpo4co3 compounds, which are stable with a si"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 40,
    "chunk_index": 5,
    "text": "may have good intercalation properties.222 carbophosphate showed high discharge (125 ma h g1) (fig. 19f), which represented 66% of the theoretical capacity (191 ma h g1). it is interesting that na3mpo4co3 underwent a topotactic solid solution reaction during cycling, activated by a two-electron electrochemical reaction of mn2+/3+ and mn3+/4+ redox couples. 2.3.6. cyanides and organic compounds. prussian blue and its analogues were investigated as hosts for alkali ions, but those works received l"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 40,
    "chunk_index": 6,
    "text": "na in the mfe[cn]6 perovskite framework: na1.4mfe[cn]6 (fm3m) and na1.72mfe[cn]6 (r3%m).229 the double-perovskite ordering of both the anion orientations and the cations introduces a rhombohedral site symmetry along each of the four [111] axes that would stabilize alkali-ion displacement along a cubic [111] axis toward the more octahedral-site complex. the four-fold degeneracy of these displacements keeps the cubic phase at higher temperature and lower na concentration, but a cooperative na disp"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 41,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3569 to 3.1 v on charge and 2.8 v on discharge, delivering a discharge capacity of approximately 120 ma h g1.230 the electrode was substantially stable over 600 cycles with excellent capacity retention. na4fe[cn]6 was electrochemically active in na cells, showing approximately 90 ma h g1 on discharge with a flat voltage plateau at 3.4 v.231 the lower capacity is due to the one"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 41,
    "chunk_index": 1,
    "text": "the c-axis and (d) galvanostatic charging and discharging profiles of the na2xfe2(so4)3 cathode cycled between 2.0 and 4.5 v at a rate of c/20 (2 na in 20 h) at 25 1c. first (1st) cycle is shown in dashed black line, and 2nd–5th cycle in solid black lines. (inset) the differential galvanostatic profiles"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 42,
    "chunk_index": 0,
    "text": "review article chem soc rev 3570 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 (dq/dv) of the na2fe2(so4)3 cathode. (reproduced by permission from ref. 219, nature publishing group, copyright 2014.) (e) the structure of na3mnpo4co3 viewed along [001]: mn octahedra, brown; po4 tetrahedra, blue; co3 triangular planar, black; sodium, green (na1 site) and yellow (na2site) spheres and (f) the resulting voltage curves of na3mnpo4co3 at the first, second, "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 42,
    "chunk_index": 1,
    "text": "displacement along a [111] resulting in rhombohedral symmetry of na1.72mnfe[cn]6 (lower) and (b) charge/discharge curves of a na1.4mnfe[cn]6/na half-cell at various current densities (follow the arrow by order of 0.1, 0.85, 3.5, 8.5, 17, 26, and 40c, 120 ma g1 at 1c). (reproduced from ref. 229 with permission, copyright 2013 wiley-vch verlag gmbh & co. kgaa.) (c) electrochemical redox reaction mechanism of na+ ions with na2c8h2o6/na4c8h2o6 at potentials of 2.3 v and (d) the resulting initial dis"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 43,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3571 3. anode materials as mentioned in section 2, several platforms of cathode materials have been introduced for sibs.239 simultaneously, as the cathode counterpart, the recent development of anodes for sibs has been achieved by the use of selected carbonaceous materials, transition metal oxides (or sulfides) and intermetallic and organic compounds, as anodes.240 research on"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 43,
    "chunk_index": 1,
    "text": "alloying compounds of group 14 or 15 elements motivated by the alloying reaction are recommended as possible candidate materials with the help of an electro-conducting carbon matrix to improve their specific capacity and cyclability.244,245 such conversion and alloying reaction materials are known to deliver high capacities but suffer from huge volume expansion of the host materials due to the continuous self-pulverization of the electrode materials.240,243 more seriously, to compete with lithiu"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 43,
    "chunk_index": 2,
    "text": "carbons have been investigated for na+ storage.241 these carbon materials are widely accepted because of their ability to accommodate na+ ions into their structure. in particular, hard carbon is interesting because of its reasonable capacity of b300 ma h g1 and low operating potential (almost zero, b0 v vs. na+/na).22,23,247 however, the na+ storage mechanism in a disordered carbon structure is still controversial.247– 251 on the other hand, titaniumbased oxide compounds have been widely studied"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 43,
    "chunk_index": 3,
    "text": "graphite with na+ ions has been studied based on the graphite/polyethylene oxide nacf3so3/na cell254 (fig. 21a). however, na+ insertion into graphite is significantly impeded and degradation of electrolyte and/or electrode materials was observed255 (fig. 21b). firstprinciples calculation results of the formation energy for na-gic exhibited that na hardly intercalates into graphite because of the energetic instability of the na-gics. graphite is stressed when some na+ intercalates into graphite b"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 43,
    "chunk_index": 4,
    "text": "gics. that is the intercalation of solvated alkali ions ‘‘co-intercalation’’ by reduction of graphite according to the following equation: cn + e + a+ + ysolv 2 a+(solv)ycn.258 zhu et al. also confirmed that solvated na+ ions intercalate into graphite via a stageevolution process, forming a set of ternary graphite intercalation compounds.259 ether-based electrolytes with a high donor number can form stable na+ solvated species with non-polar characteristics for co-intercalation into natural grap"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 43,
    "chunk_index": 5,
    "text": "graphite lattice. in contrast, carbonate-based electrolytes (ec/dec) form relatively thick insulating sei layers on the graphite surface, which block na+-solvent transport262 (fig. 21d). as a result, under the limited conditions using ether-based electrolytes, the natural graphite delivered a capacity of 150 ma h g1 with reasonable retention for 2500 cycles, and produced over 75 ma h g1 at 10 a g1 in the degdme electrolyte containing napf6 salt. on the other hand, wen et al. proposed expanded gr"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 43,
    "chunk_index": 6,
    "text": "recently, kang et al. reported the sodium ion intercalation behavior of expanded graphite oxide (go) as an anode material. according to their report, the electrochemical properties of go strongly depend on the amounts and ratios of different functional groups.264 3.1.1.2. non graphitic carbon (hard carbon). in 1993, doeff and co- workers first reported the na storage performance of disordered soft"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 44,
    "chunk_index": 0,
    "text": "review article chem soc rev 3572 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 carbon prepared by pyrolysis of petroleum coke251 (fig. 22a). they demonstrated the extent of the na+ insertion/extraction reaction into the soft carbon and discussed the possibility of its application for sibs. stevens and dahn reported the insertion mechanism of na+ ions into disordered hard carbon (fig. 22b).22,23,247 the suggested mechanism was the ‘‘house of cards’’ "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 44,
    "chunk_index": 1,
    "text": "a high specific capacity of approximately 300 ma h g1 with a low operating potential of about b0 v. later, komaba and co-workers performed a systematic study on electrochemical sodium insertion into hard carbon to understand the related structural change.27 upon reduction to 0.2 v (in the sloping region), the resulting xrd peaks shifted to lower angles, indicating that the interlayer spacing between the graphene sheets was expanded due to the sodium insertion (fig. 22c). they also confirmed the "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 45,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3573 fig. 21 (a) graphite current–potential curve in the graphite/peo-nacf3so3/na cell at 82 1c. (reprinted from ref. 254, copyright 1988, with permission from elsevier.) (b) li+ and na+ insertion mechanisms in graphene and graphite. (reproduced by permission from ref. 255, nature publishing group, copyright 2015.) (c) in operando synchrotron x-ray diffraction analysis of the "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 46,
    "chunk_index": 0,
    "text": "review article chem soc rev 3574 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 (saxs) in the voltage range of 0.2 v to 0 v (in the plateau region) enlarged interlayer spacing (d-spacing = 3.8 å) or the smaller upon reduction. from these results, they suggested that the crystallite size of the parallel graphene within hard-carbon in fig. 22 (a) first cycle of the na/dme, naclo4/(ground) petroleum coke cell. (reproduced with permission from ref. 251, "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 46,
    "chunk_index": 1,
    "text": "reduction to 0.00 v ( pvdf binder, ? unknown). (reproduced from ref. 27 with permission, copyright 2011 wiley-vch verlag gmbh & co. kgaa.) (d) potentiogram and schematic of the proposed na-ion three part storage mechanism. (reproduced with permission from ref. 250, copyright 2015 american chemical society.) (e) typical potential vs. capacity profile of hard carbon when tested against sodium metal counter electrodes. (reproduced with permission from ref. 249, copyright 2015 the electrochemical so"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 47,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3575 comparison to those of the graphite (d-spacing = 3.354 å) is responsible for the sodium insertion. in addition, the 23na nmr study demonstrated the reversible electrochemical reaction mechanism of na+ ions with hard carbon: (i) two resonance peaks at 9.9 ppm and 5.2 ppm were ascribed to reversible sodium present between disordered graphene sheets in hard carbon and (ii) o"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 47,
    "chunk_index": 1,
    "text": "using pitch carbon and investigated the co-relationships between the physico-chemical properties and the electrochemical properties with commercially available porous and non-porous carbon materials (porous carbon: timrex 100, 300, 500 and activated carbon, non- porous carbon: graphite). the highest surface area (1041 m2 g1) of activated carbon and the highest pore volume (1.008 cm3 g1) of timrex 500 show the low reversibility with na+ ions. meanwhile, their templated carbon controlled by micros"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 47,
    "chunk_index": 2,
    "text": "the only factor that helps na intercalation. additionally, the vacancy defects (mv: mono- vacancy and dv: di-vacancy) in hard carbon can greatly enhance the na+ ion intercalation because of the strong ionic binding energy between the na+ ions and the defects, which effectively overcomes the van der waals interaction.248 further, bommier et al. discussed the new storage mechanism in the sloping region (as a function of the charge–discharge curve), which can be explained through na+ ion storage at"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 47,
    "chunk_index": 3,
    "text": "lattice, and (iii) na+ ions are adsorbed at the pore surface in the plateau region. such research results show that the na+ insertion mechanism into a disordered structure is still controversial. therefore, further theoretical and experimental investigation should be conducted to clarify the related reaction mechanism for development of hard carbon materials. to date, hard carbons have been the most widely used carbon source of sib anodes and have been proved to significantly improve the electro"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 47,
    "chunk_index": 4,
    "text": "studies, we should consider some factors, including particle sizes, additives, electrolytes, vacancy defects and porosity measurements, to develop the high irreversible capacity and high rate capability in hard carbons. furthermore, we should investigate the relationship between the electrochemical characteristics of hard carbon and solid electrolyte interphase (sei) layer formation. at the same time, the computational works such as dft calculation and ab initio calculation should be conducted t"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 47,
    "chunk_index": 5,
    "text": "(rgo) help to improving the li and na storage capability in its composite anodes. recently, wang et al. demonstrated the reversible sodium ion storage performances in reduced graphene oxide (rgo).274 rgo possesses higher electrical conductivity and active sites with large interlayer distances and provides a disordered structure enabling it to store a larger amount of na+ ions. in their study, rgo anodes exhibited a moderate specific capacity of 141 ma h g1 at 40 ma g1 with stable cycle retention"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 47,
    "chunk_index": 6,
    "text": "presence of defects enhances the adsorption of na atoms in graphene sheets.276 however, such defects of graphene represent a serious drawback such as low coulombic efficiency that may cause na metal plating on the rgo surfaces.255 3.1.1.4. heteroatom doping. as an effective strategy to enhance the electrochemical properties of carbonaceous materials as anodes, heteroatom (such as n, b, s and p) doped hard carbon and graphene (or graphene liked materials) are introduced.277–291 hetero atom doping"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 48,
    "chunk_index": 0,
    "text": "review article chem soc rev 3576 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 porous nanofibers that exhibited 212 ma h g1 at 5 a g1 with stable capacity retentions of 99% after 7000 cycles282 (fig. 23a). in a recent work, sulfur-doped disordered carbon was proposed as an anode material for sibs. sulfur doping into the carbon structure provided additional reaction sites for accommodation of na+ and/or contributing to facile ion diffusion by enlargi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 48,
    "chunk_index": 1,
    "text": "anode material for sibs. biomass-derived disordered carbon materials have been widely investigated due to their low production cost and low energy consumption during the synthesis procedures.275,292–297 wood carbon anodes were derived from natural woods via a simple carbonization process, which functions as a binder-free and current collector-free anode material.292 this material exhibited a high areal capacity of 13.6 ma h cm2 with a high mass loading of 55 mg cm2. a recent work, reported by ya"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 48,
    "chunk_index": 2,
    "text": "and the elemental mapping of n-cnf (left). long term cycling performance of n-cnf at a current density of 5 a g1 (right). (reproduced from ref. 282 with permission, copyright 2015 wiley-vch verlag gmbh & co. kgaa.) (b) hr-tem image and eds elemental mapping of dc-s (left). electrochemical performances of dc-s (right). (reproduced with permission from ref. 288, copyright 2015 the royal society of chemistry.) (c) the preparation process of ndcs derived from okara (left). high rate capability and l"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 49,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3577 approximately 292.2 ma h g1 with stable cycling performances for over 2000 cycles (fig. 23c). from the green and recycle points of view, using biomass (bio-waste) is of great significance for the future direction of material development. such works present that carbonaceous materials exhibit promising na+ ion storage performances as anodes for sibs. notwithstanding, the i"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 49,
    "chunk_index": 1,
    "text": "in addition, tap density is also a crucial parameter determining the volumetric energy density of the cells. the appropriate low pore volumes and surface areas were required for higher reversible capacities. using suitable electrolytes, additives, and binders is also an effective approach for decreasing the initial irreversible capacity. and morphology and size control is a substantial strategy to facilitate mass transport and storage, which can significantly improve the rate capability. most of"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 49,
    "chunk_index": 2,
    "text": "host materials. titanium-based oxides are particularly interesting as anodes due to their reasonable operation voltage, cost, and nontoxicity;299,300 representatively, titanium dioxides,301–333 spinel-lithium titanate,334–346 and sodium- titanate compounds.347–364 note that these compounds are driven by a ti4+/3+ redox couple in na cells. recently, most related works have focused on finding the sodiation/desodiation mechanism and improving the electrochemical performance of such materials. 3.1.2"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 49,
    "chunk_index": 3,
    "text": "that high crystalline and/or micronized tio2 cannot easily support na+ insertion because of the ionic size of na+ and a much higher sodium diffusion barrier compared with li.305 recently, high electrochemical activity of tio2 with na+ ions was achieved by reducing the particles to the nanometer size for shortening of the migration length for na+ insertion. xu et al. used anatase nanocrystalline tio2 for na+ storage.306 wu et al. interpreted the reaction process during na+ insertion and extractio"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 49,
    "chunk_index": 4,
    "text": "reaction via ex situ xrd and xas studies309 (fig. 25c and d). their carbon coating on the anatase tio2 nanorod surface played an important role in improving the capacity and rate capability. furthermore, they also suggested that the presodiation technique was an effective way to minimize the initial irreversible reaction of the tio2 anode. recently, passerini’s group found that only the (de-)insertion of na+ ions in the newly formed amorphous sodium titanate phase appears to be reversible (uptak"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 49,
    "chunk_index": 5,
    "text": "crystal structures of tio2. (a) rutile, (b) anatase, (c) bronze, (d) brookite. (reprinted from ref. 299, copyright 2015, with permission from elsevier.) crystal structures of (e) spinel-type li4ti5o12 and (f) na2ti3o7. li and na atoms are represented by green and yellow spheres, respectively. (reproduced with permission from ref. 300, copyright 2016 the royal society of chemistry.)"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 50,
    "chunk_index": 0,
    "text": "review article chem soc rev 3578 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 fig. 25 (a) charge/discharge galvanostatic curves of amorphous 80 nm i.d. tio2nt in na half cell (red for discharge and black for charge). (reproduced with permission from ref. 304, copyright 2011 american chemical society.) (b) galvanostatic investigation of the influence of the lower cut-off potential based on coulombic efficiency (dis-)charge capacities. (reprinted fro"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 50,
    "chunk_index": 1,
    "text": "electrode exhibited excellent cycling performance with a reversible capacity of 160 ma h g1 at the 50th cycle. later, zhang et al. proposed rutile tio2 microspheres anchored by nanoneedle clusters, which exhibited a capacity retention of 83.1% after 200 cycles at a current density of 0.1c-rate.327 huang et al. found that one of the polymorphs, the low crystalline brookite-tio2 was available for na+ ion storage.329 pioneer works of unusual tio2 polymorphs, including the brookite-phase, the bronze"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 51,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3579 ti and high conductivity carbon additives were introduced.309,311,328,331 kim et al. fabricated pitch carbon-coated anatase tio2 nanorods, which exhibited a high capacity of 193 ma h g1 and superior rate capability.309 recently, zhang et al. proposed graphene-rich wrapped petal-like rutile tio2 tuned by carbon dots, which exhibited the outstanding sodium-storage performan"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 51,
    "chunk_index": 1,
    "text": "carbon nanotubes312 (fig. 26c). nanosized anatase tio2 partially doped with fluorine (tio2dfd) to form electro-conducting trivalent ti3+ led to facile na+ insertion into an anatase tio2 structure. in addition, tio2dfd was modified by electro-conducting carbon nanotubes (cnts) to further enhance the electric conductivity. boron doping can also enhance the photocatalytic activity of tio2 due to or partly due to the formation of ti3+ ions induced by oxygen vacancies which can increase the conductiv"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 51,
    "chunk_index": 2,
    "text": "of the valence band, and thus increases the width of the valence band, resulting in a decreased band gap energy (s-tio2: 2.6 ev, tio2: 3.0 fig. 26 (a) cycling performances of thick-film electrodes consisting of ti1xnbxo2 with rutile and anatase structure in na cell. (reproduced with permission from ref. 326, copyright 2015 american chemical society.) (b) long-term cycling performance of g–tio2(b) electrode at a current density of 500 ma g1. inset image represent the illustration of partially bon"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 52,
    "chunk_index": 0,
    "text": "review article chem soc rev 3580 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 ev).334 the high conductivity assisted in decreasing the band gap energy, which enabled delivery of a high capacity of 320 ma h g1 at 33.5 ma g1 with a stable capacity retention of 91% for over 4400 cycles at a high current density of 3.35 a g1. 3.1.2.2. lithium titanate. a spinel li4ti5o12 has been extensively studied as one of the most promising anode materials for long"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 53,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3581 fig. 27 (a) crystal structure of spinel li4ti5o12 viewed from the [110] crystallographic direction showing separated ti and o columns. (b) stem imaging of a three-phase coexistence region. haadf, abf images and abf line profile of li4ti5o12 (li4), li7ti5o12 (li7) and na6liti5o12 (na6li) phase. (reproduced by permission from ref. 337, nature publishing group, copyright 201"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 54,
    "chunk_index": 0,
    "text": "review article chem soc rev 3582 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 (fig. 24e). a reversible capacity of 145 ma h g1 was delivered with a relatively low insertion/extraction potential of 1.0 v. also, they suggested an unexpected mechanism with a mixture of lina6ti5o12 and li7ti5o12 as the final product after na+ insertion. later, sun et al. precisely interpreted the na+ insertion behavior via dft calculations and advanced electron microsc"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 54,
    "chunk_index": 1,
    "text": "of the li4ti5o12 lattice, and they simultaneously induce phase separation into two rock-salt phases of lina6ti5o12 and li7ti5o12 as follows: 2li4ti5o12 + 6na+ + 6e 2 li7ti5o12 + na6liti5o12. later, kim et al. observed the structural evolution and the chemical state of ti at the initial cycle based on ex situ xrd and xps measurements339 (fig. 27c–e). yu et al. observed three phase transition behavior of li4ti5o12 during na+ insertion through in situ x-ray diffraction. they also investigated a siz"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 54,
    "chunk_index": 2,
    "text": "(fig. 27f). they claimed that downsizing the na+ host structure of li4ti5o12 is a crucial factor to improve the sluggish na+ ion diffusion kinetics. analogous to this scenario, hasegawa et al. reported nanosized li4ti5o12 materials with hierarchically porous structures and flower-like morphologies.341 according to their reports, na+ insertion/extraction capability is strongly dependent on their nanoarchitectural design and calcination temperature. these nanostructured li4ti5o12 electrodes calcin"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 54,
    "chunk_index": 3,
    "text": "pseudocapacitance effect on a typical insertion electrode is a potential solution to overcome the capacity limit for na+ insertion anodes. another approach to improve the electrochemical performances is combining carbon additives with li4ti5o12 materials. kim et al. proposed pitch carbon-coated li4ti5o12 nanowires, which significantly increased the electronic conductivity and delivered a high capacity of 168 ma h g1 at 0.2c-rate.339 chen et al. fabricated porous li4ti5o12 nanofibers confined in "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 54,
    "chunk_index": 4,
    "text": "a long cycle life of 12000 cycles. 3.1.2.3. sodium titanate. the na2ti3o7 structure has been most investigated as a promising anode with the lowest operating potential for sibs347–353 (fig. 24f). senguttuvan et al. firstly reported that sodium titanate, na2ti3o7, can reversibly uptake 2 mol of na+ ions per formula unit with a low operating potential plateau at 0.3 v vs. na/na+347 (fig. 28a). a plateau with this voltage can be quite advantageous in a full cell with a suitable cathode in terms of "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 54,
    "chunk_index": 5,
    "text": "and experimental results for an in-depth understanding of the sodium storage mechanism of the na2ti3o7 structure.348 based on the calculations of the electrostatic interaction in the crystal structure, 2 mol of na+ ions are intercalated into the na2ti3o7 structure to form na4ti3o7 producing strong electrostatic repulsion, leading to structural instability and low operating voltage. also, this strong electrostatic repulsion in the fully sodiated state induces the selfrelaxation phenomena. in addi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 54,
    "chunk_index": 6,
    "text": "based on the ex situ xrd results, two discharge plateaus revealed the following two phase reactions: na2ti3o7 - na3–xti3o7 (black curve in fig. 28c) and na3–xti3o7 - na4ti3o7 (red curve in fig. 28c). the lower discharge plateau causes an irreversible transformation that leads to the loss of the sodium storage pathway in subsequent cycles. by controlling the cut-off potential from 0.01–2.5 v (with low plateaus) to 0.155–2.5 v (without low plateaus), the na2ti3o7 # na3–xti3o7 pathway has the lowes"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 55,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3583 directly translates to na2ti3o7 during the na+ extraction process.351 they also discussed two main reasons for the low coulombic efficiency and continuous capacity fading of the na2ti3o7 electrode: (i) partial decomposition on the na2ti3o7 particle surface (instability of the sei layer) and (ii) structural distortion upon na+ insertion/extraction. later, mun˜oz-ma´rquez e"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 55,
    "chunk_index": 1,
    "text": "(b) normalized ti k-edge xanes for na2ti3o7 at pristine state (red), after discharged to 0.10 v (blue), and after discharged to 0.01 v (green). (reproduced with permission from ref. 348, copyright 2014 the royal society of chemistry.) (c) representative c/5 cycling of na2ti3o7 ! na3–xti3o7 and na2ti3o7 ! na4ti3o7 pathways. (reprinted from ref. 350, copyright 2015, with permission from elsevier.) (d) charge–discharge curves of na2ti6o13 at 0.2c-rate in the voltage range of 0.5–2.5 v vs. na/ na+. "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 56,
    "chunk_index": 0,
    "text": "review article chem soc rev 3584 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 na-ion batteries, poor capacity retention remains the serious drawback. therefore, further investigation including reducing the catalytic activity of na+ ions with titanium and application of protective coating of active materials should be conducted to improve the electrochemical performances of na2ti3o7 electrodes. other types of sodium titanates were also widely studie"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 56,
    "chunk_index": 1,
    "text": "be enhanced from 49.5 ma h g1 (na2+1ti6o13) to 196 ma h g1 (na2+4ti6o13) by lowering the cutoff voltage from 0.3 to 0 v.356 simultaneously with experimental works, shen et al. predicted the structure and average voltage change of reduced phases at various compositions of na2+xti6o13 (x = 0–4) by using density functional theory (dft) calculations (fig. 28e). shirpour et al. suggested layered sodium titanate, structurally identical to sodium nonatitanate, which was capable of reversibly intercalat"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 56,
    "chunk_index": 2,
    "text": "the two crystal structures of trigonal na4ti5o12 (t-na4ti5o12) and monoclinic na4ti5o12 (m-na4ti5o12) by woo et al. and naeyaert et al., respectively.358,359 t-na4ti5o12 has a tunnelstructured three- dimensional framework, whereas m-na4ti5o12 has a quasi-2d layered structure. both electrodes can incorporate intercalated na+ ions into their structures, however, 2d channels with partially occupied na sites, providing broader pathways, can deliver higher reversible capacity than t-na4ti5o12. the tu"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 56,
    "chunk_index": 3,
    "text": "al. demonstrated the reversible o3–o03 phase transition of o3-natio2 and proposed the na+ insertion/extraction mechanism (fig. 28f). in an optimal voltage window of 0–1.6 v, approximately 0.5 mol of na+ can be reversibly intercalated in natio2, showing a reversible capacity of 152 ma h g1 and stable cycle retention after 60 cycles.361 for p2-na0.66[li0.22ti0.78]o2, a reversible capacity of 116 ma h g1 was delivered at an average storage voltage of 0.75 v362 (fig. 28g). in addition, it exhibited "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 56,
    "chunk_index": 4,
    "text": "of one or more of the atomic species into a host lattice to form a new compound.426 depending on the transition metal, insertion–extraction or alloying–dealloying was combined with conversion reactions. analogous to the reaction in libs, conversion materials have been considered as potential anode materials for sibs due to their high theoretical specific capacities. however, large volume expansion/contraction upon the sodiation– desodiation process accelerated tremendous damage of electrodes, wh"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 56,
    "chunk_index": 5,
    "text": "transition metal sulfides and transition metal phosphide as na conversion hosts are summarized and discussed. 3.2.1 transition metal oxide (tmo) based anode materials. alcantara et al. first introduced the conversion material concept by using nico2o4 spinel oxide as an anode material for sibs365 (fig. 29a). alcantara et al. described a reversible conversion reaction of sodium with a metal oxide in which na2o and metals are formed: nico2o4 + 8na - ni + 2co + 4na2o. subsequent to this work, many r"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 56,
    "chunk_index": 6,
    "text": "fe3o4 materials in the conversion reaction mechanism with na+ ions at a discharge voltage of 0.04 v: fe3o4 + 8e + 8na+ 2 3fe + 4na2o.367 through the conversion reaction, a discharge capacity of 643 ma h g1 was delivered during the initial cycles with a high coulombic efficiency of 57%. oh et al. suggested pitch carbon as a coating additive for nano-sized fe3o4 (fig. 29b). oh"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 57,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3585 et al. also observed the conversion reaction of the c/fe3o4 electrode upon the sodiation–desodiation process51 (fig. 29c). to further ensure electric conductivity, park et al. introduced a composite of c/fe3o4 embedded on carbon nanotubes, which delivered 440 ma h g1 for the first discharge and 321 ma h g1 for the first charge with a high coulombic efficiency of 73%.368 m"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 57,
    "chunk_index": 1,
    "text": "and nontoxicity.373–377 similar to fe3o4 materials, sodium storage in fe2o3 is mainly achieved via a reversible conversion reaction, by forming fe nanoparticles dispersed in the na2o matrix. 3.2.1.2. cobalt oxides (co3o4). rahman et al. proposed the reversible conversion reaction mechanism of co3o4 with sodium ion via cyclic voltammogram and ex situ xrd analyses: co3o4 + 8na+ + 8e 2 4na2o + 3co.378 based on the xrd suggested that the conversion reaction is not completed in the first discharge to"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 57,
    "chunk_index": 2,
    "text": "several advantages during the sodiation– desodiation process: (1) significantly decreases the absolute stress/strain, (2) accommodates a large volume change and prevents aggregation, (3) its cnt matrix provides electronic conductivity and stability, and (4) reduces the ion or electron transfer time. the results showed a high capacity of 403 ma h g1 at 50 ma g1 and a superior rate capability of 190 ma h g1 at 3.2 a g1 (fig. 29d). 3.2.1.3. tin oxides. recently, various nanostructured tin-based oxi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 58,
    "chunk_index": 0,
    "text": "review article chem soc rev 3586 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 2 wire anodes via an in situ tem technique383 (fig. 30a). at the initial stage of the na insertion process into sno2, a displacement reaction occurs, leading to the formation of amorphous naxsn nanoparticles dispersed in the na2o matrix. further sodiation led to crystallization to na15sn4 (x = 3.75) from naxsn. at this stage, the nanowire experiences a huge volume expansi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 58,
    "chunk_index": 1,
    "text": "sno2 materials386 (fig. 30b). based on ex situ xrd analysis and saed pattern results, they confirmed that sno and sno2 are able to store sodium in their structure through the combined conversion and alloying reactions: (1) sno - sno + 2na+ + 2e 2 sn + na2o, sn + na2o + xna+ + xe2 naxsn + na2o, (2) sno2 - sno2 + 4na+ + 4e2 sn + 2na2o, sn + 2na2o + xna+ + xe 2 naxsn + 2na2o (fig. 30c). according to their report, low oxygen contents of"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 59,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3587 sno showed better electrochemical performances, which implies that the sn:o ratio and the respective sn:na2o ratio in the converted electrode play important roles in delivering the capacity (fig. 30d). recently, a strategy to overcome such failures and maximize the utilization of the high theoretical capacity of sno2 (b782 ma h g1) has been introduced such as composite an"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 59,
    "chunk_index": 1,
    "text": "distribution, chemical stability, and high theoretical capacity.391–396 klein et al. reported that cu2o can be applicable and thereby exhibited a high capacity of b600 ma h g1 at 0.1c.243 yuan et al. proposed flexible and porous cuo nanorod arrays by engraving cu foils. the arrays delivered a high specific capacity of 640 ma h g1 at 20 ma g1 and good cycle retentions over 400 cycles392 (fig. 30f). liu et al. demonstrated the morphology change and phase transformations in cuo nanowires during the"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 59,
    "chunk_index": 2,
    "text": "the electronic conductivity and the accommodation of volume variation upon cycling, lu et al. proposed the micro-nanostructured cuo/c spheres. the as-prepared cuo/c spheres exhibited a high capacity of 402 ma h g1 after 600 cycles at a current density of 200 ma g1 and superior rate capabilities.395 3.2.2 transition metal sulfide (tms) based anode materials. transition metal sulfide (tms) materials have attracted tremendous attention as promising sodium storage materials with high theoretical cap"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 59,
    "chunk_index": 3,
    "text": "profiles of sno (top) and sno2/c (bottom) electrodes over the first charge/discharge cycle. (d) cycle life of sno, sno2, and sno2/c electrodes. (reprinted from ref. 386, copyright 2015, with permission from elsevier.) (e) cycling performance of sno2/ng and sno2/g composites at a current density of 20 ma g1. (reproduced with permission from ref. 390, copyright 2015 the royal society of chemistry.) (f) cycling performance of the binder-free cuo nanorod array (can) electrode at a high current densi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 60,
    "chunk_index": 0,
    "text": "review article chem soc rev 3588 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 metal oxides, transition metal sulfides have great advantages during the sodiation/desodiation process. the m–s bonds in metal sulfide are weaker than the corresponding m–o bonds in metal oxides, which can be kinetically favorable for conversion reactions with na+ ions.410 as a result, transition metal sulfides show improved mechanical stability due to their smaller volum"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 60,
    "chunk_index": 1,
    "text": "depending on the transition metal elements, the na+ ion storage mechanism of metal sulfide materials can be classified as the conversion reaction and/or combined insertion and the alloying reaction. 3.2.2.1. cobalt sulfides. cobalt sulfide is an interesting metal chalcogenide semiconductor material and has a number of applications.400–403 recently, superior li-storage properties of cobalt sulfide were achieved by designing a novel nanoarchitecture and fabricating hybrid nanocomposites with vario"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 60,
    "chunk_index": 2,
    "text": "are quite different. using mwcnts as carbon additives provides several advantages such as 3d electron conductive networks with a high surface area, which facilitate the fast penetration of sodium ions and diffusion of electrolytes. as a result, the cos2–mwcnt electrode exhibited a high initial discharge capacity of 826 ma h g1 with a high coulombic efficiency of 93%, and a stable cycle life for 100 cycles in an ether-based electrolyte (1 m nacf3so3–dgm) (fig. 31b). later, peng et al. proposed th"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 60,
    "chunk_index": 3,
    "text": "co3s4 nanotubes (fig. 31c).410 based on the cv results in the potential window of 0.05–2.0 v (vs. na+/na), they claimed that co3s4 electrodes can store na+ ions through the combined insertion and conversion reaction. in the first scan, a cathodic peak at 0.98 v is commonly assigned to an initial process of the na+ insertion reaction: co3s4 + xna+ + xe- naxco3s4. the peak at 0.72 v is related to the conversion reaction of co3s4 with na and the formation of a solid electrolyte interphase: naxco3s4"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 60,
    "chunk_index": 4,
    "text": "planes are stacked by van der waals interactions, which facilitate intercalation of the large na+ ion.411,414 according to previous reports, mos2 can store the na+ ions through the intercalation and/or conversion reactions depending on the operation voltage window.413,415–417,419 the electrochemical reaction of mos2 is interpreted as the following two step reactions: mos2 + xna+ + xe- naxmos2 (above 0.4 v), naxmos2 + (4 x)na+ + (4 x)e- 2na2s + mo (below 0.4 v).413 hu et al. prepared mos2 nanoflo"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 60,
    "chunk_index": 5,
    "text": "delivered a lower specific capacity in consideration of their theoretical capacity of 668 ma h g1 when 4na+ ions reacted with mos2 through the conversion reaction.417,419 however, a conversion type chemical reaction usually brings about a serious volume change to the electrode materials and sluggish kinetics for reconstruction of the original active materials. recently, to overcome such problems through the electrochemical conversion reactions of mos2 (below 0.4 v), high conductivity carbon addi"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 60,
    "chunk_index": 6,
    "text": "heterointerface can increase the conductivity of mos2 and capture more na atoms due to maintaining the high diffusion mobility of na+ ions on the mos2 surface and high electron transfer efficiency from na to mos2, respectively. as a result, this material delivered a high capacity of 352 ma h g1 even at a high current density of 640 ma g1 in the voltage range of 0.01–3.0 v (fig. 31e). 3.2.2.3. iron sulfides. natural and/or synthetic fes2 materials have been demonstrated to be potential electrode "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 61,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3589 environmental friendliness. ahn and co-works reported a na/synthetic fes2 battery for the first time423,424 (fig. 32a). later, hu et al. demonstrated room temperature sodium storage performances of the fes2 microspheres with only the intercalation reaction by simultaneously selecting a compatible ether-based electrolyte and tuning the cut-off voltage to 0.8 v. the interca"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 61,
    "chunk_index": 1,
    "text": "the evolution process of the as-prepared cos2–mwcnt and bare cos2 electrodes before and after the first discharge to 1.0 v (left). and, ex situ tem images of sodiated cos2–mwcnt and bare cos2 particles (right). (b) cos2–mwcnt electrodes at a current density of 100 ma g1 in 1.0 m nacf3so3–dgm and 1.0 m naclo4–ec/pc. (reproduced with permission from ref. 407, copyright 2015 the royal society of chemistry.) (c) cycling performance of co3s4, pani, co3s4@pani electrodes. (reproduced with permission f"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 62,
    "chunk_index": 0,
    "text": "review article chem soc rev 3590 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 they also observed the structural evolution of fes2 during the electrochemical reaction with na+ ions (fig. 32c). the xrd patterns collected at the chargeend state after the 50th cycle (viii) indicates the formation of a layered compound of trigonal naxfes2 with x around 1.6. also, the layered structures of fes2 could be maintained within the selected potential window of "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 63,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3591 fig. 32 (a) charge–discharge voltage profiles of the na/fes2 cell at room temperature. (reprinted from ref. 423, copyright 2008, with permission from elsevier.) (b) structural evolution of fes2 during the electrochemical reaction with sodium: tem images (left) and ex situ xrd results (right). (c) cyclic performance of fes2 microspheres. (reproduced with permission from re"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 64,
    "chunk_index": 0,
    "text": "review article chem soc rev 3592 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 charging states. (d-1: fresh electrode; d-2: after 1st discharging to 0.6 v; d-3 after 1st discharging to 0.01 v; d-4 after 1st charging to 0.8 v; d-5 after 1st charging to 2.0 v.) (reproduced with permission from ref. 433, copyright 2014 the royal society of chemistry.) (e) rate capability and long-term cyclability with coulombic efficiency of the sns2/g-20 electrode. (r"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 64,
    "chunk_index": 1,
    "text": "pyrite (fes2), a few studies on ferrous sulfide (fes) are reported due to poor cyclability and rate capability.431,432 recently, wei et al. proposed the flexible and self-supported carbon-coated fes on carbon cloth films, which display high reversible capacity and superior rate capability.431 3.2.2.4. tin sulfides. tin-based sulfide (sns, sns2) compounds have attracted considerable attention due to their high theoretical capacity with combined conversion and alloying electrochemical reactions.43"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 64,
    "chunk_index": 2,
    "text": "20ma g1 and an excellentcycling stability of97.8%after 80cycles as well as a high-rate capability. later, zhu et al. proposed a 3d porous interconnected metal sulfide/carbon nanocomposite by the esd technique without adding carbonaceous materials such as carbon nanotubes and graphene.436 sns2 has also been applied as an anode material for sibs.438–448 sns2 has a sandwich structure that consists of covalently bonded s–sn–s trilayers separated by a relatively large van der waals interaction.438 a "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 64,
    "chunk_index": 3,
    "text": "ma g1 with stable cyclability at b610 ma h g1 without notable capacity fading for 300 cycles (fig. 32e). sns2 can store the na+ ions through following three step processes: (1) intercalation reaction: xna+ + sns2 + xe - naxsns2, (2) conversion reaction: 4na+ + sns2 + 4e- 2na2s + sn, (3) alloying reaction: sn + 3.75na+ + 3.75e - na3.75sn. such improved electrochemical performances of conversion materials are attributed to the electro- conducting carbons. the introduction of carbon additives such "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 64,
    "chunk_index": 4,
    "text": "the phosphorous anode is the continuous pulverization during the sodiation–desodiation process.240 one strategy for dealing with this problem is fabricating a binary metal–phosphide form by employing secondary metals (m–p, m = ni, fe, co, cu and sn).455–466 this is because if these elements can form an intermediate compound (naxm or naxp, x z 0,) during the charge– discharge process, pulverization can be partially repaired and the accumulation of pulverization can be terminated.460,462 therefore"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 64,
    "chunk_index": 5,
    "text": "fading over 100 cycles with an appropriately low redox potential of about 0.3 v vs. na/na+. these properties of the sn4p3 electrode can be ascribed to the fact that the pulverization of sn and p during the alloy process was partially self-healed by the conversion reaction process462 (fig. 33a). recently, liu et al. proposed uniform yolk–shell sn4p3@c nanospheres.463 the rationally designed void space in between the shell and nanoparticles allows for the expansion of sn4p3 without deforming the c"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 64,
    "chunk_index": 6,
    "text": "terminates pulverization. it means that the damage can be healed by itself during cycling465 (fig. 33c). similar to sn4p3 materials, the stable cycling performances of snp3/c composites were derived by the self-healing effect of the conversion reaction for the alloying process.462 to date, binary-intermetallic systems such as nip3,455 (cup2,456 cu3p457), fep458 and cop,464 fep4466 exhibit impressive results, however, these binary inter-metallic systems still need to improve in terms of material "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 65,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3593 na+ insertion materials, such as carbonaceous materials and titanium- based oxide compounds, have been successfully applied as na storage materials that deliver a reasonable capacity with relatively small volume expansions during the electrochemical insertion/extraction reaction with na.241,300 however, these materials still suffer from limited capacity utilization due to"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 65,
    "chunk_index": 1,
    "text": "nonmetal compounds (p) in group 14 (fig. 34) or 15 elements (fig. 37) in the periodic table have been widely studied as potential anode materials for sibs. however, depending on the host materials and electrochemical sodiation levels, the large na+ ion causes huge volume changes during the alloying–dealloying reaction. this repetitive volume changes under the constraints imposed by the battery packaging give rise to complex mechanical stresses in active particles, ultimately leading to their fra"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 65,
    "chunk_index": 2,
    "text": "were intensively studied for libs due to their abundance in earth’s crust and their high specific capacity through electrochemical alloying reactions with li.467,468 theoretically, silicon can uptake 4.4 li+ ions per si atom and deliver a high specific capacity of 4000 ma h g1. morito et al. firstly demonstrated the phase diagram between na and si, which indicated the fully sodiated form of na–si.469 however, based on a single-atom diffusion model, morito et al. deduced that bulk si is not a pro"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 66,
    "chunk_index": 0,
    "text": "review article chem soc rev 3594 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 desirable electrode design to facilitate na+ intercalation and migration into si was suggested such as structural modification and control of the activation barrier.470–476 structurally modified si was predicted to demonstrate better electrochemical performance such as in amorphous si due to more favorable binding between na and si. reasonable activation barriers for na+ "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 66,
    "chunk_index": 1,
    "text": "after 100 cycles at 20 ma g1. also, through the various analysis techniques, they proposed the possible na storage mechanism as follows: xna + si 2 xnasi + (1 x)si (sodiation), nasi 2 na(1 x)si + xna (desodiation). more recently, zhang et al. precisely investigated the sodiation/ desodiation behavior of microsized and nanosized crystalline-si, hereafter referred to as c-si, electrodes during the na+ insertion/ extraction processes via cyclic voltammogram, operando xrd and raman analysis.476 the "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 66,
    "chunk_index": 2,
    "text": "35c). it means that the electrochemical behavior of c-si strongly depends on the particle size. the operando raman analysis results demonstrated that an irreversible crystal structure transformation from c-si to amorphous-si takes place during the first sodiation process. this newly generated a-si is beneficial for the reversible na+ insertion reaction due to its more disordered crystal structure (fig. 35d). according to their report, the whole process includes four phases along with a growing d"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 66,
    "chunk_index": 3,
    "text": "bonds, and crystalline si is transformed into an amorphous na–si alloy. in stage four, after the desodiation process, the amorphous structure is maintained, leading to the a-si structure (fig. 35e).476 3.3.1.2. germanium. germanium has a similar chemistry to silicon, bonding with a maximum of one na atom.477,478 the theoretical calculation predicted that sodium could alloy with germanium to form na–ge compounds which delivers a theoretical capacity of 369 ma h g1.479 however, similar to silicon,"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 66,
    "chunk_index": 4,
    "text": "nanowire form. baggetto et al. prepared a germanium thin film electrode and demonstrated the reversible reaction with a high discharge capacity of 350 ma h g1, which is close to the theoretical value.480 the shapes of the sodiation and desodiation voltage profiles are quite flat which indicates that the sodiation reaction proceeds via a two-phase reaction mechanism: a reaction front separating the sodium-rich and sodium-poor phases propagates through the material as the reaction progresses. rece"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 67,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3595 nanowires (genws-a) uniformly take up more na+ ions at the sodiated state compared to unactivated germanium nanowires (genws). for the case of genws, the na+ ion is primarily present on its surface at the sodiated state, being associated with both the sei layer and the irreversibly formed sodium oxide (fig. 35f) as a result, genws-a delivered a high reversible capacity of"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 68,
    "chunk_index": 0,
    "text": "review article chem soc rev 3596 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 analysis of the electrochemical behavior towards na+ for the nanosized c-si electrode and (e) schematic illustrations explaining the changes in the nanosized c-si during cycling. (reproduced from ref. 476 with permission, copyright 2016 wiley-vch verlag gmbh & co. kgaa.) (f) tem analysis of genws-a-0.1c and genws after initial sodiation process and haadf micrograph and ee"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 69,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3597 chevrier and ceder et al. proposed a voltage profile for sodium insertion into tin compounds244 (fig. 34a). the phase diagram of na– sn indicated that the sodiation of sn progressed in a series of steps: sn - nasn5 - nasn - na9sn4 - na15sn4.482–484 komaba et al. experimentally demonstrated that sn undergoes a reversible electrochemical redox reaction to reversibly form sn"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 69,
    "chunk_index": 1,
    "text": "two-phase regions. (reproduced with permission from ref. 483, copyright 2012 the electrochemical society.) (b) three a-naxsn phases in the single-phase sodiation and schematic illustration of the structural evolution of sn nps during the sodiation. (reproduced with permission from ref. 484, copyright 2014 american chemical society.) (c) 3d morphologies of the sodiated electrode and selected three particles with different sizes and fracture and (d) schematic illustration of two critical sizes for"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 70,
    "chunk_index": 0,
    "text": "review article chem soc rev 3598 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 na9sn4, plateau 4: 6na + na9sn4* - na15sn4 (a-amorphous, *-new crystalline phase)483 (fig. 36a). huang’s group investigated the microstructural evolution and phase transformation with volumetric expansions of tin nanoparticles during electrochemical sodiation via the in situ transmission microscopy technique484 (fig. 36b). according to their report, sn undergoes a two-ste"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 71,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3599 na15sn4 (420% expansion) phases in the second step. later, wang et al. visualized the 3d structural/chemical evolution of the sn electrode during multi-electrochemical cycles (sodiation– desodiation) via in situ synchrotron hard x-ray nanotomography485 (fig. 36c). they also suggest two important critical sizes of 0.5 mm for low complexity and 1.6 mm for high complexity, w"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 71,
    "chunk_index": 1,
    "text": "to the loss of electrical contact and accelerating the capacity decay during cycling. therefore, most works focused on dealing with the serious volume change during alloying–dealloying reactions. carbonconducting techniques such as carbon coating and/or formation of composites with a 2d or 3d carbon matrix are very effective for buffering the volume strain and creating the electric conducting pathways.487–495 xie et al. suggested a unique free standing electrode configuration with 3d architectur"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 71,
    "chunk_index": 2,
    "text": "barrier to buffer the drastic volume change and impede the aggregation of sn nanoparticles during na–sn alloying–dealloying reactions. recently, sn@c composites with ultrasmall tin nano particles (1–8 nm) are introduced by liu et al.491,492 later, luo et al. fabricated a hierarchical tin@carbon composite composed of a graphene carbonaceous matrix and well- confined tin nanoparticles with a typical size of b15 nm as anodes for na storage493 (fig. 36e). this composite delivered a high specific cap"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 71,
    "chunk_index": 3,
    "text": "of sodium (na) alloys with group 15 elements were demonstrated using first principles calculations.245 however, similar to group 14 elements, sodiation in such alloys is generally characterized with substantial volume expansion during charge and equivalent contraction during discharge (fig. 37b). this causes the serious volumetric and asymmetric expansion/ shrinkage upon cycling, which is the main difficulty in utilizing alloy-based anode materials for sibs. 3.3.2.1. antimony. antimony delivers "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 71,
    "chunk_index": 4,
    "text": "upon discharge into an intermediate amorphous phase naxsb; when, all of the sb is almost completely reacted, this naxsb amorphous phase starts converting into cubic-hexagonal na3sb mixture phases before being stabilized as hexagonal na3sb. upon desodiation, crystalline na3sb is transformed into amorphous sb. (sodiation: csb - anaxsb, anaxsb - na3sbhex/ cna3sbcub - cna3sbhex, desodiation: cna3sbhex - asb, c: cubic, fig. 37 (a) na–m voltage curves calculated using dft and (b) the volume changes fo"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 72,
    "chunk_index": 0,
    "text": "review article chem soc rev 3600 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 experimental values are also given if available. (reprinted from ref. 245, copyright 2015, with permission from elsevier.) 1 at 5 a g"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 73,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3601 at a rate of layer graphene. fig. 38 (a) the cv curve of sb/c nanocomposites. (reproduced with permission from ref. 497, copyright 2012 the royal society of chemistry.) (b) selected operando xrd patterns at various stages of discharge and charge of a sb/na cell. (reproduced with permission from ref. 498, copyright 2012 american chemical society.) (c) cycling performance o"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 74,
    "chunk_index": 0,
    "text": "review article chem soc rev 3602 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 sb–c electrode at a cycling rate at 200 ma g1 and inset image represent that tem image of the sb-c nanofibers. (reproduced with permission from ref. 504, copyright 2014 the royal society of chemistry.) anode material, and its light atomic weight can achieve a higher theoretical capacity of 2596 ma h g1 than any other sib anodes presently available.510–512 phosphorous exis"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 74,
    "chunk_index": 1,
    "text": "for this reason, the amorphous red-p and orthorhombic black-p forms are being widely studied as anodes for sibs. however, the electrochemical properties of both red-p and black-p are hindered by the enormous volume change (490%) occurring during the electrochemical sodiation/desodiation process.513 qian et al. reported the improved electrochemical activity of amorphous red-p carbon composites (a- p/c) compared to pure red-p and black-p514 (fig. 39b). upon sodiation/desodiation, the pure red p sh"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 74,
    "chunk_index": 2,
    "text": "coulombic efficiency of 87%, suggesting that the amorphous structure of phosphorus can effectively buffer the strong volumetric expansion during cycling. over the same period of time, kim et al. reported on an amorphous red phosphorus/carbon composite anode, which exhibited an appropriate redox potential of ca. 0.4 v vs. na/na+ with a reversible capacity of 1890 ma h g1 and good rate capability delivering 1540 ma h g1 at a high current density of 2.86 a g1511 (fig. 39c). they also observed the f"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 74,
    "chunk_index": 3,
    "text": "that chemically bond with the surfaces of phosphorus particles. this chemical bonding facilitates robust and intimate contact between phosphorus and graphene nanosheets. furthermore, the graphene at the particle surfaces can assist to maintain electrical contact and stabilize the solid electrolyte interphase upon the large volume change of phosphorus during cycling. as a result, this composite anode delivers a high reversible capacity of 2077 ma h g1 with an excellent cycling stability of 1700 m"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 74,
    "chunk_index": 4,
    "text": "the most stable allotrope.513 the higher bulk conductivity of black phosphorus compared with red-p is additional advantages for electrochemical activity in na cells.514,515 hembram et al. proposed an atomistic mechanism for the sodiation of black phosphorus, based on first principles calculations.521 the layered structure of black phosphorus is maintained up to the composition of na0.25p, with one- dimensional sodiation (an intercalation process) occurring in the interlayer spaces of the black p"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 74,
    "chunk_index": 5,
    "text": "test at different cut-off voltage windows.516 within the voltage window of 0.01–2 v na/na+, the composite anode exhibited a high initial capacity of 1300 ma h g1, however, the capacity gradually decreased. in contrast, attractive stable cyclic performances over 100 cycles were observed in the voltage windows of 0.33–2.0 v vs. na/na+. the post-cycling sem studies showed that the electrodes gradually disintegrated and delaminated from the current collectors when electrochemical testing was perform"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 74,
    "chunk_index": 6,
    "text": "ex situ x-ray diffraction (xrd) techniques. this nanoarchitecture delivers several advantages: (1) the graphene layers provide an elastic buffer layer to accommodate the anisotropic volumetric expansion during the sodiation process, (2) the phosphorene layers with an increased interlayer distance offer a short diffusion length for sodium ions, and (3) the graphene layers function as an electrical highway. as a result, the phosphorene–graphene hybrid nanostructure exhibited an extremely high spec"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 75,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3603 the sodiation/desodiation process via ex situ xrd analysis and electrode/electrolyte interfaces via powerful surface characterization techniques such as haxpes and tof-sims analyses.522 in the as- prepared electrode, black p exists as a crystalline phase with the orthorhombic lattice. in the full reduction state at 0 v in na cells, orthorhombic black p changes into trisod"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 76,
    "chunk_index": 0,
    "text": "review article chem soc rev 3604 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 fig. 39 (a) schematics of white, red, and black phosphorus. (reproduced with permission from ref. 518, copyright 2014 american chemical society.) (b) initial charge/discharge curves of three phases of phosphorus: red phosphorus, black phosphorus, and a-p/c nanocomposites. (reproduced from ref. 514 with permission, copyright 2013 wiley-vch verlag gmbh & co. kgaa.) (c) char"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 76,
    "chunk_index": 1,
    "text": "composites at different current density. (reproduced by permission from ref. 512, nature publishing group, copyright 2015.) the reduction product is found to be the same as red p. after forming na3p, the cell is oxidized to 2.0 v, and reformation of the crystalline phase of black p was not found. this observation shows that black p is a metastable polymorph, and amorphous p would be formed as the oxidation product in the na cell.522,524 they also observed that the vc- added electrolyte especiall"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 76,
    "chunk_index": 2,
    "text": "has been recently regarded as a potential anode material for libs525,526 and sibs527–531 due to the unique layered crystal structure with a large interlayer spacing. ellis et al. reported that the sodiation and desodiation mechanisms reversibly follow the na–bi equilibrium phase diagram with the formation of nabi and na3bi.527 bi reacts with na to form na3bi, giving a theoretical capacity of 385 ma h g1. later, sottmann et al. showed that alloying of sodium and bismuth proceeds via two distinct "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 76,
    "chunk_index": 3,
    "text": "the crystallite surfaces. on the other hand, through dft simulations, su et al. calculated that bi could provide facile sites for na+ ion diffusion and accommodation, based on the intercalation mechanism instead of the alloying process.530 their ex situ xrd and tem results consistently showed that bismuth undergoes the na+ ion intercalation process in na cells. they also prepared a bismuth– graphene nanocomposite (bi@graphene) and demonstrated its sodium storage performances in a bismuth crystal"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 76,
    "chunk_index": 4,
    "text": "= metal). among them, secondary element m is classified into two main categories; namely, electrochemical inactive elements532–537 (ni, cu, fe, zn and mo) and electrochemical active elements538–541 (sn, sb, bi) through an alloying–dealloying reaction with na. during the sodiation/desodiation process, these compounds can store na+ ions through two electrochemical reaction mechanisms of conversion and alloying. in this binary compound system, the primary beneficial role of the secondary elements m"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 76,
    "chunk_index": 5,
    "text": "- sn + 3.75na+ + 3.75e. after the first sodiation process, the ni3sn2 porous microcages are converted into both in situ formed zero-dimensional electroactive na–sn particles and three-dimensional conducting ni in hollow matrix form. the mechanical strain of sn during charge/discharge processes is effectively suppressed by the hollow core structure and the presence of the ni matrix in the hollow microcages. moreover, homogeneously encapsulated ni converted from the sodiation of ni3sn2 is benefici"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 76,
    "chunk_index": 6,
    "text": "respectively. however, the irreversible formation of intermediate compounds leads to a lower reversible storage capacity than that for a pure sb electrode. on the other hand, in the case of active alloying elements, sn–sb and sn–p (in section 3.2.3.1) binary-compounds have received much attention as anode materials for sibs due to their high reversible capacity and stable capacity retentions. xiao et al. reported a high capacity with the reversible alloy reaction in snsb/c nanocomposites for sib"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 77,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3605 charge) is mainly related to the na–snsb alloying– dealloying reaction that produces na3sb and metallic sn. the plateau in the lower potential range (0.05 v at discharge and 0.17 v at charge) is mainly attributed to the na-ion insertion into super p carbon and the na–sn alloying–dealloying process. after initial cycles, however, most of reversible capacity is led by the a"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 77,
    "chunk_index": 1,
    "text": "these porous cnf–snsb nanocomposite electrodes delivered a high reversible capacity of 350 ma h g1 at 0.2c, an excellent capacity retention for more than 200 cycles and an enhanced reversible capacity of more than high-performance m–sb alloy anodes with a long flat voltage profile, high capacity, and stable cycle, zhao et al. proposed bismuth (bi) for the secondary metal.541 they fabricated a bi–sb–c composite anode via facile high-energy mechanical milling with carbon and demonstrated a high in"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 77,
    "chunk_index": 2,
    "text": "and/or formation of composites for practical applications are as follows. first, a high electrolyte/electrode surface area may lead to more significant side reactions with the electrolyte. for instance, typical disadvantage of carbon coating and/or formation of composites is the irreversible capacity charge loss in the first cycle due to the sei formation on the carbon surface that needs to be overcome during the battery charge phase. second, the tap density of carbon coated and/or at a high rat"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 78,
    "chunk_index": 0,
    "text": "review article chem soc rev 3606 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 composite materials is generally decreased contents. as a result, the whole capacity of the active material in the electrode is decreased and limited the total energy of the cell. therefore, to achieve the high energy density and excellent battery performances at the same time, we should well-balance the carbon additive amount with active materials. 3.4. organic compounds"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 79,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3607 carboxylate-based organic materials and terephthalate based materials were widely investigated as potential anode materials 543 532–538 –na"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 80,
    "chunk_index": 0,
    "text": "review article chem soc rev 3608 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 therefore, the major organic carbonyl for sibs. zhao et al. firstly proposed the na2c8h4o4/kb (ketjen black) composite electrode for sibs, which has a reversible capacity of 250 ma h g1, corresponding to a two electron transfer, with excellent cycling performance544 (fig. 41a). in addition, ald al2o3 2 8 4 4 fig. 41 (a) the discharge–charge cycles of the na2c8h4o4/kb comp"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 81,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3609 for the first galvanostatic oxidation for the different polymeric schiff bases. (reproduced from ref. 564 with permission, copyright 2014 wiley-vch verlag gmbh & co. kgaa.) conjugated structure between the carbonyl group and the phenyl rings. br–na2tp and no2–na2tp electrodes delivered a high capacity of 300 ma h g1; however, nh2–na2tp delivered a relatively low capacity "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 81,
    "chunk_index": 1,
    "text": "capacity of 180 ma h g1 with an average operation voltage of 1.8 v. later, to enhance the fast insertion/extraction of na-ions at high current densities, wang et al. suggested an extension of the p-conjugated system by using sodium 4,40-stilbene-dicarboxylate (ssdc).552 remarkably, the designed electrodes exhibited a much enhanced high rate performance with reversible capacities of 105 ma h g1 at a current density of 2 a g1 and 72 ma h g1 at a current density as high as 10 a g1. according to the"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 81,
    "chunk_index": 2,
    "text": "the capacity fading of organic compounds is the dissolution of the active compound in polar liquid electrolytes.556 to circumvent unwanted active mass dissolution during cycling, various strategies are introduced such as the application of polymers as active materials or the immobilization of active molecules onto the conductive additives.543,556–558 recently, chen et al. proposed the use of pntcda, a kind of polyimide.557 the intrinsic stability and insolubility of the polyimide ensure that it "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 81,
    "chunk_index": 3,
    "text": "oxide (rgo) nanosheets owing to the strong p–p interaction between the aromatic structure and the carbon scaffold. optical and photoelectron spectra results demonstrated non-covalent immobilization of the redox molecules via p–p interactions on the rgo carbon scaffold, which suppresses the dissolution puzzle of organic materials and enhances both the conductivity and sodium-ion accessibility of the electrode. as a result, juglone/rgo electrode demonstrated a high capacity of 305 ma h g1 and stab"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 81,
    "chunk_index": 4,
    "text": "electron end group (–ooc–f–cqn–) (f: refers to the phenyl group) and the central (–nqc–f–cqn–) hu¨ckel units.565 they claimed that the maximum capacities are achieved for oligomers in which h+ ions are replaced by na+ ions due to the fact that the hydrogen bond of the carboxylic end groups acting as crosslinks is removed, thus helping to accommodate more easily for the inserted na+ ions. 4. electrolytes, additives, and binders sib technology is a very important and promising follow-up to lib tec"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 81,
    "chunk_index": 5,
    "text": "directed toward the searching for new electrode materials for sibs, studies dealing with the electrolyte itself are much scarcer.28,567 however, looking back through the history of libs, it is clear that a suitable choice of electrolyte and binders is equally as important as the choice of electrode material for making operational sibs; this is because the electrolyte and binders form a protective layer at both the cathode and anode, the surface layer (sl) and the solid electrolyte interfaces (se"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 81,
    "chunk_index": 6,
    "text": "are dissolved with complex containing functional additives, are mainly used in the practical development of sibs due to their large potential window, high ionic conductivity and good temperature performance. on the other hand, a water-based electrolyte has also been proposed as a cost- effective energy storage system, which was successfully commercialized.18,569 in this section, we discuss sib electrolytes, including salts, solvents, and additives. in addition, we briefly"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 82,
    "chunk_index": 0,
    "text": "review article chem soc rev 3610 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 summarized the currently employed binders as well as their effects on the electrochemical performances based on various electrodes and/or sodium ion full cells. 4.1. electrolytes a general list of properties needed for sib electrolytes complies with those usually compiled for lib oriented electrolytes: (1) chemically stable, (2) electrochemically stable, (3) thermally sta"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 82,
    "chunk_index": 1,
    "text": "with the cell component.568 the solvent should: (1) be polar with a high dielectric constant, (2) exhibit low viscosity in order to improve the ionic mobility, (3) remain inert to the charged surfaces of the cathode and the anode during cell operation, and (4) have a wide liquid range (i.e. a low melting point and a high boiling point).568 over the past few decades, based on such basic properties, the scientific community has made tremendous efforts in finding the best combination of suitable el"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 82,
    "chunk_index": 2,
    "text": "either naclo4 or napf6 is used as the electrolyte salts in carbonate-ester binary or ternary mixtures, which have become the main stream electrolyte composition used for na+ chemistry.571 although the sodium perchlorates have some concern of safety and are notoriously difficult to dry, in terms of only academic interest, the commonly used salt is naclo4 due to a combination of historical and cost reasons.28,570,573 delmas et al. demonstrated the electrochemical properties of a p2-type naxcoo2 el"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 82,
    "chunk_index": 3,
    "text": "naclo4 based electrolyte for a carbonaceous electrode demonstrated a higher capacity with high coulombic efficiency. they also reported the dependency of electrolyte solvents on the electrochemical properties of carbonaceous materials using an ec:dmc, dme, and ec:thf solvent containing 1 m naclo4 salt (fig. 42a). the thf-solvent and ec:thf mixture have shown to improve the electrochemical performance as compared to only carbonatebased solvents. komaba et al. investigated electrochemical performa"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 82,
    "chunk_index": 4,
    "text": "thf, and ec:thf as electrolytes. (reproduced with permission from ref. 575 copyright 2005 the electrochemical society.) (b) linear sweep voltammetry of a sodium cell using two electrolytes, namely, 1 m naclo4 in pc + 2 vol% fec and 1 m naclo4 in ems + 2 vol% fec. (reproduced with permission from ref. 51, copyright 2014 american chemical society.) (c) dsc heating curves of fully sodiated hard carbon in various electrolyte formulations. (reproduced with permission from ref. 28, copyright 2012 the "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 82,
    "chunk_index": 5,
    "text": "cycle test. (reproduced with permission from ref. 577, copyright 2011 american chemical society.) (f) cycle performance of sn4p3 and sn electrodes obtained with or without an fec additive. (reproduced from ref. 460 with permission, copyright 2014 wiley-vch verlag gmbh & co. kgaa.) (g) structure of polymer binder: pvdf, pva, cmc-na, paa. (reproduced with permission from ref. 610, copyright 2011 american chemical society.) (a) cyclic performance of na0.11li3.89ti5o12 electrodes with different bind"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 83,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3611 mixture solutions. interestingly, vc is commonly accepted as a suitable additive to modify the interface via thin film forming of the electrodes; however, the addition of vc in a pc solvent was not found to play the same role in hard carbon electrodes. appropriate additives for sibs are specifically discussed in the additive part. on the other hand, anodic stability witho"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 83,
    "chunk_index": 1,
    "text": "order to realize practical sibs, many researchers have explored alternative na salts with high battery performances as well as good battery safety. ponrouch et al. systematically investigated the most appropriate electrolyte formulation so as to minimize the interface reactions and enhance both cell performances and safety aspects.28 they evaluated the basic properties of the electrolyte solution such as viscosity, ionic conductivity, and thermal and electrochemical stability in diverse solvent "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 83,
    "chunk_index": 2,
    "text": "(fig. 42c). the appearance of an exothermic peak at a high temperature of napf6 in the ec:pc electrolyte can be ascribed to how a significantly more thermally stable sei layer is formed on a hard carbon surface after cycling compared to those of the other electrolytes. on the other hand, komaba et al. observed the stable cycling performances in hard carbon electrodes with the napf6-based electrolyte solution in comparison to those of the naclo4-based electrolyte.27 bhide et al. carried out a com"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 83,
    "chunk_index": 3,
    "text": "results showed that the electrolyte napf6–ec:dmc is favorable for the formation of a stable surface film and the reversibility of the na0.7coo2 cathode material. ponrouch et al. also achieved a high rate capability for the na3v2(po4)2f3 cathode and the hard carbon/na3v2(po4)2f3 full cell in 1 m napf6 in the ec:pc:dmc (45:45:10, v/v) electrolyte.574 however, when using the napf6 containing electrolyte for the electrode materials, negative effects also occurred, such as low ionic conductivity of t"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 83,
    "chunk_index": 4,
    "text": "grade napf6, 1 m napf6 was not completely dissolved in pc. however, by selecting the battery grade napf6, 1 m napf6 in the pc solution was revealed to be colorless and transparent because of the complete dissolution of 1 m napf6. as anticipated from the electrolyte coloration, the hard carbon anode exhibited better electrochemical performances in the battery grade napf6 containing electrolyte solution (fig. 42d). the above results convinced that the choice of a well-balanced mixture solvent and "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 83,
    "chunk_index": 5,
    "text": "anode material for sibs in some ether-based electrolytes.259,262 some research groups enabled transition-metal disulfides to achieve high-rate capability and long-term cyclability by optimizing the electrolytes and voltage windows in ether-based electrolytes. with regard to transition-metal chalcogenides, ether-based electrolytes exhibited a higher solvent-salt stability and a lower reaction energy barrier than those of carbonate- based electrolytes.407,413,429,578 4.2. additives another major c"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 83,
    "chunk_index": 6,
    "text": "for li-ion batteries.577 the results demonstrated that fec is the only efficient electrolyte additive for both the cathode and anode. according to komaba et al.’s reports, an appropriate amount of fec additive (2 volume%) is helpful for forming high quality passivation films on the electrode surface, as well as for suppressing the side reactions between the na metal and propylene carbonate solution containing na salts (fig. 42e). meanwhile, ponrouch et al. observed a decrease in specific capacit"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 84,
    "chunk_index": 0,
    "text": "review article chem soc rev 3612 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 used in the ec:pc solution containing 1 m naclo4 salt.249 unlike the pc only based electrolyte, the ec:pc mixture based electrolyte promoted efficient sei layer formation on the hard carbon electrode surface without the need of fec additives. recently, dahbi et al. reported the electrochemical sodium insertion for hard carbon in a cyclic alkylene carbonate based (pc, pc/e"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 84,
    "chunk_index": 1,
    "text": "a fec additive electrolyte. namely, the irreversible reaction during the initial cycle in both napf6 and naclo4 based electrolytes was effectively suppressed by the fec additive, which enhanced the reversibility of hard carbon anodes. the passivation layer would be further stabilized and become a thinner surface layer in the presence of fec because the fluorine compounds dissolved in the electrolyte would efficiently induce the formation of an electronically insulating, ionically conducting, and"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 84,
    "chunk_index": 2,
    "text": "kinetics of na by using fec additives. the main components of fec-containing electrolytes were proposed as important compounds in effectively protecting surface films. the final sei composition can be affected by a multitude of different factors, such as the order of the bond breaking events, the relative stability of resulting radical ions, and the thermodynamic feasibility of different decomposition reactions.582 when fec free electrolytes were used in na cells, the xps results suggest that th"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 84,
    "chunk_index": 3,
    "text": "through the opening of a five- membered ring, and forms very thin and stable protective films which may contain naf, na polycarbonate and polyenes (oxygen-free polymer).584–587 as a result, previous reports have indicated that fec addition in organic electrolyte solutions leads to a significant improvement of the cyclability. kim et al. and li et al. examined and compared electrochemical performances of tin–phosphide electrodes with/without fec additives460–462 (fig. 42f). more recently, dahbi e"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 84,
    "chunk_index": 4,
    "text": "and 83 (c6h11+) in tof-sims result) play an important role as components of sei layers in the electrode, which results in the improvement of electrochemical performance and suppression of sei dissolution. on the other hand, vc did not form efficient surface layer films on hard-carbon electrodes with naclo4 in pc.577 as mentioned above, a solid electrolyte interphase (sei) is one of the crucial determinants of battery life. the final sei composition can be affected by a multitude of different fac"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 84,
    "chunk_index": 5,
    "text": "theory (dft) method.583 according to their calculations, in ec based electrolytes, the high reduction potential and a low barrier for the ring opening of ec is the main cause for the continuous growth of a sei in sibs. they also studied the effect of additive molecules on the decomposition pathways of the ec. on the other hand, dahbi et al. reported the formation mechanism and the main component of surface films on the phosphorus and hard carbon electrode with different electrolyte solutions.522"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 84,
    "chunk_index": 6,
    "text": "according to step 1. f ions are also released and react with na+ ions in the electrolyte to form naf on the electrode surface. they also suggested the possible mechanism for additive (fec and vc) reduction reactions in na cells. when fec is added in a na cell, it is believed that fec reduces first, then polymerizes through the opening of a five-membered ring, and forms very thin and stable protective films which may contain naf, na polycarbonate and polyenes (oxygen-free polymers). in contrast, "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 85,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3613 reductive decomposition but also they can promote alternate pathways for decomposition, leading to qualitatively different and potentially stable sei products.584–587 4.3. ionic liquids, polymer electrolytes, all-solid electrolytes the study of ionic liquids (ils) and polymer electrolytes containing a fraction of sodium salts is still at a very early stage.99,568 ionic li"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 85,
    "chunk_index": 1,
    "text": "batteries with inorganic solid electrolytes and electrodes are promising power sources for a wide range of applications because of their safety, long-cycle lives and versatile geometries.18,99,568,593–597 by west et al. a na/naclo4-peo/v2o5 cell was proposed in 1985 to avoid the use of a na metal anode.593 later, ma et al. reported on a sib cell built using na0.7coo2 as the cathode, na15pb4 as the anode and natf(peo)8 as the solid polymer electrolyte.72 a phosphate-based all-solidstate symmetric"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 85,
    "chunk_index": 2,
    "text": "electrolyte for practical use in sibs is as follows. first, napf6 has been largely used as electrolyte salts in carbonate-ester binary or ternary mixtures, which have become the main electrolyte composition used for sibs. second, propylene carbonate (pc) is a key component in both binary and ternary solvent mixtures, which has intrinsic advantages derived from its high dielectric constant and wide operating electrochemical and temperature windows.568 third, the use of fec as an additive plays th"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 85,
    "chunk_index": 3,
    "text": "the appropriate binders. thus, investigation of desirable binders is also necessary to stabilize the electrode surface and suppress electrode distortion during the sodiation–desodiation process. commonly, most electrodes of commercial and/or scientific studies are made using poly(vinylidene fluoride) (pvdf) as a binder to form an electrode layer from a powdery electrode material on a metal current collector due to its good chemical and electrochemical stabilities.99 however, some problems remain"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 85,
    "chunk_index": 4,
    "text": "threedimensional interconnection of those binders. a na-cmc binder is an environmentally friendly and inexpensive material that is derived from cellulose as natural polymers. during the electrochemical reaction process, the na-cmc binder could play an important role in improving the solid electrolyte interface (sei) passive layer on the electrode surface, which reduces the irreversible capacity and somehow leads to a better cycle life.601–603 na-alg is a high-modulus natural polysaccharide extra"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 85,
    "chunk_index": 5,
    "text": "in the composite electrode; this is due to their amorphous and cross-linking nature via the hydrogen bonds between carboxylic groups.608–611,613 a paa binder allows for the formation of a stable deformable sei layer on the elastic binder- coated electrode surface, in which the elasticity of the polymer matrix may prevent cracking in the sei when the volume changes.609,610 the polymeric cross-linkage network can regulate the mechanical/ chemical stress that results from large volume expansion in "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 86,
    "chunk_index": 0,
    "text": "review article chem soc rev 3614 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 the na-cmc binder in their li4ti5o12 electrode.337 recently, zhao et al. introduced the na-doped li4ti5o12 electrode using the na-cmc and na-alginate binder instead of the pvdf binder. these binders exhibited a slightly higher coulombic efficiency than that of the pvdf binder. after 100 cycles, the na-cmc and na-alginate binders exhibited an excellent cyclability compared"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 86,
    "chunk_index": 1,
    "text": "with the development of libs, sib technologies have been rapidly developing. the gravimetric energy density of sibs as full cells operable at room temperature has become competitive in the state-of-the-art libs with graphite and layered oxides.99 however, current research concentrated mostly on sodium-ion half cells (employing na metal). therefore, development of practical sodium ion full cells (without na metal) remains critical challenges. recently, in order to realize the practical sibs, many"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 86,
    "chunk_index": 2,
    "text": "300 cycles.71 later, a full cell with a p2-type na0.6coo2 cathode and a petroleum coke anode was also proposed with the solid polymer electrolyte p(eo)8nacf3so3, at a high operation temperature of 100 1c251 (fig. 43a). however, these full cell systems did not attract much attention compared to libs due to their average discharge potential being lower than 3 v. on the other hand, the performances of sodium-ion full cells have dramatically improved since hard carbon anodes were introduced by dahn "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 86,
    "chunk_index": 3,
    "text": "potentials, are employed for high energy density sodium ion full cells.237 in 2003, barker et al. reported the preliminary performance data of sodium-ion full cells based on hard carbon/navpo4f chemistry181 (fig. 43b). the average discharge voltage for this cell was demonstrated to be around 3.7 v, which is comparable with commercially available lithium-ion cells based on licoo2 or limn2o4 cathode materials. however, this full cell consisting of hard carbon/navpo4f exhibited a relatively low dis"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 86,
    "chunk_index": 4,
    "text": "permission from ref. 181, copyright 2003 the electrochemical society.) (c) voltage versus capacity profiles for nvpf//hc full na-ion cells cycled in 1 m napf6 in ec0.45:pc0.45:dmc0.1. (reproduced with permission from ref. 574, copyright 2013 the royal society of chemistry.) (d) first cycle of a full na-ion cell nayc/na1– y(ni1/3fe1/3mn1/3)o2. (reprinted from ref. 50, copyright 2012, with permission from elsevier.) (e) long-term cycle test of c/rahc full cells in the voltage range of 1.5–3.9 v. ("
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 87,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3615 applying the na3v2(po4)2f3 cathode and hard carbon anode for fabricating sodium-ion full cells, this full cell exhibited a high capacity of 110 ma h g1 with an operation voltage of 3.65 v, as well as excellent capacity retention upon cycling with a satisfactory coulombic efficiency (498.5%) and very good power performance in the ec:pc:dmc (45:45:10, v/v) electrolyte solut"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 87,
    "chunk_index": 1,
    "text": "0.7, m = transition metal) result in high rechargeable capacities.46 however, a lower initial sodium content in the crystal structure of p2-type layered cathode led to an abnormal coulombic efficiency above b100% in the 1st cycle.100 therefore, the intrinsic properties hinder practical full cell fabrication. meanwhile, the practical benefits of o3-type (naxmo2; x e 1.0, m = transition metal) cathodes are that they are able to fabricate sodium-ion full cells similar to commercial libs. komaba et "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 87,
    "chunk_index": 2,
    "text": "v50 (fig. 43d). on the other hand, the sodium ion-full cells used in some works utilize a hard carbon anode that was presodiated in order to reduce the irreversible capacity during the first cycle. moreover, such a presodiated system needs a different electrode balancing to prevent sodium plating.624 this technique is not intended for commercial applications, but rather for scientific queries, to test the long-term electrochemical performance of such materials using full cells; this is because m"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 87,
    "chunk_index": 3,
    "text": "various temperatures (20, 0, 30 and 55 1c). especially, it demonstrated a superior cycle retention of b80% under extensive cycling conditions for over 300 cycles with an average operation voltage of 2.84 v on discharge at 30 1c. more recently, keller et al. proposed sodium-ion full cells based on a presodiated hard carbon anode and a mixed layered oxide cathode of p2/p3/o2- na0.76[mn0.5ni0.3fe0.1mg0.1]o2.624 presodiation of hard carbon was carried out until 135 ma h g1 to prevent excess sodium i"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 87,
    "chunk_index": 4,
    "text": "close to the sodium plating voltage, causing a safety concern. li et al. designed a full sodium-ion battery based on nanostructured na2ti3o7 and vopo4 materials as the anodes and cathodes625 (fig. 43f). in order to reduce the polarization and irreversibility effect of the electrode materials in the first discharge process (both for the anode and cathode sides), pre-desodiated na2ti3o7 and pre-sodiated vopo4 were prepared in advance. this full cell shows outstanding rate capability and excellent "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 87,
    "chunk_index": 5,
    "text": "operating voltage plateau at b2.53 v, as well as an extraordinary rate capability of 75% retention at 12c-rate and superior cycling performance. the na3v2(po4)3 materials also exhibit both cathode and anode potentials (3.4 v with a v4+/v3+ redox reaction and 1.6 v with a v3+/v2+ redox reaction), so a novel symmetric full cell system could be designed by employing na3v2(po4)3 as a bipolar electrode material.628 such present results regarding sodium-ion full cells based on several platforms of cat"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 87,
    "chunk_index": 6,
    "text": "parameters for high safety sibs. in addition, the total production cost of active materials of the electrode and the cost of battery components should be considered. in summary, a strategy for battery design in realizing practical sibs is needed to find a good balance between an increase in battery performance with high safety and a decrease in the total cost of the batteries. 6. summary even though sibs were studied around the same time as libs, they were also abandoned at one point, particular"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 88,
    "chunk_index": 0,
    "text": "review article chem soc rev 3616 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 growth of technology and the exigency for large-scale applications such as esss have opened the door for sibs to be utilized again. lithium is not uniformly scattered on the earth’s crust, and given the demand that it is continually increasing, its reserves (specifically in lithium-constrained areas) will be exhausted. this will lead to an escalating price for lithium, an"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 88,
    "chunk_index": 1,
    "text": "cannot be avoided, disruption of structure’s durability while trying to maintain its original state is bound to happen.630 moreover, sodiated transition metal materials are particularly hygroscopic, even upon brief exposure to air. thus, the preparation of sodiated cathode materials and batteries requires meticulous handling and moisture-free conditions. the hydration of materials will deteriorate the electrochemical performance of the electrode due to the formation of intrinsically insulating n"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 88,
    "chunk_index": 2,
    "text": "and computationally faster compared to li systems due to the low lewis acidity of na+. by contrast, the insertion of na+ into non na-containing compounds with a smaller bottleneck size may be slower compared to the insertion of li+. furthermore, b- al2o3; the fast na+ ionic conductor, was discovered almost 50 years ago, which is even earlier than li+. studies on cathode materials are considerably broad, including oxides, polyanions, nasicon (na super ionic conductor) types and organic compounds."
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 88,
    "chunk_index": 3,
    "text": "metal sites as a substitute to fe.39,47,50 however, the problem of insufficient cycle stability has yet to be solved. in the case of polyanion compounds, they exhibit better thermal stabilities compared to those of oxides, owing to the presence of the p–o covalent bonds in the crystal structure. they have an operating voltage comparable to that of the li system. in addition, as opposed to the earlier mentioned information regarding the kinetic diffusion of na+ ions, a few studies on nafepo4 have"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 88,
    "chunk_index": 4,
    "text": "the incorporation of transition metals into their structure. na3v2(po4)3, for example, showed improved capacity at both higher and lower voltage regions after the modification of its surface with carbons derived from sugar. their earlier work showed unsatisfactory results when tested as cathodes in a full symmetrical cell. prussian blue and its analogues have also attracted attention due to their high energy, power density and electrochemical properties. however, unlike polyanions, their poor th"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 88,
    "chunk_index": 5,
    "text": "and high structural stability is necessary in order for sibs to be successfully developed. sodium metal is not recommended for use in an anodes due to its high reactivity and formation of dendrite. many non-graphitic materials such as carbon black, pitch-based carbon- fibers have been demonstrated to insert na+. hard carbons, i.e., non- graphitic but graphene containing, carbonaceous materials, are considered as the ‘‘the first-generation’’ anode of choice for sibs.22,23,241 the low bet surface "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 88,
    "chunk_index": 6,
    "text": "responsible for the charge storage. the pseudocapacitive effect on typical insertion electrodes is believed to be a potential solution to overcoming the capacity limitation for na insertion anodes. conversion reactions of metal oxides can also be useful for anodes in sibs.243 these conversion reactions, which depend on the transition metals, occasionally combined with the insertion–extraction or alloydealloying reactions. the reaction concept was first introduced with spinel nico2o4, which deliv"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 89,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3617 sulfides (sns, sns2) have been extensively investigated as high capacity anode materials for nibs. the weaker m–s bond in metal sulfides compared to the corresponding m–o bond in metal oxides is kinetically favorable for conversion reactions with na ions.410 hence, the smaller volume changes and better table 1 summary of cathode materials for sodium-ion batteries cathode "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 89,
    "chunk_index": 1,
    "text": "fe3+/4+ 2.1–3.9 240 140 52 na[li0.05(ni0.25fe0.5mn0.25)0.95]o2 ni2+/4+ fe3+/4+ 1.7–4.4 246 180 52 na1x[fe1ymny]o2 na2/3[fe0.5mn0.5]o2 fe3+/4+ mn3+/4+ 1.5–4.3 260 190 54 na0.62[fe0.5mn0.5]o2 fe3+/4+ mn3+/4+ 1.5–4.3 263 185 55 na0.7[fe0.5co0.5]o2 fe3+/4+ co3+/4+ 2.5–4.0 256 170 47 na1xcoo2 nacoo2 co3+/4+ 2.0–4.0 239 170 33 na0.55coo2 co3+/4+ 2.7–3.5 263 140 62 na2/3[co2/3mn1/3]o2 co2+/3+ mn3+/4+ 1.5–4.3 258 180 73 and 74 na5/8ca1/24coo2 co3+/4+ 2.0–4.0 255 124 79 na1xnio2 nanio2 ni3+/4+ 2.0–4.5 23"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 90,
    "chunk_index": 0,
    "text": "review article chem soc rev 3618 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 na0.7mno2 mn3+/4+ 2–3.8 260 150 98 mn3+/4+ 1.5–4.4 260 216 97 mn3+/4+ 1.5–4.4 260 198 97 na2/3[ni1/3mn2/3]o2 ni2+/4+ 2.0–4.5 258 162 101, 107 and 113 na2/3[ni1/3xmgxmn2/3]o2 ni2+/4+ 2.0–4.5 around 258 120–145 107 na2/3[ni1/3xalxmn2/3]o2 ni2+/4+ 2.0–4.5 around 258 147 113 na2/3[ni1/3xfexmn2/3]o2 fe3+/4+ ni2+/4+ 2.0–4.5 around 258 145 113 na0.7[mn0.65ni0.15fe0.2]o2 fe3+/4+ "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 90,
    "chunk_index": 1,
    "text": "1.2–2.6 270 105 136 na2ruo3 na2ruo3 ru4+/5+ 1.5–4.0 137 147 137 table 1 (continued) cathode materials for sodium-ion batteries structure compositions redox voltages couples (v) theoretical capacity (ma h g1) experimental capacity (ma h g1) ref. two-or threedimensional layer transition metal oxide and fluorides manganese oxide vanadium oxide metal fluorides a-mno2 [hollandite] b-mno2[hollandite] a-v2o5 vo2(b) fef3 mn3+/4+ mn3+/4+ v5+/4+ v4+/3+ fe3+/2+ 1.0–4.3 1.0– 4.3 1.5–3.8 1.0–3.8 1.5–4.0 308 "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 91,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3619 threedimensional polyanion compounds phosphates and fluorophosphates amorphous nafepo4 olivine nafepo4 na2fepo4f na2[fe0.5mn0.5]po4f fe3+/2+ fe3+/2+ fe3+/2+ mn2+/3+ fe2+/3+ around 2.4 around 2.8 2.0–3.8 2.0–4.5 154 154 124 124 150 120 100 110 156 163–173 178 180 nav0.96cr0.04po4f v5+/3+ 3.0–4.5 142 80 184 and 185 na3v2(po4)2f v4+/5+ 3.0–4.2 156 87 186 na1.5vpo4.8f0.7 v3.8"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 91,
    "chunk_index": 1,
    "text": "na3mnpo4co3 mn2+/3+ mn3+/4+ 2.0–4.5 250 125 221 cyanides and organic compounds kmnfe[cn]6 mn3+ fe3+/2+ 2.0–4.0 81 70 228 kfefe[cn]6 fe3+/2+ 2.0–4.0 81 90 228 kcofe[cn]6 co3+ fe3+/2+ 2.0–4.0 81 55 228 knife[cn]6 ni2+ fe3+/2+ 2.0–4.0 80 50 228 kcufe[cn]6 cu2+ fe3+/2+ 2.0–4.0 79 55 228 kznfe[cn]6 zn2+ fe3+/2+ 2.0–4.0 79 32 228 na1.4mnfe[cn]6 mn3+/2+ fe3+/2+ 2.0–4.2 82 131 229 na1.72mnfe[cn]6 mn3+/2+ fe3+/2+ 2.0–4.2 81 120 229 na4fe[cn]6 fe3+/2+ 2.0–3.8 89 87 231 na4c8h2o6 1.6–2.8 187 180 236 na2c6o"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 92,
    "chunk_index": 0,
    "text": "review article chem soc rev 3620 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 reversibility of na2s compared to that of na2o during the sodiation– desodiation process result in better mechanical stabilities and higher initial coulombic efficiency, respectively. apart from electrode materials, suitable electrolytes, additives and binders are equally important for the development of nibs. with appropriate electrolyte formulation, the interface reacti"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 92,
    "chunk_index": 1,
    "text": "by palacin’s group, they have discovered that napf6 in the ec:pc:dmc solvent mixture is the best electrolyte for the hard carbon anode.574 on the other hand, ponrouch et al. reported that napf6 in ec:pc exhibited a low generation of heat and a high thermal stability, which can be attributed to the more thermally stable sei layer that is formed on the hc after cycling.28 as organic liquid electrolytes are less safe than the other electrolytes, using an aqueous electrolyte is a good approach to pr"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 92,
    "chunk_index": 2,
    "text": "production cost when using pvdf to make the slurry, water-soluble binders such as sodium carboxymethyl cellulose (na-cmc), poly(acrylic acid) (paa) and sodium alginate (naalg) have been introduced. na-cmc, an environmentally friendly and inexpensive material, could play an important role in improving the solid electrolyte interface (sei) passive layer, which reduces the irreversible capacity and somehow leads to a better cycle life. na-alg, which is more polarized than cmc, can ensure better int"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 92,
    "chunk_index": 3,
    "text": "solvents, and current collectors is important and must be established in order to realize the practicality of sibs in large-scale applications such as ess. we believe that improving the understanding and more findings of materials can accelerate the development of sibs which are compatible to commercial level libs. 7. perspectives libs have realized their adoption from portable devices to vehicle applications because of their high operation voltage and energy density, so that battery performance"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 92,
    "chunk_index": 4,
    "text": "a serious situation to be resolved. use of cobalt or other rare metals as electrode materials is another concern on the price of batteries for future mass production for the purpose of mounting libs to evs and energy storage applications. indeed, the battery pack price should reach 20– 30% of the current value to spread libs for those applications from 2020. this is controversial for the use of present high capacity lithiated ni-rich cathode materials because each metal price except manganese is"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 92,
    "chunk_index": 5,
    "text": "the inferior battery performance of sibs relative to libs was the main reason for the fade of sibs, which led to the birth of commercialized libs by sony in 1990s. however, the recent upsurge of evs and energy storage using libs as power sources could cause a shortage of libs so a great deal of attention has been paid again to development of sibs, in which sodium is inexpensive and evenly distributed. since 2010 with the slogan of beyond lithium, research trends in sibs have been intensively foc"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 92,
    "chunk_index": 6,
    "text": "cells, (iii) lowering of the manufacturing cost due to the use of al foil instead of cu current collectors for anodes and the transfer of the production line of libs to sibs, which does not need new production facility, (iv) superior safety properties of the cathode even at a highly charged state, and (v) less risk for sodium supply. by contrast, there are some demerits of sibs; (i) low operation approximately 0.3 v versus li, (ii) a large ionic radius of na+ (1.02 å) relative to li+ (0.76 å), w"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 93,
    "chunk_index": 0,
    "text": "chem soc rev review article this journal is ©the royal society of chemistry 2017 chem. soc. rev., 2017, 46, 3529--3614 | 3621 as mentioned in fig. 1 and table 1 development of cathode materials has been progressing towards layer and polyanion structure materials. in particular, know-hows accumulated by the development of libs are leading to significant progress in layered structure materials. o3 type layer compounds are very fascinating because they have the same crystal structure as commercial "
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 93,
    "chunk_index": 1,
    "text": "extractable sodium content in the compounds, namely, na0.7mo2 (m: transition metals), of which the first discharge capacity is similar to that of o3 type compounds. nonetheless, many works have been directed toward stabilization of cycling performances. appropriate sacrificing agents can show oxidative decomposition at the first charge, which can be used to solve the irreversible capacity at the first cycle. this enables the resulting coulombic efficiency approaching close to 100%. provided that"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 93,
    "chunk_index": 2,
    "text": "layer cathodes, the resulting coulombic efficiency at the first cycle is still not sufficient to fabricate the practical sibs in comparison with o3-type layer cathodes. therefore, to compete with libs, academic community should revisit o3-type layer cathode materials such as co-free na[ni0.5mn0.5]o283 and carbon-coated nacro2131 which show high coulombic efficiency at initial cycle and excellent cyclability. the know-hows accumulated from libs were further used to synthesize o3-type full concent"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 93,
    "chunk_index": 3,
    "text": "at the first cycle. polyanion materials are attractive because of high operation voltage and cycling stability, whereas low capacities below 100 ma h g1 and more seriously moisture uptake in air are the critical issues to be resolved for those compounds. these suggest suitability of o3 type cathode materials in practical uses for future evs and energy storage applications. anode materials are activated by insertion, conversion, and alloying reactions as summarized in fig. 1. due to the low opera"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 93,
    "chunk_index": 4,
    "text": "voltage, in which safety issues should be considered because of the high reactivity of sodium metal. in addition, capacity below 300 ma h g1, which is lower than graphite anodes for libs, is not advantageous to improve the energy density of sibs. thus, conversion and alloying reaction based materials are intensively being studied to find alternative anode materials that deliver high capacity and do not have sodium metal deposition on discharge. it is evident that these conversion and alloying ma"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 93,
    "chunk_index": 5,
    "text": "to improve energy density of sibs. so far, various anode materials are under investigation, it is believed that hard carbon is thought to be the best candidate in practical applications due to its low operation voltage, cycling stability, and high coulombic efficiency at the first cycle. reviewing many kinds of cathode and anode materials in the present review, in summary, there is no doubt about the practical use of the o3 type cathode and hard carbon anode assembly for successful full cell con"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 93,
    "chunk_index": 6,
    "text": "laboratory also promotes sibs that adopt o3 type or prussian white cathodes, hard carbon anodes, and conventional carbonatebased electrolytes for high energy density sibs.641,642 recent a report by choi et al. and doron et al.643 proposed the importance of minimization of energy consumption ($ w h1) rather than lowering of material costs to successful spread of sibs towards energy storage applications. also, sibs are faced with intrinsic low energy density relative to libs, and this further lowe"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 94,
    "chunk_index": 0,
    "text": "review article chem soc rev 3622 | chem. soc. rev., 2017, 46, 3529--3614 this journal is ©the royal society of chemistry 2017 intrinsic robustness under high compression pressure in the electrode pressing process. to date, specific energy density of sibs was only estimated based on the weight of active materials by calculation with the assumption of 300 ma h g1 for hard carbon as a negative electrode material for full cells. such an estimated specific energy density of sibs with some of the cath"
  },
  {
    "source_pdf": "Sodium_ion_batteries_present_and_future_Jang_Yeon_Hwang.pdf",
    "page": 94,
    "chunk_index": 1,
    "text": "developing high capacity cathode and anode materials and stable electrolytes including additives that operate in a high voltage region, in particular, to maximize the energy density. furthermore, more systematic studies on surface modification of active materials to minimize the side reactions with electrolytes, binders, current collectors, and the other components should be intensively progressed so as to advance the sibs in practical use towards energy storage applications."
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 1 1. introduction a rechargeable battery is a highly efficient tool for storing electrical energy via a series of chemical reactions [1–3]. typically, lithium (li)-ion batteries (libs) based on li intercalation chemistries can produce electricity by shuttling massive li ions internally from the anode to the cathode [4–6]. relying on the natures of high energy density, long cycling lifespan and affordable manufacturing cost, the lib techniques are pref"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "li mining in politically sensitive regions [11, 12]. therefore, it is greatly desirable to seek cheap and environmentally friendly alternatives to libs. sodium (na) is the highly abundant resource in earth’s crust and shares in the same periodic location as li element [13–15]. by using na as viable carrier ions instead of li, the na ion batteries (sibs) have resurfaced as a hot research topic in the recent years. such a scenario has also promoted the fundamental evaluation of sibs to identify th"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "materials with high electrochemical properties and low manufacturing cost [18]. to date, battery scientists have reported various materials that could be applied in sib anodes, such as hard carbon [16], sulfides [19–21], phosphide [22], fluoride [23], and metal oxide [24,25], as specifically illustrated in fig. 1a. among them, phosphides, consisting of the phosphorus (p) bonding with metal and nonmetal elements, exhibit sufficient specific capacities and low redox voltage (vs. na/na+) [26]. hist"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "in libs [30], thus realizing a speedy improvement in the electrochemical performance of phosphides for na storage. as such, recent studies have made numerous achievements in dealing with the adverse effect of large volume variations and simultaneously enhancing the sei flexibility for interfacial stability [31]. in particularly, the morphological designs and interfacial modifications, which have successfully enabled satisfactory specific capacity, sufficient power performance and durable cycling"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "providing an overview of future challenges and opportunities based on using phosphide anodes for sibs by analyzing the application of new characterization technologies. 2. sodiation/desodiation mechanisms electroactive materials suffer volume expansion/shrinkage during the cycling process, which is extremely related to the sodiation/desodiation mechanisms. uncovering and understanding these mechanisms helps us conduct the rational design of high-performance electroactive materials [32]. specific"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "and p phases while reacting with p to form na3p until the p phase is completely alloyed [22]. correspondingly, two different situations occur in the phosphides according to the electrochemical activities of their components to na ions. when the non-p components of phosphides are inactive to na ions, the non-p nanocrystals experience no chemical changes in the subsequent cycles. the whole process follows eq. (1). alternatively, when the non-p components of phosphides are active to na, the inserte"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "an irreversible sodiation process and subsequent reversible alloying reactions upon na insertion/ extraction. no further reformation of the axpy phase is the primary difference from the abovementioned conversion mechanism. the following discussion is still based on the electrochemical activity between a and na. for the non-p components with no na-storage properties, the sodiation/desodiation mechanism of these phosphides, such as cop [37] and fep [38], follows eqs. (3) and (4). in the initial di"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 2 fig. 1. (a) redox potential and specific capacity of various anode materials for sibs, reproduced with permission [26]. copyright 2018, royal society of chemistry. (b) schematic of the modification strategies used for in phosphide anode in high-performance sibs. fig. 2. schematic of the sodiation/desodiation mechanism of phosphide anode materials. in the other scenario, the phosphides with na-active non-p components follow the mechanism shown in eqs"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "such as sn4p3 [39] and gep5 [40], follow this mechanism. axpy +(3y + z)na+ +(3y + z)e− →nazax + yna3p(initial discharge) (5) na3p↔3na+ +3e− +p (6) nazax ↔zna+ +ze− +xa (7) 2.3. comparison between phosphorus and phosphide materials retrospecting the roles of p phase in the phosphides to enable their remarkable na storage properties, there are some similarities as the pure p anode, which deserves further discussion. firstly, elemental p is a primary part in capacity storage for both pure p and pho"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "behavior happens. as such, the fragmentation of nanoparticles and the damage of sei occur, causing the performance decay of electrode material [22]. however, there are also differences between pure p material and phosphides. the na storage mechanism of phosphide materials is more complex than that of pure p materials. after na ions break the metal- p bonds, different reactions govern the subsequent process depended on the properties of the metal components as discussed above. in addition, the ph"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 3 specific capacity of 1132 ma h g− 1 and a suitable working potential of 0.3 v vs. na/na+ [28]. sn4p3 follows an alloying mechanism that na ions are inserted into the sn4p3 crystal lattice through ion channels, simultaneously breaking the bonds between sn and p. because na and p can bond tightly, naxp begins to form and gradually reaches saturation to form na3p. meanwhile, partial inserted na ions also alloy with sn to form sn15p4 [42]. eqs. (9)–(11)"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "solvothermal [31,49,50] methods are common methods to tune the particle morphology and size at the nanoscale level. afterwards, the electrospinning techniques [51,52] are used in the synthesis of sn-based phosphides. the schematic timeline of modification strategies and synthesis methods is shown in fig. 3a. sn4p3 + 24na+ + 21e− →3na3p + na15sn4(initial discharge) (9) na3p↔p+3na+ +3e− (10) na15sn4 ↔4sn+15na+ +15e− (11) designing a coating carbon layer used for electroactive materials is a well- "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "more space for internal expansion to release physical strain and maintain structural integrity. for instance, a uniform yolk-shell sn4p3@c anode material was synthesized through the combination of preliminary reduction and in-situ phosphorization of hollow sno2 nanospheres (fig. 3b) [58]. the tem image of sn4p3@c nanosphere indicates that the sn4p3 nanoparticles were confined inside conformal, thin, and self-supporting carbon nanocages with enough space for volume expansion (fig. 3c). as such, t"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "together with deal with the volume issues. compared with a simple carbon-coating structure, 3d network structure provides an increased surface area, a better mechanical flexibility and an enhanced electronic conductivity. such a 3d network architecture is often prepared by using flexible and conductive substances such as graphene and carbon nanotubes. in 2016, a sn4p3@reduced graphene oxide (sn4p3@rgo) composite with a novel 3d mesoporous structure was reported, where rgo acts as a conductive ne"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 2,
    "chunk_index": 4,
    "text": "sn4p3 electrodes can improve their electrochemical performance. for example, ran et al. [59] anchored fructus-like sn4p3 on carbon nanotubes (cnts) through a simple hydrothermal reaction and subsequent thermal treatment, eventually achieving sn4p3@cnt/c with a biomimetic heterostructure. the fabrication scheme of the sn4p3@cnt/c electrode and sem image are shown in fig. 3d and e, respectively. relying on cnts with a high electrical conductivity and large surface area, this composite anode displa"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 2,
    "chunk_index": 5,
    "text": "meanwhile, the concept of self-healing bonding between sn and p is also proposed to hinder sn particle aggregation and, thus, serious capacity degradation is apparently inhibited during the cycling process [60]. this statement still needs for more evidences and counterproductive to provide a good opportunity for in-depth investigation on phase variation. fig. 3. (a) development of modification strategies and synthesis methods of sn-based phosphide anode materials. (b) schematic illustration of t"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 4 3.2. nickel phosphides the nip3 material was initially proposed for sib anodes in 2014. the conversion reaction mechanism of nip3 refers to eqs. (12) and (13) [27]. the high p content of nip3 helps it deliver a high theoretical specific capacity of 1591 ma h g− 1 but also causes serious volume expansion/shrinkage, resulting in its inferior cycling stability. since 2017, a series of ni-based phosphides, such as ni2p and ni12p5, have been reported for"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "on n, p-codoped carbon nanosheets to construct a covalent heterostructure (ni2p@npcs) (fig. 4b) [66]. the resultant anode delivers a capacity of 361 ma h g− 1 at 0.1 a g− 1 after 300 cycles. meanwhile, by using in situ transmission electron microscopy (tem) to observe the sodiation process of ni2p (fig. 4c), the electroactive material maintained its original morphology with an ~ 118% volume expansion. no agglomeration of ni2p was observed. in addition to pyrolytic carbon materials, graphene is a"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "rapid electron pathway, offers a buffer for the volume expansion of ni2p, and suppresses the aggregation of ni2p nanoparticles. consequently, a high fig. 4. (a) development of synthesis methods and modification strategies of nickel phosphide anode materials. (b) schematic diagram showing the synthesis of ni2p@npc. (c) the tem images of ni2p@npc showing the morphology evolution with different na transportation times of 0, 7, 12 and 17 min. reproduced with permission [66]. copyright 2018, elsevier"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 5 reproduced with permission [69]. copyright 2018, elsevier. reversible capacity of 457 ma h g− 1 at 0.3 a g− 1 is achieved after 500 cycles. similar as sn-based phosphides, ni-based phosphides were recently reported in the morphologies of nanoarrays [69] and nanosheets [70, 71]. for example, ni2p nanoarrays grown on n-doped graphene were prepared by dong et al. to construct a sandwich-like structure (fig. 4d) [69]. this special structure provides a c"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "high elemental abundance for low cost. fig. 5a shows the development of fe-based phosphides in material and structural iterations. back to 2015, fep was synthesized by the ball-milling method for use as an anode material for sibs for the first time, delivering an initial capacity of 764.4 ma h g− 1 [38]. the fep anode was believed to experience a hybrid reaction mechanism of na storage as shown in eqs. (14) and (15). the performance decay, however, rapidly occurs in the cycles. to this end, grap"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "thus, this anode exhibits high reversible capacities of 613 ma h g− 1 at 0.05 a g− 1 and 349 ma h g− 1 even at a high current density of 3 a g− 1 and retained 378 ma h g− 1 after 700 cycles at 1 a g− 1, equivalent to ~ 90% of the 6th discharge capacity. fep + 3na+ + 3e− →na3p + fe(initial discharge) (14) na3p↔p + 3na+ +3e− (15)"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 6 metal-organic frameworks (mofs) are well known for their porous structure and have recently been considered as novel precursors in the synthesis of electrode materials [76–80]. shi et al. [78] achieved the self-confined growth of fep quantum dots on a cnt-grafted p-doped 3d octahedral carbon framework (fep@ocf/cnt) through the in-situ reductive phosphorization/carbonization of mofs (mil-101) (fig. 5c). this composite anode could deliver a high-rate "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "dual-carbon-modified amorphous and mesoporous fep composite (cnts@fep) composite, of which the preparation process is displayed in fig. 5d [81]. taking advantages in the porous pathway and conductive network, and flexible structure, the resultant cnts@fep composite delivers a specific capacity of 415 ma h g− 1 at 0.1 ma g− 1. a good capacity retention of up to 90% is also achieved at a current density of 0.5 a g− 1. with increased p content, the resultant fe-based phosphides also show a higher r"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 reproduced with permission 7 3.4. cobalt phosphides cobalt (co)-based phosphides is a promising candidate for sib anodes. historically, the earliest cop material used for sib anode was obtained through a simple ball-milling method and displayed a reversible capacity of 770 ma h g− 1 [83]. the alloying mechanism of cop is shown by eqs. (16) and (17). in the initial discharging process, cop is decomposed into co and p, and then, the p alloy with na is d"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "(fig. 6a). cop + 3na+ + 3e− →na3p + co(initial discharge) (16) na3p↔p+3na+ +3e− (17) designing core-shell structure is a common method used to buffer the volume variation [84–86]. liu et al. [85] synthesized hierarchical hollow cop@c composites. this hierarchical hollow carbon structure not only guaranteed sufficient contact between the electrode material and the electrolyte but also alleviated the volume variations, thus enhancing the anode lifespan with no obvious capacity decay. this anode co"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "addition, anchoring cop on graphene is an effective strategy because graphene can act as a substrate to interconnect the cop particles and enhance the charge transfer kinetics. hierarchical architectures are constructed to further protect the electroactive materials from particle aggregation as well as improve the transfer kinetics of na+ and e-. for example, ge et al. [37] anchored mof-derived core-shell cop particles on 3d rgo to form zif-67-derived core- shell co@c polyhedral structures (cop@"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "cop anode material was also reported [87]. such a multidimensional framework provides hierarchical barriers for the volume expansion of cop (0d porous carbon shells, 1d nanosized carbon walls and 3d graphene). as a result, this anode stabilized at 398 ma h g− 1 after 300 cycles, with a retention ratio of 70% at a current density of 0.1 a g− 1. fig. 6. (a) development of synthesis methods and modification strategies of cobalt phosphide anode materials. (b) schematic diagram of the fabrication pro"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 reproduced with permission 8 3.5. copper phosphides copper (cu)-based phosphides were first considered as an sib anode material in 2015 when cup2 was directly mixed with super p via a simple ball milling process [34]. super p-coated cup2 composite delivers a large capacity in excess of 500 ma h g− 1 and demonstrates cu-based phosphides to hold great opportunities for sib anode. meanwhile, the sodiation/desodiation mechanism of cup2 was confirmed by ki"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "particles as precursors to synthesize double shelled cu3p (ds-cu3p) through a surface oxidation, etching and phosphorization process (fig. 7b). the resultant ds-cu3p material exhibits an ultrathin shell and internal 3d hollow structure. the former has low barrier for fast na diffusion in high-rate performance. the latter provides an enhanced pseudo-capacitance and an effective buffer in volume variation. thus, such a composite had a stable capacity of 325 ma h g− 1. in addition, constructing the"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "1000 cycles. subsequently, li et al. [95] synthesized a high p-content anode material for sibs by using a heterointerface of cu2p7, cup2 and multiwall carbon nanotubes (mwcnts). the resultant composite exhibited the high specific capacity of up to 1300 ma h g− 1 at a current density of 0.1 a g− 1. additionally, a 3d network for cuxpy anode can be further constructed by using pyrolytic carbon materials, such as the chitosan- derived carbon [96]. in- situ carbonization may coat a conformal and tig"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "1 at a current density of 0.1 a g− 1 after over fig. 7. (a) development of synthesis methods and modification strategies of cu-based phosphide anode materials. (b) schematic representation of the growth mechanism of ds-cu3p. reproduced with permission [90]. copyright 2020, wiley-vch. (c) schematic of the fabrication of the cu3p/n-cn composite. (d) sem image of cu3p/n-cn. [97]. copyright 2020, elsevier."
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 reproduced with permission 9 100 cycles. 3.6. germanium phosphides germanium (ge)-based phosphides are a promising candidate for sib anodes. the sodiation mechanism is shown in eqs. (19)–(21). gep5 has a layered and amorphous phase. some evidence indicates that layered gep5 has an advantage in ionic and electronic conductivities as well as its volume tolerance over amorphous gep5 [98]. apart from gep5, both gep3 and gep have wavy layered structures. t"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "amorphous nage to nayp alloys (0 < y ≤ 3). gep5 + 16na+ + 16e− →5na3p + nage(initial discharge) (19) na3p↔3na+ +3e− +p (20) nage↔na+ +e− +ge (21) recently, a dual-carbon network structure of ge-based phosphides was designed as an anode material for sibs [101]. acetylene black and gep5 particles were evenly distributed on the layered graphene oxide to obtain the gep5/ab/p-rgo composite. this composite realized a capacity retention ratio of 80% at 0.05 a g− 1 after 50 cycles. in addition, few-laye"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "et al. used an electrospinning method to synthesize a self- supporting gep electrode material with an n-doped carbon network [102]. the specific capacities of this composite at 0.1 a g− 1 and 4 a g− 1 are 830 ma h g− 1 and 330 ma h g− 1, respectively. the specific capacity was maintained with 500 ma h g− 1 after 350 cycles. 3.7. other metal phosphides zinc (zn) phosphides were also used as the anode material for sibs. li et al. [103] grafted highly ordered zn3p2 nanowires onto titanium (ti) foil"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 8,
    "chunk_index": 3,
    "text": "synthesized znp2 nanoparticles tightly covered by carbon layer through a facile solid-state thermal treatment. nanocrystals with an initial diameter of 8–12 nm fig. 8. (a) development of the synthesis methods and modification strategies of ge-based phosphide anode materials. (b–e) comparison of the morphology and structure of gep before (b–c) and after (d–e) sodiation via the tem characterization, reproduced with permission [99]. copyright 2019, elsevier. (f) synthesis procedure used for fl-gp/r"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 reproduced with permission 10 were reduced in size of 3–5 nm through repeated sodiation/desodiation processes after 10 cycles and maintained this particle size within 50 cycles (fig. 9a). the reduced size of znp2 nanoparticles shortens the na ion diffusion paths. at the current density of 0.05 a g− 1, this anode kept a specific capacity of 883 ma h g− 1 without an obvious degradation after 130 cycles. 13zn3p2 +81na+ +81e− ↔3nazn13 +26na3p (22) in 2017"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "104.5 ma g− 1 at 1600 ma h g− 1, even after 10,000 cycles, as shown in fig. 9b. mop+3na+ +3e− ↔na3p+mo (23) as similar as elemental sn, elemental indium (in) has a alloying ability with na and is further designed for in-based phosphides, which display high specific capacities and good stability for na storage property [105,106]. for example, liu et al. predicted the feasibility of using single-layer inp3 as an anode material for sibs through a first-principles calculation [107]. through a theore"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "1.49 v vs. na/na+. 4. nonmetal phosphides silicon (si) has a theoretical capacity of 3578 ma h g− 1 when used as an anode for sibs [108]. however, si experiences an 300–400% volume change during na insertion process [109]. si-based phosphides were reported for use as anode materials for sibs [110–113]. in 2016, a sip2 anode material was synthesized for sibs and exhibited its high theoretical capacity of 2900 ma h g− 1 [112]. although its initial capacity was 843 ma h g− 1, it declines to 572 ma "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 reproduced with permission 11 et al. [110] used mwcnts to coat sip2 particles through a simple ball-milling process. the electric conductivity of this composite was two times compared to that of pure sip2. mwcnts not only construct a 3d carbon network to connect sip2 particles, but also mitigates mechanical strain stemming from volume variation. such a composite maintained over 600 ma h g− 1 at a current density of 2 a g− 1 after 300 cycles. in 2019, "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "modification, the volume issue of sip2 has not been fundamentally solved, and the anode capacity still faces with a rapid decay during the limited cycling lifespan. further research should be conducted to improve the cycling performance of si-based phosphide anode materials. sip2→na3p + nasi6(discharge process) (24) na3p + nasi6→(sip2)crystalline/amorphous + p(charge process) (25) in 2017, se4p4 was first reported for an anode material for sibs [36]. elemental se can alloy with na to form na2se."
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "1048 ma h g− 1 at 0.05 a g− 1 and a capacity of 332 ma h g− 1, even at a high current density of 3 a g− 1. li et al. [114] converted crystalline p2s5 into an amorphous phase by a long-term ball-milling procedure and made it have excellent electrochemical performance. they tested p2s5 anode materials with different ball-milling times, confirming an optimized 70 h ball- milling time for the best cycling performance. the specific capacity of ~ 90 ma h g− 1 at 2 a g− 1 after 4000 cycles, with a capa"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 reproduced with permission 12 5. multiple phosphides multiple phosphides consist of two types: 1) two or more phosphides that are mechanically mixed and 2) a phosphorus alloy with two or more elements forming a uniform phase. in the recent years, the novel composite assembled by various phosphides have been reported [115,116]. for instance, a self- supporting hybrid fiber of cu3p-co2p/n-c is designed by li et al. [115]. the synergistic effects between"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "an initial capacity of ~ 650 ma h g− 1 and maintained 350 ma h g− 1 at 2 a g− 1. in addition, p can be directly alloyed with multiple metal or nonmetal elements [117–124]. it aims to increase the electronic conductivity and reduce the cost. for example, cu4snp10 was synthesized with mwcnts as a conductive additive [124]. cu4snp10 has a theoretical capacity of 1316 ma h g− 1, which is higher than that of sn4p3 because of its high p content (67%). the elemental cu can prevent active nanoparticles "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "the charge transport and improves the electronic conductivity. the capacities of this material are 496.4 ma h g− 1 and 276.1 ma h g− 1 at 0.5 c and 8 c, respectively. notably, the free-standing electrode could withstand 180 degrees of bending (fig. 10d). in addition, zhao et al. [117] reported a method to couple 3d interconnected crinkled porous ti3c2 mxenes with nicop bimetallic phosphide nanoparticles (ti3c2/nicop). this structure established a 3d flexible network that bolster na+ transport in"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "the battery community [127–129]. a dense sei layer can effectively prevent electroactive materials from electrolyte corrosion, but it enables good ionic conductivity and is an electronic insulator [130]. regrettably, a large volume variation is detrimental to the sei integrity of electrode materials [128]. as such, for unstable or inhomogeneous seis, the thickness increases constantly during cycling, along with the electrolyte decomposition and an irregular li+/na+ diffusion length [131]. those "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 11,
    "chunk_index": 4,
    "text": "organic/ inorganic materials [132–134]. as an example of the latter, zhang et al. [135] modified red p with tio2, and the sei stability was improved owing to the synergistic effect between tio2 and red p (fig. 11a). the addition of tio2 strengthens the connection between phosphorus and the sei layer so that the organic components and naf particles cannot enter the near-surface region, making the sei stable. understanding the sei layer of a phosphide anode is further reinforced by using advanced "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 13 (haxpes) technology to probe the sei formation on sn4p3 surface. the sei thickness was 15–30 nm after full sodiation. inorganic carbonate and fluoride were produced during the initial sodiation process. when this anode underwent the na extraction process, the sei thickness decreased along with the generation of oxygen and fluoride species. in addition, the electrolyte formula is critical for the sei formation. hiroyuki et al. [137] used an ionic li"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "on electrode surface. by combing tof-sims with haxpes, dahbi et al. [140] analyzed the sei composition formed on the surface of rp electrode using n-methyl-n-propylpyridinium bisfluorosulfonyl amide (mppfsa) electrolyte dissolved by sodium bisfluorosulfonylamide (nafsa). the resultant anode had a specific capacity of 1480 ma h g− 1 at 0.125 ma g− 1 and capacity retention of 93% after 80 cycles, while the comparison with napf6/pc electrolyte maintain only ~ 30%. a higher organic compositions tabl"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "most alloy-type anode materials, phosphides also face with the issues of large volume changes upon na insertion/extraction. this adverse influence includes particle pulverization, poor electric conductivity and inferior interfacial stability. fortunately, the studies of phosphides can refer to the successful experiences of oft-studied li counterpart. corresponding optimized strategies have been proposed to overcome above challenges. typically, the morphological design and structural tuning can e"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 3,
    "text": "sn4p3@c [58] sn4p3@c [55] vapor phosphorization vapor phosphorization vapor phosphorization electrospinning phosphorization vapor phosphorization vapor phosphorization calcination under ph3 vapor phosphorization vapor phosphorization annealing vapor phosphorization cvd and hydrothermal vapor phosphorization vapor phosphorization phosphorization ball milling vapor phosphorization phosphorization ball milling phosphorization solvothermal 542 ma h g− 1, 0.5 a g− 1, ~ 62%, 300 cycles 309 ma h g− 1, "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 4,
    "text": "g− 1, ~ 74%, 200 cycles 124.5 ma h g− 1, 1 a g− 1, ~ 72%, 2000 cycles 457 ma h g− 1, 0.3 a g− 1, ~ 100%, 500 cycles 107.8 ma h g− 1, 1 a g− 1, ~ 48%, 400 cycles 230.1 ma h g− 1, 0.2 a g− 1, ~ 32%, 100 cycles 124 ma h g− 1, 1 a g− 1, ~ 54%, 500 cycles 184.9 ma h g− 1, 1 a g− 1, 94%, 260 cycles 477 ma h g− 1, 0.2 a g− 1, 91%, 200 cycles 1415 ma h g− 1, 5 a g− 1, ~ 96%, 100 cycles ~ 295 ma h g− 1, 0.05 a g− 1, 87.7%, 100 cycles 420 ma h g− 1, 2 a g− 1, ~ 60%, 2000 cycles 550 ma h g− 1, 1 a g− 1, 84"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 5,
    "text": "1, 1.5 a g− 1, ~ 72%, 400 cycles 516 ma h g− 1, 1 a g− 1, 55.3%, 500 cycles 74% 48.7% 68.3% 49% 72% 55.2% 69.06% 53.6% ~ 78% 41.5% 63% 69% 88.28% 45% 68.3% ~ 80% ~ 90% 75.1% 60% 73.1% 43.8% 63.7% 187 ma h g− 1 at 8 a g− 1 62.1mah g− 1 at 2 a g− 1 421 ma h g− 1 at 2 a g− 1 ~ 240 ma h g− 1 at 5 a g− 1 262 ma h g− 1 at 20 a g− 1 500 ma h g− 1 at 4 a g− 1 237.5 ma h g− 1 at 2.5 a g− 1 208.8 ma h g− 1 at 2 a g− 1 164 ma h g− 1 at 0.4 a g− 1 172.1 ma h g− 1 at 1 a g− 1 246 ma h g− 1 at 5 a g− 1 152.1 "
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 6,
    "text": "at 5 a g− 1 152.1 ma h g− 1 at 2 a g− 1 273.3 ma h g− 1at 1 a g− 1 206 ma h g− 1 at 5 a g− 1 ~ 140 ma h g− 1 at 5 a g− 1 263 ma h g− 1 at 0.8 a g− 1 684 ma h g− 1 at 10 a g− 1 166 ma h g− 1 at 2 a g− 1 260 ma h g− 1 at 4 a g− 1 ~ 315 ma h g− 1 at 10 a g-1 421 ma h g− 1 at 3 a g− 1 508 ma h g− 1 at 2 a g− 1 sn4+xp3@(sn-p) [147] sn4p3 [56] sn4p3/c [148] sn4p3/rgo [31] sn4p3@hc [149] sn4p3@cnf [51] gep [150] gep3 [151] gep5/c [40] gep/cn [102] mop [35] v4p7/5p [152] zn3p2 [35] sip2/c [111] sip [112"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 7,
    "text": "[114] cu3p-co2p/n-c [115] cu4snp10/mwcnts [124] sb47fe39p14 [154] fesi4p4 [123] nicop/cnts [155] ball milling solvothermal ball milling solvothermal ball milling electrospinning ball milling ball milling ball milling electrospinning solid phase reaction ball milling cvd ball milling ball milling ball milling solid phase reaction ball milling electrospinning ball milling electrodeposition ball milling solvothermal 502 ma h g-1, 0.1 a g-1, 92.6%, 100 cycles 303 ma h g− 1, 0.2 a g− 1, 63%, 500 cycl"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 8,
    "text": "800 ma h g− 1, 1 a g− 1, ~ 80%, 110 cycles 553 ma h g− 1, 0.5 a g− 1, ~70%, 350 cycles 104.5 ma h g− 1, 1.6 a g− 1, 88%, 10,000 cycles 295 ma h g− 1, 0.2 a g− 1, 54%, 100 cycles ~ 450 ma h g− 1, 0.1 a g− 1, ~ 75%, 85 cycles ~ 200 ma h g− 1, 0.5 a g− 1, ~ 70%, 490 cycles 572 ma h g− 1, 0.296 a g− 1, 67.9%, 15 cycles 804 ma h g− 1, 0.05 a g− 1, 76.7%, 60 cycles ~ 654 ma h g− 1, 0.2 a g− 1, ~ 91%, 70 cycles ~ 96 ma h g− 1, 2 a g− 1, 89.4%, 4000 cycles 316.9 ma h g− 1, 5 a g− 1, 55.8%, 2000 cycles 5"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 9,
    "text": "100 cycles 422 ma h g− 1, 0.1 a g− 1, 97.8%, 200 cycles ~ 180 ma h g− 1, 0.1 a g− 1, ~ 100%, 100 cycles ~ 200 ma h g− 1, 0.1 a g− 1, ~ 200%, 200 cycles 86.6% 64.1% 61.2% 46.6% ~ 70% 72.5% ~ 90% 81.3% ~ 93% ~ 68% ~ 53% 88% 55% 76% ~ 72.5% 70% 73.9% ~ 40% ~ 71.2% 54.4% 70% 72% ~ 60% 58.2 ma h g-1 at 10 a g-1 300 ma h g− 1 at 1 a g− 1 ~ 420 ma h g− 1 at 5 a g− 1 391 ma h g− 1 at 2 a g− 1 305 ma h g− 1 at 2 a g− 1 321 ma h g− 1 at 5 a g− 1 533 ma h g− 1 at 5 a g− 1 520 ma h g− 1 at 1 a g− 1 380 ma h"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 12,
    "chunk_index": 10,
    "text": "a g− 1 380 ma h g− 1 at 5 a g− 1 330 ma h g− 1 at 4 a g− 1 115.6 ma h g− 1 at 1.6 a g− 1 155 ma h g− 1 at 2 a g− 1 280 ma h g− 1 at 5 a g− 1 198 ma h g− 1 at 1 a g− 1 520 ma h g− 1 at 0.888 a g− 1 332 ma h g− 1 at 3 a g− 1 486 ma h g− 1 at 3 a g− 1 108 ma h g− 1 at 2 a g− 1 567.7 ma h g− 1 at 5 a g− 1 412 ma h g− 1 at 1 a g− 1 245.8 ma h g− 1 at 2 a g− 1 54 ma h g− 1 at 4 a g− 1 88 ma h g− 1 at 1 a g− 1"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 14 for the research trend in phosphide anodes for sibs, the rational design of phosphides call for the support from in-depth understanding of"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 14,
    "chunk_index": 0,
    "text": "w. zhang et al. nano energy 90 (2021) 106475 15 na storage mechanism, varied component/structural design and reinforced interfacial stability. their combination is more beneficial to enable a synergistic effect in excellent electrochemical performances of phosphides. in addition to the fundamental studies in the correlation between nanostructure and electrochemical properties, researchers should be solution-focused and pragmatic. generally, the outstanding electrochemical performance of electrod"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 14,
    "chunk_index": 1,
    "text": "surfaces. the debate regarding the phase variation is urgently addressed from battery community. ii) low potential and high capacity are important for a high-energy density anode. appropriately increasing the p content in phosphides to further enhance the specific capacity is highly desired. a desirable balance between high capacity and long cyclability also requires optimized research on phosphides. iii) developing binary or ternary composites, e.g., adding active elements such as sn, se and bi"
  },
  {
    "source_pdf": "Strategies_to_improve_the_performance_of_phosphide_anodes_in_sodium_ion_batteries_Wu_Zhang_Tiefeng_Liu_Yao_Wang_Yujing_Liu_Jianwei_Nai_Liang_Zhang_Ouwei_Sheng_Xinyong_Tao.pdf",
    "page": 14,
    "chunk_index": 2,
    "text": "scenario equally brings about massive investigation to explore the new polymeric binder and novel electrolyte additive, eventually rendering new concepts in the studies of phosphides. declaration of competing interest the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper."
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "• a green biological fermentation technology to prepare hcs is firstly developed. • renewable carbon sources of various biomass starch derived hcs are achieved. • bio-fermentation effectively improve interlayer spacing with abundant closed micropores. • hc with a reversible capacity of 335 ma h g− 1 and long cycling stability is demonstrated. • such a “bread-making” strategy is a scalable route to fabricate hard carbons at a kilogram. a r t i c l e i n f o a b s t r a c t keywords: na-ion batter"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "technology to prepare hcs on a large scale using cheap and renewable carbon sources of various biomass starch. pre-treatment by bio- fermentation can effectively modify the carbon precursor for facile pyrolysis to fabricate starch-based hcs, and make its internal microstructure with larger interlayer spacing, more disordered structure and abundant closed micropores. finally, a case of cornstarch- based hard carbon exhibits a high reversible capacity of 335 ma h g− 1 at a current density of 30 ma"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "carbons with improved performance, demonstrating a very practically promising application for industrial manufacture. 1. introduction with the introduction and implementation of various carbon emission policies, na-ion batteries (sibs) are considered to be one of the most promising candidates for large-scale energy storage due to their abundant and vast resource reserves and similar storage mechanism and fabrication technology to lithium-ion batteries [1–5]. nowadays, the development of low-cost"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "on defects and functional groups, insertion into graphene layers with turbo domains and pore filling [11–16]. the dominating capacity contribution in hc comes mainly from the low voltage plateau region, thus guaranteeing the high energy density in the full battery, leading to being the only commercial anode (kuraray co., ltd) until now [13,17,18]. the biggest bottleneck and difficulty of hc anode in commercialization is the high fabrication cost in synthesizing such material with good performanc"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "the pore structure and enlarge the layer spacing by increasing the structural disorder [23–25]. for example, hu et al. used phenolic resin as the carbon precursor and ethanol as the pore-forming agent under the hydrothermal condition to prepare hc by carbonization at 1550 ◦c, which displayed much improved capacity [26]. komaba et al. used a magnesium oxide template, and successfully synthesized a hard carbon anode with a highly disordered structure and high surface area, leading to a very high c"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "concerns, high energy consumption and carbon emissions. currently, the ideal precursors for commercial hc should be renewable and cost-effective, and the fabrication route should be green and facile to scale up. biomass carbon resources like cellulose and starch are the most two abundant polysaccharides in the world, which are renewable and affordable precursors to prepare hc [33–36]. because of a highly abundant, renewable, and inexpensive natural polymer with good film-forming properties, star"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "heteroatoms doping, such as nitrogen, phosphorus and sulfur, will happen after carbonation to enhance the na-ion storage [39]. inspired by the above issue, we firstly report biological fermentation technology to fabricate hc on a large scale by using various biomass starches as renewable carbon precursors. we get an exciting finding that the number of internal closed micropores of starch-based hc can be significantly increased after yeast fermentation accompanying with larger expanding interlaye"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "y. chen et al. journal of power sources 557 (2023) 232534 2 carbons in kilogram preparation, which can be adopted in industrial engineering. 2. results and discussion fig. 1a shows a schematic illustration of fabricating hard carbons by bio- fermentation with a sustainable precursor starch. through the yeast fermentation process, the large molecules in the starch are broken down, forming smaller molecules with carbon dioxide emission. to study the role of fermentation in engineering the hard car"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "demonstrate the versatility of the yeast fermentation process. the results of the xrd characterization are shown in fig. 1b and fig. s2. the xrd patterns of the four samples showed two broadened peaks near 23◦ and 43◦, featuring the disordered carbon structure in the crystal planes of (002) and (101). after fermentation by yeast, the (002) diffraction peak left shifts, indicating an increasing averaged interlayer distance between graphene layers. calculated by bragg’s law, the averaged interlaye"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "with the interlayer spacing increasing from 3.86 å to 4.02 å. the corresponding saed patterns in fig. 1c and d also shows a decreasing trend in the bright contrast intensity of the polycrystalline rings, further indicating that the structure appears more disordered after fermentation. such phenomenon of low crystallinity and wider layer spacing for the phc sample is also found after fermentation, as illustrated in fig. s3. the pore structure evolution of corn starch and potato starch before and "
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "f-chc is more tightly connected after fermentation but f-phc becomes fragmented and finely fragmented. the open pores of various hard carbons were determined by nitrogen adsorption/desorption. as shown in figs. s5a and b, the bet specific surface area of chc decreased by fermentation treatment, probably due to the formation of more closed micropores which will be discussed in the context. accordingly, the pore volume decreased from 0.037 cm3 g− 1 to 0.007 cm3 g− 1. furthermore, carbon dioxide ad"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 1,
    "chunk_index": 4,
    "text": "the graphene edge defects, which mainly represents disorder, and the e2g symmetric vibrational mode (g-band) of the ideal graphite lattice, which mainly represents the orderliness of graphite [43]. comparing the integral intensity ratio of id/ig based on a gaussian fit: the id/ig of chc rises from 1.76 to 1.81 after fermentation, and phc also rises from 1.75 to 1.84 after fermentation, indicating the enhanced defects. this result suggests an increase in confusion and therefore potentially create"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 1,
    "chunk_index": 5,
    "text": "1.81 10.62 8.13 phc 3.85 95.81 3.86 0.33 24.82 1.75 10.99 5.12 f-phc 3.95 93.81 5.54 0.65 16.93 1.84 10.45 20.33 ( ) ( − 10) 4 ig la (nm)= 2.4×10 λnm id as seen in table 1, the la of chc and phc decreases due to the yeast fermentation process. the smaller la manifests the shorter diffusion path of fig. 1. (a) schematic illustration for the synthesis of starch-based hcs by a fermentation process. (b) xrd patterns of the two hard carbons, high-resolution tem images of (c) chc and (d) f-chc. the in"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "y. chen et al. journal of power sources 557 (2023) 232534 3 na-ion between the graphene layers, thus facilitating the rapid ion transport and storage. the surface elemental valence bonding and composition of chc and phc were further investigated by xps (table 1 and fig. s6). chc and phc both exhibit a decreasing ratio of carbon to oxygen after fermentation that chc increases from 32.39 to 17.04 of f-chc, and phc from 24.82 to 16.93 of f-phc, indicating that the fermentation process can form more"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "286.2, 287.4, 288.6 and 290.5 ev, corresponding to the c–c bond, c–o bond, c––o bond, o–c––o and π-π*, respectively [45]. the detailed results are listed in table s1. the relative content of the c–o bond decrease while the content of the c––o bond and π- π* increases, indicating better carbonation properties, which will promote the na-ion storage capacity [12]. the high-resolution spectra of o 1s for the four samples are shown in fig. 2i-l are fitted by c–o at 533.4 ev and c––o at 532.1 ev. it a"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "structure of closed pores, we adopted small-angle x-ray scattering (saxs) to further investigate the porosity. as shown in fig. 3a, f-chc induces a more curved shoulder at between 0.1 and 0.7 å− 1 (q value), which derived from the scattering of closed micropores. moreover, the quantitative analysis of the closed pores was fitted by matlab software, as presented in fig.s 3b, c. the fitted model is as follows [46]: a ba41 (q)= a +( 2)2 + d q 1 + a21q where a and b are proportional to the total sur"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "y. chen et al. journal of power sources 557 (2023) 232534 4 the electrochemical na-ion storage performance of the hard carbons was investigated by na-ion half cells. cyclic voltammetry (cv) tests (fig. s7 a-d) reveal the typical profiles of hc for na-ion storage with a pair of sharp redox peaks near 0.1 v and a broad peak in the 0.5–1.3 v range, corresponding to the plateau region and the sloping region, respectively. the cv curves of f-chc and f-phc are nearly overlapped which reflects the bett"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "83.6% of chc (270 ma h g− 1). f-phc also have a similar increase in capacity from 290 to 330 ma h g− 1 after fermentation. the rate performance of chc and f-chc from 0.03 a g− 1 (0.1c) to 5 a g− 1 is shown in fig. 4e: the corresponding reversible capacities of chc are: 253/250/245/239/223/205/171/85 ma h g− 1, respectively and 335/321/311/298/281/265/237/141 ma h g− 1 of f- chc. f-phc (fig. 4f) also delivers higher capacities than those of phc at all current rates. this elevated rate performance"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "the initial reversible capacities of f-chc and f-phc are 304.8 and 298.1 ma h g− 1, and their retention rates are 94.4% and 94.2% after 100 cycles. the 2000-cycle stability of such hard carbon was also evaluated at 1 a g− 1 (fig. 4h) that f-chc still delivers 241.8 ma h g− 1 with a 87.2% capacity retention. to verify the universality of such a strategy in improving the starch- based hard carbons, we also selected other common starches (rice starch, wheat starch) on the market for the same fermen"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "cathode. the charge- discharge profiles and the rate capability are shown in fig. s9. such full cells display a stable working voltage at 3.3 v and deliver reversible capacities of 107.4, 104.7, 98, 90.2, 83.8, and 76.2 ma h g− 1 based on the mass of cathode when the current densities are fig. 2. (a–d) raman spectra of various hcs fitted by gaussian function. the high-resolution xps spectra for c 1s of (e) chc, (f) f-chc, (g) phc and (h) f-phc. the high-resolution xps spectra for o 1s of (i) chc"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "y. chen et al. journal of power sources 557 (2023) 232534 5 0.1, 0.2, 0.5, 1, 2, and 5 a g− 1, respectively. besides the excellent rate performance, it also has good cycling stability, demonstrating a promising application. to further understand the na-ion storage mechanism and valence kinds of hcs. (h)long cycling stability of f-chc at 1 a g− 1. changes during the cycling of hard carbon electrodes, ex-situ xps spectra of f- chc (fig. s10) with surface and depth etching 1000 s were tested. the i"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "presence of c–o and c–– o, which do not change during discharge and charge. after etching 1000 s, it can be seen that the c–c bond becomes broadening and shifts to a lower state, suggesting the formation of nacx with the redox c–c bond. this change can not be fully recovered even after full charge, as revealed in fig. 5d. in the na 1s spectrum (fig. 5c, f), naf, the main sei constituent, is found during the discharge and charge process. it should be mentioned that metallic nax+ with lower energy"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 4,
    "chunk_index": 2,
    "text": "deposition because it has to overcome the nucleation overpotential, pure metallic na does not form throughout the discharge region even when the relative voltage reaches 0 v [25]. ex-situ saxs experiments were performed to correlate the pore- filling mechanism of the f-chc electrode during the first sodiation process, shown in fig. 5g–i and fig. s11. as the same material (f-chc) was used for investigating the na-ion storage mechanism, a modified porod equation (see supporting information) was us"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 4,
    "chunk_index": 3,
    "text": "while the δρ of the electrode at 0.01 v (after first discharge) is 0.64 e− cm− 3. it is worth noting that the sei formation during the first cycle can also lead to a decrease in δρ as the nanopore has already filled with solvated na-ions from the electrolyte [52,53]. the δρ at 0.01 v, 0.64 e− cm− 3, suggests that at a high sodiation level, the electron density of the nanopore exceeds that of the carbon electrode so na-ion filling into nanopores happens at the end of discharge which is in line wi"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "y. chen et al. journal of power sources 557 (2023) 232534 6 raman spectroscopy has gained increased attention as it is sensitive and non-destructive, especially for carbonaceous materials. to investigate the ion storage in hard carbons, high-resolution operando raman spectroscopy with characteristic low-frequency raman features d band and g band was performed. the low-frequency signal (100-300 cm− 1) means disorder, displacement, shear, and inner stress within graphite lattice caused by induced "
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "the sodiation curve shows two regions, a sloping region between 2.5 and 0.1 v and a plateau located between 0 and 0.1 v vs na+/na. the corresponding stacked operando raman spectra and 3d operando raman spectra are shown in fig. 6b, figs. s12 and s13. during the sloping region, the signal of the low frequency features firstly decreased and then increases, the intensity remains low during the whole sloping region. this trend suggests the insertion of na-ion enhances the degree of graphitization of"
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "further evidence of the dislocation shear and inner strain of graphene layers. the peak position of the g band remains unaffected, and no peak split was observed during the whole sodiation. hence no intercalation occurs and the mechanism during the plateau region is highly associated with pore-filling that is in line with the patterns of ex-situ saxs. during the de-sodiation process, both d- and g-band were able to shift back to their original position with the low-frequency signal decreased to "
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "the 1st cycle of hard carbon in a half-cell under 0.25 c (75 ma g− 1). (a) the 3d plot of raman spectra in the low-frequency range, the d band and g band. (b) the 1st cycle discharge-charge curve and the corresponding changes in the raman spectra (only the g band is normalized)."
  },
  {
    "source_pdf": "Sustainable_and_scalable_fabrication_of_high_performance_hard_carbon_anode_for_Na_ion_battery_Yang_Chen_Feng_Li_Zhenyu_Guo_Ziqing_Song_Yueying_Lin_Wei_Lin_Lituo_Zheng_Zhigao_Huang_Zhensheng.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "y. chen et al. journal of power sources 557 (2023) 232534 7 suggests some defects have been irreversibly occupied which also results in irreversible loss during the first cycle. the reversibility of the raman spectrum also indicates the structural stability and reversible sodiation/de-sodiation behaviors."
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "introduction and basic outlines the global pursuit of alternative sources of energy generation has been driven by the diminishing reserves of fossil fuels and associated challenges. events such as the bp-gulf oil spill and increasing calls for reduced emissions of harmful gases have underscored the necessity for transitioning away from reliance on fossil resources. [1,2]. the economic vitality of nations worldwide is intricately linked to the methods by which energy needs are met. during the lat"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "on human health [5,6]. the documented rise in carbon dioxide levels between 1995 and 2015, increasing from 360 to 400 parts per million, underscores the critical need for a transition towards environmentally sustainable energy practices [7,8]. while solar [9,10], geothermal [11,12], wind [13–15], and other renewable energy sources show significant promise in achieving these nomenclature bess battery energy storage system co2e carbon dioxide equivalents co cobalt ess energy storage system gwp glo"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "nickel manganese cobalt oxide napba sodium prussian blue analogue napf6 sodium hexafluorophosphate natmo sodium transition metal oxides ni nickel nmc nickel manganese cobalt pba polybenzimidazole pc propylene carbonate pf3 phosphorus trifluoride ppm parts per million re renewable energy swot strengths, weaknesses, opportunities, and threats vars volt-ampere reactive objectives, their reliance on variable weather conditions introduces unpredictability into energy generation processes [16]. to imp"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "peak periods (fig. 1, b) [23]. integration of energy storage systems with renewable energy is critical in the development of a reliable energy storage system. subsequently, renewable sources such as solar and wind power provide energy depending on the prevailing weather conditions and time which causes a challenge of energy mismatch. energy storage systems act as a buffer in that they can store power during production overproduction periods and release it during production deficiency times [24–2"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 0,
    "chunk_index": 4,
    "text": "integration of a high level of renewable energy into the power system [27–29]. ongoing global research endeavors are focused on exploring various energy storage technologies to fulfill these objectives (fig. 2). to store large quantities of energy capacities, pumped hydroelectric storage (phs) and compressed air energy storage (caes) are combined because of the capacity to achieve power to capacity in gw for a low starting budget, from the phs side [31–33]. pumped hydroenergy storage (phes) func"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 0,
    "chunk_index": 5,
    "text": "height the water tank is in, phs plays a significant role in storing the energy caes is highly recommended due to its capacity to store electrical energy on a huge scale of 100 mw this method results in a high efficiency in energy conversion and also major capacity of storage, making it suitable to work under the condition of fluctuating [34,37,38]. both caes and conventional gas turbines (cgt) have the same concept. a caes system has five parts including an air compressor, generator, storage, a"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 0,
    "chunk_index": 6,
    "text": "air with the assistance of high-pressure turbines produces electrical energy. these types of energy storage have a lot of benefits such as longer periods of storage, being cheap, and also a high efficiency of storing in the range of 70–90 %. flywheel storage units are ideal for energy storage [34,37,39,40]. these drawbacks restrict the applicability of * corresponding author. e-mail addresses: farbodesmailion@gmail.com (f. esmaeilion), msoltani@uwaterloo.ca (m. soltani). https://doi.org/10.1016/"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 2 flywheels to a limited set of specific purposes. table 1 and table 2 provide an overview of prominent energy storage systems, while table 3 presents a comparative analysis of various types of battery energy storage systems. table 1 and table 2 provide an overview of diverse energy storage systems, detailing their applications, unique attributes, and shortcomings respectively. flywheel energy storage systems, for "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "to their flexibility, minimal maintenance requirements, high operational efficiency, and reliability. however, challenges such as environmental impact, material requirements, and cost constraints are critical considerations, alongside issues related to lower energy densities and shelf- life limitations. the dynamic interplay between power supply and demand necessitates a close alignment between energy generation and consumption. consequently, this research aims to comprehensively analyze the pre"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "lithium is distributed rather unevenly in the earth’s crust, and due to the growing demand, especially in regions where lithium resources are quite limited, such reserves may soon be depleted. this means that lithium-ion batteries will not be as economical for use in energy storage as they fig. 1. a) load leveling & b) peak shaving."
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 3 were before since the costs of lithium are steadily increasing. sodium-ion rechargeable batteries are thus slowly coming into the scene as a better technology than lithium-ion. they are cheaper than other ores, are more easily sourced for than other locations, and present less of a hazard to the environment. fears of lithium are tied to the centrality of re and plans to connect batteries with higher energy densit"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "are cheaper and better for large-scale energy storage than lithium-ion types of batteries. the sodium–ion batteries work on a similar mechanism to the lithium-ion batteries but they contain sodium ions rather than lithium ions. after many barriers to commercialization, this technology has all the prospects to meet the energy demands of the world. the future of sodium-ion batteries seems more or less bright, as their applicability is not limited to a certain field, and future advancement is expec"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "crust at approximately 23000 ppm (parts per million) and some thousand times more than lithium at around 20 ppm. this abundance can lead to significant cost reductions. for instance, sodium as a raw material is much cheaper than lithium. lithium carbonate (li2co3) can cost up to $15,000 per ton, while sodium carbonate (na2co3) costs around $150 per ton [50]. in terms of material costs, sodium-ion batteries are estimated at 223 €/kwh, compared to lithium–iron-phosphate (lfp) batteries at 229 €/kw"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 2,
    "chunk_index": 3,
    "text": "20 7,000 to 12,000 40 to 54 2–6 0.5 to 2 [46] compressed air energy storage (small scale) over 23 over 30,000 − higher than large-scale plants similar to large-scale plants [32] flywheel energy storage around 15 over 20,000 about 90–95 20–85 1000–2000 [22] thermal energy storage 30 − roughly 30–60 80 to 120 − [34] superconducting magnetic energy storage 30 over 100,000 90 to 97 0.2 to 0.25 approx. 2500 [35] capacitor just above 5 over 50,000 between 60 and 70 around 0.05 100,000 [36] supercapaci"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 4 sibs have attracted significant attention from researchers in recent years as they offer a promising substitute for lithium batteries in large- scale applications. the exploration of sibs dates back to the same period when libs were first being developed in the 1970s and 1980s. still, due to the substantial progress and widespread commercial use of libs during that time, sib research was largely sidelined. also, "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "table 2 evaluating various electrical energy storage systems in terms of cost. energy storage type power investment ($/kwh) energy capital cost ($/kwh) o&m costs ($/kwh) reference pumped hydro energy storage 25,000 to over 42,000 5–100 0.005 [35] compressed air energy storage (large scale) 300–900 1–120 0.004 [47] compressed air energy storage (small scale) 1,300–1,550 200–250 low [48] flywheel energy storage 250 to over 350 10,000–14,000 around 0.004 [40] thermal energy storage 100 to 400 3 to "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 3,
    "chunk_index": 2,
    "text": "mechanisms, except ion carriers. lithium and sodium intercalation chemistry are comparable, hence similar molecules can be employed as cathode materials in both systems. the electrolyte formulations typically used for sibs included salts such as sodium perchlorate (naclo4) or sodium hexafluorophosphate (napf6) in solvents like carbonate esters, particularly propylene carbonate (pc) [54]. hard carbon is also preferable because the raw materials for its production such as glucose, starch, and biom"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 3,
    "chunk_index": 3,
    "text": "enhanced materials table 3 swot assessment for different energy storage systems. characterization techniques, can be employed to understand the structural features of hard carbons and the sodium storage process. thus, being a key aspect of a high energy density cell, the rather poor capacity of hard carbon needs to be increased from the current 250 to 300 mah g− 1. from the analysis in this section, sodium-ion, and lithium-ion batteries have been viewed from five lenses. the first one is water p"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 3,
    "chunk_index": 4,
    "text": "this approach of wastewater management makes wastewater treatment from standard lib more costly and off-reach in terms of ease compared to the wastewater treatment of solid-state sib. sodium-ion batteries are manufactured in a way that is less hazardous to the environment than lithium-ion batteries. the extraction of sodium ores is less harmful and is preferred. the extraction of lithium from brines requires around 500,000 gallons of water per ton of lithium. that is why, in extraction technique"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 3,
    "chunk_index": 5,
    "text": "such as phosphorus trifluoride (pf3), hydrogen fluoride (hf), diethyl carbonate, and ethyl methyl carbonate. these gases can hurt the environment. another factor is the potential for global warming (gwp). the two major sub-processes of sib that have contributed most to the gwp (to the extent of 24 %) are the utilization of sugar and anodes and cathode production. since the energy density of lib batteries is lesser as well as the gwp, larger battery cells are required more. also, because the gwp "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 3,
    "chunk_index": 6,
    "text": "capable of long-term storage (over a year) − requires underground storage- gas needed if turbines are used useful for distributed storage systems − increasing popularity- volatile fuel prices [35] pumped hydro energy storage − high capacity − low cost per kw − no need for power converters − long lifespan- reliable − location-dependent − high initial capital cost − environmental concerns it can be applied to offshore wind farms or with an underwater reservoir − distributed storage could make this"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 5 to compare sib and lib processing gwp, fig. 3 is provided as below: comparing the absolute numbers of the largest values becomes clear that sodium prussian blue analogue (napba) and sodium nickel manganese cobalt oxide (nanmc) batteries have the highest ghg emissions in several categories and should attract more attention in terms of emissions mitigation. more importantly, napba batteries record the highest resul"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "anode foil in the list of seven units while sodium manganese vanadium phosphate (namvp) batteries have five units [56]. the third perspective is the raw materials and consumption of resources. lithium is a rare, soft alkali metal found in earth’s crust, ocean, and atmosphere, with most resources in south america and australia. sodium-ion batteries are standard since sodium is the fourth most abundant metal in the earth’s crust, making up 2.36 percent [57]. excessive deficit can result from overu"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 6 batteries required to achieve a storage capacity, it has a positive environmental impact. currently, lithium-ion batteries have a higher energy density than sodium-ion batteries. lithium-ion batteries may have energy densities of 200– 250 wh/kg, while sodium-ion batteries typically have 120–160 wh/kg [59]. carbon dioxide emissions decrease with battery energy density. however, the average energy density of lfp ba"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 5,
    "chunk_index": 1,
    "text": "among the sibs, the sodium manganese magnesium oxide (nammo) variant shows the highest reduction efficiency, dropping from 72.3 to 36.1 co2e, while the namvp variant starts with the highest co2e value at 124 and reduces to 62. on the other hand, libs such as linmc (lithium nickel manganese cobalt oxides) and lfp exhibit comparable reductions, starting from 74.59 and 85 co2e respectively, and decreasing to 37.29 and 42.5 co2e. this data suggests that both sib and lib technologies are advancing to"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 5,
    "chunk_index": 2,
    "text": "on different trials and need to be carefully taken into account in analyses and assessments. nanmc and namvp batteries have high power and greater capacity due to the use of nanomaterials. in the modeling of these batteries, differential equation models are used to simulate the chemical reactions during charging and discharging. models such as spme (single particle model) and dfn (doyle- fuller-newman model), which are similarly used in lithium and sodium batteries, are also suitable for simulat"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 5,
    "chunk_index": 3,
    "text": "are used to examine the heat generated and its impact on the performance and lifespan of the batteries. in this type of battery, temperature and load tolerance tests are very important because temperature has a significant impact on their performance. temperature tests in various operational ranges of the batteries must be conducted to accurately examine the effects of temperature on their performance and lifespan [64–66]. compared to other battery types, napba and linmc batteries have unique pr"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 7 financial advantages of these batteries, technical and economic modeling is decisive. tests are performed on these batteries to determine their useable capacity, and efficiency in a range of operating scenarios, and long-term simulations to model their application in load management and power grids. these tests aid in evaluating batteries’ performance under various operating circumstances and environments [67–69]"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "viewpoint. better thermal stability in sibs lowers the possibility of overheating and fires. for instance, although libs can only function at temperatures up to 60 ◦c, sibs may safely work at temperatures as high as 100 ◦c [73]. sodium-ion batteries are safer and have less chance of thermal runaway and fire than lithium-ion batteries. sodium-ion batteries exhibit remarkable structural stability with a volume change of only 2.36 % during sodium extraction [58]. the fifth perspective consists of c"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "market. developed in the 1960s by albert humphrey, it distinguishes between internal factors (strengths and weaknesses) and external factors (opportunities and threats) [78]. this method enables systematic identification of competitive advantages, operational vulnerabilities, growth potential, and market risks. in the context of energy storage, swot analysis provides a structured approach to compare lithium-ion (li-ion) and sodium-ion (na-ion) batteries—two technologies vying for dominance in a "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 6,
    "chunk_index": 3,
    "text": "cycle life (500–1,000 cycles), reducing maintenance costs [80]. the thermal stability of li-ion batteries is moderate, which means that there is high risk of thermal runaway in them. also, the preferred temperature for them to work in is between − 20 and 60 ◦c but in some scenarios it can exceed to 150 ◦c [81]. na-ion batteries leverage abundant raw materials (sodium constitutes 2.6 % of earth’s crust vs. 0.002 % for lithium), which lowers material costs and mitigates supply chain risks [82]. th"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 6,
    "chunk_index": 4,
    "text": "they share manufacturing processes with li-ion batteries, enabling faster commercialization through existing production lines [83,84]. they become the measure of how much energy is needed to restore a balance between the amount generated and that consumed by the load to maintain the frequency of the network. this frequency can be regulated by a battery, which either charges or discharges to maintain an acceptable level. this process is often described as load following in the literature on the s"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 6,
    "chunk_index": 5,
    "text": "face resource scarcity—lithium and cobalt reserves are geographically concentrated (e.g., 58 % of lithium in chile, 50 % of cobalt in congo), leading to price volatility and geopolitical risks [79]. their flammable organic electrolytes pose safety risks, with thermal runaway incidents causing fires in evs and consumer electronics. aging mechanisms, such as cathode degradation and solid-electrolyte interphase (sei) layer growth, reduce capacity by ~20 % after 500 cycles [86]. recycling remains ec"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 6,
    "chunk_index": 6,
    "text": "and cycle life (300–500 cycles) [83]. additionally, the absence of a mature recycling ecosystem increases reliance on landfill disposal, raising environmental concerns [84]. opportunities li-ion technologies can capitalize on solid-state electrolytes, which replace flammable liquids with ceramic or polymer materials to enhance safety and energy density. innovations like silicon-anode batteries (theoretical capacity: 3,600 mah/g) promise 40 % higher energy density by 2030 [79,87]. the circular ec"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 8 threats price volatility (lithium carbonate surged from 6,000/ tonin2020to6,000/ton in 2020 to 6,000/tonin2020to70,000/ton in 2023) threatens affordability, especially for low-margin applications like consumer electronics [88]. regulatory pressures—e.g., the eu’s battery passport— mandate stricter environmental compliance, raising production costs. competing technologies, such as hydrogen fuel cells and sodium-io"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "backup). hybrid systems, leveraging na-ion’s thermal stability and li-ion’s energy density, could optimize performance in hybrid evs and microgrids. policymakers must balance subsidies to accelerate na-ion r&d without destabilizing li-ion’s recycling ecosystem. table 4 has provided some data on different statistics of both libs and sibs. technical trend investigation and future outlook for sib sibs are posited as one of the greatest potentials to contend with libs by the availability and cheap p"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "range (◦c) − 20 to 60 − 30 to 60 [81] commercial readiness mature emerging (pilot- scale production) [94] a lower energy density and a shorter cycle life than libs. this emerging development concerns the improvement of the electrode, the electrolyte, and the structural design of sibs. an area of great interest is the enhancement of the anode is a general shift towards the use of novel electrode materials. carbon anodes that are utilized in sibs are normally hard carbon and their cyclability is b"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 7,
    "chunk_index": 3,
    "text": "have attracted much interest for their high voltage and structural stability. but there are still problems such as capacity fading and poor rate performance. novel developments center on the elucidation of these cathode material structure stability challenges and refining of the electrolyte medium to avoid these deficits. further, infused research on layers of oxides and prussian blue analogs (pbas) have also drawn the capability of providing higher capacity and long cycle life. looking toward t"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 9 commercialization strategies sodium-ion batteries have become more popular recently due to the growing interest in clean energy and the limited availability of lithium resources. various companies are using different chemical compositions for the anodes and cathodes in their sibs (fig. 6). for example, in 2009, aquion energy introduced the first aqueous na-ion battery with specific components. in 2011, faradion l"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "least one cell with a potential between − 0.1 and 1 v [56]. natron energy was established at stanford university in the year 2012 with a focus of creating sibs via polybenzimidazole (pba) electrodes synthesized from eco-friendly and abundant materials. all of these sibs were fabricated employing pba electrodes together with aqueous electrolyte. faradion launched an electric bicycle model in 2015 that incorporated an sib equipped with a battery package of 418 wh. the growth of sib attracted many "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "design. at the same time, a new private indian company, recharging energy pvt. ltd., started the commercial development of sibs. sibs are considered as one of the most practically useful solutions for large-scale esss because of the low cost and the availability of sodium. the possibility for sibs commercial applicability depends on improvements in the cathode and anode materials. among them, hard carbon appears to be the most promising due to the other factors such as a suitable working potenti"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 10 and the conditions employed by these researchers. designing different structures and shapes is found to govern the ice and other electrochemical features of hard carbon materials [96]. influence of heteroatom in order to further improve the ability of carbon materials, their changes based on the addition of heteroatoms (including nitrogen, sulfur, and phosphorus) are commonly employed with the aim of altering ch"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 1,
    "text": "electrical connection between the electrodes. the factors pertaining to electrochemistry performance which are influenced by the choice of electrolyte material includes, ice, energy density, cycling stability and safety of sodium-ion batteries [53]. recycling frameworks the shortage in fossil fuel and the negative impact it has on the environment has led to the development of renewable energy like batteries, solar and fuel cells. it is a type of energy storage device, which by chemical reactions"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 2,
    "text": "density and voltage, have no memory effect, self-discharge less, have long life and have a broad working temperature range [77]. the restoration of these batteries is important for a number of reasons, which are stated below in brief. firstly, the availability of a vast number of used batteries has acted as one of the stimuli to design the recycling procedures. estimates from the united nations revealed that by the year 2020 the quantity and weight of the used batteries crossed a figure of 25 bi"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 3,
    "text": "this metal with water and, ultimately, the production of lithium hydroxide and hydrogen gas. in addition to the mentioned cases, the toxicity and flammability of the battery electrolyte are also discussed [98]. third is metal resources in consumer batteries. in addition to the economic aspects of recycling some metals (cobalt, nickel, manganese, and lithium), the limited natural resources of cobalt and lithium are another justifiable reason for recycling these batteries. lithium is usually extra"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 4,
    "text": "batteries began in 1999 in the united states, canada, and some european countries. related research on a laboratory scale has continued until now. some companies are industrially doing restoration with different methods, including umicor (belgium), oy akkuser (finland), accurec (germany), sumitomo (japan), recupy (france), and inmetco (united states). a review of the available sources shows that the recovery of all types of lithium-ion batteries is mainly focused on extracting cobalt, nickel, li"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 5,
    "text": "and lithium in some proposed methods, on the other hand, emphasize the necessity of researching and developing recycling processes and improving the quantitative and qualitative efficiency of all kinds of lithium-ion batteries. the components of games consist of two main parts: physical and chemical procedures for the separation of substances. some of the processes that come under separation include mechanical and thermal processes as well as mechanic chemical processes; dissolution or leaching "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 6,
    "text": "produced by the cyclical process of the redox reaction between the anode and the cathode, lithium-ion batteries generate current by the transport of lithium ions between the electrodes. these batteries contain heavy metals, of which its components include 20–30 % cobalt, 5–10 % nickel, 5–7 % lithium, 15 % superior metallic components and 5 % plastic [85]. table 5 summarizes key findings in the recycling of lithium‑ion (lib) and sodium‑ion (sib) batteries: recycled limn2o4 from spent libs reused "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 7,
    "text": "effluent using na2co3 and na3po4 yielded li2co3 at 74.72 % and pure li3po4 at 92.21 % [105]; and replacing naoh with ammonia for ph control effectively reduced sodium‑ion pollution and improved precursor quality [106]. lithium-ion battery recycling processes most of the lithium-ion batteries are built from graphite and silicon thus metals need to be extracted from the cathode including nickel, manganese cobalt, and lithium. the remaining battery waste as well as lithium-ion batteries are dispose"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 9,
    "chunk_index": 8,
    "text": "recycling processes. this process includes pyrometallurgical and hydrometallurgical mechanical purification. mechanical purification separates materials according to other properties such as density, conduction, and magnetic behavior. this purification process is typically performed as a pre-purification to improve the quality of metal parts before hydrometallurgical or pyrometallurgical recycling. during various separation processes, copper, aluminum, iron, cobalt, lithium, nickel, manganese, c"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 11 removed in combination. cobalt is often recycled as coso4, coco3, co3o4, coc2o4, and licoo2, while lithium is mostly recycled as li2co3 and licoo2. among all methods of recycling lithium-ion batteries, hydrometallurgical processes rank first with 57.25 %. the share of pyrometallurgy for all purification methods is 16.79 %. in the pyrometallurgy method, the excellent compounds of lithium-ion batteries, such as ca"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "an innovative hydrometallurgical procedure. the procedure begins with physical therapy to gather typical electrode materials, followed by purification by iron precipitation and liquid–liquid extraction. this method yields high- quality materials such as graphite, cobalt oxide, oxalate, nickel oxide, and lithium carbonate. besides, by- products manufacture sodium sulfate and magnetic nano-sorbents, aligning with the zero-waste concept [104]. because of their complicated chemical makeup, establish"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "the batteries have gone through its useful life. it has a very complex structure and is compact so that techniques such as pyrometallurgical or hydrometallurgical processing cannot directly be used and there is always the need for pre- concentration where valuable metals can then be extracted from the waste. in order to avoid short circuits and combustion of lithium-ion batteries, the batteries are either first discharged, and the most common method of discharge is through immersion in a salt so"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 3,
    "text": "for the early loss of sodium ions while improving initial coulombic efficiency, cycle stability, and reversible capacity. they have a direct-contact pre-sedation characteristic, which essential to formulate a thick passivation layer at the cathode electrolyte interface that prevents the dissolution of active ingredients. lithium-pretreated hard carbon (lphc) anodes also require modifications to the solid electrolyte interphase in a tetralayer-based electrolyte to achieve high initial coulombic e"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 4,
    "text": "be used as primary additives to alter the composition of the steel. metal smelting issues associated with this process include limiting the concentrations of chromium, copper, and nickel for electric arc furnaces. usually, this process is only used for manganese-alkaline batteries and zinc- carbon. another method for zinc- containing batteries is the wells process, which recovers metals from rotary kiln dust. the process also allows for the recovery of zinc, cadmium, and lead [113]. several pyro"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 5,
    "text": "generated is swiftly cooled to avoid dioxin development, converting to ash during the quenching phase. the resultant sludge includes mercury and must be cleaned by distillation, while the effluents from waste gas scrubbing require treatment. hydrometallurgical processes metal extraction from natural sources has been effectively accomplished through established hydrometallurgical methods. metal is recovered from used batteries by mechanical processing. this process’s black powder waste contains c"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 6,
    "text": "reused as cathode material for sibs. recycled limn2o4 exhibits excellent na-storage properties, with discharge capacity increasing to 163.2 mah g − 1 over 50 cycles, attributed to phase transition from spinel to layered structure. [101] reductive ammonia leaching for libs a hydrometallurgical process using ammonia-ammonium sulfate and sodium sulfite to selectively recover ni, co, and li from spent lib cathodes. they achieve over 98.6 % recovery rates for ni, co, and li with high selectivity whil"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 10,
    "chunk_index": 7,
    "text": "in anode and cathode materials. [103] recovery of lithium from effluent a novel process to recover lithium from the effluent in spent lib recycling using na2co3 and trisodium phosphate (na3po4). lithium recovered as li2co3and pure li3po4 with high recovery rates (74.72 % and 92.21 %, respectively). the process allows for the reuse of recovered lithium in new batteries. [105] sodium ion pollution in recycling addresses sodium ion pollution during the recycling process of spent libs. effective con"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "e. pilali et al. sustainable energy technologies and assessments 80 (2025) 104371 12 in the united states, a technique has been created for cleaning various types of dry cell batteries, including carbon-zinc, manganese- alkaline, nickel– cadmium, and lithium batteries. there are several processes in the butaneus process, such as hydrometallurgical recovery and mechanical purification [117]. table 6 presents a comparison of the three main recycling methods for sodium-ion and lithium-ion batteries"
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "techniques to improve recovery efficiency and promote sustainability, although they require meticulous planning and coordination to implement successfully [119,120]. authors’ perspectives our scientific study supports the assumption that sodium-ion batteries (sibs) represent a key solution for advances in energy storage solutions for expansive grid-connected systems and economical applications. lithium-ion batteries (libs) have reached commercial maturity yet their future depends on the limited "
  },
  {
    "source_pdf": "SWOT_analysis_on_the_transition_from_Lithium_Ion_batteries_to_Sodium_Ion_batteries_Ebrahim_Pilali_Faraz_Forutan_Nia_Eliyad_Yamini_Farbod_Esmaeilion_Walied_Alfraidi_Alireza_Taklifi_Davide_Asti.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "supply distribution. the second is application-oriented differentiation. we foresee a market bifurcation. portable electronics together with high-performance electric vehicles constitute sectors where libs will retain primary leadership status. the sib system gives exceptional performance under grid- scale energy storage applications and stationary deployments and low- to-mid range electric vehicles which need energy storage solutions with focus on cost-effectiveness and safety rather than energ"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 0,
    "chunk_index": 0,
    "text": "1 | introduction abstract hard carbon has been regarded as the most promising anode material for sodiumion batteries (sibs) due to its low cost, high reversible capacity, and low working potential. however, the uncertain sodium storage mechanism hinders the rational design and synthesis of high‐performance hard carbon anode materials for practical sibs. during the past decades, tremendous efforts have been put to stimulate the development of hard carbon materials. in this review, we discuss the "
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 0,
    "chunk_index": 1,
    "text": "large‐ with the growing concern of global warming, the energy community is being forced to innovate by replacing traditional fossil energy with renewable energy resources. thus, there is an urgent demand to build large‐scale electrical energy storage systems (eess) to store wind power, solar power, and other intermittent renewable energy resources.1,2 in the past several decades, lithiumion batteries (libs) have been considered as the most efficient secondary batteries, due to their outstanding "
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 0,
    "chunk_index": 2,
    "text": "materials of sibs, compared to other materials, such as alloys (e.g., sn, sb, se, ge, and p),18–22 ti‐based materials (e.g., tio2 and na2ti3o7),23–25 metal oxides/sulfides/phosphides (e.g., fe2o3, sno2, sb2o3, mos2, and fep4),26–29 the carbon‐based materials show more fascinating properties, such as high reversible capacity, low working voltage, long cycling stability, high initial coulombic efficiency (ice), small volume changes during electrochemical reactions, high electronic conductivity, lo"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 0,
    "chunk_index": 3,
    "text": "the competition between the ionization of metal atoms and the ion–substrate coupling. although it has been demonstrated that expanded graphite and na‐solvent cointercalation in ether‐based electrolytes can realize the goal of sodium storage in graphite, the high intercalation voltage and low sodium storage capacity limit their practical applications.34,35 experimental and theoretical simulation results indicated that na+ can easily insert into carbon materials with a larger interlayer distance a"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 1,
    "chunk_index": 0,
    "text": "2 chen et al . transformed into graphite even at temperatures higher than 3000°c, while soft carbon can be readily converted to graphite by heating to 3000°c. generally, soft carbon exhibits sloping charge/discharge voltage curves. along with the sloping voltage region, hard carbon also exhibits a low voltage plateau below 0.1 v that leads to a large capacity and a low average redox potential, resulting in a high energy density.39 furthermore, the ice of hard carbon is higher than that of soft c"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 1,
    "chunk_index": 1,
    "text": "adjusting the carbon precursors and pyrolysis processes. however, due to the complexity of the hard carbon structures, there is still a lack of consensus on their sodium storage mechanism, which hinders the structural design and electrochemical performance optimization of hard carbon electrodes.49 hence, a comprehensive understanding of the structure– electrochemical property relationships is very important, which has extraordinary significance for developing highperformance anode materials for "
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 1,
    "chunk_index": 2,
    "text": "density hard carbon anodes. 2 | microstructure and sodium storage sites of hard carbon unlike graphite, hard carbon lacks a long‐range ordered structure in the plane and stacking directions. the microstructure of hard carbon can be described as a combination of rumpled and twisted graphene sheet fragments consisting of sp2 hybridized carbon in a hexagonal network disrupted by defects, such as vacancies, pentagons, heptagons, and heteroatoms.50–52 because of the existence of van der waals forces "
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 1,
    "chunk_index": 3,
    "text": "is determined by the preparation process and the property of the precursor.53,54 despite the complex and versatile structure of hard carbon materials, the main active sites with the ability to uptake sodium ions are listed below (figure 1): 1) adsorption of na+ at the surface of open pores is influenced by the specific surface area, which contributes to the sloping capacity at the beginning of the sloping region.55,56 it is a surface‐induced capacitive process and inevitably causes the decomposi"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 2,
    "chunk_index": 0,
    "text": "3) insertion of na+ between graphene layers is affected by the texture of graphitic‐like nanodomains. this can be further separated into two types: procedural intercalation between graphene layers with phase transition to form na‐gics, which corresponds to the plateau capacity31 and random insertion into graphene layers with a wide energy distribution, which is related to the sloping capacity.59 4) pore filling with the formation of quasi metallic clusters is influenced by the property of pores,"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 2,
    "chunk_index": 1,
    "text": "carbon materials is still controversial and there are four prevailing models (figure 3), including the “insertion–adsorption” model,59,62–65 “adsorption– intercalation” model,37,66–69 “three‐stage” model,70–72 and “adsorption–filling” model.73–76 different models were based on different experimental results on various hard carbon samples; we will comprehensively discuss them as follows. in 2000, stevens and dahn65 first proposed the “insertion– adsorption” mechanism and “house of cards” model to"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 2,
    "chunk_index": 2,
    "text": "x‐ray diffraction (xrd) and small‐angle x‐ray scattering studies (saxs) technologies (figure 4b,c).59 in 2010, komaba et al.64 further proved this mechanism by ex situ xrd, saxs, and raman spectroscopy studies. figure 1 schematic representation of the microstructure of the hard carbon and the main active sites with the ability to uptake of sodium ions figure 2 timeline of key developments of sodium storage mechanism in hard carbon"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 3,
    "chunk_index": 0,
    "text": "4 chen et al . however, there are still some experimental phenomena that conflicted with the “insertion–adsorption” mechanism. for example, as the pyrolysis temperature increases, the surface area and total pore volume of the hard carbon material decrease while the plateau capacity appears as a “volcano”‐ shaped tendency with a maximum plateau capacity at about 1400°c.68,77,78 whereafter, some different opinions were proposed to interpret these disparities. considering that na+ storage in hard c"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 3,
    "chunk_index": 1,
    "text": "hard carbon prepared at different temperatures using in situ xrd, ex situ nuclear magnetic resonance (nmr), electron paramagnetic resonance techniques, and so forth.68,69,79–81 specifically, from the in situ xrd (figure 5a), the (002) peak shifts to the low angle, which can be ascribed that graphite sheets with relatively larger spacing are favored for na+ intercalation causing the expansion of interlayer spacing. while another part of graphite sheets with narrow spacing does not allow na+ inter"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 4,
    "chunk_index": 0,
    "text": "significantly different from the above mechanisms, zhang et al.74 demonstrated that the insertion of na+ between carbon layers did not happen during the whole sodiation process. they synthesized hard carbon nanofibers with tailored microstructure through pyrolysis in a wide temperature range between 650 and 2800°c and then systematically investigated the correlation between the electrochemical performance and microstructure. they demonstrated that the sloping capacity could be attributed to the "
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 4,
    "chunk_index": 1,
    "text": "and ex situ x‐ray photoelectron spectroscopy (xps) spectra showed that as the sodiation proceeded in the plateau region, the intensities and values of the binding energy for the na 1s spectra increased and approached the signal of metallic na (figure 6d). they further carried out in situ xrd analysis (figure 6e) for the anthracite‐derived electrode and observed that there was no shift of the (002) peak when the cell was discharged to 0 v figure 4 (a) “house of cards” model for sodium‐filled hard"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 5,
    "chunk_index": 0,
    "text": "6 chen et al . versus na/na+, indicating that na insertion did not happen during whole discharge process.73 3.2 | sodium storage mechanism in the low‐potential plateau the discrepancies in sodium storage mechanism are owing to the complex structures of the hard carbon, which bring difficulties to the characterization of hard carbon microstructure and the interpretation of the data obtained by different in situ and ex situ analyses technics, such as xrd, figure 5 (a) the in situ x‐ray diffraction"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 6,
    "chunk_index": 0,
    "text": "dependence of the mean interlayer spacing on discharge voltage. the electrodes discharged to (ⅰ) 0.2, (ⅱ) 0.1, (ⅲ) 0.05, and (ⅳ) 0.001 v versus na/na+. reproduced with permission: copyright 2014, american chemical society.66 (d) galvanostatic intermittent titration profile and diffusivity as a function of states of charge (inset) and (e) dq/dv plot from 0.12 to 0.01 v with corresponding diffusivity values. reproduced with permission: copyright 2015, american chemical society72 figure 6 (a) volta"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 6,
    "chunk_index": 1,
    "text": "2016, wiley‐vch.75 (e) in situ xrd patterns collected during the first discharge/charge of the anthracite‐derived electrode prepared at 1200°c cycled between 0 and 2 v under a current rate of 0.05 c. reproduced with permission: copyright 2016 elsevier.73 xps, x‐ray photoelectron spectroscopy raman spectroscopy, and nmr. after two decades of research, the structure–electrochemical behaviors of hard carbon materials are still controversial. of note, recent work reaches a consensus on the sloping r"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 6,
    "chunk_index": 2,
    "text": "intrinsic highly disordered structure of hard carbon. xrd analysis is a vital tool to detect the structural evolution caused by the insertion of na+ into graphitic sheets. the inserted na+ can not only expand the interlayer spacing accompanying the slight shift of (002) diffraction peaks to lower angles but also act as scattering species with the decrease of scattering intensity. however, as mentioned above, according to xrd analyses, many researchers inferred contradictory sodium storage mechan"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 7,
    "chunk_index": 0,
    "text": "8 chen et al . it may be due to the disordered structure of hard carbon, the reflection is broad and weak, and thus it is difficult to detect its changes in intensity and position. furthermore, the signal of (002) peak will inevitably be interfered with by the background, causing a shift of the apparent peak position to lower angles. therefore, the xrd analysis should be properly applied to detect structure evolution during the sodiaiton and desodiation processes, especially for ex situ xrd anal"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 7,
    "chunk_index": 1,
    "text": "results.75,89 theoretical calculations revealed that the intercalation energy depends on the interlayer spacing of hard carbon materials.90,91 for example, cao et al.34 proposed that na+ can overcome the energy barrier and intercalate into graphitic sheets with an interlayer spacing larger than 0.37 nm (figure 7f). an ab initio study revealed that the larger interlayer spacing and monovacancy, divacancy, and stonewales defects would facilitate the insertion of na+ into graphitic layers.36 sun et"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 7,
    "chunk_index": 2,
    "text": "cost for na (red curve) and li (blue curve) ions insertion into carbon as a function of carbon interlayer distance. the inset illustrates the mechanism of na and li‐ions insertion into carbon. reproduced with permission: copyright 2012, american chemical society.37 (g) schematic illustration of the evolution of the microstructure, sodium storage mechanism, and behavior with the pyrolysis temperature of hard carbons. reproduced with permission: copyright 2019, wiley‐vch88"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 8,
    "chunk_index": 0,
    "text": "intercalation” model (figure 7g) and supplemented that as the interlayer spacing increased to 0.40 nm, na+ could freely access the carbon layers with a “pseudo‐ adsorption” behavior, contributing to sloping capacity above 0.1 v. based on theoretical calculation of the formation energy, they further revealed that nac8 was the most likely na‐gic structure for hard carbon, corresponding to a theoretical capacity of 279 mah g−1. the extended “adsorption–intercalation” model can interpret well the “v"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 8,
    "chunk_index": 1,
    "text": "heat treatment temperature will further reduce the interlayer spacing to less than 0.36 nm, causing the hardly insertion of na+ into carbon layers and a reduced plateau capacity. boosting the plateau capacity from intercalation mechanism according to the intercalation mechanism, the plateau capacity can be extended by expanding interlayer spacing and improving the growth of graphitic‐like nanodomains. heteroatom‐doping is an effective method to tailor the microstructure of hard carbon. due to th"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 8,
    "chunk_index": 2,
    "text": "by adding phosphoric acid into lignin and pyrolysis at 1300°c. the p‐doping amount was increased from 0 to 1.10 at% by adjusting the ratio of phosphoric acid to lignin, and the interlayer spacings of as‐obtained hard carbon were extended from 0.375 to 0.387 nm, along with the plateau capacities improved from 183 to 223 mah g−1 (figure 8c–e). yuan et al.100 enlarged the interlayer spacing of flexible freestanding multichannel carbon nanofibers through a vacuum heat treatment method, resulting in "
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 9,
    "chunk_index": 0,
    "text": "10 chen et al . reversible capacity from 160 to 233 mah g−1. yuan et al.99 directly pyrolyzed natural potassium‐doped coconut endocarp at 1100°c (figure 8f). the as‐obtained hard carbon featured a dilated interlayer spacing (0.4 nm) and delivered an initial reversible capacity of 314 mah g−1 at 50 ma g−1. once it was pickled to remove the potassium ions, the interlayer spacing and reversible capacity decreased simultaneously. there are few reports on the expansion of the size of graphitic‐like n"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 10,
    "chunk_index": 0,
    "text": "3.2.2 | micropores filling mechanism depicting of pores filling mechanism many works have confirmed the pores filling mechanism by in situ or ex situ saxs analysis. the scattering intensity of shoulder peaks corresponding to the nanopore decreases at the plateau region, which indicates a decrease in the electron density contrast between the carbon matrix and nanopores.59,63,64,101,102 through in operando 23na solid‐state nmr analysis, stratford et al.103 observed a clear shift of the signal to p"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 10,
    "chunk_index": 1,
    "text": "(i.e., closed pores). the gas adsorption–desorption technique is only sensitive to the former, while true density analysis can detect the closed pore volume and saxs is accessible to all pores. thus, it is essential to utilize integrated characterization methods to ascribe the pore figure 9 (a) operando 23na nmr (nuclear magnetic resonance) spectra for an electrochemical cell with sodium metal and hard carbon electrodes, and napf6 electrolyte. reproduced with permission: copyright 2016, royal so"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 10,
    "chunk_index": 2,
    "text": "napf6 electrolyte and carbon a or carbon b electrodes. (f) the top is differential pair distribution functions (pdfs) for carbon a (red) and carbon b (blue) for the end of slope process, red/blue lines offset below represent the deconvolution into sharp (based on an expansion of the carbon matrix) and broad components. the green line represents the calculated pdf for sodium intercalated between two expanded curved graphene fragments; the bottom is pdfs for the end of the plateau process. the gre"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 11,
    "chunk_index": 0,
    "text": "12 chen et al . texture of hard carbon. it has been reported that several hard carbons with low‐open porosity deliver a considerable plateau capacity.69,105,106 in addition, qiu et al.68 indicated that the theoretical capacity of cellulose‐derived hard carbon calculated based on the saturated na filling into micropores (established by n2 adsorption technique) was lower than the experimental plateau capacity. therefore, it is agreed that open porosity is not the main contribution to the plateau c"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 11,
    "chunk_index": 1,
    "text": "between 800°c and 1400°c and investigated their pore information by true density, saxs, and nitrogen adsorption/desorption tests. it demonstrated that the plateau capacity suffered a weak correlation with open‐pore volume, but exhibited an obvious positive relationship with the closed‐pore diameter or volume. au et al.60 employed ex situ 23na solidstate nmr and total scattering studies on a series of hard carbons prepared at different temperatures. as shown in figure 9b–d, they observed the quas"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 11,
    "chunk_index": 2,
    "text": "two commercial relevant carbons with different average pore diameters obtained on saxs data (figure 9e). however, the differential pdf analysis of total scattering data indicated similar sodium cluster sizes (~13–15 å) in these two kinds of carbon (figure 9f). they attributed the different nmr shifts to the different electronic structures of the materials, which generated a difference na partial density of states at the fermi level. and they concluded that a larger average pore diameter does not"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 11,
    "chunk_index": 3,
    "text": "resulting in a reduced plateau capacity even with sufficient na storage sites in micropores. therefore, even for the pores filling mechanism, the structures of graphite‐like crystallites also significantly affect the low‐ potential plateau capacity, which further contributes to the difficulty to clarify the sodium storage mechanism in hard carbon materials. boosting the plateau capacity by using pore‐forming agents it has been reported that engineering close pores in hard carbon materials is an "
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 11,
    "chunk_index": 4,
    "text": "an organic polymer as a pore‐forming additive to synthesize macroporous phenolic resin block from liquid solution‐type resin (figure 10b). after further carbonization at 1500°c, the hard carbon anode delivered a larger reversible capacity of 386 mah g−1 and a plateau capacity of ~300 mah g−1 at a current density of 10 ma g−1. meng et al.106 introduced ethanol as the poreforming agent into the phenol‐formaldehyde precursor, and through the solvothermal process and further carbonization, hard carb"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 11,
    "chunk_index": 5,
    "text": "mah g−1. kamiyama et al.108 also successfully prepared hard carbon with an extremely high sodium storage capacity (478 mah g−1) by a mgo‐template method (figure 10d). they freeze‐dried the mixture of magnesium gluconate and glucose and then the obtained mixture was pyrolyzed in two steps. nano‐size mgo particles are generated in the pre‐ pyrolysis process and removed by acid pickling after the following pyrolysis process, leaving abundant pores in the carbon matrix. by adjusting the ratio of mag"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 12,
    "chunk_index": 0,
    "text": "reversible capacity of 354.6 mah g−1 at 30 ma g−1 and a high ice of 88.7%.110 converting open copyright 2018, elsevier109 pores to closed pores can also effectively increase the plateau capacity. li et al.109 coated the preheat‐treated commercial activated carbon with a pitch by the “solvent evaporation” method and then recarbonized at 1400°c (figure 10e). the as‐prepared sample exhibited a low surface area of 24 m2 g−1 and high internal porosity, delivering a high reversible capacity of 391 mah"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 12,
    "chunk_index": 1,
    "text": "treatment.112–114 lu et al.114 preoxidated pitch in the air at 300°c for 3 h and then thermal‐ treated it at 1400°c. it is found that the preoxidation process induced a more turbostratic structure, generating close voids constructed by random piled curved carbon layers, and the reversible sodium storage capacity and ice of the preoxidation‐tuned carbon increased to 300.6 mah g−1 and 88.6%, respectively. 3.2.3 | deficiencies of the interlayer intercalation and pores‐filling mechanisms despite bot"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 12,
    "chunk_index": 2,
    "text": "corresponding to form nac8. and the maximum possible specific capacity for the nanopore mechanism can be calculated using the theoretical specific capacity of metallic sodium (1128 mah cm−3) and total pores volume, including internal and external figure 10 (a) illustration of the synthesis route for multishelled hollow hard carbon nanospheres. reproduced with permission: copyright 2018, wiley‐vch.76 (b) scanning electron microscopy images and initial discharge/charge curves of microporous phenol"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 13,
    "chunk_index": 0,
    "text": "14 chen et al . pores. as discussed above, hard carbon anode materials with ultrahigh plateau capacity (>279 mah g−1) can be obtained by using pore‐forming agents. on the contrary, for example, meng et al.106 used ethanol as the poreforming agent and formaldehyde resin as carbon sources via a solvothermal method to prepare hard carbon with rich closed pores, which exhibited a high na storage capacity of 410 mah g−1. based on the true density (~1.43 cm3 g−1) measured by he gas and d002 (0.391 nm)"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 13,
    "chunk_index": 1,
    "text": "are 139, 152, 231, 240, and 239 mah g−1, respectively, larger than the theoretical specific capacity of 88, 39, 35, 218, and 225 mah g−1 calculated based on the helium pycnometer density.53 hence, a more comprehensive and in‐depth sodium storage insight is urgent to be put forward. some recent literature reported that the sodium storage mechanism is different under different circumstances.63,115 morikawa et al.63 conducted systematically ex situ saxs and wide‐angle x‐ray scattering study of a se"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 13,
    "chunk_index": 2,
    "text": "mechanisms act as an individual or a few overlapped processes, or they occurred as concurrent processes. but what is assured is that pore‐filling needs to first undergo diffusion of na+ between graphitic sheets, due to closed pores being inaccessible to the electrolyte. 4 | summary and outlook there has been a tremendous effort to develop advanced hard carbon anodes and understand their sodium storage mechanism during the past decade. in this review, we provide a comprehensive overview of the re"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 13,
    "chunk_index": 3,
    "text": "the bottleneck and controversies lie in the assignment of the plateau capacity (figure 11). up to now, debates remain in the orientation of sodium storage mechanism in the plateau region, including interlayer intercalation and pore‐filling mechanism. both mechanisms can explain the corresponding experimental results. although these disputes remain, it is assuring that the plateau capacity of hard carbon anode can be extended by expanding the interlayer spacing between graphitic sheets or generat"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 13,
    "chunk_index": 4,
    "text": "misinterpretation of experimental data obtained by advanced structural characterization techniques due to a lack of figure 11 schematic illustration of the sodium storage mechanism in hard carbons and future research directions in‐depth understanding of hard carbon structure. for instance, because of the existence of defects, the local structure of graphitic sheets in hard carbon suffers significant curvature,"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 14,
    "chunk_index": 0,
    "text": "and part of curved graphene sheets locally stack forming randomly oriented graphitic‐like nanodomains, while the other part of highly curved and randomly oriented graphene sheets form pores in the bulk of materials. however, when considering sodium storage mechanism, such curvature has rarely been introduced in the hard carbon structure model. hence, the structural models should be refined to introduce the curvature of graphitic‐like domains and closed pores, and then evaluate their impact on so"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 14,
    "chunk_index": 1,
    "text": "of quasi‐metallic sodium. and more efforts are needed to clarify the characteristics of na‐gics and quasi‐metallic sodium. in addition, new strategies are urgently demanded to precisely control the graphitic‐like domains and pore structures in the carbon framework. despite controversy remains in the sodium storage mechanism, the optimum interlayer spacing and pore structure will lead to improved plateau capacity. besides, the ice is also an important property of the carbon anodes. although engin"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 14,
    "chunk_index": 2,
    "text": "the contrary, decreasing defect concentration and regulating the degree of graphitization of hard carbon materials are also effective methods to alleviate the irreversible sodium ions trapped at defect sites and achieve a hard carbon with high ice. to facilitate the practical application of hard carbon, future research of hard carbon anodes should be focused on the development of advanced hard carbon materials with high plateau capacity and high ice. the external surface area and defect concentr"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 14,
    "chunk_index": 3,
    "text": "hard carbon as the anode materials. the as‐assembled pouch cells delivered a discharging capacity of 0.35 ah with an average discharge voltage of 2.9 v and a capacity retention ratio of 87.4% after 1000 cycles. tang et al.117 evaluated the electrochemical performance of starch packing peanuts derived hard carbon in a full‐pouch cell, which exhibited a 90% capacity retention after 200 cycles and 84% retention after 300 cycles. these reports of hard carbon in pouch cells further illustrate the cre"
  },
  {
    "source_pdf": "Understanding_of_the_sodium_storage_mechanism_in_hard_carbon_anodes_Xiaoyang_Chen_Changyu_Liu_Yongjin_Fang_Xinping_Ai_Faping_Zhong_Hanxi_Yang_Yuliang_Cao.pdf",
    "page": 14,
    "chunk_index": 4,
    "text": "acknowledgments we thank the financial support from the national nature science foundation of china (nos. u20a20249 and 21972108) and the key research program of hubei province (2020baa030). chemistry and molecular sciences, wuhan university. his research interests focus on developing advanced materials (e.g., alloys, transition metal oxides, phosphates, and novel electrolytes) for sodium‐ion batteries and lithiumion batteries."
  }
]