Impact of Sodium Salt Coating on a Graphite Negative Electrode for Lithium-Ion Batteries

Abstract

The electrochemical performance of a graphite electrode for rechargeable lithium-ion batteries was successfully enhanced by pretreatment of graphite powders with NaCl and Na 2 CO 3 aqueous solutions. The procedure of the pretreatment is simple and easy, that is, graphite powders are dispersed in the aqueous solutions, and then filtered and dried. Since the surface of the graphite powder was modified with a sodium salt coating, the irreversible capacity at the initial cycle was suppressed by the pretreatment which is capable of modifying the solid electrolyte interface layer formed on the graphite electrode. Further, reversible discharge capacities at 175 mA g −1 ͑C/2 rate when 350 mAh g −1 ͒ increased with better capacity retention in a 1 mol dm −3 LiClO 4 ethylene carbonate-diethyl carbonate electrolyte solution.Among various carbon materials which possess high electrochemical activity in a lithium cell, graphite is favored for battery applications because it exhibits a high specific capacity, low working potential close to that of lithium metal, and superior cycling behavior as the negative electrode. 1-4 When graphite powders are employed as the negative electrode, the graphite shows a large irreversible capacity at the first cycle since reductive decomposition of an electrolyte solution occurred at the graphite surface during the first charge, including the formation of solid electrolyte interface ͑SEI͒. The existence of an SEI layer plays an important role in reversible lithium intercalation into the interspace between graphene slabs; therefore, the chemical modification of a graphite surface including an SEI film has attracted wide attention for improving battery performances.Electrolyte additives exhibited a significant effect on modifying the SEI formation during the first charge ͑electroreduction͒ process. With the aim of enhancing the negative electrode performance in lithium-based rechargeable batteries, various organic/inorganic additives dissolved into an electrolyte solution are known to be effective; e.g., CO 2 , 5,6 HF, 7,8 HI, 9 AlI 3 , and MgI 2 10,11 for metallic lithium, and ethylene sulfite, 12 vinylene carbonate, 13-15 cobalt ion, 16 lithium carbonate, 17,18 and sodium ion 19 for carbon anodes. These additives successfully suppress the initial irreversibility and improve their cycle performance. We recently found several particular additives for LiMn 2 O 4 /C batteries, vinyl-pyridine, 20 LiI, LiBr, and NH 4 I. 21 On the other hand, the electrochemical lithiation properties of the carbon anode were improved by its surface treatment with metal oxides 22,23 and lithium carbonate. 24 Recently, our group has been emphasizing the key role of inorganic ingredients at the graphite surface, such as lithium, sodium, potassium, 25 and fluorine. 26 Moreover, we described that the impact of Na + ions as an electrolyte additive on the enhancement of battery performance was attributed to the entrapment of Na + ions in the SEI layer. 19 In the present study, we found that Na 2 CO 3 -and NaClcoating improve...

Water‐Soluble Binders for Lithium‐Ion Battery Graphite Electrodes: Slurry Rheology, Coating Adhesion, and Electrochemical Performance

“…However, among electrodes employing either of the water‐soluble binders, CMC‐Na or PAA‐Na, there was no notable difference in the coulombic efficiency. This is an indication that the merits of using PAA‐Na‐containing graphite electrodes, as reported previously, are dependent on the amount of binder applied and do not necessarily lead to improvements if used in practical amounts. This is reflected in the electrochemical results for the full‐cell cycling against a commercial LiFePO 4 positive electrode, for which the CMCSBR composites yielded the highest capacity retention after 100 cycles.…”

“…Experiments with laboratory-scale electrodes demonstrated that water-processed electrode formulations could consistently achieve higher coulombic efficiencies than the polyvinylidene difluoride (PVdF) composites.H owever, among electrodes employinge ither of the water-soluble binders, CMC-Na or PA A-Na, there was no notable difference in the coulombic efficiency.T his is an indication thatt he meritso f using PA A-Na-containing graphite electrodes,a sr eported previously, [22,60] are dependento nt he amount of binder applied and do not necessarily lead to improvements if used in practical amounts.T his is reflected in the electrochemical results for the full-cell cycling against ac ommercial LiFePO 4 positive electrode, for which the CMCSBR composites yielded the highest capacity retention after 100 cycles. This is in stark contrast to the trends observed in alloying materials, such as silicon, for which bindersa re generally employedi n Figure 7.…”

Solid Electrolyte Interphase (SEI) of Water-Processed Graphite Electrodes Examined in a 65 mAh Full Cell Configuration

“…It has been reported that the presence of sodium salts has beneficial effects on the SEI layer formation and improves the overall electrode performance. ,, Furthermore, Nguyen et al proposed HF scavenging in the presence of −COONa groups, since CMC-Na and PAA-Na carry sodium ions into the cell. El Ouatani et al and Komaba et al concluded that the ions are readily exchanged by lithium ions in contact with the electrolyte.…”

“…Generally, the formation of sodium salts during the SEI layer formation has previously been shown to lead to improved cycle life in the case of graphite electrodes. 31,65,66 ■ CONCLUSIONS Water-processed graphite electrodes employing either 4 wt % of CMC-Na:SBR, PAA-Na, or CMC-Na:PAA-Na were cycled in graphite:LiFePO 4 full cells (ca. 65 mAh) and analyzed by photoelectron spectroscopy (PES), using an in-house and a synchrotron light source (1486.6 and 2300 eV, respectively).…”

Sodium‐Ion Battery Anodes Comprising Carbon Sheets: Stable Cycling in Half‐ and Full‐Pouch Cell Configuration

“…Further deconvolution of the O 1s, Na 1s, and C 1s peaks reveals the presence of sodium carbonate on the surface. Previously, surface coating of Na 2 CO 3 on the graphite anode in lithium‐ion batteries and on P2‐Na x MO 2 in sodium‐ion batteries has been shown to improve cell cycling by forming an artificial SEI layer and supplying additional Na source. On the other hand, the carbon surface is also rich in carbon–oxygen functional groups (after excluding O in the carbonate), which have been reported to enhance the cycling capacities of biomass‐derived carbon in sodium‐ion batteries through redox reaction with Na ions …”