Solubility-Driven Interfacial Impedance in NCM523/Graphite Cells with Sulfonate and Sulfate Lithium Salts

Lithium-ion batteries using LiNi 0.5 Co 0.2 Mn 0.3 O 2 /graphite electrodes were investigated to clarify the effect of lithium sulfonate and sulfate electrolyte additives on interfacial impedance evolution. Electrochemical impedance spectroscopy, voltammetry, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS) were employed to analyze interfacial changes after cycling. Additives with intermediate solubility (0.5–2 wt%), particularly CH 3 OSO 3 Li, most effectively suppressed impedance growth compared with both sparingly and highly soluble salts. Total cell impedance decreased by up to 30% after 300 cycles relative to a vinylene carbonate-containing baseline electrolyte, while maintaining comparable capacity retention. Cyclic voltammetry showed no distinct redox features attributable to additive decomposition, indicating negligible electrochemical decomposition. XPS detected sulfur-containing interphase species at both electrodes without measurable changes in apparent interphase thickness. These results suggest that impedance suppression is associated with additive solubility and interfacial composition. The findings provide practical insight into electrolyte design for controlling interfacial impedance.