Hybrid electrolyte-induced corrosion mitigation of copper current collectors for lithium-sulfur battery systems

Abstract

This study investigates the corrosion behavior of copper (Cu) current collectors exposed to a hybrid electrolyte (HE) relevant to lithium-sulfur battery (LSB) environments. The HE combines lithium bis(trifluoromethanesulfonyl)imide as the primary lithium salt with lithium bis(fluorosulfonyl)imide and triethyl phosphate additives, and is designed to regulate interfacial reactions between Cu and aggressive electrolyte species, including dissolved lithium polysulfides. Rather than focusing on full-cell cycling performance, this work isolates electrolyte-induced corrosion processes at the Cu-electrolyte interface. Time-dependent electrochemical impedance spectroscopy reveals an increase in charge-transfer resistance from 215.6 Ω to 489.2 Ω over extended exposure, indicating the formation and evolution of a passivating surface layer. Tafel polarization analysis shows a reduction in the calculated corrosion rate from 3.35×10 −3 mm/y to 2.06×10 −3 mm/y (38.5%). Surface-sensitive characterization using X-ray photoelectron spectroscopy identifies CuO and Cu(OH) 2 species, while Fourier-transform infrared spectroscopy detects phosphate- and carbonyl-containing compounds associated with electrolyte decomposition and interfacial passivation. Field-emission scanning electron microscopy reveals comparatively smoother and less porous Cu surfaces following HE exposure. Together, these results demonstrate that the HE alters corrosion pathways and moderates copper degradation, providing mechanistic insight into electrolyte-driven strategies for improving current-collector compatibility in LSB systems.