Chemo-electrochemical Evolution of Cathode–Solid Electrolyte Interface in All-Solid-State Batteries

The stability of the interface between the cathode and the solid electrolyte (SE) has been found to be a key determinant of solid-state battery (SSB) performance. While interfacial failure from electrochemical cycling has been studied, temperature effects on the chemical and electrochemical evolution of interface properties are not well-understood. We utilize a dense additive-free LiCoO₂ cathode, which provides controlled morphology and crystallography, and well-known high voltage halide SEs (Li₃InCl₆ and Li₃YCl₆) to eliminate the need for cathode coating to explore the nature of interface deterioration induced by operating at up to 100 °C. By promoting temperature-induced accelerated interfacial failure, we show that at elevated temperatures (>60 °C) and higher states of charge, a significant chemo-electrochemical contribution to interfacial resistance results in rapid cell performance degradation. Our findings show that beyond the well sought-after SE electrochemical voltage stability, the atomic-scale restructuring of the cathode surface interfaced with the SE must be considered when designing stable interfaces.