Formation of an Artificial Cathode–Electrolyte Interphase to Suppress Interfacial Degradation of Ni-Rich Cathode Active Material with Sulfide Electrolytes for Solid-State Batteries

Sulfide-based electrolytes and Ni-rich cathode materials (i.e., LiNixCoyMn1–x–yO2, x ≥ 0.8) are considered as promising materials for high-performance solid-state batteries. However, their poor chemical compatibility causes stability issues and fast capacity fading, particularly at high potentials. Here, we propose a coating concept inspired by the natural cathode–electrolyte interphase (CEI) formation to overcome the degradation at the solid electrolyte–cathode active material interface. An artificial CEI (coating) is derived from sulfide-based electrolytes prior to cell assembly by a dry-coating approach combined with a heat treatment. A proof-of-concept using Li3PS4 and Li6PS5Cl as precursors confirms the interfacial stability. Accordingly, the Li6PS5Cl-derived coating enables a capacity retention of 84% after 100 cycles (2.6–4.5 V vs Li+/Li). Overall, this work emphasizes the suitability and the (as yet unexploited) great potential of this coating concept to suppress interfacial degradation in sulfide-based composite cathodes.