A Pre‐Oxidation Strategy to Establish Stable Oxide Cathode/Halide Solid‐State Electrolyte Interfaces for High Energy all Solid‐State Batteries

Abstract All‐solid‐state lithium metal batteries (ASSLBs) are promising for high energy and safety. Halide‐based solid‐state electrolytes, characterized by high ionic conductivity and a notably wide electrochemical window exceeding 4.3 V, hold significant promise for compatibility with high‐energy cathodes. However, oxygen in cathodes exhibits a strong tendency to interact with the central metal cation in halide solid‐state electrolyte, forming an unstable cathode‐electrolyte interface (CEI) and leading to cathodic degradations. Herein, a pre‐oxidation strategy is proposed for Y based halide solid‐state electrolytes, leveraging oxygen to pre‐establish robust Y─O bonds within the halide electrolyte structure Li 2 YCl 2.5 Br 1.5 O 0.5 (2LO‐0.5). The robust Y─O bonds in 2LO‐0.5 effectively hinder uncontrolled oxygen interactions with Y 3 ⁺, which would otherwise lead to the formation of oxidizable YOCl. This stabilization promotes the formation of a thin, stable Y₂O₃‐based CEI against LiNi 0.83 Co 0.11 Mn 0.06 O 2 (NCM83). Therefore, the ASSLB assembled with 2LO‐0.5 and NCM83 demonstrates an initial discharge‐specific capacity of 208 mAh g −1 and retained 80.6% of its capacity after 1000 cycles, attributed to stable CEI film derived from pre‐oxidized strategy. This work offers new insights for regulating the non‐redox reaction between halide solid‐state electrolytes and oxide cathodes, promoting the rational design of high‐performance halide solid‐state electrolytes.