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

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 Li2YCl2.5Br1.5O0.5 (2LO-0.5). The robust Y─O bonds in 2LO-0.5 effectively hinder uncontrolled oxygen interactions with Y3⁺, which would otherwise lead to the formation of oxidizable YOCl. This stabilization promotes the formation of a thin, stable Y₂O₃-based CEI against LiNi0.83Co0.11Mn0.06O2 (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.