Anode Compatibility of Halide Solid-State Electrolytes

Recently, lithium-metal-halide (Li-M-X) superionic conductors have emerged as promising solid-state electrolyte (SSEs) for all-solid-state lithium batteries (ASSLBs), owing to their high Li⁺ conductivity, excellent compatibility with cathodes, and good mechanical deformability. However, many of these conductors exhibit chemical and electrochemical instability when in contact with the reductive anodes, which hinders the direct use of lithium metal as anodes with extraordinarily high specific capacities and limits the overall energy density of halide-based ASSLBs. Therefore, enhancing the anode compatibility of halide SSEs has become a critical task in ASSLB development and has attracted broad research interest. Herein, the underlying mechanisms responsible for the instability of halide SSEs against the lithium anode are elucidated based on both experimental observations and theoretical calculations. Recent strategies and progress aimed at improving the compatibility of halide SSEs with lithium anodes are summarized. Moreover, the effects of pressure and volume changes on the interfacial compatibility between halide SSE and lithium metal are discussed. In addition, the current challenges and future research directions are analyzed, aiming to provide theoretical insights and guidance to support further advancements in Li-M-X type solid-state electrolytes and all-solid-state lithium batteries.