Halide Solid-State Electrolytes for All-Solid-State Sodium Batteries: Progress and Perspectives

Halide solid-state electrolytes (HSSEs) have recently emerged as promising candidates for all-solid-state sodium batteries (ASSSBs) due to their high ionic conductivity, wide electrochemical stability window, and good compatibility with high-voltage cathode materials. Here, we comprehensively summarize the latest progress in sodium-ion HSSEs, with a focus on their phase structure–property relationships, synthesis methodologies, stability mechanisms, and practical applications. Additionally, we critically analyze the (electro)chemical stability of HSSEs at both cathode and anode interfaces along with key modification strategies. Finally, we present key future research directions to advance HSSE for next-generation ASSSBs. This review aims to provide fundamental insights and practical guidelines for developing high-performance HSSEs toward next-generation ASSSBs.