Unraveling the Underlying Mechanism of the Li+ Migration Inside Halide Solid-State Electrolytes: Structural Tuning and Defect Manipulation

Halide-based solid electrolytes have emerged as promising candidates for next-generation all-solid-state lithium metal batteries due to their high room-temperature ionic conductivity, wide electrochemical stability window, and favorable mechanical properties. This review provides a comprehensive overview of the fundamental structure–property relationships, Li+ transport mechanisms, and performance optimization strategies for Li3MX6-type halide solid electrolytes. The unique structural framework of halide electrolytes, characterized by close-packed anion sublattices (hexagonal close-packed and cubic close-packed) and edge-sharing [MX6]3− octahedral networks, establishes three-dimensional Li+ percolation pathways with low migration barriers (0.20–0.33 eV). This review concludes by identifying key challenges and future research directions, including high-entropy halide design, scalable aqueous synthesis methods, earth-abundant material alternatives, and integrated cell architectures that combine halide catholytes with complementary anolyte materials for practical all-solid-state battery applications.