Emerging Halide Solid Electrolytes for Sodium Solid‐State Batteries: Structure, Conductivity, Paradigm of Applications

Solid-state sodium batteries (SSSBs) hold great promise for the development of safe, low-cost energy storage devices. Developing solid electrolyte (SE) materials with high ionic conductivity, high chemical and electrochemical stability, as well as good mechanical properties is the most critical step. As a promising category of SEs, halide-based solid electrolytes combine good ionic conductivity and good electrochemical stability, and they have been already widely studied for their use in lithium-based solid-state batteries. In contrast, knowledge of their sodium analogues is still limited. Here, we provide a comprehensive overview of halide SEs for sodium ion conduction with a perspective of both experimental and theoretical studies, including the correlation of structure and properties; sodium ion conductivity and diffusivity; as well as compatibility with electrode materials. We hope this perspective can stimulate more research in developing halide-based SSSBs.