Lattice engineering and ion conduction in halide solid-state electrolytes

Halide superionic conductors are among the most promising solid-state electrolytes for all-solid-state lithium-ion batteries. Elucidating the basic structural principles that govern ion transport in them will help improve the ionic conductivity or accelerate the discovery of new structural fast ion conductors. From this perspective, our focus is on the issue of ion transport in the development of all-solid-state batteries. Firstly, we discussed the structural factors that control ionic conduction in solid electrolytes, especially the structural features that enable halide superionic conductivity, and extended the discussion to examine how lattice structure and local structural effects affect ion transport. Unlike previous reviews focusing on static structural descriptors such as ionic radius, polarizability, and vacancy concentration, this review emphasizes the emerging role of dynamic lattice disorder, frustration-assisted transport, and amorphous-enabled superionic conduction in halide solid electrolytes. We provide a unique perspective on the ion conduction mechanism in inorganic halides for the design of future solid electrolytes and hope that this perspective can inspire researchers to develop solid electrolyte materials with high ion conductivity.