Lithium Chlorides and Bromides as Promising Solid‐State Chemistries for Fast Ion Conductors with Good Electrochemical Stability

Enabling all‐solid‐state Li‐ion batteries requires solid electrolytes with high Li ionic conductivity and good electrochemical stability. Following recent experimental reports of Li3YCl6 and Li3YBr6 as promising new solid electrolytes, we used first principles computation to investigate the Li‐ion diffusion, electrochemical stability, and interface stability of chloride and bromide materials and elucidated the origin of their high ionic conductivities and good electrochemical stabilities. Chloride and bromide chemistries intrinsically exhibit low migration energy barriers, wide electrochemical windows, and are not constrained to previous design principles for sulfide and oxide Li‐ion conductors, allowing for much greater freedom in structure, chemistry, composition, and Li sublattice for developing fast Li‐ion conductors. Our study highlights chloride and bromide chemistries as a promising new research direction for solid electrolytes with high ionic conductivity and good stability. Halide solid electrolytes: Lithium chloride and bromide materials exhibit low energy barriers for Li‐ion migration, wide electrochemical window, and good interface compatibility in all‐solid‐state Li‐ion battery, as illustrated by first principles computation study. These new classes of chemistries are suggested as promising new research direction of lithium solid electrolytes with both high ionic conductivity and good electrochemical stability for all‐solid‐state Li‐ion batteries.