Tailoring the Cation Lattice for Chloride Lithium‐Ion Conductors

All-solid-state Li-ion batteries require Li-ion conductors as solid electrolytes (SEs). Li-containing halides are emerging as a promising class of lithium-ion conductors with good electrochemical stability and other properties needed for SEs in all-solid-state batteries. Compared to oxides and sulfides, Li-ion diffusion mechanisms in Li-containing halides are less well understood, in particular regarding the effects of Li content and cation sublattices, which can be tailored for improving Li-ion conduction. Using first-principles computation, a systematic study is performed on the Li-ion conduction of known Li-containing chlorides with close-packed anion frameworks and a wide range of their doped compounds. A dozen potential chloride Li-ion conductors are predicted with increased Li-ion conductivities, and it is revealed that the Li-ion migration is greatly impacted by the cation configuration and concentrations. By analyzing a large set of materials data, it is proposed that low Li content, low cation concentration, and sparse cation distribution increase Li-ion conduction in chlorides, and these principles are demonstrated in designing new chloride Li-ion conductors. This study provides insights into the effects of the cation sublattice on Li-ion diffusion, highlights potential chloride Li superionic conductors, and proposes design principles to further develop halide Li-ion conductors.