Prediction of Novel Trigonal Chloride Superionic Conductors as Promising Solid Electrolytes for All-Solid-State Lithium Batteries

Abstract

Recently emerging lithium ternary chlorides have attracted increasing attention for solid-state electrolytes (SSEs) due to their favorable combination between ionic conductivity and electrochemical stability. However, a noticeable discrepancy in Li-ion conductivity persists between chloride SSEs and organic liquid electrolytes, underscoring the need for designing novel chloride SSEs with enhanced Li-ion conductivity. Herein, an intriguing trigonal structure (i.e., Li₃SmCl₆ with space group P3₁12) is identified using the global structure searching method in conjunction with first-principles calculations, and its potential for SSEs is systematically evaluated. Importantly, the structure of Li₃SmCl₆ exhibits a high ionic conductivity of 15.46 mS cm^-1 at room temperature due to the 3D lithium percolation framework distinct from previous proposals, associated with the unique in-plane cation ordering and stacking sequences. Furthermore, it is unveiled that Li₃SmCl₆ possesses a wide electrochemical window of 0.73-4.30 V vs Li⁺/Li and excellent chemical interface stability with high-voltage cathodes. Several other Li₃MCl₆ (M = Er, and In) materials with isomorphic structures to Li₃SmCl₆ are also found to be potential chloride SSEs, suggesting the broader applicability of this structure. This work reveals a new class of ternary chloride SSEs and sheds light on strategy for structure searching in the design of high-performance SSEs.

Keywords: all‐solid‐state batteries; cation ordering; chloride solid‐state electrolytes; first‐principles calculations; structure prediction method.