Design of a trigonal halide superionic conductor by regulating cation order-disorder.

Yu, Seungju; Noh, Joohyeon; Kim, Byunghoon; Song, Jun-Hyuk; Oh, Kyungbae; Yoo, Jaekyun; Lee, Sunyoung; Park, Sung-O et al. · Science · 2023

basic_science · Level V

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Abstract

Lithium-metal-halides have emerged as a class of solid electrolytes that can deliver superionic conductivity comparable to that of state-of-the-art sulfide electrolytes, as well as electrochemical stability that is suitable for high-voltage (>4 volt) operations. We show that the superionic conduction in a trigonal halide, such as Li<sub>3</sub>MCl<sub>6</sub> [where metal (M) is Y or Er], is governed by the in-plane lithium percolation paths and stacking interlayer distance. These two factors are inversely correlated with each other by the partial occupancy of M, serving as both a diffusion inhibitor and pillar for maintaining interlayer distance. These findings suggest that a critical range or ordering of M exists in trigonal halides, and we showcase the achievement of high ionic conductivity by adjusting the simple M ratio (per Cl or Li). We provide general design criteria for superionic trigonal halide electrolytes.