Computational design of a mixed A-site cation halide solid electrolyte for all-solid-state lithium batteries

All-solid-state Li-ion batteries (ASSBs) are considered as ideal next-generation energy storage devices owing to their safe operation and high energy densities. Recently, halide-based solid electrolytes (SEs) have come under the spotlight because of their wide electrochemical stability windows and high ionic conductivities. However, their usage as coating materials for cathodes is limited. To examine the wide electrochemical stability window of SEs for lithium-metal anodes and their interfacial stability with high-voltage cathodes, a systematic first-principles investigation of A-site cation and anion exchange in Li₃MX₆ (M: Lu, Sc, Bi, In, Y, Tm, Dy, Ho, Er, Tm, Sm, Tb; X: Br, Cl, and I) was conducted. The systematic analysis showed that the electrochemical behavior of chloride SEs can be modulated by mixing M³⁺ cations. Furthermore, the replacement of M³⁺ by Zr⁴⁺ and the anionic blending of Br with Cl, which exhibits a relatively high ionic conductivity, was also computed for comparison with the A-site cation-mixed halide electrolyte. Our computational work provides an overview of the evolution of lithium halide SEs in high-voltage ASSBs.