High conductivity enabled by concerted Li ion diffusion in Li3Y(Br3Cl3) solid electrolytes for all-solid-state batteries

Abstract

Halide solid electrolytes for all-solid-state batteries have recently attracted great attention due to their significantly improved ion conductivity to the level of sulfide solid electrolytes. This first-principles study unveils the Li ion diffusion mechanism in Li₃Y(Br₃Cl₃), which is a layered mixed-halide material. The most stable Li₃Y(Br₃Cl₃) structure, which was determined from systematic and extensive investigations, delivers a conductivity of 22.3 mS cm⁻¹, which is higher than those of Li₃YCl₆ (15.8 mS cm⁻¹) and Li₃YBr₆ (3.0 mS cm⁻¹) and is comparable to approximately tens of mS cm⁻¹ for sulfide solid electrolytes. Li ion transport in Li₃Y(Br₃Cl₃) occurs through the interlayer concerted diffusion across the Li, halide, and Y layers, promoted by the intralayer vacancy diffusion in the Li layer. The interlayer concerted diffusion (0.23 eV) exhibits a much lower barrier than the interlayer vacancy diffusion (0.56 eV), enabling rapid Li ion transport. The lower barrier for concerted diffusion is because the diffusion of Li⁺ cations continuously stabilizes the six Br⁻/Cl⁻ anions surrounding the 4g site in the Y layer. This work suggests that mixed halides can be promising solid electrolytes for all-solid-state batteries as an alternative to sulfides.