Optimizing solid electrolytes with 3d transition metal doped Li3YCl6 for Li-ion batteries

Abstract

Li3YCl6 is a promising candidate for solid electrolytes (SEs) in all-solid-state Li-ion batteries due to its high ionic conductivity, electrochemical stability, and compatibility with metal-oxide electrodes. The monoclinic and trigonal crystal structures of Li3YCl6 with space groups C2/c and P-3m1 have been studied extensively, while little attention has been given to the trigonal P-3c1 phase (space group no. 165). Additionally, Li-ion diffusion mechanism in 3d transition metal (TM) substituted compounds along with their structural stability are interesting to study. Therefore, we investigate the Li diffusion mechanism in Li3YCl6 and TM substituted Li3YCl6 in the P-3c1 phase using first-principles calculations. We have found that all the substituted compounds are thermodynamically stable at room temperature and show high oxidation stability. Li3Y0.875Co0.125Cl6 exhibits the lowest activation energy (0.11 eV) for Li-ion diffusion and the highest Li-ion mobility (σ = 0.39 mS cm−1 at room temperature), which is strongly anisotropic. We used the Crystal Orbital Hamilton Population method to analyze the bonding characteristics of Li3YCl6 and 3d TM substituted Li3YCl6 and found that the Co–Cl bond is weaker than the Cr–Cl bond. This may explain the lower activation energy observed for Li3Y0.875Co0.125Cl6. Our results provide insights into the substitution effect in Li3YCl6 superionic conductors, which could guide the design and development of high-performance SEs for Li-ion batteries.