The effects of anionic doping on the ion transport of Li3TMCl6 (TM=Y, Er) and the heterostructure solid electrolytes interface first-principles study

Abstract

Li₃YCl₆ and Li₃ErCl₆ are widely used as solid electrolytes in all-solid-state batteries due to their good ionic conductivity and wide stable chemical window. Li₃YCl₆ and Li₃ErCl₆, which have a tripartite lattice structure, not only have a high activation energy for transporting ions due to the strong electronegativity of the anion but also have poor interfacial stability with the cathode. The effects of anion X (X = F, Br, and I) doping on the ion transport of Li₃TMCl₆ (TM=Y, Er) and LiF|Li₃TMCl₆ are investigated using ab initio molecular dynamics and a climbing image nudged elastic band. The results show that the doping of Br^-/F^- in Li₃TMCl₆ results in different local anionic coordination in the Li site, which providing a disorder structure for ion transport. The degeneracy and splitting of electron orbitals caused by doping reduce the energy level difference from octahedral to tetrahedral states. The short-range local environment only reduces the migration energy barrier due to the strong electronegativity of F^-. However, the broader anionic coordination results in a significant improvement in overall ion transport performance due to the lower electronegativity of Br^-. The extremely low migration barrier increases the diffusion coefficient of LiF|Li₃TMCl₆-X due to weak interactions between transport ions and anions.