Effects of neutral point defects on the solid-state electrolyte Li3ScBr6†

Abstract

Li₃ScBr₆ is a novel solid-state electrolyte, and therefore, it is important to understand the atomic mechanisms affecting its Li⁺ ionic conductivity for the optimal design of potential halide SSEs, thus facilitating their application in a practical setting. In particular, neutral point defects, which play a significant role in modifying ionic conductivities, should be studied comprehensively. By a combined DFT and AIMD study, we explored the effects of neutral point defects on Li₃ScBr₆, including the stability of point defects, mechanical properties of defective states, Li⁺-ion diffusion and interfacial compatibility. Although defect formation energy generally increases with an increasing defect concentration, the relative stability of neutral point defects remains unchanged, i.e., vacancy and interstitial defects are generally easier to form than antisite defects, except for the V_Sc defect. Meanwhile, it is vital to improve the bulk and shear moduli of Li₃ScBr₆ as a small Young's modulus is beneficial for the application of Li₃ScBr₆ as a SSE. In particular, neutral point defects have negative effects on the elastic moduli of Li₃ScBr₆, and the elastic moduli generally decrease with an increasing defect concentration. The AIMD results showed that lithium ions in Li₃ScBr₆ traverse via face-shared distorted tetrahedral sites of a bcc-like anion arrangement. By studying its crystalline structures including its neck size and Li⁺-ion diffusion pathway and electronic structures including the electronegativity of atoms and projected density of states, we found that point defects generally hinder the diffusion of Li⁺ ions except for V_Sc and Li_int defects. Furthermore, it was shown that V_Sc, Li_Sc, Br_Sc and Br_Li defects can improve interfacial compatibility with cathode materials. This study provides a comprehensive overview of the effects of neutral point defects on the properties of Li₃ScBr₆ and may aid in achieving a higher ionic conductivity.