Origin of high ionic conductivity in halide solid electrolyte Li3InCl6: Insights from native defects

Abstract

Halide solid electrolyte Li3InCl6 (LIC) is a promising candidate for all-solid-state lithium-ion batteries due to its high conductivity and moisture stability. Despite its potential, the reproducible synthesis of high-conductivity LIC remains challenging due to the unknown effect of native defects on ionic conductivity. We investigate native defects and explore the impact of defects on the ion conductivity of LIC using density functional theory and ab initio molecular dynamics simulations. It is found that, on the one hand, the high conductivity in experimental LIC benefits from the dominant defects of Li vacancies (VLi) and interstitials (Lii), on the other hand, the conductivity induced by the two major defects is nearly an order magnitude higher than the experimental values, indicating the cooperative effect of minor defects. Following this, a mixed-defect system with the coexistence of VLi, Lii as well as minor defects Cl vacancies (VCl) and antisites (InLi) is proposed, which presents an activation energy of 0.31 eV and ionic conductivity of 1.8 mS/cm (300 K), well explaining the experimental results. These findings provide important insight into understanding the effect of native defects on ionic transport in LIC and offer synthesis principles for the reproducibility of LIC-type solid electrolytes with high conductivity.