Reducing oxy-contaminations for enhanced Li-ion conductivity of halide-based solid electrolyte in water-mediated synthesis

Abstract

Liquid-mediated synthesis offers a new approach to producing or applying solid electrolytes (SEs) in all-solid-state Li-ion batteries (ASSLIB). Li-ion conductive Li3InCl6 (LIC) powders are synthesized using a water-mediated process in which hydrated precursor powders are dried at progressively increasing temperatures up to 200 °C. The effects of drying environments, including high-vacuum (HV; 10−3 Torr), low-vacuum (LV; 10−1 Torr), Ar, and N2 (both at 1 atm), on the chemical, microstructural, and ionic conductive properties of the LIC powders are investigated. Oxy-contaminations in the LIC powders are determined based on synchrotron X-ray diffraction and X-ray absorption analyses. The ionic conductivity of the produced LIC powder exhibits a profound reverse trend with the amounts of oxy contaminations, including crystal water residual and In-O oxy species, such as InOCl. The vacuum drying conditions favor the formation of smaller particles, which facilitate water removal due to a shorter diffusion length and a higher surface area, resulting in less oxy-contamination and higher ionic conductivities (HV: 2.70 mS cm−1; LV: 0.96 mS cm−1). The 1-atm drying conditions, either in Ar or N2, produce compact LIC chunks, which are unfavorable to water removal, and more oxy-contaminations, leading to nearly an order of magnitude lower conductivities (Ar: 0.39 mS cm−1; N2: 0.22 mS cm−1). The HV SE powder leads to the best electrochemical performance of a high-capacity Ni-rich Li(Ni,Mn,Co)O2│SE│InLi full-cell. The revealed processing-microstructure-property relationships may facilitate the synthesis of high-quality halide-based Li-ion SEs for ASSLIB applications.