Influence of atmospheric moisture on the gas evolution tolerance of halide solid electrolytes

Much attention has been paid on research and development on solid electrolytes for all-solid-state Li batteries. Although halide solid electrolytes such as Li3YCl6 and Li3InCl6 are promising due to fast Li ion conductivity and oxidation-resistant against positive electrode, a better understanding of their reactivity with atmospheric H2O is required for commercialization. In this study, the gas evolution tolerances of Li3YCl6 and Li3InCl6 were investigated. Temperature-programmed desorption mass spectrometry (TPD-MS) experiments at dew points below − 60 °C and gas detector tube experiments at dew points of − 30 °C both revealed significant differences in the H2O and HCl evolution behavior of Li3YCl6 and Li3InCl6. In TPD-MS, the onset temperature of HCl evolution for Li3YCl6 ( 100 °C) was significantly lower than that for Li3InCl6 ( 220 °C), indicating that Li3InCl6 solid electrolytes have superior gas evolution tolerance. This difference may be attributable to differences in the retention of H2O derived from the material synthesis stage and from contact with the atmosphere during the measurements. In particular, based on first-principles calculations, the low-temperature HCl evolution observed in Li3YCl6 was ascribed to the partial replacement of Cl− ions by OH− ions upon contamination with trace H2O. Because the heating and drying of solid electrolytes (including slurries) are inevitable processes during battery manufacturing, these findings can aid in the rational design of halide solid electrolytes for all-solid-state batteries.