Fluorine-Substituted Lithium Chloride Solid Electrolytes for High-Voltage All-Solid-State Lithium-Ion Batteries

Lithium ternary halides, Li₃MCl₆, are promising solid electrolytes for high-voltage all-solid-state batteries due to their high ionic conductivity and oxidative stability. However, further improvements in oxidation stability are essential for broader applicability. Fluorine substitution in Li₃MCl₆ offers a promising approach to enhancing solid electrolyte performance in high-voltage all-solid-state batteries. Theoretical analyses suggest that fluorine can be substituted in Li₃MCl_6-xF_x within a mixing limit of x = 0.5–1.5, while maintaining ionic conductivities above 1 mS/cm for x ≤ 1.0. Additionally, the formation of fluorine-containing passivating phases is predicted to increase the oxidation potential to approximately 6.3 V for Li₃MCl₅F_x. This material design strategy was experimentally validated through the synthesis of Li₃YCl₅F, which demonstrated both high ionic conductivity and enhanced oxidation stability. These findings provide promising guidelines for enhancing halide-based electrolytes and accelerating their adoption in advanced battery technologies.