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

Lithium ternary halides are promising solid electrolytes, owing to their high ionic conductivity and reasonably high oxidative and chemical stability. Recently, fluorine substitution in Li3MCl6 has been suggested as a promising approach for further enhancing oxidation stability. Accordingly, this study outlines a material design strategy for F-substituted Li3MCl6 through systematic theoretical analyses. Calculations reveal that the mixing limit of F in Li3MCl6-xFx is in the range of 0.5-1.5, and the resulting Li3MCl6-xFx phases can retain ionic conductivity above 1 mS/cm up to x = 1.0. The calculations also predict that the formation of F-containing passivating phases could increase the oxidation potential for Li3MCl5F to similar to 6.3 V. The proposed material design strategy is validated through the synthesis of Li3YCl5F, which is confirmed to show both high ionic conductivity and enhanced oxidation stability. The design guidelines presented herein can accelerate the potential use of halide-based electrolyte chemistries in high-voltage all-solid-state batteries.