Effect of Fluorine Substitution in Li3YCl6 Chloride Solid Electrolytes for All-solid-state Battery (Supporting Information)

All-solid-state batteries experience irreversible capacity loss particularly in the initial potential cycle, owing to electrolyte decomposition at the electrode/electrolyte interface. A strategy for expanding the oxidation stability of electrolytes is replace the anion in solid electrolytes with fluorine. However, fluorine substitution has a negative influence on ionic conductivity. In this study, we introduced trace amounts of fluorine replacement in Li3YCl6 solid electrolytes which exhibit high ionic conductivities and wide potential windows. The effect of replacement on ionic conductivity, oxidation stability, and charge–discharge characteristics we studied. The trace amounts of fluorine in Li3YCl6 did not reduce the conductivity, but improved the apparent oxidation stability. The decomposed product of LiF from the fluorine-substituted electrolyte disturbed the formation of a high-resistance layer at the electrode/electrolyte interface. The initial charge–discharge efficiency of the uncoated LiCoO2 cathode was improved by the trace amount of fluorine replacement in the Li3YCl6 solid electrolyte.