LiF-doped sulfide solid electrolytes with a stabilized α-Li3PS4 analog phase for all-solid-state Li metal batteries

Abstract

All-solid-state Li metal batteries require solid electrolytes with both high reduction tolerance and high Li-ion conductivity. Adding LiF, which has a wide potential window, to these solid electrolytes effectively improves their reduction tolerance. However, this addition decreases the conductivity of the solid electrolyte. In this study, we subjected LiF-doped Li₃PS₄ glass to a heat-treatment process involving rapid heating and quenching. This process precipitated a highly ionic conductive α-Li₃PS₄ analog phase, thereby achieving both high conductivity and high reduction tolerance. The Li₃PS₄·LiF glass-ceramic electrolyte with the precipitated α-Li₃PS₄ analog phase exhibited a high conductivity of 1.3 × 10⁻³ S cm⁻¹ at room temperature. Galvanostatic cycling tests of Li symmetric cells and SEM observations of the Li/solid electrolyte interface indicated that the Li₃PS₄·LiF glass-ceramic electrolyte showed compatibility with Li metal. Therefore, Li₃PS₄·LiF glass-ceramic electrolyte successfully combines the high conductivity of the α-Li₃PS₄ analog phase with the excellent electrochemical stability of LiF. This work proposes a new approach to developing solid electrolytes for all-solid-state Li metal batteries.