Enhancement of the rate capabilities for all-solid-state batteries through the surface oxidation of sulfide solid electrolytes

Abstract

Lithium-ion conducting sulfide solid electrolytes are promising candidates for all-solid-state lithium ion batteries, which are being developed to meet the increasing demand for high-capacity rechargeable batteries. In this study, a new type of solid electrolyte with a core–shell structure consisting of oxidized-shell surrounding sulfide solid electrolyte (O-SSE) was developed. The influence of the surface oxidation of 80Li2S·20P2S5 glass–ceramic electrolyte on a battery using 4 V class cathode material was investigated. The results of X-ray photoelectron spectroscopy depth profiling confirmed that >80% of the surface of the O-SSE was oxidized from PS bonds to PO bonds, and the oxygen remained localized at the surface. The interfacial resistance between the sulfide solid electrolyte and LiNi0.8Co0.15Al0.05O2 (NCA) was significantly decreased by this surface oxidation. The ASSB cell using O-SSE as a cathode solid electrolyte exhibited better discharge performance than 80Li2S·20P2S5 glass–ceramic electrolyte and could discharge at a high current density of 2.0 mA·cm−2. These results demonstrate that surface oxidation of a sulfide solid electrolyte is a new and effective method for reducing the interfacial resistance between the cathode material and solid electrolyte and improving the charge–discharge performance.