In Situ Synthesis of Li ₃ PS ₄ Solid Electrolyte Films via Sulfur-Rich Anodization for All-Solid-State Lithium–Sulfur Batteries

All-solid-state Li-S batteries (ASSLSBs) are attractive candidates for high-energy-density and environmentally sustainable energy storage systems. However, their practical deployment remains constrained by lithium dendrite formation and interface instability with solid-state electrolytes (SSEs) when lithium metal is used as anodes. Herein, we propose a sulfur-oxidant-driven anodization strategy to construct a stable and ionically conductive interface on lithium. By anodically reacting P₄S₁₆ with lithium metal in 1,2-dimethoxyethane (DME), a conformal thiophosphate (Li₃PS₄) interphase is deposited in situ on the lithium metal surface. This solid electrolyte film exhibits high ionic conductivity (0.19 mS cm⁻¹), controlled thickness, and robust interfacial contact with lithium metal, which collectively suppresses lithium dendrite propagation and parasitic reactions during cycling. As a result, symmetric cells employing this Li₃PS₄/Li electrode demonstrate stable cycling over 600 h at 1 mA cm⁻² in liquid electrolyte systems. Furthermore, when Li₃PS₄ film serves as the solid-state electrolyte, symmetric solid-state cells assembled with two Li₃PS₄/Li electrodes demonstrate a stable cycle life exceeding 1000 h at 1 mA cm⁻² due to well-improved interfacial compatibility. When integrated into ASSLSBs, with the Li₃PS₄ interphase as the solid-state electrolyte and Li metal as the anode, the cell delivers a high specific capacity of 1351 mAh g⁻¹ at 0.1 C and a capacity retention of 89.3% after 50 cycles. This study introduces a sulfur-oxidant-induced anodization process, providing a simple and effective interfacial-engineering strategy to develop next-generation ultrathin all-solid-state lithium-sulfur battery technologies.