<i>In Situ</i> 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 P 4 S 16 with lithium metal in 1,2-dimethoxyethane (DME), a conformal thiophosphate (Li 3 PS 4 ) 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 Li 3 PS 4 /Li electrode demonstrate stable cycling over 600 h at 1 mA cm –2 in liquid electrolyte systems. Furthermore, when Li 3 PS 4 film serves as the solid-state electrolyte, symmetric solid-state cells assembled with two Li 3 PS 4 /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 Li 3 PS 4 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.