Integrating Lithium Sulfide as a Single Ionic Conductor Interphase for Stable All‐Solid‐State Lithium–Sulfur Batteries

As a very prospective solid-state electrolyte, Li₁₀GeP₂S₁₂ (LGPS) exhibits high ionic conductivity comparable to liquid electrolytes. However, severe self-decomposition and Li dendrite propagation of LGPS will be triggered due to the thermodynamic incompatibility with Li metal anode. Herein, by adopting a facile chemical vapor deposition method, an artificial solid electrolyte interphase composed of Li₂S is proposed as a single ionic conductor to promote the interface stability of LGPS toward Li. The good electronic insulation coupled with ionic conduction property of Li₂S effectively blocks electron transfer from Li to LGPS while enabling smooth passage of Li ions. Meanwhile, the generated Li₂S layer remains good interface compatibility with LGPS, which is verified by the stable Li-plating/stripping operation for over 500 h at 0.15 mA cm^-2. Consequently, the all-solid-state Li-S batteries (ASSLSBs) with a Li₂S layer demonstrate superb capacity retention of 90.8% at 0.2 mA cm^-2 after 100 cycles. Even at the harsh condition of 90 °C, the cell can deliver a high reversible capacity of 1318.8 mAh g^-1 with decent capacity retention of 88.6% after 100 cycles. This approach offers a new insight for interface modification between LGPS and Li and the realization of ASSLSBs with stable cycle life.