In Situ Formed LiI Interfacial Layer for All-Solid-State Lithium Batteries with Li₆PS₅Cl Solid Electrolyte Membranes

Sulfide-based solid electrolytes are considered ideal materials for all-solid-state Li metal batteries owing to their high ion conductivity and satisfactory mechanical stiffness. However, the interfacial reaction between the sulfide electrolyte membrane and Li anode severely limits the commercial application of such membranes. Herein, a lithium iodide (LiI) layer is synthesized at the Li metal-sulfide electrolyte membrane interface via chemical vapor deposition. The synthesized LiI layer exhibits satisfactory ionic conductivity and high interfacial energy, as confirmed via density functional theory calculations. Consequently, the LiI@Li/Li₆PS₅Cl membrane/LiI@Li symmetric cell can cycle for >150 h at 0.1 mA cm^-2. The as-prepared all-solid-state batteries exhibit a high discharge capacity of 107 mA h g^-1 and an excellent capacity retention of 76% after 800 cycles at 1 C. This work offers a simple and effective method to improve the interface between the Li anode and sulfide electrolyte membranes that facilitates the mass production and practical application of high-energy-density sulfide-based all-solid-state batteries.