Superior Air‐Stable Li4P0.9Sb0.1S4I Solid Electrolyte for All‐Solid‐State Lithium Batteries

Sulfide solid electrolytes have received particular attention due to their outstanding ionic conductivity and good mechanical ductility. Nevertheless, their chemical instability toward humid air is a significant challenge that impedes the commercialization of all‐solid‐state batteries. Herein, air‐stable Li 4 P 0.9 Sb 0.1 S 4 I solid electrolyte is synthesized by doping LiI and partially replacing P with Sb in Li 3 PS 4 electrolyte. The Li 4 P 0.9 Sb 0.1 S 4 I solid electrolyte shows superior chemical stability under 30% relative humidity air, which is attributed to the generated LiI·H 2 O protective barrier between electrolyte and H 2 O molecule. In addition, benefitting from the formation of a Li 4 PS 4 I phase with Sb substitution, the Li 4 P 0.9 Sb 0.1 S 4 I electrolyte possesses high ion conductivity of 1.6 mS cm −1 . Moreover, the Li/Li 4 P 0.9 Sb 0.1 S 4 I/Li battery can stably cycle for 1500 h at 0.1 mA cm −2 , showing enhanced stability against lithium. As a result, the LiCoO 2 /Li 4 P 0.9 Sb 0.1 S 4 I/Li battery delivers an initial discharge capacity of 109.2 mAh g −1 with a capacity retention of 83.6% after 500 cycles at 1C. These results demonstrate a promising Li 4 P 0.9 Sb 0.1 S 4 I solid electrolyte with high ionic conductivity, favorable stability against moisture and lithium for all‐solid‐state lithium batteries.