Engineering high conductive Li₇P₂S₈I via Cl^- doping for all-solid-state Li-S batteries workable at different operating temperatures

High ionic conductivity and excellentlithium compatibility for sulfide solid electrolytes are vital to developingsolid-state Li-metal batteries with high energy density and safety. Li₇P₂S₈Ihas attracted significant attention due to its low cost, good stability towardslithium metal, and low annealing temperature. However, the low conductivitycompared to liquid electrolyte and poor stability with Li metal at high currentdensity limits its applications in solid-state batteries. In this work, theconductivity of Li₇P₂S₈I is first increasedfrom 1.53 mS/cm to 3.08 mS/cm by Cl^- doping. The enhanced ionicconductivity is due to the introduction of S^2-/Cl^-/I^- disorderstructure in the structure. Then, the Li-ion conductivity of Li₇P₂S₈I_0.5Cl_0.5 isenhanced up to 6.67 mS/cm via optimizing the pellet-making pressures andtemperatures with the hot-press technique. Because of the superiorconductivity, the assembled Li₂S-LiI/Li₇P₂S₈I_0.5Cl_0.5/Li-Inbattery delivers initial discharge capacities of 1051.0 mAh/g, 1385.0 mAh/g,and 713 mAh/g under 0.13 mAh/cm² at room temperature,60 °C, and 0 °C, respectively. Moreover, the capacity contribution ofthe Li₇P₂S₈I_0.5Cl_0.5 electrolytein cathode mixture are unraveled, which shows reversible charge/discharge morethan 80 cycles and confirms the extra capacity from the electrolytes in thecathode mixture. The hot-press Li₇P₂S₈I_0.5Cl_0.5 pelletshows excellent lithium compatibility and dendrite suppression capability,achieving stable lithium plating/stripping up to 280 h at 0.1 mA/cm².The corresponding 3Li₂S-LiI/Li₇P₂S₈I_0.5Cl_0.5/Libattery delivers an initial discharge capacity of 474 mAh/g at 0.13 mA/cm² andcapacity retention of 83% after 30 cycles. This work provides a promisingstrategy to explore sulfide electrolytes enabling solid-state Li-Metal battery.