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

High ionic conductivity and excellent lithium compatibility for sulfide solid electrolytes are vital to developing solid-state Li-metal batteries with high energy density and safety. Li7P2S8I has attracted significant attention due to its low cost, good stability towards lithium metal, and low annealing temperature. However, the low conductivity compared to liquid electrolyte and poor stability with Li metal at high current density limits its applications in solid-state batteries. In this work, the conductivity of Li7P2S8I is first increased from 1.53 mS/cm to 3.08 mS/cm by Cl- doping. The enhanced ionic conductivity is due to the introduction of S2-/Cl-/I- disorder structure in the structure. Then, the Li-ion conductivity of Li7P2S8I0.5Cl0.5 is enhanced up to 6.67 mS/cm via optimizing the pellet-making pressures and temperatures with the hot-press technique. Because of the superior conductivity, the assembled Li2S-LiI/Li7P2S8I0.5Cl0.5/Li-In battery 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 of the Li7P2S8I0.5Cl0.5 electrolyte in cathode mixture are unraveled, which shows reversible charge/discharge more than 80 cycles and confirms the extra capacity from the electrolytes in the cathode mixture. The hot-press Li7P2S8I0.5Cl0.5 pellet shows 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/Li7P2S8I0.5Cl0.5/Li battery delivers an initial discharge capacity of 474 mAh/g at 0.13 mA/cm2 and capacity retention of 83% after 30 cycles. This work provides a promising strategy to explore sulfide electrolytes enabling solid-state Li-Metal battery.