Li₂S Cathode Mediated by Diphenyl Chalcogenides in All-Solid-State Batteries

Lithium sulfide (Li₂S), as one of the critical cathodes in all-solid-state batteries, shows promising potential. However, its ion and electron blocking characteristics necessitate a high charge overpotential for activation, which can result in the decomposition of sulfide-based solid-state electrolytes. In this study, diphenyl chalcogenides are applied as redox mediators to reduce the initial charge voltage and improve the utilization of Li₂S in all solid-state lithium-sulfur batteries. Among them, diphenyl ditelluride (DPDTe) enables the highest initial charge capacity (963.1 mAh g^-1) of Li₂S. The Li₂S-DPDTe composite cathode, along with Li₇P₃S₁₁ sulfide electrolyte and In-Li anode, exhibits a low charge voltage of 2.4 V. After 360 cycles, the battery demonstrates an average areal discharge capacity of 0.9 mAh cm^-2 at a current density of 0.2 mA cm^-2 (706.8 mAh g^-1 based on the mass of Li₂S). This study aims to use diphenyl chalcogenides as mediators to lower the initial overpotential of Li₂S, thereby aligning with the narrow electrochemical window of sulfide electrolytes and providing valuable insights for high-energy-density all-solid-state batteries.