Transition-Metal Sulfides for High-Performance Lithium Sulfide Cathodes in All-Solid-State Lithium–Sulfur Batteries

All-solid-state lithium-sulfur batteries (ASLSBs) have been attracting attention as next-generation batteries because of their high theoretical energy density, which exceeds that of traditional lithium-ion batteries. However, the performance of ASLSBs is limited by the sluggish redox reaction kinetics of lithium sulfide (Li₂S) and S₈ cathodes and the electrochemical degradation of cathode materials and solid electrolytes during cycling. Herein, we report a cathode design consisting of Li₂S and transition-metal sulfides. This cathode design enhances the redox reaction kinetics of the cathode and suppresses interfacial degradation between the cathodes and solid electrolytes in the composite cathodes. The interface design uses titanium disulfide, molybdenum sulfide (MoS₂), and tungsten sulfide to facilitate redox reaction kinetics, which improves the practical performance of ASLSBs. Among the composite cathodes examined in this work, the Li₂S-MoS₂ composite cathode exhibited the highest discharge capacity of 661 mA h g^-1 (2.09 mA h cm^-2) after 100 cycles. Electrochemical impedance analysis demonstrated that transition-metal sulfides, particularly MoS₂, suppressed the increase in resistance through cycling of the composite cathodes. This finding suggests that transition-metal sulfides in Li₂S composite cathodes multifunction as redox mediators and buffer layers, improving practical battery performance. Therefore, the electrode design offered in this study enhances the electrochemical utilization and long-term stability of ASLSBs.