High‐Performance Li–SeSx All‐Solid‐State Lithium Batteries

All-solid-state Li-S batteries are promising candidates for next-generation energy-storage systems considering their high energy density and high safety. However, their development is hindered by the sluggish electrochemical kinetics and low S utilization due to high interfacial resistance and the electronic insulating nature of S. Herein, Se is introduced into S cathodes by forming SeS_x solid solutions to modify the electronic and ionic conductivities and ultimately enhance cathode utilization in all-solid-state lithium batteries (ASSLBs). Theoretical calculations confirm the redistribution of electron densities after introducing Se. The interfacial ionic conductivities of all achieved SeS_x -Li₃ PS₄ (x = 3, 2, 1, and 0.33) composites are 10^-6 S cm^-1 . Stable and highly reversible SeS_x cathodes for sulfide-based ASSLBs can be developed. Surprisingly, the SeS₂ /Li₁₀ GeP₂ S₁₂ -Li₃ PS₄ /Li solid-state cells exhibit excellent performance and deliver a high capacity over 1100 mAh g^-1 (98.5% of its theoretical capacity) at 50 mA g^-1 and remained highly stable for 100 cycles. Moreover, high loading cells can achieve high areal capacities up to 12.6 mAh cm^-2 . This research deepens the understanding of Se-S solid solution chemistry in ASSLB systems and offers a new strategy to achieve high-performance S-based cathodes for application in ASSLBs.