“Win-Win” Modification of LiCoO2 Enables Stable and Long-Life Cycling of Sulfide-Based All Solid-State Batteries

Graphical Simultaneous surface coating with Li 2 TiO 3 /Li(TiMg) 1/2 O 2 and bulk Mg-doping for LiCoO 2 is proposed to achieve long-life Li 10 GeP 2 S 12 -based ASSLBs. The Li 2 TiO 3 /Li(MgTi) 1/2 O 2 coating layers effectively suppress the interface side reactions and the space charge layer effect. The gradient Mg doping stabilizes the lattice structure of LiCoO 2 under local overcharging. Interfacial side reactions and space charge layers between the oxide cathode material and the sulfide solid-state electrolytes (SSEs), along with the structural degradation of the active material, significantly compromise the electrochemical performance of all-solid-state batteries (ASSLBs). Surface coating and bulk doping of the cathodes are considered the most effective approaches to mitigate the interface issues between the cathode and SSEs and enhance the structural integrity of composite cathodes. Here, a one-step low-cost means is ingeniously designed to modify LiCoO 2 (LCO) with heterogeneous Li 2 TiO 3 /Li(TiMg) 1/2 O 2 surface coating and bulk gradient Mg doping. When applied in Li 10 GeP 2 S 12 -based ASSLBs, the Li 2 TiO 3 and Li(TiMg) 1/2 O 2 coating layers effectively suppress interfacial side reactions and weaken space charge layer effect. Furthermore, gradient Mg doping stabilizes the bulk structure to mitigate the formation of spinel-like phases during local overcharging caused by solid-solid contact. The modified LCO cathodes exhibit excellent cycle performance with a capacity retention of 80 % after 870 cycles. This dual-functional strategy provides the possibility for large-scale commercial implementation of cathodes modification in sulfide based ASSLBs in the future.