Active Regulation Volume Change of Micrometer-Size Li₂S Cathode with High Materials Utilization for All-Solid-State Li/S Batteries through an Interfacial Redox Mediator

Low electronic and ionic transport, limited cathode active material utilization, and significant volume change have pledged the practical application of all-solid-state Li/S batteries (ASSLSBs). Herein, an unprecedented Li₂S-Li_xIn₂S₃ cathode is designed whereby In₂S₃ reacts with Li₂S under high-energy ball milling. In situ electron diffraction and ex situ XPS are implanted to probe the reaction mechanism of Li₂S-Li_xIn₂S₃ in ASSLSBs. The results indicate that Li_xIn₂S₃ serves as a mobility mediator for both charge-carriers (Li⁺ and e⁻) and redox mediator for Li₂S activation, ensuring efficient electronic and ionic transportation at the cathode interface and inhibiting ≈ 70% relative volumetric change in the cathode, as confirmed by in situ TEM. Thus, the Li₂S-Li_xIn₂S₃ cathode delivers an initial areal capacity of 3.47 mAh cm⁻² at 4.0 mg_Li2S cm⁻² with 78% utilization of Li₂S. A solid-state cell with Li₂S-Li_xIn₂S₃ cathode carries 82.35% capacity retention over 200 cycles at 0.192 mA cm⁻² and a remarkable rate capability up to 0.64 mA cm⁻² at RT. Besides, Li₂S-Li_xIn₂S₃ exhibits the highest initial areal capacity of 4.08 mAh cm⁻² with ≈74.01% capacity retention over 50 cycles versus 6.6 mg_Li2S cm⁻² at 0.192 mA cm⁻² at RT. The proposed strategy of the redox mediator minimized volumetric change and realized outstanding electrochemical performance for ASSLSBs.