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

Abstract 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 Li 2 S‐Li x In 2 S 3 cathode is designed whereby In 2 S 3 reacts with Li 2 S under high‐energy ball milling. In situ electron diffraction and ex situ XPS are implanted to probe the reaction mechanism of Li 2 S‐Li x In 2 S 3 in ASSLSBs. The results indicate that Li x In 2 S 3 serves as a mobility mediator for both charge‐carriers (Li + and e − ) and redox mediator for Li 2 S 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 Li 2 S‐Li x In 2 S 3 cathode delivers an initial areal capacity of 3.47 mAh cm −2 at 4.0 mg Li2S cm −2 with 78% utilization of Li 2 S. A solid‐state cell with Li 2 S‐Li x In 2 S 3 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, Li 2 S‐Li x In 2 S 3 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.