Long Cycle Stability of All‐Solid‐State Lithium‐Sulfur Batteries at Low Pressure and Ambient Temperature: Addressing Contact and Diffusion Kinetics

Abstract The commercialization of all‐solid‐state lithium‐sulfur batteries (ASSLSBs) depends on maintaining high performance under low stack pressure. However, conventional ASSLSBs experience significant performance degradation under low pressure due to contact losses and diffusion kinetics challenges at solid‐solid triphase interfaces. This study decouples electrochemical contact area (ECA) losses from diffusion kinetics losses for the first time through a series of pressure‐dependent electrochemical tests. Additionally, the cathode volume changes are investigated using an isolated real‐time displacement test. Findings reveal that contact losses primarily occur during charging, while diffusion kinetics are more sensitive to reduced stack pressure during discharging. To mitigate this issue, metallic indium (In) is incorporated into cathode composites to enhance the triphase interfaces. During cycling, In spheres transform in situ into In 2 S 3 /InS, significantly reducing volume fluctuations and improving ECA retention and diffusion kinetics under various pressures (0.5–7 MPa). As a result, ASSLSBs with In additive demonstrate markedly enhanced electrochemical performance under low stack pressure at room temperature, achieving 810 mAh g −1 at 1 MPa and 1198 mAh g −1 at 7 MPa, (0.1C, 28 °C). The work provides revolutionary insights for the development of high‐energy ASSLSBs and other systems suffering large volume changes.