Mechano‐Electrochemical Healing at the Interphase Between LiNi0.8Co0.1Mn0.1O2 and Li6PS5Cl in All‐Solid‐State Batteries

Abstract Sulfide‐based all‐solid‐state batteries (ASSBs) are emerging as promising alternatives to lithium‐ion batteries due to their high energy density and enhanced safety. However, sulfide solid electrolytes, such as Li 6 PS 5 Cl (LPSCl), face significant chemo‐mechanical challenges at the interface with layered oxide cathodes, including LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). During cycling, oxidative decomposition of LPSCl leads to interfacial void formation and mechanical contact loss, which significantly degrade ionic conduction. Strategies such as coating stable passivation layers have been explored to suppress LPSCl decomposition, but these approaches often involve trade‐offs, including increased cost, complex synthesis, and elevated interfacial resistance. Herein, the concept of mechano‐electrochemical healing at the LPSCl–NCM811 interface is introduced to address these issues. During charging, voids form due to LPSCl decomposition; however, this mechanical contact loss can be reversed through a healing mechanism during discharge at ≈2.2 V (vs Li/Li + ). This process, driven by the lithiation of elemental sulfur − a decomposition product of LPSCl − restores interfacial contact and enhances ionic conduction. Consequently, mechano‐electrochemical healing achieves stable capacity retention over 300 cycles and superior rate capability even under pressure‐free conditions. These findings underscore the potential of electrochemical formation cycling as a practical strategy for improving the mechano‐electrochemical performance of ASSBs.