Stack Pressure Enhanced Size Threshold of Si Anode Fracture in All‐Solid‐State Batteries

Silicon (Si) has long captured the spotlight as an anode candidate for lithium‐ion batteries (LIBs) due to its exceptionally high theoretical capacity and abundant availability. However, chemomechanical failure of larger‐sized Si has plagued its electrochemical performance. Herein the presence of a stack pressure‐dependent size effect of Si particles in sulfide‐based all‐solid‐state batteries (ASSBs) is unveiled that can be harnessed to overcome the chemomechanical failure of Si. Remarkably, the application of stack pressure, necessary to enhance interface contact and charge transfer in ASSBs, shifts the size threshold from nanometer scale observed in liquid electrolyte batteries to the microscale in ASSBs. The essence of the stack pressure‐dependent size effect is the suppression of the Hoop stress that causes the fracture of Si particles during lithiation by the applied external stress. This revelation offers an effective strategy to optimize the size of Si for the desired electrochemical performance in ASSBs. These findings provide invaluable insights that offer indispensable guidance for mitigating Si anode failure in ASSBs, ultimately advancing the next‐generation high‐performance Si‐based ASSBs.