Achieving capacity-stability balance in silicon anodes through electrochemo-mechanical regulation

Silicon (Si) anodes offer a compelling route toward high-energy-density all-solid-state batteries (ASSBs), yet their deployment is severely constrained by chemomechanical degradation arising from large volume change of Si during cycling. Although external stack pressure is widely used to mitigate such degradation, how pressure requirement depends on electrochemical operating conditions remains poorly understood. Here, we systematically investigate the coupled roles of current density and stack pressure in regulating the structural integrity and cycling stability of Si-based ASSBs. Electrochemical testing, quasi-in-situ impedance spectroscopy, and X-ray computed tomography reveal a counterintuitive trend: A lower current density demands substantially higher stack pressure to suppress severe cracking and interfacial degradation, owing to deeper Si utilization and larger volume strain. We develop a mechanistic framework that captures two dominant failure modes (interfacial debonding and vertical channel cracking) and quantitatively links their evolution to accessible capacity and applied pressure. Leveraging this understanding, we demonstrate a current-dependent pressure regulation strategy that dynamically adjusts stack pressure during cycling, achieving high cycling stability while significantly reducing the required operating pressure. This work establishes a design principle for synchronizing electrochemical loading and mechanical loading, providing a practical pathway toward durable Si-based ASSBs.