Unveiling the size-dependent electro-chemo-mechanical failure mechanisms of silicon anodes in sulfide-based all-solid-state batteries

High-capacity silicon anodes hold great promise for safe and energy-dense all-solid-state lithium batteries (ASSLBs), yet their practical application is hindered by interfacial degradation and mechanical fracture, which severely limit their cycle life. Herein, we unravel the particle-size-dependent electro-chemo-mechanical failure mechanisms of Si anodes in sulfide-based ASSLBs. The micro-sized Si (μm-Si) anode exhibits favorable initial Coulombic efficiency (ICE, 79.15%) and reversible capacity (2260.5 mAh g⁻¹) but succumbs to progressive particle fracture under prolonged cycling due to cumulative mechanical stress from large volume swings. By contrast, the nano-sized Si (nm-Si) anode suffers from severe interfacial side reactions and irreversible volume expansion due to its larger specific area and dense electrode structure, resulting in lower initial performance (ICE of 72.21%, 1372.7 mAh g⁻¹). In subsequent cycles, the nm-Si anode experiences continuous interfacial side reactions, leading to substantial accumulation of interfacial decomposition byproducts and sustained capacity decay. These contrasting failure pathways establish electro-chemo-mechanical coupling as the governing principle and provide a particle-size-dependent design framework for high-performance Si-based ASSLBs.