Comprehensive Si Anode Design for Sulfide‐Based all‐Solid‐State Batteries: Insights into Si‐Electrolyte Synergy for Mitigating Contact Loss

Abstract All‐solid‐state batteries (ASSBs) are emerging as a promising alternative to conventional lithium‐ion batteries, offering improved safety and potential for energy density. However, the substantial volume fluctuations of high‐capacity anodes such as lithium and silicon induce interfacial degradation, impeding practical applications. Herein, an aluminum–silicon (Al–Si) alloy anode is introduced that effectively mitigates these challenges by stabilizing volume variation after initial volume expansion and maintaining stable interfacial integrity with the solid electrolyte (SE). By employing a SE‐free wet anode and leveraging advanced characterization techniques, including three‐dimensional X‐ray nanoimaging and digital twin‐based particle‐to‐electrode volume expansion simulations, the structural evolution and electrochemical behavior of Al–Si are elucidated. Furthermore, the integration of an elastic‐recoverable anolyte enables the formation of a robust Al–Si composite anode, effectively suppressing contact loss and enhancing reversibility. ASSBs integrating this Al–Si composite anode and a high‐areal‐capacity LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode (6 mAh·cm ⁻² ) achieve a capacity retention of 81.6% after 300 cycles, offering a viable pathway toward high‐energy‐density and durable ASSBs.