Stacking‐Sequence‐Dependent Performance and Interfacial Failure Mechanisms of Bilayer Alloy Anodes in All‐Solid‐State Batteries

Alloy‐based anodes featuring high capacity and moderate operating potentials hold great promise for high‐energy‐density all‐solid‐state batteries (ASSBs). However, the significant volume fluctuations during cycling often lead to solid–solid interfacial failure, compromising reversibility and cycling stability. Multilevel architectural designs of composite alloy anodes have proven effective in enhancing electronic conductivity, ion transport, and interfacial stability. Herein, the influence of stacking sequence on the structural evolution and electrochemical performance of electrodes composed of silicon (Si) and aluminum (Al) is investigated. The results reveal that the plastic deformability of the upper layer active material (directly interfacing with the solid‐state electrolyte) and its electrochemical potential window critically influence the reversibility, rate capability, and failure mechanism of the composite anode. Notably, when Si is employed as the upper layer, the anode delivers an initial Coulombic efficiency of 87.3% at 0.25 mA cm −2 , significantly exceeding that of the Al‐upper configuration (59.3%). These results provide mechanistic understanding for the rational design of composite alloy anodes, highlighting the importance of component stacking for mitigating kinetic limitations and enhancing the performance of ASSBs.