Unveiling Challenges and Opportunities in Silicon‐Based All‐Solid‐State Batteries: Thin‐Film Bonding with Mismatch Strain

Abstract Li‐metal and silicon are potential anode materials in all‐solid‐state Li‐ion batteries (ASSBs) due to high specific capacity. However, both materials form gaps at the interface with solid electrolytes (SEs) during charging/discharging, resulting in increased impedance and uneven current density distribution. In this perspective, the different mechanisms of formation of these gaps are elaborated in detail. For Li‐metal anodes, Li‐ions are repeatedly stripped and unevenly deposited on the surface, leading to gaps and Li dendrite formation, which is an unavoidable electrochemical behavior. For Si‐based anodes, Li‐ions inserting/extracting within the Si‐based electrode causes volume changes and a local separation from the SE, which is a mechanical behavior and avoidable by mitigating the strain mismatch of thin‐film bonding between anode and SE. Si electro–chemical–mechanical behaviors are also described and strategies recommended to synergistically decrease Si‐based electrode strain, including Si materials, Si‐based composites, and electrodes. Last, it is suggested to choose a composite polymer–inorganic SE with favorable elastic properties and high ionic conductivity and form it directly on the Si‐based electrode, beneficial for increasing SE strain to accommodate stack pressure and the stability of the interface. Thus, this perspective sheds light on the development and application of Si‐based ASSBs.