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

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.