Yaqin Wu, Jialin Lin, Shaozhen Huang, Zian Wang, Yiman Xie, Shaofei Wu, Yingchun Xia, C L Zhang, Le Chen, Liangjun Zhou, Weifeng Wei
ABSTRACT Alkali metal anodes are promising for next‐generation high‐energy‐density batteries but are hindered by the lack of scalable fabrication methods for ultrathin foils. Conventional rolling fails for alkali metals due to their weak metallic bonding and high surface energy, which cause interfacial adhesion forces to exceed cohesive strength during processing. This work introduces “adhesion work” as a quantitative indicator linking microscopic surface properties to macroscopic processability and develops a mechanochemical interfacial engineering strategy involving in situ methyltriethoxysilane (MTES) reaction. This constructs a Si─O‐based interphase that transforms strong metal‐roller bonding into weak van der Waals interactions, reducing adhesion work to levels comparable to Cu and Al foils. Ultrathin Li (≤5 µm) and Na (≤25 µm) foils with enhanced mechanical integrity are successfully fabricated. The MTES‐derived surface layer facilitates rapid ion‐transport kinetics and exceptional interfacial stability, enabling outstanding cycling and rate performance in pouch cells. Additionally, ultrathin Na foil serves as an efficient pre‐sodiation agent, boosting the initial coulombic efficiency of sodium‐ion batteries. This work provides a viable approach for scalable production of ultrathin alkali metal foils and supports the development of next‐generation alkali metal batteries.