In Situ Preparation of Thin and Rigid COF Film on Li Anode as Artificial Solid Electrolyte Interphase Layer Resisting Li Dendrite Puncture

Abstract Metallic Li is considered the most promising anode material for high‐energy density batteries due to its high theoretical capacity and low electrochemical potential. However, commercialization of the Li anode has been hampered by the safety issue associated with Li‐dendrite growth resulting from uneven Li‐ion deposition and an unstable solid electrolyte interphase (SEI). Herein, an in situ prepared 10 nm thin film of covalent organic framework (COF) uniformly covered on the Li anode (COF‐Li) is used as an artificial SEI layer for Li plating/striping stabilization and Li dendrite inhibition. Abundant microcellular structures in the COF can redistribute the Li‐ion flux and lead to the homogeneous plating/stripping process. Meanwhile, the superhard mechanical properties and mechanical behavior during needling of the ultrathin COF film is studied via the digital pulsed force mode equipped in atomic force microscopy, illustrating a high Young's modulus of 6.8 GPa that is strong enough to resist dendrite growth. As a result, stable cycling for 400 h is achieved in the COF‐Li symmetrical cell at a current density of 1 mA cm −2 , and the internal short circuit is effectively blocked by COF‐Li in Li–S batteries.