2D sp2-carbon-linked covalent organic frameworks as artificial SEI film for dendrite-free lithium metal batteries

Li metal batteries (LMBs) have been widely studied due to the unprecedented theoretical specific capacity and ultralow redox potential of Li metal anode (LMA). Nevertheless, out-of-control growth of lithium dendrite and fragile solid-electrolyte interphase (SEI) seriously limit their practical applications. Herein, 2D sp2-carbon-linked covalent organic framework (sp2c-COF) is prepared and constructed as artificial SEI film on the surface of LMA for impeding the formation of Li dendrite and regulating the interface stability. The sp2c-COF is designed to be fully π-conjugated along both the x and y orientations with high conductivity, which can reduce interface impedance and facilitate the uniform distribution of Li+ flux. Consequently, the sp2c-COF-modified symmetric batteries exhibit high Li+ transference number (tLi+) of 0.85, excellent cycle life (4000 h) and extremely low over-potential (10 mV) at a current density of 5 mA cm−2 with 5 mA h cm−2. Meanwhile, the Li deposition behavior is analyzed by in-situ light microscopy, indicating sp2c-COF significantly enhances interfacial stability of LMA. This strategy possesses potential value for restraining Li dendrite formation and promoting the progress of COF artificial SEI film.