Lithiophilic Aromatic Sites and Porosity of COFs for a Stable Lithium Metal Anode

The effective protection of a lithium metal anode is an important precondition to ensure the safety of the lithium metal battery. Herein, we found that aromatic functional groups in covalent organic frameworks (COFs), as a class of lithiophilic sites in COFs, with the evenly arranged channels of COFs, can provide a guarantee for the uniform transport of lithium ions on the surface of a lithium metal anode. When PA-COF is used as the separator coating to face the lithium metal anode, the lithiophilic aromatic sites can interact with the lithium ions in the electrolyte, reduce the solvation of lithium ions, and induce the uniform and rapid conduction of lithium ions in the PA-COF coating, thus protecting the lithium metal anode. In the Li–Li symmetrical cell with the PA-COF as the separator coating, the lithium ions can still be uniformly deposited and stripped even at the current density of 20 mA/cm2. What’s more, this excellent lithium metal protective layer cooperated with the TiO2 nanoparticles’ coating on both sides of the separator to make a Janus separator for high-performance Li-SeS2 and Li-S batteries with an ultralong cycling life.