Stabilizing Li-Metal Electrode via Anion-Induced Desolvation in a Covalent Organic Framework Separator

Abstract

Although Li-metal batteries have been widely used as high-capacity batteries, they are highly susceptible to electrolytes that lead to dendritic or dead Li growth, which significantly reduces the stability of Li-metal electrodes. Herein, we report an anionic covalent organic framework (sulfonate COF: Bd-COF) as a Li⁺-solvate dissociator that strips solvent molecules from encapsulated Li⁺ to stabilize Li-metal electrodes. The homogeneous and dense ionic COF separator was prepared using a template-assisted interface in-suit polymerization engineering. Notably, the well-developed anionic groups within the COF channels could as counter-charge ligands to Li⁺, that adsorb Li⁺-solvates and induce their partial desolvation. Meanwhile, the ordered anionic groups on the surface of COF pores provide continuous ion channels for Li⁺ migration, facilitating the removal of solvent molecules from Li⁺-solvated species. Combined with the dense nanoporous feature, the COF membrane was found to be effective in suppressing Li-dendrites and parasitic reactions. The Bd-COF/Celgard membrane realizes uniform Li deposition on Li-metal electrodes, exhibiting excellent cycling performance in Li-symmetric batteries and high-voltage Li-metal batteries with LiNi_0.6Mn_0.2Co_0.2O₂ cathodes, showcasing the application prospects of ion-conductive covalent organic frameworks in lithium battery separators.