Ionic covalent organic frameworks triggered efficient synergy: Li+ de-solvation and the formation of LiF-rich interphase

The parasitic side reaction between the electrolyte and the lithium metal (Li0) forms an unstable heterogeneous interphase, causing the poor reversibility of Li plating/stripping. The rational design of protection layer on Li0 anode is imperative to inhibit side reactions and achieve fast Li + transport on the Li0/electrolyte interface. Herein, by firstly coordinating the bis(fluorosulfonyl)imide anion (FSI−) to the protection layer, a layer consisting of 2D ionic vinylene-linked covalent organic frameworks (ivCOF-FSI) is proposed to stabilize the Li0/electrolyte interface. As demonstrated theoretically and experimentally, the triazine group in the cationic framework is identified to promote Li+ de-solvation process while partial FSI− prefers to form LiF-rich interphase. Attributed to these superiorities, the ivCOF-FSI layer endows the Li0/electrolyte interface with high reversibility in carbonate-based electrolytes by simultaneously suppressing the side effect and achieving rapid Li+ transfer. Combined with the high stability of solid-liquid interface, the LiFePO4 full cells with ivCOF-FSI/Li anode display enhanced cyclability under a high cathode loading of 9.4 mg cm−2 and a low negative/positive capacity ratio of 5. This work provides a novel route for stabilizing the interfacial chemistry of solid-liquid interface, aiming to pave the way for the next-generation high-energy-density batteries.