Exfoliation of Covalent Organic Frameworks into Few-Layer Redox-Active Nanosheets as Cathode Materials for Lithium-Ion Batteries.

Covalent organic frameworks (COFs) have attracted growing interest by virtue of their structural diversity and tunability. Herein, we present a novel approach for the development of organic rechargeable battery cathodes in which three distinct redox-active COFs were successfully prepared and delaminated into 2D few-layer nanosheets. Compared with the pristine COFs, the exfoliated COFs with shorter Li+ diffusion pathways allow a significant higher utilization efficiency of redox sites and faster kinetics for lithium storage. Unlike diffusion-controlled manners in the bulk COFs, the redox reactions in ECOFs are mainly dominated by charge transfer process. The capacity and potential are further engineered by reticular design of COFs without altering the underlying topology. Specifically, DAAQ-ECOF exhibits excellent rechargeability (98% capacity retention after 1800 cycles) and fast charge-discharge ability (74% retention at 500 mA g-1 as compared to at 20 mA g-1). DABQ-ECOF shows a specific capacity of 210 mA h g-1 and a voltage plateau of 2.8 V.