Isoreticular Regulation of TwoDimensional Redox-Active Covalent Organic Framework Cathodes for Enhanced Lithium-Ion Storage

A challenge facing scientists is the rational synthesis of highly crystalline covalent organic frameworks (COFs), consisting of both n -type and p -type redox-active units, as cathodes for high-performance lithium -ion batteries (LIBs). Herein, we apply reticular chemistry to regulate a COF platform with the kgm topology via an in -situ postsynthetic oxidation strategy. We integrate both n -type and p -type redox-active units into a resulting COF skeleton- TPDA-DQTA-COF, and this COF-based cathode shows an enhanced performance for LIBs compared to the parent TPDA-DMTA-COF. On account of dual redox-active units for PF6-/Li+ costorage, the TPDADQTA-COF cathode presents the highly reversible capacity of 308 mAh g-1 at 0.2 A g-1 and the high energy density of 800 Wh kg-1. The long-term cycling experiment reveals a capacity retention of 91% after 200 cycles at a low current density of 0.5 A g-1. The combined Fourier transform infrared and X-ray photoelectron spectroscopy experiments suggest that the in -situ electrochemical oxidation from the C -OH to the C=O group of COFs occurs during the charging process. We believe our study demonstrates that the atomic -level modification of functional groups in COF-based cathode materials has a significant impact on the macroscopic performance of lithium -ion storage, clearly illustrating the structure -property relationship.