Packing Dense Redox-Active Centers in Covalent Organic Framework Electrodes for High-Performance Sodium- and Potassium-Ion Batteries: A Review.

Sodium- and potassium-ion batteries (SIBs/PIBs) are compelling alternatives to lithium-ion batteries (LIBs) due to their similar electrochemical mechanisms and the natural abundance of sodium and potassium. However, the larger ionic radii and greater mass of Na+ and K+ ions often result in lower specific capacity, unsatisfactory rate performance, and diminished cycling stability. The advent of covalent organic frameworks (COFs) as electrode materials offers a promising avenue to address these challenges, given their robustness, uniform 1D nanochannels, and high structural designability. This review specifically summarizes the design principles for incorporating such dense redox-active sites into COFs. We explore a diverse range of COFs featuring multiple redox units, including carbonyl (C═O), imine (C═N), and π-extended aromatic electroactive centers, while correlating their structural characteristics with key electrochemical performance metrics such as capacity, kinetics, and cyclability in SIBs and PIBs. Moreover, we place particular emphasis on contributions from our own research group in this advancing field. Finally, we discuss the remaining challenges and propose potential solutions for the continued development of high-capacity COF electrodes for SIB and PIB applications.