Redox‐Active Covalent Organic Framework Nanosheets with Large Interlayer Spacing Anchored on Graphene for High‐Performance Potassium‐Ion Batteries

Abstract Covalent organic frameworks (COFs) are gaining increasing attention as renewable electrode materials for advanced potassium‐ion batteries. The main challenge for 2D COFs anodes lies in their insufficient rate capability and cycle life, which stem from the limited interlayer spacing of the π‐stacking structure that is incompatible with large‐radius K + ions, together with the high electron/ion diffusion barriers. Herein, a novel hydrazone‐linked COF composite (HT‐COF@G) is fabricated from a new module of 2,3,8,9,14,15‐hexa(4‐hydrazidocarbonylphenyl)hexaazatrinaphthalene with 2,4,6‐tris(4‐formylphenyl)‐1,3,5‐triazine linker on graphene support. Physical and structural characterization reveals the preeminent electric conductivity (12.53 S m −1 ), well‐defined mesopores (2.40 nm), and particularly large interlayer spacing (0.46 nm) of HT‐COF@G, facilitating the efficient K + /e − transport and storage. Atomic force microscopy images confirm the formation of ultrathin HT‐COF@G nanosheets (≈3.6 nm), significantly reducing the K + transport distance. These features, in combination with the various redox active sites for storing K + ions, result in a record‐high reversible capacity (534 mA h g −1 at 0.2 A g −1 ), impressive rate performance (133 mA h g −1 at 10 A g −1 ), and extraordinary cycling stability (261.9 mA h g −1 at 5 A g −1 with 100% retention up to 5000 cycles) for HT‐COF@G among organic electrodes.