Graphene-supported covalent organic framework nanosheets for high performance aqueous dual-ion batteries

In situ growth of covalent organic framework (COF) nanosheets on substrates like graphene and carbon nanotubes usually leads to significantly enhanced conductivity but is often accompanied by an obvious reduction in crystallinity, thus resulting in non-ideal electrochemical performance. Herein, the hydrothermal condensation of two molecules with aromatic conjugated structures, triphenylene-2,3,6,7,10,11-hexacarboxylic acid (HATNCA) and 1,3,5-tris(4-aminophenyl) triazine (TAPT), on graphene affords a series of graphene-supported 2D COF nanosheets, HT-COF-XGs (X = 10, 20, and 30 wt% of graphene), with controllable thicknesses of 30, 11, and 7 layers. Powder X-ray diffraction (PXRD) analysis reveals the excellent crystalline nature of the nanosheets and further characterization shows that this COF has good conductivity and a large pore size of 2.0 nm, which enable fast and stable electron/ion transport. These properties, in combination with the fully exposed abundant active sites for storing Zn²⁺ ions and anchoring polyiodides, endow these graphene-supported COF nanosheets, in particular HT-COF-20%G, with the best aqueous dual-ion battery (ADIBs) performance to date with a high reversible capacity of 792 mAh g^-1 at 2 A g^-1 and good cycling stability of 83% capacity retention at 20 A g^-1 after 8000 cycles.