A solubility limited pyrene-4,5,9,10-tetraone-based covalent organic framework for high-performance aqueous zinc-organic batteries

Pyrene-4,5,9,10-tetraone (PTO), with a high theoretical capacity of 408 mAh·g−1, is a promising candidate for rechargeable aqueous zinc-ion batteries (RAZIBs), but its zincated products during discharge process suffer from high solubility in electrolytes. Herein, a β-ketoenamine-linked two-dimensional (2D) covalent organic framework (COF) based on a 2,7-diaminopyrene-4,5,9,10-tetraone (4KT-BD) monomer and a 2,4,6-trihydroxy-benzene-1,3,5-tricarbaldehyde (Tp) node (4KT-Tp-COF) is synthesized to address the above issue. The well-designed 4KT-Tp-COF displays low solubility in 3 M Zn(CF3SO3)2 owing to the favorable π–π stacking as well as extended structure. Besides, the ingenious structural design of the active molecule and the long-range ordered nano-channels alter the intramolecular electron distribution, which facilitates the ionic diffusion. Consequently, the 4KT-Tp-COF cathode exhibits a stable capacity of 181 mAh·g−1 at 0.2 A·g−1, superior rate capability of 139 mAh·g−1 at 20 A·g−1, and a long lifetime of 1000 cycles without capacity loss at 30 A·g−1. Even at a low temperature of −20 °C, the electrode also performs an ultralong cycling life of 9000 cycles with a capacity of 106 mAh·g−1 at 5 A·g−1. The comprehensive characterizations of ex-situ analyses together with the theoretical calculations validate that the groups of C=O can contribute highly accessible redox-active sites for Zn2+ storage. The ultra-stable 4KT-Tp-COF cathode provides important insights for designing robust organic electrodes for sustainable and large-scale electrochemical energy storage.