Extended π-conjugated N-heteroaromatic molecules for fast-charging and high operating voltage aqueous zinc-ion batteries.

Aqueous zinc-ion batteries (AZIBs) with redox-active organic compounds as electrodes attract wide attention due to their structural diversity, sustainability and inherent safety. However, the rational structural design of advanced organic electrodes with high practical capacity, long cycle life and high rate performance is still a great challenge. Herein, a strategy to improve the electrochemical performance of electrodes in AZIBs by constructing an extended π-conjugated hexaazatrinaphthalene (HATN)-based structure with electron-withdrawing cyano groups, 5, 6, 11, 12, 17, 18-hexaazatrinaphthalene-2, 3, 8, 9, 14, 15-hexacarbonitrile (HATN-6CN), is reported. The reduced lowest unoccupied molecular orbital (LUMO) energy level improves the discharge voltage to 0.71 V. Furthermore, HATN-6CN features abundant redox-active sites, solvent resistance and a smaller energy gap, enabling stable and rapid co-storage of H+ and Zn2+. As expected, HATN-6CN electrode achieves a high reversible capacity of 277mAhg-1 at 0.1Ag-1, an excellent rate capability of 94mAhg-1 at 10Ag-1, and a good capacity retention of 65 % after 10,000 cycles at 10 A/g, simultaneously. The ex-situ characterization and theoretical simulation results demonstrate that Zn2+ and H+ cations coordinate synergistically with CN groups and simultaneously reversibly form zinc hydroxide sulfate hydrate. This work affords an appropriate structural design of advanced organic electrodes for AZIBs.