Achieving High‐Voltage and High‐Capacity Aqueous Rechargeable Zinc Ion Battery by Incorporating Two‐Species Redox Reaction

Abstract Herein, a two‐species redox reaction of Co(II)/Co(III) and Fe(II)/Fe(III) incorporated in cobalt hexacyanoferrate (CoFe(CN)6) is proposed as a breakthrough to achieve jointly high‐capacity and high‐voltage aqueous Zn‐ion battery. The Zn/CoFe(CN)6 battery provides a highly operational voltage plateau of 1.75 V (vs metallic Zn) and a high capacity of 173.4 mAh g−1 at current density of 0.3 A g−1, taking advantage of the two‐species redox reaction of Co(II)/Co(III) and Fe(II)/Fe(III) couples. Even under extremely fast charge/discharge rate of 6 A g−1, the battery delivers a sufficiently high discharge capacity of 109.5 mAh g−1 with its 3D opened structure framework. This is the highest capacity delivered among all the batteries using Prussian blue analogs (PBAs) cathode up to now. Furthermore, Zn/CoFe(CN)6 battery achieves an excellent cycling performance of 2200 cycles without any capacity decay at coulombic efficiency of nearly 100%. One further step, a sol–gel transition strategy for hydrogel electrolyte is developed to construct high‐performance flexible cable‐type battery. With the strategy, the active materials can adequately contact with electrolyte, resulting in improved electrochemical performance (≈18.73% capacity increase) and mechanical robustness of the solid‐state device. It is believed that this study optimizes electrodes by incorporating multi redox reaction species for high‐voltage and high‐capacity batteries.