Uncover the mystery of high-performance aqueous zinc-ion batteries constructed by oxygen-doped vanadium nitride cathode: Cationic conversion reaction works

Vanadium-based cathodes for zinc-ion batteries (ZIBs) hold a great promise for next-generation energy storage systems due to their amazing diversity, relatively high capacity and excellent stability. Unfortunately, the specific capacity of current vanadium-based electrodes is intrinsically limited by zinc site density in crystal structures, probably attributing to the ignore of exception energy storage mechanism in cationic insertion/extraction. Herein, a new energy storage mechanism in the vanadium oxide-based ZIB system via cationic conversion reactions was demonstrated for the first time. At the force of electric and weak acid conditions, the oxygen-doped vanadium nitride (O-VN) cathode was firstly electrochemically oxidized into vanadium oxide and vanadium cations via in-situ activation; the cations would be reduced to V₂O₃ that depositing on the surface of the electrode in the discharge process; and subsequently the V (III) species could be oxidized back to the cations dissolving into electrolyte upon charging. First-principle density functional theory (DFT) calculations confirm the reversible characteristics of these reactions. Owing to these cationic conversion reactions together with contributions from zinc ion de/intercalation, the O-doped VN cathode delivered an ultrahigh discharge capacity of 705 mAh g⁻¹ at 0.2 A g⁻¹. This work continues to develop the energy storage mechanism of vanadium-based cathode and reveals the arrival of a new era for high-capacity ZIBs.