Unlocking Anionic Redox by Breaking Metal–Oxygen Bonds in Aqueous Zinc Batteries

Aqueous Zn-ion batteries (ZIBs) have attracted great attention owing to their application potential for large-scale energy storage. However, their energy storage mechanisms are complicated and debatable. The reported mechanisms are mainly based on cationic redox. The reversible redox of an anion, especially nonbonding oxygen, has seldom been proposed in aqueous ZIBs. Herein, an electrochemical oxidation strategy was developed to achieve the reversible redox of nonbonding oxygen in a binary metal oxide (MnV2O6·2H2O) cathode. The electrochemical oxidation induces the fracture of the O–V bonds from Mn–O–V units, thus leading to the formation of highly active nonbonding O 2p. The redox of nonbonding O 2p and Mn ion in a MnV2O6·2H2O cathode delivers a capacity of 258 mAh g–1. Furthermore, there is no obvious capacity decay after 800 cycles, indicating the high redox reversibility of nonbonding O 2p. This work offers a new chemistry concept for aqueous ZIBs.