Joint cationic and anionic redox chemistry in a vanadium oxide cathode for zinc batteries achieving high energy density

Abstract

Rechargeable aqueous zinc batteries are promising for large-scale energy storage due to their low cost and high safety; however, their energy density has reached the ceiling based on conventional cathodes with a single cationic redox reaction mechanism. Herein, a highly reversible cathode of typical layered vanadium oxide is reported, which operates on both the cationic redox couple of V⁵⁺/V³⁺ accompanied by the Zn²⁺ storage and the anionic O^–/O^2– redox couple by anion hosting in an aqueous deep eutectic solvent electrolyte. The reversible oxygen redox delivers an additional capacity of ∼100 mAh g^–1 at an operating voltage of ∼1.80 V, which increases the energy density of the cathode by ∼36%, endowing the cathode system a record high energy density of ∼506 Wh kg^–1. The findings highlight new opportunities for the design of high-energy zinc batteries with both Zn²⁺ and anions as charge carriers.