In Operando Synchrotron Studies of NH₄⁺ Preintercalated V₂O₅·nH₂O Nanobelts as the Cathode Material for Aqueous Rechargeable Zinc Batteries

NH₄⁺ preintercalated V₂O₅·nH₂O nanobelts with a large interlayer distance of 10.9 Å were prepared by the hydrothermal method. The material showed a large specific capacity of 391 mA·h·g^–1 at the 500 mA·g^–1 current density in aqueous rechargeable zinc batteries. In operando synchrotron X-ray diffraction demonstrated that the material experienced reversible solid–solution reaction and two-phase transition during charge–discharge cycling, accompanied by the reversible formation/decomposition of a ZnSO₄Zn₃(OH)₆·5H₂O byproduct. In operando X-ray absorption spectroscopy confirmed the reversible reduction/oxidation of V, together with small changes in the VO₆ local structure. The formation of byproduct was attributed to the dehydration of [Zn­(H₂O)₆]²⁺, which concurrently improved the desolvation of [Zn­(H₂O)₆]²⁺ into Zn²⁺. Bond valence sum map analysis and electrochemical impedance spectroscopy demonstrated that the byproduct improved the charge transfer kinetics of the electrode. Cyclic voltammetry and galvanostatic intermittent titration technique showed that the electrode reaction was dominated by ionic intercalation where the discharge capacity in the voltage window of 1.4–0.85 V was attributed to the intercalation of [Zn­(H₂O)₆]²⁺, followed by the intercalation of Zn²⁺ at 0.85–0.4 V.