Oxygen-deficient ammonium vanadate/GO composites with suppressed vanadium dissolution for ultra-stable high-rate aqueous zinc-ion batteries

The structural engineering of hydrated ammonium vanadate as a cathode for aqueous Zn-ion batteries has attracted significant research interest because of its ability to suppress vanadium dissolution and accelerate the electrochemical dynamics. Herein, a feasible fabrication strategy for oxygen-deficient (NH₄)₂V₁₀O₂₅·xH₂O/GO (NVOH@GO) composites was proposed, and the charge storage mechanism was discussed. The results of characterization analysis showed that the introduction of graphene oxide (GO) not only enlarged the layer spacing and improved electrical conductivity, providing spacious channels for Zn²⁺ (de)intercalation and accelerating the ion diffusion dynamics, but also induced more oxygen vacancies, inhibited the dissolution of vanadium, and reduced self-discharging, offering additional and stable active sites for ion storage. The optimized NVOH@GO electrode delivered extraordinarily stable capacities of 334 mAh·g⁻¹ after 2000 cycles at 5 A·g⁻¹ and 238 mAh·g⁻¹ after 10,000 cycles at 20 A·g⁻¹. Furthermore, ex-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman results systematically revealed the electrochemical mechanism, including a phase transition reaction and subsequent Zn²⁺/H₂O co-(de)intercalation process. This study provides an effective strategy for expanding the interlayer spacing, inducing defect engineering, and enhancing the structural stability of vanadium-based cathodes for Zn-ion batteries and other multivalent aqueous ion batteries.