Zn2+ doped hydrated vanadium oxide as cathode: Unravelling storage mechanisms for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have attracted considerable interest owing to their low cost, inherent safety, structural stability, and low electrochemical potential. Among vanadium-based materials, V₂O₅ is widely used as a cathode material for AZIBs. However, challenges such as structural collapse and dissolution limit its cycling stability. In this work, commercial V₂O₅ is exfoliated and subsequently Zn²⁺ is doped by hydrothermal to obtain Zn_0.34V₂O₅·2.5H₂O (ZnVOH). When used as the cathode, the ZnVOH electrode exhibits a specific capacity of 183.5mAh g⁻¹ after 5000 cycles at 5 A g⁻¹. Combined with a series of ex-situ characterizations, the Zn²⁺ storage mechanism is concluded to be that ZnVOH undergoes Zn²⁺/H₂O/H⁺ co-intercalation reaction during the discharge process, and the extraction of Zn²⁺ and H₂O leads to the amorphization of V₂O₅, followed by the partial phase of amorphous V₂O₅ into Zn₃(OH)₂V₂O₇·H₂O. The change in performance under different electrolyte tests reveals that the aqueous environment can greatly improve the capacity and stability of the ZnVOH electrode. In addition, a zinc-ion hybrid supercapacitor is assembled with ZnVOH as the cathode, demonstrating excellent cycling stability. This study provides critical insights into improving the mechanism and stability of Zn²⁺ storage, offering a significant advancement in the development of AZIBs.