Valence Engineering via Polyoxometalate-Induced on Vanadium Centers for Efficient Aqueous Zinc-Ion Batteries

Layered vanadium-based compounds have attracted attention as cathode materials for aqueous zinc-ion batteries (AZIBs) because of their low cost, high theoretical specific capacity, and abundant vanadium valence states. However, the slow migration of Zn2+ ions and their poor cycling stability hinder their practical application in AZIBs. Herein, using a one pot solvothermal method, the polyoxometalates (POMs) were inserted into the aluminum vanadate interlayer spacing, and a series of novel three-dimensional nanoflower cathode materials (HAVO-MMo6-X) were successfully fabricated. The unique electron-rich structure of the POMs accelerated the migration of Zn2+ on the cathode to obtain a high specific capacity. Owing to the synergistic pillar effect of POMs and HAVO, the interlayer spacing of HAVO-FeMo6-50 increased to approximately 14.33 Å. X-ray absorption fine structure spectroscopy was used to analyze the coordination environments of the cathode materials. A combination of in situ and ex situ characterization techniques demonstrated the storage mechanism of Zn2+ during the charge/discharge process. Furthermore, the experimental results and DFT calculations indicated that the introduction of POMs had the dual function of improving conductivity and reducing the Zn2+ migration barrier. Thus, this work provides a new perspective on the synergistic interaction between POMs and metal compounds.