Controlled Heterovalent Vanadium Ion Coordinated Flower-Shaped Supramolecules Cathode for Zinc-Ion Storage

Vanadium-based materials, which offer multiple oxidation states and rich redox reactions in zinc-ion batteries (ZIBs), have gained substantial attention. However, achieving green and efficient preparation of vanadium oxides-based materials featured with a controlled content of different heterovalent vanadium remains a significant challenge. Herein, a vanadium-supramolecular flower-shaped material (VSF) with heterovalent vanadium was prepared using NH₄VO₃ as vanadium metal center and hexamethylenetetramine as organic ligand in aqueous solution. The optimal ratio of material (PVSF) after controlling VSF presintering is 2/1 (V⁵⁺/V⁴⁺). Employing PVSF-2/1 as cathode in ZIBs can achieve a high specific capacity of 398.9 mAh g^-1 at 0.2 A g^-1, which is increased by 0.2 and 3.5 times as compared with that of pure VO₂ and V₂O₅, respectively. After 2000 cycles, it still delivers a specific capacity of 225 mAh g^-1 at 5.0 A g^-1. The Zn∥PVSF-2/1 pouch cells were assembled with a satisfactory specific capacity of 339 mAh g^-1 at a current of 0.2 A g^-1. The excellent performance is ascribed to regulation and coordinated promotion of heterovalent states. The structural pathways corresponding to V⁵⁺ act as Zn²⁺ transport channels to increase Zn²⁺ transport capability. The V⁴⁺ cause high charge density distribution of the V-O lattice layer to provide abundant active sites for the adsorption/desorption process of Zn²⁺.