Controlled Heterovalent\nVanadium Ion Coordinated Flower-Shaped\nSupramolecules Cathode for Zinc-Ion Storage

Vanadium-based materials, which offer multiple oxidation\nstates\nand rich redox reactions in zinc-ion batteries (ZIBs), have gained\nsubstantial attention. However, achieving green and efficient preparation\nof vanadium oxides-based materials featured with a controlled content\nof different heterovalent vanadium remains a significant challenge.\nHerein, a vanadium-supramolecular flower-shaped material (VSF) with\nheterovalent vanadium was prepared using NH<sub>4</sub>VO<sub>3</sub> as vanadium metal center and hexamethylenetetramine as organic ligand\nin aqueous solution. The optimal ratio of material (PVSF) after controlling\nVSF presintering is 2/1 (V<sup>5+</sup>/V<sup>4+</sup>). Employing\nPVSF-2/1 as cathode in ZIBs can achieve a high specific capacity of\n398.9 mAh g<sup>–1</sup> at 0.2 A g<sup>–1</sup>, which\nis increased by 0.2 and 3.5 times as compared with that of pure VO<sub>2</sub> and V<sub>2</sub>O<sub>5</sub>, respectively. After 2000\ncycles, it still delivers a specific capacity of 225 mAh g<sup>–1</sup> at 5.0 A g<sup>–1</sup>. The Zn∥PVSF-2/1 pouch cells\nwere assembled with a satisfactory specific capacity of 339 mAh g<sup>–1</sup> at a current of 0.2 A g<sup>–1</sup>. The\nexcellent performance is ascribed to regulation and coordinated promotion\nof heterovalent states. The structural pathways corresponding to V<sup>5+</sup> act as Zn<sup>2+</sup> transport channels to increase Zn<sup>2+</sup> transport capability. The V<sup>4+</sup> cause high charge\ndensity distribution of the V-O lattice layer to provide abundant\nactive sites for the adsorption/desorption process of Zn<sup>2+</sup>.