Adjusting the Valence State of Vanadium in VO₂ (B) by Extracting Oxygen Anions for High-Performance Aqueous Zinc-Ion Batteries

VO₂ generally has a higher theoretical capacity and layered structure suitable for the intercalation/extraction of zinc ions. However, Zn²⁺ ions with high charge density interact with the crystal lattice and limit further improvement in electrochemical performance. Defect engineering is a potential modification method with very promising application prospects, but the established procedures for preparing defects are complicated. In this study, VO_2-x (B) with oxygen deficiency is prepared by a simple solution reaction with NaBH₄ . The presence of oxygen deficiencies is confirmed by positron annihilation lifetime spectroscopy, UV/Vis absorbance spectroscopy and others. Owing to the presence of oxygen defects, the aqueous Zn/VO_2-x (B) battery exhibits improved specific capacity, excellent reversibility, and structural stability. Ex situ characterization techniques are employed to demonstrate the reversible insertion-extraction mechanism of Zn²⁺ ions from and into the host material. In addition, the Zn/VO_2-x (B) batteries still exhibit considerable electrochemical performance, even with high-loading electrodes (about 4 mg cm^-2 ).