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

Abstract VO 2 generally has a higher theoretical capacity and layered structure suitable for the intercalation/extraction of zinc ions. However, Zn 2+ 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 NaBH 4 . 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 Zn 2+ 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 ).