Engineering Oxygen Vacancies on VO2 Multilayered Structures for Efficient Zn2+ Storage

Vanadium dioxide (VO₂ (B)) is a proper cathode for aqueous zinc-ion batteries (ZIBs) due to its shear structure and high theoretical capacity. However, the sluggish kinetics and structure instability derived from the strong electrostatic interaction between Zn²⁺ and the VO₂ host hinder its further application. Defect engineering is a useful way to circumvent the limitations. Herein, oxygen-defect VO₂ (O_d -VO₂ ) with tunable oxygen vacancy concentration are obtained via a facile one-step hydrothermal method by adjusting ascorbic acid addition. It is proved that oxygen vacancies can provide extra active sites for Zn²⁺ storage and reduced electrostatic barrier for Zn²⁺ transportation, but excessive vacancy content would lead to a reverse effect. The O_d -VO₂ cathode with optimum oxygen vacancy concentration achieves an outstanding performance with a high capacity of 380 mAhg^-1 at 0.2 A g^-1 , excellent cycle stability with 92.6 % capacity retention after 2000 cycles at 3 A g^-1 and a high energy density of 197 Wh kg^-1 at the power density of 0.641 kW kg^-1 . Therefore, this defect engineering method for O_d -VO₂ provides an attractive way for high-performance aqueous ZIB cathodes.