Impacts of Oxygen Vacancies on Zinc Ion Intercalation in VO2

The aqueous zinc ion battery has emerged as a promising alternative technology for large-scale energy storage due to its low cost, natural abundance, and high safety features. However, the sluggish kinetics stemming from the strong electrostatic interaction of divalent zinc ions in the host crystal structure is one of challenges for highly efficient energy storage. Oxygen vacancies (VO••), in the present work, lead to a larger tunnel structure along the b axis, which improves the reactive kinetics and enhances Zn-ion storage capability in VO2 (B) cathode. DFT calculations further support that VO•• in VO2 (B) result in a narrower bandgap and lower Zn ion diffusion energy barrier compared to those of pristine VO2 (B). VO••-rich VO2 (B) achieves a specific capacity of 375 mAh g-1 at a current density of 100 mA g-1 and long-term cyclic stability with retained specific capacity of 175 mAh g-1 at 5 A g-1 over 2000 cycles (85% capacity retention), higher than that of VO2 (B) nanobelts (280 mAh g-1 at 100 mA g-1 and 120 mAh g-1 at 5 A g-1, 65% capacity retention).