Insight into the Critical Role of Oxygen Vacancies and V=O Bonds Length in VO for Advanced Zinc Ion Storage.

Due to the larger sizes and stronger positive polarity of Zn than dominant univalent ions, Zn sluggish diffusion within VO host electrodes is an essential issue in developing aqueous zinc-ion batteries (ZIBs) of higher energy densities. Herein, a high-performance VO cathode was developed through subtly synthesizing and tuning VO with oxygen vacancies-enriched and elongated apical V=O bond by altering the gradient concentration of hydrazine hydrate in the gas-solid reaction system. This strategy can enhance both intrinsic and extrinsic conductivity to a large extent. The electrochemical testing demonstrated the oxygen vacancies-enriched and elongated apical V=O bond can not only increase the intrinsic electronic conductivity of VO, but also induce additional pseudocapacitance to enhance the Zn diffusion kinetics. We used infrared spectroscopy and Raman spectroscopy to characterize the change in the bond length structure of VO. Simultaneously, the long-term cyclability (capacity retention of 76.9 % after 1200 cycles at 4.0 A g) and rate capabilities (218 mAh g at 4.0 A g) are promoted as well. We believe that our work might shed light on the bond length engineering of VO and provide insights for the reasonable designing of novel cathodes for practical rechargeable ZIBs.