Oxygen Defects Engineering of VO 2 · x H 2 O Nanosheets via In Situ Polypyrrole Polymerization for Efficient Aqueous Zinc Ion Storage

What has been a crucial demand is that designing mighty cathode materials for aqueous zinc−ion batteries (AZIBs), which are vigorous alternative devices for large−scale energy storage by means of their high safety and low cost. Herein, a facile strategy is designed that combines oxygen defect engineering with polymer coating in a synergistic action. As an example, the oxygen−deficient hydrate vanadium dioxide with polypyrrole coating (O d −HVO@PPy) is synthesized via a one‐step hydrothermal method in which introducing oxygen vacancy in HVO is simultaneously realized during the in situ polymerization. Such a desirable material adjusts the surface adsorption and internal diffusion of Zn 2+ demonstrated by electrochemical characterization and theoretical calculation results. Moreover, it also utilizes conductive polymer coating to improve electrical conductivity and suppress cathode dissolution. Therefore, the O d −HVO@PPy electrode delivers a preferable reversible capacity (337 mAh g −1 at 0.2 A g −1 ) with an impressive energy density of 228 Wh kg −1 and stable long cycle life. This enlightened design opens up a new modus operandi toward superior cathode materials for advanced AZIBs.