Oxygen Defect Hydrated Vanadium Dioxide/Graphene as a Superior Cathode for Aqueous Zn Batteries

Zinc ion batteries have become a new type of energy storage device because of the low cost and high safety. Among the various cathode materials, vanadium–oxygen compounds stand out due to their high theoretical capacity and variable chemistry valence state. Here, we construct a 3D spongy hydrated vanadium dioxide composite (Od-HVO/rG) with abundant oxygen vacancy defects and graphene modifications. Thanks to the stable structure and abundant active sites, Od-HVO/rG exhibits superior electrochemical properties. In aqueous electrolyte, the Od-HVO/rG cathode provides high initial charging capacity (428.6 mAh/g at 0.1 A/g), impressive rate performance (186 mAh/g even at 20 A/g), and cycling stability, which can still maintain 197.5 mAh/g after 2000 cycles at 10 A/g. Also, the superior specific energy of 245.3 Wh/kg and specific power of 14142.7 W/kg are achieved. In addition, MXene/Od-HVO/rG cathode materials are prepared and PAM/ZnSO4 hydrogel electrolytes are applied to assemble flexible soft pack quasi-solid-state zinc ion batteries, which also exhibit excellent flexibility and cycling stability (206.6 mAh/g after 2000 cycles). This work lays the foundation for advances in rechargeable aqueous zinc ion batteries, while revealing the potential for practical applications of flexible energy storage devices.