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

Abstract

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 (O_d-HVO/rG) with abundant oxygen vacancy defects and graphene modifications. Thanks to the stable structure and abundant active sites, O_d-HVO/rG exhibits superior electrochemical properties. In aqueous electrolyte, the O_d-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/O_d-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.