High capacity and inexpensive multivalent cathode materials for aqueous rechargeable Zn-ion battery fabricated via in situ electrochemical oxidation of VO2 nanorods

For large-scale energy storage, aqueous rechargeable zinc-ion batteries are one of the most promising battery systems to replace lithium-ion batteries. In this study, a facile and scalable hydrothermal method is used to prepare VO2 nanorods, which are ball-milled with carbon black to prepare VO2@C nanoparticles. Characterizations using several advanced techniques confirm the successful synthesis of pure VO2 nanorods. Prior to electrochemical measurements, the VO2@C nanostructured cathode materials are transformed into V2O5·nH2O via an in situ electrochemical oxidation technique. The VO2@C/Zn aqueous zinc-ion full cell exhibits a reversible capacity of 300 mA h g−1 and a retention capacity of 85% after 1000 cycles at a current density of 5 A g−1 with a 2 M ZnSO4 electrolyte. The full cell also retains a remarkable capacity of 159 mA h g−1, even after 4000 galvanostatic charge–discharge cycles at 5 A g−1. The cell also shows excellent rate capabilities at a wide range of current densities from 0.1 to 20 A g−1, with a reversible discharge capacity and Coulombic efficiency of 100 mA h g−1 and 99%, respectively, at 20 A g−1. The remarkable performance is attributed to the nanoscale size of the prepared nanorods and the in situ electrochemical transformation.