Tunable Vanadium Oxide Microflowers as High-Capacity Cathode Materials for Aqueous Rechargeable Zinc-Ion Batteries

Aqueous rechargeable zinc-ion batteries (ARZIBs) are attractive energy storage devices for grid-scale energy storage applications because of their safety, environmental compatibility, and affordability. In this study, tunable three-dimensional (3D) vanadium oxide microflowers were prepared using a simple hydrothermal reaction method followed by heat treatment in an argon or oxygen atmosphere. The 3D VO2 and V2O5 microflowers were obtained in the argon and oxygen states, respectively, after heat pretreatment. The activated 3D VO2 microflowers exhibited an initial reversible capacity of 438 mA h g–1 and a Coulombic efficiency (CE) of 89% at a cycling rate of 0.1 A g–1, which retained 317 mA h g–1 with a CE of 99.99% after 1000 cycles at 5 A g–1. The 3D VO2 microflowers retained a discharge capacity of 168 mA h g–1 even after 5000 cycles at 5 A g–1. These remarkable properties could be ascribed to the synergistic effects of the (i) large surface area of the microflowers, (ii) facilitated electron transfer owing to the carbon coating, and (iii) initial activation of the active materials during cycling and the expanded interplanar distance of the active materials. Therefore, the outstanding performance of the microflowers in this study provides insights into the development of 3D microstructures as potential cathode materials for ARZIBs.