Anodic Oxidation Strategy toward Structure-Optimized VO Cathode Electrolyte Regulation for Zn-Ion Storage.

The lack of suitable cathodes is one of the key reasons that impede the development of aqueous zinc-ion batteries. Because of the inherently unsuitable structure and inferior physicochemical properties, the low-valent VO as Zn host could not be effectively discharged. Herein, we demonstrate that VO (theoretical capacity up to 715 mAh g) can be utilized as a high-performance cathode material by an anodic oxidation strategy. Through simultaneously regulating the concentration of the electrolyte and the morphology of the VO sample, the ultraefficient anodic oxidation process of the VO cathode was achieved within the first charging, and the mechanism was also schematically investigated. As expected, the VO cathode with a hierarchical microcuboid structure achieved a nearly two-electron transfer process, enabling a high discharging capacity of 625 mAh g at 0.1 A g (corresponding to a high energy density of 406 Wh kg) and cycling stability (100% capacity retention after 10 000 cycles). This work not only sheds light on the phase transition process of low-valent VO but also exploits a method toward design of advanced cathode materials.