Activating ZnV2O4by an Electrochemical Oxidation Strategy for Enhanced Energy Storage in Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) are recognized as promising energy storage systems to meet the ever-growing demand for grid-scale applications. Developing reliable cathode materials with superior electrochemical performance plays a decisive role in this field. In this work, an electrochemical oxidation strategy is employed to successfully activate the electrochemical activity of ZnV2O4 spinel oxide. Operating at high potentials up to 2.0 V enables the capacity activation process efficiently, in which the specific capacity increases from 86 to 232 mAh g–1 (corresponding to 170% capacity enhancement) after 50 cycles at 2 A g–1. On the contrary, ZnV2O4 operating in the potential window of 0.4–1.6 V only delivers 87 mAh g–1 after 50 cycles, whereas negligible capacity (<3 mAh g–1) is obtained in the case of 0.4–1.3 V. As characterized by X-ray diffraction (XRD), Raman microscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and in situ pH measurements, the underlying mechanism is unraveled as a hydrolysis reaction coupled with the dissolution–recrystallization process, leading to the formation of high-valent Zn0.06V2O5·1.07H2O with a localized layered structure. The activated cathode demonstrates facilitated ion transport kinetics, reduced charge transfer resistance, and high electrochemical reversibility in RAZIBs. Benefiting from these features, stable cycle stability is achieved, that is, a reversible capacity of 138 mAh g–1 (83% capacity retention) can be retained after 2000 cycles at 4 A g–1. This work sheds light on activating low-valent vanadium-based oxides for practical application in RAZIBs, opening an avenue for developing cathode materials for aqueous batteries.