Mixed-valence vanadium oxides with ultra-high rates and long cycles for aqueous zinc ion batteries

Energy storage technology plays an important role in the strategy to achieve dual carbon targets. Aqueous zinc-ion batteries (AZIBs) have become an ideal choice in the field of energy storage due to the excellent safety, high energy density, and cost-effectiveness. However, the widespread application of AZIBs is limited by the inherent drawbacks of cathode materials, such as vanadium-based oxides (VO), which are marked by poor electrical conductivity and sluggish diffusion kinetics. To address these challenges, we have developed a direct oxidation method using Vanadium (IV) oxide acetylacetonate (VO(acac)₂) as a precursor to synthesize mixed-valence VO cathode materials. This finding reveals that the VO-300 electrode showcases an enhanced rate capability of 130 mAh/g at 50 A/g, and remarkable cyclic stability, retaining 170 mAh/g after 8000 cycles at 50 A/g. Furthermore, the kinetics analysis reveals that the charging storage process is influenced by both diffusion and capacitance mechanisms. Ex-situ characterization clarifies this as a reaction mechanism involving the co-intercalation of Zn²⁺ with H⁺. This research puts forward a straightforward strategy for enhancing the performance of mixed-valence VO cathode materials, thereby contributing to the improvement of the overall performance of AZIBs.