KOH-Induced Oxygen-Deficient VO₂ for High-Rate Aqueous Zn-Ion Batteries

Due to its high safety and low cost, aqueous Zn-ion batteries (AZIBs) have become one of the most promising energy storage devices. However, the development of a stable cathode with fast kinetics and high-energy density is crucial to realize AZIBs for large-scale application. In this work, KOH-induced oxygen-deficient VO₂ (K-VO₂) was developed by activating doughnutlike VO₂ by KOH. Benefiting from the combination of a unique morphology with abundant active sites and the oxygen vacancy, increasing the interlayer spacing, both improved kinetics and enhanced Zn-ion storage capability in the VO₂ cathode are achieved. The optimized K-VO₂-3:4 delivers a specific capacity of 260.9 mA h g^–1 at 0.2 A g^–1, an excellent high-rate capability of 166.1 mA h g^–1 at 5 A g^–1, and long-term cyclic stability with a capacity retention of 88.1% after 3000 cycles. The electrochemical performance of K-VO₂-3:4 has been greatly improved compared with untreated VO₂. The KOH activation strategy proposed here also presents an encouraging pathway for developing other high-energy and stable cathodes.