A mixed-valent vanadium oxide cathode with ultrahigh rate capability for aqueous zinc-ion batteries

Abstract

The development of high-performance cathode materials is the key to realize commercial applications of zinc-ion batteries (ZIBs). Vanadium-based materials have been used as cathode candidates for ZIBs due to their low cost and high capacity. However, the low conductivity, unstable layered structure and slow diffusion kinetics of Zn²⁺ are still the main problems for vanadium-based oxides. Herein, V₁₀O₂₄·nH₂O with a large interlayer spacing and stable structure is successfully synthesized by inducing a VO₂ phase transition through a simple refluxing process. As the ZIB cathode material, V₁₀O₂₄·nH₂O demonstrates a high reversible capacity of 365.3 mA h g⁻¹ at 0.2 A g⁻¹, ultrahigh rate performance (127.2 mA h g⁻¹ even at 80 A g⁻¹), and long-term cycling stability (83.2% capacity retention over 3000 cycles at 5.0 A g⁻¹). The excellent electrochemical performance is attributed to the synergistic effects of the ultrathin nanoribbon structures, oxygen vacancy and water molecules, which are favorable for enhancing the electron/ion transfer kinetics and maintaining structural stability of the V₁₀O₂₄·nH₂O electrode in the whole cycling process. Furthermore, ex situ XRD and XPS analyses elucidate the Zn²⁺ storage mechanism of the V₁₀O₂₄·nH₂O cathode.