Zinc Vanadium Oxide Nanobelts as High-Performance Cathodes for Rechargeable Zinc-Ion Batteries

Zinc vanadium oxide (ZVO), Zn0.25V2O5·H2O, was synthesized by a facile hydrothermal synthesis and was evaluated as the positive electrode for Zn-ion batteries (ZIBs). The hydrothermal reaction time had a profound influence on the phase formation and morphology. Short reaction times (12, 24 h) lead to the formation of shorter nanobelts and secondary phases in the Zn0.25V2O5·H2O cathode. A reaction time of 48 h yielded a single-phase material with a multilayered ultralong nanobelt structure. The intercalation of water molecules into the interlayer space of ZVO increased with increasing reaction time. Cyclic voltammetry (CV) revealed that the diffusion-controlled reaction is dominant in the 48 h sample below 0.4 mV s-1 scan rate and the surface-controlled reaction is dominant above 0.4 mV s-1 scan rate. Owing to the high crystal water content and consequently increased intercalation sites, the 48 h electrode sample delivered a high capacity of 275 mAh g-1 with 99.6% coulombic efficiency at 1 C current rate and impressive cyclic stability over 200 cycles with 94% capacity retention. The 48 h electrode exhibited excellent structural and morphological stability after the Zn2+ insertion/extraction cycles, while the 24 h sample displayed degradation after the cycles as revealed by ex situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The study thus demonstrates the rate capability of ZVO and a facile synthesis route that leads to a single-phase and unique morphology, thereby providing a high-performing positive electrode for improved zinc-ion batteries.