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

Zinc vanadium oxide (ZVO), Zn0.25V2O5 center dot 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 center dot H2O cathode. A reaction time of 48 h yielded a singlephase 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.