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

Abstract

Zinc\nvanadium oxide (ZVO), Zn_0.25V₂O₅·H₂O, was synthesized by a facile hydrothermal\nsynthesis and was evaluated as the positive electrode for Zn-ion batteries\n(ZIBs). The hydrothermal reaction time had a profound influence on\nthe phase formation and morphology. Short reaction times (12, 24 h)\nlead to the formation of shorter nanobelts and secondary phases in\nthe Zn_0.25V₂O₅·H₂O cathode. A reaction time of 48 h yielded a single-phase material\nwith a multilayered ultralong nanobelt structure. The intercalation\nof water molecules into the interlayer space of ZVO increased with\nincreasing reaction time. Cyclic voltammetry (CV) revealed that the\ndiffusion-controlled reaction is dominant in the 48 h sample below\n0.4 mV s^–1 scan rate and the surface-controlled\nreaction is dominant above 0.4 mV s^–1 scan rate.\nOwing to the high crystal water content and consequently increased\nintercalation sites, the 48 h electrode sample delivered a high capacity\nof 275 mAh g^–1 with 99.6% coulombic efficiency at\n1 C current rate and impressive cyclic stability over 200 cycles with\n94% capacity retention. The 48 h electrode exhibited excellent structural\nand morphological stability after the Zn²⁺ insertion/extraction\ncycles, while the 24 h sample displayed degradation after the cycles\nas revealed by ex situ X-ray diffraction (XRD) and scanning electron\nmicroscopy (SEM) analyses. The study thus demonstrates the rate capability\nof ZVO and a facile synthesis route that leads to a single-phase and\nunique morphology, thereby providing a high-performing positive electrode\nfor improved zinc-ion batteries.