Orientation effect of zinc vanadate cathode on zinc ion storage performance

Rechargeable aqueous zinc-ion battery (ZIB) is considered as a promising energy storage device due to the low cost, high obtainable output voltage, non-toxicity, and environmental friendliness. To achieve an excellent energy storage performance, morphology engineering of cathode materials for aqueous ZIBs is regarded as an important strategy. The impact of dimension and orientation of the cathode material on the electrochemical performance are, however, less studied. Herein, we compare two types of zinc pyrovanadate (Zn₃V₂O₇(OH)₂•2H₂O, ZnVO) in nanowires and nanoflakes with the same crystal type but different orientations. ZnVO nanowires expose mostly the (001) plane lattice, in contrast to (020) and (110) lattice for ZnVO flakes. Interestingly, nanowires exhibit an excellent specific discharge capacity of 108 mAh g⁻¹ after 700 cycles at 2 A g⁻¹, contributed from Faradic and diffusion-controlled capacity. In contrast, nanoflakes deliver a very poor capacity of 1.5 mAh g⁻¹ after 700 cycles at 0.1 A g⁻¹ with only diffusion-controlled capacity. Density functional theory (DFT) reveals significantly different Zn²⁺ ion diffusion rates in ZnVO along different orientations.