Abstract:
Aqueous zinc-ion batteries have great development and application prospects due to the low cost and environmental friendliness. Vanadium-based materials with high specific surface area and layered or fast ionic conductor structures are among the most promising cathode materials for zinc-ion batteries. Layered vanadium pentoxide cathodes have higher capacity and adjustable interlayer spacing, which have been extensively examined. As a layered vanadium pentoxide, V
2O
5·
nH
2O is widely evaluated because of its high theoretical capacity, simple synthesis process, etc. However, the practical application of layered V
2O
5·
nH
2O is still hindered by structural collapse during cycling and slow Zn
2+ diffusion in the V
2O
5·
nH
2O cathode. How to improve the long-cycle performance of V
2O
5·
nH
2O remains to be solved. In this study, V
2O
5·1.6H
2O xerogel was successfully prepared by the sol-gel method combined with the freeze-drying technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the phase composition and morphology. The results showed that the prepared material was primarily V
2O
5·1.6H
2O with good crystallinity, and little V
2O
5 still existed. V
2O
5·1.6H
2O grew like macroporous lamellar fibers of approximately 100 nm thick. Compared with commercialized V
2O
5, V
2O
5·1.6H
2O has larger interlayer space, which benefits the diffusion of Zn
2+, and the crystal H
2O may help stabilize the structure. Electrochemical performance results revealed that the fibrous V
2O
5·1.6H
2O cathode material showed an initial discharge capacity of 388.4 mA·h·g
–1 at a constant current of 0.1 A·g
–1 and it still maintained at 129.7 mA·h·g
−1 after 1000 cycles, with nearly no capacity decay. At 0.1, 0.2, 0.5, 1, 2, and 3 A·g
−1, the fibrous V
2O
5·1.6H
2O xerogel show capacities of 388.4, 338.5, 282.9, 239.1, 194.4, and 165.9 mA·h·g
−1, respectively. The capacity was much higher than that of commercialized V
2O
5, which only showed 279.5, 251.0, 205.5, 174.5, 144.6, and 125.1 mA·h·g
−1, respectively, at the same discharge current density. The good electrochemical performance was mainly attributed to the large layer spacing, combined with the supporting effect of H
2O, which contributed to the good structural stability of the material during the cycle and avoided the degradation of material properties. In addition, the fibrous structure shortened the Zn
2+ diffusion path and increased the electronic conductivity also contributed to the enhanced electrochemical performance. The mechanism of the charge and discharge process was examined by
ex-situ X-ray photoelectron spectroscopy (XPS) and XRD. The results showed that the formation and disappearance of basic zinc sulfate are accompanied by the embedding and removal of zinc ions, and the process is reversible.