VO2 Nanosheets Assembled into Hierarchical Flower-Like Hollow Microspheres for Li-Ion Batteries

Vanadium dioxide (VO2) is a prospering material for lithium-ion cathode storage attributed to its unique structure and high specific capacity. However, the cycling and rate performance of VO2 is unsatisfactory due to low electrical conductivity and tendency to volume expansion during charging and discharging, which restricts its application. To improve its cell performance, we report 3D hierarchical flower-like VO2 hollow microspheres assembled from nanosheets (HVO) synthesized by a facile template-free hydrothermal method. In addition, by controlling the content of nitric acid (HNO3) and citric acid (C6H8O7), VO2 flower-like solid microspheres (SVO) and random nanosheets (NVO) were synthesized as control experiments. Compared with them, 3D hierarchical flower-like VO2 hollow microspheres have higher reversible capacity (delivers a capacity of 259.90 mA h g–1 at 0.1 A g–1), extraordinary rate capacity (168.51 mA h g–1 at 2 A g–1), and good cycling life (81.21% capacity retention over 500 cycles at 2 A g–1). Moreover, the HVO//graphite full cell was successfully assembled, which exhibits an initial capacity of 147.17 mA h g–1 at 2 A g–1 and maintains a high capacity of 114.97 mA h g–1 after 1000 cycles, with capacity retention of 78.12% and an average capacity decline of 0.022% per cycle. The superior performance of 3D hierarchical flower-like VO2 hollow microspheres stems from their ability to provide a considerable surface area, efficient self-expansion, and self-shrinkage buffering. The abovementioned results sufficiently confirm that 3D hierarchical flower-like VO2 hollow microspheres constituted from nanosheets have great latent potential and application prospects as a next-generation cathode material for fast-charging lithium-ion batteries.