Investigation On The Synthesis And Electrochemical Properties Of VO₂ Nanomaterial

In this thesis, VO2(B) nanostructures have been successfully fabricated through hydrothermal process, and the electrochemical properties of VO2(B) nanostructures were investigated in detail. The microstructure and morphology of the VO2 nanostructures were evaluated by using X-ray diffraction and scanning electron microscopy and transmission electron microscopy. Meanwhile, VO2(B) nanoflower was transformed to VO2(M/R) by heat treatment, the phase transition temperature and electrochemical property were discussed. This thesis contains the following works and innovations:1. VO2(B) nanostructures were fabricated through hydrothermal process without catalyst. The relationship between the reaction conditions and the morphologies of the as-prepared products was investigated. VO2(B) nano-carambolas was synthesized when the raw materials were vanadium pentoxide and oxalic acid; As the raw materials were ammonium metavanadate and oxalic acid, VO2(B) nanorod, VO2(B) nanoflower and flake-like VO2(B) were fabricated by adjusting the concentrations of the oxalic acid and the reaction time.2. The electrochemical properties of VO2(B) nanorod, VO2(B) nanoflower and flake-like VO2(B) were tested. The discharge and charge tests for aqueous lithium ion battery were carried out with a cutoff voltage of 1.4-0.4 V at a current density of 10 mA/g, VO2(B) nanoflower electrode possesses not only higher discharge capacity but also better capacity retention.The cyclic voltammograms tests for aqueous lithium ion battery were carried out with a scan rate of 100mV/s for 30 cycles, the result suggested that VO2(B)nanorods and VO2(B) nanoflower have a better capacity retention on cycling than flake-like VO2(B). To evaluate the Li ion diffusion coefficient in VO2(B) with different morphologies,cyclic voltammetry (CV) was carried out with different potential scanning rates. The scan rates are 5,10 50,150,200 and 300 mVs-1, respectively, obviously the DLi of VO2(B) nanoflower is about 1.7 times higher than VO2(B) nanorod,while is 3 times higher than flake-like VO2(B).3. VO2(B) was transformed to VO2(M/R) by heat treatment without destroy the morphology.The DSC measurements demonstrated the phase transition temperature of the VO2(M/R) nanoflower appears at 70℃. We also investigate the cycling behavior of discharge capacities and CV curves of the VO2(M/R), which exhibited an inferior electrochemical property on both the discharge capacities and CV curves.