Synthesis, Characterization And Electrochemical Performance Of Vanadium-based Materials

The rechargeable batteries are important ways of energy storage and conversion. Lithium ion batteries are widely concerned and applied due to their excellent electrochemical performance. The cathode and anode materials are important parts of lithium ion batteries. Searching for high capacity, low cost, excellent cycle performance, environmentally friendly cathode and anode materials is the research focus in the field of lithium ion batteries. In this paper, from the aspects of synthesis and structure design, and taking vanadium based materials as the research focus, we discuss on the preparation, characterization and electrochemical properties study of the cathode material porous V2O5 nanotubes and the anode material VN/graphene of lithium ion batteries. The microstructure and morphology of the materials were investigated by XRD, SEM and TEM. The electrochemical performances of the materials were investigated by galvanostatic current charge-discharge, cyclic voltammograms and electrochemical impedance spectroscopy and so on.In Chapter 1, the author briefly introduces the working principle of lithium ion battery,the structure features etc. And the common cathode and anode materials for lithium ion batteries are introduced briefly.In Chapter 2, the author mainly introduces main experimental chemicals, main experimental equipments, characterizations and analysis methods used in the projects of this paper. We describe the electrode fabrication and battery assembly. And test means and methods of the electrochemical performances of the batteries are also presented.In Chapter 3, porous vanadium pentoxide(V2O5) nanotubes have been synthesized by a simple electrospinning technique with using low-cost inorganic vanadium precursor. Electrospinning is a simple and versatile process for the fabrication of one-dimensional nanostructures. By controlling of relevant parameters of electrospinning, we can obtain nanofibers with uniform diameters. Porous V2O5 nanotubes have porous one dimensional nanostructures. Porous nanostructures are benefical to electrolyte infiltration and shorten the diffusion distance of lithium ion. The one-dimensional nanostructures have large aspect ratio which could prevent self-aggregation of nanomaterials effectively. In addition, the one-dimensional nanostructures provide an effective electron transport pathway along the one-dimensional direction to accelerate the electronic conduction. These advantages profit the electrochemical performance of V2O5. The electrochemical performance test results show that porous V2O5 nanotubes obtained at 400 oC for 15 min display excellent rate performance and cycling performance in the voltage range of 2.5-4.0 V. At 5C、10C、20C、30C、40C、50C, the discharge capacities are 124.8 m Ah g-1、114.9 m Ah g-1、 99.7 m Ah g-1 、 93.1 m Ah g-1、84.9 m Ah g-1 and 79.6 m Ah g-1, respectively. At 50 C, after 200 cycles, the capacity retention is 97.4%.In Chapter 4, VN/graphene nanocomposite was prepared by hydrothermal method with thermal reduction. The presence of grapheme improves the electrical conductivity of VN and alleviates the accumulation of VN in a certain degree. The presence of VN nanoparticles could also block the accumulation of grapheme. There has a synergistic effect between them. When used as cathode material for lithium ion batteries, VN/graphene nanocomposite exhibits excellent rate capability. In the range of 0.01-3 V, at current density of 1000 m A g-1、2000 m A g-1、3000 m A g-1, the reversible specific capacities are 188.7 m Ah g-1、161.9 m Ah g-1 and 148.7 m Ah g-1。...