Controllable Preparation And Electrochemical Properties Of Vanadium Oxide Cathode Materials For Lithium Ion Batteries

With the rapid development of the electric and hybrid vehicles, commercial vanadium-based cathode materials of lithium-ion batteries?LIBs? cannot meet the demands of the market due to their bad cycle performances and rate capabilities. Vanadium pentoxide?V₂O₅? has been extensively studied as a potential cathode material in rechargeable LIBs, due to its high capacity, abundant resources storage, and easy fabrication. However, the low diffusion coefficient of lithium ions and electronic conductivity impede its electrochemical properties. In order to solve this problem, here, V₂O₅ cathode materials were synthesized by hydrothermal method, and the structure and morphology of V₂O₅ were controlled to improve electrochemical properties by changing the experimental conditions. The main research works and results are shown as follows:Firstly, V₂O₅ nanoparticles were fabricated by hydrothermal method. The crystallographic phases of all the products were investigated by powder X-ray diffraction?XRD? and the morphologies of the samples were characterized by scanning electron microscope?SEM?. The results show that the V₂O₅ nanoparticles are quite uniform with a diameter about 300 nm and orthorhombic V₂O₅ phase?space group: Pmmn?59?, JCPDS card41-1426? with high purity. The V₂O₅ electrodes exhibit an initial discharge specific capacity of 131 mAh g-1 at 0.2 C. The discharge specific capacity decrease firstly and then increase to about 90 mAh g-1.Secondly, hollow V₂O₅ microspheres were fabricated by a microwave hydrothermal method with subsequent annealing in air. The vanadium precursor microspheres are quite uniform with a diameter about 1 ?m and it can be converted into hollow V₂O₅ during the annealing process in air. The electrochemical performance of hollow V₂O₅ microspheres is better than V₂O₅ nanoparticles. As a cathode material for lithium ion batteries, the hollow V₂O₅ microspheres deliver a specific discharge capacity of 131.9 and 113 mAh g-1 at the current densities of 1 C and 8 C, respectively. Moreover, the electrode also exhibit good cycling stability.Thirdly, V₂O₅ microspheres with core-shell structure were fabricated by solvothermal method used glycol as solvent. The dose of V₂O₅ and time of solvothermal were changed to control the morphologies of the microspheres and to improve electrochemical performance of V₂O₅ microspheres. The results of TEM and a series of electrochemical tests showed that the microspheres secondary size increases and electrochemical performance get bad with the decrease of the dose of addition V₂O₅; while the microspheres secondary size decreases and the electrochemical performance get better with the decease of the solvothermal time.