Synthesis And Electrochemical Properties Study Of Vanadium-based Electrode Materials For Lithium Batteries

Lithium batteries have a lot of advantages such as high operating voltage, small size, no memory-effect, pollution-free, small self-discharge and long cycle life. Therefore, they have been widely used in fields like mobile phones, laptops, PDAs, digital cameras and portable electric tools. The main raw materials of lithium batteries include electrode materials, electrolyte, electrode substrate and the isolation membrane. Among them, the electrode materials are the most critical part for lithium batteries and directly determine the safety performance and the industrialization of the lithium ion battery. In recent years, lithium battery electrode materials continue to upgrade the industrialization level and the researchers have made remarkable progress in scientific research. In this dissertation we have included1. High crystalline LiV3O8was synthesized by solid state method under three different temperatures using NH4VO3, LiOH·H2O and citric acid as raw materials. The crystal structure characterization results show that there are some differences in the chemical bonding for the samples prepared at different temperatures. As the synthesis temperature rises, the stretching vibration of the V=O and O-V-O bonds was gradually weakened and the bending vibration was gradually increased. The results of the electrochemical performance studies show that for the LiV3O8samples synthesized at600℃,640℃and680℃, there are charging-discharging platinum at2.8～2.6V,2.5～2.4V and2.3～2.1V. The charging capacities can reach273,237and241mA h g-1, and the discharging capacities can reach247,235, and208mAh g-1for the three samples. All these results show that, with higher synthesis temperatures, the samples have high crystallinity, but the specific capacities decay much faster.2. V2O5and LiV3O8nanorods were synthesized by sol-gel method under three different temperatures using similar raw materials and their structures, morphologies and electrochemical performances were characterized. The SEM results show that both the V2O5and LiV3O8synthesized were nanorods, with the LiV3O8nanorods have much more smooth surfaces than the V2O5nanorods. By comparing the electrochemical performances of the V2O5and LiV3O8nanorods synthesized at different temperatures, we can find that with the increase of synthesis temperature, both the charge and discharge capacities decreased, with the capacity of LiV3O8nanorods decreased faster than the V2O5nanorods. By comparing the electrochemical performances of V2O5and LiV3O8nanorods synthesized at the same temperatures, we can find that LiV3O8nanorods have much more stable performances than the V2O5nanorods.3. Li3V6O16, as a new cathode material for lithium-ion battery, was synthesized by sol-gel method using V2O5, CH3COOLi-2H2O and H2O2(30%) as raw materials. The product was characterized by TG, XRD, SEM, XPS and galvanostatically charge-discharge tests. The characterization results demonstrated that the synthesis products were highly pure crystals, with nanosheets or nanorods morphology. The electrochemical performances show that the products have high initial capacities, with the specific discharge capacities reaching337,224,174,123,73and42mAh g-1at the current densities of17,85,170,425,850and1700mA g-1, respectively. At low current densities, the discharge curves have3-4voltage platforms. But the platforms became less and less obvious when the current densities went higher and higher. The cycling stabilities became better and better when the current densities went higher. All these results showed that the Li3V6O16synthesized by this sol-gel method could be a cathode material for lithium ion batteries.4. Li6V10O28was prepared by a sol-gel method using V2O5, CH3COOLi-2H2O and H2O2(30%) as raw materials, and was tested as the cathode material for lithium ion batteries. The gel precursor was characterized by TG-DSC and the final product was characterized by XRD, SEM, XPS and electrochemical tests. TG-DSC analysis showed that the Li6V10O28crystals were synthesized at about400℃. Three voltage plateaus appeared in the first discharge-charge curve. The discharge capacities could reach226,135,106and80mAh g-1at the current densities of17,170,425, and850mA g-1, respectively. The material demonstrated an excellent cycling stability at high rates.5. LiCuVO4nanoparticles were synthesized by a sol-gel method using V2O5、 CH3COOLi-2H2O,H2O2(30%) and Cu(NO3)2-3H2O as raw material, and were characterized by TG, XRD, SEM and electrochemical tests. When tested at the rate of20mA g-1in2.0-4.2V voltage window, the first discharge capacity of this material can reach193mAh g-1and can be stabilized at about170mAh g-1after26charge-discharge cycles. The charge-discharge cycles are consisted by two parts:irreversible lithium-inserting process (LiCuVO4+xLi++xe+→Li1+xCuVO4) and reversible Li-Cu displacement reaction (LiCuVO4+2Li++2e-<-Li3VO4+Cu).6. LiVSi2O6was synthesized by a sol-gel method using V2O5, CH3COOLi-2H2O, H2O2(30%) and TEOS as raw material and was tested as a cathode material for lithium-ion battery. The electrochemical performance tests showed that the charge and discharge capacities of the material were low and thus the material is not suitable for applications in lithium ion batteries.