Study On The Synthesis And Modification Of Vanadium-containing Materials For Lithium-intercalation

New rechargeable battery-lithium ion batteries were widely used on mobile phones, portable computers, cameras and other electronic equipment because of their high energy density, high voltage, load capacity, wide operating temperature range, long life, safety and pollution-free advantages of. In recent years, more and more studies on the cathode materials of lithium-ion batteries.Past studies show that the electrochemical performance of vanadium based lithium materials remarkably depends on synthesis methods. In order to explore the best material preparation methods, conditions screening and process optimization, LiV₃O₈ was prepared using the sol-gel method, solid-phase method, solution method, hydrothermal method and precipitation method in this work. In order to impove the electrochemical properties of Li_1+xV₃O₈ cathode materials, we can try to resolve this problem by doping. We use the modified method of sol-gel method and hydrothermal method separately introducing cationic or anion to improve the electrochemical properties for materials doped modification. The surface of LiV₃O₈ materials were modified by a chemical process. The charge-discharge experiments were carried out between 1.5V and 4V at a current rate of 0.2C. Recently a new kind of lithium vanadium oxide cathode materials LiMVO₄ were discovered, because its cationic mixing degree can achieve 100% and its discharging voltage can be as high as 4.8V, it has aroused much attention. In this thesis, the modified materials of LiMVO₄ were prepared using the liquid method, sol-gel method and hydrothermal method. The M stand for Ni,Mn,Co,Cr or other metal ions. In addition, in this article, we doped this kind of materials, in order to improve the electrochemical properties of such materials. The charge-discharge experiments were carried out between 5MV and 3V at a current rate of 0.1C. According to the electrochemical tests, cycle characteristics, reversible capacity, charge-discharge efficiency performance of these materials were characterized and analyzed. The structure and morphology of samples were characterized by XRD and SEM techniques.Experiments indicated that the performance of materials which were prepared by sol-gel method and hydrothermal method are very well. The XRD and SEM experimennt result indicated that good crystal cathode materials were prepared with these methods. With hydrothermal method, LiV₃O₈ materials were doped positive ion Mn, Zr, Al and Fe separately. And the inital discharge specific capacity of LiMn_0.06V_2.94O₈ marterials were highest, which the capacity was 312mAh·g^-1, and the material circulation performance was good. The material was doped by anion F, Br and Cl. The inital discharge specific capacity of LiV₃O_7.85F_0.15 was 324 mAh·g^-1. With the Sol-gel method, by doped cationic Co, Zr and Fe . The initial discharges specific capacity of LiCo_0.1V_2.9O₈ material was highest, and the capacity was 346 mAh·g^-1. After 20 discharge-charge cycles, the circulation performance was well, which the capacity maintains at 260 mAh·g^-1. The cycling performance of LiV₃O₈ materials by surface modified with LiMn_1/3Ni_1/3Co_1/3O₂ used a chemical process distinct enhanced. Take LiNiVO₄ as the substrate, the discharge specific capacity of LiNi_0.93Al_0.07VO₄ was 1300 mAh·g^-1 for the first cycle with sol-gel method. The discharge specific capacity of LiMn_0.1Ni_0.9VO₄ materials can achieve 1290 mAh·g^-1 in the first cycle which was prepared by hydrothermal method. The results show that the moditify experiments effective to improve circulation performance and charging -discharging performance.