Preparation And Electrochemical Performance Of Iron Oxide Anode Materials For Lithium Ion Batteries

With the continuous development of science and technology, people's demand for energy is getting higher. The energy problem has become one of the main factors that influence the survival of mankind. The application of lithium ion battery has greatly promoted the development of energy. Nowsdays, lithium ion battery has shown its great potential, has become a kind of new performance, energy saving, clean type of a new generation of battery. In order to achieve ideal performance of lithium ion batteries, first, the anode material is required to have a high capacity of embeding lithium ion. Second,the anode material is required to have a high ionic conductivity. Finally the performance of the anode materials for stability and it is not due to external factors to change the performance.This work mainly studies the structure and morphology of iron oxide anode materials and the application of lithium ion batteries. Preparing iron oxide nano materials with different morphologies and crystalline phase by co-precipitation method, hydrothermal method, molten salt method. Through X-ray diffraction analysis?XRD? and scanning electron microscopy?SEM? characterization methods to study the influence of different preparation methods and different experimental conditions on the morphology and structure of iron oxide material. Finally the electrochemical properties of electrode materials were studied through electric blue battery test system?LAND?. The main research work is as follows:?1? By co-precipitation method to prepare different mass ratio of nickel doping Fe₂O₃ nanoparticles, the doped nickel mass ratio is 1%, 3% and 5% respectively. With sodium hydroxide precipitation agent to prepare the nickel-doped Fe₂O₃ nanoparticles. Basically it is spherical, the dispersion is good, the particle distribution is more uniform, the particle size is very small and roughly about several nanometers. While use of ammonia as precipitating agent to prepare the nickel-doped Fe₂O₃ nanoparticles, the group aggregation phenomenon is more serious. The experimental results show that the nickel-doped Fe₂O₃ nanoparticles with good charge discharge performance when the sodium hydroxide as precipitant, the quality of nickel-doped ratio is 3%, the calcination temperature is 500?. The first discharge specific capacity is 1319.9mAh/g, after 30 charge/discharge cycles, the discharge specific capacity is kept at 524.3mAh/g.?2? MgFe₂O₄ was prepared by using the hydrothermal method: first, the changes of microstructure and morphology of MgFe₂O₄ under the same calcination temperature and different hydrothermal temperature were studied. Second, through studying at the same hydrothermal temperature?180??, with the increase of the calcination temperature, the average particle size of MgFe₂O₄ nanoparticles from 74±7 nm increases to 129±4 nm, single of MgFe₂O₄ nanoparticles bonded with each other and distributed evenly. So, with the increase of the calcination temperature, the grain size of MgFe₂O₄ can be refined and the uniform nanoparticles can be obtained. The experimental results show that the best electrochemical performance of the sample is obtained when the calcination temperature is 600? and the hydrothermal temperature is 180?. The first discharge specific capacity is 712.6mAh/g, after 30 charge/discharge cycles, the discharge specific capacity is kept at 363.6mAh/g.?3? a-Fe₂O₃ material was prepared by molten salt method and the carbon coated iron oxide materials were also prepared by using glucose and citric acid as carbon source. When the calcination temperature is 850?, the synthesized a-Fe₂O₃ nanoparticles showed a quasi cubic shape, with good dispersion and uniform distribution. It is found that with the increase of the calcination temperature, the crystallization of the product can be more complete, and the crystal structure is more complete, which further shows that the higher calcination temperature is beneficial to the growth of the crystal. Using glucose and citric acid as carbon source, the initial capacity is 1370.6 mAh/g and 1245.1 mAh/g, which is higher than the theoretical capacity. After 30 charge/discharge cycles, the discharge specific capacity is kept at 589.8 mAh/g and 627.8 mAh/g respectively. Without carbon coated a-Fe₂O₃ nanoparticles, the initial capacity is 1085.9 mAh/g, after 30 charge/discharge cycles, the discharge specific capacity is kept at 351.3 mAh/g. The result is attributed to the amorphous carbon layer can keep active material of electrode connection, which is beneficial for lithium ion and electron transport, also carbon layer effectively limits the volume expansion, resulting in the improvement of cycle performance.