Preparation And Electrochemical Performance Of Transition Metal Compound As Anode Materials For Lithium Ion Battery

With the limition of conventional energy sources and increasingly prominent environmental problems, more and more attention is paid to the development of environmental protection and renewable new energy sources by many nations. Lithium ion batteries, as the representative of an electrochemical energy storage, is the most promising new energy technologies to solve the energy storage problems in new energy power generation. In recent years, with the booming of electric automobile market, lithium ion battery, which has high energy and power density, is acclaimed as the preferred technology in new energy automotive sectors energy storage. These attract research boom about lithiumion batteries worldwide. The key of the lithium-ion battery research is electrode materials. Transition metal compound, which owns a high theoretical capacity, low cost, ecofriendliness, natural abundant, safety and many other advantages, has been widely investigated by researchers. However, there are also some drawbacks of transition metal compound to be overcome when acting as anode material for lithium-ion battery, such as poor electrical conductivity, huge volume change during lithium ion insertion/extraction, which lead to pulverization of the initial particle morphology and breakdown of electrical connection of such anode materials from current collectors, seriously hindered the direct use of raw Fe3O4 material in commercial batteries. Two main strategies are commonly used to solve these problems. One is to synthesis nanostructured materials with various morphologies. The other one is to incorporate with carbonaceous materials. In this article the electrochemical properties of iron-based oxide, manganese oxide and molybdenum disulfide group will be improved through a variety of methods related to these two strategies. The main contents are as follows:Fe3O4/FeO/Fe nanoparticles coated with amorphous carbon is prepared via a facile and scalable in situ-reduction solid synthesis route. Glucose is prepared as carbon source. it is mixed with nanosized Fe2O3 powder as precursor, then heated at different temperatures. The reaction products are tested by XRD, XPS, SEM, TG and other testing methods. It is found that, the sample synthesized under 700 °C is Fe3O4, FeO, a small amount of Fe and amorphous carbon. What's more, the components are closely contacted and the carbon can form the substrate throughout the material by coating the particles uniformly, which can buffer the volume change during charge and discharge. When used as anode materials in lithium ion batteries, the as-prepared Fe3O4/FeO/Fe/Carbon composite shows super high rate capability(685, 543, and 401 mAh/g at 2, 5, and 10 C, respectively, 1 C = 1 A/g) and extremely excellent cycling performance at high rates(capacity remains 900 mAh/g after 500 cycles at 1 C). It proves that the composite has excellent cycling stability and rate capability. Wherein a small amount of elemental Fe in the material can significantly improve electrical conductivity of the material, and it plays a crucial role to improve the electrochemical properties.By using in situ-reduction solid synthesis route on another transition metal compound material, manganese-based oxide, samples are synthesized by adding MnO2 and glucose powders as precursors at different temperatures. XRD and SEM tests are performed, followed by the comparison and analysis of how reaction temperature affects the composition and electrochemical properties are made. Electrochemical tests of each group of samples are performed. It is found that that MnO/C composite synthesized at 800 °C has an excellent electrochemical performances. The reversible capacity of this sample continues to increase from 50 th cycle to 500 th cycle in a current as high as 1 A g-1, and reaches 845 mAh g-1 at 500 th cycle, showing excellent cycling stability and rate performance.Hydrothermal method and CVD are combined in this part. MoS2@GF sample is synthesized by depositing MoS2 on the three-dimensional graphene foam(GF) generated using CVD method. By adjusting the duration of hydrothermal reaction process, the deposition amount of MoS2 can be controlled. The 180 °C sample can be used directly as a Binder-free electrode material, getting rid of the need for binder and conductive agent, simplifing the fabrication process of battery. When used as anode material for lithium ion battery, MoS2@GF composite obtains a reversible capacity of 900 mAh g-1, showing a stable cycle performance and excellent rate capability. Through the comparison and analysis of different samples, it can be seen that MoS2@GF composite combines the advantages of both GF and MoS2, among which MoS2 has a high theoretical capacity, while GF can significantly improve the conductivity of composites.