Study On Preparation And Electrochemical Performance Of Iron Oxide As Anode Materials For Lithium-ion Batteries

With the daily depletion of petroleum resources, energy storage has become a crucial issue. Lithium ion batteries (LIBs), as novel energy storage device, were extensively studied during past years. The properties of anode material play a significant role in performance of LIBs. As promising anode materials for LIBs, transition metal oxides (TMOs) have gained enormous research interest because of their high theoretical capacity. Fe-based oxide as TMOs, are attractive candidate for anode of LIBs due to its environment friendliness, high abundance and high theoretical capacities. Nevertheless, a large specific volume change usually occurs in the host matrices of the metal oxide during the charge/discharge process, which will lead to rapid capacity decay and high initial irreversible capacity loss. In previous research, two main kinds of strategies have been considered to improve the electrochemical performance of Fe3O4. Such as controlling Fe3O4nanostructures and coating carbon.In this thesis, nanostructure Fe3O4/C and Fe2O3/C nanocomposite have been prepared. The structure of the as-prepared samples were characterized by X-ray diffraction(XRD), thermal gravimetric analysis (TG), Raman microscope, transmission electron microscopy(TEM) and scanning electron microscopy(SEM). Besides, the electrochemical properties of the electrodes were tested by electrochemical technology, such as cyclic voltammo grams, charge/discharge profiles, impedance spectra and so on. The main contents are as follows:1. Fe3O4/C nanocomposite has been prepared by PEG-assisted co-precipitation method. The structure and morphology of the as-prepared material are analyzed by XRD and TEM. The results show that Fe3O4/C is well-crystallized and Fe3O4and Carbon particles constitute nanocomposite, Carbon nanoparticles disperse among Fe3O4particles forming a Carbon layer, which prevent the Fe3O4particles from contacting each other. The Fe3O4/C nanocomposite keeps at a high discharge capacity of902.4mAh g-1at1C after110cycles. The result of rate test show that the electrode after the high current density charge/discharge cycling, the current density is reduced stepwise to100mA g-1, the nanocomposite with a specific capacity as high as1086.7mAh g-1is recovered, indicating that Fe3O4/C nanocomposite has an good kinetic properties.2. Fe3O4/C nanocomposite has been prepared by sol-gel method. The structure and morphology of the as-prepared material are analyzed by XRD and TEM. The results show that Fe3O4/C is well-crystallized and Fe3O4/C with small size. The results of electrochemical tests show that Fe3O4/C nanocomposite keeps at a high discharge capacity of over900mAh g-1at0.1C after160cycles. Furthermore, the sample shows much improved rate capability and better cycle stability compared with pure Fe3O4when used as anode material for lithium-ion batteries.3. Core-shell structure Fe2O3@C nanosphere has been prepared by hydrothermal method. The structure and morphology of the as-prepared Fe2O3@C nanosphere is analyzed by XRD and TEM. The results show that Fe2O3@C nanosphereare well-crystallized and with uniform small size. The average size of Fe2O3@C is in the range of20-30nm. The results of electrochemical tests show that Fe2O3@C nanosphere keeps at a high discharge capacity of over924mAh g-1at1C after100cycles. Furthermore, the Fe2O3@C nanosphere shows much improved rate capability and better cycle stability compared with pure Fe2O3when used as anode material for lithium-ion batteries.