Preparation Of Nanostructured Iron Oxide Anode Materials And Electrochemical Property Study

With the development of society and improvement of life quality, lithium-ion batteries have already been unable to meet the demands of the people in spite of their excellent performances. To improve the energy density and power density of lithium-ion batteries, exploring new electrode materials is very necessary. In comparison of the cathode materials, commercial anode materials are relatively single and possess lower power density, which affects the application of lithium-ion batteries in electric vehicles in the future. Fortunately, 3d transition metal oxides with high energy density have been intensively studied recently. Because Fe3O4 and Fe2O3 are environmentally friendly, high electrical conductivity, abundant reserves, they are particularly promising to be used as anode materials for lithium ion batteries. However, the large volume change of them during charge and discharge would lead to the quick degradation of battery capacity.In many literatures, a large number of works have been performed to improve the cycle stability of Fe3O4 and Fe2O3 by carbon coating, which brings directly about the advantages such as reducing the contact area between the electrode and the electrolyte as well as the formation of solid electrolyte interface(SEI) film. In addition, the carbon-coating layer could buffer the volume change of Fe3O4 and Fe2O3 powders during charging and discharging. As a result, the electrochemical properties of the electro-active materials are improved effectively.In this article, nanostructured iron oxide/carbon composites were prepared by one-step hydrothermal. Their electrochemical properties were investigated.(1) To optimize the process of producing nanstructured iron oxide, the effects of reaction time and solvent ratio on the electrochemical properties of the synthesized materials were studied. The results suggest that at the conditions such as 16 h of reaction time and 1:4 of volume ratio of water to glycol, the as-prepared Fe3O4 materials revealed better electrochemical performances. It could deliver an initial capacity of 1344,1210 and 980 mAh/g at the rates of 0.2, 0.5 and 1C, respectively. The corresponding discharge capacities are about 29%, 35% and 23% of the initial ones after 50 cycles. The coulombic efficiency is 67% at the 0.2C rate in the first cycle. Therefore, its electrochemical performances need improved further.(2) To improve the electrochemical properties of the Fe3O4 material, the porous Fe3O4/C composites were prepared in one step through hydrothermal treatment by using glucose as carbon source. The obtained Fe3O4/C composites have a specific surface area up to 22.1m2/g. They could deliver the initial capacities of 1550, 1350 and 900 mAh/g at the rates of 0.2, 0.5 and 1C, respectively. The corresponding capacity remaining ratios are 41%, 38% and 39% after 50 cycles. However, the coulombic efficiencies are 59%, 53% and 57% in the first cycle when the current densities are 0.2, 0.5 and 1C rate, respectively. In any case, the Fe3O4/C composites displayed the significantly improved electrochemical performances when compared with the bare Fe3O4.(3) Spherical Fe2O3/C composite material was prepared by using ferrocene as the sources of Fe and C in one step. The synthesized material appeared as spheres with an average diameter of 400 nm. This composite material could deliver an initial capacity of 998 mAh/g at the 0.1C rate, and maintained 616 mAh/g after 50 cycles. In the first cycle, the coulombic efficiency is 73%. The resul Fe2O3/C composite material ts indicate that the Fe2O3/C composite material has a good cycling performance at the low current density.