Research On Preparation And Electrochemical Performance Of Iron Oxide And Iron Oxide-graphene Nanocomposites

Lithium ion battery has high operating voltage, high energy density and good cyclestability which makes it very important in the energy storage devices and portableelectronic products. Fe₂O₃has attracted great interest due to its low cost, hightheoretical capacity and environmentally friendly synthesis processes. However, Fe₂O₃suffers from poor electrochemical performance due to the large volume changes duringthe lithium ion intercalation/extraction process. In addition, Fe₂O₃results in severe lossof capacity with a poor electrical conductivity.In this thesis, Fe₂O₃particles, flowerlike Fe₂O₃and spherical Fe₂O₃weresynthesized via solvothermal, hydrothermal and soft template route. Effect of themorphologies of iron oxide on the electrochemical properties was investigated. Themain results are listed as fellows.1) Fe₂O₃particles were prepared via solvothermal route, using ferric chloride andurea. The results show that the morphologies, structure, electrochemical performance ofFe₂O₃particles can be influenced by content of urea and reaction temperature. Theas-prepared Fe₂O₃particles showed well crystalline and uniformity. When the molarratio of ferric chloride and urea is1:2, the as-prepared Fe₂O₃particles with uniform sizeof0.35⁰.5μm showed uniform distribution and good crystallization.2) Flowerlike Fe₂O₃was prepared via hydrothermal route, using sodium sulfateand ferric chloride as raw materials, and its forming mechanism was analyzed and theelectrochemical properties were investigated. When the molar ratio of anhydroussodium sulfate and ferric chloride is1:1, flowerlike Fe₂O₃with uniform size of3⁴.5μmwas prepared via hydrothermal route in140℃reacting16hours. Flowerlike Fe₂O₃wasgalvanostatically charged and discharged at0.2C of current density. After30cycles, thespecific capacities remained relatively constant at around496.3mAh/g.3) Spherical Fe₂O₃was synthesized via solvothermal route using glycerol as softtemplate, and the electrochemical performance was studied. When the volume ratio ofglycerol and water is1:3, the as-prepared spherical Fe₂O₃showed small size, uniform distribution and good crystallization. The spherical Fe₂O₃was galvanostatically chargedand discharged at0.2C of current density. After30cycles, the specific capacitiesremained relatively constant at around533.6mAh/g.4) Fe₂O₃-graphene nanocomposites were synthetized via annealing, using graphiteoxide and the precursor of Fe₂O₃, the electrochemical properties of Fe₂O₃-graphenenanocomposites were studied. Compared to those of the Fe₂O₃anodes, the cyclingstability, specific capacity, rate performance of Fe₂O₃-graphene nanocomposites wereimproved. Spherical Fe₂O₃-graphene nanocomposites were galvanostatically chargedand discharged at0.2C of current density. After30cycles, the specific capacitiesremained relatively constant at around657.2mAh/g,23.2%higher than that of sphericalFe₂O₃without graphene.