Synthsis And Property Study Of Fe-Based Oxides And Fe-Based Oxides/GNS Nanocomposites

Due to their easily obtainable, eco-friendliness, safety and good electrochemical properties and so on, Fe-based materials have attracted considerable attention. Because of their novel optical, electronic and magnetic properties, Fe2O3 and Fe-based/GNS composite materials have potential applications in many fields, such as electromagnetic shielding, magnetic, catalyst materials, and antibacterial materials. Therefore, it has attracted much interest to controlled synthesize Fe2O3 and Fe-based/GNS composite materials with various morphologies, to study the size- or shape-dependent properties, and to find their new applied fields. On the other hand, lithium-ion batteries (LIBs) are the most competitive batteries because of their high voltage and specific capacity. Among those industrial LIBs, cathode materials are LiCoO₂ and LiMn₂O₄, anode materials are carbon materials (graphite). The initial irreversible specific capacity will increase because carbon materials as anode materials are easily to form SEI passive film; the potential of carbon materials is close to Li, so the batteries are easy to precipitate matal Li and form dendrite then cause short-circuit when overcharged; therefore, it has become the new direction of the LIBs to search and develop cathode/anode materials with low cost, environment friendly and excellent performance. In this thesis, we have successfully synthesized a series of Fe₂O₃ and Fe-based/GNS composite materials through hydrothermal and ultrasonic. The influence on the morphology and structure of the obtained products was studied, such as reaction time, reaction temperature, ratios of reactants or additive. And their related formation mechanism and magnetic and electrochemical properties were also studied.(1) The flower-like iron oxides and nanoparticles have been successfully synthesized by a hydrothemal method in the presence of a complexing agent sodium citrate. The effects of molar ratio of reactants, the reaction temperature and time on the microstructure of iron oxides were studied in details. The possible formation mechanism of these unique morphologies has been proposed based on the reduction and limitation of chelating of sodium citrate. Different morphologies of porous Fe₂O₃ also have been successfully synthesized by hydrothermal method in the presence of polymer PVP or F127.(2) Hollow Fe₂O₃/Graphene nanocomposites were synthesized by a hydrothermal method, and their electrochemical property of Li storage performances were well characterized. The obtained nanocomposites show high specific capacity and good cycle stability. Simple preparation method, easily obtainable reactants and water as solvent made this work important both on financial and environment protection.(3) In order to obtain Fe-based oxides/graphene composite with fewer layers of graphene and with well-distributed Fe-based oxides, graphene-waped Fe₃O₄ nanocomposites were synthesized by a ultrasonic method, and their electrochemical property of Li storage performances were well characterized. The influence of ratios of reactants on the formation of the obtained products was studied. And the electrochemical property at different current density of the obtained nanocomposites show better Li storage performances and cycle stability than Fe2O3/Graphene nanocomposites prepared by hydrothermal method.