Synthesis Of Transition Metal Oxides As Anode Materials For Lithium Ion Battery And Their Electrochemical Performance

Lithium ion battery is one of the best prospect power sources at present, because of its high specific energy, high efficiency and long life. Currently, globally used commercial graphite carbon anode material (The theory of specific capacity is372mA h g"1) for lithium ion battery has not been able to meet the requirement of high capacity, therefore, a lot of efforts have been devoted to searching for new anode materials with larger specific capacities, high charge-discharge efficiency and high cycle performance for the next-generation lithium-ion batteries. As the representative, MxOy (M=Co, Ni, Cu, Fe), transition metal oxides have attracted much attention, because their theoretical capacity (around1000mA h g-1) is much higher than the traditional graphite. However, they are faced with problems of low electronic conductivity, large volume change, and poor cycle performance etc. In order to solve those problems, we have tried to prepare transition metal oxide anode materials with high electrochemical performance by morphology control and design composites with the dual lithium storage mechanism.First of all, concave α-Fe2O3cubes ware prepared via hydrothermal method using copper ammonia complex as structure-directing agent. The effect of copper ammonia complex on the formation and growth of α-Fe2O3particles were systemically investigated. When tested at a current of100mA g-1as anode materials, the as-prepared concave α-Fe2O3nanocubes exhibited an initial reversible capacity of1123.2mA h g-1and a514mA h g-1capacity after95cycles, which overmatched the conventional spherical or convex polyhedral iron oxide materials of similar size, and the reason might be owing to the unique concave cube structure, and relatively uniform size and shape.Then, we have studied the preparation of porous TiO2coated α-Fe2O3ginger-like nanostructures anodes, and their electrochemical properties on different coating conditions. Due to the synergistic effect between α-Fe2O3and TiO2nanostructures, porous TiO2coated α-Fe2O3ginger-like nanostructures anode has better electrochemical performance than α-Fe2O3. The porous walls of TiO2nanoparticles provide a larger contact surface between the active materials and the electrolyte, and a conductive path for electrons and lithium-ions, which can improve the electrode conductivity. As comparison, the reversible capacity of pure α-Fe2O3anode dropped to below200mA h g-1under the rate of100mA g’1, after50times cycle, and however the reversible capacity of porous TiO2coated α-Fe2O3ginger-like nanostructures anode was higher than418mA h g-1, after150times cycle.In the end, we also studied Ti02/CoFe204nanocomposites anode and its electrochemical performance. Iron-based spinel oxides such as CoFe2O4and ferrite with general formula AFe2O4(A=Zn, Ni, Co, Mn, etc.) have been extensively studied as anode materials for lithium-ion batteries, and their specific capacity and charge/discharge voltage can be adjusted by changing their composition. CoFe2O4anode has a high theoretical specific capacity, however, it has the same problems as huge volume change during the discharge/charge progress and poor cycle ability. Thus we tried to enhance structure stability of CoFe2O4by introducing TiO2nanocrystals. TiO2/CoFe2O4nanocomposites anode showed an initial discharge specific capacity of623mA h g-1, and after200cycles, their capacity remained to be516mA h g-1, corresponding to83%retention of the initial discharge capacity.