Controlled Fabricationoftransition Metal Oxides Hierarchical Nanostructures For Lithium Storage

Recent years, more attentions in the field of nanotechnology had been paid to the hierarchical nanostructutre ?HNS? which compose of one or two dimensional nanostructure units. With complex structure and special morphology, these novel HNSs often have different physical and chemical properties from that traditional nanoparticles, as well as the more potential applications than thattraditional ones. Transitional metal oxides with HNS are usually served as anode materialsof li-ion battery. They can keep their selves higher theoretical lithium storage capacity of transition metal oxides own, avoid excessive volume expansion &contraction during lithium insertion & desertion for their higher porosities, and provide more lithium insertion locations for their higher specific surface areas. However,transition metal oxides with HNSs were usually prepared by complicated processes ?such as template method? or rough and uncontrollable ones ?such as hydrothermal method and solvothermal method?, which lead an expensive fabricating cost. In addition, as anode materials of li-ion battery, their size and structural morpholog need also to be optimized and modified furtherly. This paper is targeted to these issues and carry out optimization design of the fabrication, size and structural morphology for the transition metal oxides with hierarchical nanostructure. Based on self-assembly technology of nanomaterials and ion exchange principle under different soluble products, a new simple method had been developed to prepare transition metal oxides with HNSs in this thesis. Three types of transition metal oxides with HNSs in deferent morphology or composition were fabricated by using of aqueous-phase method which first adopted for this application under low temperature and atmospheric pressure, their formation mechanism and performance in lithium storage were investigated also in this thesis. These HNSs include the novel hierarchical hollow a-Fe₂O₃ micro/nanospheres of approximately 250 nm in diameter which composed of the hollow-nanotubes with diameter of 15nm, the flower-like hierarchical a-Fe₂O₃ nanostructure of approximately 500 nm in diameter which composed of the nano pieces with thickness of 15 nm, and the hierarchical hollow CuO flat micro/nanosphere of approximately 1-2?m in diameter which composed of the nanoparticles with size of 20 nm. In addition, it needs to be emphasized that the hierarchical hollow a-Fe₂O₃ nanostructure which composed of the hollow-nanotubes is different from traditional urchin-like structure which composed of the solid nanorods, the novel nanostructure was first designed and engineered. Moreover,the flower-like hierarchical CuC₂O₄ nanostructure was fist prepared by the same way. The aqueous-phase method for fabrication under low temperature and atmospheric pressure,which adopted in this thesis, is a simple economical process and easy to modify the morphology and size of the HNSs, and has a good prospect for industrial production and application, as comparing with the template method, hydrothermal method and solvothermal method .1. The design and fabrication of a novel hierarchical hollow a-Fe₂O₃ nanostructure for lithium storageStarting with the mixture solution of FeSO₄ and K2C₂O₄, the growth rate of FeC₂O₄ nanorods was controlled by adding the complexation of sodium polyacrylate & modifying and changing the supersaturation of the solution, the FeC₂O₄ HNSs were self-assembled by these FeC₂O₄ nanorods. Then, the precursor with hierarchical hollow structure were prepared by the way based on ion exchange principle of FeC₂O₄ and Fe?OH?₂ under different soluble products. After annealed, their morphology were kept, the novel hierarchical hollow-structured micro/nanospheres of a-Fe₂O₃ were attained finally. These novel hierarchical hollow nanostructures of 250 nm in diameter with specific surface area of 133.6 m2 g^-1 are composed of the hollow-structured nanotubes with diameter of 15 nm and length of 100 nm.Served as anode materials of li-ion battery, these HNS spresent excellent properties of lithium storage during charge-discharge tests. They retained a highly reversible capacity of approximately 970 mAh g^-1 beyond 200 cycles at a constant current density of 200 mA g^-1.After scanning at high currents of 0.5C, 1C, 2C, 4C, 8C, turn current ratio to 0.2 C, the reversible capacities of 970 mAh g^-1 were retained also.2. The fabrication of the flower-like hierarchical a-Fe₂O₃ nanostructure with small size for lithium storageThe growth rate of FeOOH from the mixture solution of FeCl₂, CO?NH₂?₂ and O₂ was controlled by citric acid to complexation of Fe₂₊ and changing the supersaturation of the solution, and the flower-like precursor of the FeOOH were self-assembled. After annealed,their morphology were kept, the hierarchical flower-like nanostructures of a-Fe₂O₃ were attained finally.These hierarchical flower-like nanostructures of 500 nm in diameter with specific surface area of 162.5 m2 g^-1 are composed of the nano pieces with diameter of 15 nm.Served as anode materials of lithium battery, these HNS spresent remarkable properties of lithium storage during charge-discharge tests. They retained a highly reversible capacity of approximately 997 mAh g^-1 beyond 200 cycles at a constant current density of 200 mA g^-1. The result is closed to the theoretical value of the a-Fe₂O₃ for li-ion storage. After scanning at high currents of 0.5 C, 1 C, 2 C, 4 C, 8 C, the current rates were reverted to and 0.2 C, whereas, the reversible capacities of 998 mAh g^-1 were retained.3. The fabrication of the hierarchical hollow CuO flat micro/nanosphere with small size for lithium storageStarting with the mixture solution of CuSO₄,K2C₂O₄ and CTAB, the CuC₂O₄ flat micro/nanosphere were prepared. Then, the hollow precursor with hierarchical structure were prepared by the way based on ion exchange principle of CUC₂O₄ and Cu?OH?₂ under different soluble products. After annealed, their morphology were kept, the hierarchical hollow CuO flat micro/nanosphere were attained finally.These nanostructures are composed of the nanoparticles with size of 20 nm, the diameter of that nanostructure is about 1-2 ?m, and the specific surface area is 52.6 m2 g^-1. Li/ CuO hierarchical hollow flat nanosphere half-cells retained a highly reversible capacity of approximately 500 mAh g^-1 beyond 50 cycles at a constant current density of 200 mA g^-1.Different surface active agents and complex agents were used to control the morphology of the precursor CuC₂O₄. The flower-like Hierarchical CUC₂O₄ nanosphere was initially designed and engineered through aqueous-phase way under low temperature and atmospheric pressure.