| With many advantages such as high energy density, low self-discharge, high specific energy, no memory effect, wide operating temperature range, high output voltage, safety and stability, rapid charge-discharge ability and so on, lithium-ion battery is considered to be the most potential energy storage system for the electric vehicles, hybrid vehicles, as well as emerging intelligent network power. However, due to the low theoretical capacity (372mA h g-1) of graphitic carbon, which is the most commonly used anode material, the current LIBs are approaching limits set by the electrode materials. Thus, the search for alternative anode materials has become an urgent task in building the next-generation LIBs, so as to meet the ever-growing performance demands. One of the feasible candidates for anode materials is nano-sized transition-metal oxides. Among them, nanostructured Fe3O4has attracted considerable attention owing to its low cost, eco-friendliness, natural abundance and high capacity.However, its practical application is still hindered by poor cyclic performance and rate capability, resulting from severe aggregation and dramatic volume change during Li+insertion/extraction processes. Moreover, the low conductivity of iron oxide often further hastens the degradation process. To improve the durability and high rate capability of iron oxides, various types of modification methods have been employed, and the carbon coating is the most effective. We attempted to fabricate iron oxide based anode materials with excellent electrochemical performance focusing on the materials preparation and structure optimization, the significant parameters such as cycling stability; rate capacity and Coulombic efficiency were the indicator during the procedure. Advanced characterization techniques such as XRD, SEM, TEM, TG, EDX and XPS were used to investigate the influence of crystal structure, micro structure morphology, composition and surface chemistry of the electrode material on the electrochemical properties of the electrode. In this thesis, the following progresses have been made:(1) The rhombic-shaped Fe2O3nanoparticles were successfully synthesized through hydrothermal method assisted with amino acids. Then, two kinds of carbon coated rhombic-shaped Fe3O4samples were obtained via hydrothermal method and grinding method, respectively. The electrochemical tests have proved that the carbon coating is an efficient way to improve the electrochemical performance of the Fe3O4-based electrode, the specific capacity was increased from230mA h g-1to660mA h g-1accompanied with initial effieiency was increased from49.8%to67.5%.(2) Dopamine as precursor has a significant advantage in tuning the compositions and properties of the coating layer, which is essential for material design and optimization. Herein, we firstly used dopamine as precursor to prepare N-doped carbon coating nano-sized FesO4(fe3O4@NC) composites through a two-step method. Such fascinating Fe3O4@NC composite as a LIBs anode exhibits outstanding electrochemical performance with a very high specific capacity of976mA h g-1at the current of0.5A g-1and the initial cycle efficiency of68.5%.(3) We developed a new "Dual confinement’" method to fabricate coaxial Fe3O4@C nanocylinders with both well developed pore structure and carbon shell. This composite has the advantags of carbon coating and hollow structure, which ensure the excellent rate capabiliity. The electrochemical performance (864and320mA h g-1at a current of1.0and3.0A g-1, respectively) of this composite with novel configuration was outstanding compared with other iron oxide anode materials. |
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