| Lithium ion batteries (LIB) become the most important secondary battery because of its high operating voltage, large capacity, stable discharge potential, long cycle life and low self-discharge, etc. LIB is considered to be the first choice for power battery of electric vehicles, solar and wind energy storage device in the future, not only widely used in mobile communications, laptop computers and other portable appliances. Synthesizing LIB with high energy density, high power density and long cycle life is the basis for its application in the power batteries.The aim in this thesis is to improve the energy density, cycle performance, and rate capability of LIB. The key point is to design the nano-micro-architectural of Co3O4active material and build a network structure of the nanostructured current collectors. Co3O4nanoarray in-situ growing in different current collectors was fabricated by a facile hydrothermal growth with subsequent calcinations. The application of nanostructured current collectors improves the areal capacity (2.1mAh cm-2) of Co3O4electrode. Compared with Ni foam current collectors, the areal capacity (0.8mAh cm-2) increases263%, compared with stainless steel current collectors, the areal capacity (0.47mAh cm-2) increases450%. The results will provide the experimental basis for future aplications in power batteries. The main contents of the paper and the corresponding results are summarized as follows:1. Free-standing Co3O4nanowire arrays have been fabricated on stainless steel by a hydrothermal growth with subsequent calcination. As an anode of LIBs, the unique architecture of Co3O4exhibits high capacity, excellent rate capability and cyclic stability. After several cycling, a very high stable capacity of1300mAh g-1can be obtained, delivering an areal capacity0.47mAh cm-2at a current density of1C, capacity retaining99%after150cycles. Significantly, the Co3O4anode cycled at a rate of6C exhibits stable capacity of1060mAh g-1after100cycles. Even at a rate as high as20C, the capacity retains77%of its capacity at the rate of0.5C. The Co3O4electrode maintains a high reversible capacity at the large current density.2. Self-supporting Co3O4with lemongrass-like morphology has been fabricated on Ni foam by in-situ growth. The lemongrass-like morphology is composed of small porous blades. As an anode of LIBs, the unique architecture of Co3O4exhibits high capacity, excellent rate capability and cyclic stability. High reversible capacity of981mAh g-1after100cycles at a rate of0.5C and high capacity of381mAh g-1(the capacity retains42%of its capacity at the rate of0.5C) at a rate as high as10C made the material a promising candidate for anode materials of high-power LIBs.3. We have developed a template-free method to fabricate the free-standing and ductile Ni nanofoams for application as nanostructured current collectors in LIBs. The approach was demonstrated to be facile, low cost, and large-scale produced and the prepared current collectors of the Ni nanofoams are compatible with various active materials. The Ni/NiO nanofoams electrodes with superior cycling stability and rate capability were prepared by in situ thermal oxidation of the resultant Ni nanofoams. A high reversible capacity of940mAh g-1(as high as2.3mAh cm-2in areal capacity) was obtained after200cycles at a current rate of0.5C. Since the Ni nanofoams skeletons show the excellent electrochemical stability in electrolytes, the prepared Ni nanofoams with highlights of interconnection, conductivity, and large surface area can be used as nanostructrued current collectors for high-performance electrochemical energy storage devices.4. Ultra-thin porous Co3O4nanosheet arrays have been synthesized on Ni nanofoam current collector. The thickness of nanosheet is8nm and the pore size is3-5nm. All the skeletons of Ni nanofoam were uniformly coated by nanosheets. The mass density of Co3O4active material is2.4mg cm-2, compared with the mass density (0.36mg cm-2) on the flat plate-type stainless steel current collector, which is improved670%. As an anode of LIBs, the ultra-thin porous Co3O4nanosheet arrays exhibits excellent rate capability and cyclic stability. The reversible capacity is912mAh g-1(as high as2.2mAh cm-2in areal capacity) after300cycles at a rate of0.5C. |
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