| At present, Li-ion batteries have been the vital power sources for mobile electronic devices, and is also the ideal power supply for the future electrical vehicles because of their advantages including high power-density and high operating-voltage, etc. With the fast development of the aforementioned applications, Li-ion batteries with higher power-density, higher energy-density and higher safety are urgently desired. However, the currently used commercialized graphite anode only have a theoretical specific capacity of 372 mA h/g, which is greatly hindering the further development of Li-ion batteries. Thus, searching for new anode materials with higher specific capacity is essential for developing advanced Li-ion batteries. At room temperature, Si and Ge have theoretical specific capacities of as high as 3579 and 1384 mA h/g, respectively, are considered as the most promising candidates for anodes of Li-ion batteries. But unfortunately, Si and Ge anodes always undergo a rapid capacity fading caused by severe volume change (-300%) during Li-ion insertion and extraction. Meanwhile, Si and Ge as the typical semiconductor materials, the conductivities are not high enough, which always leads to a poor rate performance. In this thesis, for the purpose of developing Li-ion batteries with improved rate capability and cyclability, we intend to design and fabricate Si and Ge thin film anodes on nanostructured current-collectors. And the obtained anodes was studied from the aspects of nanostructure optimization, fabricating-method exploration, micro-structure, morphology and electrochemical performance. The main contents comprise the following four parts:1. CuO nanorod was synthesized through an inexpensive and high-efficiency way instead of the commonly used solution-immersion method. The prepared three-dimensional nanostructured CuO anode displays a high cycling stability and improved rate capability. A specific capacity of 790 mA h/g is realized after 80 cycles at a rate of 100 mA/g. Even for the rate of 1 A/g, the anode exhibits a capacity of about 635 mA h/g which steadily maintained at 540 mA h/g after 100 cycles. The obtained CuO nanorod structures were used as nanostructured current-collectors in the following works.2. P-doped amorphous Si was deposited on Cu nanorod net-work by PECVD method. The nanostructured Si anode displays an improved cyclability and rate capability. Specific capacity of 2010 and 1790 mA h/g are realized after 80 cycles at rates of 2 and 4 A/g, respectively.3. CuO/Ge core-shell nanorod anode was fabricated by electro-beam evaporation method. The reactions in the first discharge could make the CuO nanorods convert to conductive composite of Cu and Li2O, which could act as an electronic-conductor for the electrode and thus made the fabrication of nanostructured current-collector easier. The nanostructured Ge anode displays an improved cyclability and rate capability. Specific capacities of 1010 and 850 mA h/g are realized after 100 cycles at a rate of 1 and 2 A/g, respectively.4. The voltage cutoff window in the last work was too small, and in order to solve such a problem, Co3O4/Ge coaxial nanorod anodes were fabricated on nickel foam. The reactions in the first discharge could make the Co3O4 nanorods convert to conductive composite of Co and Li2O, which could act as an electronic-conductor for the electrode. By limiting the voltage cutoff window in an appropriate range, the obtained Ge anodes exhibited excellent lithium storage performance in both half and full cell configurations, which indicates that the strategy of limiting the voltage cutoff window in an appropriate range to avoid the electrochemical reactions of the Co3O4 nanowires is feasible. |
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