| China is the largest country in battery production and consumption in the world,the secondary battery is a kind of energy which is clean and high efficient. It is an important technological approach to solve the energy problem, source problem and environment problem, it is the key point of electric vehicles, energy storage power station and uninterruptible power supply, at the meantime it is an important working power supply in the portable era. Rechargeable lithium ion battery(LIB) represents a well-established technology for energy storage, being nowadays the most popular power source in portable electronics. Lithium ion battery has many advantages, such as well energy storage, safe pollution-free and so on. The development of lithium ion battery is fast and paid attention by the world. Because the lithium ion battery has big energy density, high average output voltage and no pollution to the environment, lithium ion battery has been widely used in various types of electronic products. At the same time, lithium ion battery has been used widely in our life, for example, mobile phone, flashlights, even trucks, cruise ships and so on.Now, the LIB anode materials has been industrialized is carbon based materials. But, the carbon based materials is not safe in charge and discharge, in more serious case, will endanger people’s lives.Because carbon based anode materials have kinds of uncertainty, people begin to research new and highly efficient lithium ion battery anode materials. Therefore, a variety of transition metal oxides interested, and people began to use the transition metal oxides as lithium ion battery anode materials. Among them, tin dioxide(SnO2) is one of the most intensively studied anode material for its high theoretical capacity(1494 mAh g-1), safe working potential and environmental benignity. In recent years has been widely used in lithium ion battery anode materials research.Despite the high theoretical capacity, the practical use of the SnO2 anode is greatly hampered by its quick capacity fading upon extended number of cycles, which is believed to be derived from the huge volume change of SnO2 during discharge/charge process. Meanwhile, its electron conductivity is rather poor. To confront these drawbacks, several strategies have been proposed to improve its electrochemical performances. For example, one of the well-known methods is to design various SnO2 nanostructures with large surface areas and high surface-to-volume ratios, such as nanotubes, nanoboxes, nanosheets and hollow spheres, which exhibit increased capacities and improved cycling properties due to shortened diffusion distance of lithium ions and increased specific area. Some researchers use the way of cladding, they try to prepare the composite material of SnO2 and graphite. Comparing with the pure SnO2 material, after cladding, the composite material put up better electrochemical performances. And some researchers use mental ion(Ca, Co, Ti, Ni and so on) doping in pure SnO2 material, this method can increase of electronic conductivity and lithium ion diffusion coefficient, so improving the electrochemical performance of the composite material.In the present study, the SnO2 hollow spheres and the Al-doping SnO2 hollow spheres composites were prepared by one-step hydrothermal reaction. Physical properties and electrochemical performances were extensively compared. This thesis mainly comprises the following three aspects:1. In order to get the best experimental conditions, we use the method of control variable, and then we compared the electrochemical performances between the Sn O2 hollow spheres and the SnO2 nanoparticles. The results indicate that the large surface areas and high surface-to-volume ratios, such as nanotubes, nanoboxes, nanosheets and hollow spheres, which exhibit increased capacities and improved cycling properties due to shortened diffusion distance of lithium ions and improved the ability of lithium storage.2. The Al-doping SnO2 hollow spheres were synthesized by one-step hydrothermal reaction, and test the electrochemical performances. After a series of physical characterization, the results show that the phase maintained unchanged. The electrochemical performances of lithium insertion into un-doped and Al-doped SnO2 hollow spheres were studied by comparison.3. Li4Ti5O12 has excellent structural stability during discharge/charge process, but the theoretical capacity is low. So, we designed a method which take advantage of Li4Ti5O12 nanosheet to clad the SnO2 hollow spheres, in order to use the excellent structural stability of Li4Ti5O12 nanosheet to limit the huge volume change. Combining the advantage of the two materials, we want to improve the electrochemical performances of the composite material. |
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