| As the larger and larger demand of energy consumption and being exhausted non-renewable resources, the energy problem has become one of the significant topics. Although impressive progress in the technology development for new energy resources such as solar energy, bio energy, geothermal energy and nuclear energy have been obtained, the development of recycled storage devices is still lagging far behind. On the other hand, the air pollution by the exhaust emissions from traffic transportation is becoming serious, application of a new power battery for replacing the internal combustion engines is an imminent work. Lithium ion battery (LIB) as an energy storage device has attracted much attention, and high capacity, super cycle stability and safety is becoming a hotpot of LIB research. In this thesis, the fabrication and electrochemical performance of SnO2based thin film electrode for LIB were studied. The main work includes the following aspects:An ATO (SnSb0.0502) sputtering target,50mm in diameter and5mm in thickness, was prepared by a traditional ceramic fabrication process, i.e., synthesized by a wet-chemical method, sintered at1250℃with an appropriate sintering aid.The ATO thin film was fabricated by an RF magnetron sputtering (MS) technology. The effect of sputtering substrate temperature on the microstructure, phase component and surface morphology of the ATO thin film were investigated. The results show that the ATO thin films show nano-structured characteristic, and the crystallinity and grain size of the thin films increased with sputtering temperature increased. The as-deposited ATO thin film were analyzed by XPS and shows the existence of Sn4+and SbD+oxidation status.The LIBs were assembled with the ATO thin films deposited on copper foils as working electrodes and Li as reference electrodes. The CV curves of ATO thin films under different substrate temperatures have the similar characteristics, indicating the ATO thin films suffered the same electrochemical reactions during the electrochemical processes. The ATO thin film deposited at the substrate temperature of200℃shows a higher electrochemical capacity, better cycling performance and rate performance, comparing with the ones those sputtered at room temperature and100℃. The200℃deposited ATO thin films have a initial discharge capacities of1654mA h/g under a current density of100mA/g, high reversible capacities of756and679mA h/g after100and200cycles, respectively.The electrochemical reaction mechanisms were investigated with transmission electron microscopy (TEM) by analyzing the phase evolution of the ATO electrodes that had been electrochemically induced at various stages. The electrochemical reaction of ATO thin film with lithium can be summarized as the following:the decomposition of SnO2and occurrence of metallic Sn followed by the formation of the Li-Sn alloys and final form Li4.4Sn during discharge process, and then the reversible de-alloying reaction of Li-Sn alloys and generate Sn, and when the battery charged to2.0V, Sn reacting with Li2O, and partial formation of SnO2.A new simple technology was developed to analyze electrochemical reaction mechanism of the ATO thin film, i.e., the ATO thin film electrodes were deposited directly on the holy carbon grids as lithium ion battery electrode to for exam the electrochemical reaction processes, and the phase evolution and electrochemical mechanism of the ATO electrodes on the grids that had been electrochemically induced at various stages can be revealed. The results showed that the developed method is a simple and effective way to elucidate the electrochemical reaction mechanism of the active materials. |
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