| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 104 === Lithium titanate (Li4Ti5O12) has been one of the most promising anode materials for lithium ion batteries because of its negligible volume change and stable operating voltage (1.55 V) during intercalation-deintercalation. However, the intrinsic insulating property (10-13 S cm-1) of Li4Ti5O12 hinders its high power applications. Compositing and nanonization are two well-understood approaches to overcome this drawback. The former enhances the external electrical conductivity of Li4Ti5O12, while the latter shortens the length of diffusion during the intercalation-deintercalation process. Nevertheless, the effects of presence of defects, e.g. oxygen vacancies, in electrode materials are not as straightforward as compared to the former approaches. Moreover, it is technically difficult to control the concentration and distribution of intentionally introduced defects, namely to engineer these oxygen vacancies. In this work, Li4Ti5O12 anode were synthesized via a thermal reduction process. Systematic introduction of oxygen vacancies was facilitated under the thermal reduction of ethanol, where a higher degree of reduction was achieved from a compounding effect. Unlike the conventional (white) Li4Ti5O12 material, (blue) Li4Ti5O12 material were synthesized. Defect engineering presents further opportunities for exploration and optimization. The microstructures and electrochemical properties, i.e., cycle performance and rate capability of the defect engineered Li4Ti5O12 were examined. In addition, ab initio calculations based on density functional theory (DFT) were performed to clarify the enhanced electrochemical properties of the defect engineered Li4Ti5O12. The formation mechanism of the defect engineered Li4Ti5O12, as well as the origin of superior electrochemical properties, is elaborated in this paper.
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