| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系所 === 106 === Transition metal oxides have attracted much interest owing to their ability to provide high power density in supercapacitors and lithium batteries. These two kinds of energy-storage devices, however, have their own strengths and weaknesses, which influence their applications and developments. Currently, lithium-ion capacitors, which combine the principles of supercapacitors and lithium-ion batteries, possess the characteristic of high power density and high energy density simultaneously. Therefore, it is important to understand the electrochemical behaviors and the mechanisms of the lithium-ion capacitors. In this study, we successfully and directly observed the structural evolution of MnO2/CNTs composite electrodes during the lithiation processes using transmission electron microscopy (TEM). MnO2/CNTs were selected due to their high surface area and capacitance effect, and the lithiation mechanism of the CNT wall expansion was systematically analyzed. Interestingly, the wall spacings of MnO2/CNTs and CNTs were obviously expanded by 11.76 % and 2.70 %, respectively. The MnO2 layer caused structural defects on the CNTs surface that could allow penetration of Li+ and Mn4+ through the tube wall and hence improve the ionic transportation speed. This study provided direct evidence for understanding the role of MnO2/CNTs in the lithiation process used in lithium ion batteries and also offers potential benefits for applications and development of supercapacitors.
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