In Situ TEM Investigation of the Electrochemical Behavior in CNTs/MnO2 Based Energy Storage Devices

• Main Authors: Tsai, Tsung-Chun, 蔡宗錞
• Other Authors: Wu, Wen-Wei
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/5vb795

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.