In Situ TEM Investigation of the Electrochemical Behavior in CNTs/MnO-Based Energy Storage Devices.

Transition metal oxides have attracted much interest owing to their ability to provide high power density in lithium batteries; therefore, it is important to understand the electrochemical behavior and mechanism of lithiation-delithiation processes. In this study, we successfully and directly observed the structural evolution of CNTs/MnO during the lithiation process using transmission electron microscopy (TEM). CNTs/MnO 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 CNTs/MnO and CNTs were obviously expanded by 10.92% and 2.59%, respectively. The MnO layer caused structural defects on the CNTs surface that could allow penetration of Li and Mn through the tube wall and hence improve the ionic transportation speed. This study provided direct evidence for understanding the role of CNTs/MnO in the lithiation process used in lithium ion batteries and also offers potential benefits for applications and development of supercapacitors.