Anomalous Electrochemical Behavior of Multiwalled Carbon Nanotubes for Lithium Insertion/Extraction

Abstract

The anomalous electrochemical behavior of multiwalled carbon nanotubes (MWNTs) during lithium insertion/extraction have been studied. From the voltage profiles of a MWNTs/Lithium cell we found that the potential with a large charging rate is lower than that with a small charging rate. Potential relaxation experiments indicate that the shift of standard electrode potential at different charging rates is responsible for the anomalous behavior. In addition, the results from electrochemical impedance spectroscopy suggest that there are two kinds of diffusion mechanism within the bulk electrode. After discharge, some lithium ions continue to move slowly from one particular site, which the lithium ions occupy upon discharge, to another site with lower energy. Because the diffusion is very slow, there is much more time for lithium ions to move to deeper potential wells at small current density than that at large current density. Consequently, a higher potential would be needed to extract these ions than in the case where charging is done at a higher rate. © 2004 The Electrochemical Society. All rights reserved.