The effects of pristine and carboxylated multi-walled carbon nanotubes as conductive additives on the performance of LiNi0.33Co0.33Mn0.33O2 and LiFePO4 positive electrodes

The influence of two types of multi-walled carbon nanotubes, pristine (MWCNTs) and carboxylated (MWCNTs-COOH), on the electrochemical performance of LiNi0.33Co0.33Mn0.33O2 (NCM)- and LiFePO4 (LFP)-based positive electrodes is investigated. Several characterization techniques, e.g., electronic conductivity measurements, galvanostatic cycling, cyclic voltammetry, electrochemical impedance spectroscopy, and SEM/EDX, were employed. The results suggest that improved electronic conductivity is not necessarily synonymous with enhanced performance. A clear dependence of both rate capability and electrode morphology on the combination of conductive additive and active material can be observed. In particular, while LFP performs better with MWCNTs-COOH, pristine MWCNTs appear to be better suited for NCM. Although the use of MWCNTs-COOH improves the connective network between the active particles for both NCM and LFP, the presence of -COOH moieties appears to have a strong effect on the surface properties of the NCM-based electrodes. MWCNTs-COOH formed a shell around the active particles, which may function as a physical barrier and hinder Li+ insertion/extraction. (C) 2012 Elsevier Ltd. All rights reserved.