The effect of MWCNT reinforcing on the electrochemical performance of LiMn2O4/MWCNT nanocomposite cathodes

Abstract

In this study, nanocrystalline LiMn2O4 cathode materials were synthesized by a facile sol-gel method and were then mechanical alloyed with varying amounts of MWCNTs in order to obtain a high capacity nanocomposite cathode electrodes for Li-ion batteries. The structure and physicochemical properties of the obtained LiMn2O4 powders were investigated by thermogravimetric analysis (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), galvanostatic charge discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that MWCNT are uniformly distributed in LiMn2O4 particle. Compared with bare LiMn2O4, MWCNT (15.0 wt.%) / LiMn2O4 (85.0 wt.%) composite cathode material shows enhanced specific capacity of 136.5 mAh g(-1) and improved cycling stability. After 50 cycles, the 0 wt.%, 5.0 wt.%, 10.0 wt.% and 15.0 wt.% MWCNT reinforced LiMn2O4 exhibited the capacity retention of 86.1, 129.4, 134.7 and 136.5 mAh g(-1), respectively. The nanocomposites show high cycle performance with remarkable capacity retention of 93% after 50 cycles, compared with LiMn2O4 nanoparticles with a 7% loss of the initial capacity after 50 cycles. EIS measurements show that the charge-transfer resistance of the nanocomposites is better than that of spinel LiMn2O4. A CV study further confirms higher reversibility of the nanocomposites compared with LiMn2O4 particles. The improvement of the electrochemical performance is attributed to higher electrical conductivity, higher structural stability of the composites and rapid Li+ diffusion resulting from the open lattice channels and unique one-dimensional structure of MWCNTs. Furthermore, the MWCNTs can alleviate the capacity fading of the LiMn2O4 at high charging and discharging conditions, implying that the MWCNT reinforcing is very promising to be applied in the lithium-ion batteries. Copyright (c) 2013 John Wiley & Sons, Ltd.