Functionalization of MWCNTs by plasma treatment and use as conductive additives for LiFePO₄ electrode

The application of LiFePO₄ in high power battery is limited by its low conductivity. MWCNTs as conductive additives were functionalized with maleic anhydride (MA) using the plasma-induced grafting technique. A series of LiFePO₄/MWCNTs-MA composite electrodes with 1.7 wt%, 2.7 wt%, 4.7 wt%, and 9.7 wt% of MWCNTs-MA were fabricated to improve conductivity and to investigate the effects of MWCNTs-MA on LiFePO₄ electrode performance. X-ray diffraction analysis of LiFePO₄/MWCNTs-MA cathodes showed that crystallinity and lattice spacing of LiFePO₄ were not altered by incorporation of MWCNTs-MA. Field-emission scanning electronic microscopy showed that 4.7 wt% MWCNTs-MA dispersed well in LiFePO₄ particle matrix. Electrochemical impedance spectroscopy showed that charge transfer resistance was decreased by increased amount of MWCNTs-MA. The specific capacity, cyclic stability, and rate performance of LiFePO₄ coin cells were enhanced by increased amount of MWCNTs-MA, and reaching optimal performance at 4.7 wt%. The LiFePO₄/MWCNTs-MA (4.7 wt%) battery had rate capacity of 114 mAh g⁻¹ at 1 C with a capacity retention ratio of 75.6% after 200 cycles.