Enhancement of the electrochemical performance of LiFePO4/carbon nanotubes composite electrode for Li-ion batteries

LiFePO4 is very good potential cathode materials for the power lithium-ion batteries because of its high theoretical capacity and high voltage, but its electrochemical performance suffers from the low electronic conductivity. In this paper, the multi-walled carbon nanotubes (MWCNTs)/LiFePO4 composites cathode materials are prepared by ball milling. With high conductivity and the network structure existing in the LiFePO4 electrode, carbon nanotubes can reduce internal resistance and increase practical capacity and cycle stability of LiFePO4. As electrodes of lithium battery, the charge–discharge capacity, cyclic voltammetry, cycle life, alternating current impedance, and discharge temperatures characteristic of LiFePO4/MWCNTs (the loading of MWCNTs from 0 to 20 %) are investigated. The resistances of LiFePO4/MWCNTs decrease with the increase of MWCNTs loading and reach a minimal value of 56 Ω in the 10 % loading of MWCNTs, and result in the improvement of electrochemical performance. It is found that the composite electrode with 10 % loading of MWCNTs exhibits a best charge–discharge performance, and has initial charge capacities of 148 mAhg−1 and discharge capacities of 145 mAhg−1, respectively at 0.1 °C rate and the capacity retention is 98 %. The result of the pure LiFePO4 shows that the discharge capacity is 131 mAhg−1 at the rate of 0.5 °C, which means the increase in capacity of the LiFePO4/MWCNTs electrode achieves 16 %. The LiFePO4/MWCNTs composites also have perfectly high temperature performance due to the excellent thermal stability of the MWCNTs, and the discharge capacity of the composite electrode is 164 mAhg−1 at 0.1 °C rate in the temperature of 60 °C. After 30 cycles, the capacity still maintains as 163 mAhg−1 and the capacity retention is 99 %. The excellent cycle performance of the LiFePO4/MWCNTs electrode may attribute to the netlike-structure mechanical and electrical performance of MWCNTs.