Electrochemical performance of in situ LiFePO4 modified by N-doped graphene for Li-ion batteries

LiFePO 4 modified by N-doped graphene (NG) with a three-dimensional conductive network structure was synthesized via a one-step in situ hydrothermal method . The effects of N amount of NG on the phase structure, morphology, and electrochemical properties of LiFePO 4 are investigated in this study. X-ray diffraction (XRD) results show that doping suitable N amounts in NG do not alter the crystal structure of LiFePO 4, and scanning electron microscopy (SEM) images show that NG can slightly reduce the particle size of LiFePO 4 . The high-resolution transmission electron microscopy (HRTEM) results show that the LiFePO 4 particles are well covered and connected by NG. The electrochemical performance confirms that LiFePO 4 modified by 20% N-doped graphene (named LFP/NG-4) displays a perfect specific capacity of 166.6 mAh·g −1 at a rate of 0.2C and can reach 125 mAh·g −1 at a rate of 5 C. Electrochemical impedance spectroscopy (EIS) results illustrate that the charge transfer resistance value of the LFP/NG-4 composite is only 58.6 Ω, which is very low compared with LiFePO 4 . Cyclic voltammetry (CV) tests indicate that the addition of 20% N-doped graphene can effectively reduce electrode polarization and improve reversibility. The LFP/NG-4 composite with a three-dimensional conductive network structure can be regarded as a promising cathode material for Li-ion batteries.