Studies on graphene enfolded olivine composite electrode material via polyol technique for high rate performance lithium-ion batteries

Abstract

The graphene enfolded LiFePO4/C composite cathode material has been prepared via low temperature polyol process, followed by a simple chemical reaction method. The low viscous polyol solvent (DEG) (35.7 mPa s at 25°C) and usage of low temperature process (below 245°C) aid the graphene tightly encapsulated on the LiFePO4 surface that plays an important role, especially in the high rate performances over long cycles, efficiently preventing the separation of the graphene and LiFePO4 during the reaction processes, hence realizing the full potential of the active materials. The graphitization on LiFePO4/C remarkably increased the electronic conductivity of LiFePO4. The layered sheets of graphene wrapped on LiFePO4 particles provide void between graphene sheets and LiFePO4 surfaces, which facilitate the diffusion of Li+. This approach opens up a method to attain the theoretical capacity of LiFePO4. The material exhibits a superior electrochemical performance such as initial discharge capacities of 169.6 and 92 mAhg−1 at 0.1 and 30 C rates, respectively. It has an excellent capacity retention and diminutive capacity fading. The nanosize of LiFePO4 particle causes a shorter diffusion path, which reduces the time for Li+ migration between cathode and electrolyte.