Enhanced electrochemical performance of graphene modified LiFePO$_{4}$ as a cathode material for lithium ion batteries

We have synthesized LiFePO$_{4}$/graphene nano-composites using a sol-gel method by adding water dispersed graphene oxide to the LiFePO$_{4}$ precursors during the synthesis. The graphene oxide was reduced by annealing the composite at 600$^{\circ}$C for 5h in flowing forming gas (90{\%} Ar and 10{\%} H$_{2})$. The phase purity of the product was characterized by X-Ray diffraction and Raman spectroscopy. The reduction of graphene oxide was verified by Raman spectroscopy and X-ray Photoelectron spectroscopy. The electronic conductivity of LiFePO$_{4}$/graphene composite was found to be six orders of magnitude higher than that of pure LiFePO$_{4}$ synthesized following otherwise the same procedure except that no graphene oxide was added. SEM and TEM images show that LiFePO$_{4}$ particles are wrapped in uniformly distributed graphene sheets throughout the material forming a three dimensional conducting network. At low currents, the capacity of the composite cathode reaches 160 mAh/g, which is very close to the theoretical limit. More significantly, the graphene wrapped LiFePO$_{4}$ shows a dramatically improved rate capability and excellent charge-discharge cycle stability in comparison with the LiFePO$_{4}$ without graphene.