An optimized Ni doped LiFePO4/C nanocomposite with excellent rate performance

Both Ni doping and carbon coating are adopted to synthesize a nano-sized LiFePO4 cathode material through a simple solid-state reaction. It is found that the Ni2+ has been successfully doped into LiFePO4 without affecting the phospho-olivine structure from the XRD result. The images of SEM and TEM show that the size of particles is distributed in the range of 20-60 nm, and all the particles are coated with carbon completely. The results of XPS show the valence state of Fe and Ni in the LiFePO4. The electronic conductivity of the material is as high as 2.1 x 10-1 S cm-1, which should be ascribed to the coefficient of the conductive carbon network and Ni doping. As a cathode material for lithium-ion batteries, the Ni doped LiFePO4/C nanocomposite delivers a discharge capacity of 170 mAh g-1 at 0.2 C, approaching the theoretical value. Moreover, the material shows excellent high-rate charge and discharge capability and long-term cyclability. At the high rates of 10 and 15 C, this material exhibits high capacities of 150 and 130 mAh g-1, retaining 95% after 5500 cycles and 93% after 7200 cycles, respectively. Therefore, the as-prepared material is capable of such large-scale applications as electric vehicles and plug-in hybrid electric vehicles.