The effect of doping Co on the electrochemical properties of LiFePO4/C nanoplates synthesized by solvothermal route

A series of olivine LiFe1 - xCoxPO4/C (x = 0, 0.005, 0.01, 0.015, 0.02 and 0.025) nanoplates were synthesized by a facile solvothermal synthesis combined with esterification reaction. The structure, morphology and electro-chemical performance of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), galvanostatic intermittent titration technique (GITT), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS). Based on the first-principle density functional theory (DFT), the diffusion energy barriers of Li ions for LiFe1 - xCoxPO4 (x = 0-0.025) were also calculated to further investigate the influence of doping Co on LiFePO4/C cathode material. The results showed that the prepared nanoplates with a very thin thickness along b-axis grow preferentially along the [001] direction of (101) lattice planes, which can minish the distance of Li+ ion diffusion along the [010] direction. The calculated results suggested that the LiFe0.99Co0.01PO4/C had a lowest lithium ion diffusion energy barrier, accordingly possessing a highest lithium ion diffusion coefficient. The electrochemical performance was improved by doping an appropriate amount of Co, and it might be attributed to the fact that the doped Co ion can enhance exchange current density and lithium ion diffusion coefficient. Among all the doped samples, LiFe0.99Co0.01PO4/C exhibited the best rate capability and cycling stability, with the initial discharge capacity of 154.5 mAh g(-1) at 0.5 C. Remarkably, it still showed a high discharge capacity of over 96.9 mAh g(-1) and good cycle retention even at a high rate of 10 C. (C) 2013 Elsevier B.V. All rights reserved.