Effects of Ni and Mn doping on physicochemical and electrochemical performances of LiFePO4/C

The LiNixFe1-xPO4/C (x = 0.00, 0.01, 0.02, 0.03, 0.04), LiMnyFe1-yPO4/C (y = 0.00, 0.01, 0.02, 0.03, 0.04) and LiNi0.02Mn0.03FePO4 composites have been successfully synthesized by a simple solid-state method. The structure, morphology and electrochemical property of the as-prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge/discharge tests. The XRD patterns indicate that doping with Ni2+ or Mn2+ do not affect the structure of olivine LiFePO4. The results of electrochemical performance measurements reveal that the LiNi0.02Fe0.98PO4/C shows the best electrochemical performance among all of the single Ni-doped samples. Meanwhile, comparing with other single Mn-doped materials, the LiMn0.03Fe0.97PO4/C show the highest initial discharge capacity and excellent cyclic stability. In order to further improve the electrochemical performance of LiFePO4/C, LiNi0.02Mn0.03Fe0.95PO4/C composite with Ni and Mn co-doping was also synthesized by the same route. Relative to other samples, the LiNi0.02Mn0.03Fe0.95PO4/C delivers higher initial discharge capacity of 164.3 mAh g(-1) at a rate of 0.1 C. Moreover, it also exhibits excellent cyclic stability with capacity retention of 98.7% cycled at 1 C after 100 cycles. CV shows that the Ni and Mn dual-doping reduce the electrode polarization, which may be the important factors for improving the electrochemical properties of the cathode materials. (C) 2016 Elsevier B. V. All rights reserved.