Improved electrochemical performance of LiFePO4/C cathode via Ni and Mn co-doping for lithium-ion batteries

The pristine LiFePO4/C and Ni and Mn co-doping LiFe(1-x-y)Ni(x)Nn(y)PO(4)/C (x = 0.01-0.04; y = 0.04-0.01) composites are synthesized for the first time by a simple high-temperature solid-state route. The structure, morphology and electrochemical performance of the samples are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscope (SEM), charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results indicate that the Ni and Mn co-doping does not destroy the olivine structure of LiFePO4, but it can stabilize the crystal structure, lengthen the Li-O bond, decrease charge transfer resistance, enhance Li ion diffusion velocity, and thus improve its cycling and high-rate capability of the LiFePO4/C. Especially, the LiFe0.95Ni0.02Mn0.03PO4/C shows the best cycling stability and rate capability among all the doped samples. The first discharge capacity of LiFe0.95Ni0.02Mn0.03PO4/C is 145.4 mAh g(-1) with the capacity retention ratio of 98.6% till 100 cycles at 1C. Even at a high rate of 10C, it still reveals a high discharge capacity of 115.2 mAh g(-1). (C) 2013 Elsevier B.V. All rights reserved.