Electrochemical Behavior of La-doped LiFePO4/C Cathode Materials for Lithium Ion Batteries

Alien atom was used to obtain a series of LiFe1-xLaxPO4/C （x=0, 0.002, 0.005, 0.01, 0.015） cathode materials with the aim of investigating the influence of participation of La on the electrochemical behavior of LiFePO4/C. Combination of X-ray diffractometer, scanning electron microscope equipped with energy dispersive spectrometer and high resolution transmission electron microscope was applied. The results show that all the La-doped LiFePO4/C samples are olivine type crystals, La ion is sufficiently introduced into the network, and every element is well homogeneously distributed. There are many pore spaces on the surface of particles. The content of carbon in the prepared cathode materials remains 13.6% calculated by TGA/DTA curves, and the particles are wrapped by a uniformly and continuous carbon layer with the thickness of about 2 nm. Similarly, the content of Fe2P also keeps the same basically in all the cathode materials as a result of the similar ratio （2.35） of peak intensity at 36.5~ and 37.1° from XRD. The increasing trend is most pronounced at doped 0.005 which presents the highest initial discharge capacity of 163 mA-h/g, lowest charge transfer resistance of 5.52 Ω, superior diffuse ability of lithium ion （10^-11 cm2/s） and the best capacity retention current rate of about 93% after 50 cycles at 0.1 C.