Doping Effects on Electronic Conductivity and Electrochemical Performance of LiFePO4

Olivine-structured pure LiFePO4 and doped Li(M, Fe)PO4 (M=La, Ce, Nd, Mn, Co, Ni) have been synthesized by a solvothermal method. X-ray diffraction and field emission scanning electron microscopy analyses indicate that the as-prepared LiFePO4 is well-crystallized nanopowders without any detectable impurity phases. The electronic conductivity of LiFePO4 is enhanced by around 1-3 orders by doping. It was found that doping alone is not sufficient for the high-rate performance of LiFePO4 and surface coating with such as carbon should be needed. The best dopant for LiFePO4 is Nd among those studied in the present work. Accordingly, doping with 1 mol fraction Nd leads to an increase in 70 mAh/g at 0.1 C for the hydrothermally synthesized sample and 50 mAh/g at 1.0 C after carbon-coating in comparison with the undoped samples.