Carbon free composites Li(1-x)MgFePO(4) (x=0.00, 0.02) were synthesized from LiOH, H(3)PO(4), FeSO(4) and MgSO(4) through hydrothermal route at 180 degrees C for 6h followed by being fired at 750 degrees C for 6h. The samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), flame atomic absorption spectroscopy and electronic conductivity measurement. To investigate their electrochemical properties, the samples were mixed with glucose as carbon precursors, and fired at 750 degrees C for 6h. The Rietveld refinement results of lattice parameters of the samples indicate that the magnesium ion has been successfully doped into the M1 (Li) site of the phospho-olivine structure. With the same order of magnitude, there is no material difference in terms of the electronic conductivities between the doped and undoped composites. Conductivities of the doped and undoped samples are 10(-10) Scm(-1) before being fired, 10(-9) Scm(-1) after being fired at 750 degrees C, and 10(-1) Scm(-1) after coated with carbon, respectively. Both the doped and undoped composites coated with carbon exhibit comparable specific capacities of 146 vs. 144mAhg(-1) at 0.2C, 140 vs. 138 mAhg(-1) at 1C, and 124 vs. 123mAhg(-1) at 5C, respectively. The capacity retention rates of both doped and undoped samples over 50 cycles at 5C are close to 100% (vs. the first-cycle corresponding C-rate capacity). Magnesium doping has little effects on electronic conductivity and electrochemical properties of LiFePO(4) composites prepared via hydrothermal route.
