Li2−x FeSi1−x P x O4 was prepared with the intention of improving the electrical conductivity by taking advantage of the high lithium ionic conductivity of Li4SiO4–Li3PO4 solid solution. A monoclinic single phase by SPS process was obtained for x = 0, 0.1 and 0.2 in Li2−x FeSi1−x P x O4 and the process produced the samples in high dense in half an hour while their containing less than 3% of carbons. The electrical conductivity was increased by the replacing (SiO4)4− with (PO4)3−, although the conductivity value itself was not reliable due to the carbon. The electrochemical properties of the samples using Li were evaluated and showed a slight improvement on the rate performance. A desired tetrahedral divalent Fe was confirmed in all investigated samples and ionic character caused by the localized 3d electron of Fe in the structure was encouraged by the complexation.