Mg2+, Ni2+, Al3+, or V3+ ion with an atomic radius similar to or smaller than that of Fe2+ ion was doped into the Fe site to synthesize LiFe0.95M0.05PO4 samples using a solution method. The mean particle size of all samples, independent of doping species, was about 6 +/- 0.5 mu m. All samples in this study contain a carbon content of about 3 wt % and have a similar Brunauer-Emmett-Teller surface area (about 18-20.5 m(2) g(-1)). The synergetic effect of the supervalency and larger atomic size of the doping element will induce the lattice expansion and Li-O bond lengthening of the olivine structure. The lengthening and weakening of the Li-O bond will be beneficial to the electrochemical performance of cathode materials especially under the high C rate. Hence, the LiFe0.95V0.05PO4 powder with the largest volume of unit cells (longest Li-O bond length) exhibits the highest discharging capacity of 152 and 136 mAh g(-1) at C/10 and 1C rates, respectively. (C) 2008 The Electrochemical Society.