The Doping Effect on the Electrochemical Properties of LiFe[sub 0.95]M[sub 0.05]PO[sub 4] (M=Mg[sup 2+], Ni[sup 2+], Al[sup 3+], or V[sup 3+]) as Cathode Materials for Lithium-Ion Cells

, , , or ion with an atomic radius similar to or smaller than that of ion was doped into the Fe site to synthesize samples using a solution method. The mean particle size of all samples, independent of doping species, was about . All samples in this study contain a carbon content of about and have a similar Brunauer–Emmett–Teller surface area (about ). 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 powder with the largest volume of unit cells (longest Li–O bond length) exhibits the highest discharging capacity of 152 and at C/10 and 1C rates, respectively.