Synthesis and characterization of iron - doped Li^sub 4^Ti^sub 5^O^sub 12^ microspheres as anode for lithium-ion batteries

Li4Ti5O12 microspheres and the equivalent iron doped materials, with 0.1 and 0.2 mol of Fe per unit formula, were synthesized by a solvothermal method. The presence of the dopant was verified by X-Ray diffraction with Rietveld refinement and XPS experiments. It was found that the dopant is included in the lattice structure as Fe (III), at lower concentration the dopant is found primarily on Ti (IV) sites while at higher concentration it occupies both Ti and Li sites. Conductivity measurements indicate that the higher iron concentration increases the material intrinsic electronic conductivity; however, the effect of Fe doping at lower concentration on the conductivity is almost null. Because of the Fe doping, the charge/discharge plateaus are obtained at higher/lower voltages, which might be correlated to lower charge transfer resistance, even though the electrochemical measurements show slightly lower capacities and very similar rate capabilities. Additionally, EIS experiments indicate that the presence of the dopant causes lower charge transfer resistance and enhanced finite lithium diffusion. However, as the size of the particles is still very large, the improved Li+ intercalation properties do not influence the rate capability since this property should be more related to shortened diffusion paths.