A new process has been developed for the synthesis of well-crystallized Li-Mn-O spinels with a homogeneous composition Li[LixMn2-x]O4 (0.0≤x≤0.333) using the stoichiometry mixtures of lithium acetate and manganese nitrate as starting materials. The crystal structure of these compounds was studied with Rietveld refinements of the X-ray diffraction profiles. The lattice parameter of the spinels shows a strong dependence on the composition and manganese oxidation state. SEM micrographs indicate that the crystallites appear as single crystals. The size of the crystallites are in the range of 0.1 – 2μm, depending on the synthesis conditions. Samples with x≤0.125 show good electrode performance for the cell Li/Li1+xMn2-xO4 in the 4V region, whereas Li4Mn5O2 (x=0.333) spinels show good cyclability with a rechargeable capacity of over 100mAh/g in the 3V region.