Lithium iron oxides LixFeyOz were synthesized by oxidizing Fe2+ with lithium peroxide in the presence of lithium hydroxide in aqueous solutions followed by firing the precursors at 200 less than or equal to T less than or equal to 800 degrees C. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, wet-chemical analyses, and surface-area measurements. The Li/Fe ratio in the samples depends on the concentrations and volumes of the reactants used in the synthesis. Samples fired at a lower temperature of 200 degrees C with a nanocrystalline microstructure and optimum Li/Fe ratio exhibit a capacity of about 140 mAh/g in the range 1.5-4.3 V with excellent cyclability. On the other hand, samples fired at higher temperatures T greater than or equal to 400 degrees C with well-defined crystalline phases exhibit much lower capacity (<50 mAh/g).