Sol-gel synthesis of sodium and lithium based materials

Sodium and lithium cobaltates are important materials for thermoelectric and battery applications due to their large thermoelectric power and ability to (de-) intercalate the alkali metal. For these applications, phase pure materials with controlled microstructure are required. We report on the sol-gel synthesis of sodium- and lithium-based materials by using acetate precursors. The produced Na2/3CoO2, Li(Ni1/3Mn1/3Co1/3)O-2, and Li(Ni1/2Co1/2)O-2 powders are phase pure with grain sizes below 1 mu m. X-ray diffraction and energy-dispersive spectral analyses show that the cation stoichiometry is preserved in the lithium-based compounds. Despite the low temperatures, the sodium content is reduced by 1/3 as compared to the initial value. Chemical phases of the investigated powders are formed in the sol-gel route at temperatures typically 100-200 K lower than those used in the conventional solid-state synthesis of these materials. The suggested sol-gel synthesis is a low temperature process suited for production of phase pure and homogeneous materials with volatile cations.