The mixed transition metal layered compound, Li[Ni1/3Co1/3Mn(1/3-x)Mgx]O2-yFy was synthesized via coprecipitation followed by a high-temperature heat-treatment. X-Ray diffraction patterns revealed that this material has a typical layered structure with R (3) over barm space group. Spherical morphologies have been observed by scanning electron microscopy. Mg and F substitutions were effective for the improvement of physical properties such as crystallinity, morphology, and tap-density. These improved physical characteristics enhanced the capacity, retention and thermal stability, even though the electrodes were cycled between 2.8 and 4.6 V. (C) 2004 The Electrochemical Society.