Spherical Li[Ni0.4Co0.2Mn(0.4-x)Mgx]O2-yFy (x=0, 0.04,y = 0, 0.08) with phase-pure and well-ordered layered structure have been synthesized by heat-treatment of spherical [Ni(0.4)Co(0.2)Mn(0.4-x)Mgx](3)O-4 precursors with LiOH center dot H2O and LiF salts. The average particle size of the powders was about 10-15 mu m and the size distribution Was quite narrow due to the homogeneity of the metal carbonate, [Ni0.4Co0.2Mn(0.4-x)Mgx]CO3 (x=O, 0.04) precursors. Although the Li[Ni0.4Co0.2Mn0.36Mg0.04]O1.92F0.08 delivered somewhat slightly lower initial discharge capacity, however, the capacity retention, interfacial resistance. and thermal stability were greatly enhanced comparing to the Li[Ni0.4Co0.2Mn0.4]O-2 and Li[Ni0.4Co0.2Mn0.36Mg0.04]O-2. (c) 2006 Elsevier Ltd. All rights reserved.