Layered Li(Co0.33Mn0.33Ni0.33)O-2 and composite 0.3Li(2)MnO(3)center dot 0.7LiMn(0.5)Ni(0.5)O(2) electrode powders have been treated with NH3 and HNO3 prior to cell assembly. These pre-conditioning reactions improve the electrochemical properties of the electrodes when charged to high electrochemical potentials (>= 4.45 V versus Li-0) in lithium cells. NH3-treatment of Li(Co0.33Mn0.33Ni0.33)O-2 increases electrode capacity and improves the coulombic efficiency of the electrochemical reaction after the first charge/discharge cycle, whereas acid-treatment of 0.3Li(2)MnO(3)center dot 0.7LiMn(0.5)Ni(0.5)O(2) electrodes significantly improves the coulombic efficiency of the initial charge/discharge reaction. (c) 2005 Elsevier B.V. All rights reserved.