Nanostructured lithium-manganese-rich nickel-manganese-oxide xLi(2)MnO(3)(1-x)LiNi0.5Mn0.5O2 (0.3x0.6) composite materials were synthesized via spray pyrolysis using mixed nitrate precursors. All the materials showed a composite structure consisting of Li2MnO3 (C2/m) and LiNi0.5Mn0.5O2 (R3m) components, and the amount of Li2MnO3-phase appeared to increase with x, as observed from XRD analysis. These composite materials showed a high-discharge capacity of about 250 mAhg(-1). In the range of x considered, the layered 0.5Li(2)MnO(3)0.5LiNi(0.5)Mn(0.5)O(2) materials displayed the highest capacity and superior cycle stability. Nonetheless, voltage suppression from a layered-spinel phase transition was observed for all the composites produced. This voltage suppression was dependent of the amount of Li2MnO3 phase present in the composite structure. (c) 2013 American Institute of Chemical Engineers AIChE J 60: 443-450, 2014