Co, Mn and Mg co-doped lithium nickel oxides of the nominal composition LiNi0.9Co0.1-x[Mn1/2Mg1/2](x)O-2 (x=0.00, 0.02, 0.04, 0.06) are synthesized by a co-precipitation technique and solid state route. XPS results reveal that the oxidation states of Ni, Co, Mn and Mg are +3, +3, +4 and +2, respectively. An ordered alpha-NaFeO2 rock salt structure with R - (3) over barm symmetry has been confirmed by XRD. The cation mixing of Li/Ni and occupation of Mg ions have been analyzed by Rieveld refinement. Mg ions distribute between 3b and 3a sites in the crystal. Meanwhile a substantial reduction of cation mixing of Li-Ni has been confirmed by Mn-Mg substitution. Better cycling performance is observed in the compound with high Mn-Mg content compared with LiNi0.9Co0.1O2. Mn-Mg substitution for Co has been shown to suppress the increase of the cell impedance during cycles effectively. (C) 2012 Elsevier Ltd. All rights reserved.