Two new-mixed manganese-cobalt oxides for lithium battery positive electrode materials were obtained using original synthesis routes. Compound I, "LMCO" is a new form of LiMnCoO4 obtained by ion exchange from NaMnCoO4. Compound II, "MCO" is a nanometric material with formula Mn1-x CoxO approximate to 2 obtained by quenching in specific conditions. We showed recently that the electrochemical properties of this materials were dramatically enhanced by cobalt doping [P. Strobel, F. Thiery, C. Darie, O. Proux, A. Ibarra-Palos, M. Bacia and J.B. Soupart, J. Mater. Chem. 15 (2005) 4799]. The effect of cobalt content on its electrochemical behaviour is reported in detail here. Compound I gives rise to two reversible single-phase intercalation reactions centered at 2.7 and 4.4 V on discharge, corresponding to Co3+/Co4+ and Mn(3+)Ma(4+) redox couples, respectively. The initial capacity is 160 mAh g(-1) at low regime, but stabilizes at ca.100 mAh g(-1) on extended cycling. Compound H gives a single plateau with a much higher capacity. An optimum ratio of Co:Mn = 0.20 was found and gives a capacity of 175 mAh g(-1) after 60 cycles in the potential window 2.0-4.2 V. (c) 2007 Elsevier B.V. All rights reserved.