Layered positive electrode materials for rechargeable lithium-ion batteries of the general formula Li[Mn0.5-x/2Ni0.5-x/2Cox](1-y)MyO2 (x <= 1/3, 0 <= y <= 0.05) were synthesized by a solid state route. The effect of doping elements M on the electrochemical performance was investigated. It was found that doping with niobium or tantalum has a positive effect on the cycling stability compared to the undoped parent compounds (y = 0). High discharge capacities, excellent cycling stabilities and high rate capabilities were achieved. (C) 2007 Published by Elsevier B.V.