Layered positive electrode materials for rechargeable lithium-ion batteries of the general formula Li[Mn0.5−x/2Ni0.5−x/2Co x ]1−y M y O2 (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.