Solid solutions of the formula LiNi0.7Co0.3−z Al z O2 (0.0≤z≤0.20) have been synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and surface area and density measurements. Single-phase materials are obtained for z≤0.15. Their cathodic behaviour in coin cells with Li metal as anode and a liquid electrolyte is examined by charge–discharge cycling at the 0.13C rate between 2.7 and 4.3V and by cyclic voltammetry. Irreversible capacity loss occurs for all the compositions, but the phases with z=0.05 and z=0.10 show much less capacity fading at the end of 50 cycles as compared to those with z=0.0 and z>0.10. The 5at.% Al-doped compound showed a discharge capacity of 137mAh−1 g after 100 cycles that corresponds to 70% capacity retention. The beneficial effect of Al-doping (z≤0.10) is corroborated by cyclic voltammograms and differential scanning calorimetry (DSC) data on charged cathodes.