A study of the effect of synthesis techniques and conditions on the electrochemical, structural and physical properties of solution phases of Li2MnO3 and LiNi1−x Co x O2 is reported. In this system, the formal oxidation state of the manganese is +4, while that of the nickel and cobalt is +3. These materials were produced from a variety of precursors and chelating agents. Modifications in the synthesis were found to affect the microstructure of the products and their electrochemical performance. It is demonstrated that, with good compositional and microstructural control, solution phases of Li2MnO3 and LiNi1−x Co x O2 can have stable discharge capacities as high as 240mAhg−1. Furthermore, it has been found that a solution phase of Li2MnO3 and LiNi1−x Co x O2, having no nickel content, Li1.2Mn0.4Co0.4O2, can produce very high discharge capacities (∼235mAhg−1) when charged to voltages greater than 4.3V, despite an apparent theoretical capacity of only 125mAhg−1.