The layered-layered-spinel composite cathode materials Li x Mn4/6Ni1/6Co1/6O(1.75+0.5x) with different content of Li2O have been synthesized by the two-step co-precipitation method and evaluated in lithium cells. Powder X-ray diffraction provides the evidence that the structures of Li x Mn4/6Ni1/6Co1/6O(1.75+0.5x) composite transform from ‘layered-layered’ to ‘layered-layered-spinel’ as the content of Li2O decreasing. Electrochemical charge/discharge profiles suggest that Li1.3Mn4/6Ni1/6Co1/6O2.4 electrode with low content of Li2O delivers a large initial discharge capacity which is about 305.3 mAh·g−1, and that the discharge capacities of Li1.3Mn4/6Ni1/6Co1/6O2.4 electrode change little at the first three cycles, because of that a considerable amount of spinel phase in electrode facilitating Li ions diffusion. Nevertheless, the discharge capacities of Li1.4Mn4/6Ni1/6Co1/6O2.45 and Li1.5Mn4/6Ni1/6Co1/6O2.5 electrode in the first three cycles gradually rise as cycles continuing, which is expected to be that Li ions diffusion paths are not fully opened. The irreversible electrochemical reaction that Li2O component separates from Li2MnO3 to form MnO2 happens at the first charge at 4.7V, and the structure of layered Li2MnO3 component converts into the spinel component during continuously cycles. The Li x Mn4/6Ni1/6Co1/6O(1.75+0.5x) composites also display good cycling performance and rate performance. The capacity retention of Li x Mn4/6Ni1/6Co1/6O(1.75+0.5x) composites exceeds 100%, and its coulombic efficiency is greater than 98% after 50 cycles. We conclude that electrochemical performances of Li x Mn4/6Ni1/6Co1/6O(1.75+0.5x) composites are improved by using the two-step co-precipitation preparation method, especially in terms of large discharge capacity of Li1.3Mn4/6Ni1/6Co1/6O2.4 composite due to the appearance of spinel components.