Sheet-like lithium-rich cathode materials Li1.2Mn0.54Ni0.16Co0.10O2 (LMNCO) assembled by primary grains of 100–500 nm in sizes were facilely prepared by a glucose-urea bubbling and post-annealing process. The post-annealing temperature was found to play an important role on the grain size, crystallinity, cation ordering and electrochemical performance of the cathode materials. The sample post-annealed at 900 °C showed larger grains, higher crystallinity, better layered structure, higher lithium storage capacity and better rate performance than the one annealed at 800 °C. An initial discharge capacity of above 300 mA h g−1 was obtained at 0.1 C (20 mA g−1) for the sample annealed at 900 °C, and at 1, 2, 5 and 10 C, discharge papacies of 223, 192, 157 and 128 mA h g−1 were achieved respectively. The material synthesizing process proposed in this study may be extended to prepare a wide range of sheet-like functional oxides that may be potentially applied in energy storage or other fields.