Li2MnO3-stabilized LiCoO2 electrode materials were synthesized using the method of mechanochemical process. Li2MnO3 was prepared and the mechanochemical process was carried out with LiCoO2, which yielded the layered–layered integrated structure nanocomposites. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy studies confirmed the structural integration of 0.5Li2MnO3·0.5LiCoO2 electrode materials. We also performed the high temperature heat treatment, where our 0.5Li2MnO3·0.5LiCoO2 electrode materials showed improvement in the discharge capacity (∼180 mA h g−1) with good cycleability. To obtain a physical insight into the performance of the nanocomposite structure, we carried out first principles calculations to obtain activation energy barriers of Li+ de-/intercalation, which suggested that utilizing both Li2MnO3 and LiCoO2 components can enhance the Li+ diffusion for the layered–layered integrated structure.