We report herein on the synthesis of "layered-layered" integrated xLi2MnO3•(1-x) LiMn1/3 Ni1/3 Co1/3O2 materials (x=0.3, 0.5, and 0.7) using the self-combustion reaction in solutions containing metal nitrates and sucrose. The nanoparticles of these materials were obtained by further annealing of the as-prepared product in air at 700°C for 1 h and submicrometric particles were obtained by further annealing at 900°C for 22 h. The effect of composition on the electrochemical performance was explored in this work. By a rigorous study with high resolution transmission electron microscopy (HRTEM), it became clear that the syntheses with the above stoichiometries produce two-phase materials comprising nanodomains of both rhombohedral LiNiO 2 -like and monoclinic Li2MnO3 structures, which are closely integrated and interconnected with one another at the atomic level. Stable reversible capacities ∼220 mAh/g were obtained with composite electrodes containing submicrometer particles of 0.5Li2MnO 3•(1-x) LiMn1/3 Ni1/3 Co 1/3O2. Structural aspects, activation of the monoclinic component, and stabilization mechanisms are thoroughly discussed using Raman spectroscopy, solid-state NMR, HRTEM, and X-ray diffraction (including Rietveld analysis) in conjunction with electrochemical measurements. This work provides a further indication that this family of integrated compounds contains the most promising cathode materials for high energy density Li-ion batteries.