A facile synthesis method has been developed to prepare xLi2MnO3·(1−x)LiNi0.7Co0.15Mn0.15O2 (x = 0, 0.03, 0.07, 0.10, 0.20, and 0.30) cathode materials, combining the advantages of the high specific capacity of the Ni-rich layered phase and the surface chemical stability of the Li-rich layered phase. X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical charge/discharge measurements confirm the formation of a Li-rich layered phase with C2/m symmetry. The high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) reveals a spatial relationship that the Li-rich nano-domain islands are integrated into the conventional Ni-rich layered matrix ( R 3 ¯ m ). Most importantly, this is the first time that Li-rich phase has been directly observed inside a particle at the nano-scale, when the overall composition of the layered oxide Li1+δNi1−y−z−δMnyMzO2 (M = metal) is Ni-rich (>0.5) rather than Mn-rich (>0.5). Remarkably, the xLi2MnO3·(1−x)LiNi0.7Co0.15Mn0.15O2 cathodes with optimized x value shows superior electrochemical performance at C/3 rate: an initial capacity of 190 mA h g−1 with 90% capacity retention after 400 cycles in a half cell and 73.5% capacity retention after 900 cycles in a pouch-type full cell.