We have successfully synthesized a spherical core-shell structure based on Li[(Ni0.8Co0.2)(0.8)(Ni0.5Mn0.5)(0.2)]-O-2 via a coprecipitation route. According to the careful examination by scanning electron microscopy (SEM), transmission electron microscopy energy-dispersive spectroscopy (TEM-EDS), and X-ray diffraction (XRD), it was found that the core-shell particle consisted of Li[Ni0.8Co0.2]O-2 as the core and Li[Ni0.5Mn0.5]O-2 as the shell, of which the thickness was estimated to be 1 to similar to 1.5 mu m. Both the core and shell were dense as confirmed by SEM. Though the core-shell-structured Li[(Ni0.8Co0.2)(0.8)(Ni0.5Mn0.5)(0.2)]O-2 delivered a slightly reduced initial discharge capacity, the capacity retention and thermal stability were significantly improved relative to those of the Li[Ni0.8Co0.2]O-2 electrode without the Li[Ni0.5Mn0.5]O-2 shell. The carbon/Li[Ni0.8Co0.2]O-2 pouch cell underwent an explosive ignition during the nail penetration test, whereas the carbon/Li-[(Ni0.8Co0.2)(0.8)(Ni0.5Mn0.5)(0.2)]O-2 cell remained stable, demonstrating the superior thermal stability of the core-shell electrode. As a new positive electrode material, the core-shell-structured Li[(Ni0.8Co0.2)(0.8)(Ni0.5Mn0.5)(0.2)]O-2 is a significant breakthrough in the development of high-capacity lithium secondary batteries.