Spherical Ni-rich LiNi0.8CoxMn0.2-xO2 (x=0, 0.05, 0.1, 0.15) positive-electrode materials were synthesized by calcining the mixtures of LiOH·H2O and Ni0.8CoxMn0.2-x(OH)2 precursor formed from a simple continuous co-precipitation method. The influences of Co content on the microstructures and electrochemical properties of LiNi0.8CoxMn0.2-xO2 positive-electrode materials were investigated through X-Ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope and electrochemical tests. The results showed that the intensity ratio of I(003)/I(104) for positive-electrode material became higher with increasing Co content, implying the layered structure became better. The electrochemical tests confirmed LiNi0.8Co0.15Mn0.05O2 (x=0.15) exhibited the best discharge capacity of 180.8mAhg−1 after 100 cycles between 2.75 and 4.3V at 0.2C, with an excellent capacity retention of 97.31% and an high capacity of 165.2mAhg−1 at 5C. Importantly no obvious structure and morphology change was observed for LiNi0.8Mn0.05Co0.15O2 before and after cycling processes. The improved cycling stability and rate capability maybe resulted from low Li/Ni cation mixing, high electric conductivity and good structure stability.