LiNi0.6Co x Mn0.4−x O2 (x =0.05, 0.10, 0.15, 0.2) cathode materials are prepared, and their structural and electrochemical properties are investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetric (DSC) and charge–discharge test. The results show that well-ordering layered LiNi0.6Co x Mn0.4−x O2 (x =0.05, 0.10, 0.15, 0.2) cathode materials are successfully prepared in air at 850°C. The increase of the Co content in LiNi0.6Mn0.4−x Co x O2 leads to the acceleration of the grain growth, the increase of the initial discharge capacity and the deterioration of the cycling performance of LiNi0.6Mn0.4−x Co x O2. It also leads to the enhancement of the ratio Ni3+/Ni2+ in LiNi0.6Co x Mn0.4−x O2, which is approved by the XPS analysis, resulting in the increase of the phase transition during cycling. This is speculated to be main reason for the deteriotion of the cycling performance. All synthesized LiNi0.6Co x Mn0.4−x O2 samples charged at 4.3V show exothermic peaks with an onset temperature of larger than 255°C, and give out less than 400Jg−1 of total heat flow associated with the peaks in DSC analysis profile, exhibiting better thermal stability. LiNi0.6Co0.05Mn0.35O2 with low Co content and good thermal stability presents a capacity of 156.6mAhg−1 and 98.5% of initial capacity retention after 50 cycles, showing to be a promising cathode materials for Li-ion batteries.