The layered LiNi0.6Co0.2-xMn0.2MgxO2 (x=0.00,0.03,0.05,0.07) cathode materials were prepared by a co-precipitation method.The properties of the Mg-doped LiNi0.6Co0.2Mn0.2O2 were investigated by X-ray diffraction (XRD),scanning electron microscopy (SEM),and electrochemical measurements.XRD studies showed that the Mg-doped LiNi0.6Co0.2Mn0.2O2 had the same layered structure as the undoped LiNi0.6Co0.2Mn0.2O2.The SEM images exhibited that the particle size of Mg-doped LiNi0.6Co0.2Mn0.2O2 was finer than that of the undoped LiNi0.6Co0.2 Mn0.2O2 and that the smallest particle size is only about 1μm.The Mg-doped LiNi0.6Co0.2Mn0.2O2 samples were investigated on the Li extraction/insertion performances through charge/discharge,cyclic voltammogram (CV),and electrochemical impedance spectra(EIS).The optimal doping content of Mg was that x= 0.03 in the LiNi0.6Co0.2-xMn0.2MgxO2 samples to achieve high discharge capacity and good cyclic stability.The electrode reaction reversibility and electronic conductivity was enhanced,and the charge transfer resistance was decreased through Mg-doping.The improved electrochemical performances of the Mg-doped LiNi0.6Co0.2Mn0.2O2 cathode materials are attributed to the addition of Mg 2+ ion by stabilizing the layer structure. The layered LiNi0.6Co0.2-xMn0.2MgxO2 (x = 0.00,0.03,0.05,0.07) cathode materials were prepared by a co-precipitation method. The properties of the Mg-doped LiNi0.6Co0.2Mn0.2O2 were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. XRD studies showed that the Mg-doped LiNi0.6Co0.2Mn0.2O2 had the same layered structure as the undoped LiNi0.6Co0.2Mn0.2O2. The SEM images illustrate that the particle size of Mg-doped LiNi0.6Co0.2Mn0.2O2 was finer than that of the undoped LiNi0.6Co0.2Mn0.2O2 and that the smallest particle size is only about 1μm. The Mg-doped LiNi0 .6Co0.2Mn0.2O2 samples were investigated on the Li extraction / insertion events through charge / discharge, cyclic voltammogram (CV), and electrochemical impedance spectra (EIS). The optimal doping content of Mg was that x = 0.03 in the LiNi0. 6Co0.2-xMn0.2MgxO2 samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility and electronic c onductivity was enhanced, and the charge transfer resistance was decreased through Mg-doping. The improved electrochemical performances of the Mg-doped LiNi0.6Co0.2Mn0.2O2 cathode materials are attributed to the addition of Mg 2+ ion by stabilizing the layer structure.