Li1+x(Fey/2Niy/2Mn1-y)1-xO2 was synthesized by a coprecipitation-hydrothermal-calcinations method. The crystal structure and charge/discharge performance of Li1+x(Fey/2Niy/2Mn1-y)1-xO2 were analyzed by X-ray diffraction (XRD), inductively coupled plasma (ICP) and electrochemical performance measurement. The XRD tests and ICP analyses demonstrate that Fe and Ni substitute a part of Mn of Li2MnO3 to form the good solid solution structure yLiFe1/2Ni1/2O2-(1-y)Li2MnO3 (y= 0.1, 0.2, 0.3, 0.4, 0.5). SEM images show that different y values lead to different apparent morphologies of the materials. When y=0.4, the particles are spherical with uniform and small size. The electrochemical tests indicate that when y=0.4, the cathode material has the best electrochemical performance with the discharge capacity of 195.0 mAh/g after 50 cycles