LiNi0.5Mn1.5O4 as a 4.7V-class cathode material was prepared through the radiated polymer gel method that allowed homogeneous mixing of starting materials at the atomic scale. After calcinations of the polymer gels containing the metal salts at different temperatures from 750 to 1150°C, powders of a pure LiNi0.5Mn1.5O4 phase were obtained. X-ray diffraction and transmission electron microscopy were used to characterize the structures of the powders. Galvanostatic cell cycling and a simultaneous DC resistance measurement were performed on Li/LiNi0.5Mn1.5O4 cells. It is found that the powder calcined at 950°C shows the best electrochemical performance with the initial discharge capacity of 139mAhg−1 and 96% retention after 50 cycles. Adopting a slow cooling procedure for the powder calcination can increase the capacity of LiNi0.5Mn1.5O4 at the 4.7V plateau. Besides, a “w”-shape change of the DC resistance of Li/LiNi0.5Mn1.5O4 cells is a good indication of the structural change of LiNi0.5Mn1.5O4 electrode during charge and discharge courses.