The structure and electrochemical properties of LiNi x Mn2−x O4 cathode materials for lithium ion batteries were studied by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), cyclic voltammetry, and galvanostatic charge–discharge tests. The cathodes with different Ni contents (LiNi x Mn2−x O4, x =0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized by a spray-drying method and showed a single-phase spinel structure without any impurity. The amount of Ni has a large effect on the electrochemical characteristics. Capacity values of different voltage ranges (4- and 5-V ranges) change obviously with amount of Ni-doped. Also, the total discharge capacities increase with the Ni content, and all of them have good cycle stability.