Li1.05Mn2O4 cathodes doped with different amounts of SO4 2- were synthesized by sol-gel process. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge-discharge measurements. The pristine Li1.05Mn2O4 exhibits a single phase of cubic spinel structure, while Mn2O3 impurity is observed in the Li1.05Mn2O4 cathodes doped with SO4 2-, and the content of the Mn2O3 impurity rises with increasing SO4 2- dopant. With the molar ratio of SO4 2- to Mn increasing from 0 to 0.03, the initial discharge capacity of the Li1.05Mn2O4 cathodes decreases from 119.4 to 97.9 mAh g-1, and the storage performance decreases dramatically. The CV and EIS studies indicate that the reversibility of the cathodes decreases and the electrochemical impedance rises with the increase of SO4 2- dopant.