In order to improve the electrochemical properties of LiNi0.5Mn1.5O4, a series of Li-ion batteries cathode materials LiMgxNi0.5-xMn1.5O4 (x=0, 0.05, 0.1) were prepared by rheological method. XRD results reveal that the synthesized compounds had the spinel structure. Electrochemical tests show that when x was 0.1 the sample LiMg0.1Ni0.4Mn1.5O4 had excellent cycle ability in the potential range from 3.5 to 4.9 V. When the charge and discharge current was 1 C, the LiMg0.1Ni0.4Mn1.5O4 electrode delivered the initial discharge capacity of 110.22 mAh/g. Its capacity decline rate after 30 cycles was only 7.7%.