In order to improve the lifetime of the Lithium-ion battery, Mg-Y co-doped LiCoO2 was prepared by high temperature solid phase synthesis, with Co3O4, Li2CO3, Mg(OH)2 and Y2O3 as raw materials. The structure and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscpoe (SEM). The battery achieved best electrochemical performance when the cathode is doped with 0.10wt% yttrium and 0.20wt% magnesium. The results of electrochemical performance showed that the initial discharge capacity was 212.3 mAh/g at 0.5C, 3.0-4.6V and with the outstanding capacity retention of 96.28% after 50 cycles at 3.0-4.6V. The discharge capacity of co-doped LiCoO2 at 4.0C remained 60.43% of the discharge capacity at 0.2C, while that of Mg only doped LiCoO2 is only 54.92%.