Abstract: Li_1.2Mn_0.6Ni_0.2O₂ and Li_1.2Mn_0.588Ni_0.196Co_0.016O₂，cathode materials of lithium-ion batteries were synthesized by co-precipitation method.Their crystal structures，morphologies，and electrochemical properties were characterized by X-ray diffraction（XRD），scanning electron microscopy（SEM），and electrochemical tests.XRD results indicated that material′s layered structure was kept intact and cation mixing degree was lowered after Co-doping.Electrochemical tests showed that：the initial charge-discharge efficiency and rate discharge performance of the Co-doping material were superior to those of Li_1.2Mn_0.6Ni_0.2O₂， and better cycle performance was displayed. Its discharge capacities were 230.3，215.6，155.6 mA·h/g at 1，2，5 C，respectively，and the capacity retention rate was up to 90.9% at 1 C after 50 cycles.

Key words: lithium-ion batteries, cathode material, Co-doping, Li_1.2Mn_0.6Ni_0.2O₂