Oxalic-acid-based co-precipitation method was employed to prepare LiNi2/3Mn1/3O2 sample with a high-ordered structure. Li+,Ni2+ and Mn2+ acetates were used as starting materials. The influence of the amount of lithium source in the starting materials on Li+ content,disorder of Li+-Ni2+ ions,and electrochemical performance has been investigated. Rietveld refinement shows that the sample prepared with 20% excess Li-source in the starting materials exhibits a perfect ordered structure. A specific discharge capacity is as high as 172 mAh/g at C/20 in the voltage range of 4.35?2.7 V. However,the cyclability is not satisfactory:about 25.3% fade in capacity was observed over 50 cycles. Chemically stable SiO2 was coated on the surface of LiNi2/3Mn1/3O2 particles. A significant improvement in cyclability was attained with 3 wt% SiO2 coating,which is ascribable to the protection of LiNi2/3Mn1/3O2 particles from being dissolved into the electrolyte. Oxalic-acid-based co-precipitation method was employed to prepare LiNi2 / 3Mn1 / 3O2 sample with a high-ordered structure. Li +, Ni2 + and Mn2 + acetates were used as starting materials. The influence of the amount of lithium source in the starting materials Li + content, disorder of Li + -Ni2 + ions, and electrochemical performance has been investigated. Rietveld refinement shows that the sample prepared with 20% excess Li-source in the starting materials exhibits a perfect ordered structure. A specific discharge capacity is as high as 172 mAh / g at C / 20 in the voltage range of 4.35 ~ 2.7 V. However, the cyclability is not satisfactory: about 25.3% fade in capacity was observed over 50 cycles. Chemically stable SiO2 was coated on the surface of LiNi2 / 3Mn1 / 3O2 particles. A significant improvement in cyclability was attained with 3 wt% SiO2 coating, which is ascribed to the protection of LiNi2 / 3Mn1 / 3O2 particles from being dissolved into the electrolyte.