Synthesis and modification of well-ordered layered cathode oxide LiNi2/3Mn1/3O2

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/O-3(2) particles. A significant improvement in cyclability was attained with 3 wt% SiO2 coating, which is ascribable to the protection of LiNi2/3Mn1/O-3(2) particles from being dissolved into the electrolyte.