Co–precipitation synthesis of Ni0.6Co0.2Mn0.2(OH)2 precursor and characterization of LiNi0.6Co0.2Mn0.2O2 cathode material for secondary lithium batteries

Abstract

LiNi0.6Co0.2Mn0.2O2 cathode materials were synthesized from spherical and homogeneous mixed metal hydroxide Ni0.6Co0.2Mn0.2(OH)2 which was prepared by co–precipitation method. The synthetic conditions of the metal hydroxide, such as pH, amount of chelating, stirring speed, temperature, etc. were studied in detail. The homogeneous and spherical Ni0.6Co0.2Mn0.2(OH)2 precursor obtained in the optimized synthetic conditions had a high tap–density of 1.94gcm−3. A well–ordered layer–structured and spherical LiNi0.6Co0.2Mn0.2O2 cathode material, with the tap–density of 2.59gcm−3, was fabricated by calcinating the as-prepared Ni0.6Co0.2Mn0.2(OH)2 precursor and 5% excess LiOH·H2O at 820°C in the flowing oxygen. The crystal structure, morphology and electrochemical properties of the precursors and final products were investigated by using X–ray diffractometry, scanning electron microscopy, charge–discharge test and C–V method. In the voltage ranges of 2.8–4.3, 4.4 and 4.5V, the initial discharge capacities of LiNi0.6Co0.2Mn0.2O2 at 1C rate were 172.1, 177.9 and 182.5 mAh g−1, respectively, while the corresponding discharge capacity retention ratios after 100 cycles were 94.3%, 90.7% and 85.4%. For elevated temperature operation (60°C), the resulted capacity was as high as 196.9mAh g−1 in the voltage range of 2.8–4.3V and retained 89.7% after 100 cycles.