Synthesis And Study Of The Lithium-nickel-cobalt-manganese Oxides For High Capacity Lithium Ion Batteries

Layered lithium-nickel-cobalt-manganese oxides cathode materials attacted a greatdeal of attention due to their high specific capacity, high tap density a nd accepted safetyperformance. It is considered to be one of the best choice for cathode materials inlithium-ion batteries. In this paper, the synthesis process parameters of theLiNi_1/3Co_1/3Mn_1/3O₂, LiNi₀.5)Co_0.2Mn_0.3O)₂and Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂weresystematically studied to find out the optimized productive process and guide industrialproduction.In the optimization of the solid-state synthesis of the LiNi_1/3Co_1/3Mn_1/3O₂andLiNi₀.5)Co_0.2Mn_0.3O)₂, orthogonal experimental method was employed to explore theinfluence of sintering temperature, sintering time, pretreatment temperature and lithiumsource. The results indicate that the sintering temperature and sintering time dominate theelectrochemical performance of the layered cathode materials. Finally the optimizedmaterial was comprehensive charatcterized.The study shows that the sample of LiOH assource of lithium, sintering at500°C for5h and then heating up to900°C for10hexhibits the best electrochemical performance. The crystalline material shows regularmorphology and moderate particle size。The ordering of metal ions would reduce if thesintering temperature is too high or too low. The sintering time seriously affects theparticle size of the obtained sample. LiNi_1/3Co_1/3Mn_1/3O₂and LiNi₀.5)Co_0.2Mn_0.3O)₂respectively show discharge capacity of154mAh/g and165.2mAh/g at0.1C ratebetween2.9and4.3V. The discharge capacity at2C rate was114.3mAh/g and113mAh/g, respectively. Both electrodes exhibit excellent cycle and rate performa nce. Incomparison, the rate performance and cycle performance of LiNi_1/3Co_1/3Mn_1/3O₂is better.But, the capacity is lower than LiNi₀.5)Co_0.2Mn_0.3O)₂.LiNi_1/3Co_1/3Mn_1/3O₂electrode showsbetter rate and cycle performance but lower capacity than LiNi₀.5)Co_0.2Mn_0.3O)₂.The precursor of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂was obtained by using mechanicalball milling method with LiOH·H₂O, NiO, Co2O3and MnO₂. The process parameters suchas the amount of lithium source, sintering temperature and sintering time were systematically studied by the means of X-ray diffraction （XRD）, scanning electronmicroscopy （SEM） and so on. The study shows that the optimized synthesis ofLi[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂is that the precursor were mixed with excessive5%lithiumsource first and sintered at500°C for5h, then mechanical ball milled for1h, at lastsintered at900°C for10h. The electrochemical performance of two step sinteringmaterial is much better than the one step sintering material. After mechanical balling, theparticle size is more smaller and uniform. In the range of2.0to4.8V, the two stepsintering material delivers a discharge capacity of242.6mAh/g at0.1C rate and the onestep sintering material delivers only222mAh/g. The discharge capacity of the two stepsintering material at2C rate was156.5mAh/g, which was also higher than the one stepsintering material.