Synthesization And Investigation Of Spherical Cathode Material-LiNi_1/3Co_1/3Mn_1/3O₂ For Li-ion Batteries

People have been trying to find the alternate materials for commercial LiCoO₂ because of the cost and toxicity of Co.The materials of LiNi_xCO_1-2xMn_xO₂ series have been the hot point at home and abroad for a long time as it's cheaper than LiCoO₂ but may acquire better performance.A series of spherical cathode material—LiNi_1/3Co_1/3Mn_1/3O₂ was synthesized by carbonate co-precipitation method and then examined by TG-DTA,ICP,XRD,SEM etc.in this thesis.The synthetic process was optimized after a comprehensive inspection of the effect of the pretreatment and thermal treatment.The experiment results showed that the best synthetic process was as follows:pH=7.4-7.6,the concentration ratio of the precipitator to the metal salt solution was 1.5,reaction temperature was 50℃,the calcination temperature and holding time were 850℃and 15h,respectively.For the best sample of LiNi_1/3CO_1/3Mn_1/3O₂,the discharge capacity could reach 191.5mAh/g in the voltage range of 2.5-4.5V and at 0.05C;the capacity of 169.2mAh/g could be retained at 2C;cycled at 0.1C for 30 cycles,the retention rate could reach 97.2%.The results showed that increasing the Li content could improve the cycle performance significantly.Li_1.1Ni_1/3Co_1/3Mn_1/3O₂ showed the best performance.On the base of LiNi_1/3Co_1/3Mn_1/3O₂ material,the Co content was reduced to synthesize LiNi_0.4Co_0.2Mn_0.4O₂ and LiNi_0.45Co_0.1Mn_0.45O₂ which had lower cost but better cycle performance.The LiNi_0.45Co_0.1Mn_0.45O₂ had excellent cycle performance but low capacity,poor high-rate capability.The electrochemistry performance of LiNi_0.4Co_0.2Mn_0.4O₂ was very well:the discharge capacity could reach 193.3mAh/g; the capacity was 170.6mAh/g when discharged at 2C;cycled at 0.1C for 30 cycles, the retention rate was 93.0%.For comparison,LiNi_1/3Co_1/3Mn_1/3O₂ was synthesized by hydroxyl co-precipitation method.The materials had the best performance when controlled pH=10.5 and the calcination temperature at 950℃.The surface topography of the materials were lumpish as NH₃·H₂O and other complexing agents hadn't been used.The capacity and cycle performance of LiNi_1/3Co_1/3Mn_1/3O₂ synthesized by the two different co-precipitation methods were both very well,but the high-rate dischargeability of the materials prepared by carbonate co-precipitation method were much better.