Investigation On The Synthesis And Performances Of High-nickel Ternary Cathode Materials For Lithium-ion Batteries

Layered lithium cobalt nickel manganese oxide composite materials have ternary synergetic effect, combining the advantages of lithium nickel oxide, lithium manganese oxide and lithium cobalt oxide. Among which, high-nickel ternary material LiNi_0.8Co_0.1Mn_0.1O₂ has been widely focused on due to its high discharge specific capacity. The properties of LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials synthesized by hydroxide coprecipitation method and carbonate coprecipitation method were firstly compared, based on which, the process conditions of carbonate coprecipitation method were optimized. In view of the faster capacity fading problem of high-nickel material, the modification effect of AlF3 coating was also investigated.High-nickel material LiNi_0.8Co_0.1Mn_0.1O₂ were synthesized through hydroxide coprecipitation method and carbonate coprecipitation method, respectively. The process conditions, physical, chemical and electrochemical performances were analyzed and compared. The results show that although the synthesis process of carbonate coprecipitation method is simpler than that of hydroxide coprecipitation method, the material obtained from carbonate coprecipitation method exhibits worse particle morphology, lower tap density and discharge specific capacity, so it is necessary to optimize the process conditions of carbonate coprecipitation method.In view of the shortcomings of the materials from carbonate coprecipitation method, different feeding ways, precipitation agents, lithium sources, calcination system, water washing process conditions were used as the investigation factors to execute the single-factor experiment, respectively. The material micro-structures and morphology were characterized by means of XRD and SEM, the effect of the synthetic process was evaluated by charge-discharge test system. The effect of the synthetic process on the physical and electrochemical performances was systematically investigated, and the best synthetic conditions can be generalized as following: flow and feeding manner, Na2CO3 + NH4HCO3 as a mixed precipitant, LiOH·H2O as lithium source, two-step calcination system, water washing and drying. The thus-obtained high-nickel material LiNi_0.8Co_0.1Mn_0.1O₂ exhibits excellent electrochemical performances, with an initial discharge specific capacity of 188.6mAh·g-1 at 0.2C rate and a capacity retention rate of 55.7% after 50 cycles at 1C rate.In view of the poor cycling performance of high-nickel material, the modification effect of AlF3 coating was investigated. The results show that the AlF3 coating does not alter the layered structure of the material. In addition, although the initial discharge specific capacity of the coated material is slightly decreased, the cycle performance is obviously improved. Among which, the sample coated with 2wt.% AlF3 exhibits the optimum overall electrochemical performance, with a capacity retention rate of 68.2% after 50 cycles at 1C rate, 12.6% higher than that of the uncoated sample.