Study On Preparation And Properties Of High-nickel Ternary Cathode Materials For Lithium Ion Batteries

With the rapid development of portable electronic products and electric vehicles,higher requirements have been put forward for the energy density,safety,cycle life and cost of lithium-ion batteries.The high-nickel ternary layered LiNi_xCo_yMn_zO₂（x>0.6）materials has promising application prospects due to high capacity and low cost,and thus,has become one of the current research hotspot materials.This paper focused on the studies on preparation and electrochemical performance of two high-nickel ternary materials,LiNi_2/3Co_（1-x）/6Mn_（1+x）/6O₂ and LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）.The following conclusions are obtained:Firstly,the LiNi_2/3Co_1/6Mn_1/6O₂ cathode material with high cation order,low defects and excellent charge-discharge performance was successfully prepared by the rheological phase method.During the preparation,the calcination temperature,atmosphere and lithium ratio were found to be important factors that affect the structure and performance of the material.The preparation conditions were optimized as follows:the lithium ratio is 1.06（that is,the lithium excess is 6%）,oxygen atmosphere,and calcination at 800℃.The material prepared under optimized conditions exhibited fewer defects,high cation order,good crystallinity,low interface impedance,high lithium ion diffusion coefficient,and excellent charge-discharge performance.In the voltage range of 2.8-4.3 V,its discharge capacity at 0.2C rate and coulombic efficiency in the first cycle was 188.7 m Ah·g^-1 and 88.3%,respectively,and the discharge capacity at 5C rate reached 130.4 m Ah·g^-1,and 93.7%of initial capacity remained after 50 cycles of charge-discharge at 0.5C rate.Combined with previous theoretical calculations analysis,the experimental results further confirmed that LiNi_2/3Co_1/6Mn_1/6O₂ is a promising cathode material.Secondly,based on LiNi_2/3Co_1/6Mn_1/6O₂,optimizing the ratio of Co and Mn can further improve the charge-discharge performance of the material.Using hydroxide co-precipitation precursor as raw material,LiNi_2/3Co_（1-x）/6Mn_（1+x）/6O₂（x=0,0.2,0.4）was successfully prepared by high temperature solid phase method.Appropriate increasing the Mn content to increase the Ni²⁺content can further improve the charge-discharge performance and thermal stability of the material.When x=0.2,the obtained material showed lower degree of cation mixing,smaller interface impedance,better charge-discharge performance and thermal stability.Compared with x=0(i.e.LiNi_2/3Co_1/6Mn_1/6O₂)material,the initial discharge capacity at 0.2C rate and efficiency of x=0.2(i.e.LiNi_0.67Co_0.13Mn_0.20O₂)material were respectively increased to 194.9m Ah·g^-1 and 91.0%,the discharge capacity at 5C rate was increased to136.1 m Ah·g^-1,the capacity retention after 50 cycles at 0.5C rate was increased to 94.71%,and the thermal stability under 4.3V charging state was also improved,showing a better application prospect.Finally,a new method is proposed for the preparation of LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）material.Three NCM811 materials were prepared respectively by calcinating"LiNi_0.89Co_0.11O₂+manganese oxide"raw materials（referred to as process a）,"Ni_0.89Co_0.11（OH）₂+Li OH·H₂O+manganese oxide"raw materials（referred to as process b）,and"Ni_0.8Co_0.1Mn_0.1（OH）₂+Li OH·H₂O"raw materials（referred to as process c）.The NCM811 materials produced by the three processes all had a good layered structure.Among them,the material prepared by the process b showed higher crystallinity,the most perfect layered structure,the best structural stability during the charging-discharging process,the least interface impedance increases,and the best charging-discharging performance.In the range of 2.8 to 4.3 V,the material delivered a discharge capacity of 193.7 m Ah·g^-1 in the first cycle at 0.2C rate with a coulombic efficiency of 90%,and capacity retention of 91.64%after 100 cycles at 0.5C rate.The preparation of the Ni_0.89Co_0.11（OH）₂ precursor required by the process is low in difficulty,the calcination preparation process is simple,and the prepared material exhibits better structure and performance.Therefore,it is a promising method for preparing high-nickel ternary materials for lithium-ion batteries.