Synthesis And Properties Of LiNi_0.6Co_xMn_0.2M_yO₂?M=Fe,V? As Cathode Material For Tetrad Lithium Ion Batteries

With the increasing use of electronic products in recent years,especially meeting the needs of high-power,high-energy and high-reliability batteries in the battery system of new energy electric vehicles,people are constantly looking for better performance battery system.Because the high nickel content increases the energy density of the material,the low cobalt and manganese ratio reduces the cost of the material and improves the cycling performance of the material,the high nickel ternary cathode material(especially LiNi_0.6Co_0.2Mn_0.2O₂)will become one of the mainstream materials for power batteries,large batteries and energy storage batteries in the future.However,the synthesis conditions of LiNi_0.6Co_0.2Mn_0.2O₂ materials are complicated,the process is difficult to control,and the cycle stability and rate performance of the materials are relatively poor?especially at higher cut-off voltage?.This inherent defect limits its further development and application.In this paper,the LiNi_0.6Co_0.2Mn_0.2O₂cathode material is taken as the research object.Aiming at the poor cycle and rate performance of the material,the cathode materials for Li-battery with high cycle stability and high rate is prepared by optimizing the synthesis conditions and introducing the fourth component.This paper mainly carries on from the following aspects:Firstly,the synthesis conditions of the materials were explored,and the effects of the pH value of oxalic acid coprecipitation reaction and the timing of oxygen permeation on the structure and morphology of the tetrad cathode materials were studied.The optimum oxalic acid coprecipitation pH value of LiNi_0.6Co_0.1Mn_0.2Fe_0.1O₂ for lithium ion batteries is 6.5.Under these conditions,the cathode materials synthesized have the best laminar structure,the smallest ion mixing degree and the small uniform spherical morphology.In the high temperature solid phase phase,the materials obtained after 450°C and the whole process of oxygen permeation also have a good layer structure of?-NaFeO₂,lower ion mixing and higher lattice oxygen content,which make the good cycling and rate performance to be realized.Secondly,the properties of LiNi_0.6Co_0.1Mn_0.2Fe_0.1O₂ cathode material were studied under the optimized process conditions.The effect of the introduction of the fourth component Fe on the structure,morphology and electrochemical properties of the material was discussed.XRD,XPS and SEM analysis show that LiNi_0.6Co_0.1Mn_0.2Fe_0.1O₂ has more orderly layered structure,lower cationic mixing degree and more uniform spherical particles.Laser particle size analysis shows that LiNi_0.6Co_0.1Mn_0.2Fe_0.1O₂ has a narrow particle size distribution.Electrochemical measurement and analysis show that the introduction of Fe reduces electrode polarization and interface impedance,and increases the diffusion rate of lithium ions.Therefore,the first coulomb efficiency of LiNi_0.6Co_0.1Mn_0.2Fe_0.1O₂ samples can reach more than 90%and the first specific discharge capacity is 177 mAh/g at the rate of 0.1C.After 100 times charging and discharging at 1 C current density,LiNi_0.6Co_0.1Mn_0.2Fe_0.1O₂ samples has 86%capacity retention rate,and its specific capacity is still 130 mAh/g.At 2 C current density,its discharge specific capacity is151 mAh/g,which has excellent cycle and rate performance.Another component V was introduced into LiNi_0.6Co_0.2Mn_0.2O₂ by oxalic acid coprecipitation.The effects of the amount of V?x=0,0.06,0.08,0.10?on the physical and chemical properties of LiNi_0.6Co_0.2-xMn_0.2V_xO₂ cathode materials were studied.XRD and XPS fitting analysis showed that the introduction of V⁵⁺did not change the layered crystal structure.When the amount of V⁵⁺was 8%,LiNi_0.6Co_0.12Mn_0.2V_0.08O₂ cathode material had excellent crystal structure and lower cationic disorder.The results of electrochemical performance test show that the cathode material has relatively good electrochemical performance in the range of 3-4.6 V with 8%introduction.The first irreversible specific capacity is the smallest?51.74 mAh/g?.After 100 cycles of 1 C,the capacity retention rate is 92.6%and the discharge specific capacity is 149.3 mAh/g.Under the high current density at 5 C,the discharge capacity of the material is also as high as 129.4 mAh/g.