Study On Preparation And Doping Modification Of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material By Sol-Gel Method

In recent years,with the rapid development of new energy electric vehicle industry,people have higher requirements for the performance of lithium-ion batteries.High specific capacity,high energy density,excellent cycle performance and other properties are all required by electrode materials.As the cathode material is the core of lithium-ion batteries,it is also necessary to study cathodes with high specific capacity and long cycle life.Nickel rich ternary layered cathode material LiNi_0.8Co_0.1Mn_0.1O₂ is a hot research topic.Though the high specific capacity of the battery is attributed to the high Ni content,at the same time,problems occur such as poor structural stability,rapid capacity attenuation,poor cycle and rate performance,etc.Based on this,this article uses the sol-gel method to synthesize LiNi_0.8Co_0.1Mn_0.1O₂ cathode material and optimize its process conditions.Then,the LiNi_0.8Co_0.1Mn_0.1O₂ material prepared under the optimal process conditions was modified by F,Nb,and Ta doping to improve the structural stability and cycle performance of the material.XRD,SEM,EDS,TEM,constant current charge and discharge testing are used to characterize the physical and electrochemical properties of the material.Specifically studied the following:（1）The LiNi_0.8Co_0.1Mn_0.1O₂ cathode material was synthesized by the sol-gel method.The results show that the materials have good crystal structure and low cation disorder at different p H values and sintering temperatures.The growth of the material is not complete and the crystallization performance is poor when the sintering temperature is 760℃;at 780℃and 800℃,the material has good dispersibility and crystallinity,and there are a few secondary particles formed by agglomeration on the surface of the material;while at 820℃,the surface agglomeration of the material is more serious,which increases the charge transfer impedance of the material.It is found comprehensively that when the p H of the solution is 3.53 and the sintering temperature is 800℃,the LiNi_0.8Co_0.1Mn_0.1O₂ material has better electrochemical performance.At2.75～4.3 V,0.2 and 1 C rates,the first discharge specific capacity is 188.1 m Ah/g and167.4 m Ah/g,respectively.After 100 cycles,the capacity retention rate is 92.6%and84.6%,respectively.（2）The LiNi_0.8Co_0.1Mn_0.1O₂ material was modified by co-doping with F and Nb,and the cycle stability of the material was improved through the protective effect of F on the electrode material and the promotion effect of the Nb-O bond on the stability of the material structure.The results show that 450℃is the most suitable sintering temperature for F doping.The agglomeration phenomenon on the surface of the material will increase when the temperature is too high.F and Nb co-doped materials did not change the crystal structure and morphology of the material,and the material still has low ion mixing and a betterα-Na Fe O₂ layered structure.The cycle performance of co-doped materials has been significantly improved.This is due to the fact that F and Nb partially enter the material lattice,which increases the material cell parameters and volume,which facilitates the deintercalation of Li⁺and stabilizes the material crystal structure.Li(Ni_0.8Co_0.1Mn_0.1)_0.99Nb_0.01O_1.98F_0.02 material has better electrochemical performance.At 2.75～4.3 V,1 C rate cycle,the first discharge specific capacity is 170.7m Ah/g,after 100 cycles,the capacity retention rate is 94.5%;at 5 C rate,there is an initial discharge specific capacity of 146.4 m Ah/g,after 200 cycles,the capacity retention rate is 89.9%.（3）A proper amount of Ta doping is beneficial to the cycle performance of the electrode material and can stabilize the material structure.This is because an appropriate amount of Ta doping can not only increase the unit cell parameters and volume of the material,but also accelerate the Li⁺diffusion rate,and the stronger Ta-O bond also stabilizes the material structure and improves the cycle stability of the material.The initial discharge specific capacity of the original material and 0.5%Ta doped material at 2.75～4.3 V and 1 C rate are 167.1 m Ah/g and 163.2 m Ah/g,respectively.After 100 cycles,the capacity retention rates are 82.2%and 89.7%,respectively.（4）The F and Ta co-doped LiNi_0.8Co_0.1Mn_0.1O₂ materials were prepared by sol-gel method combined with hydrothermal method.XRD results show that the co-doping of F and Ta increases the a,c value and volume of the material,which promotes the diffusion of Li⁺,increases the electrical conductivity and ionic conductivity of the material,and reduces the charge transfer resistance of the material.Under the dual effect of high Ta-O bond dissociation energy as well as the rate of HF attack on electrode materials reduced by F,material structure stability is significantly enhanced.At2.75～4.3V and 1 C rate,the initial discharge specific capacity of the original material and Li[Ni_0.8Co_0.1Mn_0.1]_0.995Ta_0.005O_1.98F_0.02 material are 167.1 m Ah/g and 161 m Ah/g,respectively.After 100 cycles,the capacity retention rates are 82.2%and 93.7%,respectively.