Research On The Effect Of Precursors On Controlled Synthesis And Properties Of Single Crystal LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials

As the best power storage medium,lithium-ion battery has been widely used and studied in portable batteries and power batteries.Cathode material is a very important component of lithium battery,which is a key component affecting the safety performance,cycle performance and energy density of lithium battery.The layered LiNi_0.8Co_0.1Mn_0.1O₂ cathode material not only meets the requirements of long driving range of electric vehicles,but also meets the development direction of high nickel and low cobalt in the future.However,with the increase of nickel content,many problems that need to be solved have gradually emerged.For example,the cation mixing degree in the material is serious and the gas generation phenomenon in the cycle process,which will destroy the crystal structure and lead to the decrease of thermal stability.Besides,the secondary spherical particles of cathode materials will be broken under high pressure density,which leads to the decline of electrochemical performance.In view of the problems of high nickel ternary cathode materials,single crystal LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials were synthesized by coprecipitation and high temperature sintering.Based on the research and analysis of the theoretical basis of synthesis precursor,this study mainly explores the influence of technological conditions on precursors in the co-precipitation process,the influence of precursors on single crystal LiNi_0.8Co_0.1Mn_0.1O₂ cathode material.In addition,we provided a new method to prepare single crystal LiNi_0.8Co_0.1Mn_0.1O₂ cathode material by controlling the supersaturation of solution.The specific research contents are as follows:（1）Based on the formation of supersaturated solution,nucleation and crystal growth in the process of crystal crystallization.The mathematical model of thermodynamic equilibrium of Ni-Co-Mn-NH₄⁺-H₂O was established in the reaction system of preparing ternary precursor by co-precipitation method.The relationship between the concentration of metal ions and the total concentration of ammonia,pH value in the solution system was calculated.According to the calculation results,taking Ni_0.8Co_0.1Mn_0.1（OH）₂ as an example,the effects of total ammonia concentration,pH value,feeding speed and stirring speed on the particle size and morphology of precursor were respective explored,which provided a direction for the optimizing process conditions.（2）The effects of different morphology and size of precursors on the properties of single crystal LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials were investigated.The results show that the primary particles of the precursor are large and the secondary particles are sparse,after sintering with LiOH at high temperature,the synthesized single crystal particles not only have larger size and better dispersion,but also have better layered structure and crystal structure.However,the primary particles of the precursor are small and the secondary particles are dense.The single crystal particles obtained by sintering are not only small in size and uneven in distribution,but also most single crystal particles agglomerate to form secondary particles.According to the analysis of the electrochemical test results,it can be concluded that the first discharge performance of the single crystal LiNi_0.8Co_0.1Mn_0.1O₂ cathode material with better dispersion is greatly improved.Its cycle performance and rate performance are better than that of single crystal LiNi_0.8Co_0.1Mn_0.1O₂ cathode material with particles agglomeration.（3）A method of preparing single crystal LiNi_0.8Co_0.1Mn_0.1O₂ cathode material by adjusting the supersaturation of solution to control the crystallization of precursor is proposed.The single crystal particles have good crystal structure and excellent electrochemical properties.In the process of coprecipitation,the supersaturation of the reaction solution is controlled by changing the pH value to separate the nucleation and growth process of the precursor completely.After sintering at high temperature,the single crystal particles of obtained have good layered structure,low degree of cation mixing,good uniformity and dispersion,which has great influence on the electrochemical performance improvement.