Synthesis And Structure Optimization Of LiNi_0.8Co_0.1Mn_0.1O₂ Nickel Rich Cathode Materials

LiNi_0.8Co_0.1Mn_0.1O₂（abbreviated as NCM）nickel-rich layered transition metal oxides have attracted attention due to its high specific capacity（²00 mAh/g）,excellent cycle performance,and low cost.The coprecipitation method combined with the high temperature solid phase method is one method that is most suitable for the industrial production of NCM,and the products synthesized by this synthesis route are more uniform,more dense,and the production cost is moderate.However,the industrial application of NCM ternary materials is still affected by factors such as poor cycle performance and poor thermal stability,so its electrochemical performance needs to be further improved.In this paper,the synthesis process of NCM nickel-rich ternary cathode materials was studied by chemical co-precipitation method and high-temperature solid-phase method.The relationship between NCM precursors and lithiation ratios of different lithium sources was discussed.Furthermore,the matching of NCM materials with different conductive agents was studied.On this basis,a full concentration gradient structure was designed to improve the electrochemical performance of the material.In this project,the precursor of NCM were prepared by co-precipitation method.NiSO₄·6H₂O,CoSO₄·7H₂O and MnSO₄·H₂O were used as raw materials.NaOH and NH₃·H₂O were used as precipitants and complexing agents,respectively.The theoretical experimental range was then calculated by material balance of the system.The effects of the pH,total ammonia concentration,feed rate,reaction time,aging time,rest time,feed salt and alkali concentration,drying mechanism and other factors on the precursor morphology,tap density and crystal structure were investigated.Through experimental studies,it was concluded that a spherical NCM precursor with a uniform particle size and compact surface can be obtained at a pH of 11.50,a total ammonia concentration of 1.2 mol/L,and a reaction time of more than 24 h.The precursor and the lithium source were uniformly mixed and then calcined in a tube resistance furnace to study the effect of precalcining temperature and time,calcination temperature and time on the crystal structure and electrochemical performance of the NCM material.The calcination process study shows that the lithium-mixed precursor is pre-calcined at 500°C for 4 h,and then calcined at800°C for 12 h,showing good electrochemical performance.The initial discharge specific capacity was 198.6 mAh/g,and the discharge capacity retention rate after100 cycles of 1 C was as high as 96%or more.LiOH·H₂O and Li₂CO₃ were mixed with the precursors,respectively,and calcined to obtain the target product.The effects of different lithiating ratios on the electrochemical performance were compared.After comparison,the lithiated LiOH·H₂O material has a smoother,more dense surface and better electrochemical performance than Li₂CO₃.Based on the synthesized NCM material,three different sizes of carbon materials,Super P,acetylene black,and mesocarbon microbeads,were selected as the conductive agent.Through electrochemical performance testing,the matching relationship between NCM materials and different conductive agents was analyzed.The test found that when using Super P as a conductive agent,the material has a small impedance and has a good electrochemical performance.Through the preparation of the precursor,the concentration composition of the precursor is continuously adjusted to further synthesize a spherical precursor with a concentration gradient structure.The concentration gradient material designed in this experiment is based on a high-capacity Ni-rich material and gradually transitions to a relatively low Ni and Mn-rich surface,In this way,a gradual transition from a core with an Ni content of 84%to a secondary particle spherical surface with an Ni content of 76%is achieved.The entire concentration gradient material has a gradual change in concentration gradient,avoiding collapse of the structure due to the large difference in composition during charging and discharging,and having better performance relative to the shell-core material.Through the charge-discharge test,the capacity retention rates of the concentration gradient materials after 100 cycles of 1 C and 5 C current densities were 98.8%and 93.7%,respectively,which were higher than the 96.6%and 90.3%retention of intrinsic materials.