Study On Synthesis And Surface Coating Of Single Crystal LiNi_0.8Co_0.1Mn_0.1O₂ As Cathode Materials For Lithium Ion Batteries

With the rapid development of modern society,new energy vehicles driven by power batteries have gradually entered people’s field of vision.As a key material for power batteries,the quality of the cathode material is of great significance to the battery’s performance,cost and industrialization process.As the most promising cathode material in the lithium battery industry,the attention of the scientific research community is increasingly focused on Ni-rich cathode materials,but Ni-rich materials still have many problems that affect electrochemical performance,such as side reactions at the cathode material/electrolyte interface and high temperature sintering The resulting mixed discharge of cations,cracks in the material during the cycle,etc.,still need further research to improve these problems.In this paper,Li Ni_0.8Co_0.1Mn_0.1O₂（NCM811）cathode material is selected as the research object.Through the study of the synthesis process,the surface modification treatment of the prepared NCM811 material is carried out in the hope of improving the electrochemical performance of the material.The structure,morphology,element state and electrochemical properties of the material were characterized,and the reasons for the changes in material properties were analyzed.The specific research content is as follows:1.In this experiment,single crystal NCM811 materials with different particle sizes were prepared by wet ball milling and molten salt method,and the samples were denoted as NCM-800,NCM-850,NCM-900 and NCM-950 according to the maximum sintering temperature.The XRD results show that the higher the sintering temperature,the greater the peak ratio of I₀₀₃/I₁₀₄.This may be because the higher the sintering temperature,the larger the exposed area of the crystal plane of the sample（003）,and the greater the intensity of the XRD scan peak,resulting in I₀₀₃/I₁₀₄ ratio increases.In the SEM image,the grain size that increases with the increase of temperature can be clearly observed.The electrochemical performance analysis of the samples showed that NCM-900 performed best among several samples.The specific capacity of the first lap discharge reached 177.7 m Ah g^-1 at a rate of 0.1C.The capacity retention rate after 100cycles was 93.1%,and the cycle stability was Excellent.At a high rate of 5C,the capacity retention rate after 200 cycles has reached 74.0%,which has a good capacity retention rate.2.The micron-sized single crystal NCM811（SC-NCM）material was prepared by wet ball milling and molten salt method,and compared with the secondary spherical NCM811（M-NCM）material.The structure and morphology of the two samples were analyzed by X-ray diffractometer（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）and X-ray photoelectron spectrometer（XPS）.The analysis results show that the structure of SC-NCM is stable and may perform well during long cycles.The electrochemical performance of the sample was tested.According to the analysis of the CV test chart,M-NCM has sharper oxidation and reduction peaks than SC-NCM.This is because the primary particle size of M-NCM is～300 nm,Compared with micron-sized particles,M-NCM has a shorter lithium ion diffusion path and a smaller polarization effect.During the long-cycle test,the specific discharge capacity of the SC-NCM sample at the 0.5C and 5C rates is lower than that of the M-NCM sample,but the discharge specific capacity and voltage plateau of the M-NCM decrease the speed during the long cycle.Faster,and the discharge of SC-NCM is more stable than the capacity and voltage platform.In other words,SC-NCM has a higher discharge specific energy during a long cycle.3.The NCM811 material with titanium oxide coating layer was prepared by hydrolysis method combined with high temperature solid phase method.The final products NCM-TO0.1,NCM-TO0.3 and NCM-TO0.5（corresponding to the wt%of Ti O₂ are 0.1%,0.3%and 0.5%respectively）.Through XRD and SEM,it is found that the structure of the coated material has not changed,and the surface morphology has not changed significantly.Through TEM,it can be observed that the coating layer increases with the increase of the coating amount.After charging and discharging at a high rate of 5C and 300 cycles,the capacity retention rates of NCM,NCM-TO0.1,NCM-TO0.3 and NCM-TO0.5 are 23.4%,48.6%,79.4%and 51.3%,respectively.The high-rate cycle performance of the coated samples is better than that of the NCM sample,and the NCM-TO0.3 sample has the best cycle performance,which shows that the coating treatment significantly improves the long-cycle performance and high-rate performance of the sample.