Preparation Of High-Nickel Ternary Cathode Materials By Molten Salt Method And Its Application In Lithium-Ion Batteries

In recent years,with the rapid development of the new energy automobile industry,Lithium-ion batteries have received enthusiastic attention and been studyed by researchers,especially for the study of cathode materials.Meanwhile,people have more requirements for the using life of new energy vehicles,which is a great challenge to the energy density of batteries.Traditional LiCoO₂ materials cannot meet people's requirements,so the pursuit of higher capacity,safe and low-cost materials is imperative.Ternary cathode materials,especially high-nickel ternary materials,have been favored by researchers in rencent years.However,there are still some problems including preparation process,cycle performance,and storage conditions.In this paper,a large-size high-nickel ternary material with a single crystal structure was prepared by molten salt method,and further modified.The specific research contents are as follows:1.In this paper,Ni,Co,Mn carbonates were used as the raw materials for ball milling,and then added 1.1 and 4 times of flux?0.38LiOH-0.62LiNO₃?to prepare the nano-sized?N-NCM622?and micron-sized?M-NCM622?LiNi_0.6Co_0.2Mn_0.2O₂.The structure and morphology of the two materials were analyzed by X-ray Diffraction?XRD?,Scanning Electron Microscope?SEM?,particle size analysis and Transmission Electron Microscope?TEM?.Through SEM and particle size analysis,it can be seen the material that added 4 times of flux has a better crystal structure and a larger particle size?²?m?.The lithium ion diffusion coefficient calculated by the cyclic voltammetry?CV?test indicates that the lithium ion diffusion coefficient of the material added with4 times the flux is larger,indicating a better lithium ion deintercalation ability.It also shows a better electrochemical performance in the subsequent charge and discharge test.2.On the basis of preparing LiNi_0.6Co_0.2Mn_0.2O₂ material with micron-sized single crystal structure,a thin layer of Li₂ZrO₃?LZO-NCM?was coated on the surface for modification.By XRD and SEM analysis,the structure of the coated material did not change and still has a regular and complete morphology.In the charge-discharge test,although the initial capacity of the coated sample is lower at 0.2 C,it can still reach149.5 mAh g^-1 after 100 cycles,maintaining the first cycle discharge specific capacity of 91.8%which is much higher than uncoated material of 78%.At the 5 C rate of charge and discharge,the first cycle discharge capacity of LZO-NCM reaches 142.3 mAh g^-1,which is higher than the 132.6 mAh g^-1 of M-NCM622,and the efficiency of LZO-NCM can be maintained 81.7%after 200 cycles.It also has good electrochemical properties at a higher temperature of 50°C.3.LiNi_0.8Co_0.1Mn_0.1O₂?C-NCM811?with higher nickel content was successfully prepared by molten salt method and compared with LiNi_0.8Co_0.1Mn_0.1O₂?NCM811?which is synthesized by traditional method.From the SEM,it can be seen that C-NCM811 has a more dispersed and complete particle morphology.In the charging and discharging test,although the initial capacity of C-NCM811 is lower than NCM811 at low rate,it still has a good cycle performance.In the rate performance test,the C-NCM811 material exhibited superior performance at high current.At the same time,with increasing the cut-off voltage,the material prepared by the molten salt method has a good cycle stability.