Cathode Powder Surface Treatment Using Atmospheric Pressure Plasma

LiOH, Li₂CO₃ impurities of NCM (8:1:1) Li ion battery cathode powder were removed by using atmospheric pressure plasma. Specially designed plasma reactor was used for the study. The mixed gas of N₂, H₂, CH₄, SF₆ and NF₃ was used for dielectric barrier discharge plasma generation. N₂-SF₆ and N₂-NF₃ mixed gas plasma showed the best removal performance and when the SF₆ or NF₃ content was increased, the removal efficiency was also increased with a plateau. Addition of a small amount of hydrogen containing gas such as H₂ and CH₄ into the plasma enhanced the impurity removal efficiency but the proportional relationship with the content increment with these gases was not shown. It is well known that the fluorine containing gas extinguishes plasma, however the hydrogen containing gas seems attenuated the extinguishing effect of the fluorine containing gas for this case. In the early stage of the study, the cathode powder was treated by direct contact with the plasma, however, it was also observed that the same removal effect was shown by just mixing the powder with the gas passed through the plasma generator. The plasma treatment of 3kW applied power could remove more than 50% of impurities from the NCM powder at 13kg/hr of the treatment speed. In the same impurity removal treatment condition, it was observed that fluorine passivation layer was formed on the surface of the cathode particle at the same time. Other than the impurity removal and fluorine passivation on the cathode active material, the atmospheric pressure plasma powder treatment can offer the solution for enhancement of dispersion property in making powder slurry and carbon adsorption on the active material surface etc.