Flotation behavior and surface properties of spent lithium-ion battery electrode materials

Lithium-ion batteries contain a large amount of metals and various toxic substances. Recycling of waste lithium batteries can allow resource recycling and prevent environmental pollution. In this study, waste power lithium manganate (LiMn₂O₄) batteries are taken as the research object, and the method of “roasting enhanced flotation” is employed to solve the problem of difficult flotation separation of the positive and negative electrode materials during the recycling process of LiMn₂O₄ batteries. Conversely, the organic adhesion on the surface of the electrode materials is removed using roasting, thereby increasing the difference in surface wettability between the electrode materials and facilitating the flotation separation process. Research on the flotation behavior of single-electrode materials of lithium-ion batteries shows that the flotation behavior of commercial LiMn₂O₄ is opposite to commercial graphite, while waste LiMn₂O₄ and waste graphite perform similar hydrophobic. During the flotation separation of the mixed electrode materials, the flotation separation efficiency of waste LiMn₂O₄ and graphite is low, while that of commercial LiMn₂O₄ and graphite is high. Furthermore, X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and contact angle analysis results show that the surface of the waste lithium battery electrode material is coated with organic compounds containing carbon, oxygen, fluorine, and other elements, resulting in similar surface properties of anode and cathode electrode materials, which finally increases the difficulty of flotation separation of anode and cathode electrode materials. Furthermore, the thermal stability analysis result of the electrode materials shows that the decomposition temperature range of the organic matter is 400–600 ℃. Upon completely understanding the surface properties of the electrode materials and the thermal stability of their organics, a muffle furnace is used to investigate the effect of roasting temperature and time on the removal of organic matter on the surface of the electrode materials. The results show that after roasting at 550 ℃ for 2 h, the organics adhered to the surface can be completely oxidized and decomposed, following which the original surface of the electrode material can be exposed without altering the phase composition of the electrode material. The experimental results of the flotation separation of the electrode materials under different calcination parameters show that the flotation separation efficiency of LiMn₂O₄ and graphite after calcination at 550 ℃ for 2 h is considerably higher than the electrode materials without calcination. At this time, the grade of LiMn₂O₄ in the flotation concentrate increased from 63.10% without roasting to 90.98%; the residual graphite in the small-scale, closed-circuit flotation concentrate is low, and the purity of LiMn₂O₄ reaches 99%.