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Application of mechanical crushing combined with pyrolysis-enhanced flotation technology to recover graphite and LiCoO2 from spent lithium-ion batteries

Zhang, Guangwen, He, Yaqun, Wang, Haifeng, Feng, Yi, Xie, Weining, Zhu, Xiangnan
Journal of cleaner production 2019 v.231 pp. 1418-1427
X-radiation, crushing, electrodes, electrolytes, graphene, lithium batteries, pyrolysis, recycling, temperature, thermogravimetry
In this study, a novel process of mechanical crushing combined with a pyrolysis-enhanced flotation was developed to recover LiCoO2 and graphite from spent lithium-ion batteries, which lays the foundation for the subsequent metallurgical process. Pyrolysis technology was used to solve the problem of low flotation efficiency of electrode materials. The pyrolysis characteristics of the electrode materials were carefully analyzed, and based on the results, the effects of pyrolysis treatment on the surface micro-characteristics, surface element chemical states, and mineral phases of electrode materials were fully investigated to explore the pyrolysis flotation enhancement mechanism. Afterwards, flotation methods were utilized to separate LiCoO2 from graphite. Surface micro-characterization analysis showed that the residual organic binders and electrolytes were the main reason that resulted in a low flotation efficiency of electrode materials. The thermogravimetric analysis and pyrolysis products indicated that the organic binders and electrolyte can be removed at a pyrolysis temperature of 500 °C. X-ray powder diffractometer analysis demonstrated that the electrode particle mineral phases were not altered at a pyrolysis temperature of less than 550 °C. The optimum flotation behavior was presented at a pyrolysis temperature of 550 °C with heating rate of 10 °C/min and pyrolysis time of 15 min LiCoO2 grade is 94.72% with the recovery of 83.75% in this condition. Two stage pyrolysis-enhanced flotation processes can further upgrade the LiCoO2 grade to 98.00%. This research proposes a novel method to improve the flotation efficiency of electrode materials, and the relevant mechanism is explored, which provides an alternative recycling flowchart of spent lithium-ion batteries.