Effects of pyrolysis and incineration on the chemical composition of Li-ion batteries and analysis of the by-products.

Licentiate thesis, 2019

In the present work, the effects of pyrolysis and incineration on the composition of Li-ion battery cell materials and their dependence on treatment time and temperature were investigated. Waste from Li-ion batteries was treated at 400˚, 500˚, 600˚, and 700˚C for 30, 60, and 90 minutes. Thermodynamic calculations for the carbothermic reduction of the active materials LiCoO2, LiMn2O4, and LiNiO2 by graphite and the gas products were performed, and the results compared with the experimental data obtained by processing the pure oxides. This allowed for a very exact investigation of the behaviour of the oxides and has brought novel knowledge to the processing of Li-ion batteries. Moreover, to determine the behaviour of the real waste, NMC cathode material recovered from spent Li-ion batteries was studied. The results indicate that the organic compounds and the graphite are oxidized, by oxygen from the active material during the pyrolysis, and during incineration by the oxygen in the air present in the system, forming an atmosphere rich in CO(g) and CO2(g). Removal of the organic components increases the purity of the metal-bearing material. During the pyrolysis, reactions with C and CO(g) led to a reduction of metal oxides, with Co, CoO, Ni, NiO, Mn, Mn3O4, Li2O, and Li2CO3 as the main products. The reduction reactions transformed the metal compounds in the untreated LiB black mass into chemical forms that were more soluble. It was concluded that pyrolysis can be used as an effective tool for pre-treatment of battery waste in order to increase the efficiency of leaching in a hydrometallurgical processing of the black mass. During incineration, it was observed that the organic material was removed more efficiently than in pyrolysis and the lithium metal oxides were subjected to both carbothermic reduction and oxidation. During heat treatment, organic by-products were formed by the decomposition of the polypropylene separator and the PVDF binder. The organic residue contained both non-polar and polar compounds. One of the most important outputs of the current work is the observation of the fluorine behaviour during the thermal treatment, and detection of its presence in the oil product. It was shown that the decomposition of the PVDF facilitates the separation of the active material from the metallic layers of the electrodes by means of a mechanical treatment. An almost complete recovery of the black mass from the foils was achieved following the thermal treatment.  The results obtained can help to optimize the parameters in the industrial process that is already used for Li-ion battery recycling, since this research provides novel information about the effects of the thermal treatment and defines the most favourable conditions for the processing. The results could contribute to an increased recycling rate, especially if this process is followed by a hydrometallurgical treatment. Such optimization will decrease the energy demand and increase the metal recovery rate and the utilization of the by-products.