Comparison of incineration and pyrolysis of NMC-lithium-ion batteries – determination of the effects on the chemical composition, and potential formation of hazardous by-products

Abstract: Several industrial lithium battery recycling processes use thermal pre-treatment in an oxidative or inert atmosphere, or in a vacuum, to separate the battery components and remove organic material. However, a comparison of these pre-treatments on the microstructure and composition of waste material and production scrap LiBs has not been explored as well as there is a scarcity of information about the character of by-products generated during the processing. In this work the effects of incineration and dynamic pyrolysis on the composition of spent Li-ion batteries (LiBs) and the effects of incineration, dynamic pyrolysis, and pyrolysis under vacuum on the composition of production scrap Li-ion batteries (LiBs) were investigated. LiBs with cathode active material based on Li(NixMnyCoz)Oj, i.e. NMC-LiBs, were treated from 15 to 180 minutes at a temperature between 400-700°C. 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. During the incineration, the organic material was removed more efficiently than in pyrolysis and the lithium metal oxides were subjected to both carbothermic reduction and oxidation. During pyrolysis at 700°C for 180 minutes, the carbon content decreased to 15w%, in comparison to the initial 41w%. The incineration performed under the same conditions resulted in almost complete removal of the graphite and organic species, ~0.6w%. Gas and organic oil by-products from the decomposition of the organic components were characterized. The presence of HF was detected and fluorine was identified also in the oil by-products. The decomposition of the binder facilitated the separation by mechanical treatment of the active material from the current collector. The best method to recover cathode material was shown to be incineration at a temperature range between 550˚ and 650˚ C for at least 90 minutes, followed by ball milling. The recovered fraction of active material was >95%. The formation of HF in the case of high temperature accident involving NMC-LiB was also determined. Four commercial refrigeration liquids containing halogens were investigated. The presence of these refrigeration liquids leads to an increase of the quantity of HF released during a simulated fire.