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.
Doctoral thesis, 2020
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.
Keywords: Lithium-ion batteries
Chalmers, Chemistry and Chemical Engineering, Energy and Material, Nuclear Chemistry
The increasing use of LiBs is causing a simultaneous rapid growth in demand for the metals necessary for their production. Many of these materials are concentrated in the two electrodes that compose the LiB cells: an anode (negative pole), generally composed of a copper (Cu) layer covered by graphite, and a cathode (positive pole), generally composed of an aluminum (Al) layer coated with an active material. The active material can contain cobalt (Co), nickel (Ni), manganese (Mn), and lithium (Li). Due to the critical reserves of Co, and the instability in supply and price of Li, it is important to develop efficient and cost-effective recycling methods for LiB materials. Furthermore, the lifetime of the LiBs used in electric vehicles is around 10 years. This means that the quick growth in electric vehicle demand will soon cause a gathering up of the spent LiBs. A system for collecting spent LiBs and effective processes for recycling the used materials in them is needed to ensure the raw material supply for the production of new LiBs.
Many industrial recycling processes use hydrometallurgical methods to recover valuable metals in spent batteries. Current trends and development show that a thermal pre-treatment might be a solution for further improving the hydrometallurgical recycling route. The thermal treatment can be performed in presence of oxygen (incineration) or absence of oxygen (pyrolysis) and is used as an effective tool for battery discharging and decompose the organic component of the LiBs. This decomposition can form gas and organic residue that can be toxic and can reduce the efficiency of the process and/or be corrosive, damaging the equipment used. Furthermore, the thermal treatment can also trigger the reduction reaction of the Co, Ni, and Mn to lower oxidation and/or more soluble states, simplifying the hydrometallurgical methods.
This work aimed to study the effects of the thermal pre-treatments on the composition of the battery cell materials, as a function of treatment time and temperature, and to analyze the by-products generated during these treatments.
Areas of Advance
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4867
Chalmers University of Technology