Complex gas formation during combined mechanical and thermal treatments of spent lithium-ion-battery cells.

Spent lithium-ion batteries (LIB) contain volatile and reactive chemicals possibly generating toxic and/or flammable gases during the related recycling. In this study, two types of spent LIB cells were subjected to combined mechanical and thermal treatments at the constant temperatures of 20 °C, 120 °C, 200 °C, and 400 °C under a nitrogen atmosphere. A total of 46 gaseous species, including electrolyte components, oxygenated hydrocarbons, hydrocarbons, and others, were qualitatively and quantitatively analyzed by mass spectrometry. At higher process temperatures, the concentration or volume of the formed gases increased accordingly. Additionally, at and below 120 °C, the formed gaseous species slightly differed depending on the cell type, whereas they were analogous at 400 °C. The formation of different gas species involved the activity of electrolyte volatilization, electrolyte degradation/decomposition, and pyrolysis of the organic separator and binder, followed by complex radical reactions among the species formed by the physicochemical reactions. Possible strategies to mitigate the risks that may arise associated with the gas formation during recycling are presented.

Experimental and Numerical Investigation of Flow Field and Soot Particle Size Distribution of Methane-Containing Gas Mixtures in a Swirling Burner.

The formation of soot in a swirling flow is investigated experimentally and numerically in the context of biogas combustion using a CO2-diluted methane/oxygen flame. Visualization of the swirling flow field and characterization of the burner geometry is obtained through PIV measurements. The soot particle size distributions under different fuel concentrations and swirling conditions are measured, revealing an overall reduction of soot concentration and smaller particle sizes with increasing swirling intensities and leaner flames. An axisymmetric two-dimensional CFD model, including a detailed combustion reaction mechanism and soot formation submodel, was implemented using a commercial computational fluid dynamics (CFD) code (Ansys Fluent). The results are compared with the experiments, with similar trends observed for the soot size distribution under fuel-lean conditions. However, the model is not accurate enough to capture soot formation in fuel-rich combustion cases. In general, soot particle sizes from the model are much smaller than those observed in the experiments, with possible reasons being the inappropriate modeling in Fluent of governing mechanisms for soot agglomeration, growth, and oxidation for CH4-CO2 mixtures.