The development of highly efficient recycling processes for lithium-ion batteries (LIBs) is crucial for future sustainability of this technology, as state-of-the-art LIBs rely on critical raw materials such as graphite, lithium, nickel, and cobalt. Instrumental analytical techniques are valuable tools to elucidate chemical processes during recycling to improve the process. In contrast to conventional recycling methods, water-assisted recycling processes – such as wet crushing and electrohydraulic fragmentation – offer the possibility to eliminate elaborate pretreatment steps like electrical discharging. These techniques, however, generate large amounts of contaminated process water, resulting in increased costs for the disposal of hazardous waste. Conversely, process water represents a source of valuable raw materials that would be lost with disposal. Efficient extraction techniques can therefore increase the overall recycling efficiency of LIBs. To improve wastewater management, safety, and sustainability of water-assisted recycling processes, comprehensive knowledge of the battery components in the water are required. [1-3]
This study presents a comprehensive characterization of process water from a wet-shredding process of LIBs using suitable instrumental analytical techniques for the identification and quantification of characteristic battery contaminations. Total elemental concentrations in the water and solid black mass sediment were quantitatively analyzed using inductively coupled plasma-optical emission spectroscopy (ICP OES). Lithium hexafluorophosphate (LiPF6) was identified as the conductive salt used in the shredded batteries. PF6 undergoes hydrolysis decomposition reactions with water forming various potentially toxic organofluorophosphates (OFPs) that are of great concern for occupational and environmental safety.[4] Several of these OFPs were identified using ion chromatography-high resolution mass spectrometry (IC-HRMS). Furthermore, PF6 and its hydrolysis products were quantitatively investigated using IC with conductivity detector (IC-CD). Hydrofluoric acid, formed as a by-product of the PF6 degradation, is highly corrosive to metallic parts in the recycling plant and poses an environmental and safety risk. Therefore, the quantification of fluoride in process water was demonstrated using ion exclusion chromatography conductivity detection (IEC-CD). Carbonate based organic electrolyte solvents and common degradation products were identified by liquid liquid extraction and subsequent gas chromatography-mass spectrometry (GC MS). Additionally, a novel method using solid-phase extraction-gas chromatography-flame ionization detection (SPE-GC-FID) was developed for the quantitative extraction and analysis of electrolyte solvents. Multiple solid phase materials were compared and recovery rates were determined. Based on these results, the electrolyte solvents and decomposition products were quantified in the water sample.
Based on the presented results, this study proposes appropriate analytical techniques for the testing of process water from LIB recycling processes to enable risk assessment and improve recycling efficiency and sustainability.

[1] J. Neumann, M. Petranikova, M. Meeus, J. D. Gamarra, R. Younesi, M. Winter, S. Nowak, Adv. Energy Mater. 2022, 12, 2102917.
[2] J. Diekmann, S. Sander, G. Sellin, M. Petermann, A. Kwade, in Recycling of Lithium-Ion Batteries (Eds.:A. Kwade, J. Diekmann), Springer International Publishing. Cham 2018, p. 127
[3] D. Horn, J. Zimmermann, R. Stauber, O. Gutfleisch, New efficient recycling process for Li-ion batteries (2017).https://mediatum.ub.tum.de/doc/1462984/1462984.pdf., accessed 21.04.2023
[4] Y. Stenzel, F. Horsthemke, M. Winter, S. Nowak, Separations 2019, 6, 26.