Quantitative Electrolyte Analysis from Large Format Cylindrical Lithium-Ion Cells after Electrolyte Extraction
Authors: Schoenemeier Sabrina , Peters Verena , Horsthemke Fabian , Seo Heewoo , Matysik Frank-Michael 
Published: December 2024

In 2022, Europe’s carbon dioxide (CO2) emissions made up 11% of the worldwide output and a quarter of it was produced by the transportation sector.[1] To reduce these CO2 emissions the sector is shifting to electric vehicles with lithium-ion cells as energy storage. As lithium-ion cells gain popularity, topics such as cell lifetime and fast charging ability increase significantly. Both are closely linked to electrolyte degradation reactions and can be investigated by analyzing the electrolyte and its decomposition. In industrially produced large format cylindrical lithium-ion cells (46950) the electrolyte amount added to the cell is monitored carefully by the cell manufacturer. Almost no excess electrolyte can be found in commercially produced 46950 cells after the formation process. Few methods are described in literature to extract the electrolyte from the cell materials if no excess electrolyte is present. Thompson et al. outlined a centrifugation method of the cell materials to separate electrolyte from the cell materials.[2]
Stockhausen et.al. presented a liquid-liquid extraction for pouch cells by adding solvent to the cell.[3]
Grützke et al. performed a supercritical CO2 extraction on cylindrical 18650 cells.[4] Drawbacks to the methods known in literature are that these are either not transferable to a large format cylindrical lithium-ion cell or do not enable a representative recovery of all electrolyte components, such as lithium salts, carbonates and additives.

In this research we present a liquid-liquid electrolyte extraction method to achieve representative electrolyte extraction in large format cylindrical lithium-ion cells (46950). The electrolyte extraction was performed in a prototype electrolyte extraction chamber designed at BMW Group.

The cells are based on an NMC811/Si-graphite material and produced at the prototype plant at BMW Group in Munich, Germany. In comparison to commercially available lithium-ion cells the composition of all components, such as electrode and electrolyte materials are known. A variation of electrolytes is investigated with conductive salt concentrations of 1-1.5M LiPF6 and solvent mixtures of different carbonates to ensure a variety of applications. Quantitative analysis of the conductive salt is performed with ion chromatography–mass spectrometry (IC-MS). The electrolyte solvents are quantified with a high performance liquid chromatography-Orbitrap-mass spectrometry (HPLC-Orbitrap-MS). These extensive analysis will enable a better understanding of the function, changes and importance of the electrolyte in lithium-ion cells.

References:

[1] Statistical Review of World Energy, 2023, 72nd edition,Energy Institute London.

[2] Thompson, L. M.; Stone, W.; Eldesoky, A.; Smith, N. K.; McFarlane, C. R. M.; Kim, J. S.; Johnson, M. B.; Petibon, R.; Dahn, J. R, J. Electrochem.
Soc.
2018,
165 (11), A2732-A2740

[3] Stockhausen, R.; Hofmann, A.; Gehrlein, L.; Bergfeldt, T.; Müller, M.; Ehrenberg, H.; Smith, A., J. Electrochem. Soc.
2021,
168 (8), 80504.

[4] Grützke, M.; Mönnighoff, X.; Horsthemke, F.; Kraft, V.; Winter, M.; Nowak, S. RSC Adv.
2015,
5 (54), 43209–43217.