Challenges in extracting and characterizing electrolytes from automotive lithium-ion cells.

Background: The demand for lithium-ion cells in the automotive industry is rapidly growing due to the increasing electrification of the transportation sector. The electrolyte composition plays a critical role in determining the lifetime and performance of these large-format cells. Additionally, advancements in this field are leading to frequent changes in both electrode materials and electrolyte formulations. As a result, new analytical approaches are required to enable comprehensive characterization of the relevant components of the electrolytes used in lithium-ion cells.

Results: In this research a novel electrolyte extraction method is presented, enabling the quantitative electrolyte analysis in large format cylindrical lithium-ion cells under inert conditions. A liquid-liquid extraction of the cell materials is performed in a newly developed extraction chamber, in which the electrodes are rewound to ensure an efficient extraction. The design of the chamber allows the extraction of volatile and nonvolatile electrolyte components. The cells were filled with various electrolytes and analyzed using high-performance liquid chromatography and ion chromatography coupled with electrospray ionization mass spectrometry. Using the developed method, up to 83% of the conductive salt and up to 89% of the solvents can be recovered. The first application of this method involved analyzing a cylindrical lithium-ion cell after formation.

Significance: This method provides a crucial tool for mapping electrolyte compounds formed during degradation due to cycling or thermal aging. This analytical approach will offer valuable insights, contributing to a deeper understanding of lithium-ion cell systems and could enhance battery life and performance in the future.