A closed-loop recycling strategy is essential to establish an independent and sustainable battery value chain. Recycling end-of-life lithium-ion battery (LIB) cells is also crucial to prevent these cells from entering landfills, where they could release harmful substances into the environment, such as fluoride (F), nickel (Ni), manganese (Mn), cobalt (Co), and organic substances as the electrolyte and its degradation products. Additionally, understanding the composition of LIB recycling material (known as black mass) is vital, as these contaminants can damage business infrastructure, hinder recycling processes, and pose health risks to employees.
In this study, we present a workflow that begins with the liquid extraction of black mass and includes the quantitative analysis of the extracted electrolyte compounds using liquid chromatography hyphenated to a massspectrometer (LC-MS) and ion chromatography hyphenated to a conductivity detector (IC-CD). We developed a reversed-phase liquid chromatography (RPLC) method to analyze both linear and cyclic carbonates, such as dimethyl carbonate and ethylene carbonate, along with the degradation product ethylene glycol, which forms from ethylene carbonate in the presence of water. For identification and quantification, a scheduled multiple reaction monitoring (sMRM) method was applied using a triple quadrupole mass spectrometer (MS). To quantify fluoride and hexafluorophosphate anions a previously developed method, ion chromatography (IC) coupled with a conductivity detector was applied. These methods enabled us to evaluate three different liquid extraction techniques—Soxhlet extraction, ultrasound-assisted extraction, and shake extraction—using three solvents (water, acetonitrile, and methanol).
Our results indicate that shake extraction with acetonitrile yields reliable quantification of organic carbonates and hexafluorophosphate anions without inducing decomposition. Both water and methanol, however, show decomposition products of cyclic carbonates but enable the extraction of fluoride from black mass, which is almost insoluble in acetonitrile.