Towards Electrolyte free Li-ion Battery Waste - Utilizing supercritical CO2 extraction and thermal treatment for electrolyte recycling
Doctoral thesis, 2025
A significant challenge in the current recycling of batteries is the effective removal of electrolyte from e.g. Li-ion battery waste. Li-ion battery waste containing residual electrolyte is classified as hazardous waste, posing a financial burden for the recycling industry.
The aim of this work was to investigate potential options and finally suggest a favourable method to recover the electrolyte from spent Li-ion battery waste. The thesis is divided into three parts. In the first part, two promising approaches for the electrolyte separation from spent Li-ion battery pouch cells were investigated: low temperature thermal treatment and supercritical CO2 extraction. The results showed that low temperature thermal treatment at 130°C under N2 atmosphere is suitable for the separation of the electrolyte solvents dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate. However, lithium hexafluorophosphate decomposed while releasing toxic gases hydrogen fluoride and phosphorous oxyfluoride. Using supercritical CO2 extraction, the non-polar electrolyte solvents dimethyl carbonate and ethyl methyl carbonate were successfully extracted at 80 bar and 29°C, whereas the polar electrolyte solvent ethylene carbonate was only extracted in trace amounts. Analysis of the exhaust gas emissions and elemental analysis of the extract indicated that lithium hexafluorophosphate did not decompose during the process.
In the second part of the thesis, the solubility of ethylene carbonate in supercritical CO2 was studied. The solubility of ethylene carbonate increased with increasing pressure from 80 bar to 140 bar at 40°C from 0.24 to 8.35 g/kg CO2. In the third part, the previously obtained solubility results were applied to extract the remaining electrolyte in the LiB black mass. The volatile electrolyte components dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate were successfully extracted with an extraction yield exceeding 99% using 100 bar and 40°C. Raising the pressure to 140 bar led to high extraction yields of biphenyl, ethyl carbonate, and propylene carbonate with 98%, 95%, and 98%, respectively. The extraction curves of ethylene carbonate, propylene carbonate, and biphenyl indicate that the non-polar solvents dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate behaved as an entrainer for their extraction at 100 bar. An entrainer effect at 140 bar was not observed. The extraction rates of biphenyl, ethylene carbonate, and propylene carbonate at 140 bar and 40°C were determined to be 0.18 mg/g CO2, 1.9 mg/g CO2 and, 0.4 mg/g CO2, respectively. The extraction of lithium hexafluorophosphate remained below 5%. The results showcase the potential to utilize scCO2 extraction to separate the electrolyte from Li-ion battery waste.
The aim of this work was to investigate potential options and finally suggest a favourable method to recover the electrolyte from spent Li-ion battery waste. The thesis is divided into three parts. In the first part, two promising approaches for the electrolyte separation from spent Li-ion battery pouch cells were investigated: low temperature thermal treatment and supercritical CO2 extraction. The results showed that low temperature thermal treatment at 130°C under N2 atmosphere is suitable for the separation of the electrolyte solvents dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate. However, lithium hexafluorophosphate decomposed while releasing toxic gases hydrogen fluoride and phosphorous oxyfluoride. Using supercritical CO2 extraction, the non-polar electrolyte solvents dimethyl carbonate and ethyl methyl carbonate were successfully extracted at 80 bar and 29°C, whereas the polar electrolyte solvent ethylene carbonate was only extracted in trace amounts. Analysis of the exhaust gas emissions and elemental analysis of the extract indicated that lithium hexafluorophosphate did not decompose during the process.
In the second part of the thesis, the solubility of ethylene carbonate in supercritical CO2 was studied. The solubility of ethylene carbonate increased with increasing pressure from 80 bar to 140 bar at 40°C from 0.24 to 8.35 g/kg CO2. In the third part, the previously obtained solubility results were applied to extract the remaining electrolyte in the LiB black mass. The volatile electrolyte components dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate were successfully extracted with an extraction yield exceeding 99% using 100 bar and 40°C. Raising the pressure to 140 bar led to high extraction yields of biphenyl, ethyl carbonate, and propylene carbonate with 98%, 95%, and 98%, respectively. The extraction curves of ethylene carbonate, propylene carbonate, and biphenyl indicate that the non-polar solvents dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate behaved as an entrainer for their extraction at 100 bar. An entrainer effect at 140 bar was not observed. The extraction rates of biphenyl, ethylene carbonate, and propylene carbonate at 140 bar and 40°C were determined to be 0.18 mg/g CO2, 1.9 mg/g CO2 and, 0.4 mg/g CO2, respectively. The extraction of lithium hexafluorophosphate remained below 5%. The results showcase the potential to utilize scCO2 extraction to separate the electrolyte from Li-ion battery waste.
Electrolyte
Supercritical CO2 extraction
Li-ion battery
Recycling
thermal treatment
KA, Kemivägen 4, Chalmers, Gothenburg
Opponent: Prof. Dr. Gisele Azimi, University of Toronto, Canada
Author
Nils Zachmann
Nuclear Chemistry and Industrial Materials Recycling
Zachmann, N; Ebin, B; Supercritical CO2 extraction behavior of electrolyte solvents from Li-ion battery black mass
The growing demand for electric vehicles, renewable energy storage systems, and portable consumer electronics significantly increased the production of Li-ion batteries worldwide in recent years. However, the lifespan of Li-ion batteries is finite, and waste management has created a pressing environmental challenge. As Li-ion batteries contain hazardous substances their improper disposal can lead to long-lasting environmental damage and health risks. A major contributor to these risks is the electrolyte, which plays a crucial role in the battery’s performance. The electrolyte is typically made from organic solvents mixed with lithium salt. Many of the solvents are volatile, flammable, and toxic. Without a controlled and save recovery process of these solvents, the risks of fire, explosion, and release of hazardous gases to the environment increase significantly. Thus, the development of specialized recycling strategies is crucial to mitigate these dangers, protecting both workers and the surrounding environment.
Even though significant advances have been made to recycle the valuable critical raw materials such as lithium, cobalt, and nickel effectively from Li-ion battery waste, the recycling of the electrolyte remains a major challenge. In this work, two potential options for recovery of the electrolyte from Li-ion battery waste; low temperature thermal treatment and supercritical carbon dioxide extraction, were investigated. The results obtained in this research show that both methods enable the recovery of the electrolyte under process relevant conditions. However, supercritical carbon dioxide extraction is superior towards low temperature thermal treatment as it prevents the release of toxic gases evolved due to the decomposition of the li-salt at elevated temperatures. This work is a step forward into a safer battery recycling process.
Even though significant advances have been made to recycle the valuable critical raw materials such as lithium, cobalt, and nickel effectively from Li-ion battery waste, the recycling of the electrolyte remains a major challenge. In this work, two potential options for recovery of the electrolyte from Li-ion battery waste; low temperature thermal treatment and supercritical carbon dioxide extraction, were investigated. The results obtained in this research show that both methods enable the recovery of the electrolyte under process relevant conditions. However, supercritical carbon dioxide extraction is superior towards low temperature thermal treatment as it prevents the release of toxic gases evolved due to the decomposition of the li-salt at elevated temperatures. This work is a step forward into a safer battery recycling process.
Driving Forces
Sustainable development
Subject Categories (SSIF 2025)
Separation Processes
Infrastructure
Chalmers Infrastructure for Mass spectrometry
Chalmers Materials Analysis Laboratory
ISBN
978-91-8103-205-5
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5663
Publisher
Chalmers
KA, Kemivägen 4, Chalmers, Gothenburg
Opponent: Prof. Dr. Gisele Azimi, University of Toronto, Canada