Overview
- Date:Starts 9 May 2025, 10:00Ends 9 May 2025, 13:00
- Location:KA, Kemivägen 4, Chalmers, Gothenburg
- Opponent:Prof. Dr. Gisele Azimi, University of Toronto, Canada
- ThesisRead thesis (Opens in new tab)
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.
