A significant stride toward sustainable technology has emerged with the development of a process to recycle electrolytes from spent lithium-ion batteries using sub- and supercritical carbon dioxide. This innovative method leverages the unique properties of carbon dioxide in its supercritical state—a phase where it exhibits characteristics of both a liquid and a gas—to efficiently extract these components without generating hazardous byproducts. This breakthrough could lead to safer, more efficient recycling processes that help preserve our planet while recovering essential materials for future use.
Nils Zachmann supervised by Dr. Burçak Ebin and Dr. Martina Petranikova from Chalmers University of Technology, along with Dr. Robert Fox from Idaho National Laboratory, conducted this groundbreaking study. The work, published in the Journal of CO2 Utilization, explores the efficiency and safety of extracting electrolytes using carbon dioxide under varying pressure and temperature conditions.
The electrolyte in lithium-ion batteries, essential for cell performance, often contains flammable and hazardous components such as dimethyl carbonate, ethyl methyl carbonate and lithium hexafluorophosphate (LiPF6). Conventional recycling methods involve high-temperature treatments that destroy the electrolyte and release toxic gases like hydrogen fluoride (HF). Dr. Ebin and Zachmann aimed to address these issues by selectively extracting valuable electrolyte components without generating harmful emissions.
The study revealed that the density of carbon dioxide, influenced by pressure and temperature, is crucial for the efficient recovery of non-polar electrolyte solvents such as dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). Remarkably, these solvents could be fully extracted, while the polar component, ethylene carbonate (EC), was only minimally extracted. This selectivity reduces the complexity and potential hazards associated with the recycling process.
Zachmann explained the significance of their findings: “The most important outcome is that dimethyl carbonate and ethyl methyl carbonate were fully selectively extracted at the studied conditions, whereas the polar ethylene carbonate was extracted only in trace amounts.” This indicates a significant advancement in the recycling process, ensuring that valuable materials are recovered efficiently and safely.
The process was tested under various conditions, with a range of pressures and temperatures. The optimal extraction occurred at a moderately high pressure and a cool temperature, achieving a substantial electrolyte extraction yield. Notably, the study confirmed that the process did not lead to the decomposition of LiPF6, thus preventing the release of toxic gases.
Furthermore, the research team employed advanced analytical techniques such as gas chromatography-mass spectrometry (GC-MS) and Fourier-transform infrared spectroscopy (FTIR) to verify the composition of the extracted electrolytes and exhaust gases. These analyses confirmed the absence of harmful emissions, underscoring the environmental benefits of this method.
Dr. Ebin emphasized the environmental and economic implications: “The safe removal of the electrolyte is essential from an environmental point of view since it reduces the greenhouse gas emissions generated by the incineration of the electrolyte as well as the threats associated with the LiB waste, while increasing the safety of the overall recycling process.”
The study also highlighted the potential for integrating this process with existing hydrometallurgical techniques for recovering valuable metals from lithium-ion batteries. By removing the organic components first, the researchers suggest that subsequent metal recovery processes could be more efficient and environmentally friendly.
In conclusion, Nils Zachmann and his colleagues’ implementation of sub- and supercritical carbon dioxide for recycling electrolytes from spent lithium-ion batteries represents a promising advance in sustainable technology. This method not only enhances the recovery of valuable materials but also significantly reduces the possible environmental hazards associated with traditional recycling processes. As the demand for lithium-ion batteries continues to grow, such innovative approaches will be crucial in managing the lifecycle of these essential energy storage devices.
Author’s note: This work was financially supported by the Swedish Energy Agency Battery Fund Program (Project No: P2019-90078), FORMAS – Swedish Research Council for Sustainable Development (Project No: 2021-01699), and Horizon Europe (Project 101069685 — RHINOCEROS). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Climate, Infrastructure and Environment Executive Agency (CINEA). Neither the European Union nor the granting authority can be held responsible for them.
Journal Reference
Nils Zachmann, Robert V. Fox, Martina Petranikova, and Burçak Ebin. “Implementation of a sub-and supercritical carbon dioxide process for the selective recycling of the electrolyte from spent Li-ion battery.” Journal of CO2 Utilization 81 (2024): 102703. DOI: https://doi.org/10.1016/j.jcou.2024.102703
