Circular Economy Recycling of fluorine for lithium-ion batteries
Lithium-ion batteries contain fluorine-rich salts that decompose in humid air to toxic, highly corrosive hydrogen fluoride. The hazardous nature of this substance makes recycling more difficult and more expensive. To solve this problem, a new research project entitled "Fluoribat" is being initiated.
Batteries are ubiquitous. The Global Battery Alliance of the World Economic Forum WEF expects the number of batteries for electric mobility and stationary storage applications to increase tenfold within the next ten years. Lithium-ion batteries will account for the largest share of this growth.
The aim of the new research project of the Swiss Empa is to make the life cycle of a rechargeable battery both cheaper and safer.
A blessing and a curse
Given the large number of batteries that will have to be produced and recycled in the coming years, a chemical element is coming into focus that has hardly received any discussion so far: fluorine. Fluorine in small quantities is included in all lithium-ion batteries. The electrolyte liquid of such a battery contains hexafluorophosphate anions PF6- a fluorine compound that ensures the long-term stability of the battery and enables high cell voltages. The disadvantage: PF6- decomposes in contact with water or in humid air to form toxic, highly corrosive hydrogen fluoride HF. This means that the battery must be packed in an airtight envelope during operation. Otherwise, it will release toxic fluorine compounds. At the latest during recycling, the airtight container is slit open. The resulting hydrogen fluoride makes the recycling process complicated and expensive.
Striving for watertight fluorine salts
In the summer of 2020, Empa launched a research project called "Fluoribate", which deals with this topic. The research team led by Corsin Battaglia, head of the "Materials for Energy Conversion" laboratory, has developed a new, non-flammable water-based electrolyte for lithium-ion batteries which is compatible with the electrode materials already used in these batteries. "Our cells still show more than 80% of their initial capacity even after 200 charging and discharging cycles," says Maximilian Becker, battery researcher in the laboratory of Corsin Battaglia. The water-stable lithium salt used in Empa's experimental battery cells can be produced on a large scale at competitive prices.
For successful commercialization, the long-term stability of the battery must be further improved. However, suppose this hurdle can be overcome. In that case, such a battery could be produced and recycled much more cost-effectively - an absolutely dry environment is then no longer necessary for both steps.
Integration in recycling management
At the same time, the water-based recycling of spent lithium-ion batteries opens up new possibilities for a closed-loop economy. If the electrolyte salts can be quickly recovered from batteries, the fluorine they contain can be used for new batteries. This aspect is becoming increasingly important because of the expected volume of batteries. The Empa "Technology and Society" department headed by Patrick Wäger specializes in the recycling of batteries and the calculation of the environmental impact of new technologies along their life cycle. The analysis is designed to evaluate the benefits of batteries based on water-resistant fluorine salts. The study will compare this new generation of batteries with current-generation batteries in terms of safety and environmental impact.
Battery research in a European context
Empa is a partner in the European project Battery2030+, which will coordinate battery research at the European level. An essential goal of these activities is to improve the sustainability of batteries. To achieve this, it is crucial not only to recycle metals such as cobalt, nickel, copper, aluminium and lithium as far as possible. Potentially toxic elements such as fluorine must also be part of the sustainability considerations: they must be kept in safe, controlled ways.