Lithium-ion battery production releases PFAS. Because of course it does.
Fourteen straight months of monthly global heat records. By the time you read this it might be fifteen. Scientists predict that temperatures will continue to rise and temperature records will continue to fall given the level of carbon dioxide in the atmosphere. They’ve also been clear that if we’re to avoid the worst effects of climate change we need to dramatically reduce our emissions. This has spurred technological advances in many areas, including electric vehicle (EV) technology.
An EV requires a power source that can store a lot of energy in a small space, deliver it at the rate needed for driving, recharge efficiently, and operate in a wide range of weather conditions. For the last several decades, lithium-ion batteries have come closest to meeting this challenge. Our need for their relatively efficient energy storage and release has led us to largely ignore their risks – aside from the odd exploding smartphone. Until now.
The risks begin where lithium’s journey begins – during extraction. Lithium comes from three main sources: clay, rock, and brine. Mining for lithium brings with it the standard array of environmental issues that attend any mining operation. Both rock and clay are commonly mined using conventional techniques like open-pit and strip mining that have a long history of environmental complications. Extracting lithium from brine avoids some of the pitfalls of lithium mining, but the need for strong acids (like sulfuric acid) to generate pure lithium also results in significant environmental issues.
If that was the grand sum of the risks, though, we wouldn’t be writing this post. Lithium-ion batteries are made using several different materials that optimize its properties – one of the main ones being electrolytes. Battery electrolytes, among their energy-related properties, need to also remain stable over long periods of time and across many cycles of electrochemical and thermal abuse. In standard fluid electrolyte batteries, common materials include lithium hexafluorophosphate and lithium tetrafluoroborate. In more modern lithium-ion batteries, though, these salts have been replaced by novel chemicals from the PFAS family.
Lithium bis(trifluoromethanesulfonyl)imide – LiTFSI for short – is an emerging and unregulated replacement for the traditional lithium salts mentioned above because it improves stability of the battery’s electrolyte[1]. This relatively unknown PFAS compound might have stayed that way but for a recent study that found LiTFSI in the water and soil near factories in Minnesota and Kentucky that produce components that go into EV batteries. While this compound had previously been found in Europe and Asia this was one of the first studies to show that it was present in North American soil and rivers and that it was associated with proximity to EV battery factories. The authors of this study were able to conclude that the PFAS from the 3M plant in Minnesota were being spread by air from smokestack emissions and not solely from emission into water.
This study, however, went farther. The authors investigated the effects of LiTFSI-related PFAS on multiple animal species, finding that it affected their brain function and other markers of wellbeing, consistent with findings in other studies. They also determined that lithium batteries that are disposed in landfills lead to PFAS escaping into the leachate that then gets into surface and groundwater. Recognizing the need to remove these PFAS chemicals from water, the authors also tested standard PFAS removal techniques – ion exchange resins and granular activated carbon. LiTFSI was approximately as difficult to remove from water as PFOA in their tests, and is similarly resistant to destruction by advanced oxidation water cleaning techniques compared to other now-regulated PFAS. The authors also conclude that LiTFSI (and related chemicals) is likely to meet the criteria for classification as “very persistent, very mobile” (vPvM) under the REACH regulation in Europe, as it is similarly persistent and mobile as PFBS – another vPvM PFAS chemical.
Although most of the discussion above is with respect to lithium battery electrolytes, these PFAS can also be used in other parts of the battery. In particular, the different parts of a battery are often bound together by a polymer that satisfies many of the same stability requirements as the electrolyte, making polyvinylidene fluoride (PVDF) a common choice. Some scientists and regulators argue that fluorinated polymers (including PTFE/Teflon) are of low concern while others, including the authors of this study, argue that although the polymers themselves may be relatively inert they can – and in this study, they do – easily release shorter PFAS that are of concern.
New technology brings new risks. The proliferation of lithium-ion batteries in the last decade combined with the projected exponential increase in their use makes clear the importance of proactively assessing their risks. The articles cited above begin that process but in the meantime companies producing these batteries and their materials are buying insurance that may be called on to respond to future claims of bodily injury and property damage.
[1] LiTFSI is actually one of several of a family of bis-perfluoroalkyl sulfonimides that are used in lithium batteries. LiTFSI is the 1-carbon chain version while chains up to at least 4 carbons in length are used in lithium batteries, similar to how PFAS chains of differing lengths are used in other applications.