Taking the ‘forever’ out of ‘forever chemicals’: we worked out how to destroy the PFAS in batteries
- Written by The Conversation
Lithium-ion batteries are part of everyday life. They power small rechargeable devices such as mobile phones and laptops. They enable electric vehicles. And larger versions store excess renewable energy for later use, supporting the clean energy transition.
Australia produces more than 3,000 tonnes of lithium-ion battery waste a year. Managing this waste is a technical, economic and social challenge. Opportunities exist for recycling and creating a circular economy for batteries. But they come with risk.
That’s because lithium-ion batteries contain manufactured chemicals such as PFAS, or per- and polyfluoroalkyl substances. The chemicals carry the lithium – along with electricity – through the battery. If released into the environment, they can linger for decades and likely longer. This is why they’ve been dubbed “forever chemicals”.
Recently, scientists identified a new type of PFAS known as bis-FASIs (short for bis-perfluoroalkyl sulfonimides) in lithium-ion batteries and in the environment. Bis-FASIs have since been detected in soils and waters worldwide. They are toxic – just one drop in an Olympic-size swimming pool can harm the nervous system of animals. Scientists don’t know much about possible effects on humans yet.
Bis-FASIs in lithium-ion batteries present a major obstacle to recycling or disposing of batteries safely. Fortunately, we may have come up with a way to fix this.
There’s value in our battery wastes
Currently, Australia only recycles about 10% of its battery waste. The rest is sent to landfill.
But landfill sites could leak eventually. That means disposal of battery waste in landfill may lead to soil and groundwater contamination.
We can’t throw away lithium-ion batteries in household rubbish because they can catch fire.
So once batteries reach the end of useful life, we must handle them in a way that protects the environment and human health.
What’s more, there’s real value in battery waste. Lithium-ion batteries contain lots of valuable metals that are worth recycling. Lithium, cobalt, copper and nickel are critical and finite metal resources that are in high demand. The recoverable metal value from one tonne of lithium-ion battery waste is between A$3,000 and $14,000.
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Battery recycling in Australia begins with collection, sorting, discharging and dismantling, before the metal is recovered.
Metal recovery can be done via mechanical, high-temperature, chemical or biological methods. But this may inadvertently release bis-FASI, threatening recycling workers and the environment.
Pyrometallurgy is the most common technique for recycling lithium-ion batteries. This involves incinerating the batteries to recover the metals. Bis-FASIs are incinerated at the same time.
Yet PFAS chemicals are stable and can withstand high temperatures. The exact temperature needed to destroy PFAS is the biggest unknown in lithium-ion battery recycling.
Determining this temperature was the focus of our research.
The solution is hot – very hot!
We teamed up with chemistry professor Anthony Rappé at Colorado State University in the United States. We wanted to work out the temperature at which bis-FASIs can be effectively incinerated.
But figuring this out is tricky, not only because of the danger of working with high temperatures.
The inside of incinerators is a hot mess. Molecules get torn apart. Some recombine to form larger molecules, and others interact with ashes produced during the burning process. This could produce toxic new substances, which then exit through a smokestack into the air outside.
To make matters worse, it’s not possible to measure all the substances that bis-FASIs break down into, because many of them are unknown.
To help, we applied the science of quantum mechanics and solved the problem on a computer without ever going into the lab. The computer can accurately simulate the behaviour of any molecules, including bis-FASIs.
We found that at 600°C, bis-FASI molecules start to separate into smaller fragments. But these fragments are still PFAS chemicals and could be more harmful than their parent chemicals.
As a consequence, the absence of bis-FASIs in stack exhaust is not enough to deem the process safe. Much higher temperatures of 1,000°C and above are needed to break down bis-FASIs completely into harmless products. This is likely to be much higher than temperatures currently used, although that varies between facilities.
Based on these findings, we built an innovative model that guides recyclers on how to destroy bis-FASIs during metal recovery by using sufficiently high temperatures.
How do we avoid future risks?
We are now collaborating with operators of high-temperature metal recovery and incineration plants to use our model to destroy PFAS in batteries.
Recycling plants will have to use much higher temperatures to avoid problematic fumes and this will require more energy and financial investment.
After our new guidance is implemented, we will test the recovered metals, solid residues, and exhausts to ensure they are free from PFAS.
While we can tackle the PFAS problem now, it remains an expensive undertaking. Metal recovery processes must be upgraded to safely destroy bis-FASIs. Ultimately, consumers are likely to foot the bill.
However, sending lithium-ion battery waste to landfill will damage the environment and be more expensive in the long run. Landfilling of bis-FASI-containing waste should therefore be avoided.
Clearly, the battery recycling rate must improve. This is where everyday people can help. In the future, manufacturers should avoid using forever chemicals in batteries altogether. Development of safer alternatives is a key focus of ongoing research into sustainable battery design.
