Researchers have developed a new electrolyte that can break apart easily at the end of a battery’s life, which they believe will make recycling electric vehicles (EVs) more efficient.
EV’s are essential for decarbonising the transport sector to reach net zero emissions by 2050. But mountains of lithium-ion EV batteries still end up in landfill as they can be hard to recycle.
The researchers hope their design, a self-assembling electrolyte that serves as the battery’s connecting layer before reverting back to its original molecular form, will help simplify the process.
“Our approach is to start with easily recyclable materials and figure out how to make them battery-compatible. Designing batteries for recyclability from the beginning is a new approach,” says Yukio Cho, the study’s first author from Massachusetts Institute of Technology (MIT) in the US.
“So far in the battery industry, we’ve focused on high-performing materials and designs, and only later tried to figure out how to recycle batteries made with complex structures and hard-to-recycle materials.”
A battery is made up of 3 main parts. There’s the positively charged cathode and the negatively charged anode. The electrolyte transports ions (charged particles) in between the electrodes.
As a lithium-ion battery degrades over time, its highly flammable electrolytes degrade into toxic byproducts. The current battery recycling process involves the use of specialised technologies to safely manage these byproducts, which can be time consuming and expensive.
The researchers decided to create a more sustainable electrolyte to simplify the recycling process.
They used a class of molecules called aramid amphiphiles (AA). These molecules have a similar structure and stability to Kevlar, a strong synthetic fibre used in bullet proof vests. The researchers added polyethylene glycol (PEG) which can help conduct lithium ions and create a stable structure.
“The material is composed of 2 parts,” says Cho.
“The first part is this flexible chain that gives us a nest, or host, for lithium ions to jump around. The second part is this strong organic material component that is used in the Kevlar, which is a bulletproof material. Those make the whole structure stable.”
In water AAs self-assemble into nanoribbons about 5 to 8nm thick.
“Within 5 minutes of being added to water, the solution becomes gel-like, indicating there are so many nanofibers formed in the liquid that they start to entangle each other,” Cho says.
“What’s exciting is we can make this material at scale because of the self-assembly behaviour.”
When the team immersed their battery into organic solvents, the material almost immediately dissolved and separated the battery’s materials, making it easier to recycle. Cho likened the process to when someone submerges cotton candy into water.
“The electrolyte holds the 2 battery electrodes together and provides the lithium-ion pathways,” Cho says.
“So, when you want to recycle the battery, the entire electrolyte layer can fall off naturally and you can recycle the electrodes separately.”
The team tested the strength and toughness of the electrolyte material using a lithium iron phosphate cathode and a lithium titanium oxide anode. They found their design could survive the pressure needed to successfully make and run a battery.
However, due to a phenomenon known as polarisation, the team’s battery had slower lithium ion movements compared to the current standard.
“We don’t want to say we solved all the problems with this material,” Cho says.
“What we’re picturing is using this material as one layer in the battery electrolyte. It doesn’t have to be the entire electrolyte to kick off the recycling process.”
The research team is continuing to experiment with different materials and how they can be implemented into existing battery designs in the hopes of designing a better performing but easy to recycle battery.
“With new battery materials that may come out in 5 or 10 years, it could be easier to integrate this into new designs in the beginning,” says Cho.
He says that recycling lithium batteries like this could also help to avoid the massive lithium price spike that may be expected due to the growing demand for EVs.
“People are starting to realise how important this is,” Cho says.
“If we can start to recycle lithium-ion batteries from battery waste at scale, it’ll have the same effect as opening lithium mines in the US.”
The designs for the battery have been published in Nature Chemistry.