Self-Assembling Material Could Lead to Recyclable EV Batteries
A new electrolyte can break apart at the end of a battery’s life, allowing for easier recycling of components. Illustration courtesy Massachusetts Institute of Technology
CAMBRIDGE, MA—Engineers at the Massachusetts Institute of Technology (MIT) have developed an electrolyte that can break apart at the end of a battery’s life, allowing for easier recycling of components. It can work as the electrolyte in a functioning, solid-state battery cell and then revert back to its original molecular components in minutes.
The approach offers an alternative to shredding the battery into a mixed, hard-to-recycle mass. Instead, because the electrolyte serves as the battery’s connecting layer, when the new material returns to its original molecular form, the entire battery disassembles to accelerate the recycling process.
“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,” says Yukio Cho, Ph.D., a MIT engineer working on the project. “Our approach is to start with easily recyclable materials and figure out how to make them [work]. Designing batteries for recyclability from the beginning is a new approach.
“People are starting to realize how important this is,” Cho points out. “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 U.S. Also, each battery requires a certain amount of lithium, so extrapolating out the growth of electric vehicles, we need to reuse this material to avoid massive lithium price spikes.”
To simplify the recycling process, Cho and his colleagues decided to make a more sustainable electrolyte. For that, they turned to a class of molecules that self-assemble in water, named aramid amphiphiles (AAs), whose chemical structures and stability mimic that of Kevlar. They also designed the AAs to contain polyethylene glycol (PEG), which can conduct lithium ions, on one end of each molecule.
When the molecules are exposed to water, they spontaneously form nanoribbons with ion-conducting PEG surfaces and bases that imitate the robustness of Kevlar through tight hydrogen bonding. The result is a mechanically stable nanoribbon structure that conducts ions across its surface.
“The material is composed of two parts,” explains Yet-Ming Chiang, Ph.D., a professor of material science and engineering at MIT. “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.”
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When added to water, the nanoribbons self-assemble to form millions of nanoribbons that can be hot-pressed into a solid-state material.
“Within five 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,” says Cho. “What’s exciting is we can make this material at scale because of the self-assembly behavior.”
The engineers tested the material’s strength and toughness, finding it could endure the stresses associated with making and running the battery. They also constructed a solid-state battery cell that used lithium iron phosphate for the cathode and lithium titanium oxide as the anode.
“The electrolyte holds the two battery electrodes together and provides the lithium-ion pathways,” notes Cho. “So, when you want to recycle the battery, the entire electrolyte layer can fall off naturally and you can recycle the electrodes separately.”
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