Lithium-ion batteries use a small amount of glue, called a binder, to hold their internal components together during many charging cycles. Most binders contain fluorine, which means toxic solvents are needed during manufacturing, and hazardous waste is produced when the batteries are recycled.

Engineers from the University of California, San Diego, and the Toyota Research Institute of North America have developed a fluorine-free binder that dissolves in water. Their findings appear in Nature Communications.

Their studies show that a simple mix of two affordable polymers, polyacrylic acid and carboxymethyl cellulose, can replace toxic ingredients without losing performance.

To connect the polymers, the researchers used citric acid, which is also found in citrus fruits. The new binder lasted through thousands of charge cycles and worked with different battery types, including common graphite and silicon anodes.

“But that same stability also makes batteries much harder to recycle,” said Zheng Chen, a professor at the UC San Diego Jacobs School of Engineering, referring to conventional fluorine binders.

Making Battery Recycling Easier

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A flexible and adhesive electrode layer made using the new binder; Photo: David Baillot/UC San Diego Jacobs School of Engineering

Traditional battery production uses large drying ovens to remove toxic solvents, which adds extra cost and uses a lot of energy.

“Those extra steps significantly increase the cost and energy use — as well as the environmental impact — of battery manufacturing,” said study first author Jiao Lin, a postdoctoral researcher in Chen’s lab.

The new design removes those steps completely. To recycle a battery with the new binder, workers soak the parts in water. The binder dissolves, so the electrode material separates easily from the metal foil without leaving behind tough chemical residues.

When the team used the recovered materials to make new batteries, they worked just as well as those made with traditional parts. Next, the researchers plan to increase production for commercial use and adjust the formula for different types of batteries in the industry.