New binding agent

Linz researchers remove toxins from lithium batteries

Researchers at JKU Linz have developed a non-toxic binder for the cathode of lithium batteries.

(Bild: stock.adobe.com/salita2010)

Researchers in Linz have made lithium batteries toxin-free and their production more energy-efficient. They have developed a binder for the current-carrying pole (cathode) made from a natural substance that is processed in water at moderate temperatures instead of in an energy-intensive, reprotoxic solvent like the conventional fluorinated material. This could also make batteries more durable.

Klaus Bretterbauer and Felix Leibetseder from the Institute for Chemical Technology of Organic Materials at the Johannes Kepler University Linz explain in the journal "Advanced Energy Materials " that a substance made from castor oil from the tropical wonder tree serves as the basic building block of the new cathode binder. It is called "11-aminoundecanoic acid" and is linked to form long polymer chains.

"The binder acts as an adhesive that holds the materials to the current collector," said Leibetseder: "This prevents everything from literally falling apart during charging and discharging in the battery. The new binder adheres about ten times better to the aluminum foils that act as current collectors in such batteries than conventional polyvinylidene fluoride (PVDF, note)," explained Bretterbauer.

This significantly reduces the likelihood of a battery failing due to the electrode detaching from the current collector.

Free from toxic chemicals and water-soluble
The commonly used material PVDF and the processing aids it contains also belong to the per- and polyfluorinated alkyl compounds, PFAS for short, which are increasingly being banned in the European Union due to their many harmful effects on health. In order to use PVDF for electron production, a solvent called N-methyl-2-pyrrolidone (NMP) is also used, which is known to reduce fertility.

"Our binder is fluorine-free and water-soluble," says Bretterbauer. "This has the advantage that water can be used instead of NMP during production." There is therefore no health risk for production staff and no toxic waste is produced. Water as a solvent can also be removed at lower temperatures than NMP, which means that less energy is required to manufacture the electrode.

Better recyclability
Finally, the material can also be easily recycled when the battery reaches the end of its service life because it is water-soluble. "This also makes rare critical raw materials such as lithium, manganese and cobalt from the batteries easier to recover," explains Bretterbauer. "Batteries with PFAS, on the other hand, are difficult to recycle and pose a high risk to the environment, especially due to their toxicity."

"Overall, this makes our approach much more environmentally friendly," says the researcher. On the other side of the battery, at the anode, substitutes for materials that are harmful to health were found some time ago. "Now we have also been able to develop a material for the positive side that is harmless, comes from a renewable raw material that is not a competitor to food production and also has better adhesion than the material currently used."

Versatile in use
The researchers see no restrictions on the use of the new binding agent. The material, which has been developed from basic research to prototype at the University of Linz, could be used to hold the components together in batteries in everything from cell phones to electric cars.

Together with Karl-Heinz Pettinger from the Landshut University of Applied Sciences (Germany), they are currently testing button cells with the new material and larger battery prototypes, which are produced by a "room-filling machine", reported Leibetseder. These have proved so successful that the company is now in talks with industrial partners.

"We hope that we will soon be able to test our prototypes with them to see how they perform under high demands, for example in the automotive sector," says Bretterbauer. He is optimistic that "we can expect to see the new batteries in the near future".