ZSW uses water instead of solvent in cathode production

Researchers at the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) have been able to replace toxic solvents with water in the production of cathodes. Water-based production is also suitable for batteries for electric vehicles.

In order to increase the energy density, lithium-ion batteries consist of materials with a large proportion of nickel in the cathode mass. This means that toxic solvents and chemicals are used in production, which the ZSW has now been able to replace with water and aqueous liquids.

Specifically, the standard solvent NMP and the binder mixture PVDF were replaced in the production process. Initially, electrodes could only be produced on a millimetre scale in the laboratory. Now the researchers in Ulm have also succeeded in producing electrodes of around 100 metres in length on a scale close to production, without using water instead of solvents.

The electrodes have now been installed in round cells of the 21700 type for the first time. This cell format is used in the Tesla Model 3, for example. And the ZSW is satisfied with the result. “After 1,000 charge/discharge cycles, they still had 80 per cent of the initial capacity and are thus suitable for use in battery vehicles,” the research institute writes in its announcement.

“After working with water as a solvent for the anodes for many years, also on an industrial scale, we have now managed to do the same for the cathode materials,” says Dr Margret Wohlfarth-Mehrens, who was responsible for the work as head of the department. “In addition to eliminating toxic solvents, the use of water also makes it possible to use non-fluorinated binders, which significantly simplifies the recycling of batteries.”

The process will soon be tested for other cell formats.

“Our work aims to improve the production of electrodes in lithium-ion batteries and make it environmentally friendly without compromising battery performance,” says Prof. Dr Markus Hölzle, head of the ZSW business unit in Ulm. “The substitution of toxic solvents and non-biodegradable fluorine-containing chemicals plays an important role in this.”

And the production is of course also cheaper when using water instead of solvents. However, the ZSW did not provide any more detailed information on this.

zsw-bw.de (in German)