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The Fraunhofer IWS process enables battery electrodes to be produced on a pilot scale without the use of toxic solvents.
The Fraunhofer IWS process enables battery electrodes to be produced on a pilot scale without the use of toxic solvents.
( Bild: Fraunhofer IWS Dresden)

energy technology Battery technology for electric vehicles - alternative to wet process to reduce costs

| Author / Editor: Gerd Kucera / Florian Richert

Researchers at the Fraunhofer Institute for Material and Beam Technology IWS in Dresden have developed a new production process to be able to manufacture batteries more cheaply and environmentally friendly in the future.

Researchers at the Fraunhofer Institute for Material and Beam Technology IWS in Dresden have developed a new production process to be able to manufacture batteries more cheaply and environmentally friendly in the future.

The Fraunhofer Institute once again reports successes in its battery development: In a new production process, the Fraunhofer Institute coats the electrodes of the energy storage cells with a dry film instead of liquid chemicals. This saves energy costs and eliminates the need for toxic solvents in this process step. A Finnish company is already successfully testing the new Fraunhofer technology in practice. Better and more cost-effective production methods for energy storage are increasingly in demand in Germany, because so far the companies are purchasing the cells in Asia. This has two main reasons: Asian technology companies have decades of experience in the mass production of battery cells. A lot of energy is consumed in production, which makes production at locations with high electricity prices such as Germany cost-intensive.

The Fraunhofer engineers in Saxony want to change this. "Dr. Benjamin Schumm, project manager at the Fraunhofer IWS, emphasizes: "Our transfer process for dry coating is aimed at noticeably reducing the process costs in electrode coating. In addition, our technology also makes it possible to use electrode materials that can hardly or not at all be wet-chemically processed." But it is precisely these materials that will be needed for future batteries with higher energy density.

Pilot installation successfully started in Finland

The Finnish battery company BroadBit Batteries, together with the Fraunhofer IWS, has commissioned a pilot plant in its Espoo factory that coats electrodes using dry film instead of moist pastes. The Finns use it to produce novel sodium ion batteries. The Fraunhofer IWS can continuously coat electrode foils on a laboratory scale at several meters per minute, thus demonstrating the potential for scaling up to production scale.

In the past, cell producers used to coat the active materials, which later released the stored energy, with special additives to form a paste. They add organic solvents, which are expensive and usually toxic. In order to protect the factory workers and the environment, elaborate precautions for occupational safety and reprocessing are necessary. Once the paste has been applied to thin metal foils, a further expensive process step begins: Dozens of meters of heating distance dry the coated foils before they can be further processed. Drying usually causes high electricity costs.

Binding molecules form a spider's web

In contrast, the new transfer process for dry coating does not require these ecologically questionable process steps. Researchers mix their active material with binding polymers. They process this dry mixture in a rolling mill (calender). Shear forces in this roller system tear entire molecular chains out of the binder polymers. Such fibrils combine with the electrode particles as in a spider's web. This gives the electrode materials stability. The result is a flexible electrode film. In the next process step, the calender laminates this electrode layer, which is around 100 µm thick, directly onto an aluminum foil - this is how the battery electrode is created.

Towards a solid state refractory battery

Materials for new battery generations where conventional processes fail could also be processed in this way. These include energy storage systems that use sulfur as an active material or solid batteries that use ion-conducting solids instead of flammable liquid electrolytes. Such batteries should be able to store more energy in the same volume than today's lithium-ion batteries. But the solid electrolytes can lose their function in contact with solvents, making a solvent-free coating process much more suitable. The Dresden researchers have already reached a milestone in the production of solid state batteries: they made it possible to produce electrodes with extremely low binder contents using dry film processes.

Process could replace classic paste processes

The Dresden engineers now want to refine their technology together with industrial partners in order to help it achieve its breakthrough. In the project (DryProTex) funded by the Federal Ministry of Education and Research (BMBF), they are further developing the dry transfer process for electrode coating together with the companies Saueressig, INDEV, Netzsch Trockenmahltechnik and BroadBit Batteries. The partners expect a fundamental change in battery production.

The Fraunhofer IWS will provide detailed information on November 18 and 19, 2019 in the events "Carbon Electrode Materials" and "Lithium Metal Anodes: Processing and Integration in Next-Generation Batteries" in Dresden.

This article was first published in German by Next Mobility.

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