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Fraunhofer researchers develop new low-cost dry-film electrode production process

Researchers at the Fraunhofer Institute for Material and Beam Technology IWS in Dresden have developed a new battery cell production process that coats the electrodes of the energy storage cells with a dry film instead of liquid chemicals. This simplified process saves energy and eliminates toxic solvents. A paper on the Fraunhofer process, with colleagues from Samsung R&D in Japan, is published in the journal Energy Strorage Materials.

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Electrodes coated with the new dry transfer coating technology. Fraunhofer IWS process enables battery electrodes to be produced on a pilot scale without using toxic solvents. © Fraunhofer IWS


Better and more cost-efficient production methods for energy storage are increasingly in demand, especially in Germany: All major automobile manufacturers have launched ambitious electric vehicle programs that will ensure a sharp rise in demand for batteries. So far, German companies have been purchasing the cells for this purpose in Asia.

There are two main reasons driving this trend: one, Asian technology groups have many years of experience in the mass production of battery cells and, two, the processes are energy-intensive. Production at locations with high electricity prices—such as Germany—is, therefore, very high-cost.

The Fraunhofer engineers want to change this.

Our dry transfer coating process aims to noticeably reduce the process costs in electrode coating. Manufacturers can eliminate toxic and expensive solvents and save energy costs during drying. In addition, our technology also facilitates the use of electrode materials that are difficult or even impossible to process wet-chemically. For all these reasons, we think that our technology can help to achieve internationally competitive battery cell production in Germany and Europe.

—IWS project manager Dr. Benjamin Schumm

The Finnish battery company BroadBit Batteries, together with IWS, has commissioned a pilot plant in its Espoo factory, which coats electrodes with dry electrode material instead of wet pastes, as has been common in industry up to now. BroadBit uses it to produce new types of sodium-ion batteries.

On a laboratory scale, the IWS can already coat electrode foil with a remarkable production speed of several meters per minute. In this respect the Dresden engineers can show the potential for transferring the technology to the production scale.

Until now, cell producers have mostly coated their battery electrodes in a complex wet-chemical process. First, they mix the active materials, intended later to release the stored energy, with additives to create a paste. In this process they add organic solvents, which are expensive and usually toxic. In order to protect operators 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 meter long heating sections dry the coated films before they can be further processed. This drying procedure usually causes high electricity costs.

The new film transfer technology for dry electrode coating, on the other hand, operates without these ecologically damaging and expensive process steps: The IWS engineers mix their active material with binding polymers. They process this dry mixture in a rolling mill. The shear forces in this system tear entire molecular chains out of the binder polymers. These fibrils join with the electrode particles as in a spider web. This provides the electrode material with stability. The result is a flexible dry electrode material layer. In the next step, the rolling mill laminates the 100 micrometer thick film directly onto an aluminum foil, thus creating the battery electrode.

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Free-standing NCM sheets with a high areal loading of 6.5 mAh cm−2 were prepared showing even at room temperature the same rate performance like binder-free electrodes with 2.5 mAh cm−2. The impact of binder content on cell performance has been studied revealing significantly reduced impedance at contents below 0.7 wt%. To realize a practical cell, the cell composition was optimized and a 9 cm2 sized rocking-chair type all-solid-state battery was prepared without any solvents underlining the sustainability of the DF process. The battery was cycled for 100 cycles without any artificial pressure, demonstrating the versatility and potential of the DF process.

—Hippauf et al.

In this way, we are also able to process materials for new battery generations where classical processes fail.

—Benjamin Schumm

These new generation systems include, for example, energy storage systems that use sulfur as active material or solid-state batteries which employ ion-conducting solids instead of flammable liquid electrolytes.

On the way of processing electrodes for all solid state batteries the researchers have reached one important milestone by applying their dry film technology using extremely low binder contents.

The Dresden engineers now aim at enhancing their technology in cooperation with industrial partners. In the BMBF-funded “DryProTex” project, for example, they are further developing the dry transfer coating process together with the companies Saueressig, INDEV, Netzsch Trockenmahltechnik and Broad-Bit Batteries.

In the DryProTex project material, process and equipment developments are conducted with the aim of realizing process design for industrial scale dry cathode production.

Resources

  • Felix Hippauf, Benjamin Schumm, Susanne Doerfler, Holger Althues, Satoshi Fujiki, Tomoyuki Shiratsushi, Tomoyuki Tsujimura, Yuichi Aihara, Stefan Kaskel (2019) “Overcoming binder limitations of sheet-type solid-state cathodes using a solvent-free dry-film approach,” Energy Storage Materials, doi: 10.1016/j.ensm.2019.05.033

Comments

SJC

Reportedly Tesla bought Maxwell to get dry electrodes.

Davemart

Over the course of the last ten years I have got fed up with being hopeful about battery progress, which has been fairly glacial at the cell level for the leading NCA chemistry, but this has genuine prospects, especially when coupled with Toyota's announcement that they are going to show at least a prototype of a solid state battery for cars at the Olympics:
https://europe.autonews.com/automakers/toyota-pulls-forward-electrification-plan-eyes-solid-state-battery-next-year

Davemart

I think it especially important that this may reduce the embodied energy in a battery, as that has been wiping out much of the gains on a lifetime basis against ICE cars.

yoatmon

The EMBATT consortium (Glatt Engineering, IAV, Fraunhofer Institute, IKTS, ISOCOLL Chemicals, KMS Technologies, Litarion and Thyssen-Krupp Engineering) is preparing to enter cell mass production in 2020.
https://newatlas.com/battery-stacking-electric-cars/49324/
https://www.youtube.com/watch?v=l_glx79wJyE

gryf

@yoatmon
Definitely looks like EMBATT 3.0 Bipolar ASSB technology.
Let's hope it makes it into production in 2020.

gryf

Let's not forget that this research was done with colleagues from Samsung R&D Institute Japan.

yoatmon

Samsung is a South Korean company and not Japanese. Apart from that, I haven't got the slightest clue that Samsung was involved in EMBATT activities.

gryf

From this post just above.
A paper on the Fraunhofer process, with colleagues from Samsung R&D in Japan is published in the journal Energy Strorage Materials.
You can also check the history of the institute here - http://www.samsung-srj.co.jp/en/profile/.
Satoshi Fujiki, Tomoyuki Shiratsushi, Tomoyuki Tsujimura, Yuichi Aihara are shown in Energy Storage Materials, doi: 10.1016/j.ensm.2019.05.033 as from Samsung R&D in Japan.
Samsung is a major supplier to German auto companies for automotive batteries, e.g. BMW i3.

SJC

The EMBATT design could use a solid electrolyte to eliminate the seals.

yoatmon

@sjc
Im absolutely sure that the implemented ceramic band of that bi-polar cell has a triple function; solid electrolyte, separator for anode and cathode and carrier for both.

yoatmon

The seals you mention more than likely serve to prevent penetration of foreign particles that are likely to impair the proper function of the cell.

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