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Powerful batteries are in demand as never before. They are not only the key to electromobility and energy supply for our everyday electronic companions. Research on and into energy storage systems is also booming because they are essential for the energy transition. The Potsdam-based researcher Kerstin Zehbe is developing a battery concept based on novel gels and 3D printing.
Kerstin Zehbe is holding two small, round glass flasks filled with liquids in her hands. In one she is swirling a deep blue solution, in the other a pale yellow. More pistons containing other substances are standing under the fume hood of the chemical laboratory: some are crystalline, others colloidal. There are even some that contain compounds that luminesce under UV light. Although the substances look different, they have one thing in common: they are so-called ionic liquids. The chemist is pursuing an ambitious goal with these starting materials. In a joint research project with the Karlsruhe Institute of Technology (KIT), she intends to develop novel batteries that are stronger, more efficient, and more stable than all previous ones – yet are still inexpensive.
“The principle of a battery is quite simple,” Zehbe explains “You need two electrodes and an electrolyte in between to allow charge transport.” Up until now, mainly systems based on lithium ions have been used. But these are not without problems: If a lithium battery is damaged or heated by sunlight, it can catch fire or even explode. “That's why we’re looking for alternatives.”
The chemist is counting on ionic liquids, which are also suitable for use in battery systems. “In principle, they are salts that are usually liquid at room temperature,” Zehbe explains. These salts consist of positively and negatively charged ions. By choosing the ions, the researcher can influence how the substance behaves. Like choosing from a modular system, she selects which negatively and positively charged particles to mix and thus determines which characteristics the final product has. “The way I need it,” she says.
In her battery model, the ionic liquids act as the charge-conducting electrolyte. But the real clou of her research approach lies elsewhere: Kerstin Zehbe is developing gels from these liquids in order to connect them with a carrier matrix. For this, she mixes the ionic liquids with a synthetic resin or with silicone and prints out the mixture on a 3D printer. Laser irradiation hardens the material during the printing process.
With this method, the resulting ionogel can take any conceivable form. Zehbe’s prototypes, for example, are hard, circular discs that contain fine holes – like a sieve. A second model is cylindrical and soft, it has pores like a sponge. A third one has honeycomb pores that traverse the blank from one end to the other. “We are trying to print structures that are macroscopically optimized,” she explains. The finer, the better, so that it enables a good connection to the electrode and a faster charge transport.
The desired properties of the ionic liquids are retained by the procedure. At the same time, the gels reduce undesirable characteristics of the fluids. These are very corrosive and can attack the electrode material in a battery.
The scientist has been experimenting with various liquids and resins in her laboratory for a year determining the conductivities and testing numerous types of the ionogel. The products are to be chemically and thermally very stable, highly conductive and as efficient as possible. Zehbe is looking for “the perfect mix”. She sends the most promising prototypes to the Karlsruhe Institute where further tests will follow. She does not want to reveal too much about the components of her system. “Only so much: Our gels are based on fluorites and sulfates.”
Kerstin Zehbe is still in the midst of research into her battery systems, which she will further optimize. Nevertheless, she is already hatching the next project, and she remains true to the topic of energy: “Fuel cells are another very large field that we want to tackle.” Ionic liquids will play a role her as well, announces the chemist.
Universally shaped Batteries from Printable Ionogels (UniBat)
The researchers are developing a novel process for batteries based on ionogels. The aim of the novel battery concept is to overcome current technical problems such as unwanted chemical side reactions or thermal decomposition.
Participants: University of Potsdam, Karlsruhe Institute of Technology (KIT)
Funding: German Research Association (DFG)
Dr. Kerstin Zehbe studied chemistry at the University of Potsdam and earned her doctoral degree at the Technischen Universität Berlin. Since 2014, she has been a postdoctoral researcher at the University of Potsdam and has researched ionic liquids, ionogels, battery systems, and fuel cells.
Text: Heike Kampe
Translation: Susanne Voigt
Published online by: Marieke Bäumer
Contact to the online editorial office: onlineredaktionuni-potsdamde