Battery research and drug transport: Let the future come

Zimmermann is a process engineer and has been working at the University of Stuttgart’s Institute of Thermodynamics and Thermal Process Engineering as a research associate since January this year. As part of the project “Terra incognita”,  [de] which is a funding program of the university for frontier research, he is looking into the question of which processes take place at the molecular level during concentration balance in a liquid, and what influence temperature differences in the liquid have on mixing, among other things.

The processes that occur during such temperature-driven transport are extremely interesting, because - according to the vision - appropriately coated drugs could be transported specifically to sites of inflammation in the human body, as the temperature is higher in these places. “We are just at the beginning,” says Zimmermann. According to him, scientists need to understand the influence of electrostatics first, i.e. the fundamentally important forces for such a transport. The next step is the development of computer-based tools in order to calculate these mechanisms and, finally, model them. Due to the pandemic, Zimmermann is currently not performing his computations in Stuttgart - his desk is still in Hamburg. It doesn’t really matter, because his workplace is the computer. But he would like to meet his colleagues in real life as soon as possible, and his boss, the acting Head of Institute Prof. Dr. Niels Hansen, whom he has only known from online meetings.

Zimmermann completed his doctoral degree at the Institute of Chemical Reaction Engineering at the Hamburg University of Technology and can look back on a good 13 years of research experience in many countries. Before he came to Stuttgart, he worked in the US at the Lawrence Berkeley National Laboratory (LBL) in Berkeley, where he conducted research on next-generation batteries. Whether for cell phones, laptops, or electric cars, storage batteries are more and more in demand. However, the currently widely used lithium-ion batteries have disadvantages: Lithium is toxic, it reacts sensitively to high temperatures can even explode, and its mining involves extremely high water and energy consumption.

“There are other ways of making environmentally friendly and sustainable batteries. Alternatives to lithium are being sought after,” emphasizes Zimmermann, having magnesium already in mind as a possible replacement. Magnesium is non-toxic, it can be obtained in a relatively environmentally friendly way - and there is plenty of it in seawater. “Higher storage densities could also be achieved with magnesium,” Zimmermann adds, but immediately points out the limits: On the cathode side of the battery, the small magnesium ion, which can transfer two electrons at a time, causes problems. Small and highly charged, it is in fact characterized by a strong attractive electric force. It moves extremely slowly in the lattice of the cathode material. Once it has arrived somewhere, it doesn’t really like to leave its place. However, this is crucial when charging the battery, and so now the big question is: Which cathode material has the lowest transport barriers for magnesium? When searching among known as well as hypothetical materials, Zimmermann uses supercomputers and relies on the computational method he developed, which is called PfEFIS.

PfEFIS stands for “Potential of Electrostatic Finite Ion Size”. The method is based on finite-size ion models and allows a quantitative estimate of diffusion jump barriers for the magnesium ions based on the electrostatic potential. A good 10,000 times faster than conventional approaches, it can be used to reliably predict the progress of magnesium ions in inorganic materials. “Anode, cathode, electrolyte - batteries are complex,” Zimmermann points out. Screening numerous possible cathode materials is therefore only the beginning, because then the task is to find the best electrolyte.

Research is data-driven. Numbers tell scientists everything. Nils Zimmermann, who likes to share his knowledge, supports open access and open source, but nevertheless also appreciates good visualizations. According to him, they are extremely useful for communicating research results in the context of university teaching or for sharing the latest knowledge with society in general. He says: “I have a love for teaching and continuing education. I enjoy working with students immensely, imparting knowledge about supercomputing and simulation to them.”

His three children keep Nils Zimmermann busy, away from the computer and the molecules. With them, he is in the process of discovering playgrounds - still in Hamburg, but soon also around Stuttgart. After all, when the project “Terra incognita” is over, he would prefer to stay at the University of Stuttgart. He is putting together all the documents necessary to apply for a Heisenberg position.