Electric vehicles are to travel up to 700 kilometers with one battery charge, and smartphones to be charged much less frequently. Dresden-based “KaSiLi” under the auspices of the Fraunhofer Institute for Material and Beam Technology IWS, will carry out research into new electrode technologies for three years. “This is a quantum leap for battery technology,” hopes Prof. Christoph Leyens, Head of Fraunhofer IWS and director of the Institute of Materials Science at Technische Universität Dresden. “This disruptive technology has the potential to significantly advance Germany as a business location,” adds chemistry professor Stefan Kaskel from TU Dresden, who also heads the “ExcellBattMat Center” (Center of Excellence for Battery Materials, EBZ for short) at Fraunhofer IWS and the KaSiLi project sponsored by BMBF.
Expertise for an electromobile future
In the long value-added chain from the battery cell to the finished electric car, German economy could thus gain significantly in importance. “Ultimately, we want to establish a modern battery cell production facility in Germany. As a result, we would be less dependent than before on supplies from the Far East or the USA for the transition to electromobility and renewable energies,” Kaskel emphasized. To achieve this, the researchers are developing new materials, design principles and processing technologies for the electrodes in the smallest energy storage units of an accumulator. Important components in such a cell are the anode and cathode. The electrical charge carriers move back and forth between these two poles when a battery is charged or when it is supplying electricity for the electric motor in an electric car. Today, the anode in a lithium-ion battery usually consists of a copper conductor a few micrometers (thousandths of a millimeter) thin, covered with a graphite layer about 100 micrometers thick.
Energy densities of over 1,000 watt hours per liter achievable
The Dresden chemists want to replace this graphite layer with much thinner layers of silicon or lithium. These will then measure only about ten to 20 to 30 micrometers. In the lab, this already works quite well and already provides more energy storage capacity. “Today's lithium-ion batteries have an energy density of around 240 watt hours per kilogram or up to 670 watt hours per liter,” explains Stefan Kaskel. With our electrodes, we want to achieve well over 1,000 watt hours per liter.
On the way, however, the developers not only have to further improve the chemistry and coating processes for their cells, but also solve a mechanical problem: Under the microscope it has been shown that the electrodes, which are thinly coated with silicon or lithium, shrink again and again and expand when the batteries are charged or discharged – as if the cell were breathing. However, this poses a problem because the mechanical stress can quickly destroy the electrodes through this "breathing". For this reason, the partners are now experimenting with tiny springs. They are working on special layers for the cathode formulations: »These are to be given cushioning properties through a special adaptation of their microscopic properties to contribute significantly to a higher energy density of the new battery generation«, says Dr. Kristian Nikolowski from the Fraunhofer Institute for Ceramic Technologies and Systems IKTS.