Picture: Jörg Exner

Research project: Significantly increasing the energy density of solid-state batteries

In the umbrella concept “Research Factory Battery” of the Federal Ministry of Education and Research (BMBF), the University of Bayreuth is now also involved in the competence cluster for solid-state batteries “FestBatt”. A new research project coordinated from Bayreuth is pursuing the goal of significantly increasing the energy density of rechargeable solid-state batteries and making the production of these batteries more sustainable. For this purpose, the powder aerosol deposition (PAD) method is a promising technique that will be used in the future for the coating of cathodes and solid electrolytes. Research partners are Saarland University and the Karlsruhe Institute of Technology.

Rechargeable batteries with a solid electrolyte promise increased safety compared to cells with liquid electrolytes. At the same time, it appears possible to significantly increase their energy density. The greatest challenge for industrial production of solid-state batteries with high energy density lies in producing cathodes and electrolytes that are made up of fine ceramic layers.

In recent years, the powder aerosol deposition (PAD) method has established itself as an efficient method for producing such coatings. This spraying process can be used to apply dense ceramic layers to very different types of materials, such as steel, glass, silicon or plastic. How high the resulting layers are in detail can be determined exactly in advance. As a rule, they are between 0.5 and 50 micrometers thin. By comparison, a human hair measures about 60 microns. The coating can be carried out at room temperature, is inexpensive and consumes little energy. Therefore, the PAD is a sustainable method and in this respect also a contribution on the way to the “green battery”.

“FestBatt” is already the fifth competence cluster of the umbrella concept “Research Factory Battery”, in which the University of Bayreuth is involved with its own project. The overall management of this project with the acronym “AdBatt” (“Aerosol Deposition for the Production of Batteries with Graded Cathode”) lies with Prof. Dr.-Ing. Ralf Moos, holder of the Chair of Functional Materials at the University of Bayreuth. Together with his research team, he has driven the further development and optimization of the PAD in recent years.
“The powder aerosol deposition method is a powerful yet environmentally friendly process. We now want to use it together with our partners in Karlsruhe and Saarbrücken to realize a volumetric energy density of 1,150 Wh/l in the field of solid-state batteries,” says the Bayreuth engineering scientist. An important aspect of the research work is the development of a process that makes it possible to produce cathodes with variable proportions of different material types. These include the cathode active material, the solid electrolyte powder and electronically conductive additives.

At the same time, the Chair of Electrical Energy Systems at the University of Bayreuth, headed by Prof. Dr.-Ing. Michael Danzer, is also participating in the new project. The research work focuses on the electrochemical behavior of graded electrodes with solid electrolyte, but also on the general conditions for safe battery operation. For this purpose, suitable operating values and limits must be defined for the parameters temperature, pressure and current density.
“Of central importance to our research is precise modeling and efficient simulation of electrochemical processes, especially with regard to the interactions between electrolyte, electrode and full cell. On this basis, we will be able to gradually optimize the design of the graded solid-state batteries we are aiming for,” says Danzer, who is also head of the Bavarian Center for Battery Technology (BayBatt) at the University of Bayreuth.