Lithium metal anodes are considered a key element for the battery systems of the future. They maximize energy density both in terms of cell volume and mass. The lithium metal anode is already used in lithium sulfur cells to achieve record specific energy values of more than 400 Wh/kg. The best lithium-ion battery cells, on the other hand, are currently only 250 Wh/kg. In addition, solid state batteries could exceed the volumetric energy density of today’s lithium-ion batteries by more than 70% using the lithium metal anode.
The usual production solutions for lithium foils for use as anodes include rolling processes. Their difficulty lies in the fact that the cost of producing large-area layers with thicknesses of less than 50 micrometers is very high. The quality is also limited because auxiliary materials chemically contaminate the surface. Thus lithium foils cannot be produced on an industrial scale with the quality requirements necessary for battery applications. In addition, production technologies for high-quality and thin lithium layers are not yet commercially available and the interface between lithium and other cell components is highly reactive. This in turn requires interface engineering to enable stable and safe use of the lithium anodes.
The Fraunhofer IWS in Dresden has already been working for several years on a coating process that makes it possible to produce lithium layers with a thickness of just a few micrometers. The most important innovation lies in a lithiophilic surface that enables cost-effective and homogeneous deposition of thin layers of molten lithium on metallic substrates. “We are able to treat thin nickel and copper foils in such a way that it is possible to coat them from the liquid phase or from the lithium melt,” explains Dr. Holger Althues, head of the Department of Chemical Surface and Battery Technology at the Fraunhofer IWS.
Previously, it was not possible to wet untreated copper or nickel foils with lithium. “However, this is absolutely necessary in order to create a coating and we can do this with a lithiophilic substrate surface,” Dr. Althues concretizes. Further advantages would lie in the fact that the developed IWS technology could be implemented at particularly low cost and could already be scaled up to industrial standards in the roll-to-roll process. Modifications to the lithium surface are intended to extend this coating process in the “MaLiBa” project. The project team aims to significantly improve the handling, stability and safety of lithium anodes for use in battery cells. This work will be complemented by the development of a laser cutting process within the “LiMeCut” project, which will enable flexible assembly of lithium anodes. The result is a toolbox for adapting anodes to customer-specific cell systems and formats.
In the joint project Customized Metal Anodes for Future Battery Systems (MaLiBa) the Fraunhofer IWS in cooperation with the Justus-Liebig-University Gießen develops customized and surface-modified lithium anodes for batteries of the future, while the project LiMeCut (funded by the German Federal Ministry of Education and Research within the eurostars program) in cooperation with OxisEnergy and ULT aims at the development of a flexible laser process technology for cutting lithium anodes.