Molten lithium for more powerful, lighter batteries

April 12, 2019 //By Christoph Hammerschmidt
Molten lithium for more powerful, lighter batteries
Scientists at the Fraunhofer Institute for Chemical Surface and Battery Technology (IWS) in Dresden have developed a process for producing anodes from molten lithium at lower cost. The innovation is a further step towards increasing the capacity of lithium batteries while simultaneously reducing their weight.

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.


Lithium layer on copper foil produced by IWS melt deposition:
The process permits the production of prototype cells with
lithium anode layers of 5 to 30 micrometers in thickness.
(C): Fraunhofer IWS

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.


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