Microstructure of Highly Reactive Alkalis in Batteries Determined

Lithium and sodium metal anodes are central to the development of all solid-state batteries. Now a way has been found to elucidate the microstructure of these alkali metals after deposition in batteries.

An international research team involving the Justus Liebig University of Gießen (JLU) has demonstrated for the first time a way to determine the microstructure of both electrochemically deposited lithium and sodium metal. According to the publication in the special interest magazine Nature Materials, this should enable completely new approaches to influencing the properties of batteries.

Lithium and sodium metal anodes play a central role in the further development of high-performance solid-state batteries. In order to influence their electrochemical properties favorably, knowledge of their microstructure is necessary. The problem with this is that lithium and sodium are highly chemically reactive. Their surfaces suddenly become covered with corrosion layers in almost all environments, which makes it practically impossible to elucidate their microstructure.

Determination using Electron Backscatter Diffraction

To overcome this problem, the Giessen team, under the direction of Prof. Dr. Jürgen Janek of the Physical Chemistry Institute at JLU, developed a chain of preparation and examination steps at very low temperatures and under a protective gas atmosphere. At the end of this process, the local metal structure is determined using so-called electron backscatter diffraction.

Using this method, the team was able to show how electrochemically grown metal layers of lithium and sodium metal with thicknesses in the range of up to 100 μm are constructed. “The grain size of the layers produced was surprising for us, and the results provide important clues to the growth mechanism,” says Janek.

Problems with the Use of Metal Electrodes

According to JLU, there are still problems with the use of metal electrodes, in particular due to the strong tendency of metals to change shape when used electrochemically. This affects both the charging and discharging processes. For example, pores form in the metal when a battery is discharged. During the deposition of the metal in the charging step, dendrites often form, causing short circuits.

On the way to more powerful solid-state batteries that can compete with conventional lithium-ion batteries, the lithium metal (or the sodium metal) should now only be formed in the first charging step at all, in order to avoid the costly handling of very reactive alkali metal foils. In addition to JLU, the University of California in Santa Barbara and the Canadian University of Waterloo were involved in the research.

This is a partly automated translation of this german article.