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October

Picture of the Month - October 2024

Determination of the microstructure of deposited lithium and sodium films in anode-free solid-state batteries

In so-called ‘anode-free’ solid-state batteries, alkali metal foils are not used in cell construction. Instead, a simple current-conducting film is used. The term ‘anode-free’ is therefore not strictly speaking correct, but has become established in the battery community. The actual metal anode is only formed in the first charging step through the deposition of alkali metal ions stored in the cathode material. This approach not only increases the energy density of the cell, but also avoids the difficult handling of highly reactive lithium and sodium foils, which form unwanted passivation layers in almost any environment.

The microstructure of the deposited metal anode (e.g. grain size, orientation, grain boundaries) has a decisive influence on the charging and discharging properties. Until now, however, the microstructure of electrochemically deposited lithium and sodium was largely unknown due to analytical challenges. A recent publication in Nature Materials shows how a combination of FIB-SEM preparation at cryogenic temperatures, inert gas transfer and electron backscatter diffraction (EBSD) was used to analyse these microstructures. The necessary setup is shown in figure a), while the backscattering patterns of lithium and sodium are shown in b) and c). Using three relevant material systems (d-f), it was possible to demonstrate that very large alkali metal grains are formed (in some cases >100 µm), which have a columnar structure.

The knowledge gained and the method developed can now be used to better understand and specifically optimise the charging and discharging properties of metal anodes.

Publication: Fuchs, T.; Ortmann, T.; Becker, J.; Haslam, C. G.; Ziegler, M.; Singh, V. K.; Rohnke, M.; Mogwitz, B.; Peppler, K.; Nazar, L. F.; Sakamoto, J.; Janek, J. Nat. Mater. 2024. DOI: 10.1038/s41563-024-02006-8.

This picture was submitted by Till Fuchs and Dr. Joachim Sann, group of Prof. Dr. Jürgen Janek.

Further insights into the research activities of the ZfM groups can be found in the Gallery.