The Center for Materials Research

Picture of the Month - January 2023

Local investigation of ion movement in battery cathodes

Due to their layered structure, the extraction of lithium ions from Li(Ni,Mn,Co)O₂ cathodes during charging leads to an anisotropic volume change. This volume change and, thus, the movement of the lithium ions can be monitored locally in thin-film cathodes using atomic force microscopy, in which a tip is scanned over the surface of the sample. Measuring the forces between tip and sample provides information about the topography of the surface. When applying a voltage between tip and cathode, the lithium ions migrate. The resulting concentration gradient leads to local volume changes, which are detected by the additional deflection of the tip (electrochemical strain microscopy). The figure shows the topography of a Li(Ni,Co,Mn)O₂ thin-film cathode and the corresponding changes in amplitude when a voltage of -400 or 600 mV is applied, which was determined in cooperation with the AG Schirmeisen. The difference in amplitudes shows the change in volume of the material due to the migration of the lithium ions within the layered structure. Local differences due to the orientation of the individual grains and between grains and grain boundaries can be clearly seen.

This picture was submitted by Julius Dinter (group of Dr. Matthias Elm).

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