Did you know that every time you charge your phone, it turns golden inside?
Visualizing lithium insertion
Graphite is used in almost all commercial lithium-ion batteries, and when it’s lithiated (charged) the colour changes from grey to deep blue, then red, and finally a bright golden colour. This can be used as a simple method to analyse and troubleshoot the graphite electrode performance: By using a cell where the electrode surface is visible from the outside, the oxidation state can be monitored in situ during cycling with optical microscopy. It might also be possible to locate defects, dead electrode areas, lithium dendrites, etc.
Image color analysis
With the graphite electrode in the video, it was possible to quantify the progress of the lithiation, using a small script that counted the fraction of pixels with certain hue values in each frame, as you can see below. Of course, with this method it is only possible to monitor the surface of the graphite particles, not the bulk.
To cite this application note, please use: “Karlsson et al, rhd instruments GmbH & Co. KG, Application Note: Optical Observation of the Lithiation of Graphite in situ, April 2024,
https://docs.rhd-instruments.de/appnotes/application-note_Optical_Cell.pdf”.