Studying lithium intercalation into graphite particles via in situ Raman spectroscopy and confocal microscopy

The electrochemical intercalation of lithium into single graphite particles was studied in situ using Raman microscopy combined with confocal microscopy. The degree of intercalation during cycling was obtained from changes in the Raman bands of carbon. Confocal microscopy was used to image the graphite electrode in order to monitor the intercalation into single graphite particles. An industrial button cell was modified such that Raman spectra and microscopic images of the back side of the negative electrode could be taken through a window in the cup of the cell. The liquid electrolyte consisted of a 1:1 mixture of ethylenecarbonate/dimethylcarbonate (EC/DMC) with 1M LiPF6. The spectroscopy and microscopy showed that lithium does not intercalate into the graphite in a homogeneous manner. Inhomogeneous lithium intercalation was even observed in single graphite particles.