Combined IR and Raman In Situ Microscopy on Single Particles - A New Tool for Interface Studies

Vibrational spectroscopy is well suited to the investigation of processes occurring in lithium-ion batteries during electrochemical cycling. The combined application of Raman and IR spectroscopy offers additional advantages connected to the complementary nature of the two methods. Whereas Raman spectroscopy is particularly sensitive to local structural changes of the electrode material, IR spectroscopy provides a good way of probing the interface with the organic electrolyte. Employing microscopic methods and a specially adapted cell allowed spatial resolution and the recording of in situ data, respectively.

In this contribution, we will describe the first application of these spectroscopic methods to the characterization of the same spot at a single working particle. Originally, combined Raman and IR microscopy was first developed by using glassy carbon, which offers the advantage of exhibiting excellent IR reflectivity. However, because glassy carbon is unable to intercalate lithium, the method was further developed and applied to a single, graphite particle. Unlike conventional compound electrodes consisting of microscopic graphite powders, this allows the measurement of IR spectra with good signal-to-noise ratios. This study is thus employed to showcase a powerful application of the combined same-spot spectroscopic method. The automated measurement of Raman and IR spectra provides an efficient way of correlating information on the electronic state of the electrode (intercalation) with effects related to the interface with the electrolyte (SEI). Corresponding results are presented and discussed in this contribution.