Ex-Situ Surface Analysis of Electrode-Material with Diffuse Reflectance Spectroscopy

Summary:

Although decades of research on the aging of lithium-ion batteries (LIBs) has brought fundamental insights and consecutive improvement on LIBs performance, evolution of inhomogeneous effects on the electrode-material and the solid electrolyte interphase (SEI) due to aging is neither completely clarified nor well depicted e.g. in semi-empirical aging models. One major hindrance to reveal inhomogeneity on electrode-sheet level are limitations of investigable sample size and/or throughput of post-mortem analysis methods like scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) or X-ray photoelectron spectroscopy (XPS).
In our work, we introduce an easy applicable, fast and cost efficient method to capture inhomogeneous appearances over the entire electrode surface by using a self-designed UV-Vis-NIR spectrometer. UV-Vis-NIR diffusive reflectance spectroscopy is a fast analysis method, where the spectrum of the reflected light is used to identify chemical species and quantities. We analyze 4 different anode-sheets of the same material, whereof 3 have been aged and 1 is still in pristine aged. By dividing the electrode sheet in different spatial sections and capturing respective reflected spectra, we are not only able to distinguish between those different anodes clearly but also capture detectable differences in spectra within the same electrode. As a result, inhomogeneous appearances of the electrode can sufficiently be captured, and thereby enable a well-founded consideration of inhomogeneity during the sample selection for further analysis. Consequently future research will be able to derive electrode sheet wide conclusion by a sophisticated selection of samples e.g. for further post-mortem analysis.