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 in combination with a gantry system. 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. It has a wide range of application like composition-analysis of paintings, food quality assessment and surface analysis. The gantry system allows an exact and automated placement of the combined sensor-light unit. By dividing the electrode sheet in different spatial sections and capturing respective reflected spectra, we are not only able to capture inhomogeneity but also to cluster and quantify detectable differences in spectra. As a result, heterogeneous appearances of the electrode can sufficiently be captured, and thereby enable consideration of inhomogeneity during the sample selection. 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.