The interest in the sustainable use of lithium-ion cells especially in the automotive applications is still very high. In this context, it is particularly important to know the aging behavior of the cells as a function of the operating conditions. In particular, to understand the evolution of solid electrolyte interphase (SEI) in cells operated under realistic driving behavior, a comprehensive test matrix on pouch-cell level is performed. In addition, a more flexible and easier method to variate test matrix can be realized by lab-scale experimental cells. It shows that the SEI forms over the aging procedure comparable independent of the cell set-up. This correlation is applied for the parametrization of the SEI modelling. A model published by Kolzenberg et al. applying parameters like lithium and active material loss. [1] It will be modified and adapted to our use case. The simplification of parameters allows reducing the complexity and focus on measurable values like thickness and SEI depth structure characterized by following methods. X-ray photoelectron spectroscopy (XPS) combined with argon-ion etching on the anode surface. The resulting depth profiles of the etching method show the evolution of the relevant species as LiF or Li-carboxyl in the SEI layer. The passed time indicates when the beam resigns the SEI and enters the graphite structure. The image of the SEI layer is taken by a high resolution transmission electron microscopy (TEM). The combination with methods like electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX), enables the thickness estimation. These methods show the qualitative distribution of the SEI characteristic elements such as C1s, F1s or O1s and result in a combined image to estimate its thickness.

[1] L. von Kolzenberg, J. Stadler, J. Fath, M. Ecker, B. Horstmann, A. Latz, Journal of Power Sources 2022, 539, 231560.