Cross-sectional preparation of complex energy devices and their characterization by advanced microscopic methods

Abstract text (incl. figure legends and references)

Energy devices like batteries, fuel cells and solar cells are assembled from multiple functional components with different material properties. To gain a fundamental understanding of structure-property relations, to systematically contribute to performance enhancement and to unravel device degradation and failure mechanisms, high quality cross-sections of entire devices or of as large regions as possible are required. Since many devices not only consist of different classes of materials but also of liquid and/or air sensitive components, working under cryogenic and/or inert conditions is essential to conserve their pristine state.

To enable scale-bridging cross-sectional characterization of those devices all the way down to the atomic level, we utilize different preparation tools. A novel self-built cryo-cutter allows us to produce cross-sections of entire devices, e.g., pouch-cells, in a quick one-step process and to observe them in their pristine state by OM even on the centimeter scale. For smaller scales (cryo-)ultramicrotomy as well as FIB are routinely applied and capable to prepare cross-sections not only for investigations by OM and SEM but also for (atomic resolution) TEM, as high-quality thin samples below 50 nm are provided.

In this contribution we demonstrate the scale-bridging capabilities of those preparation techniques applied on various devices and their components in conjunction with advanced (electron) microscopic and spectroscopic methods. Examples include devices like batteries (Fig. 1) and complex PEM fuel cells (Fig. 2) as well as battery components (Fig. 3). The applied techniques are ideally suited to investigate the integrity of complete devices as well as the interfaces of individual layers and components in terms of their morphology and contact as well as the systematic identification of their composition and chemical bonding states.

Part of this work was performed at the Micro-and Nanoanalytics Facility (MNaF) of the University of Siegen.