Insights into Li-ion Battery and Stainless Steel Interfaces Using Refined Photoelectron Spectroscopy Methodology

Abstract: If sacrificing some of its material to form a passivating layer at the surface, materials may expand the range of environments where they can be used and further material degradation can decrease. This thesis aims to contribute with insights into passivating layers on especially Li-ion battery anodes (solid electrolyte interphase, SEI) but also on stainless steels, as well as the non-passivating Li-ion battery cathode/electrolyte interface layers (solid permeable interface, SPI). The studies have been performed using new possibilities offered by photoelectron spectroscopy techniques.Depth gradients in the SEI and SPI layers were studied by combining synchrotron-based hard and soft X-ray photoelectron spectroscopy (HAXPES and SOXPES), which was further developed for Li-ion battery investigations. Stainless steel depth profiles were acquired combining HAXPES with angle resolved X-ray photoelectron spectroscopy (ARXPS).In the Li-ion battery, organic species were more common in the outermost SEI, while some inorganic compounds were only detected in the more bulk sensitive measurements. No depth gradients were observed in the SPI. The interface between the graphite and the SEI was studied for the first time indicating lithium enrichment at the graphite surface. Furthermore, the influence of the film-forming additive propargyl methanesulphonate (PMS) on the electrode/electrolyte interfaces was studies, and cells cycled to end of life at 22°C and 55°C were compared.For stainless steels, the thicknesses of the oxide film as well as the nickel enriched metal layer underneath the oxide were determined. A similar methodology was applied to estimate the Li-ion battery SEI thickness.Finally, experiences from PES methodology work on the Li-ion battery systems are discussed aiming to facilitate further studies of the experimentally challenging electrochemically modified samples.