Interfaces analysis in lithium solid-state batteries using operando Auger, XPS and ToF-SIMS

Lithium solid-state batteries (SSBs) are a promising technology for electrochemical energy storage systems. So far, performance of SSBs are governed by the diverse solid/solid interfaces and their electro-chemo-mechanical evolution upon cycling and storage. However, these interfaces are buried in the battery stack so that their thorough analysis remains a challenge. Indeed, cross-sectioning of the battery stack remains often required to reveal and analyze these buried interfaces but it is not a trivial task. If reliable and reproducible cross-sections can be obtained, then ex situ analysis of the solid/solid interfaces is the preferred method so far. In situ (i.e. sequential analysis and electrochemical cycling) and operando (i.e. analysis during cycling) analysis are also attracting much interests in the recent literature. In this presentation, it will be showed that cross-sections of polymer-based SSBs can be obtained with high reliability using argon ion milling at liquid nitrogen temperature. Moreover, the interest of operando analysis using the electron beam present in the XPS, ToF-SIMS (flood gun or charge neutralizer) and Auger (primary beam) apparatus will be presented. In that case, the electron beam is directly used to flood the surface, thus creating a potential difference followed by lithium migration, SEI formation and Li platting. The main advantage of this approach is to remove the need for dedicated electrochemical cells. Here, this operando method will be presented for a model Li/Li₆PS₅Cl stack. In particular, it will be showed that operando Auger is very attractive due to its fully adjustable electron beam and its ability to follow both morphology and chemical environments evolution at the nanoscale. Comparison with operando XPS and ToF-SIMS results will be discussed. Overall, this work should greatly benefit to all researchers working on interfaces analysis in SSBs.

International Battery Association (IBA), 2022