Extended Data Fig. 1: Graphic representation of synchrotron X-ray measurements to investigate interfacial degradation in polymer electrolyte-based cells.

Schematic showing synchrotron X-ray measurements of a solid-state battery cross-section, which combines X-ray fluorescence (XRF) microscopy and X-ray absorption spectroscopy (XAS) measurements to visualize ionic concentration and probe chemical states across buried interfaces of solid-state battery components. Sulfur species from IL (TFSI⁻) and PBDT polymer (-SO₃⁻) are present in the MIC electrolyte. Tracking the sulfur species of polymer electrolytes with XRF mapping reveals local ionic concentration heterogeneities, and spatially resolved XAS analysis informs the evolution of new sulfur species from interfacial side reactions by probing the changes in the oxidation states of sulfur elements therein. From the right panel of the XRF map, the green area represents the regions containing sulfur species, the black areas indicate regions without sulfur species, and the red area represents the sample holder (see also Spatially resolved XRF/XAS measurement and Sample preparation for synchrotron measurements from Methods). The point scanning XAS on the cross-sectional sample probes sulfur chemical states across electrode|electrolyte interfaces with a spatial resolution of a few micrometers (Right part, point 1).