Electron spectroscopy investigations of sodium-based battery-relevant reference materials

Electron spectroscopy with X-ray photoelectron (XPS) and Auger electron spectroscopy (AES) is routinely used for characterization of chemical processes occurring in batteries. The coexistence of many possible chemical species at the battery electrodes and energy referencing problems at the mostly insulating surface layers are challenging for the spectroscopic investigations. Here, we present measurement results for reference materials based on the elemental sodium (Na), which is in discussion for the use in stationary energy storage modules. Typical chemical species occurring at the sample surfaces are identified, and beam-induced damage during the experiments is described. Whereas the chemical behavior of metallic Na surfaces is found to be very similar to that for Li and K metal, no substantial intercalation of Na into graphite could be observed.