To better understand the correlation between theoretical DFT calculations and experimental GC measurements, surface characterization to detect solid decomposition products was performed using XPS. Here, we investigate the effect of storage time and liquid composition on the surface passivization layer of sodium metal. PC was used as a pure solvent and as an electrolyte with NaClO 4 as salt without and with VC. To provide a clear presentation and more comparable spectra, the intensity was normalized, setting the maximum peak height to 1.