The C 1s spectrum for Na submerged in pure PC solvent (Fig. ) shows three large peaks at binding energies of 285.0 eV (C-C,C-H), 286.4 eV (C-O) and 290.4 eV (CO 3 ) in relative intensities of 1.5:2:1 (for 2min). These binding energies and relative intensity ratios are close to the observed values for liquid PC measured using near ambient pressure XPS indicating either adsorbed PC or initial reactions that do not significantly change carbon nearest neighbor configurations. In addition, a peak at 287.7 eV is observed. This binding energy may be expected for carbon in a carbonyl group (C=O). A possible assumption for the appearance of this peak may be the effect of the delocalized charge of the CO 3 species. In the case of pure PC, there are two carbonate species found, one from the PC solvent itself at 290.4 eV and one from Na 2 CO 3 at 289.3 eV. After storing a Na metal electrode in PC for 2 h, the same PC-attributed peaks can still be observed (Fig. ). However, the intensity ratio between the three main peaks (C-C,C-H/C-O/CO 3 ) changes from 1.5:2:1 for the 2 min. to 2.8:1.6:1 for 2h indicating further reactions between the Na surface and PC. Compared to the pure metal this amount of CO 3 is not found (less than 1 atom-%). Also, the pristine metal has a significantly higher proportion of C-C,C-H (47 atom-%). This indicates that the CO 3 species is formed on the surface after the addition of PC. The data presented in Fig. corresponds to C1s spectra for Na metals submerged in NaClO 4 -containing electrolytes, either without (c, d) or with VC as additive (e,f). For all these samples with the addition of salt, the spectra show prominent peaks at approximately 285 eV and 289 eV with two less intense peaks at around 286.3 eV and 287.5 eV. The peak with the highest binding energy at 289.3 eV peak is assigned to Na 2 CO 3 . The peak at 287.5 eV is assigned to C=O and (C=O)O environments contained for example in HCO 2 Na, while the peaks at lower binding energies of 286.