Cl2p emissions were observed for the samples containing NaClO 4 as electrolyte salt. In the case of Na metal soaked in 1 M NaClO 4 in PC for 2 min and 2 h, the Cl2p spectra show two doublet peaks at 198.7 eV and 209.5 eV which correspond to NaCl and NaClO 4 . Thus, even with the described washing procedure, there was a small residual amount of conductive salt left on the surface. The atomic percentage for NaClO 4 is lower than 0.1 % and therefore not included in the following evaluation. Interestingly, in the case of the electrolytes without VC as additive (Fig. ), a strong NaCl contribution is observed, indicating electrolyte salt decomposition. When VC is used in the electrolyte (Fig. ), initially, after 2 min soaking, no clear NaCl signal is observed while after 2 h, there is a NaCl contribution.