The electrolyte was prepared using anhydrous dimethyl sulfoxide (DMSO, > 99,9%, Sigma-Aldrich) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI, Sigma-Aldrich, 99,95%). The DMSO, dried during several days on 3 Å molecular sieves (Sigma-Aldrich), had a water content < 50 ppm, measured by Karl Fisher. The solution of LiTFSI in DMSO was prepared in a MBRAUN glove-box (H 2 O < 3 ppm and O 2 < 2 ppm), and stored in 10 cm 3 vessels sealed with rubber septum. Once removed from the glove-box the electrolyte was bubbled with dry O 2 (> 99.5%) or Ar (> 99.99%) during 40 minutes. In order to avoid the hydration of the electrolyte we used silica gel traps at the input and output of the vessel containing the electrolyte.