In this contribution, we focus on propylene carbonate (PC)-based electrolytes for lithium-ion batteries. In order to avoid solvent co-intercalation into graphite the presence of a solid electrolyte interphase (SEI) is required. This film is formed due to a film-forming species, i.e. a film-forming electrolyte additive. In this contribution, we focus on a vinylene compound, 2-cyanofuran (2CF) which proves to perform well in propylene carbonate electrolytes. 2CF is investigated by in situ Fourier transform infrared (FTIR) spectroscopy in a specially developed IR cell. We conclude that the cathodic reduction of the vinylene groups (=via reduction of the double bond) in the electrolyte additive is the initiating, and thus an important step of the SEI formation process. The possibility of an electropolymerization reaction of the vinylene monomers in the used electrolytes is critically discussed on the basis of the obtained IR data.