Kinetic analysis of the Li|Li+ interphase in an electrolyte based on N-metyl-N-propylpyrrolidinium bis(trifluoromethanesulfon)imide ionic liquid (MPPyrrTFSI) and lithium bis(trifluoromethanesulfon)imide salt (LiTFSI) was performed. Li|electrolyte|Li and LiC6|electrolyte|Li cells were galvanostatically charged/discharged in order to form solid electrolyte interphase (SEI) protecting layer. SEM images showed that the surface of both Li and LiC6 anodes was covered with small particles. The fitting procedure of electrochemical impedance data taken at different temperatures gave three resistances (Rel, RSEI, Rct) and hence, three lnR = f(T−1) straight lines of different slopes. Specific conductivity and activation energy of the conduction process of the liquid electrolyte, were ca. σ = 2.5 mS cm−1 (at T = 25.0 °C) and 