Impedance spectroscopy studies of the interface between lithium and ionic liquid (IL) showed the formation of a film (solid electrolyte interface, SEI), protecting metal from its further dissolution. Consequently, the potential of metallic lithium immersed in an electrolyte containing Li+ cations may be described as a Li|SEI|Li+ system, rather than simply Li/Li+. The potential of lithium-metal in a series of ionic liquids (and in a number of molecular liquids) containing Li+ cation (0.1 M) was measured versus the Ag|(Ag+ 0.01 M, cryptand 222 0.1 M, in acetonitrile) reference. The lithium-metal potential (E(Li|SEI|Li+)) was ca. −2.633 ± 0.017 V in ILs based on the [N(CF3SO2)2–] anion, while −2.848 ± 0.043 V in ILs containing [BF4–] anion (the difference is ca. 200 mV). In the case of ILs based on the triflate anion ([CF3SO3–]), the cation of ionic liquid also influences the E(Li|SEI|Li+) value: it was ca. −1.987 ± 0.075 V for imidazolium based cations and much lower (−2.855 V) for the pyrrolidinium based cation. In ionic liquid based on the imidazolium cation and hexafluorophosphate anion ([PF6–]), the Li/SEI/Li+ potential was −2.245 V. The Li|SEI|Li+ potential measured in cyclic carbonates was −2.780 ± 0.069 V while in dimethylsulfoxide showed the lowest value of ca. −3.285 V. The measured potentials were also expressed versus the formal potential of the ferrocene/ferrocinium redox couple, obtained from cyclic voltammetry.