Lithium nitride has been studied as a possible solid‐electrolyte interphase between the lithium electrode and an organic electrolyte. The electrode has been obtained by exposing lithium to a pure nitrogen atmosphere at ambient temperature. This procedure is found to lead to the formation of a porous lithium nitride film, resulting from a decrease in the molar volume during the reaction. The impedance behavior of the electrode can be interpreted by a porous‐film model deduced from a transmission‐line model. The slow filling of the micropores of the film and reaction of lithium with the electrolyte at the pore bases are responsible for changes of impedance and open‐circuit potential with time and under cycling.