We report here a detailed impedance analysis of the interface between a selected IL electrolyte, i.e. a solution of lithium N,N-bis(trifluoromethane sulfon) imide in N-n-butyl-N-ethyl pyrrolidinium and a N,N-bis(trifluoromethane sulfon) imide, LiTFSI-Py24TFSI, and two electrodes, namely a conventional lithium metal and an advanced nanostructured Sn–C alloy, respectively. We show that the Sn–C alloy, in virtue of a specific formation of a surface protecting film, has an interface much more stable than that of the Li electrode. This favourable property is exploited for using Sn–C as a new anode for the development of an advanced lithium-ion battery based on LiTFSI-Py24TFSI as the electrolyte and on olivine LiFePO4 as the cathode. The results demonstrated that this battery has very promising performances in terms of cycle life and rate capability.