Surface free energy and contact angle measurements were conducted with a series of room temperature ionic liquids (RTILs) based on N,N′-alkyl-pyrrolidinium imide. Wetting characteristics of various separators (Celgard® and Separion®) and electrodes (LiCoO2, Li4Ti5O12 and graphite), commonly used in Li-ion batteries, were performed. Initially, the free surface energies were determined for both smooth polymeric materials, constituent of the separators, and pyrrolidinium RTILs. Experimental results and calculations show that (i) N-methyl-N-pentyl pyrrolidinium imide is the most wetting RTIL whatever the separator used, and that (ii) the separator wettability is one of the most important factor to take into account in electrochemical devices.