The present report describes the investigation performed on the interface established between lithium metal and poly(ethylene oxide) (PEO)-lithium bis(perfluoroethysulfonyl)imide (LiBETI), LiN( SO2CF2CF3)(2) polymer electrolytes. The studies were performed as a function of the polymer electrolyte salt concentration and temperature both in rest and in kinetic conditions by means of impedance measurements and galvanostatic tests, respectively.