An enhancement of ionic conductivity to 2 . 10(-3) S cm(-1) at 120 degrees C was achieved by the addition of ethylene carbonate and/or polyethylene glycol dimethyl ether to LiI-based composite polymer electrolyte (CPE). These plasticizers also improved the Li-CPE interfacial contact, so the SEI resistance was low (2 ohm . cm(2)) and was stable for 1000 h. CPE characterization by differential scanning calorimetry measurements, thermogravimetric analysis, SEM and X-ray methods is presented.