Wide interest is mounting on polymers for application in energy efficient devices such as rechargeable batteries, electrochromics and photovoltaics. Solid polymer electrolytes exhibit unique advantages: mechanical integrity, variety of fabrication methods and intimate electrode/electrolyte interfacial properties. They also improve safety along with more compact and lightweight packaging. In this work, highly ionic conducting elastic and resistant PEO-based polymer electrolytes, encompassing lithium salts dissolved in Room Temperature Ionic liquids (RTIL), were successfully prepared via an innovative, rapid and efficient process (PATENT pending). The degree of PEO crystallinity was greatly reduced down to the amorphous state by addition of lithium salt and RTIL, thus a noticeably increased ionic conductivity was registered (> 10-4 S cm-1 at RT). The polymer electrolyte demonstrated a very stable interfacial stability versus lithium metal and a very wide electrochemical stability window (0-5.5 V vs. Li). In the presence of such an electrolyte, the laboratory-scale devices showed remarkable performances, comparable to those using liquid electrolyte, respect to which demonstrated a much greater durability. The obtained findings demonstrate that our proposed preparation can provide a new, easy and low cost approach to fabricate polymer electrolytes with remarkable performance for the next generation of advanced flexible energy production and storage devices