We propose in this work a polyethylene glycol dimethyl ether (MW 500) dissolving lithium trifluoromethansulfonate (LiCF3SO3) salt as suitable electrolyte media for a safe and efficient use of the lithium metal anode in battery. Voltammetry and galvanostatic tests reveal significant enhancement of the electrolyte characteristics, in terms of cycling life and chemical stability, by the addition of lithium nitrate (LiNO3) to the solution. Furthermore, PFG NMR measurements suggest the applicability of the electrolyte in battery in terms of ionic conductivity, lithium transference number, ionic-association degree and self-diffusion coefficient. Accordingly, the electrolyte is employed in a lithium battery using lithium iron phosphate as the selected cathode. The battery delivers a stable capacity of 150 mAh g−1 and flat working voltage of 3.5 V, thus leading to a theoretical energy density referred to the cathode of 520 Wh kg−1. This battery is considered a suitable energy storage system for advanced applications requiring both high safety and high energy density.