A new concept is proposed to realize high performance lithium polymer batteries. The two-phase battery concept is based on the use of two polyethers of different molecular weight. A low molecular weight polyether is used in the composite cathode to assure high ionic conductivity while a high molecular weight polyether is used in the electrolyte formulation. In this work, a composite cathode based on a solid, low molecular weight poly(ethylenglycol) dimethyl ether (PEG-DME, M.W. 2000), was coupled with a solid polymer electrolyte (SPE) based on poly(ethylenoxide) (PEO, M.W. 4×106). The electrochemical stability window, evaluated by a slow sweep voltammetry, showed that the system has an anodic breakdown voltage higher than 4.0V versus Li. The feasibility of two-phase batteries was evaluated by cycling tests. The results indicate that two-phase batteries have enhanced performance with respect to PEO based batteries.