New multicomponent organic liquid electrolytes, based on mixtures of the commercial solution EC-DEC-LiPF6 (A) and tetraglyme/LiPF6 (G4), have been examined in terms of thermal and electrochemical behaviour. The composition with 40 vol% of G4 seems to be the best compromise among thermal stability, high conductivity and wide electrochemical window. Two porous asymmetric poly(vinylidenefluoride) membranes of porosity higher than 70%, but of different morphology (sponge-like versus finger-like), prepared by the phase inversion method, are compared in terms of physical-chemical properties, after activation with the pure solution A and the optimal mixture 60:40 v/v A:G4. Conductivities exceeding 2 mS/cm at room temperature are easily obtained, and the use of these membranes assures electrochemical stability at least up to 5 V. In spite of the cross-sectional asymmetry of these kinds of membrane and of the presence of a superficial skin, no relevant differences in the anodic limit voltages are observed on changing the orientation of the skin, as demonstrated by linear sweep voltammetry tests on both the surfaces.