Composite polymer electrolytes (CPEs) have been prepared by encapsulating electrolyte solutions of inorganic lithium salts dissolved in a plasticizer or mixture of plasticizers such as ethylene carbonate (EC), propylene carbonate (PC), gamma-butyrolactone (BL) and dimethyl carbonate (DMC), into porous polymer membranes. These polymer membranes are obtained from microemulsion polymerization of the microemulsion system of acrylonitrile, 4-vinylbenzenesulfonic acid lithium salt, ethylene glycol dimethacrylate (as cross-linker), omega-methoxy poly(ethyleneoxy)(40) undecyl-alpha-methacrylate (as surfactant), and water. These CPEs exhibit conductivities of 3.1 x 10(-4) to 1.2 x 10(-3) S cm(-1) at room temperature. The lithium ion transference number, measured using a de polarization method coupled with ac impedance spectroscopy is found to be cn 0.45. Cyclic voltammetry of the CPEs on stainless steel electrodes shows electrochemical stability windows extending up to 3.9, 4.0, and 4.3 V vs. Li+/Li for CPEs with 1 M LiSO3CF3/EC-PC (1:1 by volume), 1 M LiBF4/BL and 1 MLiClO4/EC-DMC (1:1 by volume), respectively. The impedance of the Li/CPE interface for the CPE with 1 M LiClO4/EC-DMC under open circuit conditions is found to increase over storage time. Preliminary charge-discharge tests of prototype Li/CPE/LiMn2O4 cells show an initial discharge capacity of ca. 118 mAh g(-1) of LiMn2O4 at a discharge current rate of 0.10 mA cm(-2), and promising cyclability.