Ionic conductivity and electrochemical characterization of novel microporous composite polymer electrolytes

Composite polymer electrolytes (CPEs) have been prepared by encapsulating e lectrolyte solutions of inorganic lithium salts dissolved in a plasticizer or mixture of plasticizers such as ethylene carbonate (EC), propylene carbo nate (PC), gamma-butyrolactone (BL) and dimethyl carbonate (DMC), into poro us polymer membranes. These polymer membranes are obtained from microemulsi on polymerization of the microemulsion system of acrylonitrile, 4-vinylbenz enesulfonic acid lithium salt, ethylene glycol dimethacrylate (as cross-lin ker), omega-methoxy poly(ethyleneoxy)(40) undecyl-alpha-methacrylate (as su rfactant), 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 num ber, measured using a de polarization method coupled with ac impedance spec troscopy is found to be cn 0.45. Cyclic voltammetry of the CPEs on stainles s 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 vol ume), 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 d ischarge capacity of ca. 118 mAh g(-1) of LiMn2O4 at a discharge current ra te of 0.10 mA cm(-2), and promising cyclability. (C) 1999 The Electrochemic al Society. S0013-4651(98)12-013-X. All rights reserved.