Study of high-anionic conducting sulfonated microporous membranes for zinc-air electrochemical cells

High-performance electrochemical membranes have been in great demand due to the rapid market growth in the portable power source devices. The electrochemical characteristics of high-anionic conducting membrane separators were studied in this report using microporous membranes with different sulfonation degrees obtained by changing the sulfonation reaction time. The degree of sulfonation treatment and the effects on the membrane separators were carefully investigated. The room temperature anionic conductivity of the membranes was improved by 132% to 3.52 x 10(-2) S cm(-1) when the sulfonation treatment time was 128 h. It was about 1.52 x 10(-2) S cm(-1) for the unsulfonated membranes. The anionic transport number in 1 M KOH aqueous solution was also improved to 0.89 from 0.79. The characteristic properties of these membrane separators were studied by infrared spectroscopy (IR), elemental analysis (EA), X-ray diffraction (XRD), scanning electron microscopy (SEM), AC impedance, contact angle measuring system and stress-strain tests. In addition, the solid-state zinc-air cells assembled from the sulfonated membrane separators showed enhanced battery power density of 38 mW cm(-2) while the discharge current density was higher at 45 mA cm(-2). The battery power density was around 20 mW cm(-2) and the discharge current density was 25 mA cm(-2) for the unsulfonated samples. Therefore, the sulfonated microporous membranes could be tailored for the different electrochemical cell applications. (C) 2008 Elsevier B.V. All rights reserved.