Publications Details

Durability of carbon-plastic electrodes for zinc/bromine storage batteries

Arnold Jr., C.

In previous work, failure of early versions of the zinc/bromine battery was traced to degradation and warpage of the carbon-plastic electrode. These electrodes were fabricated from copolymers of ethylene and propylene (EP) containing structures that were found to be susceptible to degradation by the electrolyte. In this work, we evaluated two developmental electrodes from Johnson Controls Battery Group, Inc., in which the EP copolymer was replaced with a high-density polyethylene (HDPE) that contained glass-fiber reinforcing fillers. The glass fiber content of these two electrodes was different (19% vs. 31%). We determined the effect of electrolyte on sorption behavior, dimensional stability, chemical stability, and thermal, mechanical, and electrical properties under real-time and accelerated aging conditions. We also characterized unaged samples of both electrodes to determine their chemical composition and physical structure. We found that high glass content in the electrode minimizes sorption and increases dimensional stability. Both high and low glass content electrodes were found to be chemically and thermally stable toward the electrolyte. A slight decrease in the storage modulus (G{prime}) of both electrodes was attributed to sorption of non-ionic and hydrophobic ingredients in the electrolyte. The electrical conductivity of both electrodes appeared to improve (increase) upon exposure to the electrolyte. No time or temperature trends were observed for the chemical, thermal, or mechanical properties of electrodes made from HDPE. Since decreases in these properties were noted for electrodes made from EP copolymers under similar conditions, it appears that the HDPE-based electrodes have superior long-term stability in the ZnBr{sub 2} environment.