Publications Details

Durability of polymeric materials used in zinc/bromine flow batteries

Arnold Jr., Charles

The lifetimes of zinc/bromine flow batteries may be limited by the durability of components which are fabricated from thermoplastic materials and exposed to bromine-containing electrolytes. Examples of such components are flowframes and carbon-filled plastic electrodes. In early versions of the zinc/bromine battery, flowframes and electrodes were made from copolymers of propylene and ethylene. In later versions of the zinc/bromine battery, these materials were replaced by poly(vinyl chloride) (PVC) and polyethyle (flowframes) and polyethylene as the plastic component in electrodes. We found that carbon-plastic electrodes made from polypropylene rich copolymers were swelled and chemically attacked by the bromine-containing electrolytes. As a result, warpage occurred and the battery failed. On the basis of accelerated aging studies we estimated the lifetimes of the electrode and its polypropylene based component to be 96 and 10 months, respectively. The enhanced stability of the electrode was attributed to the presence of carbon which is known to be an antioxidant for thermoxidation. In accelerated exposure tests, bromine-containing electrolytes were also found to attack and leach out the additives used in PVC flowframes. PVC itself was only slightly degraded by the electrolyte. A commercial fluorocarbon, TefzelR, which contains no additives, was determined to be stable in bromine-containing electrolytes and is recommended as a replacement for PVC. Currently, aging studies on carbonfilled polyethylene electrodes are in progress.