Abstract
Substrate compositions having a polymeric matrix, a reinforcing compo nent, and a conductive filler were developed for bipolar electrodes to be used in zinc- bromine battery systems. Among the various possible composite combinations, those based on carbon black as a conductive filler were given special attention. They combine the inherent properties of polymers—such as toughness, flexibility, low density, etc—with a high conductivity (σ = 0.2 to 1 ohm-1-cm-1). One of the problems recognized with the use of bipolar electrodes containing high surface area carbon blacks in zinc-bromide bat teries is the warpage of the electrodes. Under service conditions, warpage causes an uneven flow distribution of the electrolyte on the electrode surface and results in loss of cell capacity at low cycle life. The warpage was found to occur because of physical expan sion of electrodes resulting from bromine absorption by the high surface area carbon black. Composite substrate compositions with excellent dimensional stability that have eliminated electrode warpage as the primary battery failure mechanism were prepared by using two novel thermoplastic-composite fabrication techniques.