Technology

The zinc/bromine battery is very different in concept and design from more traditional batteries such as the lead/acid battery. The battery is based on the reaction between two commonly available chemicals, zinc and bromine.

The battery consists of a zinc negative electrode and a bromine positive electrode separated by a microporous separator. An aqueous solution of zinc/bromide is circulated through the two compartments of the cell from two separate reservoirs. The electrolyte stream in contact with the positive electrode contains bromine which is maintained at the desired concentration by equilibrating with a bromine storage medium (Figure 1.). The bromine storage medium is immiscible with an aqueous solution containing zinc bromide. All battery components are made from a bromine inert plastic (Figure 2.).

Figure 1: The Flowing Electrolyte System

Figure 2: Battery Stack Assembly

Unlike the lead acid and most other batteries, the zinc/bromine battery uses electrodes that cannot and do not take part in the reactions but merely serve as substrates for the reactions. There is therefore no loss of performance, as in most rechargeable batteries, from repeated cycling causing electrode material deterioration. When the zinc/bromine battery is completely discharged all the metal zinc plated on the negative electrodes is dissolved in the electrolyte and again produced the next time the battery is charged. In the fully discharged state the zinc/bromine battery can be left indefinitely.
The zinc/bromine battery offers 2 to 3 times the energy density (75 to 85 watt-hours per kilogram) with associated size and weight savings over present lead/acid batteries. The power characteristics of the battery can be modified, for selected applications. Therefore, the zinc/bromine battery has operational capabilities which make it extremely useful as a multi-purpose energy storage option.