Bromine-Based Flow Batteries for Long Duration Storage – Chemicals and Developments

Flow Batteries present an optimal energy storage vessel for large applications and long durations, due to the decoupling of energy and power in the battery. The energy is dependent on the amount of electrolyte and the power on the electrodes and cell design.

Elemental bromine as a strong oxidizer with reversible electrochemical activity is well suited for use in flow batteries. There are several bromine based technologies where the most dominant are the zinc bromine and hydrogen bromine technologies. Among the advantages of the bromine based batteries are the fire proof nature and high energy density.

The use of bromine in batteries raises several challenges in cell design, safety and operations. As an example, bromine is corrosive with high vapor pressure; this creates a safety concern and requires the use of specific anti-corrosive construction materials. Also, bromine is a liquid with a fairly low boiling temperature which limits the cell operating temperatures. These challenges can be dealt with using a bromine complexing agent (BCA) within the cell. Bromine complexing agent is a material that forms a meta-stable moiety, or complex, with the elemental bromine molecules. The complex is at a constant equilibrium between free and bound bromine which allows for a lower free bromine concentration to be available while maintaining a constant supply of bromine in the cell for operation. Lower concentration of free bromine lowers corrosiveness and vapor pressure allowing cheaper construction materials and simpler design of the battery. BCAs also enable work at higher temperatures, improving electrochemical efficiencies and negating expensive chillers.

We shall present a case study of tailoring BCA properties according to customer requests.