Zinc–bromine battery

The zinc–bromine flow battery is a type of hybrid flow battery. A solution of zinc bromide is stored in two tanks. When the battery is charged or discharged the solutions (electrolytes) are pumped through a reactor stack and back into the tanks. One tank is used to store the electrolyte for the positive electrode reactions and the other for the negative. Zinc bromine batteries from different manufacturers have energy densities ranging from 34.4–54 W·h/kg.

The predominantly aqueous electrolyte is composed of zinc bromide salt dissolved in water. During charge, metallic zinc is plated from the electrolyte solution onto the negative electrode surfaces in the cell stacks. Bromide is converted to bromine at the positive electrode surface and is stored in a safe, chemically complexed organic phase in the electrolyte tank. Each high-density polyethylene (HDPE) cell stack has up to 60 bipolar, plastic electrodes between a pair of anode and cathode end blocks.

The zinc–bromine battery can be regarded as an electroplating machine. During charging zinc is electroplated onto conductive electrodes, while at the same time bromine is formed. On discharge the reverse process occurs, the metallic zinc plated on the negative electrodes dissolves in the electrolyte and is available to be plated again at the next charge cycle. It can be left fully discharged indefinitely without damage.