When the battery is fully discharged, both tanks hold the same electrolyte solution: a mixture of positively charged zinc ions () and negatively charged iodide ion, (). When charged, one tank holds another negative ion, polyiodide, (). The battery produces power by pumping liquid from external tanks into the battery's stack area where the liquids are mixed. Inside the stack, zinc ions pass through a selective membrane and change into metallic zinc on the stack's negative side. To further increase the energy density of the zinc-iodide flow battery, bromide ions () are used as the complexing agent to stabilize the free iodine, forming iodine-bromide ions () as a means to free up iodide ions for charge storage.