Pumps are used to circulate the two electrolytes through separate electrodes, each made of a porous material that provides abundant surfaces on which the active species can react.
During charging, one species is “oxidized” (releases electrons), and the other is “reduced” (gains electrons) during discharging, they swap roles.
Each electrolyte contains dissolved “active species” - atoms or molecules that will electrochemically react to release or store electrons. (The ball is set free and allowed to roll down the hill.)Īt the core of a flow battery are two large tanks that hold liquid electrolytes, one positive and the other negative. (Think of a ball being pushed up to the top of a hill.) When the battery is being discharged, the transfer of electrons shifts the substances into a more energetically favorable state as the stored energy is released. When the battery is being charged, the transfer of electrons forces the two substances into a state that’s “less energetically favorable” as it stores extra energy. That design offers many benefits and poses a few challenges.Ī flow battery contains two substances that undergo electrochemical reactions in which electrons are transferred from one to the other. “A flow battery takes those solid-state charge-storage materials, dissolves them in electrolyte solutions, and then pumps the solutions through the electrodes,” says Fikile Brushett, an associate professor of chemical engineering at MIT. In the everyday batteries used in phones and electric vehicles, the materials that store the electric charge are solid coatings on the electrodes. Flow batteries have the potential for long lifetimes and low costs in part due to their unusual design. And because there can be hours and even days with no wind, for example, some energy storage devices must be able to store a large amount of electricity for a long time.Ī promising technology for performing that task is the flow battery, an electrochemical device that can store hundreds of megawatt-hours of energy - enough to keep thousands of homes running for many hours on a single charge.
Because those sources only generate electricity when it’s sunny or windy, ensuring a reliable grid - one that can deliver power 24/7 - requires some means of storing electricity when supplies are abundant and delivering it later when they’re not. In the coming decades, renewable energy sources such as solar and wind will increasingly dominate the conventional power grid.
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