New type of ‘flow battery’ can store 10 times the energy of the next best device
Industrial-scale batteries, known as flow batteries, could one day usher in widespread use of renewable energy—but only if the devices can store large amounts of energy cheaply and feed it to the grid when the sun isn’t shining and the winds are calm. That’s something conventional flow batteries can’t do. Now, researchers report that they’ve created a novel type of flow battery that uses lithium ion technology—the sort used to power laptops—to store about 10 times as much energy as the most common flow batteries on the market. With a few improvements, the new batteries could make a major impact on the way we store and deliver energy.
Flow batteries aren’t much different from the rechargeables we’re all used to, aside from their massive size. In conventional rechargeables, electrical charges are stored in an electrode called an anode. When discharged, electrons are pulled off the anode, fed through an external circuit where they do work, and returned to a second electrode called a cathode. Liquid electrolytes between the electrodes ferry ions through the battery to balance the charges. The batteries can be recharged by plugging them in, which forces the charges—and the ions—to flow in reverse.
But in flow batteries, the charges are stored in liquid electrolytes that sit in external tanks. The charge-carrying electrolytes are then pumped through an electrode assembly, known as a stack, containing two electrodes separated by an ion-conducting membrane. This setup allows large volumes of the electrolytes to be stored in the tanks. Because those tanks have no size limit, the storage capacity of a flow battery can be scaled up as needed. That makes them ideal for storing large amounts of power for the grid.
Today, the most advanced flow batteries are known as vanadium redox batteries (VRBs), which store charges in electrolytes that contain vanadium ions dissolved in a water-based solution. Vanadium’s advantage is that its ions are stable and can be cycled through the battery over and over without undergoing unwanted side reactions. But vanadium is costly, and VRBs have a relatively low energy density. This means that the external tanks must be quite large to hold enough power to be useful.