TR10: Liquid Battery
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Discharged, charging, charged: The molten active components (colored bands: blue, magnesium; green, electrolyte; yellow, antimony) of a new grid-scale storage battery are held in a container that delivers and collects electrical current (left). Here, the battery is ready to be charged, with positive magnesium and negative antimony ions dissolved in the electrolyte. As electric current flows into the cell (center), the magnesium ions in the electrolyte gain electrons and form magnesium metal, which joins the molten magnesium electrode. At the same time, the antimony ions give up electrons to form metal atoms at the opposite electrode. As metal forms, the electrolyte shrinks and the electrodes grow (right), an unusual property for batteries. During discharge, the process is reversed, and the metal atoms become ions again.
As power flows into the battery, magnesium and antimony metal are generated from magnesium antimonide dissolved in the electrolyte. When the cell discharges, the metals of the two electrodes dissolve to again form magnesium antimonide, which dissolves in the electrolyte, causing the electrolyte to grow larger and the electrodes to shrink (see above).
Sadoway envisions wiring together large cells to form enormous battery packs. One big enough to meet the peak electricity demand in New York City–about 13,000 megawatts–would fill nearly 60,000 square meters. Charging it would require solar farms of unprecedented size, generating not only enough electricity to meet daytime power needs but enough excess power to charge the batteries for nighttime demand. The first systems will probably store energy produced during periods of low electricity demand for use during peak demand, thus reducing the need for new power plants and transmission lines.
Many other ways of storing energy from intermittent power sources have been proposed, and some have been put to limited use. These range from stacks of lead-acid batteries to systems that pump water uphill during the day and let it flow back to spin generators at night. The liquid battery has the advantage of being cheap, long-lasting, and (unlike options such as pumping water) useful in a wide range of places. “No one had been able to get their arms around the problem of energy storage on a massive scale for the power grid,” says Sadoway. “We’re literally looking at a battery capable of storing the grid.”
Since creating the initial prototypes, the researchers have switched the metals and salts used; it wasn’t possible to dissolve magnesium antimonide in the electrolyte at high concentrations, so the first prototypes were too big to be practical. (Sadoway won’t identify the new materials but says they work along the same principles.) The team hopes that a commercial version of the battery will be available in five years.