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Liquid batteries to make renewables more viable

Posted: 16 Feb 2012     Print Version  Bookmark and Share

Keywords:research  renewable energy  liquid batteries 

MIT researchers have developed a new system that could level the load from intermittent renewable energy sources such as solar or wind. The system uses high-temperature batteries whose liquid components naturally settle into distinct layers because of their different densities.

The three molten materials form the positive and negative poles of the battery, as well as a layer of electrolyte—a material that charged particles cross through as the battery is being charged or discharged—in between. All three layers are composed of materials that are abundant and inexpensive.

"We explored many chemistries looking for the right combination of electrical properties, abundant availability and differences in density that would allow the layers to remain separate," explained Donald Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT, and the senior author of the new paper in the Journal of the American Chemical Society.

"We have found a number of promising candidates," he said, "and are publishing their detailed analysis of one such combination: magnesium for the negative electrode (top layer), a salt mixture containing magnesium chloride for the electrolyte (middle layer) and antimony for the positive electrode (bottom layer)." The system would operate at a temperature of 700°C, or 1,292 degrees Fahrenheit.

In this formulation, the battery delivers current as magnesium atoms lose two electrons, becoming magnesium ions that migrate through the electrolyte to the other electrode. There, they reacquire two electrons and revert to ordinary magnesium atoms, which form an alloy with the antimony. To recharge, the battery is connected to a source of electricity, which drives magnesium out of the alloy and across the electrolyte, where it then rejoins the negative electrode.

The team is continuing to work on optimising all aspects of the system, including the containers used to hold the molten materials and the ways of insulating and heating them, as well as ways of reducing the operating temperature to help cut energy costs. "We've discovered ways to decrease the operating temperature without sacrificing electrical performance or cost," Sadoway added.

"People in the battery industry don't know anything about electrolytic smelting in molten salts. Most would think that high-temperature operation would be inefficient."

Sadoway, along with Bradwell, has founded a company, Liquid Metal Battery Corp, to bring this technology to commercialisation. "If this technology succeeds," he claimed, "it could be a game-changer" for renewable energy.

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