The team, led by MIT Professor of Materials Chemistry Donald Sadoway, has developed a liquid-metal based battery made from magnesium, antimony and a salt mixture containing magnesium chloride.
The three materials have variable densities, causing them to naturally settle into three distinct layers. The top and bottom layers (antimony and magnesium) form the positive and negative poles of the battery, and the middle layer (the salt mixture) forms the electrolyte—the material through which charged particles cross as the battery is charged or discharged.
As the battery discharges, the magnesium atoms lose two electrons, becoming magnesium ions. These ions migrate through the electrolyte to the positive electrode. There, they gain two electrons and revert to ordinary magnesium atoms, forming an alloy with the antimony. When the battery is connected to a source of electricity, the magnesium is then driven out of the alloy across the electrolyte, where it rejoins the negative electrode.
Contrary to most battery systems, which do not function well at high temperatures, Sadoway's system was inspired by his earlier work on the electrochemistry of industrial aluminum smelting, which of course involves very high temperatures. Designed to operate at temperatures as high as 1,292 degrees Fahrenheit, Sadoway says the new battery process is akin to "run[ning] the smelter in reverse."
The team isn't the first to research liquid-battery systems, but Sadoway says he and his team are the first to produce a functional storage system using this approach. Over the past three years, the team has gradually scaled up its experiments from shot glass-sized cells to cells the size of a hockey puck (three inches in diameter and an inch thick).
Now, the team has started testing a six-inch-wide prototype, with 200 times the power-storage capacity of the original version. The team is continuing to work on further perfecting methods of insulating and heating the containers used to hold the molten materials, as well as ways of reducing the operating temperature to help cut energy costs.
The work has been funded by grants from the Deshpande Center for Technological Innovation at MIT, the Chesonis Family Foundation and the U.S. Department of Energy. Sadoway has founded a company, Liquid Metal Battery Corp., and is taking a year of sabbatical to work on trying to commercialize the technology. "If this technology succeeds, it could be a game-changer," he said.