Donald Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT, has earned much recognition this year for his pioneering work on an entirely new type of battery, a promising technology that could work at far lower cost and with greater longevity than previous methods. The system is a high-temperature battery whose liquid components, like some novelty cocktails, 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 abundant and inexpensive materials.
“We explored many chemistries,” Sadoway says, looking for the right combination of electrical properties, abundant availability and differences in density that would allow the layers to remain separate.
His team has found a number of promising candidates, he says, and is 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 degrees Celsius, or 1,292 degrees Fahrenheit.
In this formulation, Sadoway continues, 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.
This innovative approach earned Sadoway a coveted spot at this year’s TED talks; a video of his remarks garnered more than 440,000 views in its first three weeks online. And in spring 2012, Time magazine included Sadoway in its annual list of “the 100 most influential people in the world.”
Sadoway’s liquid battery project has also garnered more than $13 million in government and industry funding, partly from the French energy company Total, provided through the MIT Energy Initiative (not counting money raised by a company founded to commercialize the technology---half of which came from Bill Gates, who watched Sadoway’s lectures via MIT OpenCourseWare).
Sadoway, the son of second-generation Ukrainian immigrants, was the first member of his family to attend college, let alone teach at one.
His parents ran a motel in a small town outside Toronto. His mother was a high school graduate, but his maternal grandmother was illiterate, having had a year or two of schooling at most.
“The gene pool doesn’t turn over in two generations,” he states. “The only difference between us was opportunity.”
Maybe that rise from modest origins helped spur Sadoway’s tendency to go against the grain. He suggests that one reason his TED talk has become so popular is because of its underlying message “that you could develop a leading-edge technology by ignoring the professionals and putting together your own team of novices,” he says.
The “professionals” in battery technology were indeed skeptical of Sadoway’s liquid-battery concept when he first started working on it around 2005. For one thing, conventional wisdom held that for any manufactured product, the way to achieve economies of scale was to build large numbers of small things.
The electric utility companies that would ultimately be the users of this technology, “don’t care what the stuff is made of, or what the size is. The only question is what’s the cost of storage” for a given amount of power. “I can build a gorgeous battery to a NASA price point,” he says — but when cost is the primary driver, “that changes the search” for the best materials. Just based on the rarity and cost of some elements, “large sections of the periodic table are off limits.”
By taking the opposite tack, Sadoway looked toward building fewer and bigger things. “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.”
Furthermore, his technology’s operating temperature--many hundreds of degrees Fahrenheit, required to keep the metal electrodes molten--was seen as an energy-draining showstopper: You’d need so much energy to keep the thing hot, experts reasoned, that this drain would counteract any gains in efficiency you might get.
Over the last three years, Sadoway and his team--including MIT Materials Processing Center Research Affiliate David Bradwell M.Eng.’06, Ph.D. ’11, the lead author of the new paper published in the Journal of the American Chemical Society--have gradually scaled up their experiments. Their initial tests used batteries the size of a shot glass; they then progressed to cells the size of a hockey puck, three inches in diameter and an inch thick, and next a six-inch-wide version, with 200 times the power-storage capacity of the initial version.
The inspiration for the concept came from Sadoway’s earlier work on the electrochemistry of aluminum smelting, which is conducted in electrochemical cells that operate at similarly high temperatures.
Many decades of operation have proved that such systems can operate reliably over long periods of time at an industrial scale, producing metal at very low cost. In effect, he says, what he figured out was “a way to run the smelter in reverse.”
Sparked by a suggestion from MIT colleague Gerbrand Ceder, Sadoway set out to see if this concept could be made to work as a battery system.
Most people in that situation, he says, would probably have hired top experts in the fields of electrochemistry and smelting to carry out the research. Sadoway took the opposite route, hiring students.
“They were not just any youngsters,” he explains, “they were youngsters at MIT. Nonetheless, they were novices”---and therefore didn’t quite realize how daunting the task might be. And besides, he says, “they believed that if this worked, it could change the world.”
Robert Huggins, a professor emeritus of materials science and engineering at Stanford University, says, “As for any radically different approach, there are a number of new practical problems to solve in order for it to become a practical alternative for use in large-scale energy storage, [including] electrolyte evaporation, and corrosion and oxidation of components, as well as the ever-present issue of cost.” Nevertheless, he says, this is “a very innovative approach to electrochemical energy storage, and it is being explored with a high degree of sophistication.”
“They worked miracles,” Sadoway says of his team. And the recognition he’s been getting this year, he says, is “about them, it’s not about me. It’s the group.”
The team is continuing to work on optimizing 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 says.
David Chandler, MIT News Office