A Battery Made of Molten Metals

Estimated reading time: 11 minutes

For Sadoway and then-graduate student David Bradwell MEng ’06, PhD ’11, the challenge was to choose the best materials for the new battery, particularly for its electrodes. Methods exist for predicting how solid metals will behave under defined conditions. But those methods “were of no value to us because we wanted to model the liquid state,” says Sadoway — and nobody else was working in this area. So he had to draw on what he calls “informed intuition,” based on his experience working in electrometallurgy and teaching a large freshman chemistry class.

To keep costs down, Sadoway and Bradwell needed to use electrode materials that were earth-abundant, inexpensive, and long-lived. To achieve high voltage, they had to pair a strong electron donor with a strong electron acceptor. The top electrode (the electron donor) had to be low density, and the bottom electrode (the electron acceptor) high density. “Mercifully,” says Sadoway, “the way the periodic table is laid out, the strong electropositive [donor] metals are low density, and the strong electronegative [acceptor] metals are high density” (see Figure 2 in the slideshow above). And finally, all the materials had to be liquid at practical temperatures.

As their first combination, Sadoway and Bradwell chose magnesium for the top electrode, antimony for the bottom electrode, and a salt mixture containing magnesium chloride for the electrolyte. They then built prototypes of their cell — and they worked. The three liquid components self-segregated, and the battery performed as they had predicted. Spurred by their success, in 2010 they, along with Luis Ortiz SB ’96, PhD ’00, also a former member of Sadoway’s research group, founded a company — called initially the Liquid Metal Battery Corporation and later Ambri — to continue developing and scaling up the novel technology.

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