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Storing megawatts: Liquid-metal batteries and electricity
Making aluminum requires a lot of electricity. That’s because the metal bonds tightly to oxygen and it takes a lot of energy to break that bond. In essence, the process of making aluminum is a giant battery with the silvery metal being reduced to purity at the cathode while oxygen bonds with the carbon anode to make, you guessed it, CO2. It takes roughly 15 kilowatt-hours of electricity to make just one kilogram of aluminum via electrolysis.
"What’s a big current sink? Aluminum smelters," explained Luis Ortiz, research director for materials scientist Donald Sadoway at the Massachusetts Institute of Technology (M.I.T.), at last week’s ARPA-E summit. "Maybe the aluminum industry is sitting on the answer [to large-scale electricity storage] all along."
Unfortunately, thanks to that CO2 gas floating away, this aluminum-making process turns out to be a very bad battery—it is simply not reversible. But David Bradwell, a graduate student in Sadoway’s lab, tweaked the process to involve liquid metals for the anode, cathode and even electrolyte and evolved a battery that has a high charge transfer, long life and costs "below $100 per kilowatt-hour," according to Ortiz. "It is as good or better than lithium ion in energy density but cheaper than lead acid."
Funding from ARPA-E will allow the researchers to take the liquid-metal battery from a "shot glass size cell to a pizza box cell," Ortiz said, and bring the concept closer to the goal of storing electricity at a cost of roughly $50 per kilowatt-hour. But as it stands "we get the energy back we put into it with reasonable efficiency."
And that could mean big things for storing electricity, as well as generating it from renewable but intermittent resources such as sunshine and wind. As Secretary of Energy Steven Chu told ScientificAmerican.com, "without energy storage, you can’t have a renewable electricity grid where perhaps 30, 40, 50 percent plus is coming from renewables."
Editor’s Note: David Biello is the host of a forthcoming series on PBS, tentatively titled "The Future of Electricity". The series will explore how transformation is coming to how we use and produce electricity, impacting the environment, national security and the economy. Detroit Public Television provided the video outtake embedded in this post.