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Novel Formulation Leads to Promising Liquid Metal Battery

MIT Liquid Battery

Image credit: Liquid metal battery at room temperature staging to convey design. Antimony-lead alloy bottom layer (positive electrode), mixed molten salt middle layer (electrolyte), and a metal mesh top layer (negative electrode) to collect the current / Felice Frankel

According to the article published in the latest edition of Nature this week, after several years’ efforts, researchers from MIT team have found an inexpensive and liquid-metal battery which is capable of storing energy from irregular and renewable sources like wind and solar in the electrical grid. Such battery is the combination of liquid-metal electrodes and the molten electrolyte with a high-performance metal called as antimony together with low-cost lead. The application of this battery would eventually ensure intermittent renewable energy sources to be engaged in competition with conventional power plants.

Batteries in the all-liquid built-up type consist of layers of molten material which could separate automatically, like oil and vinegar, because their densities are different. Acting as one positive electrode, one negative electrode, these two layers of molten metal would be separated by a layer of molten sodium chloride as the electrolyte battery- the layer that charged particles pass through when the battery is being charged and discharged.

In comparison of the widely-used solid-state ones, these all-liquid batteries have some potential advantages, such as the longer life cycle, and being easily manufactured as big-sized storage systems. Donald Sadoway’s team from MIT has already developed such a battery by application of an antimony-magnesium electrode. Although this system was somehow efficient, it required temperatures going up to 700 degrees Celsius owning to the high melting temperature of the antimony-magnesium alloy,

In order to perfect their liquid battery system, Sadoway and his colleagues manufactured a new battery replacing magnesium with lead and such battery was characteristic of cheapness and lower melting temperature. This novel formulation could enable the battery to operate at 450 to 500 degrees Celsius.

(A physical model is pictured here: The positive electrode (bottom) is a molten alloy of antimony and lead, the negative electrode (top) is liquid lithium, and the electrolyte between them is mixture of molten salts.)

The reduced working temperature as well as would ensure a simpler design and longer operating life of the battery, on the other hand, its desirable performance characteristics would be maintained. As antimony could generate a high working voltage, the system would return nearly 70 percent of the power which was put into it. In addition, experiments demonstrated that even after a decade of charging and discharging on a daily basis, the system could keep 85 percent of its initial efficiency.

In the interview with Nature, Sadoway said that the cost for per kilowatt-hour of electricity produced by a large-sized molten-metal unit would be around $500. As the team was better familiar with the liquid metals bond, it was trying to find out other metal combinations which could provide the systems of lower cost, lower temperature and higher efficiency.

Source: MIT News, Nature

Journal reference: Wang, Kangli, et al. “Lithium-antimony-lead liquid metal battery for grid-level energy storage.” Nature (2014).