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Latest formulation reveals improved liquid battery

Posted: 23 Sep 2014 ?? ?Print Version ?Bookmark and Share

Keywords:MIT? liquid battery? formulation? antimony? electrode?

A team of researchers at MIT has improved a proposed liquid battery system that could allow renewable energy sources to compete with conventional power plants. According to them, they have also started a company to produce electrical-grid-scale liquid batteries, whose layers of molten material automatically separate due to their differing densities. But the new formula, published in the journal Nature by Donald Sadoway, former postdocs Kangli Wang and Kai Jiang, and seven others, substitutes different metals for the molten layers used in a battery previously developed by the team.

Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT, together with colleagues, said the formula allows the battery to work at a temperature more than 200°C lower than the previous formulation. In addition to the lower operating temperature, which should simplify the battery's design and extend its working life, the formulation will be less expensive to make, he noted.

Liquid metal battery

A physical model of the liquid metal battery at room temperature, in a glass container. The bottom layer is the positive electrode. In the real battery this is an alloy of antimony and lead, represented here by mercury. The middle layer is the electrolyte, in reality, a mixed molten salt; here, a solution of salt in water. The top layer is the current collector of the negative electrode, a metal mesh of iron-nickel alloy. (Image: Felice Frankel)

The battery uses two layers of molten metal, separated by a layer of molten salt that acts as the battery's electrolyte (the layer that charged particles pass through as the battery is charged or discharged). Because each of the three materials has a different density, they naturally separate into layers, like oil floating on water.

The original system, using magnesium for one of the battery's electrodes and antimony for the other, required an operating temperature of 700°C. But with the latest formulation, with one electrode made of lithium and the other a mixture of lead and antimony, the battery can operate at temperatures of 450-500°C.

Extensive testing has shown that even after 10 years of daily charging and discharging, the system should retain about 85 per cent of its initial efficiency, a key factor in making such a technology an attractive investment for electric utilities.

Presently, the only widely used system for utility-scale storage of electricity is pumped hydro, in which water is pumped uphill to a storage reservoir when excess power is available, and then flows back down through a turbine to generate power when it is needed. Such systems can be used to match the intermittent production of power from irregular sources, such as wind and solar power, with variations in demand. Because of inevitable losses from the friction in pumps and turbines, such systems return about 70 per cent of the power that is put into them (which is called the "round-trip efficiency").

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