The batteries are envisioned to be smaller-scale versions of the utility-scale batteries being developed by Donald Sadoway, John F. Elliott Professor of Materials Chemistry at MIT, which recently received a $6.9-million award from the Department of Energy’s ARPA-E. (Earlier post.)

The ARPA-E award is supported the development of the liquid metal grid-scale battery for low-cost, large scale storage of electrical energy. This new class of batteries could enable continuous power supply from renewable energy sources, such as wind and solar and a more stable, reliable grid.

The Total-MIT research project is primarily focused on development of a low-cost, long-life battery suited to store the power generated by solar panels. The ability to store power is a major challenge and an essential ingredient for the scale up and widespread deployment of affordable solar power.

Sadoway’s basic principle is to place three layers of liquid inside a container: two different metal alloys, and one layer of a salt. The three materials are chosen so that they have different densities that allow them to separate naturally into three distinct layers, with the salt in the middle separating the two metal layers.

The energy is stored in the liquid metals that want to react with one another but can do so only by transferring ions across the electrolyte, which results in the flow of electric current out of the battery. When the battery is being charged, some ions migrate through the insulating salt layer to collect at one of the terminals. Then, when the power is being drained from the battery, those ions migrate back through the salt and collect at the opposite terminal.

The whole device is kept at a high temperature, around 700 °Celsius, so that the layers remain molten. In the small devices being tested in the lab, maintaining this temperature requires an outside heater, but Sadoway says that in the full-scale version, the electrical current being pumped into, or out of, the battery will be sufficient to maintain that temperature without any outside heat source.

Sadoway’s all-liquid metal battery is based on low-cost, domestically available liquid metals. The initial prototype used antimony on the bottom, an electrolyte such as sodium sulfide in the middle, and magnesium at the top. The researchers have since switched. The team is now testing a number of different variations of the exact composition of the materials in the three layers, and of the design of the overall device.

While some previous battery technologies have used one liquid-metal component, this is the first design for an all-liquid battery system, Sadoway says.

Resources

• TR10: Liquid Battery (MIT Tech Review, March/April 2009)