A new type of sodium-ion battery could prove to be a practical option for storing power from wind and solar farms, says Jay Whitacre, a professor of materials science and engineering at Carnegie Mellon University. Whitacre's startup, 44 Tech, based in Pittsburgh, PA, will receive $5 million from the U.S. Department of Energy, as part of the 2009 Recovery Act, to develop the technology. The funding, announced last week, is part of a $620 million package for improving the electricity grid.

The startup's batteries could be not only cheaper but also longer-lasting than existing batteries, Whitacre says. This would make them particularly useful for storing large amounts of electricity cheaply--something that will be essential for making renewable energy the primary source of energy in the U.S., rather than just the supplemental source it is now. Such storage will make it practical to store energy from wind turbines and solar farms for use when the wind isn't blowing and the sun isn't shining.

Whitacre's sodium-ion cells are similar in some ways to lithium-ion cells--the type used in portable electronics and in some electric vehicles. In both types of cell, ions are shuttled between the battery's positive and negative electrodes during charging and discharging, with an electrolyte serving as the medium for moving those ions. But because sodium is orders of magnitude more abundant than lithium, it is cheaper to use. To make the cells cheaper still, Whitacre plans to operate them at lower voltages, so that water-based electrolytes can be used instead of organic electrolytes. This should further decrease manufacturing costs, since water-based electrolytes are easier to work with.

The change to water-based electrolytes could also make it possible to eliminate much of the supporting material needed in conventional lithium-ion cells, again reducing costs. This is because increasing the ionic conductivity makes it possible to use thicker electrodes with fewer layers of separating and current-collecting materials inside the cell.

"In principle, a sodium-ion system can be low-cost, and with aqueous electrolytes, it could be really low-cost," says Jeff Dahn, a professor of physics and chemistry at Dalhousie University in Nova Scotia, Canada.