New Type Battery Designed for Solar, Wind Grid Storage

(National Renewable Energy Laboratory)

Engineers at Stanford University and Stanford’s SLAC National Accelerator Laboratory developed a lower-cost design for long term storage of wind and solar energy on the power grid. The team led by Yi Cui, a materials science and engineering professor at Stanford and part of a joint materials and energy science institute at SLAC, published its findings in the May 2013 issue of the journal Energy & Environmental Science (paid subscription required).

The electrical power grid in the U.S. is not yet set up to accept power in large quantities from wind and solar sources because of their intermittent nature and wide variations in available sunshine and wind. While the contributions of solar and wind energy are increasing as sources of electric power, they need more advanced energy management systems to smooth out these fluctuations by storing excess energy and discharging it when input slows or stops.

One technology with potential for managing these fluctuations is the flow battery that in current designs pumps liquids from two different chambers through a central chamber, where molecules in the solutions react chemically to either store or discharge energy. A membrane in the central chamber allows ions not used in the chemical reactions to pass back and forth, but keeps the active ions separate.

The current technology has important drawbacks, however. The solutions use rare materials, such as vanadium, which make the technology expensive when deployed in large quantities — a requirement for grid storage — and the membrane requires frequent maintenance.

Cui and colleagues created a flow battery with a simpler design, using less expensive materials. The Stanford/SLAC battery has only one chamber and no membrane to separate the active ions, and is based on more plentiful and less expensive lithium and sulfur.

The lithium polysulfides in the battery interact with a piece of lithium metal coated with a barrier that permits electrons to pass without degrading the metal. The entire stream of molecules in the battery is dissolved in an organic solvent, which reduces the problems of corrosion encountered with water-based flow batteries. When the battery charges, lithium ions from the lithium polysulfide molecules are added into the liquid; when discharging the lithium polysulfides absorb the lithium ions from the liquid.

The research term conducted a demonstration of the battery in a proof-of-concept test reported in the Energy & Environmental Science paper. In the demonstration, using a small-scale model, adding a lithium polysulfide solution immediate produces an electric current that illuminates an LED bulb. “In initial lab tests,” says Cui, “the new battery also retained excellent energy-storage performance through more than 2,000 charges and discharges, equivalent to more than 5.5 years of daily cycles.”

Cui’s lab group plans to make a laboratory-scale system to maximize the amount of energy the battery can store, and identify likely engineering issues, when trying to scale up the battery to an operational size. The researchers believe a utility version of the new battery can be scaled up to store many megawatt-hours of energy, and plan to start discussions with potential hosts for a full-scale field-demonstration unit.

In the following video, Ph.D. candidate Wesley Zhang demonstrates the proof-of-concept battery model.

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