Published on April 25th, 2013 | by SLAC National Accelerator Laboratory


Battery Design Could Help Solar And Wind Power The Grid

April 25th, 2013 by  

This post first appeared on the SLAC National Accelerator Laboratory website
by Mike Ross

Researchers from the US Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have designed a low-cost, long-life battery that could enable solar and wind energy to become major suppliers to the electrical grid.

Yi Cui with an experimental battery at Stanford University

“For solar and wind power to be used in a significant way, we need a battery made of economical materials that are easy to scale and still efficient,” said Yi Cui, a Stanford associate professor of materials science and engineering and a member of the Stanford Institute for Materials and Energy Sciences, a SLAC/Stanford joint institute. “We believe our new battery may be the best yet designed to regulate the natural fluctuations of these alternative energies.”

The Ideal Batteries for Grid-Scale Solar & Wind

Currently the electrical grid cannot tolerate large and sudden power fluctuations caused by wide swings in sunlight and wind. As solar and wind’s combined contributions to an electrical grid approach 20 percent, energy storage systems must be available to smooth out the peaks and valleys of this “intermittent” power – storing excess energy and discharging when input drops.

Among the most promising batteries for intermittent grid storage today are “flow” batteries, because it’s relatively simple to scale their tanks, pumps and pipes to the sizes needed to handle large capacities of energy. The new flow battery developed by Cui’s group has a simplified, less expensive design that presents a potentially viable solution for large-scale production.

Today’s flow batteries pump two different liquids through an interaction chamber where dissolved molecules undergo chemical reactions that store or give up energy. The chamber contains a membrane that only allows ions not involved in reactions to pass between the liquids while keeping the active ions physically separated. This battery design has two major drawbacks: the high cost of liquids containing rare materials such as vanadium – especially in the huge quantities needed for grid storage – and the membrane, which is also very expensive and requires frequent maintenance.

Flow battery designs

These diagrams compare Stanford/SLAC’s new lithium-polysulfide flow battery design with conventional “redox” flow batteries. The new flow battery uses only one tank and pump and uses a simple coating instead of an expensive membrane to separate the anode and cathode. (Credit: Greg Stewart/SLAC)

New Chemistry

The new Stanford/SLAC battery design uses only one stream of molecules and does not need a membrane at all. Its molecules mostly consist of the relatively inexpensive elements lithium and sulfur, which interact with a piece of lithium metal coated with a barrier that permits electrons to pass without degrading the metal. When discharging, the molecules, called lithium polysulfides, absorb lithium ions; when charging, they lose them back into the liquid. The entire molecular stream is dissolved in an organic solvent, which doesn’t have the corrosion issues of water-based flow batteries.

“In initial lab tests, 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 said.


To demonstrate their concept, the researchers created a miniature system using simple glassware. Adding a lithium polysulfide solution to the flask immediately produces electricity that lights an LED. A utility version of the new battery would be scaled up to store many megawatt-hours of energy. (Credit: SLAC National Accelerator Laboratory)

In the future, Cui’s group plans to make a laboratory-scale system to optimize its energy storage process and identify potential engineering issues, and to start discussions with potential hosts for a full-scale field-demonstration unit.

Cui and colleagues report their research results, some of the earliest supported by the DOE’s new Joint Center for Energy Storage Research battery hub, in the May issue of Energy & Environmental Science.

Yi Cui with an experimental battery at Stanford University

Citation: Yuan Yang, Guangyuan Zheng and Yi Cui, Energy Environ. Sci., 2013 (10.1039/C3EE00072A)

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About the Author

programs explore the ultimate structure and dynamics of matter and the properties of energy, space and time -- at the smallest and largest scales, in the fastest processes and at the highest energies -- through robust scientific programs, excellent accelerator-based user facilities and valuable partnerships. Located in Menlo Park, California, SLAC is operated by Stanford University for the U.S. Department of Energy Office of Science.

  • Ronald Brakels

    I see the 20% figure for penetration is still being thrown around. This example is particularly bad as it is used for wind and solar combined. It has been years since wind power has demonstrated that grids are not limited to 20% and that wind and solar don’t cause wild fluctuations that grids can’t handle. There’s no need for this. It doesn’t stop low cost batteries being astoundingly useful even if grids can handle much more than 20% penetration by wind and solar without storage.

    • Ronald Brakels

      I’ll mention that here in South Australia, thanks to wind, the wholesale price of electricity in the state has been either zero or under a cent a kilowatt-hour for over 24 hours, except for our midnight peak caused by everyone’s off peak hot water systems coming on at the same time and causing a peak. I believe this is before payments for exports to the neighbouring state are included, so the wind farms are still making some money. Now if the connectors with the next state were maxed out, which is a possibility, it does mean that some wind power could have been curtailed. Low cost energy storage could be used to stop that output being wasted, but it would have to be quite cheap to pay for itself. I hope this battery design is cheap enough to be cost effective, because just at this moment energy storage isn’t cheap enough to make it cost effective to install it here. (At least not utility scale storage.)

      Note that curtailing a little wind power every now and then is not the same as the grid being unable to handle it. Our coal power has a habit of causing negative price events and no one goes around saying the grid can’t handle more than a certain percentage of coal. (The ecosystem can’t handle coal power, but that’s a seperate issue. A monstrous huge issue, but a separate issue nonetheless.)

      • Ronald Brakels

        Gosh darn it! I misread the chart. While the cost of electricity was zero at times yesterday it did spend most of the day above one cent a kilowatt-hour. During the midnight spike it briefly went up to $2.20 a kilowatt-hour. But tomorrow, being a pleasent, breezy weekend day, electricity prices are forcast to be zero for much of the day.

        • bob

          You don’t know what you’re talking about, this new Battery will save the planet mate.

    • Yes. Unfortunately, it seems that university press rooms are especially bad about setting up out-of-date problems. I assume the reasons are 1) they need to show they are solving a problem; 2) when the research began, the problem was different, but the initial “case” for the research carries through all the way to this stage.

  • Sounds great, although, as I heard, grid-storage applications require more cycles due to economic maintenance requirements.

    Of course, this battery may be very easy to maintain after 200 cycles (replacing the solvent and possibly the separator.

    • Bob_Wallace

      My understanding of battery stuff is that a “cycle” is a 100% charge to 100% discharge and back to 100% charged. Partial discharges (down 20%, for example) are roughly cumulative.

      I think the 5.5 year estimate for 2,000 cycles is low. Many days grid storage batteries will perform two cycles, one to bring nighttime wind to the morning peak and another to bring daytime solar to late afternoon/early evening. Not everyday, but often. 2,000 cycles might mean more like a 3 year lifespan.

      If they are used for grid smoothing then they might acquire a different number of cycles per year.

      Cheap chemicals. Design them for quick drains and refills. JiffyLube….

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