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  News in Brief

   11 Physics Questions for the New Century

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  A New Way to Visualize Cells

  Astrophysicists Explore Supernovae

  Long-Life Rechargeable Batteries

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This issue...

  News in Brief

   11 Physics Questions for the New Century

   View from the Inside

  Better Airport Security

  A New Way to Visualize Cells

  Astrophysicists Explore Supernovae

  Long-Life Rechargeable Batteries

  People

  About

  Subscribe Free

Working Science

Long-Life Rechargeable Batteries

by Karen McNulty Walsh

Scientists at the Department of Energy's Brookhaven National Laboratory have developed a new metal alloy that could greatly improve the performance of rechargeable batteries for portable electronic devices and electric and hybrid electric cars.

battery sparkIf you're tired of cell phones and laptops that quickly lose their charge—or worse, their ability to be recharged—help may be on the way. Brookhaven National Laboratory scientists James Reilly, Gordana Adzic, John Johnson, Thomas Vogt, and James McBreen have developed a new metal alloy that could greatly improve the performance of rechargeable batteries.

When used as an electrode in nickel/metal hydride (Ni/MHx) batteries—the most popular rechargeables—the new alloy has a high capacity for storing charge, a long-lasting ability to be charged and recharged, and good resistance to corrosion. Furthermore, the alloy contains no cobalt, an expensive metal found in many Ni/MHx batteries, and no cadmium, a toxic metal found in nickel-cadmium rechargeables. Composed of lanthanum, nickel, and tin, "this new alloy is inexpensive and relatively environmentally benign," said Reilly, the team leader.

The alloy is based on a classic formula used for Ni/MHx batteries, which consists of a cube-like lattice with lanthanum atoms on the corners and nickel on the inside. The electrode works by storing up hydrogen atoms (from the electrolyte) in the spaces between the atoms during charging, and releasing them into the electrolyte during discharge.

But the added hydrogen atoms have an adverse effect: They cause the crystal lattice to expand, and then contract as the battery discharges. "This expansion and contraction is repeated in each charge/discharge cycle of the battery," said Reilly, "which pulverizes the alloy into small particles that are more susceptible to corrosion. That's why batteries don't recharge an infinite number of times. Eventually corrosion takes over."

dumbbell atoms
Brookhaven researchers determined that the increased energy storage potential of an experimental alloy was due to "dumbbells" made of two nickel atoms (bottom, left) replacing a lanthanum atom in the lattice. Lanthanum atoms are shown in red, nickel atoms are shown in blue and white.


Through trial and error, scientists originally found that using a mixture of metals, including cobalt, in place of nickel helps the electrode resist this tendency to break apart and corrode. But even small amounts of cobalt can drive up the cost of batteries considerably. For batteries of the sizes needed in electric vehicles, the cost can be prohibitive. So scientists have been trying to understand the role cobalt plays—and find ways to replace it.

That's what the Brookhaven scientists were doing when they were investigating several relatively simple, cobalt-free alloys. They found a combination of lanthanum, nickel, and tin with a very high storage capacity that didn't decay over many charge/discharge cycles. This surprised the scientists, because normally, combinations of these atoms in the classic ratio of one lanthanum atom to five of the other atoms decayed rather quickly.

As it turns out, there was a mistake. Accidentally, the scientists had added a bit more of the nickel/tin combo, so that the ratio of atoms was no longer 1 lanthanum to 5 nickel or tin, but 1 to 5.157. That small difference in the ratio of the ingredients made a big difference in performance. The superior performance was then confirmed in a further series of experiments, carried out by Adzic and Johnson, with other 1 lanthanum/ 5+ nickel/tin combinations.

Vogt then studied the lattice structure at Brookhaven's National Synchrotron Light Source to figure out where the extra atoms went. By beaming samples of the material with high-intensity x-rays and looking at how the beam scattered, he determined that "dumbbells" made of two nickel atoms were replacing some of the lanthanum atoms on the cube corners.

These nickel dumbbells make the structure more compact, said Vogt, which decreases somewhat its ability to store hydrogen, and therefore its initial charge capacity relative to the classic 1-5 formula. But it also decreases the alloy's tendency to corrode, therefore increasing its life-span. The result is that the long-term energy-storage capacity of this new alloy exceeds that of cobalt alloys used in commercial batteries.

Media contacts: Karen McNulty Walsh, (631) 344-8350, kmcnulty@bnl.gov
Pete Genzer, (631) 344-3174, genzer@bnl.gov
Research contact: James J. Reilly Jr., (631) 344- 4502, jreillys@bnl.gov


Related Web Links

"Scanner Lays Threats Bare," The Oregonian (Science News) (12/12/01)

"Properties of Li nanocomposite electrode materials prepared via hydrogen-driven, solid-state, metallurgical reactions," Reilly JJ, Johnson JR, Vogt T, Adzic GD, Zhu Y, McBreen J, Journal of the Electrochemical Society 148 (6): A636-A641 June 2001.

Technology Brief: Non-Stoichiometric Ab5 Alloys For Metal Hydride Electrodes—U.S. Patent No. 6,238,823, April 25, 2001.

"Patent Gives Battery Research a Charge," by Karen McNulty Walsh, Brookhaven National Laboratory News Release, July 6, 2000. U.S. Patent No. 6,022,643

"Brookhaven Lab and Gould Electronics Develop New Materials for Building Better Batteries," by Diane Greenberg, Brookhaven National Laboratory News Release, March 15, 2000.

National Synchrotron Light Source


Funding: This work was funded by the U.S. Department of Energy's Office of Science, Basic Energy Sciences division, which supports basic research in a variety of scientific fields.

The National Synchrotron Light Source at Brookhaven in New York, is a national user research facility funded by the DOE. The NSLS operates two electron storage rings: an X-Ray Ring and a Vacuum Ultra Violet (VUV) Ring, which provide intense focused light spanning the electromagnetic spectrum from the infrared through x-rays.

Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.

Author: Karen McNulty Walsh, a Senior Public Affairs Representative at Brookhaven National Laboratory since September 1999, has an MA in science journalism from New York University and a BA in biology from Vassar College. She was previously the editor of Science World, a science magazine for middle-school children, and Zillions, a kids' version of Consumer Reports. For more Brookhaven science news, see Laboratory News.

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