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Posted: Dec 16, 2014
Silver particles improve performance of battery material
(Nanowerk News) Researchers at the U.S. Department of Energy’s Argonne National Laboratory are working to create an electric car battery that is smaller, cheaper and allows drivers to go farther on a charge.
When you charge contemporary electric vehicles, lithium ions migrate from the positive electrode to the negative electrode where they are stored in a higher energy state. When you start the car, these stored ions release their energy in the form of electrons, and the lithium ion migrates back to the positive electrode. Today's electrode materials provide good charge-discharge cycles with the migration of lithium ions between electrodes, but they need to take advantage of other chemical processes to store more energy.
In the new scenario, oxygen and lithium atoms combine to create chemical bonds, releasing more energy in the same amount of space (that is, they have a higher energy density), but a metal catalyst is required to help form the bonds.
After experimentation with a variety of precious metals, the researchers found that tailored clusters of silver atoms seem to provide the surface texture required to create these lithium-oxygen bonds in abundance.
“In previous studies, we’ve had metal catalysts that helped the formation of these bonds, but we never knew what size these catalysts were—they could be from thousands to a couple of atoms in size,” said Curtiss. “Now we’re actually able to put down specific size clusters of silver and see what effect it has on the formation of these lithium-oxygen bonds.”
According to Argonne materials scientist Stefan Vajda, using the ultra-small clusters as catalysts for electric battery electrodes is new. It was proposed because multiple studies showed that the small clusters can easily activate, or break apart, oxygen to boost chemical reactions and release more energy.
“Once we understand how the process works and determine what size clusters perform the best, then we can design catalysts that work well, perhaps using lower-cost metals,” said Vajda.
These clusters are so compact that their atoms are on the surface, readily available for the chemical reactions that lead to energy production. Their ability to easily disperse could make even the most expensive catalytic metals affordable, Vajda added.
Although the commercialization of this technology is still potentially another 10 to 20 years down the road, Argonne is on the leading edge of the fundamental understanding of this chemistry. Understanding how the metal catalysts react on the electrode is just a start, as researchers need to overcome a number of other technical issues before the battery is road-worthy.
For instance, in its present stage of development, the battery wears out after only 10 to 40 charge-discharge cycles; a typical electric vehicle requires a thousand cycles or more.
It is believed that once these issues are resolved, the new lithium-oxygen architecture, with its ultra-small silver or other metal clusters directing energy productivity, could offer auto manufacturers and consumers a lower-priced, higher-efficiency alternative to today’s electric car batteries.
Source: By John Spizziri, Argonne National Laboratory