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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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New Batteries Pack More Punch
20 June 2010 1:00 pm
Electric cars face severe limits in how far they can drive before running out of juice. Better batteries that can both store more energy and give it up quickly are essential for extending that range. Now, researchers at the Massachusetts Institute of Technology (MIT) in Cambridge have come up with a novel battery-making strategy that steers in that direction. For now, the new batteries can power only small devices. But if the strategy can be made to work on a larger scale, a task more difficult than just using more battery material, it could give electric car makers the jolt they need.
Today's most popular rechargeables, lithium ion batteries, are made from negative and positive electrodes separated by an electrolyte through which positively charged lithium ions can flow back and forth. In most such cells, the negative electrode is made of graphite, a form of layered carbon, whereas the positive electrode is made from lithium cobalt oxide or a related material. During use, lithium ions stored in the graphite flow to the lithium-based electrode, where they form chemical bonds with oxygen atoms, a reaction that generates an electric current. When the battery is recharged, the lithium-oxygen bonds break and an electric voltage pushes the ions back into the graphite.
Researchers have long sought to replace the graphite in the negative electrodes with carbon nanotubes, strawlike tubes of carbon. The hope is to create a more porous material with a higher surface area that could hold on to more lithium ions and thus make longer-lived batteries.
But in a paper posted online today in Nature Nanotechnology, the MIT team, led by materials scientist Yang Shao-Horn, took a very different approach: using carbon nanotubes to replace the oxide-based positive electrode. Normally, lithium ions wouldn't bind to plain carbon nanotubes. So Shao-Horn and her colleagues decorated the outer surfaces of their nanotubes with two different types of oxygen-containing chemical groups that gave them opposite charges. They then dipped their electrode starting materials alternatively in solutions containing the oppositely charged nanotubes, binding successive layers of tubes atop one another to build up their nanotube electrodes.
The result was a highly porous carbon nanotube electrode with lots of oxygens exposed on the surface, ready to bind with lithium. Detailed tests showed the new batteries hold five times as much energy as conventional quick-discharging devices called capacitors do, and they deliver that power 10 times as quickly as conventional lithium ion batteries can.
"This is certainly pioneering work," says Ray Baughman, a chemist at the University of Texas, Dallas. Baughman cautions, however, that the MIT team achieved its best results with very thin electrodes. The performance dropped off considerably as the electrodes were made thicker. Because thicker electrodes can store more charges, they allow a battery to hold more energy. So for now, hybrid batteries will be best suited to applications with low overall power demands, such as powering electronic circuitry in smart cards, credit cards with electronic chips that hold more information than magnetic strips do. For the batteries to be useful in hybrid cars or other power-hungry applications, researchers will need to find a way to make thicker electrodes that can still move charges quickly, a project Shao-Horn says she is working on now.