Mar
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A Fast Charge Discharge Breakthrough
March 16, 2009 | 2 Comments
MIT researchers led by Gerbrand Ceder, the Richard P. Simmons Professor of Materials Science and Engineering, have developed a lithium iron phosphate electrode material that achieves ultra-high discharge rates comparable to those of “supercapacitors,” while maintaining the high energy density characteristic of lithium-ion batteries. Stop right there, by no means is the technology at the charge and discharge rates of capacitors. Nor do customers want batteries to be capacitors when the applications are thought through. Press release and media excitement aside, this is quite a significant milestone, published in Nature 458, 190-193 (12 March 2009).
Batteries are “slower” than capacitors and scientists and consumers have grated at the rate of battery charge for decades. The research at MIT deals with lithium, thinking that the lithium ions responsible, along with electrons, for carrying charge across the battery simply move too slowly through the material. Then about five years ago, Ceder and his colleagues made a surprising discovery. Computer calculations of a well-known battery material, lithium iron phosphate, predicted that the material’s lithium ions should actually be moving extremely quickly.
Further calculations showed that lithium ions can indeed move very quickly into the material but only through tunnels accessed from the surface. If a lithium ion at the surface is directly in front of a tunnel entrance, there’s no problem: it proceeds efficiently into the tunnel. But if the ion isn’t directly in front, it is prevented from reaching the tunnel entrance because it cannot move to access that entrance.
MIT New Lithium Battery Material. Click for more information.
With Byoungwoo Kang, a graduate student in materials science and engineering, they devised a way around the problem by creating a new surface structure that does allow the lithium ions to move quickly around the outside of the material, much like a beltway around a city. When an ion traveling along this beltway reaches a tunnel, it is instantly diverted into it.
Using their new processing technique, the two went on to make a small battery that could be fully charged or discharged in 10 to 20 seconds, while taking six minutes to fully charge or discharge a cell made from their unprocessed material.
The innovation is in improving the power rate of lithium-ion batteries. A side benefit came along too, further tests showed that unlike other battery materials, the new material does not degrade as much when repeatedly charged and recharged. This could lead to smaller, lighter batteries, because less material is needed for the same result.
With these points in mind, the idea that a battery can be charged in seconds and discharged as quickly changes the application choices and usage parameters. First, its important to note that lithium-ion and other metal batteries are already distinct technologies from “wet” chemical batteries such as lead acid. Until now the terminals of lithium –ion could be exposed, as the discharge rates were slow. But using the MIT materials and construction improvements will necessitate that terminals be less apt to connect. What isn’t said by the press release or the other news and bloggs is what happens when one of the MIT lithium batteries would be accidentally short-circuited. Lithium batteries are dense stores of energy, and while the milestone of fast charge and discharge is welcome, more investigation into the design’s properties is in order.
Batteries are reactive systems in charging and discharging, which makes them an important means to store electrical potential. Speeding things up is a good thing, but more needs to be known about operating characteristics before expectations can firm up.
Capacitors on the other hand are electron storage devices with near instantaneous charge and discharge characteristics. The two technologies are nicely complementary. Adding battery technology advanced for faster charge rates is particularly valuable and the added discharge speeds can be of great use as well.
In the engineering it will be cost, weight and space considerations. With the nearly nervous market for raw lithium the MIT research might be offering something very useful beyond speed. That would be a much more highly efficient use of the raw materials saving cost, weight and space leading to lower costs.
By all means Gerbrand Ceder and Byoungwoo Kang have earned a congratulations. One hopes that the media and press hype don’t cast a shadow, as these guys have an important milestone to their credit.
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very nice information keep posting
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