Friday, October 29, 2010

HOW BATTERIES GROW OLD

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In a laboratory at Ohio State University, an ongoing experiment is studying why batteries lose their ability to hold a charge as they age -- specifically lithium-ion batteries, which have generated a lot of buzz for their potential to power the electric cars of the future.
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(NC&T/API) Preliminary results presented at the AVS 57th International Symposium & Exhibition, suggest that the irreversible changes inside a dead battery start at the nanoscale.

Yann Guezennec and Giorgio Rizzoni of OSU developed new experimental facilities and procedures to charge and discharge commercially-available Li-ion batteries thousands of times over many months in a variety of conditions designed to mimic how these batteries are actually used by hybrid and all-electric vehicles. Some of the batteries were run in hot temperatures like those in Arizona; others in colder conditions similar to those in Alaska.

To understand the results of this testing, Bharat Bhushan, Suresh Babu, and Lei Raymond Cao studied the materials inside of the batteries to help determine how this aging manifests itself in the structure of the electrode materials.

When the batteries died, the scientists dissected them and used a technique called infrared thermal imaging to search for problem areas in each electrode, a 1.5-meter-long strip of metal tape coated with oxide and rolled up like a jelly roll. They then took a closer look at these problem areas using a variety of techniques with different length scale resolutions (e.g. scanning electron microscopy, atomic force microscope, scanning spreading resistance microscopy, Kelvin probe microscopy, transmission electron microscopy) and discovered that the finely-structured nanomaterials on these electrodes that allow the battery rapidly charge and discharge had coarsened in size.

Additional studies of the aged batteries, using neutron depth profiling, revealed that a fraction of the lithium that is responsible, in ion form, for shuttling electric charge between electrodes during charging and discharging, was no longer available for charge transfer, but was irreversibly lost from the cathode to the anode.

"We can clearly see that an aged sample versus and unaged sample has much lower lithium concentration in the cathode," said Rizzoni, director of the Center for Automotive Research at OSU. "It has essentially combined with anode material in an irreversible way."

This research is being performed by Center for Automotive Research at OSU in collaboration with Oak Ridge National Laboratory and the National Institute of Standards Technology.

The researchers suspect, but cannot yet prove, that the coarsening of the cathode may be behind this loss of lithium. If this theory turns out to be correct, it could point battery manufacturers in the right direction for making durable batteries with longer lifetimes.

American Institute of Physics

BATTERIES SMALLER THAN A GRAIN OF SALT

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Lithium-ion batteries have become ubiquitous in today's consumer electronics -- powering our laptops, phones, and iPods. Research funded by DARPA is pushing the limits of this technology and trying to create some of the tiniest batteries on Earth, the largest of which would be no bigger than a grain of sand.

These tiny energy storage devices could one day be used to power the electronics and mechanical components of tiny micro- to nano-scale devices.

Jane Chang, an engineer at the University of California, Los Angeles, is designing one component of these batteries: the electrolyte that allows charge to flow between electrodes. She presented her results at the AVS 57th International Symposium & Exhibition.

"We're trying to achieve the same power densities, the same energy densities as traditional lithium ion batteries, but we need to make the footprint much smaller," says Chang.

To reach this goal, Chang is thinking in three dimensions in collaboration with Bruce Dunn other researchers at UCLA. She's coating well-ordered micro-pillars or nano-wires -- fabricated to maximize the surface-to-volume ratio, and thus the potential energy density -- with electrolyte, the conductive material that allows current to flow in a battery.

Using atomic layer deposition -- a slow but precise process that allows layers of material only an atom thick to be sprayed on a surface -- she has successfully applied the solid electrolyte lithium aluminosilicate to these nanomaterials.

The research is still in its early stages: other components of these 3D microbatteries, such as the electrodes, have also been developed, but they have yet to be assembled and integrated to make a functioning battery.

American Institute of Physics

NO STANDARD FOR THE PLACEBO?

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Much of medicine is based on what is considered the strongest possible evidence: The placebo-controlled trial. A paper published in the October 19 issue of Annals of Internal Medicine – entitled "What's In Placebos: Who Knows?" calls into question this foundation upon which much of medicine rests, by showing that there is no standard behind the standard – no standard for the placebo.

The thinking behind relying on placebo-controlled trials is this: to be sure a treatment itself is effective, one needs to compare people whose only difference is whether or not they are taking the drug. Both groups should equally think they are on the drug – to protect against effects of factors like expectation. So study participants are allocated "randomly" to the drug or a "placebo" – a pill that might be mistaken for the active drug but is inert.

But, according to the paper's author, Beatrice Golomb, MD, PhD, associate professor of medicine at the University of California, San Diego School of Medicine, this standard has a fundamental problem, "there isn't anything actually known to be physiologically inert. On top of that, there are no regulations about what goes into placebos, and what is in them is often determined by the makers of the drug being studied, who have a vested interest in the outcome. And there has been no expectation that placebos' composition be disclosed. At least then readers of the study might make up their own mind about whether the ingredients in the placebo might affect the interpretation of the study."

Golomb pointed out these limitations to the placebo in a pair of letters to the journal Nature 15 years ago.

"A positive or negative effect of the placebo can lead to the misleading appearance of a negative or positive effect of the drug," she said. "And an effect in the same direction as the drug can lead a true effect of the drug to be lost. These concerns aren't just theoretical. Where the composition has been disclosed, the ingredients of the placebo have in some instances had a likely impact on the result of the study – in either direction (obscuring a real effect, or creating a spurious one). In the cases we know about, this is not because of any willful manipulation, but because it can in fact be difficult to come up with a placebo that does not have some kind of problem."

Since 15 years have elapsed, the situation might have improved. Therefore, Golomb and her colleagues analyzed just how often randomized trials published in the past two years in each of the top four general medical journals actually disclosed the makeup of placebos.

The answer is not reassuring, according to the researchers, who found that the placebo ingredients for pills were disclosed in fewer than 10 percent of cases. (The nature of the "control" was significantly more likely to be stated for other types of treatments – like injections, acupuncture, or surgery – where people are more likely to question what "placebo" actually means.)

"How often study results are affected by what's in the placebo is hard to say – because, as this study showed, most of the time we have no idea what the placebo is," Golomb concluded.

University of California, San Diego

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