The Ultra
A new type of ultracapacitor could
eventually have you throwing out your conventional batteries.
By Kevin Bullis
MIT Technology Review
A breakthrough technology is holding forth the promise of charging
electronic gadgets in minutes, never having to replace a battery again, and
dropping the cost of hybrid cars. Indeed, the technology has the potential to
provide an energy storage device ten times more powerful than even the latest
batteries in hybrid cars -- while outliving the vehicle itself.
The new technology, developed at MIT's Laboratory for
Electromagnetic and Electronic Systems, should improve ultracapacitors,
by swapping in carbon nanotubes, thereby greatly
increasing the surface area of electrodes and the ability to store energy.
Ultracapacitors, a souped-up
version of the capacitors widely used in electronics, have been around for
decades. They're well-known for being powerful, that is, able to quickly absorb
and release electricity. But they can't store much energy, so their stored
electricity is depleted in a matter of seconds. As a result, they've been
limited to niche applications, such as providing quick bursts of power in some
hybrid transit buses.
Now researchers at MIT have found what they believe is a way to
improve the endurance of ultracapacitors several-fold
-- allowing the devices to retain the power and longevity advantages, while
storing about as much energy as the batteries used in hybrids.
The amount of energy ultracapacitors can
hold is related to the surface area and conductivity of their electrodes. The
researchers have increased surface area by "more than an order of
magnitude" by using carbon nanotubes, says Joel Schindall, professor of electrical engineering at MIT and
one of the researchers on the project. One square centimeter of conductive
plate, when coated with the nanotubes, has a surface
area of about 50,000 square centimeters, compared with 2,000 square centimeters
using the carbon in a commercial ultracapacitor
today. The highly pure carbon nanotubes are also
extremely conductive, which should increase power output over existing ultracapacitors, the researchers say.
The technology may find applications beyond hybrids, too. Ultracapacitors could allow laptops and cell phones to be
charged in a minute. And, unlike laptop batteries, which start losing their
ability to hold a charge after a year or two, they could still be going strong
long after the device is obsolete. "Theoretically, there's no process that
would cause the [ultracapacitor] to need to be
replaced," says professor John Kassakian, another of the researchers.
The main hurdle the new technology is likely to face is not
technical but economic. "The nanomaterials are
probably a hundred or a thousand times more expensive, today, than the
materials that we use," says Michael Sund,
spokesperson at Maxwell Technologies,
However, the MIT researchers hope that, over time, and with help
from economies of scale, nanotube ultracapacitors
can be made for the same cost as batteries.
The next step is to measure the performance of a device using the
carbon nanotubes and to grow the nanomaterials
on a flexible substrate that can be rolled into a large-scale ultracapacitor.