Re: Nanotube Ultracapacitors from MIT

Ultracapacitors

Massachusetts Institute of Technology
Laboratory for Electromagnetic and Electronic Systems

Project Title: Carbon Nanotube Enhanced Ultracapacitors (poster)
Investigators: John Kassakian, Joel Schindall, Riccardo Signorelli

Introduction:

Introduction Ultracapacitors or double layer capacitors (DLCs) are energy
storage devices whose operation is based on the double layer effect. By
utilizing highly porous carbon material with a surface area up to 2000m2/g
as electrodes (as in Fig. 3) commercial DLCs can achieve a energy density
(6Wh/kg) much greater than the energy density of a conventional capacitor.
However, this figure is much lower than the energy density reached by
Lithium-Ion batteries (120Wh/kg).

Our analysis shows that the utilization of a matrix of vertically aligned
CNTs as electrode structure, can lead to an ultracapacitor characterized by
a power density greater than 100kW/kg (three orders of magnitude higher than
batteries), a lifetime longer than 300,000 cycles, and an energy density
higher than 60Wh/kg.



"Pluto" <pluto7@xxxxxxxxxx> wrote in message
news:efkkuh$ofo$1@xxxxxxxxxxxxxxxxxxxxxxx
MIT researchers introduce nanotech battery

Nanotube ultracapacitors would store energy on atomic level, providing
what is said to be the first technologically significant and economically
viable alternative to conventional batteries in more than 200 years.

Images of different types of carbon nanotubes. Carbon nanotubes are key to
MIT researchers' efforts to improve on an energy storage device called an
ultracapacitor.
Source: MIT (enlarge)

Just about everything that runs on batteries -- flashlights, cell phones,
electric cars, missile-guidance systems -- would be improved with a better
energy supply. But traditional batteries haven't progressed far beyond the
basic design developed by Alessandro Volta in the 19th century. Until
now.

Work at MIT's Laboratory for Electromagnetic and Electronic Systems (LEES)
holds out the promise of the first technologically significant and
economically viable alternative to conventional batteries in more than 200
years.

Joel E. Schindall, the Bernard Gordon Professor of Electrical Engineering
and Computer Science (EECS) and associate director of the Laboratory for
Electromagnetic and Electronic Systems; John G. Kassakian, EECS professor
and director of LEES; and Ph.D. candidate Riccardo Signorelli are using
nanotube structures to improve on an energy storage device called an
ultracapacitor.

Capacitors store energy as an electrical field, making them more efficient
than standard batteries, which get their energy from chemical reactions.
Ultracapacitors are capacitor-based storage cells that provide quick,
massive bursts of instant energy. They are sometimes used in fuel-cell
vehicles to provide an extra burst for accelerating into traffic and
climbing hills.

However, ultracapacitors need to be much larger than batteries to hold the
same charge.

The LEES invention would increase the storage capacity of existing
commercial ultracapacitors by storing electrical fields at the atomic
level.

Although ultracapacitors have been around since the 1960s, they are
relatively expensive .Only recently were they manufactured in sufficient
quantities to become cost-competitive. Today you can find ultracapacitors
in a range of electronic devices, from computers to cars.

However, despite their inherent advantages -- a 10-year-plus lifetime,
indifference to temperature change, high immunity to shock and vibration
and high charging and discharging efficiency -- physical constraints on
electrode surface area and spacing have limited ultracapacitors to an
energy storage capacity around 25 times less than a similarly sized
lithium-ion battery.

The LEES ultracapacitor has the capacity to overcome this energy
limitation by using vertically aligned, single-wall carbon nanotubes --
one thirty-thousandth the diameter of a human hair and 100,000 times as
long as they are wide.

How does it work?

Storage capacity in an ultracapacitor is proportional to the surface area
of the electrodes. Today's ultracapacitors use electrodes made of
activated carbon, which is extremely porous and therefore has a very large
surface area. However, the pores in the carbon are irregular in size and
shape, which reduces efficiency. The vertically aligned nanotubes in the
LEES ultracapacitor have a regular shape, and a size that is only several
atomic diameters in width. The result is a significantly more effective
surface area, which equates to significantly increased storage capacity.

The new nanotube-enhanced ultracapacitors could be made in any of the
sizes currently available and be produced using conventional technology.

"This configuration has the potential to maintain and even improve the
high performance characteristics of ultracapacitors while providing energy
storage densities comparable to batteries," Schindall said.
"Nanotube-enhanced ultracapacitors would combine the long life and high
power characteristics of a commercial ultracapacitor with the higher
energy storage density normally available only from a chemical battery."

This work was presented at the 15th International Seminar on Double Layer
Capacitors and Hybrid Energy Storage Devices in Deerfield Beach, Fla., in
December 2005.

The work has been funded in part by the MIT/Industry Consortium on
Advanced Automotive Electrical/Electronic Components and Systems and in
part by a grant from the Ford-MIT Alliance.



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