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Thursday, August 10, 2006

More on MIT's LEES Ultracapacitors - Is this the End-Game for Batteries?

[RenewableEnergyAccess (REA) has more today on MIT's high-capacity nanoengineered LEES ultracapacitors, potentially the end-game for battery energy storage. Check it out:]

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, say researchers at the Massachusetts Institute of Technology.

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.

Battery advances, particularly big breakthroughs, are widely seen as complementary to renewable energy technologies, which could benefit from improvements in electricity storage. A major battery breakthrough could also have major implications in the realm of plug-in hybrid electric vehicles whose batteries could be charged partly by renewable energy such as solar or wind.

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 and only recently began being 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.


  • Green Car Congress post on LEES ultracapacitors - Feb 2006

  • MIT: Carbon Nanotube Enhanced Ultracapacitors

  • MIT Laboratory for Electromagnetic and Electrical Systems

  • As I hinted at in the into, I think that carbon-based, high-energy density, long lasting ultracapacitors like MIT's LEES ultracap may be the endgame for battery energy storage, at least for electric and plug-in hybrid vehicles.

    Ultracaps have very high power densities, delivering great acceleration and performance, as well as taking full advantage of regenerative braking (NiMH and Li-ion batteries typically can't charge fast enough to accept all the energy potentially recoverable during regenerative braking). Additionally, ultracaps are very long-lasting (compared to batteries), can undergo several hundred cycles, last 10+ years, and have typically have no problems with cold-start conditions. Their general weakness is their lack of energy density, meaning they generally have to be coupled with a storage battery (or fuel cell) in any electric drive system.

    If MIT or someone else can develop an ultracap with the energy storage of a traditional Li-ion battery, that would be a major coup for the electric vehicle industry. And if the resulting ultracap was largely made of carbon - a material available in practically limitless supply - any potential materials supply limitation concerns (i.e. for lithium or platinum or other battery or fuel cell components) would be essentially a thing of the past.

    Let's hope MIT's researchers can deliver this ultracap (and soon) to a commerical partner for deployment in EVs or PHEVs.

    [EDIT: Upon closer examination, it appears that this REA article is the same as the one that appeared back in February (and was picked up by Green Car Congress, the Energy Blog and numerous others). It appears that REA's RSS aggregator or whatever else they are using to find posts screwed up (this happens sometimes; yesterday, for example, REA picked up a post from August 9 2005, instead of 2006).

    So, the article isn't any new development, I guess. However, since I didn't post on it here at Watthead back in February (and I've already gotten this post written), I go ahead and post it anyway.


    Anonymous said...

    Interesting, even if not breaking news. The nanotube technology sounds expensive though; EEStor claims that their Barium Titanate ultracap will be cheap as well as high performance. ("Claims" might be too strong of a term; it doesn't sound like they say anything officially.) If the EEStor tale pans out, life as we know it will be forever changed. And that would be OK as far as I'm concerned.

    Ryos said...

    Sadly, I've come to view the words "carbon nanotubes" as code for "this works really well in the lab, but it's never going to come out, ever." The tubular wonders seem to be a silver bullet for almost everything; they promise to revolutionize everything they touch. So why can't anyone make it work in the real world? Maybe we need fewer people working on potential applications of nanotubes, and more working on how to make them.