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MIT Carbon Nanotube Ultracapacitor Could Approach Storage Density of Batteries

8 February 2006

Researchers at MIT’s Laboratory for Electromagnetic and Electronic Systems (LEES) are investigating the use of nanotube structures to improve the energy storage density of ultracapacitors to a level comparable with that of NiMH batteries, while maintaining or even improving the ultracapacitors’ high performance.

Capacitors store energy in an electric field, making them more efficient than standard batteries, which get their energy from chemical reactions. Although ultracapacitors can provide quick, massive bursts of energy—ideal for acceleration with an electric drive—they need to be much larger than batteries to hold an equivalent amount of energy.

Physical constraints on electrode surface area and spacing have limited ultracapacitors to an energy storage capacity around 20 times less than a similarly sized lithium-ion battery. Commercial ultracapacitors achieve an energy density of around 6 Wh/kg; NiMH batteries of around 60 Wh/kg; lithium-ion batteries of around 120 Wh/kg.

The LEES ultracapacitor overcomes this limitation by using a matrix of vertically aligned, single-wall carbon nanotubes (CNT) as an electrode.

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; the irregularities reduce 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 MIT analysis shows that the CNT ultracapacitor could have an energy density higher than 60 Wh/kg, a power density greater than 100 kW/kg (three orders of magnitude higher than batteries), and a lifetime longer than 300,000 cycles. At 60 Wh/kg, the CNT ultracapacitors would have comparable density to NiMH batteries.

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. 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.

—Joel E. Schindall, associate director of LEES

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.


February 8, 2006 in Batteries | Permalink | Comments (18) | TrackBack (1)


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This is exciting news. It seems more and more these days like ultracaps are going to be the way to go in the near future. An ultracap like the one described above would truly make efficient EVs that satisfy both the power and operating range requirements of the typical user a reality.

In the mean time, it seems that pairing ultracaps with Li-ion (or zinc-air fuel cells) in a hybrid application where the Li-ion batteries provide the suitable energy storage from the plug-in charge and the ultracaps provide the bursts of power and absorb the energy from regenerative braking (and recharge off the Li-ions if necessary) would be a very viable option.

Does anyone know of any reasons why it wouldnt be feasible to pair ultracaps with li-ions? The only thing I can think of immediately is cost (I'm not sure how much more a hybrid system like this would cost than a straight Li-ion system) but that should be surmountable as economies of scale are realized and materials costs are brougth down through continued innovation with both ultracaps and Li-ions.

It's been a blistering 24 hours of news at GCC. Now we have a demonstration of the inner workings of a cost effective power pack that will easily last the life of the EV, and charge up fast. And with yesterday's posting of an example of a high efficiency converter, there's nothing to hold back the electric vehicle.

Don't get too excited people. This would be great...If all their carbon nanotubes had metallic conduction properties. Bulk nanotube synthesis yields mixtures of semiconducting and metallic nanotubes, and separating the two types is something that can currently only be done under a TEM microscope. Check out the poster, they've only made the nanotubes, and haven't even begun to make anything with them, much less demonstrate improved capacitor performance. Don't get me wrong, I like the idea, but at least have some promising data before you go throw this type of thing into the public.

EEStor claims several times the WH/kg; time will tell if they can really make barium titanate into Unobtanium.

Its news such as this that give me hope, and make me look forward to the future. I am excited about new technologies and ideas which will fuel our future, and that we will only need oil for the oil powered toys we chose to keep. I someday see a time when there will be a glut of oil, and the sheiks will complain about their finances being depleted.

Again, every breakthrough and announcement brings us closer to this reality, and I am excited because of it.

In rereading what I posted, "glut" is not the right word. An "abundant reserve", which cannot be sold quickly enough might be a better description in this case.

Regardless of what you call it, it won't happen so long as there's a world full of stuff built to use petroleum and no efforts to get people to convert or abandon it.  Would you dump your car if gas went back down to $1.75/gallon?

If we're going to depress the world price of oil, we're going to need both a set of alternatives for the major uses AND some hefty taxes, quotas or other disincentives to continue the status quo.

Every technology introduces new issues as it solves old ones. I just read somewhere recently that carbon nanotubes are so "indestructible" that we're likely to start seeing problems from their accumulation in the environment if we use them in any large measure. It's always something!


Gas and diesel fuel at $5/gal to $7/gal in most Euopean countries have convinced the majority to purchase smaller more efficient diesel cars with 2X mph that of the personnal vehicles on North American roads. Would $5/gal gas have the same effect on North American drivers? Most probably. Look at the effect that $3+/gal had on the sale of 4 X 4 gas guzzlers last fall. We have two choices to progressively raise the price to $5/gal, i.e. 1) Pay $120+/barrel to the OIL producing countries or 2) Apply a vriable progressive pollution taxe of up to $2/gal on all fossil fuel to maintain $5/gal at the pump. No. 1 solution may be around within 3 to 4 years but will send billions US$$ to you know where. No. 2 solution would keep the same billions US$$ home in USA. Funds from No.2 solution could be used to accellerate the transistion to PHEVs/EVs and alternate cleaner fuels and extra clean electricity production (windmills etc). The problem is the coming election. It is almost impossible to convince voters that solution No.2 is better for everybody. Most North Amercian voters will pick the status quo and vote for the party promissing to lower fuel taxes regardless of the mid and long term consequences. Is there a third solution?

To add to Engineer-Poet's comment, there is no practical alternative to oil based product as of yet.
As in, plastics.
Unless you want to start using metal alloys for everything, and I believe their fabrication can be just as bad if not worse for the environment in some respects.
So-called oil barrons will still be here 50 yrs from now. Perhaps under US or European control, but they will always exist.

Unless we build everything out of nanotubes. Nanotubes made by nanobots. The world can look like a big grey hive where people sleep in cacoons ala Matrix. :)
(The drugs don't work)

Plastics and other petrochemicals can be made from plants because ancient plants (and animals) constitute the oil we pump from the ground. We have that technology, it's being implemented right now, the real problem is the scale of oil consumption for all these things is just not sustainable in terms of the natural balance between humans and the earth. Somehow we will need to collectively become WAY more efficient in almost every aspect of life. It can be done voluntarily (now) or it will be forced upon us eventually if we try to continue on the path we're on.

Green Electricity (GEL) Initiative: Replacing Batteries with Capacitors

While heated debates still persist about the validity of global warming problem/resolution, there is one particular heavily-overlooked issue of Global Environmental Contamination by the Batteries disposed from portable electronics. This issue is REAL and URGENT AND it is continuously getting worse as Batteries production is increasing every year and many of them would be potentially improperly disposed (see the link below):

My Green Electricity (GEL) Initiative is addressing this issue and proposing the solutions, which include the replacement of the Batteries with Capacitors, especially of the modern Carbon nanotube type of Ultracapacitors):

Couple practical examples of using multi-Farad Capacitors (SuperCap™ or Ultracaps) in portable devices are described in my early articles, published in EDN Magazine:

Single capacitor powers audio mixer, Alexander Bell, USA, EDN, March 14, 1997 (recognized by “Best Design Idea” award)

Muscle power drives battery-free electronics, Alexander Bell, EDN, 11/21/2005 (Describes autonomous, cost-efficient and environmentally-friendly solution utilizing Ultra-capacitor in conjunction with alternative energy sources to power portable electronic equipment)

Fine, pursue electric vehicles.

Taxing Atlas to death to force something to happen is the wrong way to do it. Most people are sensible enough to buy something that will run cheaper than what they had before.

If you want to live in a socialist hell, move to Europe, better still 'free' Russia, or China...

Think how inefficient the Steamers and Model-T's were at the dawn of the 20th century. How many liters displacement did some of the early automotive engines have to produce what we consider average amounts of power today?

Our current internal combustion technology is damn good compared to what we produced in the 60's, and still MORE efficient compared to those "first wave" autos.

Then, there's that pesky pollution that comes from the places that produce all these technological wonders. Will producing the new stuff be more polluting than the old stuff?

The "Global Warming Crisis" is, at worst, a misdirection by those that live off of research grants. It's not the pollution, it's the sun...look at a few of the studies that address that.

Should we pursue more efficient technologies for transportation? Sure...

Should we seek to make our technologies cleaner to minimize contamination? Sure....

BUT..NEITHER should lead us to tax the American consumer into the poor house to fulfil some non-obtainable socialist dream.

The American Consumer drives the economy of the world, he doesn't need more 'ecological incentives' added to the load.

Sounds like the researchers at UC-Davis have already made a nanotube supercapacitor with 30kw/kg power density. Just hope they can get it to market soon. The LEES project is a good idea, I just don't know if it can be economical.


I just wanted to say that I see the Ultra Capacitor as the very first real alternative to fossil fuels. We are on the verge of witnessing the emergence of a new method of vehicle propulsion, that will completely erase our country's dangerous dependence on fossil fuels.

Since nanotube ultracapicitors are very scalable, the technology can be used in cars, houses, buildings, trains, etc. They can accept electrons from any intermittent power scource (solar, wind, tides, etc.). They are the key link in all sustainable, clean energy futures. The industrialized countries of the world, led by the US, need to immediately fund massive R&D (perhaps with X-prize rewards) to bring this missing link to the world.

Not only would this effort provide an explosion of high value employment, it would also greatly raise American status globally.

Hell yes I would abandon my car if gas were down to 1.75 a gallon! even at that price, you'd have to average around 90 miles per gallon to match the efficieny of the Li-Ion auto (Tesla). With the introduction of the ulta-cap and it's leaps and bounds of improvement along with large-scale manufacturing of EV components to bring down the vehicle price, the day's of big oil are numbered.

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