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New Nanocrystalline Material for Next-Generation Supercapacitors

11 July 2006

Kumta
The cover image: a high magnification transmission electron microscopy image of VN nanoparticles that exhibit enhanced supercapacitor response.

A research team led by Carnegie Mellon University Materials Science and Biomedical Engineering Professor Prashant Kumta has discovered a nanocrystalline vanadium nitride (VN) material that is cheaper, more stable and produces a higher quality energy storage capacity for use in a variety of industrial and portable consumer electronic products.

Kumta said the discovery, published this summer in Advanced Materials Journal, has important implications for increasing the longevity of rechargeable car batteries, fuel cells and other battery-operated electronic devices.

We have found that synthesis of nanostructured vanadium nitride and controlled oxidation of the surface at the nanoscale is key to creating the next generation of supercapacitors commonly used in everything from cars, camcorders and lawn mowers to industrial backup power systems at hospitals and airports.

—Prashant Kumta

Supercapacitors today generally use various forms of ruthenium oxide, a transition metal that is also expensive, selling for more than $100 per gram.

Kutma2
Gravimetric capacitance (F/g) with varying VN nanocrystallite loading scanned at various rates (2~100mV/s) using 1M KOH electrolyte.

Kutma and his team synthesized a new class of nanocrystalline transition metal nitrides (TMN) based on vanadium nitride. These new materials deliver a specific capacitance of 1,340 F/g when tested at low scan rates of 2mV/s and 554 F/g when tested at high charging rates of 100 mV/s in the presence of a 1M KOH electrolyte.

That exceeds the capacitance response of RuO2. The vanadium nitride is less expensive (about $50 per gram) and can store energy longer, according to Kutma.

Other project researchers included Tom Nuhfer, a materials science graduate student at Carnegie Mellon; and Wayne Jennings, a materials science researcher at Case Western Reserve University. The work was supported by Carnegie Mellon seed funding and a grant from the National Science Foundation.

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July 11, 2006 in Batteries, Nanotech, Vehicle Systems | Permalink | Comments (13) | TrackBack (1)

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Comments

Now that's using your Mellon! I particularly like the increased stability. Yet another reason to think that PHEV and EVs will win out over hydrogen despite the funding level difference.

Pretty good pun, Neil. I agree with you too, and wish governments would fund this technology more instead of H2O. I'm not very good with all the numbers they throw around in this article, but would love to know how these compare to the latest ultra-capacitors that MIT has developed, in terms of speed and efficiency rate of charge/discharge, lifecycle and duration of charge? These sound cheaper to make, but whether they will be as a finished product is anyone's guess.

John W. I agree with you and would also like to get more comparative details with MIT's and ESStor's ultra-caps units. These units could give PHEVs the push required to become a reality within 2 or 3 years.

Imagine where ultra-caps would be if they had been given the same research and development funds as Hydrogen Fuel Cells.

PHEVs and EVs are much better + cleaner choices for future personnal (and many commercial) transport. I don't see any Fuel Cell real advantages except as an extension to current liquid fuel industry.

A clear commitment towards a definite move to n-butanol PHEVs and electric vehicles + much more R&D funds would help.

Vanadium is found in heavy/sour oil and must be removed during refining. A new market for this metal could change the economics of refining.

Vanadium is a bulk metal, widely geologically distributed, mined, and used, primary as additive in steel alloys. It is way cheaper and more abundant then exotic Ruthenium.

The use of Vanadium was discussed elsewhere and people mentioned about the hazards of the material. I do not know what kind of properties the new material will have, but I think we would more likely see this technology in a controllable environment, rather than in higher risk environment such as an automobile.

Charles -

pure metals, their alloys, oxides, nitrides, carbides etc. are all chemically completely different animals. As Andrey indicated, Vanadium is used extensively in alloyed steels, which account for a high precentage of the parts used on modern automotive chassis. You probably have tools at home that are made from Vanadium alloys. Your safety concerns are duly note but probably overblown.

For all you EV/PHEV fans out there: supercaps are NOT an apropriate storage technology for those concepts. They are very much appropriate for mild and full HEVs featuring fuel-efficient downsized engines (fewer cylinders, lower displacement, GDI, turbo).

What surprises me is that these researchers are even advocating a transition nitride rather than activated carbon as an electrode material.

http://www.ecass-forum.org

Perhaps its a terminology thing, what some researchers call supercaps are really pseudo-capacitors, which act as a capacitor on one electrode and as a battery on the other. To me a super- or ultracapacitor is a strictly electrostatic device.

Rafael: In due time, it may become more appropriate to call those units EESD (Electrcial Energy Storage Devices) because quick charge batteries and high storage super capacitors may be variances of the same technologies.

Rafael-

"Super" or "Ultra" Capacitors are very appropriate and almost mandatory to be implemented in conjunction with a battery system. They should not be used as the primary energy storage device but they would greatly enhance the effectivity and efficiency of regenerative braking while helping to control any sudden surges of current required for initial and/or sudden acceleration for battery longevity.

Capacitors of various types (better the performance the better) will be needed for electric vehicles to help them deal with peak regenerative braking electrical load. The same could be said for heavy duty uphill acceleration.

NiMh battery have pretty constant 1.2V at any state of discharge. Rechargeable Li batteries have ugly quality to have about 4.23V at full charge, which diminishes down to 3V while battery is drained (discharge is usually limited to 3.7V to avoid damage to battery). This requires sophisticated electronics to convert and stabilize the current, which at tens of kW power range in HEV is extremely expensive. Supercaps are even worse: they are draining down to zero V. This is the main reason why supercap/battery combination is still not widely used - it will require double of power electronics vis. single battery configuration. Eventually price for power electronics should come down.

P.S. My Nikon camera, happily working on two 3V disposable Li batteries, refuses to work on two fully charged Li rechargeable batteries – until I half drain it to about 3.9V.

I was surprised to see that the raw material for supercaps is priced at 50 $/gram =:-|. There must be a lot of steel around them to make them heavy..?!

Actually, this innovative VN material shows ultra-high capacitance, upto 1300 F/g at a packing density of 0.25 mg/cm3 and a scan rate of 2 mV/s. However, in the case of 0.99 mg/cm3 and a scan rate of 100 mV/s, the available capacitance sharply reduces to only a little more than 100 F/g. In fact, the packing density of 0.99mg/cm3 is still much smaller than the real industrial packing level. So, I am seriously douting the industrial applicability of this new VN electrode material.

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