Micro ultracapacitor: This thin-film carbon ultracapacitor electrode, shown in a microscope image, is about 50 micrometers on each side. The zigzagging, porous regions are the active part of the device.
Min Heon
New ultracapacitor material could be fabricated directly on chips and solar cells.
Energy storage devices called ultracapacitors can be recharged many more times than batteries, but the total amount of energy they can store is limited. This means that the devices are useful for providing intense bursts of power to supplement batteries but less so for applications that require steady power over a long period, such as running a laptop or an engine.
Now researchers at Drexel University in Philadelphia have demonstrated that it's possible to use techniques borrowed from the chip-making industry to make thin-film carbon ultracapacitors that store three times as much energy by volume as conventional ultracapacitor materials. While that is not as much as batteries, the thin-film ultracapacitors could operate without ever being replaced.
These charge-storage films could be fabricated directly onto RFID chips and the chips used in digital watches, where they would take up less space than a conventional battery. They could also be fabricated on the backside of solar cells in both portable devices and rooftop installations, to store power generated during the day for use after sundown. The materials have been licensed by Pennsylvania startup Y-Carbon.
An ultracapacitor is "an electrical energy source that has virtually unlimited lifetime," says Yury Gogotsi, professor of materials science and engineering at Drexel University in Philadelphia, who led the development of the thin-film ultracapacitors. "It will live longer than any electronic device and never needs to be replaced." While batteries store and release energy in the form of chemical reactions, which cause them to degrade over time, ultracapacitors work by transferring surface charges. This means they can charge and discharge rapidly, and because the electrode materials aren't involved in any chemical reactions, they can be cycled hundreds of thousands of times. Researchers have begun developing thin-film ultracapacitor materials but have had difficulty getting high enough total energy storage using practical fabrication methods, says Gogotsi.
Gogotsi's group uses a high-vacuum method called chemical vapor deposition to create thin films of metal carbides such as titanium carbide on the surface of a silicon wafer. The films are then chlorinated to remove the titanium, leaving behind a porous film of carbon. In each place where a titanium atom was, a small pore is left behind. "The film is like a molecular sponge, where the size of each pore is equal to the size of a single ion," says Gogotsi. This matching means that when used as the charge-storage material in an ultracapacitor, the carbon films can accumulate a large amount of total surface charge. The Drexel researchers complete the device by adding metal electrodes to either surface to carry current into and out of the device and adding a liquid electrolyte to carry the charges. They found that the performance of the device is best when the carbon material is about 50 micrometers thick, about the same as the width of a human hair.
The Drexel researchers first developed this ultracapacitor material a few years ago; today in the journal Science they report the first demonstration of thin films made from it. Conventional ultracapacitors are made from powdered activated carbon. These powders can't be used to make large, thin films because they won't stick to the surface. Other groups have developed printable thin-film ultracapacitors based on carbon nanotubes; Gogotsi says his devices can store more charge.
Gogotsi says there is, in theory, no limit to the size of the films that could be made using these methods, which are used by the solar industry and display industries to make panels as large as nine square meters. Because the carbon films are thin and can be made at temperatures as low as 200 ºC, it might be possible to integrate them with flexible electronics.
Magnetic-field energy storage could have unique advantages, but scaling up will be a challenge.
The government funds a factory to make battery materials, but it's not even clear they'll be needed.
Batteries built into an Electric Car Body
In essence this could have a direct application for a Solar Electric Vehicle. The body of the electric car could have a printed solar cell on the outside and an ultra capacitor on the inside. In face using digital printing technologies we could literally build one on our desk top.
This could allow the generation and use of a solar module without connection to the local grid. If the ultra caps can hold energy overnight, the panel can power the station (home, office, etc) and recharge the capacitors to carry over during the night.
1. How long can the capacitors hold thier charge?
2. How large does the capacitor bank need to be?
3. How expensive is the capacitor bank in relation to the solar panel?
A more immediate use for this would be for building bypass capacitors directly onto chips. Almost all chips use external capacitors to filter their power supplies in order to keep the on-chip voltage as steady as possible. If a high-capacitance low-resistance layer could be added to the chip itself, this would improve performance and save cost. It would also lessen the demand for tantalum, much of which is mined in Africa by child slave labor.
I couldn't find the article on the Science web site, nor is there much on Drexel's site. Does anyone know what the cap per mm2 is? And at what voltage it can operate?
Re: Use for bypass cap? Density?
Also would decrease the power and ground pins required to reduce packaging size and cost.
Re: Use for bypass cap? Density?
It would also vastly simplify a hw designers job in design and layout as well as allow circuits to shrink considerably in size. smaller devices with higher performance and faster to market. this could very well be the next revolution in electronics.
Two major problems with electric cars are amount of toxic materials created for the batteries, and $3000+ to replace every 3 to 5 years. If this technology matures, then these two problems may be solve as well.
Storing enough electricity to smooth output is also a valuable service for ultracapacitors on the back of solar cells.
But we need numbers - we need how much energy density, how long to store and discharge, how to control them.
This would be wonderful if it actually worked. Vast value.
I think a major use of these will for for regenerative braking for cars. This needs high power but fairly low energy as you only have to store one stop / start.
They could also be used to increase the lifetime of conventional batteries by smoothing out their power delivery requirements.
Solar applications, where the power builds up slowly and decays slowly can be served by batteries - they do not need the high power requirements of capacitors.
Solar powered cars are a nonsense* as the top surface of a car is not large enough to generate enough electricity to power a car. If you want an electric car, charge it from the grid (at night).
If you want solar power, stick a few cells on your roof, pointing south and drive your house / the grid.
There is negative synergy in adding solar cells to cars (they make cars heavier, darker, and cannot be pointed in the optimal direction). Adding a few, to trickle charge your battery is probably harmless, but you would be better adding a few big solar cells to your house roof.
However, this technology sounds very good, but the numbers are a bit unclear - the Volumetric density is 3x better than conventional ultracaps - do we have any actual numbers ?
And what about the mass density ?
Nonetheless, it looks interesting.
*I know about solar racers, but these are fig leaves for Shell etc. and have no practical application.
Re: Regenerative Braking for cars
With regard to solar powered cars: It's worth remembering that the solar constant amounts to only about one horsepower per square yard. A car might spend seven hours in the sun for each hour of travel, but solar cells are not more than 14% efficient, so you still would have only about 1 HP per square yard of cells available to run the car.
Re: Regenerative Braking for cars
Don't jump to conclusion so quickly: Solarprint and FIAT are doing just that in an effort to reduce fuel/energy consumption. Solarprint's solar cells are a DSC (dye-sensitized solar cell) and can be made transparent so you can cover a transparent surface and collect light from both sides - that means you can cover your entire car with them. And these cells collect difuse light so they're not so sensitive to the orientation towards the Sun - they can produce electricity even turned towards the ground or north or under a street lamp at night (not much, of course, but still). Seems perfect for a car application (and buildings for that matter). And why should cars weigh 2 tons if they only have to carry one or two persons? If cars would be lighter and more aerodynamic than solar cars would make a lot of sense. You mention 7 hours of sunshine for 1 hour of driving. Don't we all drive half an hour or so to and from work and sit in the office for 8-9 hours? 1kW per m2 at 10% on a car with a surface area of 10 m2 is 1kW of power. That adds up quite a bit after 10 hours. But probably not worth it with a current paradigm of driving a huge and heavy and poorly shaped boxes on wheels (SUV, anyone?) some of us drive today.
Cool! Could it provide long-duration battery-like power if you had thousands of modules of these, each releasing its stored energy in succession? Then having some circuitry to smooth-out the released current?
Take a look at the Y-carbon website for some limited technical details.
http://www.y-carbon.us/Technology.aspx
The essential element of the technology is the ability to produce "tunable nanoporous carbon" with high surface areas. Therefore they are able to story and release energy quickly.
Hi,
Can you provide a link to the actual paper's abstract? Thank you.
Why doesn't TR do this as general practice?
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
On Twitter
Become a Fan on Facebook
Subscribe to the Feed
KeplersThirdLaw
11 Comments
Density
What's the power density percentage compared to a battery? Any idea on the cost to produce a 1F 5volt capacitor or a 3000F cap?
Reply