Researchers develop graphene supercapacitor holding promise for portable electronics

Mar 15, 2012 By Jennifer Marcus
Schematic showing the structure of laser scribed graphene supercapacitors.

(PhysOrg.com) -- Electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, differ from regular capacitors that you would find in your TV or computer in that they store substantially higher amounts of charges. They have garnered attention as energy storage devices as they charge and discharge faster than batteries, yet they are still limited by low energy densities, only a fraction of the energy density of batteries. An EC that combines the power performance of capacitors with the high energy density of batteries would represent a significant advance in energy storage technology. This requires new electrodes that not only maintain high conductivity but also provide higher and more accessible surface area than conventional ECs that use activated carbon electrodes.

Now researchers at UCLA have used a standard LightScribe DVD to produce such . The electrodes are composed of an expanded network of — a one-atom-thick layer of graphitic carbon — that shows excellent mechanical and electrical properties as well as exceptionally high surface area.

UCLA researchers from the Department of Chemistry and Biochemistry, the Department of Materials Science and Engineering, and the California NanoSystems Institute demonstrate high-performance graphene-based electrochemical capacitors that maintain excellent electrochemical attributes under high mechanical stress. The paper is published in the journal Science.

The process is based on coating a DVD disc with a film of graphite oxide that is then laser treated inside a LightScribe DVD drive to produce graphene electrodes. Typically, the performance of is evaluated by two main figures, the and power density. Suppose we are using the device to run an electric car — the energy density tells us how far the car can go a single charge whereas the power density tells us how fast the car can go. Here, devices made with Laser Scribed Graphene (LSG) electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high power, flexible electronics.

"Our study demonstrates that our new graphene-based store as much charge as conventional batteries, but can be charged and discharged a hundred to a thousand times faster," said Richard B. Kaner, professor of chemistry & materials science and engineering.

"Here, we present a strategy for the production of high-performance graphene-based ECs through a simple all solid-state approach that avoids the restacking of graphene sheets," said Maher F. El-Kady, the lead author of the study and a graduate student in Kaner's lab.

The research team has fabricated LSG electrodes that do not have the problems of activated carbon electrodes that have so far limited the performance of commercial ECs. First, The LightScribe laser causes the simultaneous reduction and exfoliation of graphite oxide and produces an open network of LSG with substantially higher and more accessible surface area. This results in a sizable charge storage capacity for the LSG supercapacitors. The open network structure of the electrodes helps minimize the diffusion path of electrolyte ions, which is crucial for charging the device. This can be accounted for by the easily accessible flat graphene sheets, whereas most of the surface area of activated carbon resides in very small pores that limit the diffusion of ions. This means that LSG supercapacitors have the ability to deliver ultrahigh power in a short period of time whereas activated carbon cannot.

Additionally, LSG electrodes are mechanically robust and show high (>1700 S/m) compared to activated carbons (10-100 S/m). This means that LSG electrodes can be directly used as supercapacitor electrodes without the need for binders or current collectors as is the case for conventional ECs. Furthermore, these properties allow LSG to act as both the active material and current collector in the EC. The combination of both functions in a single layer leads to a simplified architecture and makes LSG supercapacitors cost-effective devices.

Commercially available ECs consist of a separator sandwiched between two electrodes with liquid electrolyte that is either spirally wound and packaged into a cylindrical container or stacked into a button cell. Unfortunately, these device architectures not only suffer from possible harmful leakage of electrolytes, but their design makes it difficult to use them for practical flexible electronics.

The research team replaced the liquid electrolyte with a polymer gelled electrolyte that also acts as a separator, further reducing the device thickness and weight and simplifying the fabrication process as it does not require special packaging materials.

In order to evaluate under real conditions the potential of this all solid-state LSG-EC for flexible storage, the research team placed a device under constant mechanical stress to analyze its performance. Interestingly enough, this had almost no effect on the performance of the device.

"We attribute the high performance and durability to the high mechanical flexibility of the electrodes along with the interpenetrating network structure between the LSG electrodes and the gelled electrolyte," explains Kaner. "The electrolyte solidifies during the device assembly and acts like glue that holds the device components together."

The method improves the mechanical integrity and increases the life cycle of the device even when tested under extreme conditions.

Since this remarkable performance has yet to be realized in commercial devices, these LSG supercapacitors could lead the way to ideal energy storage systems for next generation flexible, portable electronics.

Explore further: Pinpoint laser heating creates a maelstrom of magnetic nanotextures

More information: www.sciencemag.org/content/335/6074/1326.full

Provided by University of California - Los Angeles

5 /5 (27 votes)

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210
2 / 5 (4) Mar 15, 2012
WOW...OUTSTANDINGLY high conductivity numbers...now if I can just locate some ESR numbers for it, I can start building a new kind of 'switching' (or, new class of operation for switching) power supplies.

word-
bg1
5 / 5 (1) Mar 15, 2012
How many farads? How many KWH/kg?
maxcypher
not rated yet Mar 15, 2012
Could somebody look at the actual study to determine how this new EC stands up to the latest electric car battery?
ichigo kurosaki
not rated yet Mar 15, 2012
wow.this could help to make eveything ultra fast and stronger
Howhot
5 / 5 (2) Mar 15, 2012
Wow, this could be fantastic for Solar Energy,
Vendicar_Decarian
0.3 / 5 (38) Mar 16, 2012
Should make a great bomb once they figure out how to stack gazillions of layers into a compact volume.
antialias_physorg
4 / 5 (2) Mar 16, 2012
Don't be too quick to get your hopes up. Supercapacitors have other drawbacks, like fast self-discharge (i.e. you can't park your car without having to recharge it before you want to travel again). If they get that one solved, however, then it would be a big step forward.
kochevnik
2.3 / 5 (3) Mar 16, 2012
you can't park your car without having to recharge it
Parking is where you plug the car in! Not a dealbreaker.
antialias_physorg
3.7 / 5 (3) Mar 16, 2012
Parking is where you plug the car in! Not a dealbreaker.

You ever go shopping? Or to work? Or visiting people who might not have a charger? Or to the beach? Or ....
Scottingham
not rated yet Mar 16, 2012
these are supposed to be in conjuction with batteries...think of an 80/20 mix...
kaasinees
1 / 5 (1) Mar 16, 2012
Parking is where you plug the car in! Not a dealbreaker.

You ever go shopping? Or to work? Or visiting people who might not have a charger? Or to the beach? Or ....

A driver(a computer chip that controls the power, not a car driver) could predict when a super capacitor discharges and take advantage of it to use that power to supply a battery or the grid.
antialias_physorg
not rated yet Mar 16, 2012
So your car will still be discharged when you get there. Great

And charging will take a while. Supercapacitors CAN charge in a short time. However a normal outlet cannot deliver that amount of juice in a short while. If you want to take advantage of the quick charging times you'll have to go to dedicated stations.
SongDog
not rated yet Mar 16, 2012
For automotive use, this would be used for regenerative braking and acceleration. They'd be sized to store enough energy to go from a standing start to top speed, and maybe a little more to offset lost performance due to aging phenomena. About 100kW for 6 seconds should do. Regular secondary batteries are for overcoming friction losses, wind resistance, etc. These still have to handle a full day's worth of duty, but because the supercaps take over the high-current requirement, the batteries can be lighter and longer lived: they only need to deliver the steady-state current needed for highway speeds and recharging. Whether the right mix is 80/20 or not depends on detailled performance characteristics.
210
1.7 / 5 (3) Mar 16, 2012
So your car will still be discharged when you get there. Great

And charging will take a while. Supercapacitors CAN charge in a short time. However a normal outlet cannot deliver that amount of juice in a short while. If you want to take advantage of the quick charging times you'll have to go to dedicated stations.

Or....have a stand-by power pack ready to drop in at the house or, also....a charge station that uses the same power-pack/supercap arrangement. Now, cost to performance,divided by longevity would be the issue.

word-to-ya-muthas
210
1 / 5 (3) Mar 16, 2012
Should make a great bomb once they figure out how to stack gazillions of layers into a compact volume.

Hummm...maybe, not a bomb, but, a much more compact trigger. If I can manage the power flux yield at the nanomaterial level, I could build a pulse rifle, featuring square casings, no CASELESS, in the 10 to 20 millimeter range, explosively formed rounds -from the Supercap's ignitor, using preformed metal slugs, protect the barrel with a mag field and ablative inserts (graphene?), pushed out at better than 6000 meters per second would make them inherently armour piercing. Enhance accuracy by ionizing the rounds flight path with a pulse of free electron laser fire. Facilitate effective fire by pushing out at least 20 rounds a second limited to three-second burst. Manage recoil using an opposing mag field, just enough to do the job (Have to raise my bench press a bit!) I might need a Man-Magnifier suit -Vendi, get on that w/camouflage! OHH! Biggy...armour-protect the weapon!!
word
fmfbrestel
not rated yet Mar 16, 2012
"If you want to take advantage of the quick charging times you'll have to go to dedicated stations." Oh NO!! You mean I might have to drive somewhere other than my house to add more energy to my car??? NEVER!!!
Eikka
1 / 5 (1) Mar 16, 2012
I don't think the inventor of this thing has even measured how much capacity it has, other than sticking a LED to it and seeing that it shines.

http://www.youtub...FwyoWKXo

antialias_physorg
1 / 5 (1) Mar 16, 2012
Or....have a stand-by power pack ready to drop in at the house

So...lemme get this straight: you get rid of the expensive battery in the car to buy supercapacitors and a LARGER expensive battery set at home...Makes sense. Oh no, wait...it doesn't.
(and again: unless everyone has that type of battery -including at the beach- you're stranded unless you only drive from your home to...your home)

Oh NO!! You mean I might have to drive somewhere other than my house to add more energy to my car??? NEVER!!!

Remember: you park at home. The cap discharges over night. How are you going to get to the station? Lay down 20km of heavy duty cable?
210
1 / 5 (3) Mar 16, 2012
Or....have a stand-by power pack ready to drop in at the house

So...lemme get this straight: you get rid of the expensive battery in the car to buy supercapacitors and a LARGER expensive battery set at home...Makes sense. Oh no, wait...it doesn't.
(and again: unless everyone has that type of battery -including at the beach- you're stranded unless you only drive from your home to...your home)

No, the battery/SuperCap modules, are well placed, as now.... You 'trade' them! Something like recycling and leasing combined. Instead of pulling up to the pump and paying for gas, you pull up...drop your discharged module - trade. It's tested for lifespan..you pay LESS when your module is new...you pay more, as the module becomes antiquated and more difficult to charge. Not that different from the burden of running an older car as opposed to newer tech. Gas stations are not inside a friends house/beach/school... (U have friends or...oh well) charge stations can B anywhere.
antialias_physorg
1 / 5 (1) Mar 16, 2012
you pull up...drop your discharged module - trade

*sigh*

How will you 'pull up' when you CANNOT GET THERE because your supercap discharged over night or while you were inside the mall power-shopping or at your in-laws in the sticks or...anywhere where you didn't park RIGHT NEXT TO A SWAPPING POINT?
210
1 / 5 (3) Mar 17, 2012
you pull up...drop your discharged module - trade

*sigh*
How will you 'pull up' when you CANNOT GET THERE because your supercap discharged over night or while you were inside the mall power-shopping or at your in-laws in the sticks or...anywhere where you didn't park RIGHT NEXT TO A SWAPPING POINT?

OKAY, it was plugged in all night, and somehow...YOU probably would ride it into the ground and drain every last drop of juice out of it and get on Physorg and cry about it...I get it now..OKAY you win...Most people run out of gas rarely, and know how to read the gas gauge...and I assumed you do too. My bad..You should stick with gasoline forever...just ignore all this tech stuff that leaves you in the middle of a Kansas cornfield without a spare drop of, or hope of getting to, a charge station...I see your point, none of this could possibly work for you...good luck...stick to those liquid dinosaurs until you become one of them. It won't work for you...ok, ok, ok!
word-
antialias_physorg
1 / 5 (1) Mar 17, 2012
Most people run out of gas rarely, and know how to read the gas gauge

Most people don't expect to park their car with a full tank and come back a few hours later to discover it's empty. THAT is the problem with (super)capacitors.
This has nothing to do with not being able to read a fuel gauge. It doesn't matter what your fuel gauge says. You will not be able to top up your car sufficiently to ensure that you can start it the next time you want to use it.

I love this tech, but it's not for use in EVs as the main energy storage solution UNLESS they figure this problem out.
There are uses in brake energy recuperation and quick acceleration boosting as SongDog already pointed out.
RJS
3.7 / 5 (3) Mar 17, 2012
A. The self discharge rate was not disclosed; it varies dramatically for cap technology type. Most ultra-caps are only a bit faster than lead-acid batteries, and stored energy of an organic electrolyte supercap decreases to 50 percent in 30 to 40 days. My golf car more than tops itself off every day with sunshine. No plug needed for maintenance.

B. I wouldn't take any vehicle on a trip where there is not a known refueling opportunity within range (others aren't so stringent). When I learned to drive cars did not have an idiot light for low fuel; it is a telling example that it appears all new cars do.

Modern gas cars have fuel tanks sized to the average area density of modern gas stations and average driver habits. 100 years ago drivers on longer trips often bought gasoline in pharmacies. The future will have a different infrastructure for different fuel.
topkill
1 / 5 (1) Mar 18, 2012
Guys, you can't remotely extrapolate other EC characteristics (e.g. self discharge) to these devices. Supercaps vary from each other tremendously in every way. These will probably have some other drawbacks, but you have no idea which ones yet and you certainly have no idea if self discharge is one of them.
topkill
1 / 5 (1) Mar 18, 2012
Vendicar_Decarian & 210,

About the bomb stuff...uh, have you guys checked your meds lately? LOL
alfie_null
not rated yet Mar 18, 2012
If leakage is an issue, it will affect more than just not being able to park away from a recharging station. Imagine the energy required to balance the leakage rate. Imagine a nation/world full of cars with super-vampire rechargers continually topping off these capacitors as they sit in their owners' garages. All that energy being dissipated as waste.
JRR Polkin
not rated yet Mar 21, 2012
What if this technology could be integrated into solar cells produced with the twin creeks method of hydrogen exfoliation of silicon? I could see some brilliant, cheap solar cells with integrated power storage. Anyone see any drawbacks to such a system? I'm thinking cheap and effective. How much would leakage be a factor in such a system?
JRR Polkin
not rated yet Mar 21, 2012
http://www.physor...eks.html

Here's the link BTW.
antialias_physorg
not rated yet Mar 21, 2012
Anyone see any drawbacks to such a system?

- Production vs. storage density.
- Discharge
- Different lifetimes of the two systems (i.e. you have to throw it away when the less long-lived one gives out).
- Different voltages (solar produces a constant voltage, supercaps deliver variable voltages depending on level of discharge)
- ...

Apart from that I'm not entirely sure what you would want to gain from combining these two systems?
JRR Polkin
not rated yet Mar 21, 2012
I was just thinking of possible integrated storage for solar cells. If there was a way for units to store the energy they produce integrated into a solar cell, I think it would make implementation much more desirable.

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