Transparent, flexible supercapacitors pave the way for a multitude of applications

May 23, 2016 by Lisa Zyga feature
The transparent, flexible supercapacitor prototype, based on single-walled carbon nanotube thin films, is shown during charging and discharging. Credit: Kanninen et al. ©2016 IOP Publishing

(Phys.org)—The standard appearance of today's electronic devices as solid, black objects could one day change completely as researchers make electronic components that are transparent and flexible. Working toward this goal, researchers in a new study have developed transparent, flexible supercapacitors made of carbon nanotube films. The high-performance devices could one day be used to store energy for everything from wearable electronics to photovoltaics.

The researchers, Kanninen et al., from institutions in Finland and Russia, have published a paper on the new supercapacitors in a recent issue of Nanotechnology.

In general, supercapacitors can store several times more charge in a given volume or mass than traditional capacitors, have faster charge and discharge rates, and are very stable. Over the past few years, researchers have begun working on making supercapacitors that are transparent and flexible due to their potential use in a wide variety of applications.

"Potential applications can be roughly divided into two categories: high-aesthetic-value products, such as activity bands and smart clothes, and inherently transparent end-uses, such as displays and windows," coauthor Tanja Kallio, an associate professor at Aalto University who is currently a visiting professor at the Skolkovo Institute of Science and Technology, told Phys.org. "The latter include, for example, such future applications as smart windows for automobiles and aerospace vehicles, self-powered rolled-up displays, self-powered wearable optoelectronics, and electronic skin."

The type of supercapacitor developed here, called an electrochemical double-layer capacitor, is based on high-surface-area carbon. One prime candidate for this material is single-walled carbon nanotubes due to their combination of many appealing properties, including a , high strength, high elasticity, and the ability to withstand extremely high currents, which is essential for fast charging and discharging.

The problem so far, however, has been that the carbon nanotubes must be prepared as in order to be used as electrodes in supercapacitors. Current techniques for preparing thin films have drawbacks, often resulting in defected nanotubes, limited conductivity, and other performance limitations.

In the new study, the researchers demonstrated a new method to fabricate thin films made of single-walled carbon nanotubes using a one-step aerosol synthesis method. When incorporated into a supercapacitor, the thin films exhibit the highest transparency to date (92%), the highest mass specific capacitance (178 F/g), and one of the highest area specific capacitances (552 µF/cm2) compared to other carbon-based, flexible, transparent supercapacitors. The films also have a high stability, as demonstrated by the fact that their capacitance does not degrade after 10,000 charging cycles.

With these advantages, the new device illustrates the continued improvement in the development of transparent, flexible supercapacitors. In the future, the researchers plan to further improve the energy density, flexibility, and durability, and also make the supercapacitors stretchable.

"One more important characteristic to be realized and urgently expected in future electronics is the stretchability of the conductive materials and assembled electronic components," said coauthor Albert Nasibulin, a professor at the Skolkovo Institute of Science and Technology and an adjunct professor at Aalto University. "Together with Tanja, we are currently working on a new type of stretchable and transparent single-walled carbon nanotube supercapacitor. We are confident that one can create prototypes based on carbon nanotubes that might withstand 100% elongation with no performance degradation."

Explore further: Highly stretchable fiber-shaped supercapacitor based on carbon nanotubes

More information: Kanninen et al. "Transparent and flexible high-performance supercapacitors based on single-walled carbon nanotube films." Nanotechnology. DOI: 10.1088/0957-4484/27/23/235403

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8 comments

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ab3a
5 / 5 (1) May 23, 2016
Wouldn't the flexible nature of the capacitor change the capacity much like an electret microphone? Wouldn't the act of flexing it cause releases of energy?
MR166
1 / 5 (1) May 24, 2016
Also, the charge and discharge rates of super caps are a lot lower than traditional caps as proven by the super caps frequency limitations.
Da Schneib
5 / 5 (3) May 24, 2016
Also, the charge and discharge rates of super caps are a lot lower than traditional caps as proven by the super caps frequency limitations.
Ummm, they're very high compared with batteries. You're comparing them with the wrong thing. They're not intended for high frequency charges and discharges like RF caps are. They're intended for energy storage.

It's obvious you don't know much about either RF or energy storage, not to mention very little about EE in general. Maybe you should go find somewhere to post that's a little closer to your intellectual level.
MR166
1 / 5 (1) May 24, 2016
"In general, supercapacitors can store several times more charge in a given volume or mass than traditional capacitors, have faster charge and discharge rates, and are very stable."

Da, English might be your second language but that quote was pretty clear to me. They weren't comparing super caps to batteries in that sentence were they? Even in comparison to electrolytics super caps have a slow discharge rate.
Da Schneib
not rated yet May 24, 2016
Measure the charge rate in coulombs/s.

Now try to put that into an RF cap. I suggest wearing goggles.

Like I said, you don't know much about RF, energy storage, or EE.

Dumb da dumb dumb. Dumb da dumb dumb duuuuhhhhh.
MR166
not rated yet May 25, 2016
"Measure the charge rate in coulombs/s.

Now try to put that into an RF cap"

That might just be the dumbest statement that I ever read.
Mike_Massen
1 / 5 (2) Jun 29, 2016
Ah just came across this article, um so...

MR166 says
They weren't comparing super caps to batteries in that sentence were they? Even in comparison to electrolytics super caps have a slow discharge rate.
I just put 6 x 3000F super caps in one of my cars to replace the batteries for a trial.

If it works fine with a means to top up the self discharge rate with just a simple solar cell or two then I won't be using batteries ever again, not only do they run cool, they don't have acid can do > 5000 cycles so should last much longer and less weight too.

Also used a supercap bank to move a vehicle (via starter motor) that wouldnt fire - ie To substitute for the car battery as the super caps are very quick to re-charge...

In both cases the super caps can easily supply 100's of amps yet not heat up, overall their discharge rate is comparable to batteries and better than standard electrolytics, so what were you getting at in any sort of quantitative way ?
Mike_Massen
1 / 5 (2) Jun 29, 2016
MR166 claimed, when faced with Da Schneib's electronic engineering input
"Measure the charge rate in coulombs/s.
Now try to put that into an RF cap"
That might just be the dumbest statement that I ever read.
No MR166 !
The issue with frequency & capacitors has to do with the rate charge can be stored/removed and for this reason the higher the capacity the lower the frequency of operating in a *tuned circuit*.

In Radio Frequency (RF) smaller capacitors used for tuning, decoupling, isolate DC bias etc

Higher Farad value capacitors such as electrolytics in Eg power supplies for RF & comms/control devices provide filtering so any unwanted troublesome noise (high freq AC superimposed on DC etc) is absorbed & this can only occur when capacity is high enough & provided there is low Equivalent Series Resistance (ESR). There is also Equivalent Series Inductance (ESL) which affects transient pulse operation & fortunately low enough for super caps re automotives...

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