Paper-thin supercapacitor has higher capacitance when twisted than any non-twisted supercapacitor

Sep 21, 2010 By Lisa Zyga feature
(A) Using three of the new highly flexible supercapacitors arranged in series, the researchers demonstrated lighting a red LED. (B) An illustration of the flexible, all-solid-state paper-like polymer supercapacitors. Image credit: Chuizhou Meng, et al. © 2010 American Chemical Society.

(PhysOrg.com) -- In an effort to develop wearable electronics, researchers have designed a new ultra-thin supercapacitor that has a capacitance that is six times higher than that of any current commercial supercapacitor. What's more, the new supercapacitor was tested in a twisted state to demonstrate its good electrochemical properties with high flexibility.

The researchers, Chuizhou Meng, et al., from the Tsinghua-Foxconn Nanotechnology Research Center at Tsinghua University in Beijing have published their results in a recent issue of .

As the researchers explain, portable electronic devices are becoming increasingly small and flexible. However, the energy management components - e.g. batteries and supercapacitors - tend to lag behind the other components when it comes to small size and flexibility. Specifically, supercapacitors are limited by their conventional configuration, which is a separator sandwiched between two electrodes sealed in liquid . The two major drawbacks with this configuration are that the liquid electrolyte requires safety encapsulation materials to prevent leakage, and the multiple parts of the system that move relative to each other decrease the performance and cycle life of the device.

In an attempt to design an energy-storage device that is smaller and more flexible than previous devices, the researchers turned to carbon-based materials. By using two slightly separated electrodes made of polyaniline (a conductive polymer) and carbon nanotubes, and solidifying them in a gel polymer solid-state electrolyte (acting simultaneously as a separator), the researchers could fabricate a highly flexible supercapacitor that was as thin as a standard piece of paper. The and no moving parts enabled the researchers to overcome the problems with the conventional configuration, and further decrease the size and increase the flexibility of the device.

“We innovatively designed the and optimized the configuration of our supercapacitors so as to effectively make full use of each necessary component,” coauthor Changhong Liu told PhysOrg.com. “We omitted the heavy metal current collectors and bulky encapsulation of conventional supercapacitors. Here, carbon nanotubes formed a good electric conducting network, polyaniline provided extremely large pseudocapacitance, and the ultra-thin middle gel polymer electrolyte layer acted simultaneously as a separator. Overall, the devices are very flexible and paper-like.”

In tests, the researchers demonstrated that the new supercapacitor has a capacitance of 31.4 F/g when twisted, compared to 5.2 F/g for current commercial supercapacitors. The new supercapacitor also showed superior characteristics in other areas, such as a high power density, low leakage current, and long cycle life. The researchers predict that these properties could be further improved by optimizing the device's materials and structure, such as by shortening the distance between electrodes.

“To the best of our knowledge, this flexible paper-like supercapacitor has much higher specific capacitance than current high-level conventional commercial ones,” Liu said, adding that the researchers could not guarantee that they were aware of every commercial device.

The researchers also showed how three twisted supercapacitors connected in series could be used to light a red LED. After 15 minutes of charging at 2.5 V, the rolled-up supercapacitors lit the LED for almost 30 minutes. Given its high and flexibility that surpass current commercial supercapacitors, the new should be attractive for use in wearable electronics, an area which is still only beginning to be explored.

“We think that this lightweight and flexible energy storage device will have great application potential in future wearable electronics,” Liu said. “For example, incorporated with flexible display technology, it will make a flexible electronic book truly paper-like, by saving much weight and space. And in the future, when flexible large-scale integrated circuits come true, a lightweight and flexible notebook computer is much expected.”

Explore further: Discovery is key to metal wear in sliding parts (w/ Video)

More information: Chuizhou Meng, et al. “Highly Flexible and All-Solid-State Paperlike Polymer Supercapacitors.” Nano Lett. ASAP. DOI:10.1021/nl1019672

4.9 /5 (58 votes)

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BillFox
3 / 5 (1) Sep 21, 2010
The only thing I am curious about is the method they used because weight is involved in the measurement.

31.4 F/g when twisted, compared to 5.2 F/g for current commercial supercapacitors


This could imply that the capacitor is lighter per storage, but not necessarily smaller. I'm no electrical engineer though.
ricarguy
1.7 / 5 (3) Sep 21, 2010
Today's super-capacitors are known for their low impedance and thus high power capabilities. This device, while an interesting advance in specific capacitance, seems to have a very low working voltage and high impedance i.e. a very low power device. That makes sense given the flat form factor. So this charges and discharges quite slowly, more comparable to a battery than a capacitor. Still good potential usefulness in very low power applications.

Per the above message, they are talking about capacitance per gram of material.
ormondotvos
3 / 5 (1) Sep 21, 2010
31 Farads/Gram needs to be compared to battery capacities in terms of KWh/gram. Who's up for the conversion? A Farad's an amp for a second, right?
TheQuietMan
1 / 5 (1) Sep 21, 2010
Hmmm, so what happens if (when?) it shorts out while you're wearing it? Spontaneous human combustion anyone?

I'm still waiting to hear more from the Estor.
TheQuietMan
not rated yet Sep 21, 2010
I meant eestor, it was a supercap that hit the news over a year ago and dropped out of site.
Graeme
4 / 5 (1) Sep 22, 2010
0.5CV^2 is the formula for energy stored. so 0.5x31x2.5^2=98 Joules per gram

How does that compare to a battery? it sounds small compared to lithium.

Super caps are still around and in use in cameras, cars and other things as a backup power.
axemaster
4 / 5 (2) Sep 22, 2010
31 Farads/Gram needs to be compared to battery capacities in terms of KWh/gram. Who's up for the conversion? A Farad's an amp for a second, right?


A farad means 1 Coulomb of charge stored per volt of potential difference. It has nothing to do with the power output, it only measures total storage capacity.

I must agree though, this sounds like a very low voltage, low power device, if only because the extreme thinness wouldn't withstand much voltage.
kuro
2 / 5 (1) Sep 22, 2010
Well, first, I can totally light up a red LED without using three supercapacitors and a research team behind them, in series or in parallel.

If the lofty goal is powering wearable electronics, the generate-it-as-you-walk approach makes a lot more sense than carrying large amounts of charge in your clothing.
Ulg
1 / 5 (1) Sep 25, 2010
Most super caps are low voltage, 5 volt is rather high for anything labeled a super cap. That does not mean you cannot use them with say a 10 volt circuit, you just need to use two in series. The potential voltage difference from one cathode to the other will only be 5 volt on a 10 volt circuit. This certainly does effect the capacitance though.