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National University of Singapore researchers devise membrane-based supercapacitors; possible new route to high-performance supercapacitive energy storage

xie
(a) Chemical structure of the PEDT:PSSH polymer blend. (b) Formation of hydrated ionic conduction channels in the PEDT:PSSH film network due to the presence of the hydrophilizing SO3 groups. Xie et al. Click to enlarge.

A team from the National University of Singapore's Nanoscience and Nanotechnology Initiative (NUSNNI), led by principle investigator Dr. Xian Ning Xie, has developed a polystyrene membrane-based supercapacitor that they say will be easier to scale up than the current alternatives. Unlike more conventional supercapacitor electrode materials with large surface areas and high porosities, the new hydrophilized polymer network uses ion-conducting channels for fast ion transport and charge storage.

When sandwiched between and charged by two metal plates, the membrane can store charge at 0.2 farads per square centimeter, well above the typical upper limit of 1 microfarad per square centimeter for a standard capacitor. They reported on their work in a paper published earlier this summer in the Journal of Polymer Science Part B.

Conventional electrode materials for supercapacitors are based on nanoscaled structures with large surface areas or porosities. This work presents a new electrode material, the so-called hydrophilized polymer network. The network has two unique features: 1) it allows for high capacitance (up to 400 F/g) energy storage in a simple film configuration without the need of high-surface-area nanostructures; 2) it is unstable in water, but becomes extremely stable in electrolyte with high ionic strength.

The above features are related to the hydrophilizing groups in the network which not only generate hydrated ionic conduction channels, but also enable the cross-linking of the network in electrolyte. Because of its practical advantages such as easy preparation and intrinsic stability in electrolyte, the hydrophilized network may provide a new route to high-performance supercapacitive energy storage.

—Xie et al.

The polymer membrane includes PSSH (poly(styrene sulfonic acid)). PSSH is an excellent hydrophilizer due to its high density of sulfonic SO3 hydrophilizing groups, the team notes in their paper. The incorporation of SO3 groups allows for the formation of hydrated paths for enhanced ionic conduction in proton-conducting fuel cell membranes.

In the PEDT:PSSH network presented...the hydrophobic PEDT forms a water-insoluble framework, while the superhydrophilic PSSH provides SO3 groups for hydration channel formation throughout the framework. Due to the ion-conducting channels, the network facilitates fast ionic transport and charge storage, and thus is a promising electrode material for supercapacitors.

—Xie et al.

Use of the membrane could also reduce the cost. With existing technologies based on liquid electrolytes, it costs about US$7 to store each farad. With the advanced energy storage membrane, the cost to store each farad falls to US$0.62. This translates to an energy cost of 10-20 Wh per US dollar for the membrane, as compared to just 2.5 Wh per US dollar for lithium ion batteries.

Compared to rechargeable batteries and supercapacitors, the proprietary membrane allows for very simple device configuration and low fabrication cost. Moreover, the performance of the membrane surpasses those of rechargeable batteries, such as lithium ion and lead-acid batteries, and supercapacitors.

—Xian Ning Xie

The research is supported by grants from the Singapore-MIT Alliance for Research & Technology (SMART) (Ignition Grant ING10022-ENG(IGN)), and National Research Foundation. Dr Xie and his team started work on the membrane early last year and took about 1.5 years to reach their current status, and have successfully filed a US patent for this invention.

The team is currently exploring opportunities to work with venture capitalists to commercialize the membrane.

Resources

  • Xian Ning Xie, Junzhong Wang, Kian Keat Lee, Kian Ping Loh (2011) Supercapacitive energy storage based on ion-conducting channels in hydrophilized organic network. Journal of Polymer Science Part B: Polymer Physics Volume 49, Issue 17, pages 1234–1240 DOI: 10.1002/polb.22295

Comments

HarveyD

If this can be scaled up, it could soon compete favorably with the best lithium batteries. Will this type ultra-caps be able to be cycled quickly many thousand times?

HealthyBreeze

Are they really saying they have increased energy density 4-5 orders of magnitude (1 microFarad to 0.2 Farad)?

That seems, um, huge. Wouldn't that put capacitors ahead of lead acid batteries in energy density?

Arne

HealthyBreeze,

The 1 microfarad is for a standard capacitor, not a supercapacitor. They need to sell it, read the last sentence:

"The team is currently exploring opportunities to work with venture capitalists to commercialize the membrane."

Is this the sequel to EEStore? Don't get too excited.

kelly

".. the membrane can store charge at 0.2 farads per square centimeter, well above the typical upper limit of 1 microfarad per square centimeter.." --

IS stating 'they have increased energy density 4-5 orders of magnitude'

If true, should they work with non venture capitalists?

kelly

BTW, is something lost in translation?

Capacitance is via metal plates INSULATED from each other, not via "ion-conducting channels" or am I missing something?

Engineer-Poet

Cheapness of energy storage matters, but so do weight and bulk. Even if this pans out it may not be a panacea.

Trevor Carlson

So how much energy could this capacitor hold if it weighed the same and had the same Voltage as the current NiMH Prius battery?

Prius IV: 201.6 Volts at 29,120 grams with a nominal capacity of 6.5 Ah.
Membrane Supercap: 201.6 V at 29,120 grams (*4F/g)
gives 652,288 Ah!

surely I did something wrong cause that's just crazy talk.

Darius

Singapore National University? Is it really so? If it is respectful academic institution matters could cleared immediately. No fake secrecy like in eestore case.

kelly

I keep looking for a misplaced decimal, but these are the supercapacitive energy storage claims and they are very public: http://esciencenews.com/articles/2011/09/29/national.university.singapore.researchers.have.devised.worlds.first.energy.storage.membrane

yarross

@Trevor
You've assumed 200+V per unit. Doubt that any ionic capacitor could reach even 10V before electrolyte starts to decompose.

marketquant

A quick google search turns up around 100 F/g for current super-capacitors, and around 200 F/g for experimental graphene based ones, so this one at "up to 400 F/g" (if cheap) would be a notable achievement.

Roy_H

They really are making extraordinary claims. 1/4 to 1/8 the cost of lithium batteries on energy storage. They make no mention of voltage capability, but to get that kind of energy storage they need to have 200 to 300 volts. Typical supercapacitors only are good for 2 to 4 volts.

If they can truly make 200 volt 1 farad caps for $0.62 then this will be a major revolution.

Roy_H

Correction 50 volts on 1 farad caps for $0.62, still a major revolution.

Darius

I am waiting for development of the story.

HarveyD

Darius...should we do more and actively support this approach?

HarveyD

Will super-caps, ultra-caps and batteries soon become storage devices using similar technologies? Caps may play a much large role when their energy density goes up to 100+ Wh/Kg. Combo (caps-batteries) may also have a bright future.

kelly

More media http://www.sciencedaily.com/releases/2011/09/110929074021.htm

Bob Wallace

From the paper linked in the Resources section...

"film S1 was subjected to repeated charge/discharge operation of 2000 cycles under different current density and in different electrolytes, respectively. As shown in
Table 3, after 2000 cycles, there is no obvious decrease in
the specific capacitance of the film"

The fact that they are looking for capital to start manufacturing rather than saying something like "more research will be required to make this scale" is interesting.

Even if too bulky/heavy for EVs it could be a killer for grid storage. Very low cost and very long life. That's what we need to speed the transition away from fossil fuels.

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