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Ultracapacitors - the Batteries of the Future?

Posted March 21, 2012 10:00 AM by cheme_wordsmithy

My first experience with capacitors was in my college physics class. The professor had us putting together circuits with microfarad capacitors, observing the rate of charge and discharge in setups with various resistances.

That's about as far as it went for me: capacitors store and discharge power like a battery, but at faster speeds with a comparably larger footprint.

It wasn't until I looked further into the future of energy storage that the words ultracapacitors and supercapacitors began to surface. And although these devices are not new (the first was made in 1957 by General Electric), the interest and potential of the technology has grown tremendously over the past decade.

What's "Super" About SuperCapacitors?

Supercapacitors, also called ultracapacitors, are capacitors with a high energy density (i.e. they store more energy relative to their size). What makes them different than capacitors is their ability to store much more capacitance. While the Farad used to seem like an incredibly large unit for a capacitor, some supercapacitors can reach into the kiloFarad range.

(The internal mechanism of the supercapacitor. - Credit: Ultracapacitors.org)

Currently, supercapacitors are used in some electric and hybrid vehicles as temporary energy stores for regenerative braking. They can also be connected to batteries to regulate the power they supply. However, future research aims to make ultracapacitors a competitive alternative toh batteries as energy storage devices.

But what do they offer over batteries? Well, in comparison, supercaps (as they are sometimes nicknamed) have faster power transfer than batteries. This means that charge time is measured in seconds or minutes rather than hours, and that more energy can be discharged (used) in a shorter time. In addition, they do not degrade noticeably over time, meaning the life cycle of the ultracapacitor is much longer than the battery.

Why is this exciting? The biggest inadequacies of batteries are charge time and life cycle. In everything from smart phones to EVs, charging and battery replacement are often the most inconvenient, expensive, or application-limiting problems. Replacing batteries with ultracapacitors could revolutionize the energy storage industry.

What's the Holdup?

The biggest problems with ultracapacitors are expense and energy density. Even though they can generate more power than a battery, they can't hold as much energy. Supercaps are much heavier and larger than batteries of the same rating. A battery of the same weight can store anywhere from 10 to 25 times more energy than an ultracapacitor. For perspective's sake, a 300 mile range EV powered by current supercapacitor technology might weigh anywhere up to 10 tons, equivalent to a partially loaded tractor trailer.

The quick-charge advantage of larger ultracaps is also somewhat deceiving for larger applications. The amperage required to charge an EV-sized capacitor in mere seconds would be massive, and the cables used would thus be a major safety problem for any human operator. Thus the charging time is limited by the charger technology

Recent Advancements

One of the ways to make supercapacitors more effective is to improve the electrode materials. The porous carbon electrodes in the ultracapacitor are what give it the ability to store much larger amounts of energy than normal capacitors can. Though standard supercaps use electrodes made of activated carbon, researchers at UCLA have found a way to produce graphene electrodes which provide even more accessible surface area. The process to make the graphene uses a graphite oxide coating on a DVD disc inside a LightScribe DVD drive.

(Architecture of the grapheme supercapacitor. - Credit: University of California, Los Angeles)

In addition to increasing the energy capacity, Laser Scribed Graphene (LSG) electrodes are said to lower the expense of supercapacitors by eliminating the need for binders or current collectors as is the case for conventional devices using activated carbon.

In addition, the team has utilized a polymer gelled electrolyte which acts as both a separator and an electrolyte in the device architecture, providing greater mechanical integrity and ease of fabrication.

The Future

Ultracapacitors for EVs and high energy applications are likely still a long ways off, and perhaps advances in batteries will always be one step ahead. But I see a lot of potential in their implementation in smaller appliances, especially considering developments being made at places like UCLA.

What are your thoughts on the supercapacitor? Will it replace the battery, or is the idea of an inexpensive, quick charge storage device still too far off to think about?

Sources:

Solar Feed - The Future of Electric Vehicles: Batteries or Ultracapacitors?

ScienceDaily - GrapheneSupercapacitor Holds Promise for Portable Electronics

Battery University - Supercapacitor

Carhistory4u - Super (Ultra) Capacitors

Ultracapacitors.org - About Ultracapacitors

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#1

Re: Ultracapacitors - the Batteries of the Future?

03/22/2012 6:08 AM

The people at MIT continue to blow my mind with the things they come up with. Yes, I think ultracaps, or some completely different version of them will play a huge role.

http://web.mit.edu/erc/spotlights/ultracapacitor.html

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#2

Re: Ultracapacitors - the Batteries of the Future?

03/22/2012 7:30 AM

INMHO ultracaps will complement rather than replace batteries.

They can store large charges available for short times (--> huge currents which cannot be used to charge a battery). But you'd better transfer those charges to the battery asap, because self discharge is worse in the ultracap. And it must be "empty" for the next cycle.

brgds

Snel

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#3
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Re: Ultracapacitors - the Batteries of the Future?

03/22/2012 7:55 AM

"When we were done, we realized that it wasn't really a capacitor anymore," Schindall said. "Our adapted ultracapacitor actually mimics the molecular lattice of a battery but without the chemical reactions. It's sort of a synthetic battery." The device could be made in all the sizes needed to replace today's commercially available batteries-at roughly the same cost.

We might have to come up with a new name for tomorrow's storage devices.

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#4

Re: Ultracapacitors - the Batteries of the Future?

03/22/2012 10:22 AM

They sound like the "Shipstones" from Heinlien's Friday novel

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#5

Re: Ultracapacitors - the Batteries of the Future?

03/22/2012 12:47 PM

I wonder if we can couple this with high-speed levitation vehicles? I keep thinking that we're so locked into circular motion (wheels, anyone?) that it might not be the most efficient means of transportation for larger numbers of persons. The linked article above does some analysis about this. These vehicles are more popular in other countries. Seems like in some areas (how many?) the U.S. is always "gonna"... (heard this sort of hype before? Why no action?)

I suppose this could be another thread all by itself. Sorry if this is a distraction. I'll mark it OT.

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#6
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Re: Ultracapacitors - the Batteries of the Future?

03/22/2012 7:21 PM

Whether it's maglev or something else, we should be looking at ways to move goods, particularly produce, from one part of the country to another. Unlike people, stuff can be moved at crazy speeds. I'm thinking along the lines of the vacuum tubes that stores and banks use, with distribution centers located around the US. From those, trucks would take care of only local distribution.

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#7
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Re: Ultracapacitors - the Batteries of the Future?

03/23/2012 12:12 PM

I think I'll try to find a way to throw your name in the hat for Secretary of Transportation.

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#8
In reply to #6

Re: Ultracapacitors - the Batteries of the Future?

03/26/2012 5:49 AM

You mean railways?

I heard the USA is finally going to start building a network of tracks to allow cheap transport of huge volumes of stuff. Welcome to the 19th century! ;-)

I know you guys are wedded to the idea of driving 3000 miles for a "road trip", but how much better would it be to drive your car to the railway, put it on the back, then be ferried a few thousand miles by more efficient railway, and then have your car at the final destination?

(I wish I could do that in the UK, too.)

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#9

Re: Ultracapacitors - the Batteries of the Future?

04/02/2012 9:18 AM

I think that there are a lot of places where higher energy density capacitors could be used. IMHO some batteries are going backwards. For example, there's a reason why Milwaukee Electric Tool used NiCd batteries so long in their tools. Neglecting the toxic aspect, NiCd has a much higher drain rate capability while still maintaining nearly their rated capacity (up to 50C -- which is not something that other batteries can come close to claiming). They also last for years under heavy use such as with high temperature operation, very quick discharge and charging times and sitting long periods of time fully in various charge states. Lithium Ion batteries are damaged by any of those conditions. How long does a laptop battery last? A year or two maybe? Of course the energy density is like 4x better, but they aren't durable for tool use. With current battery tech, I'd rather have a durable battery even if it weighs twice as much and has a lower capacity because I don't want to have to spend $200 on tool batteries every couple years. NiCd batteries in my old cheap tools have lasted 6 years before failure with no maintenance (especially certain types of NiCd, there are low capacity and high capacity. The low capacity ones have a crazy high service life because the materials are built thicker inside reducing inter-cell shorting from cadmium whiskers forming. It also means they can have higher charge/discharge rates). I suspect my 4 year old Milwaukee batteries will last many more years because they still operate at what seems to be nearly 100% of what they were when they were new.

I could imagine ultracapacitors in conjunction with lithium batteries being a good match in some tool applications. I'd say that a lot of the time, power tools just use fairly short bursts of power like when you're doing a bunch of deck screws at a second or two each (unlike in a laptop which is a fairly constant draw). Even in cameras it might be beneficial. The shutter mechanism in some SLRs use a lot of power for a very short time. So do flashes. Lithium Ion batteries would most assuredly benefit from not having short high power draws. I think that even in cars it could help with starter motors. Lead acid batteries have a pretty large energy capacity, but at the high discharge rate the total energy capacity is a lot lower than with a constant low discharge rate.

Just my two cents. Anyone agree with me? :p

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#10
In reply to #9

Re: Ultracapacitors - the Batteries of the Future?

04/02/2012 10:54 AM

Hi Nickjd,

agree 100%.

I guess charging with a very low ripple must be benefical for any kind of battery.

Ultracaps have been proposed for the shutter mechanism (in pre-digital cameras) at the time of Siemens Components magazine.

mfG

Snel

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