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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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