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electric double-layer capacitor (EDLC), supercapacitor, supercondenser, electrochemical double layer capacitor, or ultracapacitor.
Their energy density is hundreds of times greater than conventional electrolytic capacitors
Compared to lead-acid batteries, the have lower energy density, but they can be over a million times and can also charge and discharge much faster than any battery. Because of this they are used for energy smoothing or evening out sudden loads or spikes. They can be used as an electronic shock absorber.
Graphene micro supercapacitors.
These are in development and promise great things. They charge 100 to 1,000 times faster than a battery.
A "digital quantum battery" concept proposed by a physicist at the University of Illinois at Urbana-Champaign could provide a dramatic boost in energy storage capacity--if it meets its theoretical potential once built.
The concept calls for billions of nanoscale capacitors and would rely on quantum effects--the weird phenomena that occur at atomic size scales--to boost energy storage. Conventional capacitors consist of one pair of macroscale conducting plates, or electrodes, separated by an insulating material. Applying a voltage creates an electric field in the insulating material, storing energy. But all such devices can only hold so much charge, beyond which arcing occurs between the electrodes, wasting the stored power.
If capacitors were instead built as nanoscale arrays--crucially, with electrodes spaced at about 10 nanometers (or 100 atoms) apart--quantum effects ought to suppress such arcing. For years researchers have recognized that nanoscale capacitors exhibit unusually large electric fields, suggesting that the tiny scale of the devices was responsible for preventing energy loss. But "people didn't realize that a large electric field means a large energy density, and could be used for energy storage that would far surpass anything we have today," says Alfred Hubler, the Illinois physicist and lead author of a paper outlining the concept, to be published in the journal Complexity.
Hubler claims the resulting power density (the speed at which energy can be stored or released) could be orders of magnitude greater, and the energy density (the amount of energy that can be stored) two to 10 times greater than possible with today's best lithium-ion and other battery technologies.
What's more, digital quantum batteries could be fabricated using existing lithographic chip-manufacturing technologies using cheap, nontoxic materials, such as iron and tungsten, atop a silicon substrate, he says. The resulting devices would, in principal, waste little or no energy as they absorbed and released electrons. Hubler says it may be possible to build a benchtop prototype in one year.
... EEStor claims that its device, which is one-quarter the weight of a similar Donna Coveney/MIT Work being done by Daniel Nocera at MIT could open up the possibly that electricity could be stored by splitting (and later recombining) abundant water molecules.
lithium ion battery, can hold a large charge for days. Its patent describes a 281-pound device that would hold almost the same charge as a half-ton lithium ion battery pack installed on the Tesla Roadster. The company’s ultracapacitors have yet to prove themselves in commercial products. But industrial giant Lockheed Martin has already signed up with EEStor to use future ultra capacitors in defense applications, and Toronto-based Zenn Motors, which has also taken an ownership stake in EEStor, says it will have electric cars on the road using the technology in 2010. Ref
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The CUNY Energy Institute has been developing Metacapacitors™ , a novel electrically insulating material for a new breed of capacitors that increases the capacitor's storage capability and allows for low-cost, efficient grid interfaces for applications from solid-state lighting to solar photovoltaics. The thin film capacitor can be printed in rolls similar to newspaper printing. Transistors are sealed into these capacitor films to form Metacapacitors™. The resulting Metacapacitors™ are a flexible fabric for electrical power conversion. The CUNY Energy Institute’s novel research on Metacapacitors,™ led by Dr. Stephen O’Brien, received a grant of $1,568,330 from the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E). The prestigious ARPA-E grants were awarded to innovative projects that will help the US deploy next generation clean energy technologies.