Solid-state capacitor said to combine best qualities of batteries and capacitors


August 25, 2011

A method developed at Rice University allows bundles of vertically aligned single-wall carbon nanotubes to be transferred intact to a conductive substrate

A method developed at Rice University allows bundles of vertically aligned single-wall carbon nanotubes to be transferred intact to a conductive substrate

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Capacitors are able to charge and discharge more quickly than batteries, and can do so hundreds of thousands of times. Batteries, on the other hand, are able to store more energy than capacitors. There are also electric double-layer capacitors (EDLCs), otherwise known as supercapacitors, that can hold battery-like amounts of energy while retaining the charge/discharge speed of regular capacitors. EDLCs incorporate liquid or gel-like electrolytes, however, which can break down under hot or cold conditions. Now, a new solid-state supercapacitor developed at Houston's Rice University is using nanotechnology to get around that limitation.

The Rice researchers started out by growing an array of 15-20 nanometer bundles of single-walled carbon nanotubes, each up to 50 microns in length. This "nanotube forest" served to maximize the surface area available to electrons.

That array was subsequently transferred to a copper electrode, that included thin layers of gold and titanium to help with electrical stability and adhesion. In an atomic layer deposition process, the bundles (which served as the primary electrodes) were next doped with sulfuric acid to boost their conductivity. They were then covered with aluminum oxide, which served as a dielectric layer, and aluminum-doped zinc oxide, which acted as the counterelectrode. Finally, the circuit was completed with a top electrode of silver paint.

The Rice supercapacitor is reportedly stable and scalable, holds a charge under high-frequency cycling, and isn't adversely effected by harsh temperatures. It could also be incorporated into other materials, allowing for electric car bodies that double as batteries, or microrobots that serve as their own power supply.

"All solid-state solutions to energy storage will be intimately integrated into many future devices, including flexible displays, bio-implants, many types of sensors and all electronic applications that benefit from fast charge and discharge rates," said Cary Pint, who co-led the research.

Technology that combines the attributes of capacitors and batteries is also being developed at the University of Illinois, where scientists are creating nanostructured lithium-ion batteries that charge and discharge 10 to 100 times faster than regular li-ions.

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

So, could you guys include some performance numbers for this tech? Specifically how much energy per kg this might store (or similar comparison to current battery tech.)

The frustrating thing to me with these innovations is how long it takes to commercialize them. These have such potential for many industries (my particular interest being in transportation) but it just seems to take soooo long for them to be leveraged! (As testimony, just take a look at the ages on the \"related articles\" links below! They\'ve been dangling the ol\' \"capacitor potential\" carrot for years now! Yet applications are virtually nonexistant - I can only think of cap-regen-equipped buses, ATM. Anyone got others?)


I wonder why I didn\'t think of that! There are some very clever people around, and I am not one of them. One thing. Doesn\'t high power mean a heating problem on discharge? Also, if the battery is part of the car body, any damage could cause a discontinuity.


Heating on discharge is due to resistance. Batteries have internal resistance due to them being a chemical storage device. However capacitors are not chemical, they store electrical energy as electrical energy.


MzMk: You can purchase super capacitors (or \"ultra capacitors\") on ebay, but due to low voltage tolerance they don\'t work for very many applications. I wonder if these have higher voltage tolerance as well as heat tolerance?

Charles Bosse

Presumably as you scaled the components up you would need larger media to carry the charge. Within the individual cells, I expect, the heat generated would be minimal. It is when the output of the cells are combined that you would need larger \"wires\" to reduce resistance/friction.

As to discontinuity, yes if there is a rip this may well cause some of the cells to no longer be disconnected. However if the entire frame/body of the mechanism is multiple collections, you would have more of an effect of reduced power unless of course the discontinuity was after all the units are concentrated together. But then if you smash the front of your vehicle into another and do even reasonable amounts of damage, you may not be able to drive today. (Cut belt, punctured radiator or oil cooling system, fender bent to where it is cutting a tire, etcetera.) Hopefully for automotive purposes this location is centralized, resulting in requirement for profound damage before you would cut off all power storage systems.


Would this be consisdered better than a fuel cell?

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