Ultracapacitors, electronic devices that can absorb and discharge electricity rapidly, aren't part of mainstream cars now, but it won't be long, according to Dileep Agnihotri, CEO of Graphene Energy.

"The combination of ultracapacitors and batteries is the future," he said in an interview. Graphene is a spin-out from the University of Texas that is working on an ultracapacitor based around graphene, a planar form of pure carbon that conducts electricity rapidly. The company has built experimental cells and hopes to have prototypes in about nine months.

If things go well, the company might be in a position to deliver graphene material to larger manufacturing partners in 18 to 24 months, said David Anthony, a partner at 21 Ventures that has invested in Graphene along with the Quercus Trust. (Graphene was one of the new companies we recently indentified with Quercus.)

The company is still debating whether to just sell graphene sheets (and license intellectual property) or build complete subsystems. Either way, a larger manufacture will like be involved.

Granted, startup executives often predict that their products will become household names in a short period, but the circumstances do seem at least potentially favorable to ultracapacitors. A large number of automakers – General Motors, Ford, Honda, Toyota, Nissan, Tesla Motors, Fisker Automotive – have committed publicly to making plug-in vehicles. Peugeot, Volvo and others, meanwhile, are already making hybrid or electric buses and delivery vehicles.

Japan, Finland and others have or are putting tax policies in place to goose the sales of electric cars and consumer polls overwhelmingly indicate that consumers want electric cars.

The problem with this picture? Batteries. They remain expensive and can take several hours to charge. Ultracapacitors can reduce charge time to minutes.

"Ultracapacitors can charge and discharge faster," said Anthony.

They can also deliver a large amount of power in a short amount of time, added Angihotri. "Batteries have great energy density, but poor power density. When you try to accelerate, you drain the battery," he said.

Ultracapacitors can also extend the life of a battery by several years and harvest power from regenerative braking systems more efficiently than plain battery systems.

The ideal configuration, he said, might be for a car to have two-thirds of its electrical storage dedicated to batteries and one-third dedicated to ultracapacitors.

So why don't electric car makers just use ultracapacitors instead of batteries now? "They don't have as good energy storage as batteries," Angihotri said. Graphene's goal is to get close to the energy storage capacity of lead acid batteries. While lead acid batteries hold far less electricity than lithium-ion batteries, they hold five times as much or more than existing ultracaps.

Other companies are pursuing ultracaps as well. Freescale, formerly Motorola Semiconductor, is working with McLaren on a Kinetic Energy Recovery Systems for Formula One Cars. KERS are essentially electric booster for gas cars. Formula One drivers will use them in the 2010 season and KERS should start appearing in commercial buses and trucks in 12 to 18 months.

A few startups, such as APowerCap Technologies, are also working on ultracapacitors to complement batteries in cars.

Anthony and Angihotri argue that Graphene will have an edge because of its material. Graphene conducts electricity as well as or even better than many metals. (Carbon nanotubes – which are also made up only of carbon atoms – conduct electricity well). Graphene sheets can also be made with a wide aspect ratio: a sheet measuring 25 by 15 microns might only be two to three atoms thick. A large, proportional surface area like that is idea for power delivery.

The company's prototypes can store two to three times the performance of standard, existing ultracapacitors and the company hopes to scale that up to seven times as much, said Anthony.

"The issue now is how to mass produce [graphene]. This is where the challenges are," said Angihotri.