Judged by media buzz and venture capital dollars, lithium ion batteries are the name of the game in the emerging field of storage for electric vehicles and the power grid. But there is a cadre of companies pursuing ultracapacitors that can work hand in hand with batteries.
South Korea-based Neescap on Tuesday said that it has raised $9 million in bridge financing to expand production of its ultracapacitors for the transportation, power industry, and consumer electronics markets.
In the U.S., early-stage companies designing the materials and electrolytes for ultracapacitors include Graphene Energy, EnerG2, and Ioxus. Much hyped EEStor, backed by venture capital firm Kleiner Perkins Caufield & Byers, has signed a supply deal with electric vehicle company Zenn, although its products are still not commercially available.
Compared to batteries, ultracapacitors can't store a lot of energy, so they wouldn't typically be used alone to run plug-in electric vehicles. On the other hand, ultracapacitors are "power dense," which means that they can discharge the energy they do have quickly. Conversely, they can be recharged quickly--in seconds or minutes, and with almost no degradation in performance over time, say backers.
Ultracapacitors are already used in consumer electronics such as digital cameras to help provide a burst of power for flashes, which extends overall run time, said Chad Hall, the chief operating officer of Oneonta, N.Y.-based Ioxus, on Tuesday. The technical challenge for ultracapacitor companies in the coming years is to build storage devices that can operate in high-voltage applications, he said.
Ioxus, which means "power" in Greek, was spun off from its parent company three years ago to pursue energy storage in electric transportation, renewable energy storage, and backup power. Rather than replace batteries, the company expects that its ultracapacitors, which it began manufacturing earlier this year, will complement them. "It all comes down to hybridization. We've got hybrid cars, so you need to hybridize energy storage," he said.
One of the first markets the company is pursuing is fork lifts. An ultracapacitor could be used for the jolts of power needed to lift heavy things, which would give a longer life to fork lifts' lead acid batteries, said Hall. Other promising uses include maintaining the stability of grid frequency, he said.
"Ultracapacitors enable battery technology, or fuel cells, or solar and wind. They become the bridge you need for most of those applications to go forward. It's gotten to the point technology-wise so that you can do that," he said.
Another advantage is that Ioxus ultracapacitors don't use hazardous materials. But getting the price low enough for these applications remains a barrier, he said.
Joel Schindall, a professor of electrical engineering and computer science at Massachusetts Institute of Technology, predicts that ultracapacitors will make a jump in energy storage capacity in the years ahead.
Right now, ultracapacitors discharge 10 times faster than batteries but only store about 5 percent of the energy as comparably sized batteries, Schindall said last Wednesday at the EmTech emerging technology conference.
"It's still useful in applications when you charge and discharge frequently, such as regenerative braking, but it's not a replacement for batteries at a large scale," he said.
For the past five years, Schindall has been leading research on ways to replace activated carbon--the porous material in ultracapacitors that stores electric charge--with a "shag carpet" of carbon nanotubes on a conducting substrate. The company FastCap Systems was formed earlier this year to commercialize the technology.
Schindall projects that ultracapacitors eventually will be able to store as much as 25 percent of the energy of batteries, a jump he said would be "disruptive." Right now, nanostructures developed by MIT researchers can hold twice as much energy as activated carbon. In the coming months, his team expects to show it can hold five times the energy as activated carbon, he said.