A startup called EnerG2 recently started building a factory in Oregon to produce materials that could improve ultracapacitors for batteries and energy-storage devices. The factory is being funded with $21.3 million from the U.S. Department of Energy as part of a $2.4 billion grant program authorized by the Recovery Act of 2009. The grant was intended to speed up the production and deployment of electric vehicles in the United States, but it's not clear that battery manufacturers and automakers will have much use for the material in the next few years.
The Seattle-based company says its material–a form of activated carbon used in electrodes–can improve the performance of ultracapacitors. These devices store a fraction of the energy of batteries, but can deliver larger bursts of power and survive many more charge and discharge cycles. Ultracapacitors are being used now in applications such as hybrid buses and wind turbines (to adjust the pitch of the blades). EnerG2 says the materials could also be used in advanced batteries and suggests that its technology could be the key to "making gasoline obsolete."
The company's technology is based on a new way to make the activated carbon materials used in ultracapacitor electrodes. Currently, commercial ultracapacitors are made from organic sources–one common source is coconut husk. But the original organic material can contain impurities that limit the voltage of the ultracapacitors. EnerG2's materials are synthetic, made by a process that lets the company vary the qualities of the ultracapacitor.
For example, changing the size and shape of the nanoscale pores in the material can increase surface area, which can increase energy-storage capacity. Or the company can manipulate the degree to which an electrical charge flows freely through the material, allowing it to deliver varying bursts of power. And the fact that the material contains fewer impurities could allow ultracapacitor makers to redesign their energy-storage devices to operate at higher voltages, which could increase energy capacity by about 20 percent. Eventually, the material could cut the cost per watt-hour for some ultracapacitors in half. "This is not one of those nanotechnologies that is too expensive to be commercializable," says Rick Luebbe, CEO of EnerG2.
But some ultracapacitor manufacturers aren't convinced. Maxwell Technologies, one such manufacturer, has agreed to test the new materials, says Michael Sund, vice president of communications and investor relations for the San Diego-based company. But he says that "all of the synthetic materials we have tested are significantly more expensive than activated carbon from organic sources," so organic activated carbon remains "the best material available to us in terms of having sufficient quantity, and proven performance and cost." When companies are considering using ultracapacitors in new applications, their biggest concern is cost, "so no way we can pay more for carbon to get a marginal performance improvement," he says.
EnerG2's technique for making activated carbon may prove more useful for overcoming some key challenges facing proposed advanced battery designs. Lithium-air batteries and lithium-sulfur batteries could store more than twice the energy of today's batteries, although that's still much less than the amount of energy stored in fuels such as gasoline. It's been challenging to make these batteries practical. Many test batteries stop recharging after only a few cycles, or don't come close to their theoretical energy-storage capacity because of problems with conductivity or unwanted chemical reactions. Having a precisely controlled pore structure within a carbon electrode could help with many of these problems.
For example, researchers recently demonstrated that well-ordered carbon electrodes–composed of regular rows of carbon nanostructures–allowed for relatively high energy storage in lithium-sulfur battery electrodes by improving conductivity and promoting desired chemical reactions within confined spaces in the material. The techniques for making these electrodes, however, would be expensive. EnerG2's methods might provide a cheaper way to make such ordered carbon structures.
But these battery technologies still face several other problems, and might not be ready for commercial production for many years, if ever. "There must be a dozen challenges," says Stanley Whittingham, professor of chemistry and materials science and engineering at the State University of New York, Binghamton. The new activated carbon materials might solve some problems, he says, but then it's "on to the next issue."
