Using a conventional electrolyte, the company has demonstrated energy storage of 20 watt-hours per kilogram, as opposed to roughly five watt-hours for a conventional ultracapacitor. Using a more expensive ionic-liquid electrolyte, it has made ultracapacitors that store 35 watt-hours per kilogram. By the end of the year, the company hopes to approximately double this storage capacity, says Nanotune CEO Kuan-Tsae Huang. At 40 watt-hours per kilogram, the ultracapacitors would be an improvement over the batteries used in some hybrid vehicles
Eventually, Huang says, it may be possible to make ultracapacitors that store 500 kilowatt-hours per kilogram—about three to four times more than the lithium-ion batteries used in cars today. The practical benefit could be even greater. Cars are often engineered to use only half the storage capacity of their batteries, to keep them from degrading. But almost all of an ultracapacitor's storage capacity can be used.
Nanotune's technology is very expensive now—between $2,400 and $6,000 per kilowatt-hour. (The Department of Energy has proposed a goal of $250 per kilowatt-hour to make electric vehicles competitive with conventional ones.) Nanotune says, however, that its costs could come down to less than $150 per kilowatt-hour if the prices of some key materials, such as electrolytes, continue to fall, and as manufacturing is scaled up.
The company's energy-storage projections are based on several advances it is working on. Nanotune is currently making electrodes with pores that are about 4 to 5 nanometers across, but it says it can make them smaller (high porosity leads to high surface area, which makes it possible to store a large amount of charge) and tune them to match the needs of different electrolytes—the ion-conducting materials the electrodes are immersed in.
The company is also looking into using ionic liquids rather than conventional organic electrolytes. These increase the voltage of the system, greatly increasing energy storage, but typically they aren't compatible with conventional ultracapacitor electrodes. Finally, the company hopes to make use of recent academic findings that suggests that adding small amounts of ruthenium to the ultracapacitors can increase energy storage.
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