MIT developing carbon nanotube ultracapacitors to replace batteries

Cambridge (MA) - Batteries provide power for most of our daily gadgets, but they are bulky and must be replaced often. Researchers at the Massachusetts Institute of Technology's Laboratory for Electromagnetic and Electronic Systems (LEES) are studying a new breed of ultracapacitors, which use carbon nanotubes (CNTs) to generate and store energy at the atomic level. Their goal is to make use of the unique properties of CNTs to produce batteries that are both longer-lasting and faster-charging.

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Carbon Nanotubes vertically lined up.

Professors Joel Schindall and John Kassakian, along with Ph.D. candidate Riccardo Signorelli, presented their latest renditions of their research at a seminar on hybrid storage devices in Deerfield Beach, Florida, last December. Ultracapacitors have actually been with us for quite some time; they're beefed-up versions of capacitors, which use two layers of conductive material, separated by an insulator, to store electricity. Oppositely charged ions, which are stored in pores of activated carbon, are produced when the capacitor is connected to a power source. These ions can be discharged quickly to produce a burst of electricity. You see this in use with camera flashes, where batteries supply electricity to capacitors, which then fire off the flash.

While the ability to provide bursts of power is good for ultracapacitors, their energy density, measured in watt-hours per kilogram (Wh/kg), is quite low at 5 to 6 Wh/kg versus lithium-ion batteries, which can store 100 to 150 Wh/kg. The MIT researchers believe that vertically aligned CNTs are much better at holding a charge versus activated carbon because of the CNTs uniform shape, pore size and huge ion-cradling surface area, which can be up to 50,000 square centimeters per gram.

The goal of the research is to make a CNT ultracapacitor that can store 60 watt-hours per kilogram. This may not seem that great compared to lithium-ion batteries, but researchers predict that such ultracapacitors could be recharged in just a few minutes, and withstand up to 300,000 discharge cycles.

While this new technology is promising, MIT researchers have just begun their research. Also, we've noted the market price of CNTs remains far too expensive for the casual buyer. Although we did locate some high-quality nanotubes on eBay the other $20,000 per kilogram.