Status of Carbon Nanotubes for Wiring, Superink, Super-Batteries and other Applications

1. Super carbon nanotube batteries

MIT Technology Review reports researchers at MIT have made pure, dense, thin films of carbon nanotubes that show promise as electrodes for higher-capacity batteries and supercapacitors. Dispensing with the additives previously used to hold such films together improved their electrical properties, including the ability to carry and store a large amount of charge.

The MIT group, led by chemical-engineering professor Paula Hammond and mechanical-engineering professor Yang Shao-Horn, made the new nanotube films using a technique called layer-by-layer assembly. First, the group creates water solutions of two kinds of nanotubes: one type has positively charged molecules bound to them, and the other has negatively charged molecules. The researchers then alternately dip a very thin substrate, such as a silicon wafer, into the two solutions. Because of the differences in their charge, the nanotubes are attracted to each other and hold together without the help of any glues. And nanotubes of similar charge repel each other while in solution, so they form thin, uniform layers with no clumping.

The resulting films can then be detached from the substrate and baked in a cloud of hydrogen to burn off the charged molecules, leaving behind a pure mat of carbon nanotubes. The films are about 70 percent nanotubes; the rest is empty space, pores that could be used to store lithium or liquid electrolytes in future battery electrodes.

2. A compound synthesized for the first time by Berkeley Lab scientists could help to push nanotechnology out of the lab and into faster electronic devices, more powerful sensors, and other advanced technologies. The scientists developed a hoop-shaped chain of benzene molecules that had eluded synthesis, despite numerous efforts, since it was theorized more than 70 years ago.

The much-anticipated debut of the compound, called cycloparaphenylene, couldn’t be better timed. It comes as scientists are working to improve the way carbon nanotubes are produced, and the newly synthesized nanohoop happens to be the shortest segment of a carbon nanotube. Scientists could use the segment to grow much longer carbon nanotubes in a controlled way, with each nanotube identical to the next.

“This compound, which we synthesized for the first time, could help us create a batch of carbon nanotubes that is 99 percent of what we want, rather than fish out the one percent like we do today”.

3. Bulk quantities of semi-conducting Carbon nanotube ink for solar cells and flexible electronics

Scientists at DuPont and Cornell University in Ithaca, N.Y., have used a simple chemical process to convert mixtures of metallic and semiconducting carbon nanotubes into solely semiconducting carbon nanotubes with electrical characteristics well-suited for plastic electronics. This new finding, reported in the January 9 issue of the journal Science, identifies a commercially viable path for the production of bulk quantities of organic semiconducting ink, which can be printed into thin, flexible electronics such as transistors and photovoltaic materials for solar cell technology.

4. Researchers at Rice University and the National Renewable Energy Laboratory (NREL) have engineered single-walled carbon nanotube (SWCNT) fibers to become a scaffold for the storage of hydrogen. The 3-D nanoengineered fibers absorb twice as much hydrogen per unit surface area as do typical macroporous carbon materials.

5. In March 2008 at the Materials Research Society’s spring meeting in San Francisco, a team of ­engineers from Stanford and Toshiba reported that they have used ­carbon ­nanotubes to wire logic-circuit components on a ­conventional silicon CMOS chip. They claim to have shown that nanotubes can shuttle data at speeds of a little faster than 1 gigahertz, close to the range of state-of-the-art microprocessors, which run at speeds of 2 to 3 GHz. In principle, nanotubes can handle a current density 1000 times as great as that of copper or silver.

6. Pursuit of carbon nanotube wiring and electrical transmission

The Air force funds and wants carbon nanotube wiring.

– Copper wiring makes up as much as one-third of the weight of a 15-ton satellite
-Similarly, reducing the weight of wiring in UAVs would enable them to fly longer before refueling or carry more sensors and weapons.
– CNT wiring would yield the same sort of savings for commercial aircraft, Antoinette said. A Boeing 747 uses about 135 miles of copper wire that weighs 4,000 pounds. Replacing that with 600 or 700 pounds of nanotube wire would save substantial amounts of fuel, he said.
-In addition, CNT wires do not corrode or oxidize, and are not susceptible to vibration fatigue

Nanocomp Technologies has nanotube wire but in Air Force tests so far, it has not proved to be more conductive than copper, Bulmer said. “In theory, it should be real conductive. In real life, we have a ways to go.”

Nanocomp says its own tests show that at high electrical frequencies, its nanotube wire has been more conductive than copper.

If conductivity can be increased by factors of five to 10, Bulmer said, the lightweight wire will be very attractive for uses as varied as wiring in aircraft to building lightweight motors.

Nanocomp Technologies has been covered here before for making large sheets of carbon nanotubes.

Nanocomp Technologies has gotten new Air Force funding in 2009

Since the spring of 2008, Nanocomp has also managed to increase the scale of its product, going from a 3-foot-by-6-foot sheet to a 4-by-8 unit. The development of larger sheets is an ongoing process.

A 2006 article discussing the dream of a carbon nanotube (quantum armchair) wire capable of transmitting millions of amps.

7. Florida State University expects to spin off a company in 2009 that will attempt to commercialize a breakthrough using carbon nanotubes. Scientists there feel they have developed a new technology that will allow commercial production of sheets that are 50 to 100 percent loaded with carbon nanotubes. To date, carbon nanotubes are only used in loadings of 2 to 3 percent in plastics because they tend to tangle and clump in high loadings.

Professor Ben Wang told Design News when he exposes the tubes to high magnetism they line up in the same direction like soldiers in a drill. He says he also creates some roughness on the surface so the nanutubes can bond to a matrix material, such as epoxy. The nanotubes can, in effect, take the place of carbon fiber in a composite construction — only the results are much more stunning.

You can make extremely thin sheets with the nanotubes — leading to use of the term “buckypaper.” The name “Bucky” comes from Buckminster Fuller who envisioned shapes now called Fullerenes. Stack up hundreds of sheets of the “paper” and you have a composite material 10 times lighter but 500 times stronger than a similar-sized piece of carbon steel sheet. Lockheed Martin is one of the companies very interested. Unlike CFRP, carbon nanotubes conduct electricity like copper or silicon and disperse heat in the same manner as steel or brass.