2014-10-16

Fun With Nanotubes

Carbon nanotubes enable yet another way to produce a flat panel of light, and titanium nanotubes result in batteries that promise to charge in two minutes and last 20 years.

Flat light
Researchers from Tohoku University and Dowa Holdings Co. Ltd. (a Japanese manufacturer of nonferrous metals) have demonstrated planar light from a CRT-like diode structure in which the cathode is prepared from a solution of single-walled carbon nanotubes, and the anode is a phosphor screen. Their study -- not peer reviewed (nor copy edited very well) as far as I can see -- appeared in the AIP journal Review of Scientific Instruments.

Based on AIP Publishing's press release, a number of outlets, some of which should know better, have regurgitated a tale of the successor to the LED.

I don't think so.

The research paper doesn't characterize the light produced from the device, other than to say that it achieved around 60 lm/W. There was no roadmap to improving that figure. The press release included a quite confused statement about the "very low power consumption of around 0.1 Watt for every hour's operation -- about a hundred times lower than that of an LED."

The researchers do say that the field emission current from the nanotubes operated without flicker, and that the light showed good homogeneity in brightness.

One attractive feature of the technique described is its simplicity. The carbon nanotubes were suspended in a liquid that was painted on to the anode and roughened with sandpaper after drying. That was sufficient to provide electron beams from the nanotubes that were a thousand times denser than those from traditional thermionic cathodes.

Still, I will be very surprised if this technique ever competes even with OLEDs, let alone with light-guide ILED technology, in general-purpose lighting applications.

Amazing batteries
This development doesn't relate directly to lighting, but I hope you will forgive me taking the space to tell you about it. Through the years, we have heard breathless stories of one breakthrough technology after another that was finally going to catch batteries up to the improvement curve of Moore's Law. Perhaps this one will be the charm.

Researchers at Nanyang Technological University in Singapore, led by Chen Xiaodong, have developed a lithium-ion battery whose anode uses a gel made from titanium dioxide nanotubes, in place of the bonded graphite traditionally used. Titanium dioxide occurs naturally in spherical form, and the NTU researchers have found a simple way to coerce it into tubular form. The increased surface area speeds up the chemical reactions occurring in the battery, allowing for much faster charging -- up to 70% charge in two minutes, according to the press release.

Another factor speeding up charging is the new battery's lack of additives binding electrodes to the anode. These affect the speed with which electrons and ions can move about in the batteries. "Prof. Chen's new cross-linked titanium dioxide nanotube-based electrodes [eliminate] the need for these additives and can pack more energy into the same amount of space," according to the press release.

The researchers say the battery can sustain 10,000 recharge cycles before beginning to drop off from its maximum power. That's 20 times more recharge cycles than typical Li-ion batteries.

The press release tells us, "Manufacturing this new nanotube gel is very easy. Titanium dioxide and sodium hydroxide are mixed together and stirred under a certain temperature." Presumably, the details are to be found in the paper in the journal Advanced Materials; only the abstract is freely available.

— Keith Dawson , Editor-in-Chief, All LED Lighting