Really Thin Skin

What do you call a substance that has width but virtually no depth? Lightyear Technologies calls its one-molecule thick nano-sheets “TDM”-short for Two-Dimensional Material. A sample of TDM measured with x-ray diffraction appears to be, well, about as flat as flat can be.

The Vancouver firm is gearing up to produce these ultra-thin leaves for a range of commercial applications, among them extending the life of metal hydride batteries, increasing the range of fuel-cell vehicles and purifying water and fossil fuels.

Monolayers, which are used in everything from silicon chips to flat-screen monitors, generally are produced by laying down a micron-deep layer of molecules-a kind of molecular spray painting, with expensive, complicated techniques such as chemical vapor deposition or vapor-phase epitaxy.
Lightyear says it produces monolayers in a solvent at room temperature and pressure.

Researchers at Simon Fraser University in Vancouver discovered the TDM technique in 1995 by coaxing semi-conducting, corrosion-resistant molecules of “transition metal dichalcogenides” into flexible sheets only a single molecule thick.

Transition metal dichalcogenides have a sheet-like molecular structure to begin with, says Dr. Sharon Blair, Lightyear’s head of research. By inserting metal atoms between the compound’s sheets and adding a solvent that reacts with the metal, it is possible to separate the sheets.

Once in single-molecule-thick form in a solvent, the sheets will self-assemble into a monolayer on a properly prepared surface. “It’s a rough analogy, but think of how a drop of oil spreads itself across the top of water,” Blair says.

Blair claims the approach also is quite versatile. “Our TDMs can be produced in commercial quantities and applied to powders, flat or rounded surfaces, or even onto dissolved solids,” she says.

Assault with Batteries

Lightyear’s flagship TDM project aims to help nickel metal-hydride batteries in devices like mobile phones and computers live longer. Currently, time and repeated recharging cause the electrolyte to corrode the metal hydride in the electrodes and slowly end the battery’s “cycle life.”

So how would this thin-as-can-be material solve the problem? The tiny sheets of TDM wrap themselves around the hydride particles to block corrosion from the electrolyte yet leave hydrogen atoms free to flow and produce juice. Depending on the composition of the metal hydride, Blair says, TDM can improve battery life from 30 to 230 percent.

TDM technology could also help reduce the cost of metal hydride batteries by allowing manufacturers to use less expensive materials such as magnesium, says Blair. Normally, magnesium hydride would ignite within an electrolyte. But within the molecular “saran-wrap” of TDM, it could power better, cheaper batteries.

Lightyear opened the first commercial TDM factory in September 2000. The facility aims to provide early-stage customers with enough TDM for 300,000 AA cells a day. “In scaling up, we’ve reduced the price of TDM from $10,000 per gram to less than $1 per gram,” says Blair. However, Lightyear plans to license its technology to companies.