Focus on energy: Nanomaterials enable alternative energy

By David Forman

Aug. 10, 2004 — A classic rule of design — be it automotive, industrial or interior — states that the fewer the components in a system, the more elegant it is. The basic sticks and connectors of Tinkertoys? Pretty elegant. But the all-purpose Lego brick — that’s the epitome.

Judging by that standard, hybrid gasoline-electric vehicles, the new generation of vehicles with two motors instead of just one, look like a clumsy, clunky compromise.

Except for another classic design rule: When things aren’t working, break the rules. And with a fleet of gas guzzling SUVs on the road, high gas prices and unpredictable geopolitics weighing heavily on future supplies, it’s fair to say plenty of things aren’t working.

The result is a rapidly growing market for hybrids that combine gasoline and electric motors. Honda Motor Co. and Toyota Motor Corp. already have hybrids on the road, and Ford Motor Co. and other brands will soon follow.

Meanwhile, research in the areas of automotive fuel cells and other alternative fuels is increasing.

Experts say nanotechnology research and development will be key in helping these alternative power technologies overcome the market hurdles ahead.

A few cases in point: Last year, a major Japanese auto manufacturer partnered with materials developer Ener1 Inc. to use its nanoscale electrodes in the batteries of hybrid gasoline-electric cars.

Honda has leased its FCX fuel cell vehicle, powered by fuel cells that use nano-perforated membranes, to the city of San Francisco, among other customers, and has put more than a dozen of the cars on the road.

And one of the biggest nano-related financing rounds of last year was the $32 million funding of Catalytic Solutions Inc., a company using nanostructures to make catalytic coatings.

But such nanoscale developments come with correspondingly macroscale technical challenges, says battery and energy cell specialist Subhash Narang. He is director of product development at SRI International, a Menlo Park, Calif.-nonprofit technology research institute.

For example, he says, long life and high power are difficult to combine in a single battery. What’s more, as batteries become more powerful, they are often less safe. And despite the benefits of hydrogen-powered PEM fuel cells, Narang and other experts say building a hydrogen distribution infrastructure may be prohibitively expensive.

To understand the longevity-power conundrum, consider runners. Marathoners aren’t usually very good at the 100-meter dash. And good sprinters don’t win marathons.

In the case of batteries, says Narang, the kind that store lots of energy aren’t usually good at supplying it in the powerful bursts required to accelerate a car. And the high power batteries don’t store energy for very long.

By definition, says Narang, the smaller electrolyte particles that allow energy to move faster do not store as much energy as larger particles.

But Narang and other researchers have found ways to combine high energy density with high power using nanotechnology.

In SRI’s case, the approach involves using high aspect ratio nanomaterials, or nanofibers. The nanofibers are minutely small in one dimension (about 20 nanometers) so energy flows rapidly across them. But because they are, relatively speaking, long in the other dimension (50 to 200 nanometers) they can store much more energy than nanoparticles with small dimensions all around.

The result, Narang maintains, is a battery that can deliver about eight times the power of a traditional battery while providing comparable energy. Plus, there’s a bonus: The nanoscale dimensions that let energy move rapidly also allow the battery to recharge faster when the energy flow is reversed, a feature that’s important for hybrid cars designed to harvest energy from braking and use it to recharge the batteries.

Other organizations are working on the same problem. Ener1, of Fort Lauderdale, Fla., is researching enhancements for electrolytes and cathodes, using nano-structured powders for electrolytes and nano-structured, iron-disulfide for cathodes.

The company says that by combining its nano-structured, iron-disulfide cathode with its polymer electrolyte it can provide high energy and a long cycle life.

The ordinarily inverse relationship between energy and longevity is hardly the only problem plaguing the development of hybrid car batteries. According to Narang, there is a similarly inverse relationship between how much energy a battery can store and its inherent safety.

“The trend in the industry is to pack more and more energy into a smaller volume,” he said. As a result, today “we’re making batteries that have more energy than TNT.”

Safety concerns have compelled automakers to rely on less volatile but poorer performing materials for their hybrids. Honda and Toyota currently use nickel metal hydride (NiMH) batteries in hybrids, despite the fact that lithium-ion (Li-ion) is generally regarded as a better technology.

“Lithium-ion is dangerous in big form factors,” said Alexei Andreev, a solid-state physicist at Draper Fisher Jurvetson. He negotiated the company’s investment in Solicore Inc., a Florida startup that makes a solid-state electrolyte for batteries.

Lithium-ion is fine in cell phones and laptops, he says, but in the size required for a car, the electrolyte becomes flammable. Automotive use makes it doubly dangerous because a battery crushed in an accident can short circuit.

SRI researchers have been working on a solution using fire retardant materials to overcome the technology’s shortcomings. “When the battery starts heating up,” Narang said, “components become fire extinguishers.”

As of yet, however, neither the high-power/long-life solutions nor the safety technology has made it into a production car.

SRI’s nanofiber electrolyte first will be targeted toward other markets with similar demands, such as contractor-grade cordless power tools. And the fire-retardant materials face an uphill public relations battle: If manufacturers adopt the technology, they’ll have to acknowledge Li-ion’s inherent flammability problems, something Narang says they may not want to do.

Batteries, however, are not the only nano-enhanced technology poised to augment alternative energy efforts. Academic and corporate researchers also are inventing ways to complement diesel engines and build new types of fuel cells.

California-based Proton Power proposes using solid acid fuel cells to supplement diesel engines inside long-haul trucks. Currently, truckers idle their engines when resting to power heating, air conditioning and other amenities.

Proton Power would provide a supplemental fuel cell that truckers could use when not driving.

Calum Chisolm, Proton Power’s president and co-founder, says his company’s technology could offer a safer, more efficient alternative.

“The thinner the electrolyte layer,” Chisolm said, “the more power.” Currently funded by friends and family, the California Institute of Technology spinout is looking at longer-term financing opportunities and broad markets.

SRI is working on a form of solid oxide fuel cell that would use military-grade diesel fuel. The design takes advantage of nanostructures for catalysts and uses 200-nanometer powders for a thin electrolyte, upping the power in the same manner as Chisolm’s solid acid cell.

That suggests that one day the roads may hold not only hybrid gasoline-electric cars, but also of hybrid diesels, and, over the long term, a variety of automotive fuel cell technologies. Talk about breaking the rules.

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