The combination could be shaped to form the main structural panels of spacecraft

All this has now changed, though, according to A123 Systems. This month the Watertown, MA startup announced a new lithium ion battery, based on research done at MIT, that’s suitable for applications requiring high power output. The battery’s high power density — a measure of the watts of power it can produce per kilogram — means it’s also lighter than conventional batteries of similar size.

To improve the performance of these materials, Manthiram coated the particles with an electrically conductive polymer, which was itself treated with small amounts of a type of sulfonic acid. The coated nanoparticles were then incorporated into a small battery cell for testing. The battery will get a chance to prove itself soon: it’s being incorporated into a new line of power tools, scheduled to reach store shelves next spring, that can outperform plug-in drills and saws.

At slow rates of discharge, the materials showed an impressive capacity: at 166 milliamp hours per gram, the materials came close to the theoretical capacity of lithium iron phosphate, which is 170 milliamp hours per gram. This capacity dropped off quickly at higher discharge rates in initial tests. But Manthiram says that the new versions of the material have shown better performance.

It’s still too early to say how much the new approach will reduce costs in the manufacturing of lithium iron phosphate batteries. The method’s low temperatures can reduce energy demands, and the fact that it is fast can lead to higher production from the same amount of equipment–both of which can make manufacturing more economical.

The company’s technology is based on a new way to make the activated carbon materials used in ultracapacitor electrodes. Currently, commercial ultracapacitors are made from organic sources–one common source is coconut husk. But the original organic material can contain impurities that limit the voltage of the ultracapacitors. EnerG2’s materials are synthetic, made by a process that lets the company vary the qualities of the ultracapacitor.

For use in commercial electric vehicles, lithium battery electrodes need to last through at least 300 charge cycles. In this respect, the nanowires could face stiff competition. In December 2008, a team from Hanyang University in Ansan, South Korea, unveiled nanoporous silicon anodes that lasted for more than 100 charging cycles and could store more charge than the nanowires.

Chemist Jaephil Cho, who led the work, says that the nanoporous material has more silicon-per-unit volume than nanowires, so it can hold more charge per unit volume. However, he says, “carbon fiber [manufacturing] is easy to scale up and therefore [Cui’s] method for making carbon-silicon nanowires is believed to be very practical.”

General Motors and Applied Sciences, meanwhile, are developing nanowire anodes that are very similar to those of the Stanford team. The companies coat carbon nanofibers with silicon particles, as opposed to amorphous silicon, resulting in anodes that can store charge of 1,000 to 1,500 milliamp hours per gram.

Today’s energy-storage devices won’t work for these purposes, because they are too expensive, too cumbersome, or too limited in capacity. Take batteries, the best-known storage technology. Sodium-sulfur batteries have the capacity to store wind power that can’t be used immediately, but adding them to a wind farm would quintuple the price of electricity per kilowatt-hour, according to one estimate.

The combination could be shaped to form the main structural panels of spacecraft, saving space and allowing lighter weight or more power, claims Lithium Power president Zafar Munshi. BMDO is interested because of the potential to build lightweight micro- and nano-satellites, a key component in future versions of the missile defense system.

Eventually, cars might have similar surfaces generating power for their electrical systems (though not electric motors), Munshi says. State-of-the-art rechargeable lithium-ion batteries, which are used in laptop computers and plug-in hybrid cars, are likewise too expensive to be incorporated into the grid in bulk.

The first phase of the project aims at proving the feasibility of combining solar technology with thin-film polymers. “We’re going to be building some hardware to demonstrate the basic concept,” Munshi says. If the second phase is funded, commercial products, such as global positioning system (GPS) devices with roll-up solar cells that provide power in remote areas, could arrive within two years, Bailey predicts.

The organic solar cell used in the prototype is the same technology being developed by Konarka. (See “Solar-Cell Rollout.”) It’s based on a mix of electrically conducting polymers and fullerenes. The cells can be cut or produced in special shapes and can be printed on a roll-to-roll machine at low temperature, offering the potential of low-cost, high-volume production.

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