Nonetheless, thin-film batteries may not be the next-generation choice for most laptops. That's because the processes used to make them, such as physical vapor deposition, are still too expensive for producing large batteries. Also, these batteries, which can be a mere one-tenth of a millimeter thick, each hold only micro-amounts of energy--as little as one-thousandth the amount in today's laptop batteries. While they could be stacked to provide adequate storage capacity, the layers of packaging separating the active materials in each battery would cancel out their capacity advantages. That is, they'd likely cost more, but not necessarily be smaller.

The first applications, such as in industrial sensor packages in high-temperature equipment or oil wells, will be ones in which buyers are willing to pay $100 apiece for batteries that meet their needs. Bradow says their batteries could be made for much less in high volumes, however, eventually making them practical for distributed sensor networks.

In spite of the current drawbacks to thin-film batteries, Donald Sadoway, professor of materials chemistry at MIT, says some versions of them will power laptops--and electric vehicles--in the future. To his thinking, their key advantage, in addition to safety, is that they allow the use of pure lithium in one of the electrodes, which isn't possible using liquid electrolytes: "If you can switch to lithium, you've achieved the ultimate in anode capacity," he says.

In contrast to the glass-like electrolyte used by Infinite Power Solutions and others, Sadoway has developed a solid-polymer electrolyte (today's lithium-ion polymer batteries use a gel) for use in thin-film batteries. This electrolyte, he says, could be processed in rolls like newspaper, or some other high-throughput process. Such a process for thin-film batteries, although not now being developed by industry, could bring down costs, he says, while innovative ways of packaging electrodes could reduce size. "We've made batteries in the laboratory that are 300 watt-hours per kilogram," he says. "That's two times the best lithium-ion [battery] on the market today."