What's That You're Wearing?

Nanotechnology makes paper and cloth batteries possible.

May/June 2010

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What's That You're Wearing?

Mark Matcho

The fun stuff is delicious to talk about. Think of a shirt that doubles as a battery, enabling you to literally plug a device into what you're wearing. Or envision an "eTextile" carpet that would power the robotic vacuum cleaner roaming over it. Most simply, imagine a cell-phone or iPod case that would charge the device placed inside it.

These are potential applications that Yi Cui, assistant professor of materials science and engineering, recognizes as attention-grabbing ideas. But in the end, his research on new ways to store and deliver energy is far more open-ended than anything suggested by "wearable batteries" or the perfect phone charger. The ultimate value of his experimentation, which includes making batteries and related devices called supercapacitors from fabric and ordinary paper, is to "enable applications we haven't thought about yet. . . . It's hard at this moment to know what will come first."

John A. Rogers, a professor of materials science and engineering (and chemistry) at the University of Illinois at Urbana-Champaign, notes that Cui's research has a distinct scientific allure.

"Personally, I find this type of use of 'low tech for high tech' to be very appealing," Rogers said by email. "Paper is a very old technology, but it has many attractive characteristics, i.e., it's low in cost, flexible, lightweight, robust, stackable, foldable, etc. The ability to use it as a platform for batteries, electronics, microfluidics, optoelectronics and other high technology systems is being explored by several groups. Cui's efforts are quite prominent among these."

Cui and his team of student researchers have demonstrated how to create batteries by permeating common printer paper with ink containing electricity-conducting carbon nanotubes, structures just billionths of a meter in size. A similar process can be used to make conductive fabric with high energy density, which Cui said early this year has prompted interest in potential uses ranging from sportswear to military gear.

Battery garments, Cui says, will have to be designed and manufactured with a level of safety that can protect a wearer's skin against any possible toxic chemical leakage. That's the main reason he thinks a conductive shirt is less immediately doable than some other applications. But musing out loud, Cui ends up focusing on a variety of other possibilities, including wallpaper.

"There's a certain thing which can be exciting," he says. "Let's say you have a solar-cell rooftop and you generate electricity, where do you store it? Maybe wallpaper."

Cui is quick to emphasize the relative simplicity and small cost of the processes his team has been developing (see a short video demonstrating the work). Rogers made the same point.

"An underlying notion in all of this," wrote Rogers, "is 'cost as a performance metric,' considered at the outset of device design and on an equal footing with more traditional metrics for electronics and power systems: operating speed, efficiency, storage capacity, level of integration, etc. Paper, viewed in this sense, appears to be a very interesting class of substrate to explore."

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