Weaving Batteries into Clothes
A novel machine that makes nanostructured fibers could be the key to a new generation of military uniforms that take on active functions such as generating and storing energy.
The fibers can be made of up to three different materials, arranged in regular, nanoscale patterns visible in cross section. (See slide show.) The machine, manufactured by Hills, of West Melbourne, FL, is one of only two in the world capable of producing such fibers, says Stephen Fossey, a researcher at the U.S. Army Natick Soldier Research Development and Engineering Center, in Natick, MA. The machine is scheduled to be delivered early next year to the Natick facility, where it will serve as the centerpiece of a program geared to making multifunctional uniforms.
Among the machine’s many potential uses is assembling fibers that act as rechargeable batteries. Angela Belcher, a professor of biological engineering and materials science and engineering at MIT, says that some of the sample structures the device has made could be useful for combining positive and negative battery electrodes and electrolytes into individual threads. Such threads could be woven into uniforms and paired with threads that act as fuel cells or photovoltaics.
The machine was featured last week as part of a workshop on wearable power held at the United States Army Research Laboratory, outside of Washington, DC. The workshop was part of a major push to develop better alternatives to today’s batteries as foot soldiers come to depend more on electronic devices, from night-vision goggles and laser range finders to advanced radios and networked computers. Today, a typical platoon requires almost 900 batteries of up to seven different types for a five-day mission, says Charlene Mello, a member of the macromolecular-science team at the Natick soldier center. Besides being cumbersome to manage and carry, the batteries don’t last very long, which could put soldiers in the position of having to change them in the middle of a fight.
See cross sections of fibers made by an earlier version of the new machine.
What’s needed are ways to store energy in less space and relieve soldiers of logistical burdens so that they can concentrate on their jobs, says Dave Schimmel, a project manager at the Natick facility who works with experimental technologies that are close to being tested in the field.
Proposed solutions include lightweight fuel cells and batteries molded to the shape of a soldier’s body armor. The Natick machine is important for longer-range research on power sources that would simply disappear into the background.
The machine is a variant on a common manufacturing technology used to extrude polymers: heated materials are forced through a die and then drawn down to make thin fibers. Its ability to combine three different materials into intricate patterns, however, depends on separate control of the temperature of each material (the upper temperature limit is 350 ºC).
The machine can process materials besides polymers, which could be key to making functional fabrics. Metals with low melting points could be used to make conducting fibers. A wide array of inorganic materials that can be useful for batteries, fuel cells, and photovoltaics could be incorporated into the fibers by embedding them within polymers. The fibers, once formed into novel shapes, could also serve as templates for inorganic materials deposited using other techniques.
One of the more exotic possibilities is creating fibers from viruses that Belcher has genetically engineered to bind to and organize inorganic materials. She has already shown that the viruses can be used to make high-energy-density battery electrodes and fibers. The machine could combine battery electrodes with a polymer separator and electrolyte to form a complete battery. A similar approach could be used with photovoltaic materials. (Indeed, photovoltaic fibers made by other means have been demonstrated in the past.)
Among the cross-sectional patterns possible with the machine (and illustrated by the slide show accompanying this article) are some that look like sliced pies or concentric rings, and others that are much more complex. Once made, the fibers can be modified by dissolving certain polymers, leaving behind fibers with increased surface area. In one example, called “islands in the sea,” a fiber thinner than a human hair is divided into dozens of nanoscale fibers. The machine can also produce fibers with cross sections that, instead of being circular, could have the shape of a cross or a three-lobed structure.
“Pretty much any cross section can be made,” Fossey says. Indeed, what’s lacking now is not the capabilities of the machine, he says, but enough researchers with ideas for how to use it.
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