Charging your electronics in a rainstorm cleantechnica electricity kanji

Anja Lund tugs at the shoulder strap of her bag, which is made of a textile that generates electricity when stretched. Pulling on the shoulder strap causes a light-emitting diode to flash (right). Source: Johan Bodell, Chalmers University of Technology

The idea was to test an experimental material’s response to moisture. That’s why she doused the arm strap in tap water, hoping that the special electricty-generating fabric she and her team developed not only would keep producing power when wet but would become even stronger. It succeeded on both counts.

“The reason we focus on the functionality underwater is that most electronic textiles have a structure that means they would probably cease to function when wet,” she said. “For practical use, it’s important that this textile can withstand both foul weather and wash, as this would be expected from other textiles. Our textiles can be used in a shoulder strap, but can also be produced on a larger scale and used in upholstery, mats or as filler in composite structures. The larger the textile, the more power it will produce.”

The concept of wearable electronics or electronic textiles isn’t new, but efforts to improve them with practical and innovative power sources is an ongoing quest, made all the more important now. Climate change has prompted researchers to try to devise novel clean energy sources that emphasize comfort, utility and sustainability — in particular, new options in batteries. Conventional alkaline or lithium-ion batteries typically end up in waste piles, where they risk leaking toxic materials into the soil. They also are heavy, bulky and rigid, making them cumbersome to use.

Several groups of scientists — using different approaches — have been working to design functional alternatives to conventional batteries using fabric or yarn. “We’ve developed high-performance, wearable and stretchable yarn batteries that can be woven into smart textiles,” said Chunyi Zhi, a materials scientist at City University of Hong Kong, whose team has produced a rechargeable battery made of yarn that is waterproof and still can function even if cut into small pieces. “It can be easily integrated… in flexible electronics, smart fabrics and smart clothes,” and maintains its power even when “bent, stretched, hit or even washed in water,” he said.

Lund and her colleague, Christian Müller, both researchers at Sweden’s Chalmers University of Technology, created a textile that converts kinetic energy into electricity and actually works best when it’s wet — meaning someone wearing the textile could generate power by going for a walk in the rain. “Wouldn’t it be great to use your jacket or socks as power sources, just by wearing them while carrying out your everyday tasks?” Lund said.

The technology used by Lund’s group for its woven fabric is based on the piezoelectric effect, that is, the generation of electricity when materials are stretched, or compressed. She produced her textile after spinning a polymer with an electrically conducting yarn. “We found that fiber spinning is a great way to do this, since it entails stretching the material many times,” she said.

The only challenge remaining for the Swedish team before practical implementation involves the interface between the soft textiles and the hard conventional electronics, such as watches, laptops and smartphones. They are working on “how to connect these two without breaking the textile, or without the conventional electronics being ruined by water,” Lund said.

For the rechargeable yarn battery, the Chinese scientists twisted carbon nanotube fibers into a yarn, then coated one piece of yarn with zinc to form an anode, and another with magnesium oxide to form a cathode. They then twisted both pieces like a double helix. The battery was stable, rechargeable and waterproof, researchers said. It also could be cut into several pieces, each of which could power a watch.

“Compared with the traditional lithium-ion batteries which suffer from intrinsic safety and cost issues, this yarn battery can work well under various severe conditions including being cut, bent, stretched or even soaked in water, demonstrating greatly enhanced safety performance, good knit-ability, high stretch-ability and excellent waterproof performance,” Zhi said. “After soaking in water for 12 hours, the battery retained 96.5 percent of its initial capacity.”