The Twistron material is made from yarns that generate electricity when twisted or stretched

The 'Twistron' material is made from yarns that generate electricity when twisted or stretched

Researchers at the University of Texas and Hanyang University in South Korea have developed a yarn that generates electricity when twisted or stretched, potentially paving the way for smart clothing that powers itself without the need for batteries.

The 'Twistron' material – detailed in a study published in the journal Science – is made from yarns constructed from carbon nanotubes. The researchers first twist-spun the nanotubes into high-strength, lightweight yarns. To make the yarns highly elastic, they introduced so much twist that the yarns coiled like an over-twisted rubber band. To generate electricity the yarns are submerged or coated with an ionically conducting material or electrolyte.

As well as offering the apparel industry an option for developing smart clothing, the yarn – which can use human motion and ocean waves to generate power – could potentially result in a lower reliance on fossil fuels too. 

"Fundamentally, these yarns are supercapacitors," says Dr Na Li, a research scientist at the NanoTech Institute and co-lead author of the study. "In a normal capacitor, you use energy – like from a battery – to add charges to the capacitor. But in our case, when you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself. No external battery, or voltage, is needed."

When a harvester yarn is twisted or stretched, the volume of the carbon nanotube yarn decreases, bringing the electric charges on the yarn closer together and increasing their energy. This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity.

"Although numerous alternative harvesters have been investigated for many decades, no other reported harvester provides such high electrical power or energy output per cycle as ours for stretching rates between a few cycles per second and 600 cycles per second," adds Dr Ray Baughman, director of the NanoTech Institute.

The researchers tested the use of the yarn in clothing. In one test, twistron harvesters were sewn into a shirt. Normal breathing stretched the yarn and generated an electrical signal, demonstrating its potential as a self-powered respiration sensor.

"Electronic textiles are of major commercial interest, but how are you going to power them?" Baughman asks. "Harvesting electrical energy from human motion is one strategy for eliminating the need for batteries. Our yarns produced over a hundred times higher electrical power per weight when stretched compared to other weavable fibres reported in the literature."

Earlier this month, researchers at the university of Manchester also revealed research being conducted into flexible batteries that are printed directly on to fabric.

Nazmul Karim, knowledge exchange fellow at the University of Manchester, said: "It will open up possibilities of making an environmentally friendly and cost-effective smart e-textile that can store energy and monitor human activity and physiological condition at the same time."

Researchers power wearable devices with printed batteries