Insulating thread gives safety boost to ‘smart textiles’

The team at North Carolina State University (NC State) reported in npj Flexible Electronics that they prevented short-circuiting in yarns that act as supercapacitors by wrapping the yarns with insulating thread. They also tested the strength and durability of the yarns to ensure they worked after going through knitting and weaving processes.

“A supercapacitor functions like a battery, but in this case, we’re working on a flexible battery shaped as a textile yarn that you could weave or knit into your T-shirt or sweater,” said Wei Gao, associate professor of textile engineering, chemistry and science and a University Faculty Scholar at NC State. “In this study, we have woven this yarn into a piece of fabric so that it can store electrical energy, and eventually we want to use it to power whatever electronic devices you need, whether it be a sensor, a light or even a cell phone.”

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According to NC State, research into these so-called ‘yarn-shaped supercapacitors’ is promising, but developers face a consistent problem with their design because the yarn-shaped supercapacitors are more likely to short circuit as their length increases.

“Everybody is trying to make smart electronics that can be incorporated into cloth or fabric,” Gao said in a statement. “What we found is if you try to make a supercapacitor yarn longer than eight inches, it’s pretty easy for this device to short-circuit.”

Resolving this, the researchers tested what would happen when they wrapped the super-capacitor yarn electrodes with insulating threads. According to NC State, the idea was that the threads would act as a physical barrier, keeping the opposite electrodes from contacting each other and preventing short-circuiting. They tested their device’s performance by connecting the electrodes to a power source and recording the device’s current response. They also tested how well the yarns were able to hold a charge. They found that the yarns kept 90 per cent of the initial energy after charging and discharging them 10,000 times.

The researchers also tested to see if they could withstand bending and stretching by weaving their yarn-shaped supercapacitors into a fabric.

“The yarns need to be flexible and strong enough so that when you bend, stretch and press them, they keep their original electrical performance after all of those mechanical deformations,” said the study’s lead author Nanfei He, postdoctoral research scholar in textile engineering, chemistry and science at NC State. “The yarns all kept their original performance, even after going through weaving and knitting.”