Design Tweak helps prevent malfunctions in wires designed to store energy

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In a new study, researchers at North Carolina State University have found a way to prevent electrical malfunctions in wires designed to store electrical energy. Ultimately, the findings could help advance the development of “smart textiles” that capture energy from wearer movements and power sensors and wearable electronics.

The researchers reported in npj Flexible Electronics that they were able to prevent short circuits in wires that act as supercapacitors – which are electrical devices that store energy – by wrapping the wires with insulating wire. They also tested the yarns for strength and durability to ensure they could still function after going through the knitting and weaving processes.

“A supercapacitor works like a battery, but in this case we’re working on a flexible battery in the shape of 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 academic researcher at NC State. “In this study, we’ve woven this wire into a piece of fabric so it can store electrical energy, and eventually we want to use it to power whatever electronics you need, whether it’s a sensor , a light or even a cell. call.”

While the research on these so-called “wire-shaped supercapacitors” is promising, the researchers say that developers face a constant problem with their design: wire-shaped supercapacitors are more likely to short out as they go. as their length increases. Short circuit occurs when electric current flows in an unintended path. It is a safety issue because a short circuit can lead to a thermal energy explosion or even a fire.

“Everyone is trying to make smart electronic devices that can be embedded in cloth or fabric,” Gao said. “What we found is that if you try to make a supercapacitor wire longer than 8 inches, it’s quite easy for this device to short out. It’s pretty dangerous, and it’s something no one wants to encounter while wearing a fancy suit.

To solve this problem, the researchers tested what would happen when they wrapped the wire electrodes of the supercapacitor with insulating wires. The idea was that the wires would act as a physical barrier, preventing opposing electrodes from contacting each other and preventing short circuits. They tested the performance of their device by connecting the electrodes to a power source and recording the current response of the device. They also tested the wires’ ability to hold a charge. They found that the wires retained 90% 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-like supercapacitors into fabric.

“The wires need to be flexible and strong enough that when you bend, stretch and squeeze them, they retain their original electrical performance after all that mechanical deformation,” said the study’s lead author, Nanfei He, postdoctoral researcher in textile engineering, chemistry and science at NC State. “The yarns all retained their original performance even after being woven and knitted.”

The researchers said they made the wire-like supercapacitor using conventional processes in textile manufacturing.

“All of these processes can be scaled very easily,” he said.

In future work, the researchers want to incorporate their design into clothing and attempt to integrate it with other power-generating devices.

“Materials innovation and process engineering are key to device scalability and performance,” said Feng Zhao, CEO of Storagenergy Technologies Inc., the project’s industry partner. “We have developed a process to produce thousands of meters of high performance yarn continuously.”

The study, “Separator Threads in Yarn-Shaped Super-capacitors,” was published online in npj Flexible Electronics. In addition to He, Gao, and Zhao, the other authors were Junhua Song and Jinyun Liao from Storagenergy Technologies Inc. The study was supported by Storagenergy Technologies Inc. and funded by the US military under contract numbers W911NF19C0074 and W911NF18C0086.

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Note to Editors: Summary follows.

“Separating wires in wire-shaped supercapacitors to prevent short circuits along the length”

Authors: Nanfei He, Junhua Song, Jinyun Liao, Feng Zhao and Wei Gao.

Posted online in npj Flexible Electronics on March 18, 2022.

DO I: 10.1038/s41528-022-00150-2

Abstract: Wire-shaped supercapacitors (YSCs) are emerging as promising power supply units with decent mechanical flexibility to be integrated into e-textiles of various shapes and locations. However, a robust YSC configuration capable of delivering reliable, long-lasting power output, especially after rigorous weaving and knitting processes, as well as all sorts of end uses, has yet to be established. Most YSCs today still suffer from shorts along the length, primarily due to failure of the gel electrolyte structure which also functions as a separator. Here we report the incorporation of spacer wires into a twisted YSC, to resist repetitive mechanical deformations. Separator wires are wound outside the wire electrodes like a scaffold to accommodate the gel electrolyte, while the chemistry and packing density of these wires are studied. With optimized processing parameters, we present a YSC configuration that can withstand mechanical deformations in almost any direction, leading to reliable power units in woven or knitted fabrics.

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