Researchers at Duke University and Michigan State University have designed a new type of supercapacitor that will perform well even if it is stretched to eight times its original size.
Researchers at Duke University and Michigan State University have designed a new type of supercapacitor that will perform well even if it is stretched to eight times its original size. It will not cause any wear due to repeated stretching, and its energy performance is only lost by a few percentage points after 10,000 charge and discharge.
The researchers envisioned a supercapacitor as part of a power-independent, scalable, and flexible electronic system for wearable electronics or biomedical devices.
The results were published online March 19 in the journal Matter. The research team includes Changyong Cao, assistant professor of packaging, mechanical engineering, electrical and computer engineering at Michigan State University, and Jeff Glass, senior author and senior professor of electrical and computer engineering at Duke University. Their co-authors are doctoral students Yihao Zhou and Qiwei Han from Duke University, research scientist Charles Parker, and doctoral student Yunteng Cao from MIT.
"Our goal is to develop an innovative device that will not lose performance under mechanical deformation such as stretching, twisting, or bending." Changyong Cao said he is the director of Michigan State University's Soft Machinery and Electronics Laboratory. "But if the power source of a stretchable electronic device is not stretchable, the entire equipment system will be limited to non-stretchable."
Supercapacitors store energy like batteries, but there are some important differences. Unlike batteries that store energy and generate charge through chemical reactions, electrostatic double-layer supercapacitors (EDLSC) store energy through charge separation and cannot generate electricity on their own. It must be charged from an external source. During charging, electrons are built up in one part of the device and then removed from the other, so when the two sides are connected, electricity flows quickly between them.
Unlike batteries, supercapacitors can release large amounts of energy in a short period of time, rather than through a slow, long stream of water. They also charge and discharge much faster than batteries and have longer charge and discharge cycles than rechargeable batteries. This makes them ideal for short-term, high-power applications, such as setting a flash in a camera or an amplifier in stereo.
But most supercapacitors are as hard and fragile as other components on the board. That's why Changyong Cao and Jeff Glass have spent years researching the stretchable version.
In their new paper, the researchers showed what they had achieved at this point, making a stamp-sized supercapacitor that could carry more than 2 volts. When 4 super capacitors are connected together, just like many devices require AA or AAA batteries, super capacitors can power 2 Volt Casio watches for an hour and a half.
To make a retractable supercapacitor, Glass and his research team first planted a forest of carbon nanotubes on silicon wafers-made up of millions of nanotubes, only 15 nanometers in diameter and 20-30 microns high. This is approximately the width of the smallest bacterium and the height of the animal cells it infects.
The researchers then covered a thin layer of gold nanofilm on top of the carbon nanotube forest. The gold layer is like an electrical collector, reducing the resistance of the device by an order of magnitude, enabling the device to charge and discharge faster.
Glass then gave the engineering process to Changyong Cao, who transferred the forest of carbon nanotubes to a pre-stretched elastomer substrate with the gold layer facing down; and then relaxed the gel-filled electrode to release the pre-strain and shrink it To a quarter of its original size. This process crushes a thin layer of gold and squeezes together the "trees" in the carbon nanotube forest.
"This bending greatly increases the surface area available in a small piece of space, which increases the amount of charge it can hold." Glass explains, "if we have all the space in the world, flat surfaces will work. .But if we want a supercapacitor for real devices, we need to make it as small as possible. "
This dense "forest" is then filled with gel electrolyte, capturing electrons on the surface of the nanotubes. When the last two electrodes are clamped together, the applied voltage loads the electrons on one side and the electrons on the other side are drained, forming a charged super stretchable super capacitor.
"We still need to do some work to build a complete scalable electronic system." Changyong Cao said, "The supercapacitors shown in this paper have not reached the level we want. But with this powerful pull extending foundations of supercapacitors, we will be able to integrate it into a system of stretchable wires, sensors and detectors to create fully stretchable devices. "
The researchers explain that stretchable supercapacitors can power some future devices themselves, or can be combined with other components to overcome engineering challenges. For example, supercapacitors can be charged in seconds and then slowly charge the battery, which is the main source of energy for the device. This method has been used for regenerative braking of hybrid vehicles, in which energy is generated faster than stored. Super capacitors increase the efficiency of the entire system. Or, as has been proven in Japan, supercapacitors can power urban commuter buses with a short time to complete a full charge at each station.
"A lot of people want to connect supercapacitors with batteries," Glass said. "Supercapacitors charge fast and can withstand thousands or even millions of charges, and batteries can store more power and therefore last longer. Putting them together is the best way, after all, there are two different functions in an electrical system. "
Original source: https://www.sciencedaily.com/releases/2020/03/200319142441.htm
