Georgia Tech and Korea University researchers have developed a paper-based flexible supercapacitor to power wearable devices.
According to the researchers, the device uses a simple layer-by-layer coating technique featuring metallic nanoparticles to coat cellulose fibers in the paper.
The technique is said to create large surface areas that function as current collectors and nanoparticle reservoirs for the electrodes. Testing shows that devices fabricated with the technique can be folded thousands of times without affecting conductivity.
“This type of flexible energy storage device could provide unique opportunities for connectivity among wearable and internet of things devices,” said Seung Woo Lee, an assistant professor in the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. “We could support an evolution of the most advanced portable electronics. We also have an opportunity to combine this supercapacitor with energy-harvesting devices that could power biomedical sensors, consumer and military electronics, and similar applications.”
Energy storage devices come with namely three properties: their energy density, power density and cycling stability. Supercapacitors often have high power density, but low energy density – the amount of energy that can be stored – compared to batteries, which often have the opposite attributes.
In developing their new technique, Lee and collaborator Jinhan Cho from the Department of Chemical and Biological Engineering at Korea University set out to boost energy density of the supercapacitors while maintaining their high power output.
They began by dipping paper samples into a beaker of solution containing an amine surfactant material designed to bind the gold nanoparticles to the paper. Next they dipped the paper into a solution containing gold nanoparticles.
By repeating the dipping steps, the researchers created a conductive paper on which they added alternating layers of metal oxide energy storage materials such as manganese oxide. The ligand-mediated layer-by-layer approach helped minimize the contact resistance between neighboring metal and/or metal oxide nanoparticles.
The next steps will include testing the technique on flexible fabrics, and developing flexible batteries that could work with the supercapacitors.
The researchers used gold nanoparticles because they are easy to work with, but plan to test less expensive metals such as silver and copper to reduce the cost.
Image credits and content: Georgia Tech