Dr Chunyi Zhi, Associate Professor at the Department of Physics & Materials Science at the City University of Hong Kong and his group developed a stretchable and compressible polyelectrolyte which, in combination with carbon nanotube composite paper electrodes, forms a supercapacitor that can be stretched to 1000 percent in length and compressed to half its thickness.
This amount of stretching makes the supercapacitor well suited to flexible and wearable applications.
Electrolytes in supercapacitors are often based on polyvinyl alcohol gels with added elastic components. The new electrolyte is based on a different principle, using a polyacrylamide (PAM) hydrogel reinforced with vinyl-functionalized silica nanoparticles (VSPNs). This is very stretchable as a result of the cross-links in the vinyl-silica nanoparticles and highly conductive as it swells with water and both holds and transfers ions. "VSNPs cross-linkers serve as stress buffers to dissipate energy and homogenize the PAM network,” said Zhi. “These synergistic effects are responsible for the intrinsic super-stretchability and compressibility of our supercapacitor.”
To build the supercapacitor, two carbon nanotube composite paper electrodes were directly deposited on each side of the pre-stretched polyelectrolyte film. Upon release, a wavy, accordion-like structure developed.
"The electrochemical performance gets enhanced with the increase of strain," said Zhi. This follows work in 2015 that led to a supercacitor with 6x stretching that coped with over 20 charging cycles.
The work is published in Angewandte Chemie
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