The researchers from the U.S. and France report the development
of a micro-supercapacitor with "remarkable" properties.
The micro-supercapacitors, researched at Drexel University, have the potential
to power nomad electronics, wireless sensor networks, biomedical implants,
active radiofrequency identification (RFID) tags and embedded microsensors,
among other devices.
Supercapacitors, also called electric double layer capacitors (EDLCs) or ultracapacitors,
bridge the gap between batteries, which offer high energy densities but are
slow, and “conventional” electrolytic capacitors, which are fast
but have low energy densities.
The newly developed devices have powers per volume that are comparable to
electrolytic capacitors, capacitances that are four orders of magnitude higher,
and energies per volume that are an order of magnitude higher. They were also
found to be three orders of magnitude faster than conventional supercapacitors,
which are used in backup power supplies, wind power generators and other machinery.
These new devices have been dubbed “micro-supercapacitors” because
they are only a few micrometers (0.000001 meters) thick.
What makes this possible?
“Supercapacitors store energy in layers of ions at high surface area
electrodes,” said Dr. Yury Gogotsi, Trustee Chair Professor of materials
science and engineering at Drexel University, and a co-author of a paper on
the subject. “The higher the surface area per volume of the electrode
material, the better the performance of the supercapacitor.”
Vadym Mochalin, research assistant professor of materials science and engineering
at Drexel and co-author, said, “We use electrodes made of onion-like
carbon, a material in which each individual particle is made up of concentric
spheres of carbon atoms, similar to the layers of an onion. Each particle is
6-7 nanometers in diameter.”
This is the first time a material with very small spherical particles has
been studied for this purpose. Previously investigated materials include activated
carbon, nanotubes, and carbide-derived carbon (CDC).
“The surface of the onion-like carbons is fully accessible to ions,
whereas with some other materials, the size or shape of the pores or of the
particles themselves would slow down the charging or discharging process,” Mochalin
said. “Furthermore, we used a process to assemble the devices that did
not require a polymer binder material to hold the electrodes together, which
further improved the electrode conductivity and the charge/discharge rate.
Therefore, our supercapacitors can deliver power in milliseconds, much faster
than any battery or supercapacitor used today.”
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