International research team develops ultrahigh-power energy storage devices

A team of researchers from the U.S. and France report the development of a micro-supercapacitor with remarkable properties.
The paper was published in the premier scientific journal Nature Nanotechnology online on August 15.

These micro-supercapacitors 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 described in Nature Nanotechnology 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 the paper. “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.”