Posted on 08/03/2015 11:08:59 AM PDT by Red Badger
Samples of the new hybrid sol-gel material are shown placed on a clear plastic substrate for testing. Credit: John Toon, Georgia Tech
=================================================================================================================
Using a hybrid silica sol-gel material and self-assembled monolayers of a common fatty acid, researchers have developed a new capacitor dielectric material that provides an electrical energy storage capacity rivaling certain batteries, with both a high energy density and high power density.
If the material can be scaled up from laboratory samples, devices made from it could surpass traditional electrolytic capacitors for applications in electromagnetic propulsion, electric vehicles and defibrillators. Capacitors often complement batteries in these applications because they can provide large amounts of current quickly.
The new material is composed of a silica sol-gel thin film containing polar groups linked to the silicon atoms and a nanoscale self-assembled monolayer of an octylphosphonic acid, which provides insulating properties. The bilayer structure blocks the injection of electrons into the sol-gel material, providing low leakage current, high breakdown strength and high energy extraction efficiency.
"Sol-gels with organic groups are well known and fatty acids such as phosphonic acids are well known," noted Joseph Perry, a professor in the School of Chemistry and Biochemistry at the Georgia Institute of Technology. "But to the best of our knowledge, this is the first time these two types of materials have been combined into high-density energy storage devices."
The research, supported by the Office of Naval Research and the Air Force Office of Scientific Research, was reported July 14 in the journal Advanced Energy Materials.
The need for efficient, high-performance materials for electrical energy storage has been growing along with the ever-increasing demand for electrical energy in mobile applications. Dielectric materials can provide fast charge and discharge response, high energy storage, and power conditioning for defense, medical and commercial applications. But it has been challenging to find a single dielectric material able to maximize permittivity, breakdown strength, energy density and energy extraction efficiency.
Perry and colleagues in Georgia Tech's Center for Organic Photonics and Electronics (COPE) had been working on other capacitor materials to meet these demands, but were not satisfied with the progress. The hybrid sol-gel materials had shown potential for efficient dielectric energy storage because of their high orientational polarization under an electric field, so the group decided to pursue these materials for the new capacitor applications.
Using an aluminized mylar film coated with the hybrid sol-gel capacitor material, they showed that the capacitor could be rolled and re-rolled several times while maintaining high energy density, demonstrating its flexibility. But they were still seeing high current leakage. To address that, they deposited a nanoscale self-assembled monolayer of n-octylphosphonic acid on top of the hybrid sol-gel. Less than a nanometer thick, the monolayer serves as an insulating layer.
"Our silica sol-gel is a hybrid material because it has polar organic groups attached to the silica framework that gives the sol-gel a high dielectric constant, and in our bilayer dielectric, the n-octylphosphonic acid groups are inserted between the sol-gel layer and the top aluminum layer to block charge injection into the sol-gel," Perry explained. "It's really a bilayer hybrid material that takes the best of both reorientation polarization and approaches for reducing injection and improving energy extraction."
In their structures, the researchers demonstrated maximum extractable energy densities up to 40 joules per cubic centimeter, an energy extraction efficiency of 72 percent at a field strength of 830 volts per micron, and a power density of 520 watts per cubic centimeter. The performance exceeds that of conventional electrolytic capacitors and thin-film lithium ion batteries, though it doesn't match the lithium ion battery formats commonly used in electronic devices and vehicles.
"This is the first time I've seen a capacitor beat a battery on energy density," said Perry. "The combination of high energy density and high power density is uncommon in the capacitor world."
Researchers in Perry's lab have been making arrays of small sol-gel capacitors in the lab to gather information about the material's performance. The devices are made on small substrates about an inch square.
"What we see when we apply an electric field is that the polarization response – which measures how much the polar groups line up in a stable way with the field – behaves in a linear way," said Perry. "This is what you want to see in a capacitor dielectric material."
The next step will be to scale up the materials to see if the attractive properties transfer to larger devices. If that is successful, Perry expects to commercialize the material through a startup company or SBIR project.
"The simplicity of fully solution-based processes for our dielectric material system provides potential for facile scale-up and fabrication on flexible platforms," the authors wrote in their paper. "This work emphasizes the importance of controlling the electrode-dielectric interface to maximize the performance of dielectric materials for energy storage application."
Explore further: High-performance energy storage
More information: Yunsang Kim, et al., "Bilayer Structure with Ultra-high Energy/Power Density Using Hybrid Sol-Gel Dielectric and Charge Blocking Monolayer, Advanced Energy Materials, 2015. www.dx.doi.org/10.1002/aenm.201500767
Journal reference: Advanced Energy Materials search and more info website
Provided by: Georgia Institute of Technology
But does it have to? Can’t it be a regulated release?
Now...why didn't I think of that?
I mean, really, it’s so obvious, now.........................
It can be. The discharge rate is inversely proportional to the load resistance...................
Discharge rate is hi - but as one post here noted the voltage drops. The other issue is the time constant for either discharge or charge. Usually the time contact is very small because the total capacitance is low. Ultra capacitors or this tech will have bigger time constants which is function of the total capacitance. Anything that rivals the energy density of a battery will take significant time to charge.
Also, at some point you will be pushing the limits of a common 15A outlet.
“The new material is composed of a silica sol-gel thin film containing polar groups linked to the silicon atoms and a nanoscale self-assembled monolayer of an octylphosphonic acid, which provides insulating properties.”
That’s what my mom used to say, but us kids never listened.
IIRC, every house is wired for 230V, being split into two sections of 115V, usually delivered thru, as you say a common 15A outlet. But a 230V high amperage outlet can be installed by a competent electrician without much hassle......................
Thanks! That helps...... I think.
Yes - of course. The biggest problem with using capacitors as energy storage devices is that the voltage drops rapidly as the capacitor discharges.
Of course if you're blasting the whole thing to pump a laser or simultaneously fire a bunch of exploding bridgewire detonators for example that doesn't matter.
A four-switch buck-boost DC-DC convertor can take a range of input voltage and produce a regulated range of output voltage. No matter the change on the input, within the acceptable range, the desired output will be maintained.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.