Common Fatty Acid Could Yield High Density Energy Storage For Electric Vehicles

July 31st, 2015 by Tina Casey

Way back in 2011, Tesla Motors CEO Elon Musk was caught on tape predicting that powerful capacitors, not batteries, would be the future energy storage mode of choice for electric vehicles. That future is still a long way off, but a research team at the Georgia Institute of Technology has developed a new type of high-performance capacitor that could be used to complement, if not replace, electric vehicle batteries.

What Is This Capacitor Of Which You Speak?

For those of you new to the topic, a capacitor is an energy storage device like a battery, but it behaves differently.

Batteries charge slowly, while capacitors charge up rapidly. That makes them alluring as candidates for electric vehicles, except that they also discharge very quickly, which limits their application to providing quick bursts.

Capacitors are already being used in that capacity for electric vehicles, for example in regenerative braking systems (same for trains). Specialty markets, such as auto racing, are also eyeing capacitor technology as a performance enhancer.

Capacitors are also alluring for EV energy storage because they don’t need to be replaced before the rest of the vehicle wears out. That’s an improvement over conventional battery technology, at least for folks who like to keep the same vehicle as long as possible.

In the context of finite resources, that longer lifespan could provide capacitors with another important edge over batteries… eventually (unless Mr. Musk has changed his mind).

The Georgia Tech Dielectric Capacitor

The Georgia Tech research team has come up with a new material for dielectric capacitors.

According to the team, the challenge is to find a dielectric material that can maximize “permittivity, breakdown strength, energy density and energy extraction efficiency.”

So far the work is at lab scale, but the team is confident that the new material will outperform typical electrolytic capacitors in real life, as well as rivaling certain types of batteries.

The team fabricated the new material using a sol-gel process, which starts with a solution of solid nanoparticles. The tiny particles then self-assemble throughout the liquid to form a gel.

Here’s the rundown from Georgia Tech:

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.

Did you catch that thing about octylphosphonic acid? That’s the secret sauce. Octylphosphonic acid is a common fatty acid used as a corrosion inhibitor in consumer products, among other things.

The lab results indicate that the new material will outperform thin-film lithium-ion batteries as well as conventional electrolytic capacitors:

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…

Energy Storage For US Navy, Air Force

The research was supported by the US Office of Naval Research Dielectric Films for Capacitors Program (DFCP) and the US Air Force Office of Scientific Research.

Energy storage for electric vehicles isn’t exactly a priority for either the Navy or the Air Force, but capacitors certainly are important.

Here’s the lowdown from DFCP:

Dielectric films for capacitors are critical for the development of energy- and power-dense systems for shipboard use impulse power, power conditioning and back-up power applications. The Office of Naval Research program focuses on the materials and structures that have the capacity to increase energy density, reducing weight and volume allocation for capacitor banks while extending service life in extreme conditions.

DFCP falls under the Naval Materials Division, which aims for developing materials that enhance performance, affordability, and reliability. That includes high risk, high return foundational research:

…the Office of Naval Research encourages proposals identifying new concepts and projects to advance the science and technology of advanced materials of potentially extraordinary value. The interdisciplinary and multidisciplinary nature of materials science and technology is reflected in programs involving the full range of academic science and engineering disciplines, including materials science and engineering, chemistry, physics, chemical engineering, mechanical engineering, and electrical engineering.

We bring this up because certain federal legislators have established a track record when it comes to trying the Navy from investing in new clean tech. Here’s the relevant section of Senator John McCain’s statement on last year’s omnibus spending bill:

The bill also includes $375 million for Army, Navy and Air Force ‘alternative energy research’ initiatives. As I have stated in the past, this type of research has yielded such shining examples as the Department of the Navy’s purchase of 450,000 gallons of alternative fuels for $12 million (over $26 per gallon).

As we see it, $26 per gallon is a big improvement over the $400+ cost of transporting conventional fuel into a war zone, so there’s that.

Go, Navy.

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Photo Credit (cropped, altered): Samples of hybrid sol-gel material on a clear plastic substrate for testing, by John Toon, Georgia Tech.









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