A recent $2.25 million stimulus grant from the U.S. Dept. of Energy’s Advanced Research Projects Agency – Energy, or ARPA-E, will go toward perfecting a super-capacitor that would provide a 10-fold or better energy density than current models, yet would be a fraction of the size and weight. The new design could also be quite reliable because it can heal leaks of electrical current that plague models now in use.
The goal of the project run by Case Western Reserve University materials science and engineering professor Gerhard Welsch will be to make a capacitor ready for market within three years.Working with him are colleagues Chung-Chiun Liu, professor of chemical engineering, and Frank Merat, professor of computer science and electrical engineering.The keys are the materials and design of the device. The anode of Welsch’s capacitor is a titanium alloy so finely textured that it absorbs almost all the light hitting it. A large surface area squeezed into a small volume enables high capacitance and a high energy density. The fine porous structure is laid out on a spine with many branches, further increasing the surface area.
A layer of titanium oxide, made by coating the porous surface with metal oxide, creates a dielectric barrier layer. This likely will be made from homogenized titanium alloys, e.g. of Ti-Zr-X-Y compositions, where X and Y are elements from the groups of Be, Pb and Ca, Ba, Sr. A layer of an ion-conducting electrolyte followed by a metallic layer, probably of carbon or titanium, serves as the cathode.
Typically, defects in the dielectric let electrons leak between the anode and cathode, limiting the energy density or leading to failure of the device. Welsch and his colleagues came up with a new synthesis process that reduces the size and number of defects in the dielectric formed. When a defect does form, the same forces that store energy in the dielectric draw ions from titanium and the electrolyte, forming a new oxide in or near the defect, sealing the leak.
The spine and branches’ design, high surface area, synergistic materials and the instant healing of the dielectric would make for a super-efficient energy storage device, Welsch says. In addition to demonstrating the capacitor in power supplies for electric cars and LED lighting, Welsch’s group aims to show how it can be used in a miniaturized implantable defibrillator. When a sensor detects uncontrolled contraction of heart muscle, a battery will send energy to the capacitor, which will in turn jolt the muscle with a pulse of electricity lasting a microsecond, restoring a normal beat.
Welsch has patented a super-cap design that covers the underlying technology upon which the work will be based. According to the patent filing, that design enables the production of capacitors with energy densities of 10-2 to 100 Wh/kg and power densities of 100,000 to 10,000,000,000 W/kg, or more. For capacitors with liquid metal-backed electrolytes, even higher power densities are possible, the filing says.
Another advantage of at least one embodiment of Welsch's design is that the capacitors produced cna operate at frequencies between 20 Hz and 20 kHz.
Case Western put out a short blog entry about the work: http://planet.case.edu/
You can find Welsch's super-capacitor patent filing here: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3&f=G&l=50&co1=AND&d=PTXT&s1=%22Welsch,+Gerhard%22.INNM.&OS=IN/%22Welsch,+Gerhard%22&RS=IN/%22Welsch,+Gerhard%22