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Funding to boost development of high-energy density capacitors for hybrids and EVs


December 5, 2010

Lightweight capacitors are being developed to meet the high energy demands of hybrids and EVs (Photo: Noel McKeegan)

Lightweight capacitors are being developed to meet the high energy demands of hybrids and EVs (Photo: Noel McKeegan)

Research into capacitors for use in hybrid vehicles, EVs, computer power supplies and pacemakers has been given a boost in the order of US$2.25 million. Professor Gerhard Welsch, who began patenting his designs for capacitors a decade ago, will use the grant to complete development of a small, light, powerful and reliable capacitor that promises a 10-fold or higher increase in energy density over current models.

Welsch, a professor of materials science and engineering at Case Western Reserve University, received the stimulus grant from the U.S Department of Energy’s Advanced Research Projects Agency – Energy, (ARPA-E).

ARPA-E is especially interested in the capacitor for hybrid and EV technology. Batteries can’t supply or absorb energy nearly as fast as a capacitor.

“Electric vehicles need power inverters to convert battery power into higher voltage AC power for their electric motors and to harvest braking power,” Welsch said.

Capacitors eliminate this need for inversion as they can deliver their stored energy at high voltages.

Welsch’s capacitor uses of a finely textured titanium alloy anode providing a large surface area to volume ratio which enables high capacitance and a high energy density. This fine porous structure is laid out on a spine with many branches increasing the surface area. A layer of titanium oxide creates a barrier called a dielectric which separates positive and negative electrical charges with a certain voltage, thus holding energy. A layer of an ion-conducting electrolyte and a metallic layer of carbon or titanium acts as the cathode.

“A capacitor is the equivalent of an electron pressure tank, and the trick is to make the dielectric film (or the wall of the pressure tank), impenetrable to electrons by making it strong and as perfect as possible,” Welsch said. “Perfect is not possible, but we can make a material that’s close.”

Welsch also aims to use his capacitor in a miniaturized implantable defibrillator that can sense uncontrolled contractions of the heart and jolt the muscle with a pulse of electricity supplied by a battery, restoring a normal beat.

Welsch is collaborating on the design with Chung-Chiun Liu, professor of chemical engineering, and Frank Merat, professor of computer science and electrical engineering.

It is hoped that a product will be ready for market within three years.


The reason electric vehicles need power inverters is not to step up the voltage (to do that all you do is add more batteries). Rather the power inverters are what drive the AC synchronous motors. AC motors need a 3 phase source, and inverters provide the conversion from DC to AC. The battery packs in EVs that use AC motors are already over 300 volts, and don\'t need any stepping up.

I just hope this isn\'t another EEStor.


@Eletruk: While I admit the author didn\'t really explain things clearly nor use the correct terms, a converter for uC based EV\'s will be needed. For techie reasons: it is the area under the cap discharge curve that determines the ultimate boost capability, so higher voltages will deliver more power. Having the cap run at traction pack voltage is not good enough. So triple Vpack is appropriate.

Another reason is that you need to electronically regulate the charge on the cap, so a special bi-directional power transfer gate would be needed, if nothing else than to manage the system impedence differences. (That cap looks like zero ohms when discharged completely, and that presents a problem.)

I also hope this isn\'t another EEStor(y)! R

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