Research aims to develop high-capacity automotive supercaps

July 03, 2014 // By Christoph Hammerschmidt
Despite their good ecological footprint, battery electric cars have a number of properties that limit their appeal as an alternative to conventional vehicles: cost, short driving range, long charging times are just a few of them. Many of these undesired properties could be eliminated if the batteries could be replaced by a better means to store electric energy. Supercapacitors could offer an interesting alternative, as the results of a European research project indicate.

In the ElectroGraph project, ten partners from research institutes and industry develop innovative supercaps with a much higher energy storage capacity compared to available supercaps. The researchers, led by Fraunhofer Institute for Production Technology and Automation, started from the premise that the capacity of such a capacitor grows proportionally with the usable area of the electrodes. For this reason, the researchers explored graphene as a promising nanomaterial with a high surface per volume. The "inner surface" of up to 2600 square metres per gram (m 2/g) is considered extremely high, making graphene an ideal material for supercap electrodes. In addition, graphene has very good current conducting properties.

Graphene consists of an ultra-thin single-layer lattice of carbon atoms which significantly increases the electrode surface area. The space between the electrodes is filled with a liquid electrolyte on the basis of ionic liquids. "Graphene-based electrodes in combination with ionic electrolytes are the ideal combination of materials", explained Carsten Glanz who oversees the project at Fraunhofer.

The Fraunhofer researchers are not alone with their assessment - currently several research projects are investigating this topic. (see link list at the end of this article).

The researchers in Stuttgart chose a  specific approach: by arranging the graphene layers in a way that results in a certain distance between the layers, they were able to establish a manufacturing method that makes the theoretically-usable area of the nano material, actually usable in practice. The method also prevents layers connecting to each other, which would result in a reduction of the storage area and thus of the amount of storable energy.

According to Glanz, the electrodes devised in the project have 75% more storage capacity than commercially available electrodes currently used in supercaps. The researcher believes that in future e-car generations a battery will be coupled with a multitude of supercaps that are distributed across the car. These supercaps could store the energy required to run HVAC,