Graphene tested to boost battery storage

University of Texas at Austin researchers said today recent data suggest a one-atom thick carbon-based material shows remarkable promise for storing electrical charge in ultracapacitor devices.

The researchers said preliminary data results suggest that the nano-scale material graphene could be used to double the capacity of ultracapacitor devices. The team plans future experiments to determine if the material can deliver those higher storage capacities.

“We have reason to think that we can double the capacity,”  Rod Ruoff, a mechanical engineering professor and a physical chemist at the University of Texas at Austin told the Cleantech Group.

Based on these findings and planned experiments, the researchers think the carbon-based ultracapacitors could be used in a variety of applications including solar, electric and hybrid cars, wind, and consumer electronic devices (see Lockheed Martin to use EEStor's ultracapacitors). The team's findings will be published in the Oct. 8 edition of Nano Letters.

The research team modified graphene material with chemicals and then constructed an ultracapacitor cell that used common electrolytes.  In the first phase of the research work, the team was able to store an electrical charge in a unit weight measurement, called specific capacitance, that rivaled existing ultracapacitors.

Graphene’s surface area is a significant part of its ability to offer greater storage capacity. The surface area is roughly 2,630 square meters per gram. That large surface area means a larger number of positive or negative ions in the electrolyte can form a layer on the graphene sheets.

“What is a critical part here is these individual platelets or graphene sheets are electrically conductive, which means electrons can hop from one to the other,” Ruoff said.  “It is the double layer structure [of graphene] combined with the close proximity of ions and the carbon that give it its high capacitance,” he added.

Power delivery and long lifetimes are critical for battery devices (see PowerGenix non-toxic batteries coming to market). Re-chargeable batteries and ultracapacitors are the two main methods by which electrical energy is stored. Ultracapacitors have several inherent advantages over batteries, such as greater power capability, longer life, operating in broader range of temperatures, lighter, flexible packaging and lower maintenance.

"Electrical energy storage becomes a critical component when very large quantities of renewable electrical energy are being generated,” Ruoff said.

The U.S. Department of Energy has issued a challenge for electrical energy storage methods that are sorely needed for the wind and solar energy markets. Electrical storage is vital, epecially when the wind doesn't blow or the sun doesn't shine. During those times, the stored electrical energy can be delivered through the electrical grid as needed.

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