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Graphene Electrodes Developed for Supercapacitors

Graphene molecular illustration (Lawrence Berkeley National Laboratory)

Graphene molecular illustration (Lawrence Berkeley National Laboratory)

Researchers at University of California in Los Angeles have developed electrodes for supercapacitors, energy storage devices that charge and discharge faster than batteries, using a one-atom-thick layer of carbon called graphene. Their findings appear in his week’s issue of the journal Science (paid subscription required).

In addition to faster charging and discharging, supercapacitors store substantially larger numbers of charges, but they have only a fraction of a battery’s energy density. The UCLA researchers were able to develop electrodes — the cells that charge and discharge — with the characteristic high conductivity, but with much more accessible surface area than conventional supercapacitors.

The UCLA team’s process coats a DVD disc with a film of graphite oxide, the graphene source, that is then laser treated inside a LightScribe DVD drive (the kind found in computer and home electronics) to produce the graphene electrodes. The LightScribe laser causes the simultaneous reduction and exfoliation of graphite oxide and produces an open network of laser scribed graphene (LSG) with substantially higher and more accessible surface area.

The open network structure of the electrodes helps minimize the diffusion path of electrolyte ions, which is crucial for charging the device. This structure makes it possible for LSG supercapacitors to deliver ultrahigh power in a short period of time, while traditional activated carbon electrodes cannot.

The researchers found that LSG electrodes can be used as both the active material and current collector in a single layer. This structure offers a simpler architecture and helps make LSG supercapacitors more cost-effective devices. The research team also replaced the liquid electrolyte usually found in traditional supercapacitors with a polymer gelled electrolyte that also acts as a separator, reducing the device thickness and weight, and eliminating the need for special packaging materials. As a result, this graphene-based supercapacitor is a better candidate to power flexible electronic devices than traditional supercapacitors.

Tests of the new supercapacitors found them to be mechanically robust, with high conductivity compared to activated carbon. The research team placed a device under constant mechanical stress to analyze its operation, and found almost no effect on performance.

“We attribute the high performance and durability to the high mechanical flexibility of the electrodes along with the interpenetrating network structure between the LSG electrodes and the gelled electrolyte,” says Richard Kaner, senior author and UCLA professor of chemistry, materials science, and engineering. “Our study demonstrates that our new graphene-based supercapacitors store as much charge as conventional batteries, but can be charged and discharged a hundred to a thousand times faster.”

Read more: Solid-State Supercapacitor Created with Carbon Nanotubes

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