UWashington team develops fast, cheap method to make supercapacitor electrodes

Researchers at the University of Washington (UW) have designed a supercapacitor electrode that is both cost efficient and quick to develop.

Full x-ray reconstruction of a coin cell supercapacitor. Photo credit: William Kuykendall

The team, led by UW assistant professor of materials science and engineering Peter Pauzauskie, has developed a process for manufacturing supercapacitor electrode materials that will meet these stringent industrial and usage demands.

The method starts with carbon-rich materials that have been dried into a low-density matrix called an aerogel. This aerogel on its own can act as a crude electrode, but Pauzauskie’s team more than doubled its capacitance, which is its ability to store electric charge.

Two of the biggest challenges for developing supercapacitor electrodes is the cost and speed. The UW team believes that through the inexpensive starting materials and streamlined synthesis process, these common barriers are minimized.

“In industrial applications, time is money,” said Pauzauskie. “We can make the starting materials for these electrodes in hours, rather than weeks. And that can significantly drive down the synthesis cost for making high-performance supercapacitor electrodes.”

Effective supercapacitor electrodes are synthesized from carbon-rich materials that also have a high surface area. The latter requirement is critical because of the unique way supercapacitors store electric charge — a supercapacitor instead stores and separates positive and negative charges directly on its surface.

“Supercapacitors can charge and discharge very quickly, which is why they’re great at delivering these ‘pulses’ of power,” said co-lead author Matthew Lim, a UW doctoral student in the Department of Materials Science & Engineering.

“In moments where a battery is too slow to meet energy demands, a supercapacitor with a high surface area electrode could ‘kick’ in quickly and make up for the energy deficit,” explains fellow lead author Matthew Crane, a doctoral student in the UW Department of Chemical Engineering.

The team used aerogels to get the high surface area for an efficient electrode. These wet, gel-like substances that have gone through a special treatment of drying and heating to replace their liquid components with air or another gas. These methods preserve the gel’s 3D structure, giving it a high surface area and extremely low density.

“One gram of aerogel contains about as much surface area as one football field,” said Pauzauskie.

Crane made aerogels from a gel-like polymer, a material with repeating structural units, created from formaldehyde and other carbon-based molecules. This ensured that their device, like today’s supercapacitor electrodes, would consist of carbon-rich materials.

Although the team tried other options they eventually loaded aerogels with thin sheets of either molybdenum disulfide or tungsten disulfide. Both chemicals are used widely today in industrial lubricants.

The researchers treated both materials with high-frequency sound waves to break them up into thin sheets and incorporated them into the carbon-rich gel matrix. They could synthesize a fully-loaded wet gel in less than two hours.

After obtaining the dried, low-density aerogel, they combined it with adhesives and another carbon-rich material to create an industrial “dough,” which Lim could simply roll out to sheets just a few thousandths of an inch thick. They cut half-inch discs from the dough and assembled them into simple coin cell battery casings to test the material’s effectiveness as a supercapacitor electrode.

Not only were the electrodes fast, simple and easy to synthesize, but they also sported a capacitance at least 127 percent greater than the carbon-rich aerogel alone.

The researchers published a paper on July 17 in the journal Nature Microsystems and Nanoengineering describing their supercapacitor electrode and the fast, inexpensive way they made it.

www.washington.edu