Cheap supercapacitor electrodes enable coin cells
The method starts with carbon-rich materials that have been dried into a low-density matrix called an aerogel. The aerogel on its own can act as a crude electrode, but the team led by UW assistant professor of materials science and engineering Peter Pauzauskie more than doubled the capacitance
“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.”
A high surface area is a key requirement for storing chare as separate positive and negative charges directly on its surface. “One gram of aerogel contains about as much surface area as one football field,” said Pauzauskie.
“Supercapacitors can act much faster than batteries because they are not limited by the speed of the reaction or the by-products that can form,” said researcher Matthew Lim, a UW doctoral student in the Department of Materials Science & Engineering. “Supercapacitors can charge and discharge very quickly, which is why they’re great at delivering these ‘pulses’ of power.”
“They have great applications in settings where a battery on its own is too slow,” said researcher Matthew Crane, a doctoral student in the UW Department of Chemical 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.”
He made aerogels from a gel-like polymer, a material with repeating structural units, created from formaldehyde and other carbon-based molecules. He and Lim loaded aerogels with thin sheets of either molybdenum disulfide or tungsten disulphide 10 to 100 thick. Both materials are widely used in industrial lubricants and so available at low cost.
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, while other methods would take many days.
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 their electrodes fast, simple and easy to synthesize, but they also showed a capacitance at least 127 percent greater than the carbon-rich aerogel alone.
Lim and Crane expect that aerogels loaded with even thinner sheets of molybdenum disulfide or tungsten disulfide would show an even better performance but wanted to show that loaded aerogels would be faster and cheaper to synthesize.
The method to trap materials quickly in aerogels could be applied to high capacitance coin cell batteries or catalysis in fuel cells.
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