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Aerogel process cuts cost of supercapacitor electrodes for EVs

An inexpensive and fast process to create supercapacitor electrodes for use in electric cars and high-powered lasers has been developed by a team at the University of Washington.

Supercapacitors are an aptly named type of device that can store and deliver energy faster than conventional batteries. They are in high demand for applications including electric cars, wireless telecommunications and high-powered lasers.

Future electric cars, such as BMW’s concept i8 pictured above, could use the component to enable faster acceleration and a charging time of just a few minutes, compared to several hours for a standard electric car battery.

But they are often hampered by their electrodes, which connect them to the devices that depend on their energy.

These electrodes need to be both quicker and cheaper to make on a large scale and also able to charge and discharge their electrical load faster.

The Washington research team has developed a process for manufacturing supercapacitor electrode materials that will meet these stringent industrial and usage demands.

Their novel 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 the new process has almost doubled its capacitance, which is its ability to store electric charge.

These inexpensive starting materials, coupled with a streamlined synthesis process, minimise two common barriers to industrial application: cost and speed.

“In industrial applications, time is money,” said team member Peter 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 synthesised 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. While a conventional battery stores electric charges via the chemical reactions occurring within it, a supercapacitor instead stores and separates positive and negative charges directly on its surface.

“Supercapacitors can act much faster than batteries because they are not limited by the speed of the reaction or byproducts that can form,” said Matthew Lim who also worked on the project. “Supercapacitors can charge and discharge very quickly, which is why they’re great at delivering these ‘pulses’ of power.”

The component complements traditional batteries when their electricity output is too slow to meet energy demands. A supercapacitor with a high surface area electrode is able to ‘kick’ in quickly and make up for the energy deficit.

To get the high surface area for an efficient electrode, the team used aerogels. These are 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 3-D structure, giving it a high surface area and extremely low density. One gram of aerogel supposedly contains about as much surface area as one football field.

After obtaining the dried, low-density aerogel, they combined it with adhesives and another carbon-rich material to create an industrial ‘dough’, which is rolled out into sheets just 10 to 100 atoms thick.

13mm (half-inch) discs were cut from the dough and assembled 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 synthesise, but they also sported a capacitance at least 127 per cent greater than the carbon-rich aerogel alone.

The team believes that these efforts can help advance science even outside the realm of supercapacitor electrodes.

Their aerogel-suspended molybdenum disulfide might remain sufficiently stable to catalyse hydrogen production. And their method to trap materials quickly in aerogels could be applied to high capacitance batteries or catalysis.

In May a prototype system was demonstrated that allows electric cars to be charged during transit by driving on specially adapted roads that can wirelessly power vehicles. 

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