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Novel carbon mat'l boosts supercapacitor performance

Posted: 03 Jun 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Stanford University? supercapacitor? carbon? batteries?

"We call it designer carbon because we can control its chemical composition, pore size and surface area simply by changing the type of polymers and organic linkers we use, or by adjusting the amount of heat we apply during the fabrication process," explained To.

Raising the processing temperature from 400C to 900C can result in a 10-fold increase in pore volume.

Subsequent processing produced carbon material with a record-high surface area of 4,073 square metres per gram, the equivalent of three football fields packed into an ounce of carbon. The maximum surface area achieved with conventional activated carbon is about 3,000 square metres per gram.

"High surface area is essential for many applications, including electrocatalysis, storing energy and capturing carbon dioxide emissions from factories and power plants," said Bao.

To see how the new material performed in real-world conditions, the Stanford team fabricated carbon-coated electrodes and installed them in lithium-sulfur batteries and supercapacitors.

Postdoctoral scholar Zheng Chen, a co-lead author, said: "For supercapacitors, the ideal carbon material has a high surface area for storing electrical charges, high conductivity for transporting electrons and a suitable pore architecture that allows for the rapid movement of ions from the electrolyte solution to the carbon surface."

In the experiment, a current was applied to supercapacitors equipped with designer-carbon electrodes. Electrical conductivity improved threefold compared to supercapacitor electrodes made of conventional activated carbon.

"We also found that our designer carbon improved the rate of power delivery and the stability of the electrodes," explained Bao.

Tests were also conducted on lithium-sulfur batteries, a promising technology with a serious flaw: When lithium and sulfur react, they produce molecules of lithium polysulfide, which can leak from the electrode into the electrolyte and cause the battery to fail.

The Stanford team discovered that electrodes made with designer carbon can trap those pesky polysulfides and improve the battery's performance.

"We can easily design electrodes with very small pores that allow lithium ions to diffuse through the carbon but prevent the polysulfides from leaching out," Bao said.

"Our designer carbon is simple to make, relatively cheap and meets all of the critical requirements for high-performance electrodes."


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