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Researchers create supercapacitors out of silicon

Posted: 24 Oct 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Vanderbilt University? supercapacitor? solar cell? silicon chip?

A team of material scientists from Vanderbilt University has developed a supercapacitor design that allows the storage of energy in chips. According to them, the results of the study could pave the way for solar cells that produce electricity 24/7 even when the sun isn't shining and mobile phones with built-in power cells that recharge in seconds and work for weeks between charges.

It is the first supercapacitor that is made out of silicon so it can be built into a silicon chip along with the microelectronic circuitry that it powers. In fact, it should be possible to construct these power cells out of the excess silicon that exists in the current generation of solar cells, sensors, mobile phones and a variety of other electromechanical devices, providing a considerable cost savings.

"If you ask experts about making a supercapacitor out of silicon, they will tell you it is a crazy idea," said Cary Pint, the assistant professor of mechanical engineering who headed the development. "But we've found an easy way to do it."

Instead of storing energy in chemical reactions the way batteries do, "supercaps" store electricity by assembling ions on the surface of a porous material. As a result, they tend to charge and discharge in minutes, instead of hours, and operate for a few million cycles, instead of a few thousand cycles like batteries.

Silicon chip with porous surface next to the special furnace where it was coated with graphene to create a supercapacitor electrode.

Figure 1: Silicon chip with porous surface next to the special furnace where it was coated with graphene to create a supercapacitor electrode. Credit: Joe Howell / Vanderbilt.

These properties have allowed commercial supercapacitors, which are made out of activated carbon, to capture a few niche markets, such as storing energy captured by regenerative braking systems on buses and electric vehicles and to provide the bursts of power required to adjust of the blades of giant wind turbines to changing wind conditions. Supercapacitors still lag behind the electrical energy storage capability of lithium-ion batteries, so they are too bulky to power most consumer devices. However, they have been catching up rapidly.

Research to improve the energy density of supercapacitors has focused on carbon-based nanomaterials such as graphene and nanotubes. Because these devices store electrical charge on the surface of their electrodes, the way to increase their energy density is to increase the electrodes' surface area, which means making surfaces filled with nanoscale ridges and pores.

"The big challenge for this approach is assembling the materials," said Pint. "Constructing high-performance, functional devices out of nanoscale building blocks with any level of control has proven to be quite challenging, and when it is achieved it is difficult to repeat."


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