A team of researchers at the Vanderbilt University in Nashville, Tennessee has designed a supercapacitor made primarily of silicon that has shown much improved power density over its commercially available alternatives. The advance could allow for interesting integration of battery technology in everyday electronics, from solar cells to smartphones.
Supercapacitors store electricity by gathering ions on the surface of two plates soaked in an electrolyte solution. Because the number of ions that can be stored depends on the surface area of the plates, these are usually coated with materials, such as activated carbon, that are highly porous at the nanometric scale.
While supercapacitors can't quite match the energy storage capabilities of lithium-ion batteries, they can absorb and release charge much more rapidly and have a significantly longer lifespan. Today, supercapacitors are used in applications ranging from stabilizing the power supply in portable electronics to supporting the KERS system in Formula 1 cars.
Scientists have tried to improve on the amount of energy that supercapacitors can store by depositing even more porous materials materials such as carbon nanotubes on their plates, but these attempts have only produced marginal improvements that have been hard to replicate consistently.
Assistant professor Cary Pint and his colleagues at Vanderbilt chose to attack the problem from a new and unusual angle by attempting to build a capacitor out of porous silicon.
At first this seemed like an unlikely path, since silicon is known to react strongly with the electrolyte, disrupting the working mechanism of supercapacitors. On the other hand, the electronics industry is very familiar with ways to manipulate silicon precisely and make it highly porous.
Pint and his colleagues coated the porous silicon in carbon and heated the ensemble to about 800° C (1500° F). The process formed a layer of graphene only a few nanometers thick that insulated the silicon from the electrolyte while retaining its highly porous structure.
The researchers found that supercapacitor plates manufactured in this fashion were up to 40 times more energy-dense than those made out of the "naked" silicon, and achieved a performance that significantly improved on current commercial supercapacitors.
Silicon is the second most abundant element on Earth, and the ability to manufacture supercapacitors from it along with the integrated circuits that it powers could have very interesting repercussions all across the electronics industry.
According to the researchers, it should be possible to build cheap silicon supercapacitors out of the excess silicon contained inside many electronic devices. One such example are solar cells: supercapacitors built out of the silicon in the back side of solar cells could store energy during the day and gradually release it into the energy grid during the hours of peak consumption.
The advance is described in an open-access paper in the journal Nature Scientific Reports.
Source: Vanderbilt University
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