A newly designed supercapacitor could help create solar cells that provide electricity even overnight and cell phones that could recharge itself in seconds.
The supercapacitor is the first of its kind to be made from silicon, which means it can get integrated into a silicon chip along with the "microelectronic circuitry that it powers," a Vanderbilt University news release reported.
The device could be created from excess silicon from current solar cells, cell phones, and other sources.
"If you ask experts about making a supercapacitor out of silicon, they will tell you it is a crazy idea," Cary Pint, the assistant professor of mechanical engineering who headed the development, said. "But we've found an easy way to do it."
Instead of storing energy from chemical reactions in a similar fashion to batteries, "supercaps" store electricity by assembling ions on the surface of a porous material." This process could allow them to recharge within minutes.
These supercaps are currently used in brake systems on buses and electric vehicles and in wind turbines. They are not quite as energy-storing-efficient as lithium-ion batteries, so are not used in most markets.
Past research on improving supercaps has only looked at carbon-based materials such as graphene; since the device stores electricity on the surface of electrodes, increasing the electrode's surface area and providing a porous surface is essential for improving energy density.
The team decided to try porous silicon instead, which allowed them to create a surface perfect for supercapacitor electrodes.
The big problem was silicon has been known to react with certain chemicals in the electrolytes that create energy-storing ions. The team tried coating the surface with carbon to see if it would protect the silicon.
"We had no idea what would happen," Pint said. "Typically, researchers grow graphene from silicon-carbide materials at temperatures in excess of 1400 degrees Celsius. But at lower temperatures - 600 to 700 degrees Celsius - we certainly didn't expect graphene-like material growth."
After removing the experiment from the furnace, the team found the material changed from "orange to purple or black." They found the material looked almost identical to how it did before, but was coated with a thin layer of graphene.
"When the researchers tested the coated material they found that it had chemically stabilized the silicon surface. When they used it to make supercapacitors, they found that the graphene coating improved energy densities by over two orders of magnitude compared to those made from uncoated porous silicon and significantly better than commercial supercapacitors," the news release stated.
The graphene layer was able to provide protection, but the researchers believe there are even more options for protecting the crucial surface.
"The ability to engineer surfaces with atomically thin layers of materials combined with the control achieved in designing porous materials opens opportunities for a number of different applications beyond energy storage," Pint said.
The team will continue working on energy storage that can be created from excess material from solar cells and other devices.
"All the things that define us in a modern environment require electricity," Pint said. "The more that we can integrate power storage into existing materials and devices, the more compact and efficient they will become."
