Solar cells that produce electricity 24/7, not just when the sun is shining. Mobile phones with built-in power cells that recharge in seconds and work for weeks between charges.
Those are just some of the possibilities raised by a novel super-capacitor design invented by material scientists at Vanderbilt University that is described in a paper published in the Oct. 22 issue of the journal Scientific Reports.
It is the first super-capacitor that is made out of silicon so it can be built into a silicon chip along with the microelectronic circuitry that it powers.
The currently use super-capacitors built from carbon are already applied as energy storage systems in electric vehicles and in wind turbines to ensure blades turn smoothly, but their bulk and cost have limited them to these niche applications.
The first-ever silicon supercap stores energy by gathering ions on the surface of the porous material. Different from batteries, which work on chemical reactions, the silicon supercaps can be charged in minutes and last way longer. Silicon had been considered unsuitable for supercaps because of the way it reacts with the electrolytes that make the energy-storing ions.
The team, headed by engineering professor Cary Pint, used porous silicon in their research because the method of etching billions of tiny pits on to the material is well established. All those nano-scale features give the material a huge surface area relative to its size and help it store a significant electrical charge.
“If you ask experts about making a super-capacitor out of silicon, they will tell you it is a crazy idea,” said Assistant Professor Cary Pint, who headed the development team at Vanderbilt. “But we’ve found an easy way to do it.”
To begin, Pint and his colleagues coated porous silicon in carbon and heated it to about 800°C. The process formed a layer of graphene only a few nanometres thick that insulated the silicon from the electrolyte while retaining its highly porous structure.
The researchers found that super-capacitor plates were considerably more energy dense (up to 40x) than those made out of pure silicon, and achieved a performance that significantly improved on current commercial super-capacitors.
The team is now looking into ways to integrate the coated silicon into existing manufacturing processes so the super-capacitors can be more widely used in gadgets such as phones.
One of the possible variant of using such super-capacitor could be as a storage system for solar power plants. Super-capacitors on the rear of solar cells could store power as it is collected and then dispense it during the night when demand grows, reports BBC News.
Unfortunately, super-capacitors 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.
“All the things that define us in a modern environment require electricity,” said Pint. “The more that we can integrate power storage into existing materials and devices, the more compact and efficient they will become.”