We've seen flexible supercapacitor designs before, but how about one that's stretchable? A new discovery by researchers at Duke University and Michigan State University could lead to an excellent stretchable power source for wearable electronics.

Supercapacitors, of course, are known for their excellent power density, charging and discharging a lot of energy quickly and having a longer lifespan than chemical batteries, which usually (but not always) have the advantage of storing significantly more energy.

This research team set out trying to develop a truly flexible power source for the wearables they were working on. "Our goal is to develop innovative devices that can survive mechanical deformations like stretching, twisting or bending without losing performance,” said Yunteng Cao, director of the Laboratory for Soft Machines and Electronics at MSU. “But if the power source of a stretchable electronic device isn’t stretchable, then the entire device system will be constrained to be non-stretchable.”

The team struck pay dirt with a design that starts out with a small "carbon nanotube forest" on a silicon wafer – millions of nanotubes about 20-30 micrometers tall in a patch about 15 nanometers in diameter. The ends are covered in a gold nanofilm layer, which drops the resistance of the final device and allows it to transfer charge much faster than previous designs.

This is laid, gold side down, onto an elastic substrate that's stretched out to four times its normal length under tension. Once it's on, the tension is released, and the whole thing crumples up, smashing the nanotube "trees" in the "forest" together in even higher density. Finally, the nanotube "forests" are filled up with a gel electrolyte capable of trapping electrons on the surfaces of the nanotubes. At this point, sandwiching two of these electrodes together and applying a voltage sends all the electrons from one side to the other, where they can be stored and later released as power.