Power storage for wearable devices poses problems. The ideal solution would pack a lot of energy in a small package, be flexible, be stretchable, and could discharge or recharge rapidly. Unfortunately, that does not describe your typical battery technology. Supercapacitors (supercaps) offer the fast charge and discharge features, but how can you get the rest of the desired attributes?
In a paper presented at the American Chemical Society, scientists from Nanyang Technological University, Singapore have reported on their research into stretchy supercaps. They start by making tiny ribbons of graphene, the one-atom-thick form of carbon that has remarkable capabilities. Instead of shaving them from carbon by a mechanical process, they developed a way to grow the ribbons using chemistry. The ribbons are excellent conductors and flexible, but they do not stretch.
The next step was to create a plastic substrate with tiny, parallel, pyramid-shaped ridges, much like the ridges on the skin of a finger. The team also created “kirigami” structures — similar to paper origami techniques — to allow the electrodes to stretch and flex without breaking. The experimental prototype is able to store enough electricity to power the LCD display from a desktop calculator for about one minute.
Even in its current configuration, the supercap could store enough power to be useful for wearable sensors and other devices, especially when coupled with an energy-harvesting system. The researchers are working to increase the electrode surface area so that the device can store even more power.