Supercapacitors offer a lot of advantages over batteries when it comes to energy storage. They can store a lot more of it, they can take on or transmit energy much more quickly and they typically last way longer. But incorporating supercapacitors into things like wearables has been difficult because making them flexible and stretchable comes with some costs. Usually, flexible supercapacitors are made with complex and pricey methods or are limited to just a few types of materials. They can also end up being less stable and, thus, short-lived. And a major problem with these sorts of supercapacitors is actually getting the ions inside of them, which are needed for energy transport, to the area where they need to be in order to be useful.
However, researchers at the University of Cambridge and Queen Mary University of London have come up with a new method that solves all of these problems. Their work was just published in ACS Energy Letters.
The research team used polymers that contain the necessary ions and interwove them with the conductive material of the supercapacitor, so that they were always in contact and allowed the ions to constantly be in close proximity to the active areas where energy transfer goes down. "Our supercapacitors can store a lot of charge very quickly, because the thin active material (the conductive polymer) is always in contact with a second polymer which contains ions," lead researcher Stoyan Smoukov told Phys.org. "Just like the red thin regions of a candy cane are always in close proximity to the white parts. But this is on a much smaller scale."
The material can also last a long time and not wear out with repeated charging and discharging. After 3000 cycles, the supercapacitor retained 97.5 percent of its original energy storage ability. And bending the material didn't affect its performance either -- 99 percent of capacitance was retained after 1000 bends and unbends. "This interpenetrating structure enables the material to bend more easily, as well as swell and shrink without cracking, leading to greater longevity. This one method is like killing not just two, but three birds with one stone," said Smoukov.
The researchers say the material shows promise for wearable electronics and other technologies that require flexible energy storage devices.