One of the key limitations of wearable electronics is the battery. Currently batteries are thick and rigid - not and not ideal for wearable devices. The development of smart T-shirts and other werable devices may depend on the development of stretchy power sources. A team of researchers at Nanyang Technological University, Singapore have produced a stretchy micro-supercapacitor using ribbons of graphene.
Xiaodong Chen, and his research team have developed stretchable electrodes, and have integrated them into a super-capacitor, which is an energy storage device which can be used to power electronic gadgets. Supercapacitors, developed in the 1950s, have a higher power density and longer life cycle than standard capacitors or batteries. Over the years, supercapacitors have shrunk in size, enabling a generation of two-dimensional micro-supercapacitors that are integrated into cell phones, computers and other devices. However, these supercapacitors have remained rigid, and are thus a poor fit for soft materials that need to have the ability to elongate.
In this study, Xiaodong Chen, and his team have developed a micro-supercapacitor from graphene. This carbon sheet is renowned for its thinness, strength and conductivity. Graphene can be flexible and foldable, however it cannot be stretched. The team took a cue from skin. Skin has a wave-like microstructure and they tried to figure out how they could make graphene more like a wave.
The first step was to make graphene micro-ribbons. Most graphene is produced with physical methods, like shaving the tip of a pencil. However, it is very difficult to control its structure and thickness using a physical method. Thickness can really affect the conductivity of the electrodes and how much energy the supercapacitor overall can hold. So they used chemistry to build his material.
The next step was to create the stretchable polymer chip with a series of pyramidal ridges. The researchers placed the graphene ribbons across the ridges, creating the wave-like structure. The design allowed the material to stretch without the graphene electrodes of the superconductor detaching, cracking or deforming. In addition, the team developed kirigami structures, which are variations of origami folds, to make the supercapacitors 500 percent more flexible without decaying their electrochemical performance. As a final test, they powered an LCD from a calculator with the stretchy graphene-based micro-supercapacitor. Similarly, such stretchy supercapacitors can be used in pressure or chemical sensors.
In future experiments, the researchers hope to increase the electrode's surface area so it can hold even more energy. The current version only stores enough energy to power LCD devices for a minute.
