by Briton Lee
Scientists have been searching for a way to make batteries hold longer charges, on both a commercial and industrial scale. South Korean researchers have made headway in this development, creating a form of 3D graphene “pom-poms” that have a much more efficient energy capacitance than normal graphene.
Graphene can be used as a supercapacitor due to its stability, high conductivity, and large surface area. 3D graphene capacitors are even better because their greater surface area enhances their capacitance. Graphene capacitors are relatively simple, with a carbon-only structure, and versatile enough to incorporate into batteries as electrodes. However, current ways of manufacturing graphene electrodes yield thin films that may stack and aggregate, which decreases surface area and makes the resulting material more difficult to process. These issues have led to the development of graphene foams and aerogels, but these can’t be used as electrodes because they’re too irregular and not as carbon-dense. Thus, scientists are currently looking to develop ways to create 3D carbon nanostructures for potential use as battery electrodes.
The South Korean material scientists created these “pom-pom” like structures by passing a graphene oxide suspension through an ultrasonic nozzle. This process generates graphene oxide droplets that are sprayed into a hot organic solvent – a process very similar to deep-frying. The 160°C solvent has a reducing agent that reacts with graphene oxide to form graphene sheets that clump together, creating the 3D structure. Water in the graphene oxide droplets evaporates quickly and is not miscible with the organic solvent, and this flash vaporization is likely responsible for the filamentous, outwardly-radiating structure. Through this process, 5 μm microspheres are precipitated out of solution.
While this is not the first time 3D graphene nanostructures have been developed, this process is much simpler and can feasibly be scaled up to industrial applications. Currently, researchers are working to create silicon-loaded graphene particles because silicon is promising for use as electrodes in lithium-ion batteries but have difficulty maintaining structural integrity due to distortion during charge/discharge cycles. This issue is overcome by encapsulating the silicon in a carbon scaffold, which can be done by spraying the adding silicon to the graphene oxide before spraying it into the hot organic solvent.
Though the carbon “pom-poms” are simple, versatile, and scalable, this development is only one piece of the puzzle, and it may be a while before we see its implementation in consumer electronics, such as smartphones, or industrial applications.
Fingas, Jon. 2015. “”. (http://www.engadget.com/2015/01/18/deep-fried-graphene/)
Patel, Prachi. 2015. “Deep-Frying Graphene Spheres for Energy Storage”. (http://cen.acs.org/articles/93/web/2015/01/Deep-Frying-Graphene-Spheres-Energy.html)
TAGS: graphene, capacitor, batteries, silicon, carbon nanostructure