The new graphene structure helps make batteries last longer

The group of materials scientists in Korea has successfully fabricated micro-sized graphene particles shaped like a paper sphere that animators often use by spraying graphene oxide droplets into a hot solvent. . According to them, the technique could provide a simpler and more flexible method to create electrode materials for batteries and supercapacitors, thereby improving the energy problem for many types of devices. suffered.

>>>Manufacturing high quality graphene thanks to the ultrasonic spray system

The reason scientists want to use graphene in capacitors is because it is a magic material with excellent electrical conductivity, high stability and a large surface area. However, standard graphene production methods often produce overlapping, thin sheets of graphene that reduce surface area and make materials more difficult to handle.

To exploit the electrical and mechanical properties of materials while maintaining a large surface area, researchers around the world have tried to create a 3-dimensional graphene structure. The first is the foam-shaped graphene or airgel structures (a super-light synthetic material, gel-derived foam in which the gel's liquid composition is replaced by a gas). However, these structures are not suitable for electrodes because they are uneven or too large, and have low carbon material density, Sang-Hoon Park material scientist at Yonsei University, Seoul, Korea. said. The second method is to create a nanoscale graphene structure , microphones with 3D molds and apply techniques such as chemical deposition evaporation or freeze drying.

Park and his colleagues decided to choose the second method but customize it. Accordingly, instead of creating hollow graphene spheres or looking like a piece of paper, the Korean team mimicked the shape of a paper sphere often used by animators. In it, each paper is a nano graphene sheet radiating from the mind. This arrangement increases the surface area of ​​graphene exposure and creates nano channels that enhance the ability to convert electrical charge, Park said.

To do this, the team made small suspicious graphene oxide containing water through an ultrasonic speed nebulizer and used sound waves to break down the graphene suspension into micro droplets. Then, the graphene oxide droplets were sprayed onto a mixture of 160 degrees C and organic ascorbic acid acting as reducing agents.

In the hot mix, graphene oxide transforms into graphene sheets and binds together. Water in each drop evaporates and escapes the surface of each drop."We believe that rapid evaporation of water has caused nano graphene sheets to radiate," Park said. Finally, micro graphene spheres with a diameter of 5 μm precipitate out of the solution and the team just filters to take them out.

In addition, the team also fabricated silicon-padded graphene particles with an initial component of suspended silicon nanoparticles and graphene oxide. Silicon is a very promising material to use as anode in Li-ion batteries due to its high charge storage capacity but the anodes made from it are often inflated and distorted during charging / discharging. Therefore, encapsulating silicon in a carbon structure can solve this problem.

To test, the team made 1cm-sized electrodes, one of which is the graphene spheres that have the same fringed pattern and one that contains untreated graphene sheets. Both are dipped in a sulfuric acid electrolyte. The measured results show that the electrode contains a bridge-shaped graphene with a capacitance of 151 farad / gram while the electrode containing sheet graphene has a capacitance of 118 farad / gram. Thus, the 3D structure of the particles helped improve performance, greater capacitance showed longer capacity of the material.

The capacitance of the electrode with the above spherical graphene is comparable to that made with other 3D graphene materials. However, the fabrication technique of the Korean research group has opened up a new, more efficient method of production. Compared to conventional 3D graphene manufacturing methods, this method is "simple, direct, and more scalable for industrial applications , " the research team emphasized.