A group of researchers under Tohoku University in Japan has created new materials for supercapacitors, which have better stability and higher voltage when compared to other materials. Their work was recently reported in the journal Energy and Environmental Science.
Supercapacitors are rechargeable energy storage devices and serve a wide range of applications, from machinery to smart meters. They provide several benefits over batteries, such as longer lifespans and quicker charging; however, they are not too good at storing a large amount of energy.
For a long time, researchers have been searching for high-performance materials for supercapacitors that can fulfill the demands of energy-intensive applications, for example, cars.
It is very challenging to find materials which can both operate at high-voltage and remain stable under harsh conditions.
Hirotomo Nishihara, Materials Scientist, Tohoku University.
Nishihara, who is also the co-author of the paper, and his team partnered with the supercapacitor production company TOC Capacitor Co. to create a new material that shows extremely high stability under conditions of high temperature and high voltage.
Traditionally, activated carbons are employed as the electrodes in capacitors; however, these are restricted by low voltage in single cells, which are the building blocks that constitute capacitors. Therefore, in order to achieve the necessary voltage, many cells must be stacked together. Remarkably, the new material has higher single-cell voltage, thereby minimizing the stacking number and enabling devices to be smaller.
The new material is a sheet composed of a continuous three-dimensional framework of graphene mesosponge, a carbon-based material which has nanoscale pores. Being seamless is the significant feature of the materials, which means that it consists of a very small amount of carbon edges, the places where corrosion reactions begin, and this makes it very stable.
The scientists examined the physical properties of their new material with the help of electron microscopy and a series of physical tests, such as vibrational spectroscopy and X-ray diffraction techniques. In addition, they tested commercial graphene-based materials, including reduced graphene oxides, 3D graphene, and single-walled carbon nanotubes using activated carbons as a standard for comparison.
They demonstrated that the material had exceptional stability at a high voltage of 3.5 V and high temperatures of 60 °C in a traditional organic electrolyte. Notably, it exhibited ultra-high stability at 25 °C and 4.4 V, which is 2.7 times greater when compared to traditional activated carbons and other graphene-based materials. “This is a world record for voltage stability of carbon materials in a symmetric supercapacitor,” says Nishihara.
The new material opens the door for development of highly durable, high-voltage supercapacitors that could be used for several applications such as motor vehicles.