Supercapacitor material with energy density 2.7 times higher than conventional materials.


The GMS blade and its supercapacitor were connected to two LEDs. Credit: Hirotomo Nishihara

A research team led by Tohoku University in Japan has developed new materials for supercapacitors with higher voltage and better stability than other materials. His research was recently published in the magazine. Energy and environmental science.

Supercapacitors are rechargeable energy storage devices with a wide range of applications, from machinery to smart meters. They offer many advantages over batteries, including a faster charge and a longer lifespan, but they are not as good at storing much energy.

Scientists have long searched for high-performance materials for supercapacitors that can meet the requirements for energy-intensive applications, such as automobiles. "It is very difficult to find materials that can operate at high voltage and remain stable in difficult conditions," says Hirotomo Nishihara, materials scientist at Tohoku University and co-author of the article.

Nishihara and his colleagues collaborated with the TOC Capacitor Co. supercapacitor production company to develop a new material that exhibits extraordinarily high stability under high voltage and high temperature conditions.

The activated carbons are used for the electrodes in the capacitors, but are limited by the low voltage in the individual cells, the building blocks that form the capacitors. This means that a large number of cells must be stacked to achieve the required voltage. Crucially, the new material has a higher single cell voltage, which reduces the number of stacking and allows the devices to be more compact.

The new material is a sheet made of a continuous three-dimensional graphene mesosponge frame, a carbon-based material containing nanoscale pores. A key feature of the materials is that it is transparent: it contains a very small amount of carbon edges, the sites where the corrosion reactions originate, and this makes it extremely stable.

The researchers investigated the physical properties of their new material through electron microscopy and a series of physical tests, including X-ray diffraction and vibrational spectroscopy techniques. They also tested commercial materials based on graphene, including single-walled carbon nanotubes, reduced graphene oxides and 3D graphene, using activated carbons as a benchmark for comparison.

They showed that the material had excellent stability at high temperatures of 60 ° C and high voltage of 3.5 volts in a conventional organic electrolyte. Significantly, it showed ultra-high stability at 25 ° C and 4.4 volts, 2.7 times more than conventional 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 paves the way for the development of high-voltage supercapacitors and very durable that could be used for many applications, including motor vehicles.

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More information:
Keita Nomura and others. 4.4 V supercapacitors based on a superestable mesoporous carbon sheet made of graphene walls without borders, Energy and environmental sciences (2019). DOI: 10.1039 / C8EE03184C

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