New material developed for high-voltage supercapacitors

Researchers at Japan’s Tohoku University have developed a stable and high-voltage material for supercapacitors, with the results of their work published in the journal Energy and Environmental Science.

Supercapacitors are rechargeable energy storage devices with a broad range of applications, from machinery to smart meters. They offer many advantages over batteries, including faster charging and longer lifespans, but they are not so good at storing lots of energy. Scientists have thus been looking for high-performance materials for supercapacitors that can meet the requirements for energy-intensive applications such as cars.

“It is very challenging to find materials which can both operate at high voltage and remain stable under harsh conditions,” said Hirotomo Nishihara, a materials scientist at Tohoku University. With this in mind, he and his colleagues collaborated with supercapacitor production company TOC Capacitor Co to develop a new material that exhibits extraordinarily high stability under conditions of high voltage and high temperature.

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

Conventionally, activated carbons are used for the electrodes in capacitors, but these are limited by low voltage in single cells, the building blocks that make up capacitors. This means that a large number of cells must be stacked together to achieve the required voltage. The new material has higher single-cell voltage, reducing the stacking number and allowing devices to be more compact.

The researchers investigated the physical properties of their material using electron microscopy and a range of physical tests, including X-ray diffraction and vibrational spectroscopy techniques. They also tested commercial graphene-based materials, 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 V in a conventional organic electrolyte. Significantly, it showed ultrahigh stability at 25°C and 4.4 V — 2.7 times higher than conventional activated carbons and other graphene-based materials.

“This is a world record for voltage stability of carbon materials in a symmetric supercapacitor,” Nishihara said.

The new material thus paves the way for development of highly durable, high-voltage supercapacitors that could be used for many applications, including motor vehicles.

Image caption: The graphene mesosponge sheet and its supercapacitor connected to two LEDs. Image © Hirotomo Nishihara.

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