A team of scientists has developed a highly efficient supercapacitor. The heart of the energy storage device is a new, powerful, and sustainable hybrid graphene material with performance comparable to those currently in use.
Typically, batteries and accumulators are used to store energy, which provides energy to electronic devices. However, nowadays, supercapacitors are increasingly being installed in laptops, cameras, mobile phones, or vehicles.
Unlike batteries, they can quickly store large amounts of energy and discharge it just as quickly. If, for example, a train slows down when entering a station, supercapacitors store energy and provide it again when the train quickly needs a lot of energy to start.
However, today one of the problems with supercapacitors has been their lack of energy density. While lithium batteries achieve energy densities of up to 265 kWh per kilogram, supercapacitors still only deliver a tenth of that level.
A team of scientists working with a professor of inorganic and organometallic chemistry at the Technical University of Munich (TUM) \ developed a new, powerful and stable hybrid graphene material for supercapacitors. It serves as a positive electrode in an energy storage device. The researchers are combining it with a proven titanium-carbon negative electrode.
The new energy storage device not only provides an energy density of up to 73 kWh / kg, which is roughly equivalent to the energy density of a nickel-metal hydride battery. That being said, the new device performs much better than most other supercapacitors, at a power density of 16 kWh / kg. The secret of the new supercapacitor lies in combining different materials, which is why chemists call the supercapacitor “asymmetric.”
To create a new device, the researchers relied on a new strategy to overcome standard materials’ performance limits and use hybrid materials.
The abstract idea of combining basic materials was carried over to supercapacitors. They used a new positive storage electrode with chemically modified graphene as a base and combined it with a nanostructured organometallic framework, the so-called MOF.
The decisive factors for the characteristics of graphene hybrids are, on the one hand, a large specific surface area and controlled pore sizes, and on the other hand, high electrical conductivity.
For good supercapacitors, a large surface area is important. This allows a correspondingly large number of charge carriers to be collected in the material – this is the basic principle of storing electrical energy. Through clever material design, the researchers were able to bond graphenic acid to MOF. The resulting hybrid MOFs have an extensive internal surface area of up to 900 square meters per gram and are very effective as positive electrodes in a supercapacitor.
A stable connection between nanostructured components has tremendous advantages in long-term stability: the more stable the connections, the more charge, and discharge cycles are possible without significantly degrading performance.
For comparison: a classic lithium battery has a service life of about 5000 cycles. The new cell, developed by the TUM researchers, retains almost 90% capacity even after 10,000 cycles.