Can ultracapacitors replace batteries

Powerful and durable Energy storage: super capacitors instead of batteries

Have you come across a super capacitor today? Guaranteed. Because we are in constant contact with them. They are in our smartphones, laptops, but also in vehicles. Supercapacitors store energy and have an advantage over batteries and rechargeable batteries: They can store the energy more quickly and also release it more quickly.

"A super capacitor is good when it comes to storing a lot of energy in and out," explains Dr. Andreas Battenberg, press officer at the Technical University of Munich.

Problem child energy density

In contrast to conventional lithium-ion batteries, however, they weaken in terms of energy density. Supercapacitors would have to be much larger in order to be able to store the same amount of energy as batteries. Lithium ion batteries achieve an energy density of up to 265 watt hours per kilogram, previous supercapacitors only about a tenth of that.

The new supercapacitor from the Technical University of Munich achieves 73 watt hours per kilogram, almost three times as much as conventional supercapacitors. But still significantly less than the common lithium-ion batteries that are built into smartphones, for example.

But not only the energy density is much higher than before. The super capacitor also lasts longer. After 10,000 charge and discharge cycles, it still has 88 percent of its original capacity. For comparison: smartphone batteries only have around 80 percent of their initial capacity after 500 charging cycles.

A capacitor is an energy store. It consists of two electrodes (made of conductive material) and the dielectric (insulation material between the electrodes). If a current source with a direct voltage is applied, an electric field is created between the electrodes. Electric charges and thus their energy are stored in the field. The capacitor is charged.

The stored charge per voltage is called capacity. The capacitance depends on the area of ​​the electrodes, the material of the dielectric and the distance between the electrodes. The higher the capacity, the more charge and energy the capacitor can store.

If the capacitor is now disconnected from the power source, the voltage remains constant and the energy is retained. Now you can connect an energy consumer to the capacitor and the capacitor will discharge.

Supercapacitors do not have a dielectric like conventional capacitors, but are connected by an electrolyte. They have a greater energy density and capacity. There are different types of supercapacitors, depending on the material and construction of the electrodes.

Graphene hybrid miracle weapon

The new material for the positive electrode - a graphene hybrid material - ensures success. The negative electrode is not new. It is based on titanium and carbon. "It would be great if it were just graphs," says Dr. Andreas Battenberg, because graphene consists only of carbon. But there is a problem, explains Battenberg: "Graphene layers tend to stick together and then the electrode does not have enough surface."

A large surface area is important for supercapacitors so that a large amount of charge carriers can accumulate on the electrode. The team from the Technical University of Munich avoids this problem with a so-called nanostructured organometallic framework. This means that they chemically combine graphene with an organometallic compound based on zirconium. This combination has large internal surface areas and is very effective as a positive electrode in the supercapacitor.

Environmentally friendly?

The new supercapacitor scores above all with better performance, but it is also sustainable - especially in comparison to other battery and accumulator materials. Batteries are generally very inefficient. The manufacture of a battery consumes more energy than the battery later supplies. This also has an impact on the wallet. Batteries are more expensive than electricity from the socket. Batteries are also not always sustainable and environmentally friendly. Nickel-cadmium batteries were still available until 2016. Because cadmium is a poisonous heavy metal, they are now banned.

But it will take another five to ten years before the new supercapacitor from the Technical University of Munich can be used commercially, predicts Dr. Andreas Battenberg. There is still a lack of production processes and long-term tests.