How are aircraft doors operated

30.01.2017 17:09

Researchers are significantly improving the fundamentals for simulating energy storage systems

Thorsten Mohr Press office of the Saarland University
University of Saarland

Camera flashes, aircraft doors and braking energy recovery all work on the basis of ultra-fast storage technology based on ion storage in a porous carbon electrode - so-called supercapacitors. The efficiency of such energy stores could be significantly improved if the carbon could be designed in such a way that there is space for as many ions as possible. Saarland and Austrian researchers have now developed a process that can simulate the properties of a carbon electrode much more precisely on the computer than previous - idealized - computer simulations. The study was published today in the journal Nature Energy.

It is the Gordian knot that still cuts off the sustainable use of renewable energies: energy storage. More than enough energy can actually be obtained from the sun, wind and water. But when the sun is not shining and the wind is not blowing, there is often not enough reserve to cover the energy demand. The reason also lies in the storage media. Common batteries, based on lithium-ion technology, for example, take too long to charge and discharge in order to be able to absorb and release excess energy quickly.

A sword that could break this Gordian knot are double-layer capacitors, also known as supercapacitors or supercaps for short. The carbon electrodes used in such systems can store and release electricity much faster than conventional batteries. But they have one major disadvantage: if you look at two energy storage devices of the same size, a conventional battery and a supercap, the latter can hardly store ten percent of the energy that can be stored in the battery.

The problem lies in the nature of the carbon that makes up the supercap: the electrical energy is stored in the form of attached ions, i.e. positively and negatively charged particles, in the pores that run through the carbon like a complicated cave system in a mountain range. There are huge bulges and tiny caves, narrow canals and wide boulevards, all in a random arrangement that differs from piece to piece. How and where exactly the charged ions are distributed in this tangle of channels, pores and holes, researchers have so far been unable to predict adequately. The question of their distribution is elementary for the efficiency of energy storage. It is based on a simple physical principle: the better the available surface can be used, the more ions fit into a carbon electrode or, to put it colloquially, the more electricity can be stored.

Due to the complexity of porous carbon materials, computer simulations have so far only been based on models in which the pores are idealized, i.e. distributed following a simple symmetry, for example. This idealized representation has little in common with the construction of a real piece of carbon. "This has meant that there has so far been hardly any work based on real materials," explains Volker Presser, professor for energy materials at Saarland University and head of a program area at INM - Leibniz Institute for New Materials in Saarbrücken.

The development of new, more efficient supercap energy storage systems is therefore tedious and time-consuming and involves extensive experiments. But the team of materials scientists, chemists and physicists from Saar University, the Montan University Leoben, University of Vienna and Graz University of Technology has now found a way to simplify the simulation considerably and developed a powerful method to simulate new materials on the computer, their Structure that corresponds to real carbons.

In doing so, the researchers were able to gain a fundamental insight: the ions always push themselves into the pores into which they barely fit. With a wink, Volker Presser describes this property as "nano-cuddling". In addition, the ions strip off parts of their so-called solvation shell. These are, for example, water molecules that are firmly attached to the ions floating in an aqueous solution. “With these findings, we will be able to create much more precise designs for storage materials and for materials for water treatment in the future,” says Nicolas Jäckel, who played a key role in the study as part of his doctoral thesis. In the future, thanks to Saarland-Austrian cooperation, it could be possible to design new, much more efficient materials without having to carry out complex laboratory tests. “That simplifies our research immensely and makes it possible to examine optimized structures that we cannot even manufacture in the laboratory,” adds Volker Presser.

In order to achieve their groundbreaking insights, Nicolas Jäckel, Volker Presser and their colleagues from Austria first had to put in a lot of effort themselves. They x-rayed three carbon electrodes and, on the basis of the signal that came out, calculated detailed computer replicas, each with an edge length of 16 nanometers and the exact position of the pores. Simulating a single sample kept the Austrian supercomputers busy for several months. “Even during the lecture-free period, the computers in Leoben were running hot,” recalls Nicolas Jäckel. The edge length of 16 millionths of a meter is sufficient to reproduce a characteristic electrode with all its properties. This also made it possible for the researchers to predict the exact distribution and behavior of the ions, which, with a size of just over a billionth of a meter, were again 1000 times below the dimensions of the carbon cube.

It will be many years before a usable technology can actually develop from their findings. Because the work of the researchers from Saar-Uni and INM is basic research that aims to discover and understand scientific processes and rules in the first place. However, this understanding is the basis of all progress in industrial applications.

The study Quantification of ion confinement and desolvation in nanoporous carbon supercapacitors with modeling and in-situ X-ray scattering was published on January 30, 2017 in the journal Nature Energy. DOI: 10.1038 / nenergy.2016.215. Link to the online version:

Additional Information:
Prof. Dr. Volker Presser
Tel .: (0681) 9300177
Email: [email protected]

Nicolas Jackel
Tel .: (0 681) 9300312
Email: [email protected]

Prof. Dr. Oscar Paris
Tel .: +43 3842 402 4600
Institute for Physics
Montanuniversitaet Leoben
E-mail: [email protected]

Additional Information:

Nicolas Jackel

Features of this press release:
Chemistry, physics / astronomy, materials science
Research results, collaborations