Ammonia is nothing like Lithiumbatteries – or is it?

All researchers write publications, but the vast majority doesn’t get the front page on two renowned international scientific journals on two different subjects within a timespan of only two weeks.

Researchers from the Section of Atomic Scale Modelling and Materials (ASC), Department of Energy Conversion and Storage at Technical University of Denmark (DTU), have done the deed.

The two articles published in "The Journal of Chemical Physics", vol. 138, p. 164701, 28th of April 2013, and "The Journal of Physical Chemistry C", vol. 117, p. 9084, 9th of May 2013, deals with two different and yet very similar scientific approaches on how to improve lithium batteries and how to store ammonia better for use in energy storage or reduction of automotive NO_x emissions.

Tiny atomic bottlenecks
"Lithium batteries and ammonia storage are two very different processes - with very similar problems”, says Professor and Head of ASC, Tejs Vegge.
"No matter how different the chains of reactions are and no matter how complex their functionality, almost everything comes down to a single process that limits everything at the atomic level; a single weak link in the chain that determines the speed of the entire process. In ASC, we are good at identifying and characterizing these processes."

It's no simple task to boil the incredibly complex chains of reactions down to identify the tiny atomic bottlenecks in the fundamental processes, but the researchers at ASC used the supercomputers at CAMD at DTU Physics to identify and simulate the atomic processes at the quantum mechanical level.

"We calculate what happens if we change the process or the properties by moving or exchanging a single atom or molecule. It is comparable to doing a huge complex jigsaw puzzle using millions of calculations in the process, but it enables us to predict new combinations of materials, making materials go from nearly useless in one condition to be 1000 times more effective in another combination," says Tejs Vegge.

How a solid electrolyte is better than a liquid
In the article "Li-Ion Conduction in the LiBH4: Lil System from Density Functional Theory Calculations and Quasi-Elastic Neutron Scattering" by Jon Steinar Gardarsson Myrdal, et al., in The Journal of Physical Chemistry, the ASC researchers describes how to improve the efficiency and lifetime of lithium batteries by replacing the current liquid electrolytes with a solid and crystalline electrolyte.

"Lithium batteries currently use liquid electrolytes as solid electrolytes presently don’t work at low temperatures. But liquid electrolytes have problems, ranging from evaporation due to punctuation to the risk of short-circuiting the battery due to dendritic growth", says Tejs Vegge.

After numerous calculations and experiments the ASC-researchers have demonstrated that use of iodide in solid electrolytes makes applications at room temperature possible, which in theory enables the use of solid electrolytes in lithium batteries.

The discovery has been underway for a long time, with the May issue of "The Journal of Physical Chemistry" being the third article on the subject. First Tejs Vegge and his researchers cooperated with researchers from the Tohoku University of Japan to make theories on and later do calculations on what would happen, if they added iodide to the electrolyte, and then they described the optimal quantity of iodide to be used. Now they describe the atomic transport mechanism and why iodide works so well, using quantum mechanical simulations combined with neutron scattering.

"We can’t describe the entire process quantum mechanically, as these are far too complex, but we can make approximations and advanced calculational predictions showing why it works - and why it actually works better than expected. Now we look at how to improve stability, as this is a very important aspect before the material can be used in real batteries," says Tejs Vegge.

Simulations showed a brand new condition
The article "Surface adsorption in strontium chloride ammines" by Andreas Ammitzbøll, et al. in The Journal of Chemical Physics, is part of a National Danish Advanced Technology Foundation project together with Amminex Emissions Technologies A/S. Here, the researchers used the same calculational methods to describe materials for storage of ammonia for automotive NO_x or as energy storage media for, e.g., fuel cells.
"The Lithium-ion battery is an electrochemical process, while ammonia storage is a purely chemical process, so the patterns of reaction are substantially very different. But we use the same complex computer simulations to predict the mechanisms of both processes", says the Head of Section Tejs Vegge.

"In the ammonia project, we looked at why the ab- and desorption mechanisms behave as they do, and we discovered a new and hitherto unknown condition of ammonia storage materials through combined calculational and experimental work, that nobody has taken into account before. We identified this condition in both the reaction pattern and also where it is located physically in the surface-structure, which is important for understanding and improving the entire ab- and desorption process".