How do lithium-air batteries work?

Thanks to their high energy content, lithium-air batteries could provide solutions for the storage of regenerative energies or for electromobility. The aim of a research project is therefore to better understand the chemical reactions in lithium-air batteries in order to overcome the obstacles on the way to market launch.

Projektpartner ist die Colorado School of Mines in Golden, Colorado (USA), im Hintergrund mit Blick auf die Rocky Mountains. © D. Grübl

The Colorado School of Mines in Golden, Colorado (USA), shown against the backdrop of the Rocky Mountains, is the project partner. German scientists took several research trips to this site. © D. Grübl

Objective of the funding project

Future technologies such as electromobility and the storage of regenerative energies require high-performance, affordable batteries. Conventional lithium-ion batteries do not yet have the required energy content for high vehicle ranges and storage durations. As a result, research activities across the world are being stepped up to find alternative battery storage.

Vergleich der praktisch nutzbaren und theoretischen Energie von ausgewählten Batteriesystemen im Vergleich zu Benzin.

Comparison of the practically usable and theoretical energy of selected battery systems compared to petrol.
© D. Grübl

Lithium-air batteries are of interest because they have the biggest energy content of all batteries – theoretically almost as high as petrol, and practically 5 times more than lithium-ion batteries (see figure on the left). In addition to lithium, aerial oxygen is used as a chemical source of energy. The weight and cost of the battery is reduced because oxygen from the air is available “for free”. Until this product can be launched on the market, however, many obstacles must still be overcome (useful life, effectiveness, power density), all of which relate to complex chemical reactions within the battery.

As a result, the aim of the project is to shed some light on the chemical reactions which occur in lithium-air batteries. Computer simulation methods are used for this purpose. The project manager is Prof. Bessler from the University of Offenburg; the partner is Prof. Kee from the Colorado School of Mines.

Use of the results

Funding announcement
Scientific and technological collaboration (STC) with the USA

Partner region/country
USA

Term
01.01.2015 – 30.06.2016

Partner institutions
University of Offenburg, Institute for Energy Systems Technology

Colorado School of Mines, Golden, USA

Potential future application areas for the lithium-air technology include both stationary energy storage (e.g. for regenerative energies or network stabilisation) and electromobility. The working group surrounding Prof. Bessler has already been active in the area of lithium-air batteries since 2011. The BMBF-financed association research project “Strom aus Luft und Lithium [Electricity from Air and Lithium]” (2011–2014) researched electrochemical battery models for the positive oxygen electrode. Based on this, the present project focused on electrochemical reaction mechanism. Since January 2016, the activities of the University of Offenburg have continued in the “Battery 2020” project “Lithium Batteries with Air/Oxygen Electrode” (2016–2018). As part of this project, the project partner Varta among others is to produce first lithium-air battery demonstrators. The University of Offenburg is developing the cell design for this.

Added value of international cooperation

Prof. Kee (USA) is a world-leading expert in the field of simulating complex chemical systems. He developed the relevant computer programs as early as the 1980s, at the time for combustion research. Today, he is one of the key developers and users of the open-source software CANTERA (together with the renowned Massachussetts Institute of Technology, MIT, and the Sandia National Laboratories). This software is ideally suited to simulating lithium-air batteries. This international exchange allowed significant expertise to be established regarding the CANTERA software, which is now being developed further at the University of Offenburg. In addition to the scientific project objective, i.e. understanding lithium-air batteries, this project is also contributing significant methodical added value: It is enabling us to continue to use the high-performance software independently and to also apply it to other projects.

Outstanding results and successes of the measure

Several trips have already taken place in the context of this project, including a three-month trip of the German project doctoral student to Colorado, a two-week trip of Prof. Bessler and trips of Prof. Kee to Germany. A one-day workshop on the topic of “CANTERA and lithium-air batteries”, which took place in Colorado in the autumn of 2015 and was attended by eight participants from the Colorado School of Mines, the University of Offenburg, Sandia National Laboratories and two US industrial companies, was a highlight of the project.

Forschungsergebnisse der Hochschule Offenburg: Chemische Reaktionen in der positiven Elektrode der Lithium-Luft-Batterie.

Research results of the University of Offenburg: Chemical reactions in the positive electrode of the lithium-air battery.
© D. Grübl

The project has already resulted in several scientific publications, while others are being prepared. For instance, we were able to show that the typical asymmetry of the discharge/charge behaviour of lithium-air batteries is caused by an irreversible disproportioning reaction of lithium oxides (see figure on the left) – a result which had previously only been suspected, but that we could now also demonstrate quantitatively.

 

 

DLR Project Management Agency| European and international collaboration
Barbara Hellebrandt
Tel.: +49 228 3821-1433

University of Offenburg
Prof. Dr. Wolfgang G. Bessler
Tel.: + 49 781 2504653