The further improvement of energy density, cycleability and safety of batteries requires a detailed understanding of the fundamental physical, chemical, and fluid mechanical processes occurring within the cell. To this goal, multi-scale and multi-physics models as well as modern numerical simulation methods are developed and applied. We have two areas of activities (Fig. 1), commercial lithium-ion batteries and highly energetic next-generation lithium batteries. The work is located at the German Aerospace Center (DLR) in Stuttgart and at the Helmholtz-Institute Ulm for Electrochemical Energy Storage (HIU).
Fig. 1: Overview of the battery activities within the modeling and simulation group
Today's commercially available lithium-ion systems require improvement in the areas of cycleability (lifetime) and safety (so-called thermal runaway). Ageing and safety event are caused by chemical side reactions taking place within the electrodes of the cell. Goal of the activities is the understanding of these side reactions as well as their interaction with regular cell operation (Fig. 2). As a result, model-based operation strategies are developed.
Fig. 2: Computer tomography of a lithium-ion battery and simulated discharge curves
Highly energetic lithium batteries of the so-called next generation are lithium-sulphur and lithium-air cells. These batteries allow the storage of considerably more energy (factor 2-5) than state-of-the-art lithium-ion systems. Goal of the activities is to contribute to the solution of some of the inherent problems of these systems, which are connected to complex chemical reactions (Fig. 3), transport processes, as well as microstructural features.
Fig. 3: Coupling of electrochemistry and transport in a lithium-sulphur cell