With the rise of renewable energy sources, energy storage becomes an important issue. In particular for electromobility applications, where mainly Lithium-Ion batteries are used, the demands on charge capacity, power density, life time and safety are high. The development of new materials that fulfill all these demands is expensive and time-consuming. Thus, computer simulations can become a valuable tool to asses the performance of a new types of battery cell. Moreover, an understanding of the microscopic reasons for its behavior can be developed more easily. This allows for a more efficient battery development.

 

discharge curve

Lithium-Ion accumulators consist of two porous electrodes and an electrolyte filled separator that keeps both electrodes apart from each other. During operation (charging or discharging) Lithium ions are exchanged between the electrodes via the electrolyte. In the framework of “Fraunhofer Systemforschung Elektromobilität (FSEM)” the “Complex fluids” group is developing mathematical models based on the relevant physical and electrochemical phenomena to describe the transport and reaction processes inside a battery cell. Two different mesoscopic scales are considerered. In both cases partial differential equations for lithium ion concentration, current density and temperature are formulated. They are solved using a finite-volume method that is implemented in the in-house software “BEST” (Battery and Electrochemistry Simulation Tool).

3d simulation of a li-ion battery

Within the microscopic transport model the microscopic structure of the electrodes is resolved, which allows for a detailed study of ion transport in electrolyte and active particles separately.

The porous electrode model on the other hand allows for the simulation of a complete battery cell by using effective transport equations that are obtained by volume averaging from the microscopic description. These approaches allow for a computer aided optimization of material composition and geometry.

Understanding aging phenomena of batteries are another unsolved challenge – especially for automotive applications. Therefore, we develop aging models that can help to reduce the experimental and financial costs in this field.