Modeling & simulation of Li-ion batteries

BatteryDict is the GeoDict module to model battery cells and simulate the electrochemical cycling of Li-ion batteries. Solvers for fully resolved (micro-scale) and for fast (meso-scale) simulations can be used for the electrochemical simulations.

The LIR solver developed by Math2Market and the BEST solver (Battery and Electrochemistry Simulation Tool) of the Fraunhofer Institute for Industrial Mathematics (ITWM) are integrated in GeoDict. 

The charge curve at a user-chosen charging rate or a user-chosen charging potential is obtained and compared to the corresponding equilibrium curve. The curves are displayed in the simulation result summary.

BatteryDict also analyzes the microstructure of battery materials and shows inactive regions in material and electrolyte.

• Design Battery to model battery structures. 
• Analyze Battery to analyze battery structures.
• Charge Battery to simulate battery charging and discharging.
• Charge Half Cell to simulate half-cell charging and discharging.
• Degradation to calculate mechanical stress and strain due to lithium intercalation upon electrochemical cycling.

BatteryDict application examples:

• Check for inactive material in the cell 
• Simulate with different boundary conditions - either specified charge rate or specified potentials
• Determine the connected capacity of the battery structure
• Estimate the performance of the battery by comparing the cell potential over state of charge to the open-circuit voltage 
• Track down different contributions to overpotentials to improve the structure for better cycling performance
• Observe changes in Li-ion concentration in each particle during charging
• Monitor mechanical stress and strain upon lithium intercalation indicating the mechanical degradation of the structure

The Design Battery command produces digital battery materials with material models generated in GeoDict. Separation distance and orientation of the electrodes are specified to obtain the cell geometry. This includes the amount and location of all the components of the cell and the unconnected components, which reduce the energy density of the cell.

The following parameters and materials can be digitally defined and modified:

• Anode material 
• Cathode material
• Separator
• Lithium reservoir as counter electrode
• Current collectors on anode and cathode side

The Analyze Battery command checks the digital battery model for connected and unconnected materials and displays the different volume fractions in the anode and cathode. With Analyze Battery, the battery is checked to reduce unconnected material and for correct balancing between cathode and anode.

The Charge Battery command features three solvers for fully resolved battery charging simulations on the micro-scale.

The LIR solver in BatteriDict emphasizes fast and memory efficient charging simulations, which makes it indispensable for simulations on large structures.

Two feature-rich solvers, known in the field of battery simulations and developed at the Fraunhofer ITWM, allow using concentration dependent parameters in the fully resolved, micro-scale battery charging simulation:

• BESTmicro (new since GeoDict 2023) and
• BESTmicro (legacy version of BESTmicro, default until GeoDict 2022). 

The Charge Battery command includes the BESTmeso solver for meso-scale simulations. Using this solver developed at the Fraunhofer ITWM, BatteryDict calculates effective parameters, such as active surface area, volume fractions, etc., from the loaded micro-structure and starts simulations on the cell-scale level.

Such meso-scale simulations run much faster and with less memory usage than micro-scale simulations, but do not allow to track local variations in lithium-ion concentration, conductivities etc. Accordingly, they are suitable for fast simulation results on large structures.

The BatteryDict-Degradation add-on uses the FeelMath mechanical solver to compute the resulting stress and strain occurring in the battery structure due to lithium intercalation upon electrochemical cycling.

The expected volume change is visualized and maxima in the stress and strain are spotted during the process of optimizing battery electrode structures. Minimize mechanical degradation and enhance the expected lifetime of electrodes!