Electrical and Electrochemical Modeling

Electrical simulations are used at Fraunhofer ISE in various fields. In addition to the simulation of inhomogeneities in PV modules, the simulation of batteries - on cell and system level - as well as their production processes is a main focus.

Batteries are rapidly gaining in importance for the success of the further expansion of fluctuating renewable energies (PV, wind). Also they represent the foundation for the transport transition, as a highly efficient mobile storage system. The complex behavior of the electrical performance and its sensitive dependencies on temperature, constructive, mechanical and chemical parameters as well as, in particular, the aging mechanisms and their interactions are the subject of extensive scientific and technical research. Modeling and simulation of batteries as well as their production processes (e.g. welded joints or interface formation) are substantial tools for their efficient processing. The scope of time-consuming tests in the laboratory, which are associated with high safety precautions, can thus be significantly reduced, enabling cost-optimized development towards the product (time to market).

R&D Services for Electrical and Electrochemical Modeling

In the business area Hydrogen Technologies and Electrical Energy Storage and the research topic Photovoltaic Modules and Power Plants we offer the following services in the field of electrical and electrochemical modeling.

  • Representation of any battery cells or battery systems in an FEM model or in an equivalent circuit model, depending on the respective scientific-technical issue
  • Material characterization to determine the model parameters
  • Experimental validation in the test laboratory
  • Simulation of battery pack interconnection
  • Simulation of welding processes
  • Simulation of battery cells and battery systems in different applications
  • Virtual product development and optimization
  • Virtual analysis of critical operating conditions
  • Simulation of inhomogeneities in PV modules

Application Examples

Simulation of Battery Cells and Battery Systems

Fraunhofer ISE creates highly accurate, locally resolved models of battery cells. These are necessary to understand the close interplay between temperature and temperature distribution, pressure and pressure distribution, cell voltage or efficiency and aging. In this way, local differences in the various aging mechanisms can be understood, leading to a better understanding of the overall aging process. Based on this, for example, the cell design (e.g., thicknesses, design of connections) can be optimized or cooling can be adjusted to minimize temperature differences in the battery cell.

In order to minimize temperature differences in the entire battery system, to achieve an efficient coupling to the heating and cooling system and thus to be able to guarantee the performance, reliability and safety of the system, the battery system is transferred to a CFD model, analyzed and optimized.

Modeling the voltage distribution across the surface of a large-scale lithium-ion cell
© Fraunhofer ISE
Modeling the voltage distribution across the surface of a large-scale lithium-ion cell.
CFD model of a pouch cell module with side-mounted cooling
© Fraunhofer ISE
CFD model of a pouch cell module with side-mounted cooling.

Brief Description:

  • Goal
    • Safe, reliable and efficient battery system with long service life
    • Fulfillment of application-specific requirements, particularly with regard to the supply of electrical power or energy
    • Efficient adapted thermal management
  • Procedure
    • Analysis of the requirements and selection of suitable cells or modeling of a preselected cell
    • Design of the battery system (number and interconnection of the cells to modules or directly to the system, adaptation to installation space, selection of passive components)
    • Design of thermal management with respect to type (air cooling, liquid cooling, etc.), contact areas and necessary heating and cooling capacity
    • Investigation of worst-case scenarios (high power, high temperatures)
    • Optimization of the operation management by definition of suitable dynamic parameters (e.g. set points for cooling, current limits)
  • Results

Electrochemical Modeling of Battery Cells

In addition to electrical equivalent circuit models, models based on actual electrochemical processes are also developed and applied at Fraunhofer ISE. These models reproduce the electrical and also thermal behavior of the battery cell. Among others, the pseudo two-dimensional battery model (P2D model) is used, which provides reliable values and is widely applied. However, both the equivalent circuit model and the P2D model require cell-specific parameters, including cell chemistry and cell geometry. Fraunhofer ISE can create and parameterize different battery models and verify their precision over all operating ranges (temperatures, current rates) in experimental tests. In addition to commercially available lithium-ion battery cells, alternative cells based on zinc or sodium ions, for example, are also developed, tested and simulated at Fraunhofer ISE.

Pseudo 2D-Modell einer Lithium-Ionen-Zelle
© Fraunhofer ISE
Pseudo 2D-Modell einer Lithium-Ionen-Zelle (auch Doyle Fuller Newman Model). Diskretisierung entlang der x-Achse und dem Partikelradius.

Brief Description:

  • Goal
    • Simulation of battery cell properties (voltage, aging, etc.) over a wide range of applications (e.g. temperatures, currents)
    • Insight into internal cell processes such as aging, formation and growth of the solid electrolyte interface (SEI), balancing of anode and cathode
  • Procedure
  • Results
    • Simulation model with universal validity
    • Sound understanding of electrochemical processes and adaptation of battery operation management (e.g. fast charging protocols)
    • Optimized cell design
    • Reliable synthetic data for machine learning
    • Algorithms for state estimation (state of charge, state of aging, remaining range, power readiness)
    • Usable for simulating the interconnection of cells in the battery pack

Simulation of the Connection of Battery Packs

The core property of a PV module is the power generation, which can be analyzed very well, e.g. with SmartCalc.CTM. If, on the other hand, inhomogeneities play a role, this is often difficult to capture analytically. Therefore, we also use the finite element method to simulate currents and high voltages in PV modules. We also apply FEM simulations for interconnection technologies, such as resistance welding.

Battery packs are now frequently used as intermediate storage for regeneratively generated energy. Here, individual battery cells are connected to each other, e.g., by means of a welding process. In the research projects ElVis and Leopard, on the one hand the welding process for the production of the battery packs is investigated by means of FEM. On the other hand, both the vibration and the impact test according to UN38.3 are simulated in order to analyze the mechanical stability of the battery packs and to uncover any weak points at an early stage.

The FEM simulation shows the temperature profile over time during the resistance welding process.

Brief Description:

  • Goal
    • Analysis of welding parameters and their influence on the welding process
    • Identification of suitable process parameters for a good welding process
    • Mechanical analysis of the complete battery pack
  • Procedure
    • Fully coupled simulation consisting of
      • 3D global model of the battery and the connector
      • 2D submodel of the actual weld spot
    • Simulation of the temperature at the weld spot, as well as the expansion of the melted area
    • Evaluation of the mechanical stability by means of the analysis of the response spectrum
  • Results
    • Identification of suitable process parameters for a good welding process
    • Identification of critical areas in the battery pack during vibration as well as impact testing
    • Adaptation of the battery pack design for better mechanical stability

Further Information on this Research Topic:

Research Project

ElVis

Electric Battery Interconnection: Innovative, Flexible, Fast and Cost-Effective

Software tool

SmartCalc.CTM

SmartCalc.CTM is a free tool to analyze losses in selected module designs.

Forschungsthema

Batterie­verbindung

Verbindungstechnologien für die Batterieverschaltung

Field of Work

Modeling and Optimization of Batteries

Modeling and simulation-based methods for the optimized development of battery cells and systems as well as for the formation during battery cell production

Field of Work

Development of Battery Systems