Session 5: Computer Simulations to Aid Automotive Battery Design and Performance Prediction
Computer simulation is a powerful tool in vehicle and battery design, including the electrical, thermal, and mechanical aspects, and life, safety, and reliability simulation. This session will discuss the major features of battery modeling software and its application to electrical and thermal battery design and life estimation with the aim of improving design while reducing validation time and cost.
Session Chairman: Robert Spotnitz, President, Battery Design LLC
Dr. Spotnitz is a leading developer of mathematical models that simulate battery operation. Dr. Spotnitz, who previously held several senior technical positions in materials and battery development, founded Battery Design in 1999 to provide consulting and develop custom software for battery developers and users. He is a well-known speaker on various aspects of battery engineering.
SESSION AGENDA
Development and Validation of a Thermal Simulation Model for Li-Ion Batteries in HEVs/PEVs Jenny Kremser, Project Manager and Research Scientist, ASCS - Automotive Simulation Center Stuttgart e.V
Abstract
For the past four years now the Automotive Simulation Center Stuttgart e.V. - asc(s - has managed to successfully bring together automotive manufacturers, suppliers, soft- and hardware vendors, and science in the precompetitive stage. The Adam Opel AG, Daimler AG, Dr. Ing. h.c. F. Porsche AG, and the software companies CD-adapco and Battery Design LLC are associated with and cooperate in the international asc(s project “Development and Validation of a Thermal Simulation Model for Li-Ion Batteries in Hybrid and Pure Electric Vehicles (HEV/PEV)”. The partners are working towards a consistent development plan of a simulation environment for the electrothermal layout of a lithium-ion battery module which at present is being consistently implemented. Dr. Kremser from the asc(s is in charge of the entire project coordination. The asc(s is the ideal platform to promote the exemplary cooperation between practice, theory, software development, model parameterization on an experimental basis, and the validation of an electrochemical system. It is this combination of expertise from all participating partners which is likely to achieve the best possible results.
Our new simulation model couples a thermal fluid-mechanical 3D model of the complete lithium-ion battery module including its cooling system (based on the CAD data from Behr GmbH and Co. KG) with an electrothermal circuit model. The latter describes the local current/voltage characteristics as well as the locally released heat loss of the individual accumulators (battery cells) built into the module. The overall model can be used to investigate heat and energy management and to optimize the layout of the battery cooling system. Knowledge about the temperature and charge distribution between cells within the battery module is crucial, since potential inhomogeneities can have a negative impact on battery life.
The developed simulation environment can be applied during the early phase of the virtual vehicle development process to verify the narrow electrothermal requirements on the battery module in coordination with vehicle development. This is an important preliminary requirement for the development of optimized design concepts for electrified vehicles to fulfill increasing demands on energy consumption, driving range, and durability.
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Full 3D Modelling and Simulation of Li-Ion Battery Cells with BEST (Battery and Electrochemistry Simulation Tool) Arnulf Latz, Senior Scientist, Fraunhofer Institute
Abstract
In order to improve qualitatively power density or lifetime of Li ion batteries first the design of the cells has to be improved. The separate transport phenomena in the electrolyte and in the active particle as well as their complex interplay due to the electrochemical reactions at the interfaces between the electrode particles and the electrolyte will influence the performance and the lifetime of a battery. Heat sources are in general not homogeneously distributed over the cell, but concentrated in regions where large potential differences and currents are located. Also the overall temperature increase will be strongly influenced by the spatial distribution of the electric current in the cell. This not only applies locally to the scale of the active particles but also on the scale of the whole cell, where also the positioning of the current collector and the shape of the electrodes influence the distribution of ions, currents and heat sources. With the possibility to study the relevant processes dependent on load conditions in 3D an intuitive understanding is created which can help to identify more robust battery designs by eliminating potentially destructive or local, aging accelerating electro-thermal conditions. The software BEST developed by the Fraunhofer ITWM provides such a tool for transport processes on the scale of the active particles as well as on the scale of a full cell without any restriction on the three dimensional shape of the cell or the electrodes.
We will present:
The electrochemically based modelling approach used in our simulations
Example applications on the micro- as well as on the cell scale
Detection of potential hot spots in the microstructure
Multi-electrode cell design
Strategies to achieve fast and realistic 3D simulations
Features of the software BEST
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From Battery Modeling to Battery Management Peter Notten, Professor, Energy Materials and Devices Group, Eindhoven University of Technology
Abstract
Rechargeable batteries are nowadays widely applied in the field of consumer electronics and (Hybrid) Electrical Vehicles ((H)EV). These include aqueous battery systems, such as Nickel-Cadmium (NiCd) and Nickel-Metal Hydride (NiMH) and non-aqueous Li-ion batteries. Each battery type has its own specific advantages and disadvantages. The design of efficient charging algorithms and accurate State-of-Charge and State-of-Health indication methods are a continuous drive to set-up optimal Battery Management Systems (BMS). In order to simulate the interaction between rechargeable batteries and the surrounding electronics, physical and chemical models have been designed. These models are all electrochemically-based and accurately describe the development of the battery voltage, the internal partial gas pressure and battery temperature, and the interaction between these under a wide variety of battery operating conditions, ranging from simple dc- to more complex ac-conditions. Our models are based on the relevant thermodynamics, charge transfer kinetics and diffusion processes occurring at/in both electrodes and in the electrolyte. How the battery models are set up will be outlined on the basis of NiMH and Li-ion examples. Modelling and optimisation results will be presented together with how these results contribute to a better understanding of battery operation in various applications.
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Analysis of the Polarization in a Li-Ion Battery Cell by Model Simulations Mårten Behm, Researcher and Teacher, School of Chemical Science and Technology, Applied Electrochemistry, KTH, Royal Institute of Technology
Abstract
The rate performance of a battery cell is the result of a number of factors which can broadly be divided into materials properties and geometric factors related to the design of the electrodes and the entire cell. Physically based mathematical models can be a valuable tool in understanding the impact and interrelation of these factors, and help identifying where to focus R&D efforts. The work that is presented here addresses the need for models based on solid experimental characterization of the electrochemistry of the system, and for better tools for analysis and discussion of simulation results.
We have modelled a power-optimized battery cell based on graphite (MAG-10) | 1.2 M LiPF6 in EC:EMC (3:7 by weight)|LiNi0.8Co0.l5Al0.05O2. This cell is interesting from an application point of view while there are also data and models available for the description of its electrochemistry.
Simulations of HEV type test cycles were run at different states-of-charge and were found to agree very well with experiments.
A method for analyzing the simulation results was developed. The total polarization of the cell is split up into six polarizing subprocesses and three different subdomains: positive electrode, separator and negative electrode.
During an EUCAR test cycle one of the major factors limiting the performance is the ohmic potential drop in the electrolyte, e.g. At SOC 40 it contributes to 28 % of the total energy loss.
The diffusion polarization in the electrolyte and the solid phase accounted for 15 and 16 % respectively at SOC 40.
A comparison of the EUCAR and an ISO energy cycle shows that the latter is more limited by diffusion polarization, due to longer duration of current pulses.
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Mechanical Modeling of Li-ion Batteries for Short Circuit Detection Tomasz Wierzbicki, Professor and Director, Impact and Crashworthiness Lab., MIT
Abstract
The paper reports on a comprehensive experimental and numerical study on response of individual pouch and cylindrical cells subjected to various types of mechanical loading, including:
Indentation by hemispherical, flat nose, and conical punches
Lateral indentation by a cylindrical punch
Axial crush (confined and unconfined)
Three-point bending
Measured in the tests were load, displacement, voltage, and surface temperature. The tests were performed in a special environmental chamber on 90% discharged batteries. Some of the tests were used for calibration of a suitable constitutive model and the reminding tests served for validation. A finite element model was developed, composed of shell elements representing outside casing, and solid elements for the active material with a binder lumped together with the current collectors and the separator. Very good correlation was obtained between LS Dyna numerical simulation and test results. The FE model was also capable of predicting the onset of short circuit of the cell. The above homogenous model assumes different properties in tension and compression but does not account for the effect of structural anisotropy caused by the layered nature of the jelly roll. The work is in progress to develop a more advanced homogenized computational model.
