Battery

Introduction

The ANSYS Fluent battery model is provided as an add-on module with the standard ANSYS Fluent censed software. This module is accessible from the console with defined models addon-module.

 

 

Modules 7 and 8 are related to battery simulation, and this document describes the model theory that includes mathematical equations and physical interpretations of independent and dependent variables used in the models.

Once you enable the battery model, the Energy equation will be automatically enabled to solve for the temperature field.

Given the important role of a battery in electric and/or hybrid electric vehicles, several models have been proposed to simulate the transient behavior of the rechargeable battery. These models vary in complexity from a zero-dimension resistor-capacitor to a multi-dimension potential current distribution. The general model available in the software is known as MSMD (Multi-Scale Multi physics Battery) model.

The computational domain includes only the anode and cathode electrodes and their current collectors. The separator layer is modeled as an infinitely thin interface between the two electrodes across which there is a potential jump due to loss. The battery geometry consists of a cell and positive and negative tabs the cell consists of an active zone, and the tabs are as passive zone. Electrochemical reactions only accrue in active zones that the potential field solves in active and passive zones.

Model tab

The battery model includes different tabs. The first tab is in model options. In the solution method section, 4 method is available to select.

 

. CHT coupling: pure conjugate heat transfer method to simulate steady-state or transient heat production is known or obtained by other methods. The purpose of this simulation is to predict the temperature field of the module or pact.

This is the easiest method in the electric thermocouple.

. MSMD: Multi-Scale Multi physics Battery

. FMU-CHT coupling:  functional mock-up unit coupled is suitable for users who have used electrochemical models of various ECMs in the third-party component. It is used in ANSYS Fluent, and co-simulation can be achieved by importing FMU into fluent.

. Circuit Network: the user wants to use the electrochemical model to calculate the heat source of the battery, such as the ECM model. In this type of coupled calculation, the heat source of the cell is uniformly distributed and can be obtained from the sub-electrochemical model. And it’s generally transient.

E-Chemistry models

 

There are multiple models to study thermal behavior under discharge and charge conditions. These two theoretical models use porous electrodes and a concentrated charge condition. However, this way is not ideal for the heat treatment industry. The other is to use empirical parameters to predict the temperature evolution. The second approach is presently considered the best research direction. The two models widely used in commercial software are the equivalent semi-empirical model (ECM) and the Newman, Tiedemann, Gu, and kin (NTGK) model.

The NTGK model is set up by a curve fitting the experimental data. This model is used to obtain the total heat from an electrochemical reaction and predict the temperature distribution of the battery cell.

Newman p2D model The so-called pseudo-two-dimensional (P2D) model developed by the Newman group is probably the most widely used lithium-ion battery model of this type. It is composed of a one-dimensional macro-scale model describing the evolution of lithium concentration and electric potential in the electrolyte across the anode, separator, cathode, and micro-scale models for the electrodes.

The pseudo-second dimension arises from these coupled one-dimensional micro-scale models describing the solid-phase diffusion of lithium in the porous active material of the electrodes. These micro-scale models solve the diffusion of lithium occurring in a spherical particle at each local position of the macro-scale porous electrode model.

Energy source options

 

. Enable joule heat passive/active source: to include the joule heating source in their thermal energy equation

. Enable E-chem heat source: to include the heat source due to electrochemistry in the thermal energy equation.

Solution controls

 

For Solution controls, you can set the current under the relaxation factor.

In the case of having a cluster cell for simplification, the cluster cell option is available, and the number of clusters can be added in their direction.

Note: this tab is available only with the MSMD method.

Electrical Parameters

 

You can set the nominal capacity (the battery cell capacity) for electrical parameters. If you select lifetime, you can specify a nominal DoD value (depth of discharge). For the solution options, if you select :

. Specified C-Rate, The C-rate is the unit battery experts use to measure the speed at which a battery is fully charged or discharged. For example, charging at a C-rate of 1C means the battery is charged from 0-100% in one hour. A C-rate higher than 1C means a faster charge. For example, a 3C rate is three times faster, so a full charge in 20 minutes. Likewise, a lower C-rate means a slower charge: C/5 (or 0.2C) would be five times slower than 1C, amounting to a five-hour charge. You can set the value for Discharge C-rate (the hourly rate at which a battery is discharged). In this case, the total current at the cathode tabs is fixed as the product of C-rate and nominal capacity, while the electrical potential is anchored at zero on the anode tabs.

. Specified system current, you can set a value for the total current (applied to the anode tabs). In this case, the electrical potential is set to zero at the anode tabs.

. specified system voltage. You can set a value for the system voltage ( applied to the cathode tab, the anode tab has a voltage of  0v).

. specified system resistance, you can set a value for system resistance ( applied to the anode tab)

. Set in the boundary condition, you can set the uds boundary condition directly.

Conductive Zone tab

For this single-cell case, there are no busbar zones. Electrochemical reactions occur only in the active zone. Battery tabs are usually modeled as passive zones, in which the potential field is also solved.

 

Electric Contacts

Under the Electric Contacts tab, configure the contact surface and external connector settings. The corresponding current or voltage boundary condition will automatically be applied to those boundaries. Under the Electric Contacts tab, you can define extra contact resistance for each zone.

 

Model Parameters tab

 

Figure 1 MSMD with ECM parameters

 

For the Electric Circuit Model, you can specify the function coefficients for the resistors’ resistances, capacitors’ capacitances, and the open circuit voltage (Voc) to be used in If you want to specify the ECM model functions in the polynomial form, select Using polynomials and enter parameters, In addition, you can turn on the Using different coefficient for charging and discharging option and specify the coefficients for Charging parameters.

You can also set values for the Initial State of Charge and Reference Capacity. The default value of 1 for the Initial State of Charge indicates the fully-charged state of the battery cell.

The coefficient values for the Electric Circuit Model are battery specific and need to be specified before conducting a simulation. The default values are taken from Chen. If you model a battery of a different design, you should specify a different set of battery parameters.

 

Figure 2 MSMD with NTGK parameters

 

For the NTGK model, you can specify the U coefficients, Y coefficient, and temperature correction. The coefficient values for the NTGK Model Polarization Parameters are based on battery cell polarization test curves. Obtaining coefficient values (other than the default values) can depend on your battery configuration and material properties. The default values are taken from Kim’s paper. If you model a battery having a different design, you must provide a different set of battery parameters.

 

Figure 3 MSMD with P2D parameters

 

Complete and comprehensive explanations of all inputs are available in the software documentation.

MR-CFD, an Expert in the Field of Battery Simulations

With several years of experience in simulating various problems in different CFD fields using ANSYS Fluent software, the MR-CFD Company is ready to offer extensive modeling, meshing, and simulation services. Our simulation Services for Battery Engineering simulations are categorized as follows:

• Simulation and analysis of Batteries with different methods such as MSMD, NTGK, etc.
• Thermal CFD simulation of Batteries in case of nanofluids.
• Cooling of Batteries with the existence of PCM material.
• …

You may find the related products to the Battery simulation category in Training Shop.

Our services are not limited to the mentioned subjects, and the MR-CFD is ready to undertake different and challenging projects in the Battery Engineering modeling field ordered by our customers. We even accept carrying out CFD simulation for any abstract or concept design you have in your mind to turn them into reality and even help you reach the best design for what you may have imagined. You can benefit from MR-CFD expert consultation for free, and then order your project to be simulated and trained.

By outsourcing your project to the MR-CFD as a CFD simulation freelancer, you will not only receive the related project’s resource files (Geometry, Mesh, Case & Data, …), but also you will be provided with an extensive tutorial video demonstrating how you can create the geometry, mesh, and define the needed settings(pre-processing, processing and post-processing) in the ANSYS Fluent software all by yourself. Additionally, post-technical support is available to clarify issues and ambiguities.