Search

Jie Deng is a research engineer in the Department of Electrification Subsystems and Power Supply at Ford Motor Company. He has extensive experience in computer-aided engineering analysis (structural, fluid, and thermal), battery simulations, and material characterization. He got his PhD in Mechanical Engineering from Florida State University and has published over 30 papers. His current research mainly focuses on battery array design and multi-physics modeling and testing of battery behaviors under various abuse conditions. Chulheung Bae is a high-voltage battery systems group supervisor at Ford Motor Company, where his research activities focus on lithium ion battery system development and validation for automotive applications. Dr. Bae has over 22 years of experience in advanced battery materials and various energy storage devices, including Lithium Ion, NiZn, Lead-Acid and redox flow batteries, and ultra-Capacitors. Dr. Bae has a Doctorate in Chemical Engineering from University of Manchester in the UK. Adam Denlinger is manager of high-voltage systems research and development at Ford Motor Company. Adam’s team is responsible for delivering high-voltage battery system innovations—including packaging, durability, thermal, management and controls, and EMC—as well as human-centered technologies targeting an enhanced electrified vehicle ownership experience. The team also leads multiple collaborations in this field with industry, university, and national lab partners. Adam has worked with Ford for 22 years, with experience delivering powertrain technologies, including Ford’s first Ecoboost engine application, industry-first hydrogen internal combustion engine vehicle fleet, and multiple high-voltage battery systems for battery electric (BEV) and plug-in electric (PHEV) vehicles. Ted Miller is manager of electrification subsystems and power supply research. His team is responsible for Ford global electrification subsystem and power supply research, delivering battery system design innovations in advanced cell technology, packaging, thermal, EDS, EMC, charging, power conversion, and energy management and modeling. They provide subject matter expertise from raw materials to end-of-life recycling. The team also leads collaboration with university, industrial, and National Lab partners. Mr. Miller is chairman of the United States Advanced Battery Consortium and a member of the Idaho National Laboratory Strategic Advisory Committee and the University of Michigan Energy Institute External Advisory Board.

Structural responses of separators are critical to battery safety. Commonly used separators are dry-processed polymers with anisotropic microstructures. Due to the material anisotropy, rate dependence, and temperature dependence, developing a model for predicting the thermomechanical response of polymeric battery separators has been challenging. This paper presents an orthotropic nonlinear thermoviscoelastic model for predicting the response of polymeric battery separators in thermal ramp scenarios. The model was based on the Schapery nonlinear viscoelastic model and the temperature dependence was introduced through the time-temperature superposition principle (TTSP). The model was implemented in LS-DYNA® finite element (FE) package as a user-defined material model. The model parameters were determined for a polypropylene (PP) separator. The predicted material responses under large deformations in isothermal and non-isothermal temperature conditions for stress relaxation, creep and tensile loadings at different rates agree well with the experimental data.

This paper presents a 3D microstructure model to predict mechanical behaviors of the anisotropic battery separator. A statistical characterization and stochastic reconstruction method is established to enable 3D microstructure modeling based on 2D microscopic images. Statistics of the key microstructure characteristics, such as porosity and the shape of the voids, are quantified by image-based characterization. Furthermore, a stochastic reconstruction algorithm is proposed to generate random but statistically equivalent 3D microstructure models for mechanical property analysis and uncertainty quantification. The proposed method is demonstrated on a commercial separator. Uniaxial tensile simulations are conducted with Finite Element Analysis (FEA) and the results are validated by experimental data. The 3D microstructure model captures anisotropic properties of the separator, and gives insights about the microstructure features under tensile load.

Battery safety is a critical factor in the design of electrified vehicles. As such, understanding the battery responses under extreme conditions have gained a lot of interest. Previously, abuse tolerance tests were applied to measure the safety metrics of different types of batteries. Nevertheless, conducting these tests in various conditions is usually expensive and time consuming. Computational modeling, on the other hand, provides an efficient and cost-effective tool to evaluate battery performance during abuse, and therefore has been widely used in optimizing the battery system design. In this Perspective, we discuss the main progresses and challenges in battery safety modeling. In particular, we divide the battery safety models into two groups according to the stage in a typical battery failure process. The first group focuses on predicting the failure conditions of batteries in different scenarios, while the second one aims to evaluate the hazard after the onset of battery failure like thermal runaway. Although the models in these groups serve different purposes, they are intercorrelated and their combination provides a better understanding of the failure process of a battery system. The framework, capabilities, and limitations of typical models in each group are presented here. The main challenges in building battery safety models and their future development and applications are also discussed.

The in-plane characterization of an orthotropic porous polymer thin film used as separators in lithium-ion batteries was investigated. The mechanical behavior of an orthotropic material is described by the stress-strain relationships in the principal material directions and shear, and the Poisson's ratios. The measurements of the shear properties and the Poisson's ratio for polymer films with a thickness of tens micrometers has not been well established. In this work, these measurements were attempted for a separator of 25 μm thickness. The mechanical testing was performed with a dynamic mechanical analyzer (DMA). Digital image correlation (DIC) was used for strain measurements. The measured major Poisson's ratio was at a constant value whereas the minor Poisson's ratio increased linearly with strain. The symmetry condition for the elastic orthotropic relation was found to be valid up to 1% strain under transverse tension. The shear properties were measured with an off-axis tensile experiment. The shear modulus determined from the DIC strain measurement agreed well with that from the off-axis modulus and elastic constants. Based on the analogy for anisotropy between the elastic and linear viscoelastic domains, the shear creep response was measured with the off-axis tensile creep experiments. The creep compliances in shear and in the principal material directions were determined. This work laid the foundation for the development of orthotropic elastic and viscoelastic models for battery separators.

Polymer separators for lithium ion batteries are thin, porous membranes of 20–30 μm thickness. At elevated temperatures, some separators can shrink considerably. To predict the deformation and stresses in the separator in battery cells, it is necessary to measure the expansion/shrinkage property of a separator as expressed by the coefficient of thermal expansion (CTE). The reported CTE measurement techniques for thin films have their limitations. This paper examines the use of a dynamic mechanical analyzer (DMA) for the measurement of the thermal expansion/shrinkage property of polymer separators. The effect of the dimensional change of the testing fixture was considered. The influences of the preloading levels and heating rates were investigated. The measurements were carried out for three common types of polymer based separator. The CTE as a function of temperature was determined from the DMA data. DMA offers continuous measurements in an automatic fashion, which is an efficient and convenient method to characterize the thermal expansion/shrinkage behavior of thin polymer films.

To optimize the safety of batteries, it is important to understand their behaviours when subjected to abuse conditions. Most early efforts in battery safety modelling focused on either one battery cell or a single field of interest such as mechanical or thermal failure. These efforts may not completely reflect the failure of batteries in automotive applications, where various physical processes can take place in a large number of cells simultaneously. In this Perspective, we review modelling and testing approaches for battery safety under abuse conditions. We then propose a general framework for large-scale multi-physics modelling and experimental work to address safety issues of automotive batteries in real-world applications. In particular, we consider modelling coupled mechanical, electrical, electrochemical and thermal behaviours of batteries, and explore strategies to extend simulations to the battery module and pack level. Moreover, we evaluate safety test approaches for an entire range of automotive hardware sets from cell to pack. We also discuss challenges in building this framework and directions for its future development. Battery safety is a key focus in the design of electrified vehicles. Here, the authors survey literature approaches for modelling and testing battery safety under abuse conditions, and propose a multi-physics modelling and testing framework for real applications.

We report the first cradle-to-gate emissions assessment for a mass-produced battery in a commercial battery electric vehicle (BEV); the lithium-ion battery pack used in the Ford Focus BEV. The assessment was based on the bill of materials and primary data from the battery industry, that is, energy and materials input data from the battery cell and pack supplier. Cradle-to-gate greenhouse gas (GHG) emissions for the 24 kWh Ford Focus lithium-ion battery are 3.4 metric tonnes of CO2-eq (140 kg CO2-eq per kWh or 11 kg CO2-eq per kg of battery). Cell manufacturing is the key contributor accounting for 45% of the GHG emissions. We review published studies of GHG emissions associated with battery production to compare and contrast with our results. Extending the system boundary to include the entire vehicle we estimate a 39% increase in the cradle-to-gate GHG emissions of the Focus BEV compared to the Focus internal combustion engine vehicle (ICEV), which falls within the range of literature estimates of 27-63% increases for hypothetical nonproduction BEVs. Our results reduce the uncertainties associated with assessment of BEV battery production, serve to identify opportunities to reduce emissions, and confirm previous assessments that BEVs have great potential to reduce GHG emissions over the full life cycle and provide local emission free mobility.

The responses of pouch and prismatic battery modules when they are impacted by two types of indenters from three different directions are investigated experimentally. The test results show that the failure mechanism, peak force and penetration that leads to short-circuit in modules strongly depend on the impact direction, indenter shape, cell form factor and module design. It sheds lights on the abuse tolerance of batteries in different scenarios and demonstrates that the cell type, orientation and module structure should be considered simultaneously in order to improve the battery safety in electrical vehicles.

Battery separators are thin, porous membrane of 20∼30 microns thickness. Polymer separators display a significant amount of shrinkage at elevated temperatures. It is difficult to quantitatively characterize the large shrinkage behavior with a free standing separator sample. This paper examines the use of a dynamic mechanical analyzer under tensile mode in measuring the coefficient of thermal expansion (CTE) of three commonly used separators.

Understanding battery response under impact is critical to improve the safety of electrified vehicles. Nevertheless, predicting the impact behaviors of batteries is not straightforward since a battery cell usually contains hundreds of thin layers with dramatically different material properties and multiple physical processes occur simultaneously during cell deformation. Here we utilized both empirical tests and numerical models to capture the failure process of pouch and prismatic cells in various impact scenarios. In each test, a cell was hit once by an indenter dropped from a certain height. During which the cell penetration, loading force, voltage and temperature were monitored to characterize the cell’s response. Meanwhile, numerical models were developed to capture the coupled mechanical, electrical, electrochemical and thermal responses of batteries. In these models, the cell bulk was treated as a homogeneous part to achieve computational efficiency required by large-scale simulations, and it was represented by the geologic cap model that allows both shear and compaction deformation. Simulation results showed agreement with experimental data in essential features of cell behaviors during impact. Details of the test setup, model development and cell failure behaviors are presented in this paper. Additionally, capabilities, limitations and future improvement of the battery safety modeling are discussed.

The separator is one of the most important components for battery safety since its failure can cause short-circuit that may lead to thermal runaway. As such, understanding the mechanical behaviors of separators is critical to improve battery safety. Nevertheless, modeling the mechanical behaviors of separators is challenging since they usually depend on multiple factors such as orientation, temperature and strain rate due to the microstructure of separators. Here we develop an orthotropic linear viscoelastic model for separators, which takes both anisotropy and strain rate effects into account. This model is the first step of a future model that considers more factors such as temperature and large deformation. The model has been implemented as a user material model in a finite element package, where a discretization algorithm is developed to evaluate the stiffness-based hereditary integral with a kernel of Prony series. The user model has been applied to a polypropylene (PP) separator Celgard® 2400. The simulation results agree well with experimental data, which include the rate dependent uniaxial tensile behavior of the separator in the two in-plane material directions and in shear, and the strain contour patterns of every strain component during biaxial tension.

Battery electric vehicles (BEVs) offer significant potential to reduce the nation's consumption of petroleum based products and the production of greenhouse gases however, their widespread adoption is limited largely by the cost and performance limitations of modern batteries. With recent growth in efforts to accelerate BEV adoption (e.g. the Department of Energy's (DOE) EV Everywhere Grand Challenge) and the age of existing BEV battery technology targets, there is sufficient motivation to re-evaluate the industry's technology targets for battery performance and cost. Herein we document the analysis process that supported the selection of the United States Advanced Battery Consortium's (USABC) updated BEV battery technology targets. Our technology agnostic approach identifies the necessary battery performance characteristics that will enable the vehicle level performance required for a commercially successful, mass market full BEV, as guided by the workgroup's OEM members. The result is an aggressive target, implying that batteries need to advance considerably before BEVs can be both cost and performance competitive with existing petroleum powered vehicles.

Lithium-ion batteries have been widely used for an energy storage system in electrified vehicles due to their high energy and power densities. Improving the safety of lithium-ion battery system is one of the top priorities in the electrified vehicle design since it is directly related to the safety of passengers. Various abuse tolerance tests have been developed to evaluate the failure conditions of lithium-ion battery cells, modules and systems. Nevertheless, these tests can be expensive and time consuming, and in some cases provide limited information on the failure mechanisms of batteries. As such, computational modeling has gained a lot of interests and played a more and more important role in evaluating the battery safety under different abuse scenarios. Here we present a multi-physics battery safety model that is able to predict coupled mechanical, thermal, electrical and electrochemical responses of automobile lithium-ion batteries under abusive conditions. In this model, the electrochemical behavior of batteries is described by a spatially distributed equivalent circuit model, where polarization and damping effects are captured by a resistance-capacitance network. During simulations, the mechanical solver predicts the onset of short circuit, and then the coupled thermal, electrical and electrochemical solver captures the evolution of temperature, voltage and current distribution after short circuit initiation. In order to make the proposed model applicable to module or pack level simulations, various element formulations and strategies have been developed to improve computational efficiency without scarifying much accuracy. Details of model set up, parameters evaluation, and case studies that demonstrate the model capabilities will be presented. Experimental validation of model prediction as well as the future development of this framework will also be discussed.

The technical performance for the operation of a stand alone redox flow battery system for solar energy storage is presented. An undivided reactor configuration has been employed along with porous graphite felt electrodes and ruthenium acetylacetonate as electrolyte in acetonitrile solvent. Limiting current densities are determined for concentrations of 0.02 M and 0.1 M ruthenium acetylacetonate. Based on these, operating conditions for 0.02 M ruthenium acetylacetonate are determined as charging current density of 7 mA/cm2, charge electrolyte superficial velocity of 0.0072 cm/s (through the porous electrodes), discharge current density of 2 mA/cm2 and discharge electrolyte superficial velocity of 0.0045 cm/s. An optimum power output of 35 mW is also obtained upon discharge at 2.1 mA/cm2. With an increase in the concentration of ruthenium species from 0.02 M to 0.1 M, the current densities and power output are higher by a factor of five approximately (at same superficial velocities) due to higher mass transport phenomenon. Moreover at 0.02 M concentration the voltage efficiency is better for battery full of electrolytes prior to charging (52.1%) in comparison to an empty battery (40.5%) due to better mass transport phenomenon. Voltage efficiencies are higher as expected at concentrations of 0.1 M ruthenium acetylacetonate (55% when battery is full of electrolytes and 48% when empty) showing that the all-ruthenium redox flow battery has some promise for future applications in solar energy storage. Some improvements for the system are also discussed briefly.

The charge/discharge characteristics of an undivided redox flow battery, using porous electrodes and chromium-EDTA electrolyte are discussed. The results indicate that a high current efficiency can be achieved using this system with single pass, flow through electrodes. With 0.2 M electrolytes and a charging current density of 30 mA cm−2, 100% current efficiency was achieved with 48% conversion of Cr(III) to Cr(II). However, the overall energy efficiency of charge/discharge of this redox flow battery was less than 7%. The results suggest that this poor efficiency was associated with the slow kinetics and consequently large overpotential of the Cr(V)-EDTA/Cr(III)-EDTA redox couple.

As lithium-ion batteries are more and more widely used in electrical vehicles and hybrid electrical vehicles, their safety has become a primary concern due to their high energy densities and wide-range working conditions. Previously, experiments such as crush tests, have attempted to mimic the failure process of batteries under abuse conditions, but they usually only give binary pass/fail results and provide limited details of the root causes of failure. Recently, computational modeling has gained a lot of interest because it provides an efficient tool to capture fundamental mechanisms of battery failure. Nevertheless, most of existing models of battery safety either treat the battery as a homogeneous solid and only consider its mechanical response, or focus on the thermal-electrical coupling without consideration of mechanical influence. Here we present a three-dimensional multi-physics model of battery safety that is able to predict coupled mechanical, thermal, electrical and electrochemical responses of automobile lithium-ion batteries under mechanical abuse. This model resolves each component in unit cells of a large format Li-ion cell and applies one-way coupling between mechanical and other types of responses to accommodate the significant differences in time scales. In particular, the mechanical solver predicts the onset of internal or external short circuit at the initial stage of an impact, and then the coupled thermal and electrical solver captures the evolution of temperature and current distribution after short circuit initiation. The electrochemical response is captured by a spatially distributed equivalent circuit model, where empirical parameters are obtained from experimental data. This model has been applied to capture internal and external short circuits and subsequent thermal and electrical responses in different types of cells and modules. Various element formulations have been evaluated to achieve the computational efficiency that will be required for future pack simulations. Model predictions have been compared with experiment data, demonstrating the model capacity and providing insights into the failure mechanisms of batteries during an impact process.

An isothermal, physics-based model was developed in COMSOL multiphysics software to simulate the galvanostatic discharge performance of LixC6/Liquid Electrolyte/ Liy(NiaCobMnc)O2 dual lithium-ion insertion cell at 298 K. Modeling results are compared with experimental data to provide further insight into design and optimization of these cells for advanced electric vehicles.