Battery Pack Design Research Articles

Evolution of Flexible Modular Electric Vehicle Platforms among Automotive Industry and its Influence on Battery Integration

The recent increase in electric vehicle (EV) growth influencing the need for dedicated EV platform development work among vehicle manufacturers. The EV Platform is an aggregation of sheet metal components, battery pack and electric powertrain components. The platform architecture influences design, development and integration of battery pack into vehicle and the lead time for new product development and Time to Market (TTM). This article discusses the evolution of conventional Body in White (BIW) to flexible modular skateboard platforms in EV segments and how it influences the battery pack integration. It discusses the benefits and challenges in the platform workstream and how automakers are preparing for a shift from conventional Internal Combustion Engine (ICE) derivative platform to native EV platform to take advantages in policy decisions and scale benefits on the overall EV ecosystem.

Investigation of the Impact of Flow of Vented Gas on Propagation of Thermal Runaway in a Li-Ion Battery Pack

The venting of hot gases due to rupture of a Li-ion cell during thermal runaway may rapidly transfer thermal energy to neighboring cells in a battery pack and cause propagation of thermal runaway. While thermal runaway has been studied extensively through both measurements and simulations, there is a relative lack of research on the impact of the venting process on thermal runaway propagation. This work presents a non-linear thermal-fluidic simulation of supersonic turbulent flow of hot gases ejecting from a trigger cell and spreading to neighboring cells. Assuming isentropic flow, temperature and speed of the gas flow as functions of time are estimated based on past measurements. These data are used in simulations to determine the thermal impact of the venting process on neighboring cells. The impact of various geometrical parameters of the battery pack on the spreading of venting gases is investigated. Results indicate that cell-to-cell gap, overhead gap and the location of the vent hole on the cell body strongly influence the nature of propagation of thermal runaway to neighboring cells. This work develops a fundamental understanding of an important process during thermal runaway, and may help in the design and optimization of safe Li-ion battery packs for energy conversion and storage.

Structural design and thermal performance analysis of hybrid electric vehicle battery pack cooling system

In this paper, the flow channel structure and battery of battery cooling system are taken as the research object, and the heat transfer simulation is carried out. In order to analyze the temperature and influencing factors of battery pack in the initial scheme of cooling system structure at high ambient temperature of 40 °C, 50 °C and 60 °C, the temperature of battery pack under many working conditions is simulated, and then the optimization scheme is put forward, and the feasibility of the two schemes is compared with that of the initial scheme.

Simulating Electrochemical Behaviour of Lithium-Ion Cylindrical Cells Using Two-Dimensional Physics-Based Model

High energy storage density and energy conversion efficiency, rechargeability and zero tailpipe emissions of lithium-ion batteries make them an attractive choice for powering automobiles. However, significant research and improvement are still required to make these batteries comparable with the convenience associated with the use of fossil fuels. One of the major concerns associated with batteries in electric vehicles (EVs) is of safety due to the high current requirements. In this regard, battery pack designs can benefit tremendously by simulating adverse thermo-electrochemical scenarios. Due to the coupled nature of the electrochemical behaviour of the cell on its temperature distribution, the knowledge of temperature distribution and heat generation in constituting cells is required to predict the cell charge-discharge behaviour, local hot-spots formed within the cell and their influence on thermal runaways during pack operation. Various attempts towards this goal make use of several assumptions to simplify the cylindrical cell modelling. Lumped thermal models with constant temperature were used to determine the cell temperature directly using experimental data [1] or using the pseudo-2D model [2,3] on unwounded cells [4]. Heat generation was homogenized in the energy balance [5] and used along with experimental data for computation [6]. The lack of spatial-dependence in such models is not a good representation of physics expected in large format cylindrical cells due to their low effective transport and thermal properties, and the highly non-homogeneous material used to fabricate these cells.Some models that consider spatial dependence of physics employ this either in the one-dimensional radial direction [7], or the two-dimensional transverse section [8], or in the three-dimensions using two-dimensional resistor circuits for current collectors with one-dimensional resistors between adjacent current collector nodes [9]. For a proper understanding of local heat generation, the local three-dimensional coupled nature of thermo-electrochemical behaviour needs to be taken into account in the model. In a step towards this goal, the present work aims at developing a two-dimensional physics-based thermo-electrochemical model for cylindrical cells. The differential-algebraic governing equations have been solved implicitly with the non-linear term in each linearized for one variable using the Taylor series expansion. This approximation method ensures second-order accuracy for the linearized variable being computed while the non-linearity is retained for the other unknown variables. A variable time step solver based on the stability of the output voltage profile enables improved computational speed. A second-order differencing in space and backwards differencing in time have been implemented for discretizing the partial differential equations into algebraic equations. The Gauss-Seidel method is employed to iterate for the variables at each time step. This discretization technique has been validated (Fig.1a) over a range of C-rates (up to 6C) against an available solver [10]. Subsequently, the method is adapted for polar coordinates to simulate the two-dimensional cross-section of cylindrical cells. The discretization of the double-sided cylindrical cell geometry, as shown in Fig.1b, has been done ensuring nodes on all the boundaries separating various domains along the windings. The different domains within the coil have been discretized using Archimedean spirals with nodes at uniformly distributed angular coordinates. The number of tabs and their corresponding locations in the cell can be specified. The simulation results will be validated using data obtained from cycling of Samsung INR18650-29E lithium-ion cells on a high-current cell cycler in controlled temperature environment. In the future, the coupling of the electrochemical and thermal models for the cylindrical cell geometry will also be attempted.

Coupled electrochemical-abuse-heat-transfer model to predict thermal runaway propagation and mitigation strategy for an EV battery module

Safe and reliable design of lithium-ion battery packs necessitates prevention of thermal runaway and its propagation. To characterize the propagation behaviour in a battery module, a three-mode heat transfer model coupled with electrochemical and abuse-reaction-kinetics models is developed here. The efficacy of an active thermal management system in preventing damage-cascade for a standard EV module geometry (as used in Tesla) is elucidated. The model effectively captures the temperature profile, heat generation rate, and the extent of resulting decomposition of cell-components as validated against the literature. A temperature spike is applied to a cell within a standard battery module to emulate abuse driven runaway. The propagation of damage to other cells due to the temperature-spike in the triggered cell is simulated through the model as developed. A counter-intuitive non-monotonic trend (increasing first, decreasing later) is observed for the damage-severity as a function of coolant flow rate. Through a unified analysis of cumulative heat generation and heat dissipation through coolant, a mitigation strategy for runaway propagation is obtained in terms of a generalized non-dimensional parameter, Runway Mitigation Number (RMN), which predicts runaway propagation beyond a value of ~1.8 for similar module designs.

Scalable constrained attributes/issues about risk, reliability and optimization in large scale battery pack

This study focuses on the optimization of scalable battery pack designs, as a scalable battery pack design can tolerate cell failures, implement a fail-safe mode, rapidly reconfigure itself, and adequately supply the load without interruptions. Hot-swapping, bypass mechanisms, configurability, and redundancy are the key attributes of scalable architecture, which enable the batteries to perform the aforementioned tasks. Scalable designs proposed in the literature still have many limitations, such as suboptimal utilization of the battery packs, low practicality, risk of internal short-circuiting of the batteries, increased weight and size of the battery packs, reliability issues under variable loads, and undesired delays in the reconfiguration of switches. The attributes and issues identified above form the basis of this study. First, the concept of practicality is highlighted for realization of scalable designs in real applications. Scalability associated issues, such as switching risk and sub-optimal sizing are explored. The tree algorithm is applied to develop a scalable design with higher power reliability and faster power redistribution. An SOH balancing method is proposed to optimize the utilization of battery pack. Sample of scalable designs and a physics-based electrochemical battery model are used to implement the proposed algorithms. The results confirm that the proposed SOH balancing can prolong the battery life. Additionally, the tree algorithm based design improves the power reliability, and enables fast redistribution of power.

Parameter Identification for Electrochemical Models of Lithium-Ion Batteries Using Sensitivity Analysis

Abstract Predicting the chemical and physical processes occurring in Lithium-ion cells with high-fidelity electrochemical models is today a critical requirement to accelerate the design and optimization of battery packs for automotive and aerospace applications. One of the common issues associated with electrochemical models is the complexity of parameter identification, particularly when relying only on experimental data obtained via non-invasive techniques. This paper presents a novel approach to improve the common methods of parameter calibration that consists of matching the predicted terminal voltage to test data via optimization methods. The study is conducted for an nickel-manganese-cobalt (NMC)-graphite cell, modeled using a reduced-order Extended Single Particle Model (ESPM). The proposed approach relies on using a large-scale particle swarm optimization (PSO), modified by including a term that accounts for the parameter sensitivity information, such that the rate of convergence and robustness of the algorithm to obtain a consistent solution in the presence of uncertainties in the initial conditions are significantly improved.

Using Virtual Product Development with Design of Experiments to Design Battery Packs for Electrified Powertrain

<div class="section abstract"><div class="htmlview paragraph">Stringent automotive legislation is driving requirements for increasingly complex battery pack solutions. The key challenges for battery pack development drive cost and performance optimisation, growth in architecture solutions, monitoring and safety through lifetime, and faster-to-market expectations.</div><div class="htmlview paragraph">The battery Virtual Product Development (VPD) toolchain addresses these challenges and provides a solution to reduce the battery pack development time, cost and risk. The battery VPD toolchain is built upon scalable, validated sub-models of the battery pack that capture the interactions between the various domains; mechanical, electrical, thermal and hydraulic. The model fidelity can be selected at each stage of the design process allowing the right amount of detail, and available data, to be incorporated. The toolchain is coupled with vehicle simulation tools to rapidly assess performance of the complete electrified powertrain.</div><div class="htmlview paragraph">The aim of this study is to demonstrate an agile approach to battery pack concept development using VPD, enabled by Design of Experiments (DoE) and optimisation. Key battery parameters such as cell type, electrical configuration, thermal heat path design and cooling strategy are chosen as the design variables of a multi-staged DoE. The DoE test matrices of these parameters are generated and imported into the battery VPD toolchain with the vehicle simulation model to perform the energy efficiency and performance simulations.</div><div class="htmlview paragraph">Finally, the simulation results are analysed to create surrogate models which can be used to predict powertrain attributes and optimise the battery pack design. The ability to front-load virtual battery pack concepts with vehicle simulations allow for wholistic performance assessment, ensuring that vehicle attribute targets such as pure electric range of WLTP, acceleration and maximum speed are met and reducing concept development time by up to 50% compared to the baseline approach.</div></div>

Design of battery pack & controller for combined auto driven mini-harvester

The mechanized farming can promisingly increase the profitability and prevent the dependency of farmers on foreign labours. The design and implementation of Battery pack and controller for specially designed combined auto-driven mini harvester is presented in this paper. The mechanical load estimation and its mapping with electrical drives are formulated. The interfacing of electrical drives with remote operation is achieved by Electronic Arduino system. The relay control system is designed with individual drive system. The sketches are mapped with the functionality of drives. The drive selection is a dependant function of mechanical load requirement. The mechanical load estimation is done with actual mechanical failure consideration and design approach. The pin-out connections for all the ports are done on the basis of logical sketch command. The open source Arduino software is used to run the sketches. The sketch written for all the drives is compiled and demo prototype machine is tested for functioning. The run trail is successful and can conclude that the Arduino mega gives the sound interface with 8 channel relay. The computation and measurement results of power requirements for the controller and drive are within the limiting conditions.

Adopting a Conversion Design Approach to Maximize the Energy Density of Battery Packs in Electric Vehicles

Innovative vehicle concepts have been developed in the past years in the automotive sector, including alternative drive systems such as hybrid and battery electric vehicles, so as to meet the environmental targets and cope with the increasingly stringent emissions regulations. The preferred hybridizing technology is lithium-ion battery, thanks to its high energy density. The optimal integration of battery packs in the vehicle is a challenging task when designing e-mobility concepts. Therefore, this work proposes a conceptual design procedure aimed at optimizing the sizing of hybrid and battery electric vehicles. Particularly, the influence of the cell type, physical disposition and arrangement of the electrical devices is accounted for within a conversion design framework. The optimization is focused on the trade-off between the battery pack capacity and weight. After introducing the main features of electric traction systems and their challenges compared to conventional ones, the relevant design properties of electric vehicles are analyzed. A detailed strategy, encompassing the selection of battery format and technology, battery pack design and final assessment of the proposed set-up, is presented and implemented in an exemplary application, assuming an existing commercial vehicle as the reference starting layout. Prismatic, cylindrical and pouch cells are configured aiming at achieving installed battery energy as close as possible to the reference one, while meeting the original installation space constraint. The best resulting configuration, which also guarantees similar peak power performance of the reference battery-pack, allows reducing the mass of the storage system down to 70% of its starting value.

Experimental investigation of thermoelectric cooling for a new battery pack design in a copper holder

Solid-state thermoelectric refrigeration and heat pump systems can be integrated with battery packs in electric vehicles (EV) and hybrid electric vehicles (HEV) for effective thermal management in both hot and cold environments. Operating modes can be switched by changing the polarity of the input voltage to the thermoelectric system. In this paper, a new design of a battery pack is proposed which includes an acrylic battery container, copper battery holders, liquid cooling medium, and battery cells. This battery pack is integrated with a battery thermal management system (BTMS) which includes thermoelectric cooling (TEC) in combination with liquid and air circulations. The aim of the BTMS is to handle heat generation during operation of the battery pack. Heat, generated by the battery pack, is transported to the cold end of the TEC and then dissipated to the surrounding environment by a heatsink. Fundamental design optimization is carried out on a single cell first. System performance is then validated in the battery pack experiments. For the 40 ​V test, the proposed system reached approximately 20 ​°C lower when compared with only liquid cooling. In the 30 ​V power supply test, the battery pack temperature did not exceed 30 ​°C in a period of 5000 ​s. Furthermore, the battery pack temperature was under 60 ​°C at 3000 ​s during a continuous discharge condition with a 50 ​V input, which is considered an extreme condition for battery operation.

Model-Based Design of an Electric Bus Lithium-Ion Battery Pack

Abstract This study details a framework for an iterative process which is utilized to optimize lithium-ion battery (LIB) pack design. This is accomplished through the homogenization of the lithium-ion cells and modules, the finite element simulation of these homogenized parts, and submodeling. This process enables the user to identify key structures and materials to be modified to optimize performance while keeping simulation time per iteration to a minimum. These iterations can be used to accurately estimate the force and strain values at various points including the lithium-ion cells and can be used to determine failure locations. The study demonstrates this through the examination of an electric bus lithium-ion battery pack as it is processed through the aforementioned steps and iterations to arrive at a conclusion that enabled the author to select appropriate fasteners and optimize for lithium-ion battery integrity in the event of a side impact with a pole on the bus chassis and battery assembly. The steps outlined in the study could be expanded to include an array of different loading scenarios and to include additional levels of homogenization/submodeling such as jellyroll components.

Research on the Influence of Battery Cell Static Parameters on the Capacity of Different Topology Battery Packs

The parameter inconsistency of the battery cells and the series-parallel connection mode are closely related to the battery pack capacity. Studying the degree of influence of battery pack capacity by battery cell parameters is of great significance to the series-parallel design of battery packs. This paper establishes battery cell models and battery pack models with different topologies. In the MATLAB/Simulink environment, simulation studies were conducted to study the influence of the battery pack capacity by the monomer parameters as the number of cells in series and parallel in the topology changes. Then, from a statistical point of view, the simulation results were analyzed in principle. Finally, a small-scale battery pack experimental platform was built in the laboratory environment to verify the correctness of the simulation conclusions and theoretical analysis.

Fully coupled simplified electrochemical and thermal model for series-parallel configured battery pack

Battery packs are often designed with multiple battery cells configured in series and/or parallel combinations to meet the energy and/or power requirements of target applications. Modeling of these battery packs is very complex, computationally challenging and requires extending a single cell model to multi-cell models including electrical connections between cells. Also, the cell-to-cell variations of capacity, resistance, and temperature in the pack are vital in the battery pack design and battery management system development. Therefore, a robust modeling platform with in-built physics and fully coupled models both at the cell and the pack level is developed. The modeling framework consists of Simplified Electrochemical and lumped Thermal Model (SEM-T) at the cell level and Equivalent-Circuit Model (ECM) for Ohmic calculations and natural Convective Thermal Model (CTM) for thermal distribution at the pack level. A 7S4P battery pack with 21700 NCA cylindrical cells is considered in this study and the model is validated with the experimental data sets at different c-rates and temperatures. The developed model is able to successfully predict the pack voltage, capacities, and temperatures. The proposed model is computationally efficient and can be easily adopted for on-board implementation in battery management system for safe and reliable operations.

A calibration calorimetry method to investigate the thermal characteristics of a cylindrical lithium-ion battery

Thermal characteristics of lithium-ion battery cells are crucial in the thermal design of power battery packs for electric vehicles. In this paper, a calibration calorimetry method of considering the heat loss is proposed to investigate the thermal characteristics of a commercial cylindrical 21700 cell. In the meantime, an existing heat-flux meter method is employed to analyze the present method effectiveness. Furthermore, a cell thermal model by considering the physical specifications and thermal parameters is established to predict the cell's temperature rise during its operation. It is shown that the proposed calibration calorimetry method matches well with the existing heat-flux meter method in determining the cell heat generation rate. The cell heat generation rate increases as the decreasing temperature and the increasing discharge rate, and there exists a quadratic-relationship in them between each other. The established thermal model to predict the cell temperature rise is effective with accuracy of within 3.0 °C. This work is fast and cost-effective in characterizing the thermal characteristics of the commercial cylindrical cells, without resorting to the specialized instruments.

Competition and Valuation: A Case Study of Tesla Motors

Tesla’s rapid rise to become one of the world’s most influential automakers has marked the start of a new era in the global automobile industry, where many of the traditional auto companies were overshadowed by Tesla’s dominance. Judging from Politics, Economy, Society and Technology perspectives, Tesla’s market value can potentially be overvalued due to its leading role in the Electrical vehicle market. Economically, Tesla facilities the growth of global economy by creating more employments and manufacturing factories. Socially and politically, Tesla’s Electrical Vehicle reduces the level of negative externalities (e.g., pollution), which aligns with the developmental frameworks proposed by governmental policies and regulations. Meanwhile in technological aspect, Tesla pioneers the innovative design of battery pack to reduce the overall cost of battery and seeks to integrate better automatic driving system into electrical vehicle. Given those merits of Tesla, overoptimism on its stock price is expected. Therefore, it is important for stock traders who are willing to throw money at Tesla to ruminate over their choices before making the investment. In this study, the results of valuation methods indicate that true market value of Tesla has been overestimated due to its irregularly high operating cash flow, price-to-earnings ratio and enterprise value to earnings before interest, taxes, depreciation, and amortization ratio, suggesting its stock price is overvalued.

Optimal cell tab design and cooling strategy for cylindrical lithium-ion batteries

The ability to correctly predict the behavior of lithium ion batteries is critical for safety, performance, cost and lifetime. Particularly important for this purpose is the prediction of the internal temperature of cells, because of the positive feedback between heat generation and current distribution. In this work, a comprehensive electro-thermal model is developed for a cylindrical lithium-ion cell. The model is comprehensively parameterized and validated with experimental data for 2170 cylindrical cells (LG M50T, NMC811), including direct core temperature measurements. The validated model is used to study different cell designs and cooling approaches and their effects on the internal temperature of the cell. Increasing the number of tabs connecting the jellyroll to the base of the cylindrical-can reduces the internal thermal gradient by up to 25.41%. On its own, side cooling is more effective than base cooling at removing heat, yet both result in thermal gradients within the cell of a similar magnitude, irrespective of the number of cell tabs. The results are of immediate interest to both cell manufacturers and battery pack designers, while the modelling and parameterization framework created is an essential tool for energy storage system design.

Performance reliability analysis and optimization of lithium-ion battery packs based on multiphysics simulation and response surface methodology

Reliability optimization has always been an important topic in the application of lithium-ion batteries in electric vehicles. To optimize the redundancy and layout design of battery packs accurately and efficiently, a novel reliability optimization method based on a multiphysics coupling simulation and a response surface methodology is proposed. An electrochemical-thermal-fluid dynamics model, a temperature-dependent stochastic degradation model and a multistate performance reliability model are developed. A response surface method with the Box-Behnken design method is applied to reduce the number of simulation trials. Then, the redundancy scheme and two layouts of a battery pack are optimized, followed by a sensitivity analysis of the design parameters. The results show that a large spacing in the direction of air flow contributes to improving system reliability. In this case, for the layout of a cross arrangement with equal spacing, the optimal reliability design scheme of a 5 × 5 parallel series with optimal design parameters can improve the cycle life from approximately 1989 to 2933 when taking 90% system reliability as the criterion. The collaborative optimization of redundancy and layout is of great importance to extend the service life and improve the system reliability of battery packs.

Experimental and numerical approach for analyzing thermal behaviors of a prismatic hard-cased lithium-ion battery

Pinpointing the thermal behaviors of lithium-ion battery cells is a premier work for the thermal design of vehicular traction battery pack. An experimental and numerical approach is developed in this paper to study the thermal behaviors of a prismatic hard-cased cell. A computational model of considering heat loss to analyze the cell heat generation rate was first established, correspondingly a measurement method was presented to reveal the cell heat-generating performance depending on the cell′s temperature evolution of each thermogenic part. A thermal model of considering the cell′s detailed physical specifications was established to numerically analyze the cell′s thermal profile. The results show that there exists an excellent effectiveness in present characterization technique to the cell thermal behaviors. The cell heat generation rate quadratically increases with ascending discharge rate and lower temperature. Effects of lugs and housing on the cell thermal distribution are exceedingly. The cell′s lower part temperature is higher when the cell discharges at the low-rate, however, this phenomenon will be opposite at the high-rate discharge. The present approach has higher cost-advantage to pinpoint the thermal behaviors of the prismatic hard-cased cells when comparing with several recent studies which using the costly calorimeters.

Investigation of the potential for an automated disassembly process of BEV batteries

Current electric vehicle battery recycling processes often begin with the manual dismantling of the battery packs. In consideration of occupational safety and in view of the increasing sales of electric vehicles, an automated dismantling of batteries has to be investigated. Therefore, different manufacturers’ battery pack designs are examined first and especially the common joining elements are determined and characterized. The results show a high diversity between the individual systems, which influences the potential for automation. Based on these investigations, a possible layout of an automated dismantling cell is developed.