Mechanical Design and Packaging of Battery Packs for Electric Vehicles
Abstract
Safety and reliability are the two key challenges for large-scale electrification of road transport sector. Current Li-ion battery packs are prone to failure due to reasons such as continuous transmission of mechanical vibrations, exposure to high impact forces and, thermal runaway. Robust mechanical design and battery packaging can provide greater degree of protection against all of these. This chapter discusses design elements like thermal barrier and gas exhaust mechanism that can be integrated into battery packaging to mitigate the high safety risks associated with failure of an electric vehicle (EV) battery pack. Several patented mechanical design solutions, developed with an aim to increase crashworthiness and vibration isolation in EV battery pack, are discussed. Lastly, mechanical design of the battery pack of the first fully electric bus designed and developed in Australia is presented. This case study showcases the benefits of adopting modularity in the design of EVs. In addition, it highlights the importance of packaging space for EVs, particularly in low-floor electric buses, as weight distribution becomes a challenge in these applications.
... The 1xxx series, particularly AA1050 and AA1060, consisting primarily of pure aluminum, is used in battery pack manufacturing as an alternative to copper to reduce weight and material costs. 1,2 Laser beam welding has gained popularity in battery pack manufacturing, offering competitive advantages, such as low thermal deformation, high depth-to-width ratio, small heat-affected zone, high power density and welding speed, and good adaptability and flexibility. 3,4 One of the leading challenges in laser beam welding of the 1xxx series is the occurrence of weld porosity, which severely affects the reliability of the welding process and can have detrimental effects on the mechanical and electrical performance of the final products. ...
... The laser beam is divided into a finite number of rays, which propagate in the direction of laser beam irradiation. When a ray encounters the surface of the material, it undergoes reflection following vector equation (1). In this equation, R represents the direction of the reflected vector, I denotes the direction of the incoming ray, and n signifies the normal direction of the material surface, ...
In the attempt to produce lighter battery packs at a lower cost, replacing common copper parts with aluminum components has been a popular approach in recent years. With regard to joining technologies, there is a growing interest in applying laser beam welding in battery pack manufacturing due to several advantages such as single-sided and noncontact access while maintaining a narrow heat-affected zone. Motivated by the need to control and reduce weld porosity in AA1060 battery busbar welding with the ultimate goal to enhance durability and reduce electrical resistance, this paper has been developed with the aim to studying the effect of laser beam shaping on porosity formation and, hence, generate knowledge about the underlying physics of the welding process itself. First, a multiphysics computational fluid dynamics model has been developed and calibrated to experimental data; then, the model has been deployed to study the effect of both circular and tailing beam shapes on melt pool dynamics and the evolution of porosity due to the instability of the keyhole. The study elucidated the importance of the keyhole’s necking on porosity formation. Findings showed that the tail beam shapes, compared to the circular spot, have a pronounced effect on the reduction of the necking effect of the keyhole—this helps to reduce number of collapsing events of the keyhole itself, thereby leading to the reduction of porosity formation.
... • Impulse force or crushing force developed due to a sudden crash exerts an enormous number of forces transferring to the module of the pack and to the individual cells which can result in premature failure. The exerted load on the pack is unpredictable and can lose mechanical stability, resulting in thermal runaway [36,37]. ...
... Roland Uerlich et. al. 2019, in their experimental study comparing the space occupancy and volumetric efficiency on rectangular, hexagonal, and trapezoidal geometric module rectangular structure of the pack has 100% volumetric efficiency and 81.79% of space occupancy with 675 cells [36], for which rectangular modules are selected for the analysis. The enclosure must also compile with a high level of packing efficiency and carry all the necessary electronics intact within the structural body. ...
Recently, Electric Two-Wheelers ETW are changing the face of the global automotive market. This study focused on selecting proper material and mechanical isolation gap to design a protective enclosure for the battery pack of ETW. The integration of the Failure, Modes, Mechanism and Effect Analysis (FMMEA) method is utilized to develop the interface matrix and the severity index of different components of the enclosure. By analyzing different forces from the road conditions, dynamics during turn, acceleration, and deceleration with the enclosure, it becomes a crucial load-bearing element. Employing Finite Element Modeling (FEM), structural strength using materials like AL6061, Q235, C22000, DC 01 and Teflon are assessed under varying static, dynamic and thermal conditions. Modal analysis is conducted to observe the excitation frequencies where the maximum deformation for the metal enclosure is observed beyond 500Hz. AL6061 material that can withstand the stresses and deformations that are under allowable stress limits with negligible deformation is most preferable material based on the results. Minimal of 2.5 mm gap to be provided in case of metal casing and 10mm in case of Teflon is proven.
... This practice aims to define a module that can be shared and re-used in different battery layouts without affecting other components of the system [60]. Arora and Kapoor reported a modularity-in-design example in [61]. This study describes modularity in the context of design for safety and reliability. ...
Nowadays, battery design must be considered a multidisciplinary activity focused on product sustainability in terms of environmental impacts and cost. The paper reviews the design tools and methods in the context of Li-ion battery packs. The discussion focuses on different aspects, from thermal analysis to management and safety. The paper aims to investigate what has been achieved in the last twenty years to understand current and future trends when designing battery packs. The goal is to analyze the methods for defining the battery pack's layout and structure using tools for modeling, simulations, life cycle analysis, optimization, and machine learning. The target concerns electric and hybrid vehicles and energy storage systems in general. The paper makes an original classification of past works defining seven levels of design approaches for battery packs. The final discussion analyzes the correlation between the changes in the design methods and the increasing demand for battery packs. The outcome of this paper allows the reader to analyze the evolutions of the design methods and practices in battery packs and to understand future developments.
... However, it is important to highlight that the impact of the current and thermal imbalances is limited to Module 1, thus the other modules (Module i, ∀i = 2, . . . N ) are not affected by cell 11 , according to the pack-level KCL reported in (5). Differently, with reference to the pack-level KVL reported in (6), the voltage of the whole battery pack is affected by the voltage of Module 1, which is strongly related to the behavior of cell 11 . ...
Nowadays, the series-parallel (SP) and the parallel-series (PS) configurations represent the main architectures considered for designing a battery pack. In both architectures, cell-to-cell parameters’ variations due to manufacturing tolerances, thermal gradients, and cell degradation can strongly impact the overall performance of battery packs. However, the effect of the parameter variation on the pack performance changes depending on the architecture and the number of cells. This manuscript aims at providing a method for the assessment of the impact of cell-to-cell parameters’ variations due to potential different aging and thermal conditions for the cells in a generic SP and PS pack architecture. For this purpose, a generalized reduced order equivalent circuit model for the battery pack is defined, leading to a set of steady-state equations for easily and systematically calculating the current and voltage imbalances due to capacity and internal resistance variations independently from the pack architecture and the number of cells. A parametric analysis is reported for quantitatively evaluating the severity of the imbalances due to the cell-to-cell parameters’ variations for both battery pack architectures. The results of the comparative analysis demonstrate that PS architecture is more impacted by parameters’ variations with respect to the SP one, since a higher current imbalance is always obtained. The difference in the severity of the current imbalance in the pack architectures strongly increases as the number of series-connected cells rises. Moreover, among the cell parameters’ variations, a major impact of the capacity imbalance on the reduction of the overall performance of the battery pack is observed.
... Two indicators are used to determine the energy absorption capability of a structure: the amount of energy dissipated by deformation and the peak crushing force registered during deformation. The peak crushing force is related to deceleration during impact, and the energy absorption is determined by measuring the value of the crushing force as the structure deforms [3][4][5]. ...
It is necessary to reduce the weight of components while maintaining or improving their mechanical properties to withstand dynamic loads in lightweight structures. In this study, heat treatment and a trigger mechanism were implemented for a thin-walled tube of aluminium to increase energy absorption while reducing the peak crushing force. Different geometries and locations were proposed to trigger deformation in a controlled manner, in combination with heat treatments. Experimental designs for each energy absorption mechanism were performed, and designs were tested by quasi-static crushing. Data obtained from experiments were used to calculate energy absorption indicators that were used to compared designs with components without mechanism to analyse performance. By comparing proposed designs with tubes without modification, the best combination of design variables for each trigger mechanism were identified. It was determined that 160 mm from the upper side, 250 mm2 area and a rectangular trigger shape reduced peak crushing force by 22.03% and increased energy absorption by 37.76%. For heat treatment, the optimal combination was heating in a furnace at 175 ∘C for 1 h and cooling in water at 70 ∘C during 10 min while only soaking half of its length. This combination reduced peak crushing force by 19.02% and increased energy absorption 15.08%. When these mechanisms were combined on a single tube, peak crushing force was reduced by 21.63%, and energy absorption increased by 42.53%.
div class="section abstract"> Making a sturdy battery box or enclosure is one of the many challenging issues that the expansion of electrification entails. Many characteristics of an effective battery housing contribute to the safety of passengers and shield the battery from the harsh environment created by vibrations and shocks due to varying road profiles in the vehicle. This results in stress and deformations of different degrees. There is a need to understand and develop a correlation between structural performance and lightweight design of battery enclosure as this can increase the range of the drive and the life cycle of a battery pack.
This paper investigates the following points: I) A conceptualized CAD model of battery enclosure is developed to understand the design parameters such as utilization of different material for strength and structural changes for performance against vibration and strength.
II) Further, the study would be followed with a series of Finite Element Analyses (FEAs) on simplified models for different load cases, modal analysis, and random excitations of acceleration. The responses of the numerical experiments are the stiffness and natural frequency, evaluated together with the mass of the system.
III) Finally, Design gauge optimization for the battery enclosure is explored through thickness analysis, showing improvement in the static and dynamic characteristics.
The introduction of numerical procedure and design optimization process is shown to be beneficial to reduce the number of physical tests and product development cost and cycle.
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Reducing greenhouse gas emissions has become a priority for civil transport aviation. One of the possible solutions investigated by current aeronautics research is the introduction of electric propulsion, which would drastically reduce greenhouse gas emissions related to flight. This paper addresses this topic in depth; the work is structured in two intertwined parts. The first relates to an extensive review of the state of the art, starting with the analysis of electrical technology enablers for aviation applications, and leading to the investigation of current proposals of aircraft conceptual designs, both for short-medium range and regional class. This review section, which is presented with a critical approach, provides the relevant indications for the definition of the technical framework of the second part of the paper, in which the conceptual development of a novel hybrid-electric aircraft is proposed. Specifically, the outcomes from the analysis of the state of the art suggest that the hybrid-electric aircraft should belong to the regional category, and that energy efficient solutions for the airframe should be considered. Moreover, potentials and limitations of integrating hybrid-electric propulsion are carefully detailed, and reasonably realistic technology levels for the next decade have been selected for the design of the proposed aircraft. A box-wing airframe architecture has been adopted as it has the potential to minimize induced aerodynamic drag while increasing the load transport capacity, thus representing an aerodynamic efficient solution. A design and optimization framework has been developed to evaluate the integration of the hybrid-electric propulsion with the box-wing lifting system. The coupling of these two technologies, together with a paradigm change in the aircraft design approach, allow to identify conceptual solutions that minimize fuel consumption throughout the typical regional mission envelope, leading to a potential emission-free regional aircraft.
div class="section abstract"> The increased prevalence of larger and more energy-dense battery packs for transportation and grid storage applications has resulted in an increasing number of severe battery thermal events. The implications on product reliability, consumer safety, and the surrounding environment are significant. While there are many potential root causes for battery thermal runaway, these events often start within a single battery cell or group of cells that cascade to neighboring cells and other combustible materials, rapidly increasing the hazard profile of the battery pack as more stored energy is released. Reducing these hazards requires preventing severe thermal runaway scenarios by mitigating cell-to-cell propagation through the improved design of both individual cells and battery packs.
This work provides a fundamental understanding of how thermal runaway events can start in large-format battery packs, the mechanisms for thermal runaway propagation between individual cells, and the mitigation strategies currently available on the market. Understanding these mechanisms and implementing appropriate mitigation strategies into battery packs can enable the design of less hazardous and more reliable battery systems. There is an interplay between mitigation strategies and the ever-increasing energy density of cells toward enabling improved duration and longer-range applications, which will be highlighted below.
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Safety failures in energy storage systems are gradually increasing in urban electric transport. Under mechanical impact conditions, lithium-ion cells can present damage. The main objective is to develop and evaluate the storage system of an electric bus under dynamic impact. The dynamic simulation has been done in LS Dyna® to analyze indenter effects, at different heights, on a battery module placed on the roof of an electric bus. A simplified CAD model of the main components of the module was proposed. Similarly, only the protective housings were analyzed for the modeling of the 18650 cells. The results show the impact's stress and deformation in the cells.KeywordsSDG11Electric vehiclesE-BusEnergy Storage SystemCylindrical lithium-ion cellsDynamic impact
A thermal management system is provided that minimizes the effects of thermal runaway. The system includes a sealed battery pack enclosure configured to hold a plurality of batteries and at least one exhaust nozzle assembly. The exhaust nozzle assembly includes an exhaust nozzle that passes and directs the flow of hot gas from within the battery pack to the ambient environment during a thermal runaway event, a nozzle seal mounted within the exhaust nozzle that seals the exhaust nozzle during normal operation of the battery pack, and a shape memory alloy (SMA) retaining member that is configured to capture an end portion of the nozzle seal and hold the seal within the exhaust nozzle when the SMA retaining member is configured in its first shape, and that is configured to release the seal from the exhaust nozzle when the SMA retaining member is heated to its transformation temperature.
A spacer assembly, comprised of a plurality of rigid spacers, is provided that is configured for use with a cell mounting bracket within a battery pack. The spacer assembly maintains the positions of the batteries within the battery pack during a thermal event and after the cell mounting bracket loses structural integrity due to the increased temperature associated with the thermal event. By keeping the battery undergoing thermal runaway in its predetermined location within the battery pack, the minimum spacing between cells is maintained, thereby helping to minimize the thermal effects on adjacent cells while ensuring that the cooling system, if employed, is not compromised. As a result, the risk of thermal runaway propagation is reduced.
As society becomes increasingly more dependent on electricity, the development of systems capable of storing directly or indirectly this secondary energy form will be crucial for the 21st century. Batteries, which are devices converting the energy released by spontaneous chemical reactions to electricity work, have some extraordinary properties in these regards. They store and release electrical energy; they are portable and can be used flexibly with a short lead time in manufacture. By placing electrical separators between the electrodes, the flow of electrons from one electrode to the other is only permitted through a circuit external to the cell. Internally, the electrical circuit is completed by ion transport through an electrolyte and porous separator or solid state ionic conductor. The main parameters of energy storage systems are energy density (gravimetric and volumetric), power density, energy efficiency and energy quality [1].
Thermal management is critical for large-scale, shipboard energy storage systems utilizing lithium-ion batteries. In recent years, there has been growing research in thermal management of lithium-ion battery modules. However, there is little information available on the minimum cell-to-cell spacing limits for indirect, liquid cooled modules when considering heat release during a single cell failure. For this purpose, a generic four-cell module was modeled using finite element analysis to determine the sensitivity of module temperatures to cell spacing. Additionally, the effects of different heat sink materials and interface qualities were investigated. Two materials were considered, a solid aluminum block and a metal/wax composite block. Simulations were run for three different transient load profiles. The first profile simulates sustained high rate operation where the system begins at rest and generates heat continuously until it reaches steady state. And, two failure mode simulations were conducted to investigate block performance during a slow and a fast exothermic reaction, respectively. Results indicate that composite materials can perform well under normal operation and provide some protection against single cell failure; although, for very compact designs, the amount of wax available to absorb heat is reduced and the effectiveness of the phase change material is diminished. The aluminum block design performed well under all conditions, and showed that heat generated during a failure is quickly dissipated to the coolant, even under the closest cell spacing configuration.
In current electric vehicles batteries fulfill only the role of power source and are stored within the passenger cabin, protected from external impact loads. This study considers a multifunctional, damage tolerant battery system which combines the energetic material with mechanically sacrificing elements that control mechanical stresses and dissipate energy. With such a multifunctional battery system in place it is proposed to place the battery pack into the secondary safe zone of a unibody-type vehicle. Full-vehicle crash analysis via finite element simulations are conducted for several battery pack configurations, thereby comparing the multifunctional battery system to battery packs with batteries alone and battery packs where cellular solids are used as energy absorbers. The analysis demonstrates the use of a multifunctional (damage tolerant and energy storage capable) battery system to ensure battery safety and aid in the energy absorption in a crash overall. The use of the multifunctional battery systems can aid in solving technology limitations of electric vehicles.
The critical challenges to enlarge the market share of electric vehicles (EVs) are cost, performance, reliability and safety. These issues are closely linked to the energy storage system in the EVs. Lithium-ion batteries have revolutionized the EV industry to become the preferred battery choice for EVs. This is due to their outstanding characteristics including high energy density, high voltage, low self-discharge rate, long cycle life, high charging and discharging rate capability. In EVs, Lithium-ion cells are connected in series and/or parallel to deliver the required power to the traction motor and auxiliary systems. However, due to the operating environment of EVs, the Lithium-ion battery may not perform to the best of its ability when integrated into an EV battery pack. In this work, the integration of Lithium-ion battery into an EV battery pack is investigated from different aspects, namely different battery chemistry, cell packaging, electric connection and control, thermal management, assembly and service and maintenance. In addition, benchmarking study using different cell packaging of Lithium Iron Phosphate cell as an energy storage system is conducted. This study provides a basic guideline for cell selection and integration of cell for the EVs battery pack.
Battery packs are highly sensitive to operating environment and their interactions with other systems in electric vehicles (EVs). Control of the operating environment and understanding of the influences of these interactions on battery performances are required to maximise their energy capacity and cycle life in EVs. This paper presents a modified parameter diagram (P-diagram) which is a part of systematic effort to design a robust battery pack. In the modified P-diagram, the physical inputs that affect the performance of a battery pack are identified and categorised into noise factors and control factors, where the former limits the performance and the latter can be used to improve it. Different noise factors are conceptually analysed in conjunction with various control factors and graded according to their relative influence on the performance of a battery pack. The performance is measured in terms of ideal function output and potential error states. The error states are subsequently broken down into inherent losses and undesired response(s). With such systematic understanding, a robust battery back can be designed for EVs.
There has been little published research critically examining the mechanical integration of battery systems within either EVs or HEVs. Many of the existing Standards are designed to validate the fail safe function of the battery pack as opposed to assessing the mechanical durability of the complete system. If excessive vehicle warranty claims are to be avoided it is important that engineers tasked with the design of the battery installation properly understand the magnitude and frequency of the vibration inputs that the battery will be exposed too during the vehicle's predicted life. The vibration characteristics of three different commercially available EVs have been experimentally evaluated over a wide range of different road surface conditions. For each vehicle, a durability profile has been sequenced to emulate the vibration energy that the battery pack may be exposed too during a representative 100,000 miles service life. The primary conclusions from the results presented are that the battery packs may well be exposed to vibration loads outside the current evaluation range of existing Standards.