structure of new energy vehicle battery PACK

Research on the lightweight structure of new energy vehicle battery PACK cases Fasteners industry solutions

By analyzing the research status of existing battery pack cases, the material selection, structural design, and manufacturing technology of battery pack cases are sorted out. In terms of material selection, a lightweight alloy box is the main material used in the lightweighting of the battery pack box; in terms of structural design, the impact-resistant structure of the box, reinforcement, and internal module partition are important factors considered in the design. Body-chassis battery pack structural integration, one-time molding, and connection technology will be the main trends of the battery pack box structure design. If you need to manufacture or supply EV automotive Flange Nuts, Flange screws, Hexagon High-Strength Nuts, Square Head Nuts, Nylon Nuts, Cap Nuts, Assembled Washer Nuts, Hexagon Slotted Nuts, Castle Nuts, Sealed blind rivet nuts, Wheel Nuts, Welding Nuts, Coupling Nuts fasteners, you can always contact our customer service team at Adelajonly@gmail.com or www.juxinfasteners.com.

New energy vehicles, in the case of the total energy of the battery system, do not change the battery system to reduce the quality of the battery system, which can effectively improve its range. Electric vehicle quality reduction of 10% can improve the range of 5.5%. The weight of the battery system accounts for a large proportion of the total weight of new energy vehicles. Compared with traditional fuel vehicles, electric vehicles, the core of the three electric systems (batteries, motors, electronic control) and intelligent equipment, making electric vehicles compared to similar models of electric passenger car weight increased by 10% -30%, electric commercial vehicle weight increased by 10% -15%, of which the battery Pack Pack accounted for the vehicle's overall quality of 18% to 30%. Material iteration + structural optimization, lightweight structural components. Taking the Tesla Model 3 as an example, among the main components of the battery Pack, the largest mass is the cell body (62.8%), followed by the lower box of the Pack (6.2%), the module shell and bracket (12.3%), and the integrated system of BMS and other components (11.1%). Starting from these components, through the replacement of materials and optimization of structural design, the development of lightweight batteries. Cell to pack (CTP): technology that reduces or removes the three-stage pack structure of battery "cell-module-pack".

Currently, there are two different technology routes: the complete elimination of modules, represented by blade batteries, and the combination of small modules into large modules, which improves energy density and volume utilization; in CTP, it is more difficult to manage the thermal runaway of the battery cells, and there are higher requirements on the internal structure of thermally conductive adhesive to dissipate the heat of the modules, as well as on the external thermal insulating adhesive to insulate the heat and flame retardant.

Electric vehicle powertrain is a complex structural body combining mechanical and electrical, and its stiffness, strength, vibration, and service life should be fully considered during design. With the urgent demand for high energy density and short charging time of electric vehicles, the application of ternary cathode materials and fast charging technology makes lithium-ion batteries very susceptible to mechanical abuse, electrical abuse, and thermal abuse, which in turn leads to thermal runaway of the battery system and fire and explosion of the whole vehicle, so the power of the lithium-ion batteries has become a hotspot and a difficulty in the field of new energy automobile power system research. The battery pack case (shell) is the primary bearing part of the battery pack, with only the case's static and dynamic (stiffness, modal, etc.) stability to ensure that the power battery does not abuse the working conditions so that the power system runs smoothly.

1. Battery pack case material lightweight research

Battery pack case materials should be characterized by electrical insulation, high heat dissipation chemical stability, etc. The case is generally composed of upper and lower cases and sealing systems. The quality of the battery pack accounts for 18% to 30% of the total vehicle system quality, while the quality of the case accounts for about 10% to 20% of the total quality of the battery pack. At present, metal is commonly used as the battery pack case material, and composite materials have also been gradually emphasized due to their excellent specific stiffness.

2. Battery pack case with metal materials

Among the metal materials used in the battery pack case, steel plate material has a simple manufacturing process, low cost, good thermal conductivity, impact resistance, and thermal management capability, and is the commonly used material for the case, but its main drawback is its large mass. With the deepening of the concept of automotive lightweight design, aluminum alloy has gradually become the main material for realizing automotive lightweight due to its advantages of low density, high rigid strength, and good die-casting performance, and cast aluminum battery box, aluminum sheet battery box and aluminum profile battery box have been produced. Among them, the bearing structure of aluminum battery pack boxes is mainly divided into bottom plate type and frame type. VW company research found that the frame-bearing structure of the box can meet the strength requirements of different structures, and it is easier to realize lightweight. In addition, the combination of metal and plastic is also the main way to realize the lightweight of the battery pack case, such as (Pro EV500) battery pack, the upper and lower shells are made of Sheet Molding Com⁃pound (SMC) and high-strength aluminum, respectively. Considering the cost, processing, and other factors, the battery pack shells of entry-level and economical electric vehicles mostly use steel cases, and some new energy vehicle battery packs use metal case materials.

3. Battery pack case composite materials

Battery pack cases using composite materials, such as carbon fiber composites, glass fiber reinforced composites, SMC composites, and other lightweight materials, different materials made of battery pack case structure, scholars at home and abroad on composite cases and also targeted research. For example, foam aluminum composite sandwich material successfully reproduced a 20 kW-h battery pack in a lower case, reducing the lower case quality by 10% to 20%. Choi et al. nylon 6 (PA6) as a substrate by changing the content of carbon fibers and glass fibers (the total amount of fibers doped not more than 40%) to satisfy the strength, impact, and other properties of the conditions of the Succeeded in developing a reinforced plastic lower case that reduces mass by 31% compared to ordinary steel. The carbon fiber battery pack case reduced the case mass from 110 kg to 19 kg. Carbon fiber-reinforced composite materials with low density, high stiffness, and other advantages have been used in many battery pack cases. Germany ICT Institute of Chemical Technology developed a polyurethane-based thermosetting plastic battery pack box with a box quality of 35 kg, which can carry 340 kilograms of battery packs, compared to the exact specifications of steel quality reduction of more than 35%. Using continuous glass fiber woven fabric as the base material and epoxy vinyl resin as the matrix of the glass fiber reinforced composite material through the prepreg molding process to make the battery box also achieves a lightweight effect.

The lightweight R&D and design process of battery packs will continue, but the high manufacturing costs associated with new materials and methods are not conducive to large-scale applications. The design of a power battery pack case for new energy vehicles needs to consider the internal heat dissipation, waterproofing, dustproof, and safety of the battery pack, so it will be an essential challenge to balance the lightweight and other performance of the power battery pack.

4. Battery Pack Shape and Arrangement

At present, the battery pack structure of new energy vehicles mainly includes the "earth" type, "concave" type, "T" type, and "skateboard" type. "Its shape and arrangement are primarily affected by the development platform of the model. The arrangement of the battery pack box makes full use of the space structure between the automobile floor and the ground so that it can be fully adapted to the passenger compartment floor. Still, the upper shell is close to the body floor, and the floor part of the structure will conflict with the battery pack box, so the battery pack arrangement should also consider the gap between the floor of the car and the car and other factors. So, the layout of the battery pack should also consider the gap between the battery pack and the body floor and other factors. The thickness of the stamping material used for the box is correspondingly reduced in the structure and assembled with an external convex rib, simplifying the battery pack's structural features, reducing the quality, and improving the battery pack's sealing and reliability. Still, the battery pack lacks an effective thermal management system for the battery, which reduces the performance in extreme environments. In the design of the battery pack box structure, the battery pack is integrated with the body chassis, which significantly saves the space used and utilizes the frame of the entire vehicle to protect the battery pack. This structure has become a significant trend in the design of battery packs for electric cars.

The arrangement of electric vehicle battery packs needs to be designed according to the overall spatial structure and layout of the car, and the ground clearance, driving mode, and load are essential factors to be considered. With the continuous breakthroughs in battery pack technology, the arrangement is more scientific and reasonable. The arrangement of the bottom plate can reduce the center of gravity of the body, improve the handling stability of the vehicle, optimize the collision transmission path, and it has become the primary way of battery pack arrangement.

5. Battery pack lower box structure

As a load-bearing component of the battery pack system, its lowercase's internal structure and layout directly affect its service life. The internal layout of the lower box is related to the design of its crash-resistant structure, reinforcement, and internal module partition.

For the design of the lower box collision structure, due to the complexity of the road and the diversity of collision forms, it is not guaranteed that an impenetrable lower box structure can be designed, and scholars around the world have conducted relevant research on the collision structure of the battery pack box. By choosing different materials and thicknesses of aluminum alloy box to verify the compressive performance of the battery pack structure and the local deformation of the battery, the results show that the failure displacement of the bottom plate of the battery pack box is independent of the plate thickness. The battery pack case with a double-layer protection plate and foam sandwich plate has an excellent anti-crash effect. In addition, some scholars have also established a finite element model of the battery pack box body and analyzed the safety performance of its frontal and side collision. It is generally agreed that selecting the energy-absorbing sandwich structure and double-layer structure for the lower box collision structure can improve the collision safety of the lower box body of the battery pack.

To avoid damage from compression and impact deformation, and at the same time to meet the lightweight design concept, the reinforcing plate with local reinforcement has also received attention. Scholars around the world have studied it. The battery pack box is set with reinforcing bars so that the box is not easy to deform when subjected to force, and at the same time, it fixes the battery pack array, improves the bending and torsion strength, and improves its resistance to imbalance. Reinforcement bar design should fully consider its cross-section, the direction of the starting bar, and layout to ensure the box's stiffness as much as possible to reduce its space occupancy inside the battery box.

New energy vehicle battery packs are mostly 2-layer or multi-layer arrangements, and there are partitions inside the battery box to realize the installation and fixation of each layer of the battery pack. Partition design should consider its stability with the box and connecting structure to ensure the rigidity of the partition under the conditions, as far as possible, to reduce the quality. The interior of the battery box is mainly arranged in the form of through-section beams, tubes, and tubular beams, with multiple cross beams and longitudinal beams dividing the interior of the battery pack into multiple battery module installation areas. Part of the new energy vehicle battery pack has a lower shell inside.

6. Optimization of battery pack case lightweighting method research

To develop products with excellent and stable performance in a short period, the research and development stage not only uses traditional testing techniques but also often uses finite element simulation technology to assist in completing the optimization design of the product. International experts and scholars in the battery pack box lightweight simulation optimization also carried out targeted research, such as Hartmann et al. using finite element optimization software OptiStruct on the electric vehicle battery pack box shape optimization design, successfully reduce the wall thickness of the battery pack box, so that the overall quality of 20% reduction; Wang et al. to establish a finite element model of the battery pack, multi-objective topology optimization, and establish the optimal distribution of materials. Wang et al. established a finite element model of the battery pack, carried out multi-objective topology optimization, and established the optimal distribution of materials, which reduced the mass of the battery pack case by 10%; Kaleg et al. optimized the thickness of the battery pack plate by using aluminum alloy and obtained the battery pack case with the best quality; LIU et al. developed an optimal design method of carbon fiber woven fabric, and the design of the battery pack case was optimized by using aluminum alloy.

7. Lightweight battery pack case manufacturing technology

Manufacturing technology is crucial to determining whether the battery pack case can be commercialized. The battery pack case molding technology and connection technology are also necessary to achieve its lightweight. Optimization from the box body molding technology and connection technology can, to a certain extent, also reduce the weight of the battery pack.

8. Battery pack case molding technology

Battery pack box body molding technology, is mainly based on the choice of materials used to determine the current aluminum and fiber-reinforced materials for the battery pack box body materials; different companies use different molding technologies. The central forming technology of aluminum plates is stamping aluminum welding, extrusion aluminum stirring friction, and casting. Under the condition of not changing the box's strength, the Tesla Model series and BMW i3 use a stamped aluminum welding process to reduce the box mass by 40%; the Volkswagen Golf GTE plug-in hybrid and BMW X5 battery pack box are made by casting molding process. There are also some new aluminum alloy forming technologies, such as aluminum alloy large parts vacuum die casting technology and aluminum alloy semi-solid rheological die casting technology; the latter's cost is only slightly higher than the conventional die casting and can achieve 35% to 48% of the effect of lightweighting, the application of automotive parts is extensive, is expected to become the primary manufacturing process of the battery pack box in the future.

There are numerous composite molding processes, such as hot press tanks, resin transfer molding (Resin Transfer Molding, RTM), vacuum introduction, injection, extrusion, and jetting. In the production and manufacturing process, the most suitable manufacturing process can be selected according to the characteristics of the parts, cost, and the type of composite material chosen. Currently, injection one-shot molding is often used to produce fiber-reinforced composite battery pack cases. Carbon fiber-reinforced composites are only used in some models. After the material and manufacturing costs drop to a certain degree, carbon fiber composite boxes will be the mainstream of new energy vehicle battery pack boxes.

9. Battery pack box connection technology

The battery pack box from the pure metal box to the metal-composite hybrid box transitions to the combination of heterogeneous materials as the main form. The most significant advantages of heterogeneous materials connected to the composite structure are fatigue resistance, corrosion resistance, and better lightweight, incredibly lightweight. The primary connection between different materials is glued, mechanically attached, and mixed. At present, the new energy vehicle box to aluminum or mixed materials, mostly fasteners with high-strength flange bolts, hexagonal flange face female form of a fixed connection, aluminum box and the body of the connection of higher stability requirements, mainly with lap bolts, riveted pieces of waterproof rivet nut and the reinforcement of the connection. In the battery pack box itself connection technology, scholars at home and abroad have also carried out research. Schneller et al., in the case of no damage to the fiber material, adhesive bonding, and other ways to achieve a good connection between the sandwich structure of the battery pack box parts. The 5052 aluminum alloy battery pack case's sealing welding was successfully completed using Tungsten Inert Gas (TIG) welding. The aluminum alloy battery pack case was connected by Flow Drill Screw (FDS) process, which realized the compelling connection between the aluminum alloy case plates. The research results of international battery pack case connection technology are systematically analyzed. It is proposed that fasteners are the main form of battery pack case connection at present, and some specific materials need to be sealed by laser welding. The connection between dissimilar materials must be targeted according to their connection parts, rigidity, and strength requirements to choose the appropriate connection method.

Each enterprise adopts a different method for the battery pack box and the body of the connection form, so the current international research results are few. For example, the carbon fiber box and the connection body often use metal joints, joints, and materials. The body structure layer uses adhesive bonding assistance bonding and is fixed in a hybrid connection. "Mechanical fixing + gluing" hybrid connection can also effectively improve the fatigue strength of lightweight components and body structure, torsional stiffness, and crashworthiness, and make the connection stable.

10. Power battery pack standards and performance evaluation methods

The safety of battery packs for electric vehicles is getting more and more attention. Due to the variety of battery packs and the different environments of electric cars, the relevant standards for power battery packs at home and abroad are also different. Currently, the standards for power battery packs are mainly formulated by the European Union, the International Organization for Standardization, China, the United States, and Germany. Safety is a key factor restricting the application of battery packs. The standards of various countries have explicit provisions on safety evaluation methods, and the main content of the evaluation centers on three aspects, namely mechanical safety (vibration, shock, and drop, etc.), environmental safety (thermal shock and thermal stability), and electrical safety (short-circuit and over-charging and discharging).

Conclusion

Comprehensive international battery pack case materials and structures used in the choice of materials: if you choose metal as the case material, the manufacturing process is not one-time molding, and the need for follow-up welding (the need to use high-strength welded bolts, welded nuts) reinforcement and other steps to increase the quality of the battery pack; if you choose composite materials, you need to balance the manufacturing cost of the battery pack case, stiffness and fatigue durability, and other properties. The battery pack case is mainly based on an aluminum alloy lower case and SMC composite material upper cover, and the mixed material case structure will be the primary development trend. In the structural design, the battery pack box needs to consider the space, sealing, heat dissipation collision safety performance, and other factors, and at the same time, needs to ensure that the battery pack box on the upper and lower structural connections and the reliability of the entire box and the connection of the body, the comprehensive body - chassis battery pack structural integration and the battery pack box lightweight materials used in lightweighting will be the two most important direction of development of lightweighting. In addition, the battery pack performance test evaluation standards should increase the vehicle level and the whole life cycle of the comprehensive verification.

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