In recent years, climate change has become a global focus, with increasing emphasis on environmental protection and sustainable development. In this context, electric vehicles (EVs) have emerged as a critical solution. Compared to traditional internal combustion engine vehicles, EVs offer lower carbon emissions and higher energy efficiency. From both environmental and economic perspectives, the promotion of EVs holds profound significance for achieving sustainability. While reducing energy consumption and carbon emissions, EVs provide new solutions to the depletion of petroleum resources. Therefore, the optimization and improvement of EV technology are integral to national development strategies, and the power EV battery pack, as a core component, plays a vital role.
The EV battery pack is one of the most important parts of an electric vehicle, as its performance and quality directly impact the vehicle’s safety and functionality. Consequently, researchers worldwide have extensively studied the structural design of EV battery packs. In this work, we aim to enhance the lightweight effect and safety performance of a commercial vehicle EV battery pack. Based on safety test requirements from national standards, we first analyze the original all-aluminum EV battery pack under various conditions, identify design flaws, and then propose a novel lightweight structure with multi-material integration. Through finite element simulations and optimization, we develop an optimized EV battery pack frame structure that meets safety standards while achieving significant weight reduction. Physical extrusion tests validate our design, demonstrating improved performance and lightweight outcomes.
To begin, we establish a finite element model of the original all-aluminum EV battery pack for analysis. The EV battery pack structure primarily consists of a plastic upper cover, battery modules, an all-aluminum lower shell with an integrated cold plate, and connection boards. The lower shell is welded from aluminum alloy profiles and plates using 6061 material, with a total mass of 16.64 kg. After geometric cleaning and simplification, we import the model into Hypermesh for meshing. Most parts are discretized with shell elements, while thicker sections use solid elements. The mesh size ranges from 3 to 5 mm, resulting in 363,149 shell elements and 28,848 solid elements. Welds are simulated via node coupling, bolt connections with rigid elements (RB2/RigidBody), and a concentrated mass of 0.3 tons is applied at central nodes to represent the EV battery pack and other components. The aluminum alloy is modeled with material type 82 to capture anisotropic damage under large deformations, using a failure strain of 0.08. Basic material properties are summarized in Table 1.
| Material | Poisson’s Ratio μ | Elastic Modulus E (GPa) | Yield Strength σ (MPa) | Density ρ (t/mm³) |
|---|---|---|---|---|
| 6061 | 0.33 | 70 | 370 | 2.7×10⁻⁹ |
We first perform modal analysis on the EV battery pack to determine its natural frequencies, as resonance can occur if excitation frequencies match these frequencies during vehicle operation. Using Optistruct software and the Lanczos method, we compute the first four free modal frequencies, as shown in Table 2 and Figure 1. The vibration sources in EVs mainly include the excitation frequency from the driving motor (typically below 25 Hz) and road-induced frequencies due to uneven surfaces. The road excitation frequency can be calculated as:
$$ f = \frac{V}{3.6L} $$
where \( f \) is the excitation frequency in Hz, \( V \) is the vehicle speed in km/h, and \( L \) is the road unevenness wavelength in meters. For common road types, wavelengths vary: smooth highways (1.0–6.3 m), gravel roads (0.32–5.6 m), and unpaved roads (0.77–2.5 m). Given that the commercial vehicle operates primarily on urban flat roads at speeds up to 100 km/h, the maximum road excitation frequency is less than 27.78 Hz. Therefore, to avoid resonance, the EV battery pack’s natural frequencies should exceed 30 Hz. From Table 2, the first natural frequency of the original EV battery pack is 46.2 Hz, which meets this requirement, indicating satisfactory vibration safety.
| Mode Order | Frequency (Hz) | Mode Shape Description |
|---|---|---|
| 1 | 46.2 | First bending |
| 2 | 61.1 | First torsion |
| 3 | 66.8 | Local mode |
| 4 | 157.9 | Second bending |
Next, we conduct dynamic performance analyses based on the national standard “Safety Requirements for Traction Batteries of Electric Vehicles” (GB 38031-2020). Three dynamic conditions are considered: impact, simulated collision, and extrusion. For the impact condition, the EV battery pack is fixed at connection points, and a sinusoidal acceleration pulse of 7g in the Z-direction is applied for 6 ms. For the simulated collision condition, accelerations of 28g in the X-direction and 15g in the Y-direction are applied for 120 ms. For the extrusion condition, a semi-cylindrical rigid indenter with a radius of 75 mm applies gradually increasing force up to 100 kN in the X and Y directions, with a rigid plate as support. We use LS-DYNA software for these simulations, with self-contact between components (friction coefficient 0.2) and surface-to-surface contact between the EV battery pack and indenter/support (friction coefficient 0.2). Results are summarized in Table 3 and Figure 2.
| Condition | Maximum Stress (MPa) | Extrusion Force (kN) |
|---|---|---|
| Impact | 186.9 | N/A |
| X-direction Collision | 324.5 | N/A |
| Y-direction Collision | 59.2 | N/A |
| X-direction Extrusion | N/A | 106.7 |
| Y-direction Extrusion | N/A | 76.9 |
From these results, the original EV battery pack shows adequate performance in impact and collision conditions, with stresses below the yield strength (370 MPa), though the safety margin is narrow in X-direction collision. However, in the Y-direction extrusion, the EV battery pack can only withstand 76.9 kN, significantly below the required 100 kN, indicating a design flaw in anti-extrusion capability. This highlights the need for structural improvements to enhance the safety of the EV battery pack.
To address these issues, we redesign the EV battery pack structure. The original all-aluminum lower shell integrates a cooling plate, which has thin walls and poor cooling efficiency. We propose a novel lightweight structure that separates functions into distinct components: an aluminum frame, a plastic flow channel plate, and a thermal conductive aluminum plate. This multi-material fusion approach aims to improve strength, reduce weight, and enhance thermal management. The EV battery pack frame, made of aluminum extruded profiles via laser welding, provides primary load-bearing capacity against impacts, collisions, and extrusions. The plastic flow channel plate, molded into an S-shaped parallel flow path, is bonded to the aluminum plate to form a sealed cooling system. This design leverages the frame’s cavities as part of the coolant inlet and outlet, reducing volume and improving sealing. The overall EV battery pack structure combines plastic and aluminum materials, offering high strength, good thermal insulation, and lightweight benefits, as illustrated in Figure 3.
Focusing on extrusion resistance, we optimize the cross-sections of the EV battery pack frame profiles. Since extrusion loads primarily cause out-of-plane bending, we analyze side beams and end crossbeams separately. For mesh convergence, we test different sizes and find that a 4 mm mesh ensures accuracy and computational efficiency, as shown in Figure 4. For side beams, we evaluate six cross-section schemes under extrusion at two locations: between crossbeams and directly opposite crossbeams. The extrusion force per unit mass is calculated to select the optimal design. Results are shown in Table 4, where Scheme 3 offers the highest force per mass (34.47 kN/kg) and is chosen for the side beams. The deformation before fracture involves buckling at extrusion points and overall rotation at connections.
| Scheme | Cross-Section Shape | Side Beam Mass (kg) | Extrusion Force (kN) | Force per Mass (kN/kg) |
|---|---|---|---|---|
| 1 | Simple rectangular | 2.77 | 71.0 | 25.63 |
| 2 | With internal ribs | 3.02 | 87.0 | 28.81 |
| 3 | Multi-chamber design | 3.22 | 111.0 | 34.47 |
| 4 | Similar to Scheme 2 with modifications | 3.08 | 87.1 | 28.28 |
| 5 | Complex reinforcement | 3.34 | 78.9 | 23.62 |
| 6 | Enhanced multi-chamber | 3.43 | 101.8 | 29.68 |
For end crossbeams, which affect X-direction extrusion resistance, we test five schemes, including additions of support ribs. As shown in Table 5, Scheme 3, with a mass of 0.83 kg and an extrusion force of 100.5 kN, is selected (force per mass not computed due to support rib variations). Deformation involves overall inward bending and rib folding.
| Scheme | Cross-Section Shape | Crossbeam Mass (kg) | Extrusion Force (kN) |
|---|---|---|---|
| 1 | Basic I-shape | 0.71 | 73.8 |
| 2 | I-shape with thicker flanges | 0.84 | 85.8 |
| 3 | Scheme 2 with 1.8 mm support rib | 0.83 | 100.5 |
| 4 | Box section | 0.78 | 77.8 |
| 5 | Scheme 4 with 1.8 mm support rib | 0.78 | 100.0 |
With optimized sections, we develop four overall EV battery pack frame schemes for finite element analysis, as shown in Figure 5. Scheme 1 modifies the original by removing the aluminum cooling plate and adding crossbeams and longitudinal beams, using 6061 aluminum with a frame mass of 11.58 kg. Scheme 2 adjusts side beam thickness (mass 11.26 kg). Scheme 3 removes two partitions from side beams (mass 10.58 kg). Scheme 4 changes the side beam cross-section (mass 11.52 kg). We analyze these under modal, impact, collision, and extrusion conditions. Results in Table 6 indicate that Scheme 1 performs best, with a first natural frequency of 42.3 Hz, stresses below yield strength, and extrusion forces exceeding 100 kN in both X and Y directions. The weight reduction compared to the original EV battery pack is 13.1%, considering additional components like the plastic flow channel plate (mass 2.88 kg).
| Scheme | First Frequency (Hz) | Impact Stress (MPa) | X-collision Stress (MPa) | Y-collision Stress (MPa) | X-extrusion Force (kN) | Y-extrusion Force (kN) | Frame Mass (kg) | Weight Reduction* (%) |
|---|---|---|---|---|---|---|---|---|
| Original All-aluminum | 46.2 | 186.9 | 324.5 | 59.2 | 106.7 | 76.9 | 16.64 | 0 |
| Frame Scheme 1 | 42.3 | 180.0 | 323.6 | 160.4 | 116.6 | 111.9 | 11.58 | 13.1 |
| Frame Scheme 2 | 40.2 | 191.7 | 325.2 | 163.1 | 117.4 | 99.2 | 11.26 | 15.0 |
| Frame Scheme 3 | 39.9 | 175.2 | 327.5 | 174.8 | 116.2 | 92.3 | 10.58 | 19.1 |
| Frame Scheme 4 | 41.8 | N/A | N/A | N/A | >100 | 108.2 | 11.52 | 13.5 |
*Weight reduction includes other components (e.g., plastic flow channel plate) with a mass of 2.88 kg.
However, for improved manufacturability and cost reduction, we simplify the profiles by adjusting the yield strength to 300 MPa and selecting Scheme 6 for side beams and Scheme 5 for end crossbeams. The optimized EV battery pack frame scheme is then analyzed, with results in Table 7. The first natural frequency is 42.7 Hz, above the 30 Hz target. The X-direction extrusion force is 98.7 kN, slightly below 100 kN, but considering that battery modules are not included in the model, this is acceptable. The frame mass is 11.71 kg, and with other components, the total mass is 14.59 kg, yielding a weight reduction of 12.3% compared to the original EV battery pack (16.64 kg). Figure 6 illustrates the optimized EV battery pack frame structure.
| Scheme | First Frequency (Hz) | Impact Stress (MPa) | X-collision Stress (MPa) | Y-collision Stress (MPa) | X-extrusion Force (kN) | Y-extrusion Force (kN) | Frame Mass (kg) | Weight Reduction* (%) |
|---|---|---|---|---|---|---|---|---|
| Adjusted Original | 46.2 | 187.0 | 301.3 | 59.2 | 83.7 | 63.4 | 16.64 | 0 |
| Optimized Frame | 42.7 | 180.5 | 292.6 | 160.4 | 98.7 | 102.4 | 11.71 | 12.3 |
*Weight reduction includes other components with a mass of 2.88 kg.
To validate our design, we conduct physical extrusion tests on the optimized EV battery pack frame according to national standards. A rigid semi-cylindrical indenter with a radius of 75 mm applies force at 0.05 mm/s in the X and Y directions, with a rigid plate as support. The force-displacement curves are shown in Figure 7. In the X-direction, the EV battery pack frame withstands 99.9 kN, and in the Y-direction, it withstands 123.1 kN. Although the X-direction force is slightly lower than the theoretical value due to welding and manufacturing factors, it still meets the requirement of 100 kN when battery modules are added. These results confirm that the optimized EV battery pack structure achieves both safety compliance and lightweight objectives.
In conclusion, our study addresses the design flaws in an original commercial vehicle EV battery pack through innovative lightweight structure development and optimization. By analyzing modal and dynamic performances, we identify insufficient anti-extrusion capability and propose a multi-material fusion EV battery pack design. Cross-section optimization of aluminum profiles leads to an efficient frame structure, and finite element simulations compare multiple schemes to select an optimal one. The final EV battery pack frame reduces mass by 12.3% while maintaining natural frequencies above 42.3 Hz, stresses within limits, and extrusion forces exceeding safety thresholds. Physical tests verify these improvements, demonstrating that the lightweight EV battery pack enhances safety and supports sustainable EV development. Future work could explore advanced materials like composites or further topology optimization to achieve even greater weight reduction and performance gains for EV battery packs.
Throughout this process, we emphasize the importance of the EV battery pack in electric vehicles, and our approach showcases how structural optimization can lead to significant advancements. The integration of aluminum and plastic materials not only reduces weight but also improves thermal management and manufacturability, making it a viable solution for mass production. As EV adoption grows, continued innovation in EV battery pack design will be crucial for meeting safety, efficiency, and environmental goals.