Lightweighting of battery packs

Lightweighting of battery packs

Battery pack and battery enclosure

The battery pack is a complete unit assembled from multiple battery modules, designed for the storage and provision of electrical energy. It is a higher-level component in the battery system, typically composed of several battery modules, connectors, battery management system, cooling system, electrical interfaces, and casing.

The battery enclosure is the primary structural component of the battery pack. Only when the enclosure is stable in both static and dynamic conditions (such as rigidity, modal properties, etc.) can it ensure that the power battery operates under normal conditions, enabling the power system to run smoothly. The main function of the battery pack enclosure is to support components of the power battery system, such as battery modules, electrical modules, cooling modules, etc. Additionally, it serves to protect the battery and electrical system from damage in the event of external collisions or compression.

Why is it necessary to lightweight the battery

Lightweighting is an effective energy-saving and emission-reducing technology. Global automotive industry policies on energy efficiency and emissions are becoming increasingly stringent, with constant advancements in fuel consumption and emission standards. Lightweighting technology, as a crucial avenue for enhancing energy efficiency and reducing emissions in automobiles, achieves weight reduction while meeting safety and cost control requirements. Simultaneously, reducing vehicle weight can lessen the load on the power system, improve vehicle power performance, decrease braking distance, and enhance driving stability.

Lightweighting is beneficial for cost control in new energy vehicles, particularly in pure electric vehicles where the battery pack contributes significantly to the overall weight, resulting in a higher weight compared to equivalent conventional fuel vehicles. Taking Tesla Model 3 as an example, with a range of 556 km, the curb weight of the vehicle is 1761 kg, and the 60 kWh power battery pack weighs 480 kg. Assuming a cost of 800 yuan per kWh for the battery pack, the battery cost would be 48,000 yuan. Lightweighting reduces energy consumption, allowing for a lower energy requirement for the same range, consequently leading to a reduction in battery pack weight and cost.

How to Lightweight the Battery Enclosure?

Utilizing composite materials to lightweight the battery pack enclosure

Composite materials are created by blending two or more materials with different properties through physical or chemical methods, forming a material with new characteristics on a macroscopic scale. The various materials complement each other in terms of performance, creating a synergistic effect that enhances the overall properties of the composite material beyond those of its individual components, meeting a variety of different requirements.

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With the development of energy efficiency, environmental friendliness, and lightweighting in the automotive industry, various lightweight materials have emerged for battery pack enclosures, including glass fiber-reinforced composite materials, carbon fiber-reinforced composite materials, and PC long fiber-reinforced thermoplastic materials.

SMC Composite Material

Sheet molding compound (SMC) is a sheet-like molded plastic material that uses unsaturated polyester resin as a binder, incorporating glass fibers, fillers, pigments, and other additives. It is made by impregnating glass fiber yarn and covering both sides with a thin film, forming an unsaturated polyester glass fiber composite material. SMC materials offer the following advantages compared to traditional metal materials:

1. High specific strength, high specific modulus.

2. Low thermal conductivity, small coefficient of expansion, dimensional stability.

3.Chemical corrosion resistance, never rusts.

4.Good shock absorption, impact resistance, and low resonance.

5.Insulation performance superior to metal materials.

6.Flame retardant performance can achieve V0 level.

7.High design flexibility (can be molded as a whole through structural optimization, reducing secondary assembly).

Carbon fiber-reinforced composite material

Carbon fiber composite material has become an ideal alternative to traditional metal materials for battery pack casings. Compared to metal materials, carbon fiber has a density of approximately 1.7g/cm³. It boasts a tensile strength of 3000MPa, an elastic modulus of 230GPa, making it lightweight, high-strength, resistant to high temperatures, friction, seismic forces, and with a low coefficient of thermal expansion.

PC+LFT-D Long Fiber Reinforced Thermoplastic Material

The excellent flame retardant performance, dimensional stability, and mechanical properties of PC material, combined with the high retention rate of long fibers in the LFT-D process, perfectly meet the application requirements for battery pack enclosures. The material features good flame retardancy, high rigidity, high toughness, and reduced likelihood of part cracking, allowing for a tighter connection between upper and lower enclosures, enhancing the airtightness of the battery pack over extended periods of use.

Utilizing aluminum material to lightweight the battery pack enclosure

Rolling aluminum sheets, extruding aluminum profiles, and casting aluminum, three different types of aluminum materials, have been widely applied in various battery pack projects, becoming the mainstream technological approach for power battery system casings. Die-cast aluminum is extensively used in small power battery casings, such as those for hybrid vehicles, while large power battery casings primarily follow the trend of using welded structures with aluminum profiles and aluminum sheets.

1.Excellent lightweighting effects

The density of steel is 7.8, while aluminum has a density of 2.7. In traditional automobiles, the body accounts for about 30-40% of the total vehicle weight. Substituting high-strength steel for ordinary steel can reduce weight by approximately 11%, whereas using aluminum alloy can result in a weight reduction of about 40%. Aluminum alloy can be applied in a vehicle for over 500kg, leading to an overall weight reduction of around 40%.

2.Increasing body strength to enhance safety

In terms of absolute strength, aluminum alloy is slightly inferior to steel, but its lower density gives it a greater advantage. For materials with equal strength, the thickness ratio between steel and aluminum alloy is 1:1.4, while the weight ratio is only 1:0.5. This means that aluminum alloy can achieve the same strength with only half the weight.

3.Enhance maneuverability

Lightweighting reduces vehicle inertia, increases power-to-weight ratio, and significantly enhances power performance at the same power level. By improving the body’s rigidity and torsional resistance, it is akin to reinforcing the body with strengthened rods, allowing for more ample space for suspension tuning and enhancing the vehicle’s limits. Additionally, models with all-aluminum bodies typically undergo some optimizations in chassis and suspension.

4.Exceptional corrosion resistance

Aluminum itself is not stable and is prone to oxidation. However, the oxidation of aluminum results in the formation of a dense oxide layer on the surface, which firmly binds with the substrate. This high stability allows for the creation of a tight protective layer over the aluminum base. Moreover, in humid atmospheric conditions, this protective layer can thicken.

5.Improved ductility

Aluminum alloy can shape extremely beautiful car body curves, as seen in the aluminum bodies of Jaguar C-Type, D-Type, and the iconic ‘Most Beautiful Car,’ the E-Type. Even today, these designs remain aesthetically pleasing. The flowing and convex curves of this styling, which were challenging to achieve with steel at the time, still captivate with their elegance.

With the rapid development of emerging markets such as global new energy vehicles, energy storage, data centers, and power computing, striking a balance between energy security, stable operation, and cost-effectiveness has become a pressing survival issue for battery pack manufacturers.

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