Application status of carbon fiber composite in battery pack housing

The use of lightweight materials to reduce the quality of vehicles has become one of the important ways to achieve lightweight new energy vehicles.

With the continuous development of the material field, a variety of lightweight fiber composite materials such as glass fiber reinforced composite materials and carbon fiber reinforced composite materials have begun to be applied in the field of new energy vehicles.CFRT.

Low-density, high-strength, corrosion-resistant, fatigue-resistant carbon fiber composite materials are the most widely used high-performance fiber composite materials in the automotive field, and have a large number of applications in many system parts of the automobile, such as: the door of the car body, the roof, etc. Push rod, rocker rod and pump impeller in engine system; The drive shaft and clutch blade in the transmission system; Underbody frame, suspension, spring, etc., in chassis system.

With the rapid development of new energy vehicles, the safe storage of batteries has always been a research focus. Electric vehicle battery pack shell is the mainstream way of energy storage for new energy vehicles at present, and carbon fiber composite materials with many advantages have also begun to emerge in this field.

Carbon fiber is generally not used directly, usually as a reinforcement, and resin matrix, metal matrix, ceramic matrix and so on combined to form carbon fiber composite materials

Carbon fiber has the following advantages:

① Low density, high strength, density is only 1.5~2.0g/cm3, equivalent to the density of light aluminum alloy 1/2, the strength is 4~5 times of steel, 6~7 times of aluminum;

(2) High temperature and low temperature resistance, the thermal elastic coefficient of carbon fiber is small, it does not melt and soften under 3000℃ non-oxidizing atmosphere, and it is still not embrittlement under liquid ammonia temperature;

(3) Good electrical conductivity, at 25℃, the specific resistance of high modulus carbon fiber is 775Ω·cm, and the specific resistance of high strength carbon fiber is 1500Ω·cm;

④ Acid corrosion resistance, carbon fiber resistant to concentrated hydrochloric acid, phosphoric acid, sulfuric acid and other corrosion.

Carbon fiber is usually used as a reinforcement material, so it is usually classified according to mechanical properties in actual use, mainly according to tensile strength and modulus. The strength of high-strength type is 2000MPa and the modulus is 250GPa, the modulus of high-strength model is above 300GPa, and the strength of ultra-high-strength type is greater than 4000MPa. The modulus of the ultra-high model is greater than 450GPa.

Second, the application status of carbon fiber composite materials in the automotive field

According to the European Aluminum Association data, when the quality of the car is reduced by 10%, the energy efficiency will be improved by 6% to 8%, and the emissions of pollutants per 100 km will be reduced by 10%. For new energy vehicles, the mass reduction of 100kg can increase its endurance by about 6% to 11%.

Lightweight and high-strength carbon fiber composite materials have rich applications in automobiles. Table 2 shows the application of carbon fiber composite materials in some models.

Third, the application of carbon fiber composite materials in the battery pack housing

1. Development of battery pack housing

The power battery pack is the power source of new energy vehicles, and the body of the battery pack is formed by the shell covering the battery module. The battery pack shell plays a key role in the safe operation and protection of the battery module, and its material is required to have the characteristics of anti-corrosion, insulation, resistance to normal temperature and low temperature (-25℃) impact and flame retardant

As the carrier of the battery module, the battery pack housing plays a key role in the stable operation and safety protection of the battery module, which is generally installed in the lower part of the car body and is mainly used to protect the lithium battery from being damaged when it is affected by external collisions and extrusion.

The traditional car battery box is cast with steel plate, aluminum alloy and other materials, and then the surface is sprayed. With the development of automotive energy saving, environmental protection and lightweight, battery shell materials have also appeared a variety of lightweight material choices such as glass fiber reinforced composite materials, sheet molding plastics, carbon fiber reinforced composite materials.

Steel battery pack shell is the most original power battery pack shell material, generally welded by casting steel plate, with the advantages of high strength and high rigidity, but its high density and mass, need to increase the anti-corrosion process.

Aluminum alloy shell is the current mainstream power battery shell material, with light weight (density is only 35% of steel), easy processing, corrosion resistance and other characteristics.

With the development of lightweight vehicles and the development of thermosetting plastic molding technology, new plastics and composite materials have gradually been used as battery case materials. The thermoset plastic battery shell itself has a mass of 35kg, which is about 35% smaller than the mass of the metal box, and can carry a mass of 340kg of batteries.

2. Development of battery pack housing

Carbon fiber composite materials with many advantages have become an ideal substitute for traditional metal battery boxes, and have been initially applied in some models.

Nio and Germany's SGL Carbon jointly developed the 84kW·h carbon fiber battery pack, the carbon fiber shell mass is 40% less than aluminum structure, energy density greater than 180(W·h)/kg.

The 84 kW · h carbon fiber battery case displayed by NIO

The total mass of the carbon fiber composite battery shell developed by Tianjin Zhongke Advanced Technology Research Institute and Lishen is about 24kg, which is 50% less than that of the aluminum alloy structure, and the energy density is as high as 210(W·h)/kg.

Duan Anxiang et al. carried out lightweight design and layup process optimization for the carbon fiber composite battery pack shell, and the obtained shell mass was reduced by 66% compared with the steel structure under relevant working conditions.

Zhao Xiaoyu et al. used carbon fiber composite materials to carry out lightweight design of the battery pack shell using the stiffness equivalent design method, which reduced the mass of the steel structure by 64% ~ 67.6%.

LIU et al. adopted the RBDO method to solve the lightweight design problem of the upper cover of the carbon fiber composite battery pack shell, and achieved a mass reduction of 22.14% when the performance met the requirements.

Tan Lizhong et al. conducted a comparative study on the three schemes of 1.5mm thick aluminum upper cover (scheme 1), 1.5mm thick carbon fiber upper cover (scheme 2) and 0.5mm carbon fiber +3mm thick bee plate +0.5mm thick carbon fiber composite upper cover (Scheme 3), and found that scheme 3 was the best, which could reduce the mass by 31% compared with scheme 1.

The battery pack shell made of aramid hybrid carbon fiber has also been studied at home and abroad, and the high-performance fiber company represented by Nanjing Altron Advanced Material Technology Co., Ltd. has also begun related research and has begun to lay out in the patent field, such as patent CN113764801A.

Limited by the cost problem, the current high-performance fiber composite materials based on carbon fiber composite materials have not been widely used in the field of battery shell, I believe that with the development of new energy and the expansion of the application of fiber composite materials, the use of fiber composite materials will gradually reduce the cost of fiber composite materials in the future new energy market will also shine.

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