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Vehicle Battery Cases: Suppliers Propose to Use Aluminum, 1.2GPa High-strength Steel for Weight Reduction

Amid continued announcements of new automobiles and technologies by global automakers and suppliers in the electric vehicle sector, attention is increasing toward battery packs, which are the most important parts of electric vehicles. What is required of the battery pack is not only high efficiency and high performance of the battery cells, but also light weight and high rigidity of the outer case. In order to extend the cruising range in ZEV driving mode of BEVs and PHEVs, it is essential to reduce the weight of the battery pack which is one of the heaviest components. The weight of the battery pack varies depending on the vehicle type, concept and application, but is generally in the range of 300-500kg. Looking at the weight of the battery pack, battery cells amount to 70 percent of the total weight, the battery casing to 20 percent and cooling / electronic parts to 10 percent. However, BEVs proposed in recent years often aim for a cruising range of 300 km or more. As a result, cell capacity must be 40 kWh or more, making it difficult to reduce the weight of the cell itself. Therefore, weight reduction of the battery pack focuses on the housing. Iron, aluminum, and resins (mainly super engineering plastics) are used as materials to reduce the weight of the housing. Iron is used for mass-market cars and aluminum for luxury cars. However, some mass-market-brand BEVs are also shifting toward incorporating aluminum. GM and Hyundai among others are using a mix of iron and aluminum. However, when aluminum cannot be used, proposals for the use of ultra-high strength steel of 1.5 GPa or more are also on the table in order to reduce cost. In addition to reducing weight, there is also the aspect of ensuring the safety of the pack by increasing its rigidity. Looking at the battery packs and cases that were exhibited at IAA 2019, the mainstream proposals were to use a mixture of iron and aluminum or to use only aluminum materials. Germany’s Kirchhoff Automotive has proposed a case in which the cell part is made of 1.5GPa iron and the outer frame is made of aluminum in order to reduce weight and ensure rigidity. China’s BHAP has displayed a battery case for BEVs using 7000 series aluminum material. Similarly to BHAP, Canada’s Linamar and Germany’s Webasto also exhibited aluminum battery cases.
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