39 E-Mobility Engineering | September/October 2025 Battery pack materials | Tech focus with a 30% reduction in weight. It also allows for tight radii and inherent leak tightness owing to the one-shot process, which means that there are no bad welds that could leak. Using a one-shot process allows for integration of multiple components into the design, reducing the need for secondary process steps. This reduces costs by reducing the bill of materials and amount of equipment required. The carbon footprint also drives other choices. Some providers chose not to use duroplastic because of its high footprint. This is a type of thermosetting plastic, similar to Bakelite, made from a mixture of synthetic resin and a renewable resource like cellulose or cotton waste that hardens permanently under heat and pressure. Instead, up to 50% recycled plastic material can be used with up to 20% biomass such as cellulose to reduce the carbon footprint and help to meet the end-of-life vehicle directive from the European Commission. This requires at least 25% recycled plastic materials in a newly produced vehicle. The base materials are sourced from suppliers with long-term contracts to ensure global coverage as well as sufficient availability. Sources range from post-consumer recycled (PCR) materials, for example, with granulate recycled from fishing nets discarded in the ocean. Investigation To explore the different material options for battery enclosures, a consortium in Germany investigated several alternative multi-materials. Alternative materials included both thermoset and thermoplastic materials, solid laminate or sandwich designs, short fibre overmoulded structures as well as steel and aluminium, and combinations of all these materials were compared with a reference welded aluminium battery casing. All relevant load cases were considered in the CAE analysis, as defined by safety regulations, in combination with specific OEM requirements. In total 20 different multi-material concepts were optimised on weight and cost and then compared with the aluminium reference design. All the production steps were costmodelled in detail to obtain reliable cost estimates for each variant. Consequently, each concept resulted in different weight savings of up to 36% and cost savings of up to approximately 20%. Weight is key because an average 70 kWh battery pack can weigh as much as 500 kg with the casing weighing as much as 100 kg, including bottom protection or skid plates. Eight design families were developed. The material choices were varied in each family, and CAE optimisation analysis was performed to find the lightest possible designs. Some components could be considered individually in the optimisation process, such as the lid, which could be applied to many different box concepts. The same applies to the bottom protection plate. Each design was also developed to comply with EMI shielding, ranging from the simple application of aluminium foils or using aluminium-coated glass fibres as an integral layer in a composite layup. Tests are still underway on fire resistance, but researchers expect composites to compare favourably in comparison with aluminium because a five-minute thermal runaway flame exposure will melt a hole in aluminium quite quickly, while long or continuous fibre material will survive much better. Many concepts, both in thermoset and thermoplastic material, were shown to be cheaper than the aluminium reference part. This has partly to do with the high cost of aluminium, such as in the form of extrusions, while glass fibres are still relatively cheap. A key finding was that the choice of the right alternative geometries has much more impact on weight saving than using The eight families of designs under investigation (Image courtesy of AZL Aachen)
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