Using plastic components to optimize high-voltage batteries

The development of lithium-ion batteries has by no means run its course. In order for electric vehicles to meet with acceptance in the long term, manufacturers are making considerable efforts to increase both the power of batteries and the range they deliver, reduce their weight, improve their safety, including fire safety, and their sustainability, and reduce their costs. Developers of high-voltage batteries* must continually optimize materials and design concepts and regularly review their own product decisions.

Important requirements concerning the mechanical integration of components are their electrical insulation, heat resistance, flame retardant properties and, depending on the component, further criteria such as dimensional stability, resistance to chemical attack and impact resistance.

Electric vehicles are operated at high voltages of around 400 V, rising to 800 V and more for elevated power requirements. Higher voltages reduce power losses and permit faster charging. However, they also place higher demands, for example on the electrical insulation of the battery systems.

Plastics are by their nature electrical insulators, whereas metals are electrical conductors. Plastic is therefore the material of choice in HV batteries where electrical insulation is required.

The performance of high-voltage batteries depends to a large extent on the temperatures of the application. Owing to their chemical properties, the optimum operating temperature range of lithium-ion batteries is 20 °C to 40 °C.

Thermal management is therefore crucially important for the performance and safety of high-voltage batteries. Components manufactured from plastic fulfil important tasks in this area, both for insulation of the battery case against external thermal influences, and for the desired dissipation of heat from cells and components within the battery system.

Besides electrical and thermal properties, mechanical properties such as stiffness, strength and impact resistance are particularly important in the selection of suitable materials for structural components of high-voltage batteries.

A key objective in the design of HV batteries for electric vehicles is fire safety and retardancy. Intelligent battery management systems help to prevent battery overload and the generation of critical heat levels. Flame-retardant and heat-resistant materials such as thermoplastics help to prevent or significantly retard fires.

Their batteries make electric vehicles heavier than comparable vehicles with internal combustion engines. Weight reduction is thus a crucial factor in the design of electric vehicles, and especially in battery design. The relative densities of materials commonly used in high-voltage batteries speak for themselves: for a given performance, engineering plastics are significantly lighter than metals, even very light metals such as aluminium and magnesium.

The targets of the Paris Agreement for CO2 emissions to be cut by 55 % by 2030 and climate neutrality attained by 2050 are forcing battery manufacturers to review the carbon footprint of their products andoptimize them continually. “Batteries placed on the EU market should become sustainable, high-performing and safe all along their entire life cycle.” – European Green Deal