Engineering Plastics for Prismatic Battery Packs

e-motec
July 14, 2022

Engineering Plastics for Prismatic Battery Packs

Steven Daelemans

Looking at the roadmap for the future of cars it is clear, the electric powertrain will have a dominant position. The connected car is forcing the OEM to reposition their brands and adapt to new business models tapping into the major drivers such as climate change and growing cities. Traditional borders between the electro/electronic/automotive industry are dissolving.

There are a range of materials to choose from when designing battery enclosures for electric vehicles (EVs). Because metal has limitations in terms of design, cost and weight, many battery designers are switching more and more to thermoplastics. Polycarbonate and its blends have been used for decades in the electronics sector, packing batteries and electronics, resulting in safe products, produced in mass production. Today Polycarbonate can be found in newer battery applications for e-bicycles and e-cars. Several parts in the e-car battery are made from specific compounds like Makrolon® PC and Bayblend® PC/ABS.

Image of Polycarbonate Prismatic Battery Pack

These material improvements enable new design possibilities The materials are used for their high impact resistance and high ductility. They show good flame retardant properties without using bromine, antimony or red phosphor-based flame retardants. The amorphous structure of the material allows for tight tolerances, low warpage and dimensional stability over a wide temperature range. This results in flat parts with tight tolerances enabling automated mass assembly and a fast scaling of the battery production lines, widely valued by the electronics industry.

Bayblend®

A material that showed its value in several applications is the Bayblend® FR3080 EV. Globally available; UL 94 V-0; …demonstrated good dynamical strength in all vibration tests; While being able to hold its dimensional stability at elevated temperatures, means it can be used in thin wall applications. It allows for increased assembly efficiency thanks to his low isotropic shrinkage. Flat, dimensional stable parts allow fast positioning, easy to weld or glue.

Bayblend® FR3080 EV shows transparency for laser light in natural and special colours whereas the black tinted version efficiently adsorbs the energy without scattering the light.

Close up image of Bayblend® FR3080 EV

Another grade that enables increased assembly efficiency for thin wall parts is the Bayblend® FR3040 EV. Flame rated UL 94 V-0 at 1mm, it shows UV transparency. It allows for accurate positioning and fast UV curing of the adhesive in the assembly. For instance, in large cylindrical cell spacers.

Several parts in the battery of an e-car are today made from Bayblend® FR grades. Examples are cell spacers; covers and insulation plates; current collectors; brackets fixing cables and heating elements.

Makrolon®

In Premium e-vehicles faster discharges are required. This results in higher short term temperature requirements. Makrolon® FR6005 HF with high heat resistance enables such rapid discharging of a battery. This high flow grade allows for integrated busbar designs withstanding elevated temperatures (up to 120°C).

If we talk about heat management, Covestro has developed a broad range of thermally conductive compounds. For instance, the Makrolon® TC110 FR demonstrates thermal conductivity and electrical insulation. Compared with other highly loaded conductive materials, it shows an excellent impact performance. Today already used in non-automotive batteries, it increases the lifetime of the pack and allows for faster charging thanks to a more homogenous temperature distribution. We are exploring the use of such thermally conductive grades in battery packs, battery electronics, vehicle control units, and also in high voltage applications.

This brings us to the outside of the battery pack. For such control units we look into the replacement of the metal housings. Our PC glass fibre filled grades like a Makrolon® 9425 or Makrolon® 9415 can potentially replace metal casings. It excels in its high stiffness and a low warpage resulting in a cheaper and lighter housing. If the environment is more aggressive to polycarbonate, we offer Makroblend® grades, for instance Makroblend® UT4045 G, a 20% glass filled PC+PBT blend, or other unreinforced grades. Being mechanically stable over a wide temperature range even without glass fibre reinforcement makes the non-reinforced grades the best solution to fully gain the amorphous plastics advantages of low warpage and precise moulding.

Next to an increased chemical resistance, our unreinforced Makroblend® grades show an excellent low temperature ductility, particularly essential in crash scenarios.

Covestro has extensive experience in supporting the development of such elements to protect the battery. This can be against intrusion of other components like the invertor or in a crash event like the side pole impact. In real life applications, our Makroblend® KU2-7912/4 shows a superior performance. We have constructed our own demonstrator to evaluate our materials, which enables us to support our customers in their design with accurate high speed material data.

Close up image of unreinforced Makroblend®

Sustainability

That electro mobility will contribute towards a sustainable future is evident. A more sustainable battery pack is the target. Different solutions will be seen like Cell2pack, or the modular Choco-SEB design and they all need to meet this sustainability trend. The push for more sustainable solutions will also allow for new business models, like decoupling the batteries from the application. How can battery packaging contribute to these goals? How can battery packaging facilitate repair, re-purposing and remanufacturing? How can the packaging material help to recover the residual value of the battery packs in their life transition?

Covestro is already offering material solutions for these developments with our Makrolon® RE and Bayblend® RE grades with renewable attributed raw materials, certified via ISCC PLUS. We offer several of our grades, used in different battery applications, in a RE version. They allow a reduction of CO2 emissions by up to 70% for our Bayblend® RE and up to 100% for our Makrolon® RE.

Covestro set a clear goal to have net zero emissions by 2035 for scope 1 and scope 2. Making Covestro an industry leader. Our strategic vision is to become fully circular. We are accompanying our customers in accelerating the transition to the circular economy, as well as helping to build an industrial ecosystem that favors circularity.

One such example is the study for a battery top lid. 3 years ago, we introduced a thermoplastic polycarbonate top cover for a battery lid. Such a thermoplastic top cover can be easily recycled. We will launch also a Makrolon® 6165 X RE material for such a battery lid made by the LFT-D process at the battery show in Stuttgart, further reducing the CO2 emission of the pack.

Covestro sees the battery packaging as an enabler for the different solutions that will emerge and grow as an answer to the questions raised before. Our application development team supports customers to design-for-recycling concepts. We help customer develop swappable battery packs where the high impact properties help to make lightweight robust housings. We investigated the blockchain solutions and how this will facilitate repurposing the modules in other industries and later at end of life to recycling the materials.

Steven Daelemans Market Development Manager Covestro

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