Arguably one of the most important components in an electric vehicle (EV) is what keeps the battery dry, strong and safe in the event of a crash or fire.

There are many terms used to describe this component: housing, casing, tray, box and enclosure;  the main materials currently used for battery pack enclosures include steel, aluminum and plastic composites.

Not surprisingly, a complete EV battery pack is quite heavy, typically accounting for around 40% of the vehicle's total weight;  when considering the makeup of the battery pack (cells and modules, thermal management, battery management system (BMS), separators, etc.), it's easy to Discover why they're also very expensive, totaling up to 50% of the vehicle's value.

This is why batteries need to be handled with care while in use and after use in electric vehicles;  when the power battery in an electric vehicle reaches the end of its life, whether through recycling or secondary use, it still has a lot to offer the world , so the power battery needs to be easy to disassemble and recycle.

1.Removable

But the battery casings used in the first electric cars launched after 2010 were designed to be tightly sealed. This drives the need for impenetrability, impact resistance, fire resistance, water resistance and tamper resistance to an extreme, resulting in batteries and recycling processes that are nearly impossible to repair, often requiring people in hazmat suits to pry open the protective casings. Key to current battery enclosure design strategies are disassembly, fire and thermal runaway protection, crash performance and recyclability. But the electric vehicle battery market is growing rapidly, with frequent changes in battery chemistries, battery packaging formats (soft pack, cylindrical, prismatic) and battery technology, and the arrival of solid-state battery technology is getting closer. All of this has an impact on electric vehicle battery enclosures.

As we will see, the role of battery enclosures in vehicle structures is constantly evolving, increasing structural requirements, which in turn raises questions about material availability, joining techniques and serviceability requirements. About 80% of electric vehicles currently use aluminum battery casings, with the remainder dominated by steel, but new thermoplastic solutions offer a lightweight and innovative alternative to metal solutions.

2. Battery pack shell material selection

The age-old debate between steel and aluminum continues in the world of battery casings, with each supplier claiming to be a better fit than the other. Steelmakers tout its advantages in high strength, formability and repairability, as well as cost-effectiveness and lower carbon intensity during production than other materials.

3. Battery pack shell

Clearly, a battery enclosure is more than a simple box, it is a large structural safety component whose role and performance requirements create opportunities for creativity and innovative engineering. For the material supplier, this is reflected in its multi-part integration (MPI) program, which sequentially combines multiple parts stamped from an LWB (laser welded sheet) into a hot-stamped part. Reduce the number of join operations required.

4. Thermal runaway protection

A major area of focus for EV batteries is thermal management and thermal runaway protection, and this is where thermoplastics shine. Safety organization UL Solutions has developed a new stringent thermal runaway test called UL 2596 ("Method for Testing Thermal and Mechanical Properties of Battery Enclosure Materials") that involves 25 cylindrical cells of the material to be verified. Thermal runaway (18650) in a steel battery pack. The properties of SABIC thermoplastic materials are such that when a sample of the material was subjected to a flame at 1,000 degrees Celsius for more than 5 minutes in this test, the temperature on the side of the battery pack was below 200 degrees Celsius, without the need for the thermal insulation required for aluminum and steel casings. blanket). This is because the thermoplastic materials developed by SABIC begin to char when exposed to fire and expand over time. This means it does not transfer heat, a unique property of thermoplastic materials. Over time, like a turtle shell, it becomes a protective layer against fire and heat transfer. Standard plastics fail this test, but plastic in millimetre-thickness passes every time. In addition, the molding of thermoplastic shells can inspire creativity and increase the material's versatility.

5. Electric car battery replacement

A special development in electric vehicle battery technology is that in battery replacement, the casing will play a key role, where the safe and effective removal and storage of the battery will largely depend on the performance of the battery casing. Until Better Place bowed out in 2013, battery swapping seemed to have a place in any electric vehicle ecosystem. But the numbers are rising, especially thanks to Chinese automakers Nio and Geely(LFT-G works for Geely).

Uwe Frieß, head of the body construction, assembly and disassembly department at the German research institute Fraunhofer Institute for Machine Tools and Forming Technology (IWU), believes that if plug-and-play battery replacement is realized, the impact will be huge. Actual experience with the way shared items are handled requires additional impact protection enclosures and necessary condition monitoring systems to detect improper handling. Both systems require additional components and cost.

6. The role of the battery housing in the body-in-white

Another key development in battery technology affecting enclosures is the evolution of the role of electric vehicle batteries in the body-in-white. Originally a body-in-white support component, battery casings are now becoming structural parts of the body-in-white, and automakers are even exploring battery-to-body and structural batteries, where the design of the casing may be a key factor. For battery packs integrated into the body-in-white, the steel industry is currently competitive in terms of cost and performance for battery top covers, lower shrouds and frames. Aluminum is a very efficient cell-to-battery pack solution compared to some other options, with its thermal conductivity and weight savings. The design freedom offered by thermoplastics, in battery-to-chassis designs, can provide good value in terms of functional integration and production of complex geometries with reduced component count.

7. Sustainable

However, developing battery packs as structural components has significant implications for other aspects, in particular for sustainable production, component lifecycle and circularity.

Most automakers focus on repairability, so battery cases can often be accessed, removed, and replaced. But he also acknowledged the current lack of repairability. Most dealers will not repair the battery, but instead send it back to the OEMs or other designated third parties for processing. When it comes to electric vehicle batteries, repairability is at least as important as, and far more efficient than, recyclability in the pursuit of sustainable transportation. The rapid development of electric vehicle battery technology is good news for consumers. It also presents exciting opportunities and challenges for automakers and suppliers.

8. Performance requirements for electric vehicle battery pack shells

1)Mechanical behavior
The stiffness of the battery pack casing is particularly important. In most electric vehicles, the battery pack casing is an important part of the vehicle structure, and its performance plays an important role in the overall stiffness of the body-in-white. This requires the battery pack shell to meet the safety requirements for frontal and side impacts.

2)Thermal management and flame retardancy
Another advantage of the composite battery pack casing is that the thermal conductivity of carbon fiber reinforced composites is 200 times lower than that of aluminum alloy, and it has better insulation. Therefore, the composite battery pack casing can withstand better than traditional metal casings. High and low temperature performance. The ideal operating temperature of currently commonly used lithium-ion batteries is between 10 and 40°C, which generally requires the addition of a cold/thermal management system. The composite shell has better thermal insulation and requires less energy in thermal conditions, further improving the vehicle's efficiency and reducing overall power consumption. In addition to the positive impact on thermal management, low thermal conductivity is an excellent prerequisite for effective flame retardancy.
By adding flame retardants, composite shells can easily meet flame retardant requirements such as UL94-V-0 and UL94-5VB.

3)Other properties
In addition, the sandwich battery pack casing can better meet corrosion protection requirements and provide better sealing. Electromagnetic shielding in critical areas can be achieved through the design of fiber layup and fiber volume content. At the same time, the application of composite materials provides more space for integrated design, and related enhanced components, additional components, connecting components, sensors, etc. can all be integrated into the design.

9. Analysis of the manufacturing process and value reflection of thermoplastic and reinforced plastic materials in battery casings

Compared with metal components, large-area all-plastic casings can shorten cycle times and help reduce vehicle weight, thereby increasing the range of electric vehicles (EVs). Lanxess and Kautex Textron have spent several years collaborating to investigate whether battery casings for electric vehicles can be designed and manufactured from engineering thermoplastics. Using direct long fiber thermoplastic (D-LFT) and polyamide 6 (PA 6) resin, they developed a technology demonstrator in a feasibility study. The research system measures 1,400*1,400 mm (length*width) and is a large, complex all-plastic enclosure weighing in the two-digit kilogram range. The goal of the research project is to demonstrate the advantages of thermoplastics over metals in terms of weight and cost reduction, functional integration and electrical insulation properties. Felix Haas, director of product development at Coster, explained: “As a first step, we have eliminated the use of metal reinforced structures and at the same time proved that we can commercially produce these complex and large components.” Dr. Christopher Hoefs, project manager for electronic power systems at LANXESS, added: “Coaster and LANXESS hope to use the results of the collaboration to enter into series production R&D projects with car manufacturers.”