Arguably one of the most important components in an electric vehicle (EV) is the one that keeps the battery dry, secure, and safe in the event of a crash or fire.
There are many terms used to describe the component housing, casing, tray, box, and enclosure; The main materials currently used in battery pack housings include:Steel, aluminum, and plastic composites
Not surprisinglyA complete EV battery pack is quite heavy, typically accounting for around 40% of the vehicle's gross weight；When considering the composition of the battery pack (cells and modules, thermal management, battery management system BMS, separators, etc.), it is easy to see why they are also very expensive, totaling up to the value of the vehicle
This is why batteries need to be handled with care when they are in use and after they are used in electric vehicles; When the power battery in an electric vehicle reaches the end of its useful life, whether it is through ** or secondary use, it can still provide a lot to the world, thereforeThe power battery needs to be easy to disassemble**
Detachable
But the battery housings used in the first electric vehicles that hit the market after 2010 were designed to be tightly sealed. This has led to the extreme need for impenetrable, crash-resistant, fire-resistant, water-resistant and tamper-proof, resulting in batteries and processes that are virtually irreparable, often requiring people wearing protective clothing to pry open to protect these enclosures.
The keys to current battery enclosure design strategies are removability, fire and thermal runaway protection, crash performance, and scalability. However, the EV battery market is developing rapidly, with frequent changes in battery chemistry, battery packaging form (pouch, cylindrical, prismatic) and battery technology, and the arrival of solid-state battery technology is getting closer and closer. All of this has an impact on EV battery housings. As we will see,The role of battery enclosures in vehicle construction is evolving, increasing structural requirements, which in turn raises questions about material availability, connection technology, and suitability requirements. Currently, about 80% of electric vehicles are made of aluminum battery housings, with the rest predominantly made of steel, but new thermoplastic solutions offer a lightweight and innovative alternative to metal solutions. 
Selection of battery pack shell materials
In the world of battery enclosures, the age-old debate between steel and aluminum continues, with each vendor claiming to be a better fit than the other. Steelmakers advertise their presence inHigh strength, formability and repairabilityand cost-effectiveness advantages and a lower carbon intensity than other materials in the production process. 
Plastic solutions canReduced weight, lower costs, improved safety, and reduced environmental impact in terms of appability, with lower CO2 emissions than steel or aluminum
SABIC received an Edison Award for supplying a thermoplastic battery enclosure for the Honda CR-V plug-in hybrid. Compared to a steel solution with insulation, a 6kg injection molded polypropylene fiberglass resin solution is a size 1The large 6 m x 1 m, 2 mm thick components reduced Honda's weight by 10 percent and cost savings by 10 percent. 
Battery pack housing
Obviously, the battery case is not just a simple box, it is oneLarge, structurally safe components, whose role and performance requirements create opportunities for creativity and innovative engineering. For material manufacturers, this is reflected in their Multi-Part Integration (MPI) program, which combines multiple parts stamped by an LWB (laser welded plate) into a single hot-stamped part. Reduce the number of connection operations required. 
Batteries will be integrated into the body-in-white (BIW), and automakers and tier 1 chassis** companies are starting to centralize their chassis or BIW divisions in the same engineering center as the battery divisions to design the vehicles of the future. This is both a threat and an opportunity for the steel industry.
Thermal runaway protection
A major area of focus for EV batteries is thermal management and thermal runaway protection, and this is where thermoplastics shine. UL Solutions, a safety organization, has developed a new rigorous thermal runaway test called UL 2596 ("Test Method for the Thermal and Mechanical Properties of Battery Enclosure Materials"), which tests the thermal runaway of a material to be verified involving 25 cylindrical cells (18650) in a steel battery pack. The property of SABIC's thermoplastic material is that in this test, the temperature on the side of the battery pack was below 200 degrees Celsius when the material sample was subjected to a flame of 1000 degrees Celsius for more than 5 minutes, without the need for the thermal blanket required for aluminum and steel housings. This is because the thermoplastic material developed by SABIC begins to scorch when exposed to fire and expands over time. This means that it does not transfer heat, which is a unique property of thermoplastic materials. After a while, it acts like a turtle shell, becoming a protective layer for fire and heat transfer. Standard plastics fail this test, but plastic in millimetre-thickness does, every time. In addition,The molding of thermoplastic enclosures can spark creativity and increase the versatility of the material
Electric vehicle battery swap
A particular development in EV battery technology is in battery swappingThe enclosure will play a key role, where the safe and efficient removal and storage of the battery will largely depend on the performance of the battery enclosure。Prior to the exit of Better Place in 2013, battery swapping seemed to have a place in any EV ecosystem. But that number is rising, especially thanks to Chinese automakers Nio and Geely. 
Uwe Frie, head of the body construction, assembly and disassembly department at the Fraunhofer Institute for Machine Tool and Forming Technology (IWU), a German research institute, believes that if plug-and-play battery swapping were to be realized, the impact would be enormous. Based on practical experience with how shared items are handled, additional impact protection enclosures and the necessary condition monitoring systems are required to detect improper handling. Both systems require additional components and costs.
The role of the battery enclosure in the body-in-white
Another key development in battery technology influencing the enclosure is the evolution of the role of EV batteries in the body-in-white. Originally a BIW-supported component, the battery enclosure is now becoming a structural component of the BIW, and automakers are even exploring battery-to-body and structural batteries, where the design of the enclosure could 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 of battery top covers, lower shrouds and frames。A very effective battery-to-pack solution compared to some other options, aluminum is thermally conductive and lightweight. The design freedom offered by thermoplastics, in cell-to-chassis design, can provide good value in terms of functional integration and the production of complex geometries that reduce the number of components.
Sustainable
However, the development of a battery pack as a structural component can have a significant impact on other aspects, especially for:Sustainable production, component life cycle and circularity
Most automakers value repairability, so battery housings can often be touched, removed, and replaced。But he also acknowledges the lack of repairability. Most dealers will not repair the battery and will instead send it back to the OEMS or other designated third party for disposal. In the case of EV batteries, repairability is at least as important as feasibility in the pursuit of sustainable transportation, and it is much more efficient than scalability. The rapid development of EV battery technology is good news for consumers. It also presents exciting opportunities and challenges for automakers and merchants.
Performance requirements for EV battery housings
Mechanical propertiesThe stiffness of the battery pack housing is particularly important, and in most electric vehicles, the battery pack housing 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 housing to meet the safety requirements for both forward and side impacts, as shown in Fig.
The rigidity of the battery housing is highly dependent on the sandwich structure used, and aluminum foam is generally used as the sandwich layer material. In addition,The high specific stiffness, low weight and good damping characteristics of fiber-reinforced components also have a positive impact on the noise, vibration, and NVH performance of the vehicle. Thermal management and flame retardancyAnother advantage of composite battery housings is that carbon fiber reinforced composites have a thermal conductivity 200 times lower than aluminum alloys, and they have better insulation, so composite battery housings can withstand high and low temperatures better than traditional metal shells. The ideal operating temperature for lithium-ion batteries in common use today is between 10 and 40°C, which generally requires the addition of a cooling and heating management system. The composite housing, on the other hand, provides better thermal insulation and requires less energy in thermal conditions, further increasing the efficiency of the vehicle and reducing overall power consumption. In addition to the positive impact on thermal management, a low thermal conductivity is an excellent prerequisite for effective flame retardancy.
By adding flame retardants, the composite shell can easily meet the flame retardant requirements such as UL94-V-0 and UL94-5VB.
Other featuresIn addition, the sandwich battery housing can better meet the requirements for corrosion protection and provide a better seal. Through the design of fiber layup and fiber volume content, electromagnetic shielding of critical areas can be realized. At the same time, the application of composite materials provides more space for integrated design, and related reinforcement components, add-on components, connecting components, sensors, etc. can be integrated design.
Thermoplastic and reinforced plastic materials in the battery housing
analysis of the manufacturing process and value embodiment
The large, all-plastic enclosure not only reduces cycle times compared to metal components, but also helps reduce vehicle weight, which can increase the range of electric vehicles (EVS). Lanxess and Kautex Textron have spent several years working together to see if battery housings for electric vehicles can be designed and manufactured by engineering thermoplastics. Using direct long-fiber thermoplastics (D-LFT) and polyamide 6 (PA6) resins, they developed a technology demonstrator in a feasibility study. Measuring 1,400 x 1,400 mm (L x W), the research system is a complex large, all-plastic enclosure weighing in the range of two kilograms. The goal of the research project is to demonstrate the advantages of thermoplastics over metals in terms of weight and cost reduction, functional synthesis and electrical insulating properties. Felixhaas, Director of Product Development at Coaster, explains: "As a first step, we have moved away from the use of metal reinforcement structures and at the same time proved that we can produce these complex and large components commercially. Dr. Christopher Hoefs, Project Manager for Electronic Powertrains at LANXESS, adds: "Coaster and LANXESS want to use the results of their collaboration to enter into a development project for series production together with the car manufacturer. ”
Single-stage manufacturing processThe demonstrator is based on the battery housing on a C-segment electric vehicle. It consists of a housing tray with an anti-collision structure, a housing cover and an underbody protection device. The housing components are produced using a single-stage D-LFT molding process, while LANXESS has optimized Durexon B24cmH20 polyamide 6 (pa 6) as molding compound. Coaster blends PA6 with fiberglass roving for this process. Partial reinforcement of the housing structure was carried out using TEPEX Dynalite fiber-reinforced thermoplastic composites from LANXESS. "The process reduces cycle times, so it's more economical than machining cycles in steel or aluminum," Haas explains. ”
Today, the housing of high-voltage batteries was originally made of extruded steel or aluminum. Depending on the vehicle category, the length of the case can exceed 2,000 mm and the width can exceed 1,500 mm. The size, number of parts, and numerous manufacturing and assembly steps make metal enclosures very costly. For example, complex structures made of strand pressed profiles require a lot of auxiliary operations, such as welding, punching, fixing, etc. In addition, in an additional process step, the metal parts must be protected from corrosion by cathodic dip coating. Simplify assembly and logistics"Plastics, on the other hand, can be fully designed," Hoefs says. By integrating fasteners and thermal management components, the number of individual components in the battery enclosure can be significantly reduced. Simplified assembly and logistics reduce costs. "Plastics are also corrosion-resistant and insulating. For example, plastics can reduce the risk of short circuits in the system. The low density and lightweight construction of plastic can reduce the weight of the housing, which is beneficial for increasing the range of electric vehicles. High-voltage battery enclosures must be highly adaptable to a wide range of needs. For example, it must be hard and strong enough to absorb a lot of energy in the event of a collision. This is tested by mechanical impact and crush tests. In the event of a car** or in the event of a thermal runaway of the battery, the casing must be flame retardant. Eventually, the enclosure must be integrated into the vehicle structure. "We will continue to work on optimizing component production and structural design," Hoefs said. Our goal is to work virtually, save costs in prototype trials, and reduce time-to-market for future series components. At the same time, in recent years, there has been a huge focus on reinforced plastics in automotive battery boxes, as evidenced by the fact that SGLCan, in collaboration with Chinese automaker NIO, has been working with Chinese automaker NIO to develop composite battery boxes, with SGLCARBON (Wiesbaden, Germany) announcing that it has partnered with Chinese automaker NIO to develop a carbon fiber reinforced plastic (CFRP) prototype battery case for electric vehicles. The CFK battery box is claimed to be 40 percent lighter than traditional aluminum or steel battery boxes and has high rigidity and about 200 times higher thermal conductivity compared to aluminum. "In addition, the composites have the best values in terms of water and air tightness as well as corrosion resistance," says Sebastiangrasser, Automotive Market Unit Manager of SGL Composites - Fibers & Materials. The bottom of the case and the lid include a sandwich core and several layers of carbon gel. The tool designs used to produce floors and lids were developed at SGL's Lightweight and Application Center, and the carbon fiber of these components is manufactured at SGL facilities in Moseslake, Washington, USA, and MUIR, ORD, UK. It is processed into scrim cloth in Wackersdorf, Germany. SGL manufactures the floors and covers as well as the assembly of the individual components at the plant in Riedim Innkreis, Austria. The case of the battery is said to be particularly lightweight, stable, and safe. According to reports, the entire battery compartment, including the batteries, can also be replaced within three minutes at NIO's own exchange station. SGL Carbon expects the demand for lightweight battery box solutions in the automotive industry to increase dramatically in the coming years as electric vehicles increase. The company is already working with various partners to further develop different battery boxes made of composite materials, which can be expanded to EV batteries of various sizes and designs in the future. "Lightweight construction is one of the core elements of NIO's technology roadmap. Using composite materials, especially high-performance carbon fiber in the battery compartment system, our vehicles offer better dynamic driving performance, longer range and very high energy density battery packs (more than 180Wh kg). These features are a perfect fit for NIO brand values such as ultimate product and system efficiency.
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