- New composite material passes thermal runaway tests
- Very large battery housings can also be injection-molded
- Comprehensive material tests for the thermal management of batteries
Düsseldorf, May 19, 2023 – Envalior will have its own booth at Battery Show Europe 2023 in Stuttgart, Europe’s biggest trade show for cutting-edge technologies and production processes for batteries for electric and hybrid vehicles. “We regard new forms of mobility such as electric vehicles as being among the top growth areas for our versatile range of thermoplastic structural materials,” says Julian Haspel, head of the e-Powertrain team in application development at Envalior. “One of the highlights of our appearance at the show will be a new continuous-fiber-reinforced composite in the Tepex range that targets battery housings. It has been designed to withstand the extreme stresses to which battery housings are exposed when battery cells catch fire, as simulated in typical testing.” Envalior will also be presenting a study showing that even large battery housings can be injection-molded in a way that is cost-effective, partly with the aid of large blanks made from Tepex composites. “That means that in addition to compression molding, there is another method available for using thermoplastics to manufacture these highly complex safety components subject to considerable stress,” adds Haspel.
Thermal runaway tests passed with a test specimen thickness of less than three millimeters
Vehicle battery cells are at risk of exothermic reactions leading to fires as a result of factors such as electrical malfunctions or mechanical damage. These can involve temperatures well in excess of 1,000°C as well as very high pressures due to gases escaping and flames emanating in specific directions with incandescent particles from components such as the cell cathode and anode. This is known as a thermal runaway process and needs to be contained as effectively as possible. It is therefore essential for materials used in battery housings to be capable of withstanding these exceptional conditions so as to prevent the entire vehicle from catching fire, or at least to give the occupants enough time to get themselves to safety. “Our new composite material passes the tough thermal runaway tests that currently represent the market standard, simulating just such extreme stresses, and it does so on test specimens less than three millimeters thick. That makes it a lightweight alternative to materials such as steel and aluminum in the production of battery housings,” explains Dr. Stefan Seidel, head of research and development for Tepex. The outstanding resilience of the composite, which is nearing the end of development, is based primarily on the continuous-fiber fabric used to reinforce its matrix. Another point in the composite’s favor is that its thermoplastic matrix makes it easy to recycle. It is therefore suitable for use in setting up sustainable material cycles. At Battery Show Europe, Envalior is planning to show a video depicting a thermal runaway test on a Tepex specimen.
Tepex inserts lower injection pressure by around two thirds
Injection-molding large battery housings for electric vehicles is technically challenging and has undergone little in the way of comprehensive analysis and testing to date. That is because it requires very large injection-molding machines with high clamping forces. The latter are a consequence of the expansive component geometries and the considerable injection pressures. Greater wall thicknesses are also required so that the large tools can be completely filled with molten plastic. That calls for a lot of material. For example, when polyamide 6 is used, it means plasticizing 40 kilograms of material, if not more. In response to customer demand, Envalior has devised another new system for injection-molding such housings that overcomes these obstacles. Components measuring 220×160 centimeters were tested as part of a feasibility study. The concept involves large Tepex sections inserted into the tool and overmolded to be used as bases for the housings, which are usually very flat. “Our simulations show that this can cut injection pressure by around two thirds relative to a purely injection-molded part. That, in turn, makes it possible to use smaller and more affordable injection-molding machines with much lower clamping forces. At the same time, the wall thicknesses in the floor area can be reduced significantly – thanks in part to the excellent mechanical performance of Tepex. All in all, this approach results in exceptionally competitive manufacturing costs for battery housings,” explains Haspel.
Resistant to dielectric coolants and water–glycol coolant mixtures
The Envalior booth will also highlight thermal management in batteries for electric vehicles. This is essential not only for vehicle performance and range but also for fast battery charging. Envalior will be presenting the results of long-term stability testing on selected thermoplastics for battery components in widely used dielectric immersion cooling fluids. Entire battery housings are often submerged in these electrically non-conductive and highly flame-retardant fluids as a means of direct cooling. This is known as immersion cooling. “The tests have shown that the polyamide 6, polyamide 66 and PBT compounds do not change their mechanical properties even after more than 1,500 hours of storage, nor do they swell like many polyolefins do, and they also do not lose their flame-retardant characteristics. Consequently, there is no problem with using them in dielectric fluids,” says Haspel.
Water–glycol mixtures are also used in the cooling circuits of electric vehicles. Instead of polyamide 66, the associated cooling components can be made out of polyamide 6 compounds, which are substantially more affordable. This is because even though they are not hydrolytically stabilized, they usually offer perfectly adequate durability owing to the fact that the water–glycol mixtures do not reach temperatures as high as those found in internal combustion engines. This has been shown in the results of long-term stability testing on both components and test specimens that was originally carried out for applications in the cooling systems of internal combustion engines. Envalior is currently performing tests at 80°C and 100°C in which the storage time has been extended from the usual 1,000 and 1,500 hours; respectively, to 10,000 hours. “We are already seeing that the polyamide 6 compounds do not suffer any deterioration in their properties under these conditions. We will be presenting the initial findings at Battery Show Europe,” says Haspel.
Envalior is a new company formed as a result of the merger of two industry leaders, DSM Engineering Materials (DEM) and LANXESS High Performance Materials (HPM). It is one of the world’s leading manufacturers of engineering materials. It is owned by private equity investor Advent International and specialty chemicals company LANXESS.
Battery Show Europe will take place on May 23–25, 2023, at the exhibition and trade center in Stuttgart. Envalior will be at booth F70 in Hall 10.
