Decrease risk of battery housing fires when using our Tepex® composite, a lightweight sustainable material

The materials used to make electric vehicle battery housings play a key role in passenger safety. In order to focus on safety and performance of EVs, engineers need to use a material that enhances the thermal stability of batteries, prevents thermal runaway, and mitigates the risk of fire or explosion. At Envalior, we tested a new composite under our Tepex® brand, which is ideal for components inside an EV battery. The composite, with very low test specimen thicknesses, passed the standard thermal runaway tests for EV battery housings.

As electric vehicles (EVs) continue to play an increasingly important role in motorized transportation, battery safety is of utmost importance. EVs have been gaining momentum—last year global sales of EVs rose 31% to 13.6 million units, according to market research firm Rho Motion. Fully electric vehicles, known as battery electric vehicles (BEVs), made up 9.5 million units of that total.

As an engineer, you know that the materials used to make EV battery housings play a key role in containing possible fires. To ensure EVs are safe and to maintain their performance, you need to utilize a material that enhances the thermal stability of batteries, prevents thermal runaway, and mitigates the risk of fire or explosion. 

We tested a new composite material to ensure it can withstand a fire

As you are well aware, every effort must be made to ensure that fire does not spread to the entire vehicle and endanger occupants. To make sure the material you use for battery housings can withstand extreme stresses to which the battery housing is exposed when a fire breaks out, a thermal runaway test must be done. And we did just that for you.

We tested a new composite under our Tepex® brand, which is ideal for components inside an EV battery. The composite, with very low test specimen thicknesses, passed the standard thermal runaway tests for EV battery housings. The composite has a high resistance to the extreme conditions of a battery cell fire, which is attributed to the non-flammable long and continuous fibers that reinforce the material in a multi-layer structure. The structural material is capable of withstanding the extreme pressures and temperatures in excess of 1000°C, and in particular the rude bombardment by abrasive hot particles that occur during the thermal runaway of battery cells.

The composite can pass the standard tests covering this – such as the battery enclosure thermal runaway (BETR) test to UL 2596 – with test specimen thicknesses of just two millimeters or less. Even with wall thicknesses of just two millimeters, the material easily meets the requirements of the battery stress test involving particle bombardment, as conducted by svt Holding GmbH, a leading company in various areas including industrial fire safety applications.

Upon exposure to particle bombardment, the Tepex® test specimen did not undergo burn through, neither when the temperature at the end of the test was as high as 1400°C nor for another 20 seconds after. This was without any additional protective measures in the material and without supporting metal sheets.

A high degree of safety is ensured even with low wall thicknesses and, in turn, low weight. The composite also acts as an effective barrier against external fire sources. In the fire pan test, based on UN regulation 180, 6.2.4, and simulates highly realistic battery fire scenarios in accident situations, burning fuel did not create holes in the material. The fibers did not ignite.

You can create a lightweight design

Another benefit of the new composite material is that it is much lighter than steel or aluminum. The density of an exclusively glass-fiber-reinforced material variant is around 70 percent less than that of steel. And if the core layer of the composite is reinforced with carbon fibers, the difference in density is greater. When compared to aluminum, our composite can be significantly more than one third lighter. 

You have many choices of fibers, fiber arrangements, and matrix materials 

The composite comprises several layers of long and/or continuous fibers. Depending on the requirements, each layer can be reinforced with special fiber textiles. The total fiber content in the composite is more than 50 percent by weight. Polyamides or other engineering plastics can be used as matrix materials. Thus, you can request that the composite be specially adapted to your requirements.

The composite is available in a variant containing recycled carbon fibers, putting the proportion of recycled material in the composite as a whole at around 36 percent by weight. This composite is especially good for housings that are subject to very high mechanical loads. Carbon fibers make it the material of choice when the housing needs to be electromagnetically shielding. All fibers  are impregnated with matrix plastic, which creates a closed plastic surface. This ensures outstanding electrical properties such as high dielectric strength and surface resistance. It also offers excellent tracking resistance (CTI A > 400 V, Comparative Tracking Index).

You can use the composite in immersion cooling fluids 

The polyamide-based composites are also resistant to 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 done in order to dissipate the significant amount of heat that is generated when batteries undergo quick charging. Long-term storage in standard dielectric immersion cooling fluids showed that even after 1,500 hours, the composite does not undergo any changes to its mechanical properties or start to swell, nor does it release any substances into the cooling fluid. 

You can easily recycle the composite 

As a thermoplastic material, the new composite – like all other products in the Tepex® organic sheet range – can be easily recycled, meaning that production waste can be shredded and then reused as quality-assured recycled compounds for injection molding. Components can also be recycled in this way. Plus, composites and components can also be recycled by means of solvolysis and depolymerization. 


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Dirk Bonefeld

Dirk Bonefeld

Head of Global Product Management and Marketing Tepex

After working for different companies in the field of thermoplastics processing, Dirk Bonefeld joined Bond-Laminates GmbH, now a company of Envalior, in 2011 as Head of Research and Development. From 2017 to 2021 he was Head of Marketing and Sales for Consumer Electronics and Sports, and in 2021 became the Head of Global Product Management and Marketing for Tepex. Dirk has a PhD in Mechanical Engineering and Polymer Technology.

Published on

15 March 2024


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