Despite the predicted weight and cost advantages for various alternative multi-material concepts, today’s battery pack structures are predominantly made from aluminum and/or steel. As a first step OEMs are looking at replacing the less complex components, such as the lid and bottom protection plate, parts that don’t affect the battery pack internal design very much. In fact, these are the most common parts during the development phase of the complete battery pack. It is expected that experience with composite solutions in lids and protection plates will promote further use for more structural parts in future.

Electric vehicles brought on to the market require 5 minutes safe escape time after a thermal runaway has been detected, as e.g. stated in regulation ECE R100 in Europe, or GB38031-2020 in China. It means that the box structure, and for many layouts especially the lid, must resist high flame temperatures and particle blast resulting from such a thermal runaway. Depending on cell chemistry and layout type, flame temperatures can typically vary between 800 to 1200°C, and unprotected aluminum will burn through in just a matter of seconds. Aluminum can be protected with intumescent coatings, mica layers, or thermal blankets, but also composite materials may have good inherent burn-through resistance, while at the same time protecting the car interior from too high temperatures. Many different solutions are proposed by material suppliers and tiers, but it is difficult to compare them on effectivity and efficiency, the more as everybody tests fire resistance in a different way. For this reason, AZL designed a fire resistance test stand that can test various materials and joints on a material sample level, while collecting strength data under fire loading. In this way the strength results as function of temperature can be used in a CAE analysis to predict whether a complete pack could survive an internal (or external) fire and will not burst open, releasing flames and setting the car on fire.

AZL’s standard comprehensive test procedure includes:

Material Strength Test:

• 3 different nominal flame temperatures: 800°C, 1000°C, 1200°C
• During exposure to fire: tensile force of 0.5 kN during 10 minutes, simulating the stresses due to overpressure in a real pack
• If no failure occurs, the force is increased up to 5 kN to measure the strength of the material under fire.

Particle Blast Test:

• Calibrated setting with equal damage effect of thermal runaway with real battery cells
• Flame exposure to 1200°C for 80 seconds
• This is followed by 10 seconds of blasting at ~5.5 bar local overpressure, resulting in a particle mass flow of 20 g/s.

Test specimen size for both tests is 200 mm x 100 mm, flame exposure along the full specimen width, to obtain tensile strength data under fire, that can be used in CAE simulations. Approximately 10 test specimens required, 2 for each tests and temperature.

Currently, AZL has tested over 100+ different material solutions under these conditions, enabling a robust comparison of fire resistance capabilities across a range of materials. This method provides OEMs and material suppliers with valuable data to guide material selection, enabling development of future battery pack components with much higher levels of safety and durability.

Ongoing Development for Future Battery Pack Protection

As battery technologies, their properties and test strategies continue to evolve, AZL is constantly expanding its testing capabilities. Working closely with OEMs, AZL has recently developed a new test procedure for high temperature and high intensity particle blast testing.

This customizable testing profile is designed to simulate a range of thermal runaway behaviors based on real-world experiments and data from other sources, ensuring the test method remains relevant as cell chemistries and pack layouts change.

This continuous improvement in application-relevant fire testing positions AZL as a leader in helping OEMs meet the stringent safety requirements of next-generation electric vehicles. With AZL’s rigorous testing protocols, manufacturers can more confidently develop battery packs that comply with regulations and show high safety for their customers.