Phase-change Thermoplastics Can Prevent EV Battery Thermal Runaway

Engineering plastics provider Sabic recently reported test results that underscore the potential of thermoplastic-based thermal runaway barrier solutions to prevent fire spread in electric vehicle (EV) batteries. The Sabic sub-system level test series showed that a battery module box made from the company’s Stamax 30YH570 long-glass-fiber polypropylene (PP) resin with an intercellular thickness as thin as 1 mm has potential to prevent thermal runaway propagation in 18650 cylindrical cells.

The Stamax grade reportedly provides the necessary thermal insulation and flame resistance to reduce the chances of cell-to-cell propagation in a thermal runaway scenario and, thus, mitigate the risks of a catastrophic safety incident. This material in combination with compressible foams also has shown promising results in containing thermal runaway propagation in prismatic and pouch cells.

Performance verified by UL.

The new results build upon previous independent evaluations of Sabic’s Stamax 30YH570 resin. In 2023, the product earned the UL Verified Mark from Underwriters Laboratories (UL) for effective flame-delay performance. The assessment was based on UL 2596, Test Method for Thermal and Mechanical Performance of Battery Enclosure Materials, using the thermal runaway box method.

Cylindrical battery cells arranged within a thermal runaway barrier made of Sabic’s flame-retardant Stamax resin with a minimum intercellular gap of 1 mm. Image courtesy of Sabic.

“We are pleased to share this additional validation of our thermoplastic's’ strong potential for use in EV battery components and systems,” said Fahad Al-Harthi, global director, automotive. “Our portfolio of flame-retardant materials, combined with our expertise in application design and fire-polymer interaction, can help enable new thermal runaway barrier approaches. We look forward to continued collaboration across the automotive value chain to help improve the safety, efficiency, and performance of EV battery systems.”

Thermal runaway barrier testing.

The thermal runaway propagation tests are performed using a cluster of 15 commercial 18650 and 11 21700 lithium-ion battery cells enclosed in a steel chamber, with and without injection-molded Stamax 30YH570 resin blocks serving as a thermal barrier. Initiating cells were thermally abused by heating them through an electrical tape to begin thermal runaway. In tests without the thermal barrier in place, the electric and chemical energies stored in these cells were discharged in the form of high-temperature gas, open-flame, high-speed particles, and a sudden increase of pressure inside and around the test chamber. The thermal runaway immediately propagated to all neighboring cells due to the uncontrolled heat transfer, creating fire hazards and severe damage to the EV battery pack.

Conversely, in tests using the thermal barrier made from Stamax 30YH570 resin, heat transfer and thermal propagation from thermal abuse of initiating cells were effectively suppressed, and all remaining cells remained safe and intact.

This flame-retardant material changes phase from solid to liquid and gas and removes heat via latent heat and intumescent capabilities during severe thermal events, allowing it to act as an effective thermal shield to mitigate heat transfer and fire spread.

Applications in EV batteries and more.

At the recent NPE show, Sabic also highlighted EV battery applications that successfully employ the company’s advanced thermoplastics. One is the battery module from the 2023 Hyundai Ioniq 6. This application uses Sabic’s H1030 PP compound for module enclosures. The 30% glass-fiber-reinforced, non-halogenated, flame-retardant material meets China’s GB/T 41467.3-2015 fire safety regulation for EVs surviving five minutes at 1000°C.

Additional EV battery components on display, such as enclosures, end plates, and busbars, either in production or developed as prototypes, demonstrated various performance advantages of thermoplastics over conventional metals for these applications. Benefits include weight and cost reduction, increased functional integration, and enhanced electrical and thermal insulation.