The initial reaction pathway of the thermal runaway phenomenon that triggers electric vehicle battery fires has been revealed. It is expected to be utilized as basic data to enhance battery safety.
A research team led by Hong Jong-seop from Yonsei University’s Department of Mechanical Engineering has precisely identified the decomposition mechanism of the solid electrolyte interface (SEI), which has been pointed out as a major cause of electric vehicle battery fires. The study results were published in the international academic journal ACS Energy Letters on the 24th.
As the adoption of electric vehicles has recently expanded, ensuring battery safety has emerged as a significant global challenge. In particular, the ‘thermal runaway,’ where exothermic reactions occur in succession inside the battery, can lead to critical incidents such as fires and toxic gas emissions. However, the decomposition reaction mechanisms of the internal substances that induce this phenomenon have remained unresolved challenges for a long time.
Specifically, the SEI, a key protective layer of electric vehicle batteries, is a thin layer that naturally forms on the electrode surface during the migration of lithium ions, playing a decisive role in the battery's lifespan and safety. However, the decomposition reaction pathways of the substances within this SEI at high temperatures have not been clearly established until now.
The research team focused on lithium ethylene monocarbonate (LEMC), a representative organic component that makes up the SEI. They synthesized high-purity LEMC samples and quantitatively analyzed the pyrolysis reaction using these samples, combining various analytical techniques and simulations to accurately trace the actual reaction pathways.
As a result, it was found that a large amount of heat and flammable gas is released in the initial decomposition reaction of LEMC, which starts at around 110 degrees Celsius. This elevates the temperature and pressure inside the battery, increasing the risk of fire. In other words, it scientifically demonstrated that this could be a precursor to the thermal runaway phenomenon.
Professor Hong Jong-seop noted, "Thermal runaway is not merely a phenomenon that occurs at high temperatures, but rather a very sophisticated reaction process that begins with the decomposition of specific organic materials within the SEI." He expressed hope that this research would serve as an important foundation for the design and safety enhancement of next-generation batteries.
References
ACS Energy Letters (2025), DOI: https://doi.org/10.1021/acsenergylett.5c01003