(41ba) Assessing the Risks of Thermal Runaway and Fire Propagation in Battery Energy Storage Systems with ARC, GC-MS, and Burning Velocity Testing

Lithium-ion batteries (LIBs) play a critical role in modern energy storage and power supply applications. As the global demands for portable power sources and sustainable energy alternatives continues to elevate, reliance on lithium-ion technology is expected to grow correspondingly. However, the inherent risks associated with LIBs necessitate rigorous safety testing. Such batteries are susceptible to thermal runaway (TR), a condition in which a battery overheats and potentially leads to fires or explosions. Consequently, safety testing is essential to assess the batteries' performance under stress conditions and ensure their reliability throughout their lifecycle.

The UL 9540A standard is an important safety testing method for evaluating the fire characteristics of a battery energy storage system (BESS) that undergoes TR. The standard outlines cell testing protocols, including methods for inducing thermal runaway, documenting vent temperature and TR onset temperature, and collecting vent gas and quantifying its composition. The vent gas mixture is then replicated to determine its flammability characteristics, including the lower flammability limit (LFL), burning velocity (BV), and maximum explosion pressure (P_max). The data generated then informs the fire and explosion protection requirements for BESS installations.

This study evaluates TR and fire propagation hazards according to UL 9540A standard methodology, utilizing a combination of testing techniques. Accelerating Rate Calorimetry (ARC) is employed to initiate battery thermal runaway and provide insights into the thermal behavior of battery cells under various conditions. This allows for the identification of critical temperature thresholds (TR onset and vent temperatures) and exothermic reactions that can lead to thermal runaway. Gas Chromatography-Mass Spectrometry (GC-MS) analyzes the composition of volatile hydrocarbons (C1-C7), while Gas Chromatography-Thermal Conductivity Detector (GC-TCD) quantifies permanent gas components (H₂, CO, CO₂) emitted during the TR event. Minor acidic gases (e.g., HF) are detected using a Draeger Tube test. The determined vent gas composition facilitates the replication of a synthetic gas for assessing fire propagation hazards. Burning velocity tests are conducted to evaluate the combustion characteristics of the vent gas and the resultant fire propagation dynamics. The LFL is measured according to ASTM E918, and explosion severity (P_max and rate of pressure rise) is determined using the EN 15967 method.

The Li-ion chemistries compared in this study are lithium iron phosphate (LFP) and lithium cobalt oxide (LCO). TR initiation methods include external heating, nail penetration, and overcharge. Results concerning vent temperature, onset temperature, gas release quantity, and gas composition are also compared.