Suppression of Thermal Runaway Propagation in Large-Capacity Battery Energy Storage Systems Using Immersion Cooling

Thermal runaway propagation in large-capacity battery energy storage systems can be driven by casing conduction, vented products, and pack-level thermal coupling. This study experimentally evaluated whether a static dielectric-liquid boundary can prevent propagation between 314 Ah rectangular cells. Three-cell modules were tested in air and in two liquids at relative immersion heights of 10–20 mm, followed by two non-circulating 1P52S pack tests. Propagation was assessed using trigger-cell temperature and venting, adjacent-cell voltage and venting, and post-test state. Under AIR-0, adjacent-cell voltage fell to 0 V and propagation occurred; the trigger cell reached its primary peak of 613 °C at 1560 s, followed by a secondary-heating maximum of 971 °C at 1893 s. All six immersed module tests maintained stable adjacent-cell voltages, with no adjacent-cell venting or propagation, while trigger-cell maximum temperatures were 403–498 °C. Using a common window from trigger-cell venting to its primary peak, the apparent equivalent surface-averaged heat-flux indicator was 31.2 kW/m2 in AIR-0 and 22.5–29.3 kW/m2 under immersion, corresponding to a reduction of approximately 6.1–27.8%. In both pack tests, no fire, explosion, adjacent-cell venting, or pack-level propagation occurred. Under the tested module and pack configurations, no propagation from the trigger cell to adjacent cells was observed with static immersion, supporting its potential as a passive safety boundary for large-capacity battery storage systems.