Quantitative evaluation of venting-induced heat flux in semi-confined battery packs during lithium-ion battery thermal runaway

The high-temperature multiphase flow vented by lithium-ion batteries (LIBs) during thermal runaway (TR) can significantly influence thermal runaway propagation (TRP) within confined battery packs. Quantitative analysis of the heating effect of unignited TR venting on neighboring cells is essential for understanding and predicting TRP behavior, particularly under semi-confined packaging conditions. In this study, we designed a modular experimental platform featuring an adjustable ceiling and peripheral baffles to emulate the semi-confined space of a battery pack. A distributed array of temperature-monitoring plates surrounding the triggered cell was used to record the transient heat flux induced by TR venting. Three critical parameters were systematically investigated in a stepwise spatial confinement framework: ceiling gap, trigger position, and state of charge (SOC). Reducing the ceiling gap from 100 mm to 15 mm markedly intensified the venting-induced heating: the maximum temperature rise of the plate adjacent to the trigger cell increased from approximately 44.1 °C–102.8 °C, while its thermal exposure integral (TEI) more than doubled. Center-triggered venting produced a more uniform but lower-intensity heat distribution over a wider area. In contrast, side-triggered venting-constrained by the enclosure-generated a localized high-heat region, where the maximum temperature rise and TEI on adjacent plates were approximately 20 % higher than in the center case, albeit over a smaller affected zone. Higher SOCs amplified the heating effect: at 100 % SOC, maximum temperature rise and TEI on adjacent plates were nearly double those observed at 50 % SOC. Based on these findings, an empirical heat-flux correlation incorporating multiphase venting effects was derived. While currently applicable to LFP cells under the tested conditions, this methodology can be extended to other battery configurations, supporting TRP modeling and informing future pack-level thermal protection strategies.