Study on explosion venting efficacy of thermal runaway gases from lithium-ion batteries in a confined space: Impact of venting area

In thermal runaway (TR) incidents of lithium-ion battery (LIB) energy storage systems (ESSs), large quantities of toxic, flammable, and explosive gases are released. When these combustible gases accumulate in an enclosed space, they can easily trigger severe combustion and explosion events upon encountering an ignition source. Explosion venting is commonly employed as an effective measure to mitigate explosion hazards. This study investigated the TR explosion venting characteristics of 26700-type cells: a TR gas explosion experimental platform was constructed to trigger cell TR through electrical heating and ignite the released high-temperature gases, examining flame characteristics and explosion overpressure under different vent areas. Dimensionless coefficients $K_v$ and $K_s$ are used to quantify the venting capacity of the explosion vent. The research found that during the explosion venting process, the flame color transitions from initial yellow-white to red. After the flame front descends to the height of the vent, it transforms into oscillating flame. Three overpressure peaks occur inside the test chamber during the TR gas explosion of LIBs. The explosion overpressure can be reduced by more than 93 % through the installation of a vent in the 80 L test chamber. The dimensionless venting coefficient $K_v$ effectively characterizes the nonlinear relationship between vent area and explosion hazards: as $K_v$ decreases from 74.26 to 6.19, the average maximum overpressure peak drops from 27 kPa to 7.2 kPa, and the average deflagration index decreases from 220.73 kPa$\bullet$m/s to 3.96 kPa$\bullet$m/s. The venting efficiency is maximized when $K_v$ =8.25. This research verifies the effective protection of explosion vent design against TR gas explosions in LIBs and provides quantitative guidance for vent area design.