Post-venting immersion cooling of over-heated battery: Effect of thermal runaway risk, cell scale, and quenching strategy

The risk of thermal runaway, fire, and explosion remains the ultimate barrier to battery systems. The costly immersion cooling offers a good thermal management solution, but it still cannot quench the battery thermal runaway. This study explores the emergency immersion cooling of a battery by dielectric fluid (HFE-7200) in the time window between venting and thermal runaway for 13 types of cylindrical cells, ranging from 18650 to 32650 and from 447 to 1,190 Wh/L. Three post-venting modes are observed: (I) internal meltdown with a high risk of thermal runaway, (II) lid open during venting with a low risk of thermal runaway, and (III) safe venting without risk of thermal runaway. We found that larger cells undergoing safe venting or lid open require no more than 1/16 of the cell volume of dielectric coolant to completely eliminate thermal-runaway risk. The high-power smaller cells, exhibiting internal meltdown, reach peak temperatures over 600 °C during thermal runaway, requiring up to 1/2 of the cell volume of coolant to prevent the onset of thermal runaway. Heat transfer analysis is proposed to reveal the minimum coolant-to-cell volume ratio for post-venting immersion cooling of a battery with different volumes, specific surface areas, and energy densities. This study further verifies the early emergency cooling strategy for preventing battery thermal runaway and explores its scale effect for larger batteries, guiding the design of future battery safety management systems.