Investigation on the thermal runaway characteristics of Lithium-ion batteries based on the immersion cooling using supercritical carbon dioxide

Lithium-ion batteries (LIBs) are widely used in electric vehicles and energy storage systems, but thermal runaway (TR) poses serious safety risks. Conventional immersion coolants (mineral oil, lipids) suffer from low thermal conductivity, low specific heat, and high viscosity, limiting their cooling capacity. Supercritical carbon dioxide (sCO 2 ) offers unique advantages near its critical point, including high specific heat and low viscosity, making it a promising alternative. Extending sCO 2 cooling beyond conventional battery heat-dissipation scenarios, this study numerically evaluates sCO 2 immersion cooling for suppressing thermal runaway propagation (TRP) by directly comparing the TRP characteristics of LIB modules under sCO 2 and mineral-oil immersion cooling across different cell spacings and coolant flow rates and by clarifying the associated energy-transfer pathways. The results show that, for mineral oil at a cell spacing of 1 mm, increasing the mass flow rate from 1.17 g/s to 3.00 and 6.50 g/s delays second-cell TR from 65.5 s to 68.6 and 80.7 s, respectively, whereas further increases to 10.0 and 15.0 g/s advance it to 51.7 and 28.8 s, respectively. Increasing the cell spacing from 1 mm to 3 and 6 mm blocks TRP in the mineral-oil system; in contrast, sCO 2 prevents TRP under all tested spacings and flow rates. The near-pseudocritical specific-heat peak of sCO 2 provides pseudo-critical heat-capacity enhancement with minimal temperature rise, while its gas-like low viscosity enhances convective heat transfer; consequently, sCO 2 rapidly absorbs and disperses heat, prevents heat propagation to adjacent cells, and improves temperature uniformity.