Electrochemical-thermal numerical model of a lithium-ion battery under natural convection liquid immersion cooling conditions

• P2D electrochemical battery model fully coupled with dielectric fluid domain. • High charge and discharge rate of 4C investigated. • Significant heat flux at electrode terminals due to battery material anisotropy. • Large core-to-surface thermal gradients under natural convection liquid immersion. The suitability of direct contact liquid immersion cooling as a method of battery thermal management is investigated numerically in this study, where a 26650 LiFePO 4 cylindrical cell is subjected to natural convection liquid immersion conditions. The internal electrochemical behaviour of the cell is replicated through the implementation of the Newman pseudo two-dimensional model, while the liquid domain is also simulated to capture the heat transfer from the cell during both charging and discharging at a rate of 4C. The average surface temperature of the cell is limited to maximums of 294.6 K and 300 K during charging and discharging respectively as a result of the strong fluid agitation induced by natural convection from its surface. The convective heat flux is significantly elevated at the electrode terminals due to their smaller surface area and the higher thermal conductivity along the cell’s vertical axis. The poor radial thermal conductivity contributes to the establishment of notable core-to-surface temperature differences, reaching 2.5 K and 6.8 K during charging and discharging respectively. These thermal gradients are of concern with regard to accelerated degradation of the cell.