Reducing Temperature Gradients in High-Power, Large-Capacity Lithium-Ion Cells through Ultra-High Thermal Conductivity Heat Spreaders Embedded in Cooling Plates for Battery Systems with Indirect Liquid Cooling 2013-01-0234

For lithium-ion battery systems assembled with high-capacity, high-power pouch cells, the cells are commonly cooled with thin aluminum cooling plates in contact with the cells. The cooling plates extract the cell heat and dissipate it to a cooling medium (air or liquid). During the pack utilizations with high-pulse currents, large temperature gradients along the cell surfaces can be encountered as a result of non-uniform distributions of the ohmic heat generated in the cells. The non-uniform cell temperature distributions can be significant for large-size cells. Maximum cell temperatures typically occur near the cell terminal tabs as a result of the ohmic heat of the terminal tabs and connecting busbars and the high local current densities. In this study, a new cooling plate is proposed for improving the uniformity in temperature distributions for the cells with large capacities. This new cooling plate consists of an aluminum base plate with the strategically incorporated heat spreaders made of thermal pyrolytic graphite (TPG). TPG has a low density and an ultra-high in-plane thermal conductivity. The performance of the new composite cooling plate is simulated using a 3D finite element analysis model for a battery module stacked with 70Ah Li-ion battery cells cooled indirectly with liquid. The electro-thermal behavior of the battery system is simulated under 210A continuous discharge from 100% to 20% state of charge. Simulations results demonstrate that the composite cooling plate with embedded TPG heat spreaders can rapidly conduct, spread and dissipate the cell heat to the cooling medium. The achieved uniform cell temperature distributions improve the safety and durability of the cells as well as the battery pack; it may also eliminate the need for cooling the cell terminal tabs and busbars with a separate cooling system.