Short charging times of BEVs and a long battery life are seen as key enabler for a convenient e-mobility and a broad customer acceptance. The battery thermal management system plays an important role to meet these requirements.

Battery immersion cooling is a very promising approach to manage the increased heat losses during fast charging and to achieve a long lifetime of the cells by improving the temperature homogeneity within and between the cells. With immersion cooling, the cells, cell tabs and all electrical connections are in contact with a dielectric fluid. To take advantage of its full potential, a deep understanding of the interacting electrical, thermal and fluid dynamic phenomena occurring inside such a battery module is required.

In this contribution, the setup and the results of an experimental study of an immersion cooled module and a module with a state-of-the-art cooling concept are presented. The battery modules (Fig. 1), equipped with 65 Ah automotive NMC pouch cells, are explicitly designed and built for the detailed investigation of the dependency of the thermal management on the battery behavior. Defined and equal boundary conditions are the basis for a comparison of the thermal performance of the two cooling concepts, for the first time in an application-related setup.

Particular attention is paid to the fluid distribution and the flow concept with built-in options for the flow manipulation in the immersion cooled module. The effect of the fluid flow conditions on the temperature and the temperature homogeneity in the cells and the module, as well as the potential for the optimization of the thermal performance is addressed. The investigations are supplemented by the comparison of the immersion cooled module with the conventionally cooled battery module. The performance differences in various operating points for charge and discharge are demonstrated and analyzed. Furthermore, the variation of boundary conditions e.g., the volume flow rate or the fluid temperature allows for the analysis of relevant differences in the cooling concepts’ operating principles.

The experimental measurements reveal the advantages of immersion cooling over conventional cooling concepts. The benefits of a reduced average temperature and smaller thermal gradients within the cell as well as the cooling of electrical conductors are discussed in the light of currently limited fast charging rates of BEVs and battery lifetime. The application-related setup enables transferability of the insights to automotive applications and will help researchers and developers from industry and academia towards developing better thermal management solutions for BEVs.