Innovation – Thermal Management

Immersed liquid thermal management with high tech fluid Novec

To meet the requirements of LiBAT, the battery weight needs to stay low while powerful operation over extended periods of time needs to be possible. The innovative thermal management approach in LiBAT realizes a high degree of integration with respect to thermal management for both batteries and power electronics and is thereby contributing to weight saving while meeting the power demands.

The LiBAT design addresses these challenges with an immersed liquid thermal management approach using the high-tech fluid Novec from 3M, a dielectric liquid already in use in some high-performance applications and for cooling servers. Due to the fact that the operating temperature in the battery system has considerable impact on the aging process and the power output of the individual battery cells it is absolutely necessary to keep the cells effectively and homogenously well-tempered. Cooling is needed due to power loss heat generation of the battery cells during use. Furthermore, heating might be needed before using the cold soaked cells at low temperatures to prevent damage. To regulate the optimal operating temperature of the cells in the LiBAT Battery they are directly immersed in the coolant, which is also an integral part of the safety concept. Moreover, the immersed approach allows to handle cells and power electronics within a single thermal cycle.

All cells in the string are contained in a block region with dedicated housing. The space between cells and housing is immersed by coolant. The arrangement of the cells approaches the tightest density but leaves some space between them building a thin channel pattern. The MLIs are cooled indirectly trough an aluminium plate which is in contact to the cooling fluid on its bottom side, as pictured in figure 1.

Figure 1: Design of thermal management

A thermal management system with dielectric fluid is recommended to behermetic closed.  All components should be resistant to the used liquid. The further components in the test rig thermal design are arranged similar to the schematic in figure 2:

Figure 2: Schematic description of thermal test rig design