Electrification of private transport will be required and is expected to be mandated by governments to reduce carbon dioxide emissions from this sector. This transformation is expected to significantly increase requirements on electric vehicles to meet customer demands. Battery charging time is one of the top concerns of consumers who consider buying an ev. batteries need to deliver and handle much higher currents to allow dynamic vehicle driving and ultra-fast re-charging as well as meeting highest battery safety standards to reduce fire risk. Very careful thermal management will be required to pre-condition the battery for fast charging and then during fast charging to prevent local cell temperatures exceeding 50°c. consequently, BEV and PHEV battery management systems are surprisingly sophisticated and can monitor individual cell temperatures and regulate charging rates to cap peak temperatures. overall rates of charging are thus influenced by temperature excursions within individual cells such that charging rates and charging times can be slowed considerably. The simplest and cheapest cooling technologies utilize air, but these are becoming obsolete as the demand for increased energy densities rise, more advanced thermal management schemes are appearing that use liquid cooling with water–glycol mixtures. Immersive thermal management designs are under development for next generation of electric vehicles. in these systems the fluid is in direct contact with electric parts in a battery, cells and busbars, which allows to transfer heat directly and thereby control temperature more effectively than indirect systems with a cold plate design. Conventional water/glycol coolants are significantly more conductive for electric currents, these are therefore not suitable for immersive systems. Immersive thermal management systems require fluids with good dielectric properties to ensure electrical insulation and to prevent electric shorts over the lifetime. Shell is currently developing thermal fluid technology aimed at matching these needs through collaborative relationships with leading primary and tier 1 equipment manufacturers. A newly designed battery module test rig equipped with pouch cells and immersive cell tab cooling was installed at the shell technology center Hamburg. Ultra-fast charging with an uplift from 10% to 90% soc was demonstrated with this system in less than 12 minutes. Immersive thermal management with dielectric fluids is also beneficial in meeting the latest safety and abuse requirements. Shell demonstrated “passes” in abuse tests with cylindrical, prismatic and pouch cells preventing thermal runaway propagation in collaboration with several partners using shell thermal fluids in different immersive battery module designs. Experiments without dielectric fluid present in the modules resulted in massive thermal propagation. In conclusion, the thermal fluid can play a key role to enhance battery safety. Thermal fluids can also be considered as an alternative fluid to transmission fluids for direct e-motor cooling when the fluid is not required to lubricate the e-motor bearing. Shell thermal fluids have already been successfully used in direct cooling of e-motors and inverters. A low viscous shell thermal fluid is used inside the Nissan formula e race car to cool both the e-motor and inverter.
Dr. Volker Null, Technology Manager Thermal & Dielectric Fluids, Shell