Experimental study on the effect of discharge modes and coolant types for single-phase immersion cooling of LiFePO4 batteries

As the power and energy density of lithium batteries increase, effective thermal management becomes crucial. Immersion cooling has emerged as a promising solution for this challenge. This study experimentally investigates the effect of coolant type on the electro-thermal performance and heat transfer intensity of immersion-cooled LiFePO4 battery systems under constant power discharge (CPD) and constant current discharge (CCD) modes. Through the self-designed refined test platform, the evolution of the critical electro-thermal performance of the battery system was accurately obtained. Results show that CCD is more affected by coolant types on thermal performance at discharge rate above 2C or 2P, while CPD leads to faster deterioration in the electrical performance of battery modules (eta(e)) as the P-rate increases. Moreover, C-V,C-Qf, the effect of coolant type on the coolant heat absorption is more pronounced during CCD, with stabilization of approximately 6.4 % at 2 similar to 4 C-rates or P-rates. Considering the temperature-dependent properties of coolants, the effect of coolant type on Nu (C-V,C-Nu) is more significant between 22 % and 27 %, which is higher than the effect on temperature difference. The dimensionless Mouromtseff Number (Mo/Mo-0) ranks the heat transfer capacity of coolants that can be called dielectric fluids (DFs) as DF1 > DF2 > DF3 > DF4, with DF2 being the most stable at 3.8 % change at 4C/P rate and DF4 the largest at 11.8 %. This paper provides data and theoretical support for the engineering application of immersion cooling technology.