Investigating Lithium-ion Battery Sleep Mode Cooling in Extreme Ambient Conditions with Experimental and Predictive Modeling

Ambient conditions affect the thermal behavior of lithium-ion batteries in electrified vehicles. In hot climates, when a vehicle is parked and cooling is inactive (sleep mode), high battery temperatures can arise, leading to three key issues: (1) accelerated battery degradation and reduced lifespan, (2) temporary power limitations affecting vehicle performance, and (3) increased cooling demands, reducing cabin cooling capacity and affecting passenger comfort. This study evaluates an indirect liquid cooling system operated in sleep mode cooling. The system, using a water-glycol mixture at flow rate of 1.2 L/min, was tested on a battery pack of 36 prismatic cells in a thermally isolated chamber, exposed to initial temperatures of 50.0◦C, 60.0◦C, and 69.5◦C. A group of 26 thermocouples monitored the thermal response, along with the inlet coolant temperature. Results revealed an exponential cooling response across all cases, with maximum temperature differences of 7.6◦C, 10.5◦C, and 12.7◦C observed at approximately 15 minutes for initial temperatures of 50.0◦C, 60.0◦C, and 69.5◦C, respectively. Higher initial temperatures extended cooling durations, with every 10◦C increment adding approximately 15 minutes for the battery temperature to stabilize. The cooling trend remained consistent, with temperature differences gradually decreasing over time after the peak. Furthermore, a physics-based lumped model was calibrated to predict thermal behavior, achieving mean absolute and root mean square errors of 0.3◦C and 0.4◦C, respectively. The predictive model provides valuable insights into optimizing sleep mode cooling strategies. The findings contribute to enhancing battery thermal management in extreme climates, promoting energy efficiency and vehicle reliability.