Background
In recent years, the potential benefits of immersion cooling have expanded into the realm of battery cooling, particularly for electric vehicles (EVs). Thermal runaway (TR) remains a significant concern in lithium-ion battery systems, especially under abuse conditions such as nail penetration, which can simulate real-world vehicle crash scenarios. The goal of this project was to explore how immersion cooling with controlled fluid flow rates and durations could mitigate TR during nail penetration abuse tests. This research investigated the cooling system’s ability to not only prevent the initial onset of TR but also to suppress its spread in battery packs under crash-induced cell abuse scenarios. By controlling coolant flow rates and durations, the project established optimized parameters for enhancing thermal management during such extreme conditions.
Approach
The experiments were conducted on a seven-cell configuration of LG M50T INR 21700 cylindrical cells, housed in an enclosure filled with continuously circulated coolant, as shown in Figure 1. The system was designed to mimic the dynamic conditions of a vehicle crash, focusing on how varying the cooling flow affected the cells' response to thermal abuse. All the experiments were conducted using an off-the-shelf dielectric coolant. The main objectives were to assess how effectively the dielectric immersion coolant could prevent the spread of thermal runaway from the penetrated cell to the other cells in the module and to determine the optimal cooling strategy for minimizing the likelihood of thermal propagation. Each test was carefully monitored, with thermocouples placed at key points in the battery module to track the thermal response of the system.
Figure 1: (a) schematic of module orientation inside the enclosure, (b) schematic of immersion cooled nail penetration setup & (c) picture of original setup
Accomplishments
Ten tests were completed that included variations in flow rate and duration. The study found that when the flow was sustained for a longer period, the system was better able to maintain cooling effectiveness and limit the spread of thermal runaway to adjacent cells. Conversely, when the coolant flow was cut off shortly after the penetration event, TR was more likely to occur and propagate through the module. These results suggest that the duration of active cooling post-abuse is a critical factor in minimizing the risk of TR propagation. Figure 2 depicts the results from this project, showing good tests on the left side based on total cell mass loss, supported by other experimental observations like temperatures and propagation duration.
Figure 2: Test result factors vs. Mass loss
The findings also highlighted the importance of achieving an optimal balance between flow rate and duration to maximize cooling efficiency while minimizing energy consumption. The tests showed variability in outcomes, with some effectively preventing thermal runaway while others did not, even under similar conditions which highlights the need for further investigation to improve the consistency of immersion cooling strategies. In conclusion, this research supports the broader adoption of immersion cooling for EV battery systems, emphasizing the importance of flow duration over the flow rate value in preventing thermal propagation during abuse conditions.