Introduction
In recent years, there has been a significant upsurge in the popularity of electric vehicles (EVs). Li-ion batteries are the most popular energy sources used in EVs due to their high energy density and low self-discharge. However, these batteries have an optimal average temperature range of operation as well as a temperature uniformity requirement to ensure an extended battery pack lifespan. This necessitates the need for a battery thermal management system (BTMS). Coolant flow-based cold plates have been extensively studied in the literature for their ability to control the temperature of the battery pack for long and high heat dissipation. However, these require additional pumping power, show a high thermal gradient along the direction of the flow, leading to poor thermal uniformity, and require power to cool down the coolant itself. Phase change materials are also a popular cooling solution in battery packs, as they have proven effective in maintaining thermal uniformity without needing external pumping power. However, these lose their cooling effect once the PCM has completely melted. Hence, a hybrid cooling solution utilizing the advantages of both these methods is a promising solution.
Methodology
This study develops a manufacturable and scalable hybrid cooling plate with parallel PCM and coolant channels. A series battery pack of Li-ion pouch cells is simulated with alternating battery and cold plates at a 3C discharge rate. The heat load is taken from experimental studies at an ambient temperature of 20°C. The results of the hybrid cooling are compared to pure PCM-based and coolant-based solutions, and the lifecycle analysis of an EV with the hybrid cooling system is compared to the case with no cooling system.
Results
The results show that the hybrid cooling plate maintains the average battery pack temperature at nearly the same temperature as the coolant-based solution but shows an 18.4% improvement in thermal uniformity. The hybrid system achieves this at half the mass flow rate compared to the purely coolant-based solution, reducing the energy required to cool down the coolant, which more than compensates for the marginal increase in pumping power required. Further, the hybrid system can handle additional heat load after the PCM melts due to partial forced-convection-based cooling. This shows that the hybrid cooling system is the best solution among the three methods analyzed in this study. The lifecycle analysis of the battery pack shows that the additional weight of the cooling system in an EV reduces the battery-pack life by 6.25%. In contrast, in the absence of a cooling system, the life is reduced by 37%, showing an overall benefit of nearly 31% utilizing the hybrid cooling system.