Multiphysics Approach for Thermal Design of Liquid Cooled EV Battery Pack

Thermal management of battery packs is essential to keep the cell temperatures within safe operating limits at all times and, hence, ensure the healthy functioning of an EV. The life cycle of a cell is largely influenced by its operating temperature, maintaining the cell temperature in its optimum range improves its longevity by decreasing its capacity fade rate and in turn extending the life of an EV. The battery thermal management solution being presented employs a tabbed type liquid cooling technology that achieves low-temperature differentials for an in-house designed battery pack consisting of 320 LFP cells (Size: 32700) with a total voltage and capacity of 27V and 240Ah respectively. Thermal design of the battery pack considers maximum dissipation when continuously operating at 1C-rate conditions. Furthermore, an intelligent methodology was adopted for higher reliability - cooling the entire battery pack from 50°C to 25°C within 30 min. Cooling system design was split into different parts viz. CFD + Thermal for cold-plate design, Electrical-thermal characterization for single-cell, and finally coupled Electrical + CFD + Thermal for the entire battery module. Electrical-thermal simulations also consider the variation of cell electrical resistivity with the temperature that helped to capture the transient thermal behavior of the battery pack more realistically. Temperature computations with 1C-rate charging conditions, for ambient of 25°C and a coolant flow rate of 5LPM, showed the maximum cell temperature at 27.8°C. The temperature differential within the cell and between the cells in the module was 2°C & 2.5°C respectively. The thermal design proposed can maintain the cell temperature in the optimum range while also satisfying important constraints like temperature variation of cells in the pack to be within 5°C.