Hybrid thermal management system for a lithium-ion battery module: Effect of cell arrangement, discharge rate, phase change material thickness and air velocity

To address global energy concerns, the use of rechargeable lithium-ion batteries in electric vehicles (EVs) is one of the most tempting option in terms of electrochemical energy storage. However, in order to achieve the best thermal performance and long cycle life of these batteries, an efficient cooling technique is required to minimize excessive temperature build-up during charging/discharging. The current numerical study thus examines the performance of a hybrid air-phase change material (PCM) cooled lithium-ion battery module at various air inflow velocity (U-0 = 0-0.1 m/s) and different thickness of PCM encapsulation (t = 1-3 mm) for 1C, 2C and 5C discharge rates. Commercial SONY 18650 cells (25 nos.) were placed in a square box with two different cell arrangements, namely, square and diamond. Governing equations of the coupled 1D electrochemical and 2D thermal model were solved using COMSOL Multiphysics. Extensive results of cell average temperature, maximum temperature, and melt fraction of PCM have been reported. In absence of PCM, ~20 K drop in the maximum temperature was observed as U0 varied from 0 to 0.1 m/s. In absence of PCM, the diamond cell arrangement yields a better cooling performance than square arrangement (by ~3-4 K) but only at low discharge rate and high air velocity. At high discharge rate and low air velocity, this improvement disappears. The presence of a thin PCM layer (t = 1 mm) over the cells significantly improves heat removal by dropping the average cell temperature (up to ~45 K at 5C) albeit the cell arrangement exhibits negligible impact on results. Lastly, our observations suggest the existence of a threshold PCM thickness for a combination of C-rate and air flow rate beyond which there is no effect of cell arrangement on battery performance.