Liquid cooling vs hybrid cooling for fast charging lithium-ion batteries: A comparative numerical study

Abstract

Lithium-ion batteries (LIBs) rely on efficient thermal management systems for their safe and reliable operation. Issues like overheating of LIBs due to excessive heat generation, thermal runaway and thermal propagation are still a challenge for engineers. To address the challenge, numerous cooling methods viz. liquid cooling, air cooling, cooling using phase change materials (PCMs), hybrid cooling (i.e., combining liquid and PCM cooling), etc., have been proposed by different authors in the past. Though all the above methods are best suited for LIBs under normal charging/discharging operations, their suitability for cooling fast charging LIBs remains unexplored. In general, the heat generation and risks due to thermal runaway in LIBs are relatively more during fast charging than normal charging. As regards hybrid cooling employing PCMs, the method is yet to be benchmarked, as PCMs themselves suffer from low thermal conductivity issues that may affect their overall thermal performance. The present work is an attempt to address the above-stated aspects. Detailed 3D numerical simulations on three different design configurations (D1-D3) of a prismatic LIB module consisting of four 10 Ah batteries fast charged at 8C rate are reported herein. Two different cooling methods viz. (i) liquid cooling employing a dielectric liquid coolant (STO-50) and (ii) hybrid cooling combining liquid dielectric and a PCM (RT35) are investigated, and their performances compared. The results reveal interesting facts on the ability of liquid cooling (D2) over hybrid cooling (D3) for fast charging LIBs. Parametric studies show that the coolant flow direction (horizontal/vertical) and thermal conductivity of the PCM (kpcm) have a profound influence on the cooling obtained compared to PCM’s melting temperature (Tm) and latent heat (λ). It is concluded that PCM based hybrid cooling is not suitable for cooling LIBs under fast charging unless kpcm is enhanced to 1 W/mK or above. A minimum coolant flow rate of 2 lpm is needed to limit the battery temperatures to 40 °C or below for the module under fast charging conditions. An increase in PCMs latent heat from 160 to 200 kJ/kg has no significant influence on the cooling achieved.