Polymeric hollow fibers: Uniform temperature of Li-ion cells in battery modules

Abstract

In the present work, a new heat exchanger is introduced for conventional liquid cooling of cylindrical type lithium-ion cells which are contained in battery packs/modules of electric vehicles. The coolant channels are made of polymeric hollow fibers (ø1 mm) embedded in a durable polydicyclopentadiene housing. Unlike commercially available metallic counterparts, the proposed design is lightweight, electrically non-conductive, and made of low cost materials. The prototype is stacked with 18650-type lithium-ion cells which are cycled with 1 C in the range of state-of-charge between 0 and 100%. Water/coolant circulates in the hollow fibers in the range of 0.1–0.7 l/min corresponding to the flow rate supplied to a battery delivering one kilowatt hour of electrical energy. For the coolant temperature of 23 °C at the inlet, maximum temperature of the hottest cell is between 49 and 35 °C in the given range of flow rates. Furthermore, temperature spread among cells is in the range between 14.6 and 4.6 °C. With the help of the mathematical optimization coupled with computational fluid dynamics simulations, we found that having a homogeneous temperature distribution among all the Li-ion cells is achievable. For that purpose, a non-uniform thickness of thermal insulation is suggested. The temperature homogeneity is preserved for a given flow rate of the coolant and even when temporal variations in the heat generation rate occur.