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

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 (empty set 1 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 0.1-0.71/min corresponding to the flow rate supplied to a battery delivering one kilowatt hour of electrical energy. For the coolant temperature of 23 degrees C at the inlet, maximum temperature of the hottest cell is between 49 and 35 degrees C in the given range of flow rates. Furthermore, temperature spread among cells is in the range between 14.6 and 4.6 degrees 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.