Analytical and numerical investigations on optimal cell spacing for air-cooled energy storage systems

Abstract

Electric vehicles (EVs) are the promising candidate of zero-carbon transportation all over the world. Today, EV industry dominantly prefers Li-ion battery cells due to their superiorities on lifetime, cyclability, thermal and electrical stability. Li-ion batteries generate heat during the charging and discharging operations as a result of the electrochemical reactions between the layers. Generated heat is nonuniform, and it causes nonhomogeneous temperature distribution on the cell surfaces. Exceed temperature levels lead to capacity fade, layer degradation, and even thermal runaway. At this point, battery thermal management systems have emerged to avoid battery pack from these performance and safety risks. In this study, we investigate optimal cell spacing of an air-cooled battery energy storage system ensuring enhanced thermal performance with lower energy consumption. Evolution of the thermal boundary layer and the amount of heat transfer performance are analytically examined for two limit cases of small and large spacing. Once the heat transfer curves are obtained, intersection of asymptotes methodology is applied to determine the optimal battery cell spacing. In parallel with the analytical part, numerical modelling is conducted to check the optimal cell spacing. The results indicate that the optimal cell spacing of battery energy storage systems varies between 3.5 mm and 5.8 mm in a range of Re ≃ 250 to 2000.