Numerical optimization study on the thermal management of planar sodium nickel chloride battery module

A numerical study is conducted to build up a thermal management strategy for a battery module consisting of stacked planar sodium metal chloride (Na-MCl2) unit cells at the intermediate temperature of 180 degrees C. Because the sodium metal chloride battery for an energy storage system operates for a long cycle period and maintains a high temperature, a different approach is required considering uniform temperature distribution and efficiency compared with lithium-ion battery. This study starts with a lumped analytical model for preliminary investigation and moves on to a computational fluid dynamics (CFD) analysis for a more sophisticated optimization. In this study, the 2 x 4 and 3 x 3 arrangements of cylinders, each of which represents a 10-cell stack, are considered. From the lumped model in the preliminary design, the insulation thickness and initial approach values of the detailed design are determined by predicting the temperature and heat generation throughout the entire operating cycle of the module. In the detailed CFD analysis, passive thermal management through natural convection has a limitation of cell temperature uniformity. To achieve a uniform cell temperature distribution, case studies are conducted with active fans inside the module. The optimal operating points are proposed based on the overlaid response surface. Finally, for the operating points in this study, the module efficiencies are compared considering the cell failure mode. The efficiencies of optimized module are increased to 26.9 % for 2 x 4 and 21.2 % for 3 x 3 arrangements.