This article proposes a novel methodology for the definition of an optimized immersion cooling fluid for lithium-ion battery applications aimed to minimize maximum temperature and temperature gradient during most critical battery operations. The battery electric behavior is predicted by a first order equivalent circuit model, whose parameters are experimentally determined. Thermal behavior is described by a nodal network, assigning to each node thermal characteristics. Hence, the electro-thermal model of a battery is coupled with a thermal management model of an immersion cooling circuit developed in MATLAB/Simulink. A first characterization of the physical properties of an optimal dielectric liquid is obtained by means of a design of experiment. The optimal values of density, thermal conductivity, kinematic viscosity, and specific heat are defined to minimize the maximum temperature and temperature gradient during a complete discharge of the battery at 2.5C. Through a statistical analysis, it is also possible to recognize which effects among those previously mentioned are statistically relevant for this analysis. With the optimized fluid, a second design of experiment is carried out to define an optimized design of the module (in terms of distance between cells, and staggered angle), in relation to the operating conditions (volumetric flow and discharge rate). Once the optimal design has been identified, a final comparative study is carried out between different fluids used in immersion cooling systems, whose characteristics have been found in the literature, to find which of the fluids analyzed comply with the maximum temperature and maximum gradient conditions set for this study.
