Investigation of thermal performance of battery inside the structure consisting of phase change material and porous media

This study experimentally investigated the thermal performance of lithium-ion batteries at different discharge rates and different cooling conditions. The thermal management system of lithium-ion batteries should be well designed as well as the battery management system. High temperatures are undesirable in lithium-ion batteries. Operating the battery at high temperatures causes the internal structure to deteriorate, the capacity to be lost and the high discharge cycle life to decrease. Battery temperatures in different cooling conditions of batteries and battery modul are investigated. First, studies are conducted for a single battery and the temperatures of the battery and battery box are determined at different air thicknesses and different discharge rates. Increasing air thickness is very important for battery thermal performance. Then, two different phase change materials (PCM) are placed in the battery box with the same air thicknesses and the effect of PDM on battery thermal performance is investigated. At low discharge rates, both PCMs showed almost the same thermal properties. However, as the discharge rate increased, the PCM 35 material showed better performance. However, the PCM 35 material is a very hard material in the solid phase, which poses a disadvantage when creating a battery module. Therefore, it is determined that the PCM 42, which is softer in the solid phase, is more suitable. Two identical battery modules consisting of four series and two parallel connections are created and the thermal performance of the battery module is investigated at different discharge rates under the conditions of empty battery box, PCM and composite PCM. In these battery modules, two different battery boxes with 2 and 8mm distance between the batteries are considered. The empty battery module allowed experiments at a maximum discharge rate of 2C. At higher discharge rates, the recommended temperature value of the battery module is exceeded. However, when both PCM and composite PCM are placed inside, the battery discharge rate increased to 5C. At a 5C discharge rate, the highest battery temperature is approximately 60℃, which is within the safe temperature range for the battery. At low discharge rates, the battery surface temperatures in PCM and composite PCM battery modules are almost the same. The effect of the porous structure began to be seen as the discharge rate increased. It is determined that the battery surface temperature is lower in pure PCM thanks to the composite PCMs formed with copper mesh and metal wool porous domain. In addition, thanks to the porous domain, the effective thermal conductivity of composite PCM has increased and the battery has transferred the heat produced to the environment faster. It is observed that PCM melts earlier thanks to the porous structures. Although the two metal porous environments exhibit almost the same performance in terms of battery surface temperature, copper braided PCM exhibited the best thermal performance. It is observed that the distance between the batteries is also very important in the battery module with PCM and composite PCM. It is observed that as the distance between the batteries increases, the battery surface temperatures are lower and better. As the distance between the batteries increases, the volume of the battery box and therefore the PCM volume increases. It is determined that the presence of a higher weight PCM in the battery box is important for the battery thermal performance. Thanks to PCM and especially composite PCM, the temperatures of the batteries in the battery module are more homogeneous and at the same temperatures as each other. Keywords: Battery thermal management system, Phase change material, Porous domain, Lithium-ion battery, Passive cooling