Performance Analysis of an Innovative PCM-Based Internal Cooling Design for Cylindrical Lithium-Ion Battery Considering Compact Structure and Uniform Temperature

Abstract

Limited by the small space size of electric vehicles (EVs), a more concise and lightweight battery thermal management system (BTMS) is in great demand to keep the lithium-ion battery safe. In the current study, the phase change material (PCM)-based internal and external cooling models were constructed for a cylindrical lithium-ion battery, and the effectiveness of the cooling design and the accuracy of the numerical model are verified. The effects of different cooling modes, PCM melting point, PCM mandrel size, and thermal conductivity anisotropy on the cooling performance were systematically evaluated from the perspectives of maximum temperature, maximum temperature difference, and temperature distribution. The results revealed that the internal cooling method exhibited optimal performance; the maximum temperature difference was only 1.77 K compared to 6.77 K when cooled in external mode. Moreover, the bidirectional heat transfer process using a PCM-based internal cooling mode was investigated and the results showed that the heat transfer resistance reduced, the temperature gradient lowered, and the temperature distribution more evenly distributed. When the mandrel diameter of PCM increased from 2 to 5 mm, the maximum temperature of the battery dropped from 316.65 K to 314.10 K, and the maximum temperature difference decreased from 2.23 K to 1.32 K on one accord. The internal heat transfer process of a lithium-ion battery was influenced by the radial thermal conductivity, which directly determined the uniformity of the temperature difference inside the battery. With regard to the structure design, minimizing the battery size in the stratiform direction on the premise of ensuring energy density helped to enhance temperature uniformity. The lithium-ion battery is the power source of electric vehicles. However, an excessive temperature rise during battery operation will put the battery in danger. Based on this, the research of more advanced thermal management systems for power batteries has become a hot topic in the field of new energy vehicles. A 2.6 Ah 26650-type LiFePO4 cylindrical battery was considered in the present research. The phase change material (PCM)-based internal and external cooling models were constructed for a cylindrical lithium-ion battery. The internal cooling model has been constructed by filling the PCM into the core of the battery with the help of the hollow mandrel that already exists inside the cylindrical lithium-ion battery. An external PCM cooling model was built by wrapping the 1 mm of thickness PCM around the outside surface battery. The cooling system was evaluated in terms of maximum temperature, maximum temperature difference, and temperature distribution. The results showed that the internal cooling method exhibited the best performance, lowered temperature gradients, and produced a more uniform temperature distribution. This study proposes an important reference for the design and optimization of the battery thermal management system.