Numerical Simulation of Low-Temperature Thermal Management of Lithium-Ion Batteries Based on Composite Phase Change Material.

Phase change materials (PCMs) have attracted greater attention in battery thermal management systems (BTMS) applications due to their compact structure and excellent thermal storage performance. This work developed a BTMS model based on composite phase change material (CPCM) for a cylindrical lithium-ion battery pack. The initial state of the CPCM was set as a liquid phase, and the insulating performance of the BTMS was investigated numerically, considering the CPCM solidifying from liquid phase to solid phase in a low-temperature environment. The numerical model was built, and calculations were performed using Ansys Fluent 19.2. The research results showed that a CPCM effectively can extend the time that the battery pack remains above 0°C by releasing a large amount of latent heat during the solidification process in a low-temperature environment. As the convective heat transfer coefficient increased, the insulation effect provided by CPCM to lithium-ion battery packs decreased, exacerbating the temperature inhomogeneity inside the low-temperature thermal management system. Increasing the thermal conductivity of the CPCM ensured that the maximum temperature difference of the battery pack during operation remained within a safe range. Finally, the simulation results indicated that adding different thicknesses of insulation materials at the periphery of the low-temperature thermal management system effectively can improve the insulation effect. However, it also is necessary to select the appropriate thickness of insulation materials in combination with the actual demand. This paper establishes a model based on CPCM for the low-temperature thermal management system of cylindrical lithium-ion batteries. The thermal insulation and temperature homogenization performance of the CPCM-based BTMS were analyzed under various conditions, including different ambient temperatures, convective heat transfer coefficients, and thermophysical properties of materials, as well as the addition of insulation layers, considering time-dependent variations. Based on this analysis, the physical requirements of CPCM and the package structure for BTMS under different operating conditions were determined. The simulation results demonstrate that the liquid-phase CPCM solidifies and releases the stored heat through latent heat to warm and insulate the battery when the discharging process is stopped at lower temperatures. This effectively extends the battery's holding time in the high-temperature domain and above 0°C. As the external convective heat transfer coefficient increases, the effectiveness of CPCM in insulating the battery decreases, exacerbating the temperature nonuniformity within the low-temperature thermal management system. Increasing the thermal conductivity of the CPCM ensures that the maximum temperature difference during battery operation remains within safe limits. In addition, the results indicate that the insulation effect can be improved significantly by adding an appropriate thickness of insulation material to the periphery of the thermal management system, based on specific requirements. This study provides a valuable reference for the design and optimization of thermal management systems for batteries operating in a wide temperature range. [ABSTRACT FROM AUTHOR]