A novel thermal management system for cylindrical lithium-ion batteries using internal-external fin-enhanced phase change material

This study introduced a phase change material (PCM)-based battery thermal management system (BTMS) using an innovative combination of internal and external fins to create PCM silos around the battery surface, addressing the low thermal conductivity of PCM. The lumped-capacitance thermal model and enthalpy-porosity approach were employed for the battery heat generation and PCM melting process, respectively. The BTMS was evaluated under transient and constant heat generation of the battery at various discharge rates. The effects of fin quantity on thermal management performance, energy density, heat storage capacity, and PCM melting time were investigated. The developed BTMS showed superior performance compared to the battery system with natural air convection cooling and the PCM cooling system without fins. At the end of the PCM complete melting process, the BTMS with 4 internal-external fins decreased the battery surface temperature by 9.90 and 17.45 K compared to the PCM cooling system without fins at the discharge rates of 3C and 5C, respectively. The BTMS with 4 internal-external fins kept the battery surface temperature under the optimum temperature of 318.15 K even at a high ambient temperature of 308.15 K while providing up to 10.02% higher energy density, 11.11% higher heat storage capacity, 32.79% higher fin efficiency, and only 1.08% lower overall fin effectiveness compared to greater fin quantities. The proposed BTMS provided an almost uniform cooling effect on the battery surface compared to the system without fins, which has been largely overlooked in previous studies on BTMSs. Various heat transfer regimes were identified during the PCM melting process. Correlations for predicting the PCM liquid fraction and Nusselt number were proposed as a function of a group of dimensionless numbers. These findings provided valuable insights for designing efficient PCM-based BTMSs.