Thermal management for transient integrated battery and power electronics systems using phase change materials

Integrating lithium-ion batteries with power electronics enhances compactness, flexibility, and multifunctionality but poses thermal management challenges due to their distinct working temperatures. This paper evaluates the transient thermal characteristics of a battery-phase change materials (PCMs)-converter integrated system at both high (10C) and low (1C) battery discharge rates. A transient three-dimensional thermal model of the system is developed and experimentally validated to assess the performance of the integrated system with transient heat generation. The model goes beyond existing work, which largely focuses on steady heat generation and overheating of battery, by evaluating two key metrics: the system's delay time (${\tau }_{s-d}$), i.e. the operational duration before overheating of either the battery or the converter, and the maximum temperature difference on the battery surface ($\Delta T$). Results indicate that increasing the PCMs' horizontal thermal conductivity $k_{xy}$ (parallel to heating surfaces) consistently benefits the system by extending ${\tau }_{s-d}$ and reducing $\Delta T$ at both low and high discharge rates. However, increasing the vertical thermal conductivity $k_z$ does not always enhance ${\tau }_{s-d}$. The optimum value of $k_z$ depends on the battery discharge rate: with a constant $k_{xy}$ of 2.5 W m⁻¹ K⁻¹, the optimal ${\tau }_{s-d}$ is observed as 2542 s at $k_z$ = 0.4 W m⁻¹ K⁻¹ at a 1C discharge rate and 273 s at $k_z$ = 2.5 W m⁻¹ K⁻¹ at a 10C discharge rate. At a 1C discharge rate, ${\tau }_{s-d}$ can be consistently prolonged by increasing the PCM thickness. However, at a 10C discharge rate, this enhancement becomes negligible when the PCM thickness exceeds 15 mm. Thicker PCM also improves the temperature uniformity of the battery.