Comparative Thermal Analysis of Paraffin-Based PCM and Graphite Composite PCM in Lithium-Ion Battery Packs

Abstract

Introduction: Thermal regulation remains a critical challenge in lithium-ion battery systems used in electric vehicles, particularly under high load, fast charging, and prolonged operating conditions. Inadequate heat dissipation can accelerate battery degradation, reduce energy efficiency, and increase safety risks. Phase change materials (PCMs) have emerged as promising passive thermal management solutions due to their ability to absorb excess heat during phase transition. Among available PCMs, paraffin-based materials are widely used for their high latent heat capacity and cost effectiveness, while graphite composite PCMs offer enhanced thermal conductivity and structural stability. However, a direct comparative evaluation of these two materials under identical operating conditions remains limited.

Objectives: The primary objective of this study is to comparatively assess the thermal performance of paraffin-based PCM and graphite composite PCM when integrated into a lithium-ion battery module used in a Tesla Model S. The study aims to evaluate their effectiveness in controlling battery temperature, maintaining thermal stability, and regulating phase change behavior during operation.

Methods: A three-dimensional computational fluid dynamics (CFD) model of a single battery module containing 444 cylindrical 18650 cells was developed using CATIA and analyzed in ANSYS Fluent. Separate simulations were conducted for paraffin-based PCM and graphite composite PCM under identical boundary and operating conditions. Transient simulations were performed for 1800 seconds using a forced convection cooling approach. Key performance metrics, including volume-average PCM temperature, area-weighted average battery surface temperature, and volume-average liquid fraction, were evaluated to quantify thermal behavior and phase change characteristics.

Results: The results indicate that the paraffin-based PCM achieved slightly lower average battery surface temperatures, demonstrating effective short-term heat absorption and dissipation. In contrast, the graphite composite PCM exhibited a substantially lower liquid fraction throughout the operational cycle, indicating prolonged solid-phase retention and improved thermal stability. This behavior reflects the superior heat conduction capability of the graphite composite material during extended operation.

Conclusions: The comparative analysis reveals that paraffin-based PCM is more suitable for applications requiring rapid thermal response, such as fast charging or high-power demand conditions. Conversely, graphite composite PCM provides enhanced long-term thermal stability, making it advantageous for sustained driving and continuous operation. The findings highlight the importance of selecting PCM materials based on specific operational requirements to optimize battery safety, performance, and lifespan in electric vehicle applications.