A critical review of advances in phase change materials for electric vehicle thermal safety

The widespread deployment of lithium-ion batteries (LIBs) enables cleaner transportation and greater flexibility in energy systems, but their thermal safety remains a critical concern. LIBs operate optimally within a temperature range of 15-40 °C, and the intercell temperature difference should be maintained below 5 °C to ensure safe and reliable performance. Effective thermal management, thermal runaway (TR) mitigation, and TR propagation prevention are therefore essential for electric vehicle applications. This review systematically analyzes recent advancements (2020–2025) in phase change material (PCM) based battery thermal management systems, focusing on three interconnected aspects: thermal management during normal operation, TR mitigation at the single-cell level, and TR propagation suppression at the module level. Both experimental and numerical studies are examined, and their findings are discussed in detail. High-thermal-conductivity composite PCM, particularly paraffin–expanded graphite, has emerged as a practical solution for thermal management due to its balance of thermal enhancement and scalability. In TR mitigation, rapid heat absorption delays the onset of TR, although paraffin flammability remains a key limitation. In contrast, TR propagation suppression requires insulating PCM barriers; studies indicate that 1–3 mm layers can effectively prevent cell-to-cell propagation. A key finding of this review is that thermal conductivity presents a fundamental trade-off: high-thermal-conductivity PCM is required for thermal management and TR mitigation, whereas low-thermal-conductivity PCM is required for TR propagation mitigation. Finally, future research directions for PCMs in electric vehicle battery safety systems are outlined. • Expanded graphite composites dominate thermal management • Distinguishes thermal runaway mitigation and propagation. • 1–3 mm PCM layers suppress thermal runaway propagation • Unified framework clarifying PCM roles in LIB safety. • Hybrid cooling and pack-level validation needed.