Safety–Performance Trade-Offs of Phase-Change Materials in Battery Thermal Management: Materials, Systems, and Deployment

Lithium-ion batteries (LIBs) typically operate within a temperature range of 20–50 °C, depending on the chemical composition and application of the battery. Overheating may lead to degradation and thermal runaway, while overcooling may cause lithium plating and internal short circuits. Absorbing heat during the melting of phase-change materials (PCMs) has become an attractive passive thermal management strategy. However, organic PCMs such as paraffin are flammable, and most strategies for improving their inherently low thermal conductivity, such as adding carbon fillers and engineering porous scaffolds, sacrifice latent heat, electrical safety, or cost. Flame retardants achieve flame retardancy at the cost of 15–25% of latent heat, while inorganic PCMs eliminate flammability but introduce undercooling and corrosion. This study synthesizes the PCM–battery thermal management system (BTMS) literature with this safety–performance tension as its organizing principle, covering composite PCM strategies for thermal enhancement, flame-retardant approaches and thermal runaway mitigation, hybrid PCM–active cooling systems, and emerging directions that transcend rather than manage the trade-off. It also identifies the gaps between laboratory demonstration and commercial deployment: durability data measured in hundreds rather than thousands of cycles, absent standardized testing protocols, and manufacturing routes that have not left the university laboratory.