Enhancing thermal stability of flame-retardant composite phase change materials via interfacial compatibility engineering for battery modules

The practical application of composite phase change materials (CPCMs) is often limited by interfacial incompatibility between flame-retardant additives and phase change matrix, which accelerates material aging and degrades thermal management performance. This study presents the first demonstration that a melamine- thiocyanuric acid shell engineered on ammonium polyphosphate (MTA) significantly enhances interfacial adhesion within a polyethylene glycol-based matrix, thereby simultaneously suppressing long-term aging, preserving flame retardancy, and maintaining thermal regulation stability under operational conditions. Comprehensive characterization reveals that the MTA core shell-structured CPCMs exhibit exceptional aging resistance, retaining 99.34 % of their mass after a 40 h leakage test and showing only a 4.91 % decrease in thermal conductivity after thermal aging. The core–shell architecture further enables a gas–solid synergistic flame-retardant mechanism, allowing the material to self-extinguish within 5 s. In battery module tests, the aged MTA core shell-structured CPCMs continued to provide effective thermal management, constraining the maximum temperature to 54.24 °C and maintaining a temperature difference below 5.3 °C at a 3 C discharge rate. By elucidating the critical role of interfacial compatibility in mitigating performance decay, this study not only advances the fundamental understanding of CPCM durability but also offers a scalable materials strategy for developing reliable thermal management systems in energy storage and electric vehicles.