Flexible Multifunctional Composite Phase Change Materials for Enhanced Thermal Safety of Battery Energy Storage Systems

The leakage and flammability issues of composite phase change materials (CPCMs) may pose fire hazards in the case of thermal runaway. Addressing the issues, this paper leverages the reaction between hydroxyl-terminated PEG and the isocyanate groups in isophorone diisocyanate (IPDI) to form urethane bonds. These bonds restrict the free movement of molecular chains to enhance anti-leakage performance. The expanded graphite and ammonium polyphosphate are distributed in the polymer via a hot-pressing process to enhance thermal conductivity and flame retardancy. It's the first flexible-form CPCMs applied in BTMS, simultaneously demonstrating exceptional anti-leakage stability (above 99.7% of original quality in anti-leakage tests), thermal durability (the anti-leakage tests indicated a thermal cycle lifetime about sixfold longer than that of PEG), anisotropic thermal conductivity (the radial and axial thermal conductivity are about 2.61 and 3.45 W/(m·K)), highest-level flame retardancy (UL94, V0 level), and thermal runaway resistance (thermal runaway was delayed to 1653 s, a 34.3% improvement over the widely used paraffin-based CPCMs). The proposed material enhances the practical battery energy storage systems' safety, facilitating the safer and more reliable deployment of large-scale energy storage technologies.