Flame‐Retardant Bio‐Based Thermo‐Flexible Phase‐Change Composites with Antivibration and Low‐Contact Resistance for Advanced Battery Thermal Management

Batteries face critical challenges in thermal management, including overheating risks, poor interfacial contact, and mechanical vibration–induced performance attenuation. To address these issues, we developed a flame‐retardant bio‐based thermo‐flexible phase‐change composite (VHPs) by integrating vanillin‐derived polyols (VED), hexachlorocyclotriphosphazene‐modified expanded graphite (HPEG), and polyethylene glycol (PEG). The HPEG hybrid filler effectively suppresses the “popcorn effect” of EG while significantly enhancing thermal conductivity, achieving a 246.90% improvement over neat polyurethane (PU). The thermally flexible polyurethane matrix reduces interfacial thermal resistance by 40% at 60 °C due to PEG soft‐segment melting, enabling conformal wrapping around batteries. During 36 000 s of charge/discharge cycles, the VHPs reduced the battery temperature by 10 °C and increased the discharge capacity by 53.84% at 3C rates. Compared to the reported phase‐change materials, VHPs uniquely integrate flame retardancy (peak of heat release rate reduced to 136.58 kW m −2 ), vibration resistance (compressive strength of 0.28 MPa at 50% strain), and infrared stealth (IR transmittance <0.04% in 3–25 μm). This work provides a sustainable, multifunctional solution for advanced battery thermal management, enhancing both safety and energy efficiency in high‐power applications.