Multifunctional Multilayered Fe 3 O 4 ‐ CCNTs /Polyimide Composite Film Exhibits Excellent Electromagnetic Interference Shielding Performance

With rapid development of communication technologies and flexible electronics, multifunctional electromagnetic interference shielding materials for specific scenarios are highly demanded. Herein, we prepared multilayer Fe 3 O 4 ‐carboxylated carbon nanotubes (CCNTs)/polyimide composite films by dispersing Fe 3 O 4 nanoparticles and CCNTs in polyimide matrix through layer‐by‐layer blade coating and thermal treatment. This bilayer filler gradient structure was designed to optimize impedance matching, mitigate secondary electromagnetic reflection pollution, and boost interfacial polarization as well as multiple reflection loss for enhanced electromagnetic wave absorption. With bilayer filler loadings of 25% and 30% and a constant 1:3 mass ratio of Fe 3 O 4 to CCNTs in each layer, the film achieves an EMI SE of 36.8 dB and specific shielding effectiveness of 525.7 dB/mm, maintaining stable performance under harsh environments. Under 6 V voltage, it rapidly reaches 145.7°C with excellent long‐term Joule heating stability. The composite also has favorable mechanical performance, high thermal stability (weight loss > 500°C) and flame retardancy (limiting oxygen index: 39.1 vol%). Thus, this film shows promising applications in communication devices and wearable electronics.