In Situ Growth of PDA Layer on PEI Film: Enhanced Dielectric Energy Storage Performance and Its High‐Temperature Limitation

ABSTRACT To improve the insulation and energy‐storage performance of polyetherimide (PEI) films, surface‐modified PEI/polydopamine (PDA) films were fabricated via in situ polymerization of dopamine. This study explores the influence of the PDA layer on the wide‐temperature dielectric and energy‐storage properties of PEI. The self‐growth process of the PDA layer promotes the rearrangement of PEI molecular chains and enhances the films' mechanical properties. Its Coulomb blockade characteristics effectively suppress the injection of electrode carriers and improve the breakdown strength. The modified films present enhanced room‐temperature performance. The breakdown strength reaches 647.2 kV/mm, which is 64% higher than that of pure PEI films. The discharge energy density ( U d ) reaches 9.51 J/cm 3 , 326% higher than that of pure PEI films. The corona resistance time is extended to 2.3 times that of pure PEI films. At 150°C, the dielectric loss at 1 kHz increases from 0.0095 to 0.019. The film maintains U d of 2.54 J/cm 3 but shows discharge efficiency of only 34.2%. This study clarifies the enhancement of the PDA layer on the room‐temperature performance of PEI films and inherent limitations in high‐temperature energy storage. It provides an important experimental basis for the design of PEI films modified for wide‐temperature energy storage.