Interface‐enhanced polyimide‐based nanocomposites with superior dielectric energy storage properties

Abstract Tailoring the interfacial structure is a critical approach for modulating the dielectric characteristics of nanocomposites. Herein, the energy storage properties of polyimide/silica (PIS) were improved by grafting 4‐carboxyphenyl (PhCOOH), 4‐aminophenyl, isocyanate, phenyl and amino groups on the interfaces. The results demonstrated that the PhCOOH groups not only optimized the interfacial structures, but also enhanced both the relative dielectric permittivity (ε_r) and dielectric strength (E_b) of PI‐based films. The PhCOOH endowed the PI‐based films with high ε_r by elevating the intrinsic polarization and suppressing the relaxation polarization. Moreover, the PhCOOH elevated charge injection barriers and reduced carrier hopping distances, resulting in a lower current density. Molecular simulations revealed that the PhCOOH raised the SiO₂ electron affinity and the trap depth of PIS composites, achieving the enhancement of E_b. The PIS‐PhCOOH films with high ε_r (7.57, 10³ Hz) and E_b (421 kV⋅mm⁻¹) exhibited superior discharge energy density (6.20 J⋅cm⁻³) and energy storage efficiency (88.80%), which was 119.08% higher than that of PIS (2.83 J⋅cm⁻³, 75.91%). This work provides insights into interface engineering to synergistically improve dielectric permittivity and dielectric strength of polymer‐based composites, paving the way for fabricating high‐performance dielectrics. Highlights Polarization response were modulated by interface modification. Both permittivity and dielectric strength of PI‐based films were enhanced. PI‐based films showed an energy density as high as 6.20 J⋅cm⁻³.