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

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 SiO 2 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, 10 3 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 .