RESUMEN
Dielectric polymer composites exhibit great application prospects in advanced pulse power systems and electric systems. However, the decline of breakdown strength by loading of single high dielectric constant nanofiller hinders the sustained increase in energy density of the composites. Here, a sandwich-structured nanocomposite prepared with mica nanosheets as the second filler exhibits decoupled modulation of dielectric constant and breakdown strength. The traditional layered clay mineral mica is exfoliated into nanosheets and filled into polyvinylidene difluoride (PVDF), which shows a special depolarization effect in the polymer matrix. In Kelvin probe microscopy characterization and thermally stimulated depolarization current indicates that the mica nanosheets provided space charge traps for the polymer matrix and effectively suppressed the carrier motion. A sandwich structure composite material with mica nanosheets as the central layer has achieved a high energy density of 11.48 J cm-3, 2.4 times higher than the pure PVDF film. This is due to the fact that randomly oriented distribution of nanosheets in a polymer matrix provide better current blocking. This work provides an effective method to improve the energy density of dielectric polymer composites by synergistically introducing insulating nanosheets and high dielectric constant nanofillers.