  Dielectric capacitors are critical components in electronics and energy
storage devices. The polymer based dielectric capacitors have advantages of
flexibility, fast charge and discharge, low loss, and graceful failure.
Elevating the use of polymeric dielectric capacitors for advanced energy
applications such as electric vehicles (EVs) however requires significant
enhancement of their energy densities. Here, we report a polymer thin film
heterostructure based capacitor of poly(vinylidene fluoride)/poly(methyl
methacrylate) with stratified 2D nanofillers (Mica or h-BN nanosheets)
(PVDF/PMMA-2D fillers/PVDF), that shows enhanced permittivity, high dielectric
strength and an ultra-high energy density of 75 J/cm3 with efficiency over 79%.
Density functional theory calculations verify the observed permittivity
enhancement. This approach of using oriented 2D nanofillers based polymer
heterostructure composites is expected to be universal for designing high
energy density thin film polymeric dielectric capacitors for myriads of
applications.
