Polymer Nanocomposites with Interpenetrating Gradient Structure Exhibiting Ultrahigh Discharge Efficiency and Energy Density

Poly(vinylidene fluoride) (PVDF) based polymer nanocomposites with high-permittivity nanofillers exhibit outstanding dielectric energy storage performance due to their high dielectric permittivities and breakdown strength. However, their discharge efficiency is relatively low (usually lower than 70%), which limits their practical applications. Here, polymer nanocomposites with a novel interpenetrating gradient structure are designed and demonstrated by cofilling a PVDF matrix with barium zirconate titanate nanofibers and hexagonal boron nitride nanosheets via modified nonequilibrium processing. The interpenetrating gradient structure is highly effective in breaking the trade-off between discharge energy density and efficiency of the corresponding nanocomposite, as indicated by the concomitantly enhanced discharge energy density (U-e approximate to 23.4 J cm(-3)) and discharge efficiency (eta approximate to 83%). The superior performance is primarily attributed to the rational distribution of nanofillers in the polymer matrix, which raises the height of the potential barrier for charge injection at the dielectric/electrode interface, suppresses electric conduction and contributes to enhanced apparent breakdown strength. Meanwhile, the gradient configuration allows higher volume fraction of high-permittivity nanofillers without compromising the breakdown strength, leading to higher electric polarization compared with the random configuration. This work provides new opportunities to PVDF-based polymer nanocomposites with high energy density and discharge efficiency for capacitive energy storage applications.