Two-dimensional sheet-like K0.5Na0.5NbO3 platelets and sandwich structure induced ultrahigh discharge efficiency in poly(vinylidenefluoride)-based composites

Abstract Polyvinylidene fluoride (PVDF) -based composites have received great attention in high-energy-density capacitors due to their high breakdown strength and ease of processing. In this work, sandwich structure K0.5Na0.5NbO3(KNN)/PVDF composite films with a middle of PVDF layer containing 2D sheet-like KNN platelets were prepared by a simple layer-by-layer casting process. Experimental results indicate that the reasonably distributed 2D sheet-like KNN platelets and sandwich structured are very effective for reducing the conductivity and dielectric loss of the composite film, manifested by a significant improvement of discharge efficiency (η = 80.2%), which is the highest η value reported so far. In addition, the finite element simulation results confirm that the synergy between the 2D sheet-like KNN platelets and the sandwich structure can effectively hinder the development of electric tree. The high breakdown strength of the composite film and high dielectric constant of KNN platelets result in high discharge energy density of 14.5 J cm−3. This work provides a new reference for PVDF-based polymer composites with excellent comprehensive energy storage performance for capacitive energy storage applications.