Significantly enhanced breakdown strength and energy density in sandwich-structured nanocomposites with low-level BaTiO3 nanowires

Low energy densities of polymer-based composites restrict their application in miniaturization and integration of dielectric capacitors. Recently, multilayered hierarchical polymer composite is emerging as a promising route to address the aforementioned challenges. In most cases, high loading (>10 wt%) of ceramic nanoparticles were incorporated into polymer matrix to act as a hard layer for high permittivity. In fact, high-loading filler will inevitably cause agglomerations and deteriorate electric breakdown strength due to the poor dispersion and compatibility between the fillers and matrix. One-dimension nanowires exhibit obvious superiority to increase the permittivity of the nanocomposites due to large dipole moments from its high aspect ratios. In this work, a novel strategy of designing sandwich structured PVDF nanocomposites with low-loading BaTiO3 nanowires was proposed. The motivation is to maintain high breakdown strength by the contribution of barrier effect from the sandwich structure and low-loading of BaTiO3 nanowire fillers. Two sandwich structures including "3-0-3" and "0-3-0" (the digit representing BaTiO3 nanowires mass fraction in each layer) and single-layered BaTiO3/PVDF nanocomposites are fabricated for optimization and comparison. The results revealed that due to the contribution of interfacial polarization and barrier effect between adjacent layers, sandwich-structured BaTiO3/PVDF nanocomposites deliver greatly improved polarization, enhanced electric breakdown strength, and limited leakage current density, which significantly outperform single-layered films. For instance, a high breakdown strength of 519 kV mm 1 with a high maximum polarization of 12.1 mu C cm(-2), and an impressive discharged energy density of 19.1 J cm(-3) accompanied with energy efficiency of 68.6% were achieved even at a very low filler loading of 3 wt% BaTiO3 nanowires. In addition, the potential applications of the nanocomposites for energy storage have been further demonstrated by keeping stable performance after 106 charge-discharge cycles.