Novel designed core-shell nanofibers constituted by single element-doped BaTiO3 for high-energy-density polymer nanocomposites

Core-shell nanofillers designed for dielectric nanocomposites are expected to integrate high relative permittivity (er) and breakdown strength (Eb). However, conventional core-shell nanofillers exhibit two major drawbacks: (i) the low-er shell greatly limits the er of the entire nanofiller, and (ii) the differences of calcination performance and lattice constant between the core and shell materials induce extra imperfections, which can cause premature breakdown. As a result, significantly enhancing the discharge energy density (Ud) at low filling content is difficult. Herein, core-shell nanofibers constituted by single element-doped BaTiO3 are prepared as fillers. They integrate relatively high er and Eb, helping to obtain high-Ud dielectric nanocomposites. The single-layer nanocomposite films with 2 wt% polydopamine-modified BZT15@BZT35 nanofibers (BZT15@BZT35@PDA_nfs) show 64% enhancement of Ud compared with pristine poly (vinylidene fluoride) (PVDF) matrix. The sandwich nanocomposite films (PVDF/BZT15@BZT35@PDA_nf/PVDF/PVDF) with 2 wt% nanofibers in the middle layer achieve approximately 100% enhancement. The proposed nanofiller design strategy can be easily realized by coaxial electrospinning and further developed by tri-axial electrospinning and other multi-nozzle electrospinning methods. This study provides valuable insights into developing high-energy-density polymer nanocomposites with low filling content.