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 ( ε r ) and breakdown strength ( E b ). However, conventional core–shell nanofillers exhibit two major drawbacks: (i) the low- ε r shell greatly limits the ε r 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 ( U d ) at low filling content is difficult. Herein, core–shell nanofibers constituted by single element-doped BaTiO 3 are prepared as fillers. They integrate relatively high ε r and E b , helping to obtain high- U d dielectric nanocomposites. The single-layer nanocomposite films with 2 wt% polydopamine-modified BZT15@BZT35 nanofibers (BZT15@BZT35@PDA_nfs) show 64% enhancement of U d 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.