Regulation of electron depletion layer in polymer-based nanocomposites for superior energy storage capability.

[Display omitted] • Energy density of 22.7 J cm−3 and efficiency of 72% are obtained at 759 kV mm−1. • Al 2 O 3 @BiFeO 3 nanofillers with different thickness of BiFeO 3 shell are prepared. • Breakdown strength is enhanced by core shell structured Al 2 O 3 @BiFeO 3 nanofillers. • A large heterojunction electric field helps to improve the breakdown strength. • Regulation of electron depletion layer for high breakdown strength. Polymer-based dielectrics trigger great interests in advanced electric systems due to their high breakdown strength and power density. However, a major drawback is that excessive addition of high- ε r ceramic nanofillers may deteriorate their breakdown strength and further reduce energy density. Herein, a general strategy is provided to dramatically enhance the breakdown strength by introducing a small amount of core–shell structured Al 2 O 3 @BiFeO 3 nanofibers into PVDF/PMMA polymer matrix. The thickness of BiFeO 3 shell is regulated by controlling its molar concentration. A significantly enhanced breakdown strength (759 kV mm−1) and an ultrahigh energy density (22.7 J cm−3) with an energy efficiency of 72% are observed. The greatly improved breakdown strength is ascribed to the regulation of electron depletion layer. When the width of heterojunction region gradually approaches to the scale of electron depletion layer, more annihilation of electrons happens and thus contributes to the enhancement of the breakdown strength. The results suggest that our designed structure can help to address the issue of both enhancing the breakdown strength and energy density for diverse nanocomposites over a broad application. [ABSTRACT FROM AUTHOR]