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

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 Al₂O₃@BiFeO₃ nanofibers into PVDF/PMMA polymer matrix. The thickness of BiFeO₃ 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.