Superior capacitive performance achieved in wide HOMO–LUMO gap cyanoethyl cellulose nanocomposites via forming a built-in electric field

Flexible dielectric and electronic materials are widely employed in emerging fields. Dielectric energy storage technologies and materials are needed to simultaneously cope with stringent requirements, such as high-stability and compact-size energy storage. Nonetheless, many mainstream polymer dielectrics prematurely fail under the coupling of rising electric field strength and space charge accumulation. Herein, we constructed a one-dimensional core–shell heterogeneous filler (BiFeO3@Al2O3) and added it to wide HOMO–LUMO gap cyanoethyl cellulose, achieving ultrahigh breakdown strength (∼801 MV m−1) and dielectric constant (∼17.3), thus obtaining a substantial discharged energy density of ∼31.3 J cm−3, accompanied by stabilized cyclic charge/discharge of 105. The superior energy storage performance is ascribed to the shell (Al2O3) having a higher work function, forming built-in electric fields with core (BiFeO3), simultaneously decreasing the density of state and increasing the bandgap of nanofibers. This research provides an optimization technique for crafting advanced polymer dielectrics, catering to the evolving demands of modern energy storage applications.