High energy density nanocomposites with layered gradient structure and lysozyme-modified Ba0.6Sr0.4TiO3 nanoparticles

• Self-assembly by phase-transitioned lysozyme to improve interfacial compatibility of polymer/inorganic fillers. • Gradient films were prepared by a designable electrospinning-hot pressing process, and finite element analysis and phase-field simulations were used to reveal the mechanism of breakdown strength ( E b ) enhancement. • The optimized gradient-structured P(VDF-HFP)/ m BST 1-4-1 composites have significantly enhanced energy storage performance (445 MV/m, 13.1 J/cm 3 ) compared to pristine polymer (311 MV/m, 5.7 J/cm 3 ) or anti-gradient-structured composites (384 MV/m, 10 J/cm 3 ). Polymer nanocomposites with high-dielectric-constant ceramic fillers have been supposed to a positive candidate for electrostatic capacitors owing to their higher energy density. Herein, the P(VDF-HFP)/BST (poly(vinylidene fluoride-hexafluoropropylene)/Ba 0.6 Sr 0.4 TiO 3 ) nanocomposites films were carefully prepared by layer-by-layer electrospinning, hot-pressing, and quenching processes. In an effort to overcome this challenge that the decrease in breakdown strength due to the high load of ceramic nanoparticles, self-assembly phase-transitioned lysozyme (PTL) is utilized to modify BST ( m BST) to improve interface conditions and layered gradient structure is designed to reduce charge injection at the electrode/films respectively. Studying its microstructure and electrical properties found the gradient structure can simultaneously weaken interface defects and improve energy storage performance. Consequently, a remarkable energy density (13.1 J/cm 3 @450 MV/m) has been obtained compared to that of pure polymer films (5.7 J/cm 3 ). This work presents an attractive approach to enhancing the energy storage properties of polymer nanocomposites by surface modification and structure modulation.