Achieving Superior Capacitive Energy Storage in Polymer Nanocomposites via a Hierarchical Interfacial Engineering of Gradient-Dielectric Ba(Zr,Ti)O3@BaTiO3 Core-Shell Nanofibers.

Harnessing dielectric polymers for next-generation pulsed-power capacitors mandates ultrahigh energy density and efficiency simultaneously, yet the antagonism between large polarization/dielectric constant and high breakdown strength remains a fundamental bottleneck. Here, we implement a hierarchical interfacial engineering approach that reconciles this conflict by constructing gradient-dielectric Ba(Zr,Ti)O3@BaTiO3 (BZT@BT) core-shell nanofibers via coaxial electrospinning and a mussel-inspired poly(catechol/polyamine) (PCPA) interlayer. The lattice-matched BZT core and BT shell suppress interfacial defects during co-calcination, while the progressive dielectric constant gradient mitigates severe field distortion in the polymer matrix. The PCPA interlayer facilitates to significantly strengthens the bonding between the inorganic fibers and P(VDF-HFP) and the exceptional filler dispersion. The optimized nanocomposite containing only 2 wt.% BZT@BT@PCPA filler delivers a record-high discharged Ue of 33.8 J cm-3 with an η of 82.6%. Phase-field simulations reveal that the introduction of gradient permittivity and PCPA interfacial modifier synergistically homogenizes the electric field and enhances the breakdown strength. This work demonstrates the profound effectiveness of synergistic lattice-matched core-shell filler design and tailored interfacial molecular engineering in overcoming the performance bottlenecks of polymer nanocomposites for high-power energy storage applications.