High-Performance Energy Storage Enabled by Symmetrical Gradient Multilayered Polymer Dielectrics with Superior Breakdown Strength

Dielectric polymer capacitors are widely used in advanced electronics and power systems. However, achieving a simultaneous improvement in energy density and efficiency remains challenging due to the intrinsic trade-off among high polarization, large hysteresis loss, and limited breakdown strength in ferroelectric polymers such as polyvinylidene fluoride (PVDF). In this work, a symmetrical gradient multilayered dielectric architecture is rationally designed to address this limitation by integrating interfacial engineering and crystallization modulations. The multilayer films are constructed by alternately stacking PVDF and PVDF/poly(ether imide) (PEI) composite layers via a hot-pressing process, while calcium sulfate oligomers (CSOs) are incorporated into the PVDF layer to regulate the crystalline structure. The resulting architecture introduces abundant macroscopic (interlayer) and microscopic (phase-separated) interfaces, enabling electric field redistribution and interfacial charge trapping, while the CSO-induced ion-dipole interactions promote the formation of polar crystalline phases and suppress excessive dipole switching. As a result, the optimized multilayered P8E2-P0.7C-P8E2 film with 0.7% CSO exhibits a high discharged energy density of 13.5 J/cm3 with an efficiency of 80.1% under a breakdown strength of 398 kV/mm, representing a 6.43 times enhancement compared with pristine PVDF (2.1 J/cm3 under 250 kV/mm). This work demonstrates that the synergistic regulation of multiscale interfaces and crystalline structures provides an effective strategy to overcome the performance limitations of PVDF-based dielectrics, offering new insights for the design of high-energy-density polymer capacitors.