Electric Field Modulation Enables High Energy-Storage Density and Low Loss in All-Organic Polymer Films with Gradient Dielectric Constants

Achieving a balance between high energy-storage density and high charge/discharge efficiency remains a key challenge for polymer film capacitors. In this study, a gradient-dielectric all-organic sandwich composite film (PFHP) was fabricated, comprising a polypropylene (PP) outer layer, an irradiation-cured in situ acrylate (HD) intermediate layer, and a polyvinylidene fluoride (PVDF) outer layer. The HD layer, with its moderate dielectric constant (εr ≈ 4.2), mitigates the dielectric discontinuity and local electric field distortion at the PP/PVDF interface. Furthermore, in situ curing forms a dense interface and deep traps, thereby suppressing carrier migration and conduction losses. This structure synergistically combines the high polarization capacity of PVDF with the high breakdown strength and low loss characteristics of PP. Under a maximum test electric field of 450 MV m−1, the PFHP film achieved a discharge energy storage density of 4.09 J cm−3, with a charge–discharge efficiency of over 90%. This energy storage density was 2.13 times that of the pure PP film under the same electric field. Overall, the introduction of an acrylate interlayer not only mitigates the dielectric constant mismatch at the interface but also regulates charge transport by forming a cross-linked network, thereby suppressing leakage current and space charge accumulation, which helps improve energy storage performance. This work provides an effective strategy for developing all-organic thin-film capacitors with high energy storage capacity and high efficiency.