Decoupling control of dielectric permittivity and breakdown strength in GNS/PVDF nanocomposites via introducing insulating MgO interlayer

• The GNS@MgO/PVDF nanocomposites outperform GNS/PVDF in dielectric characteristics. • The MgO interlayer mitigates strong interfacial dielectric mismatch, enhancing the E b . • The MgO shell introduces deep traps, elevating the charge de-trapping barrier energy height. • Dielectric properties of the nanocomposites can be modulated by the MgO interlayer thickness. Flexible polymeric composites featuring large dielectric permittivity ( ε ) and breakdown strength ( E b ) coupled with low loss hold extensive industrial applications, however, decoupling control of these parameters remains a formidable challenge due to their inverse relationship. To synchronously hoist the ε and E b in graphite nanosheet (GNS)/polyvinylidene fluoride (PVDF), the magnesium oxide (MgO) encapsulated GNS were prepared and dipped into PVDF to explore the MgO interlayer’s impact on the polarizations and charge carrier migration in the nanocomposites. The results demonstrate that in comparison to virginal GNS/PVDF, the MgO decoration not only improves the interfacial compatibility between pristine GNS and PVDF but also significantly reduces the dielectric loss and leakage conductivity of GNS@MgO/PVDF by suppressing the formation of conductive networks and inhibiting long-range charge carrier transport. Moreover, the interlayer with appropriate ε effectively alleviates the strong interfacial dielectric mismatch between the two components and introduces deep traps to immobilize free charges. Thus, both local electric field distortion and electrical trees growth are significantly restrained, subsequently enhancing the E b of nanocomposites. Precise optimization of the MgO thickness allows for effective tuning of the overall dielectric properties of GNS@MgO/PVDF. Theoretical fitting and simulation reveal the hidden polarization mechanisms and unlock the MgO's role in governing charge transport for elevated ε and E b in the nanocomposites. This study offers deep insight on designing and fabricating flexible polymeric dielectrics with concurrently high ε and E b along with low loss, making them suitable for potential applications in electrical equipment and power systems. The MgO interlayer suppresses charge migration and elevates breakdown strength of PVDF nanocomposites The MgO interlayer suppresses charge migration and elevates breakdown strength of PVDF nanocomposites.