Greatly enhanced dielectric charge storage capabilities of layered polymer composites incorporated with low loading fractions of ultrathin amorphous iron phosphate nanosheets

Two-dimensional nanomaterials are promising fillers for dielectric nanocomposites because of their high specific surfaces which can induce strong interfacial polarization and result in improved dielectric permittivity. In this work, ultrathin amorphous FePO4 nanosheets with a thickness of about 3.7 nm are successfully obtained using a one-step solvothermal method and are further dispersed into P(VDF-HFP) matrix, forming FePO4/P(VDF-HFP) nanocomposites. Obviously enhanced dielectric permittivities are achieved owing to the strong interfacial polarization at the huge interfaces between the FePO4 nanosheets and P(VDF-HFP) matrix. A greatly enhanced dielectric permittivity of 18.5 @10 kHz, which is about 240 % that of P(VDF-HFP) matrix, is obtained in the composite with merely 2 wt% FePO4 nanosheets. Furthermore, bilayer paraelectric/ferroelectric composites, in which pure polyetherimide acts as the paraelectric layer and the FePO4/P(VDF-HFP) composite as the ferroelectric layer, are fabricated. It is found that, the synergistic effect between the two layers results in substantially suppressed loss and elevated breakdown strengths, as well as obviously improved energy density and discharge efficiency in comparison with the single layer FePO4/P(VDF-HFP) composites. Consequently, a high energy density of 7.58 J/cm3 along with a high discharge efficiency of 81.6 % are concurrently achieved in the bilayer composite with merely 0.5 wt% FePO4 nanosheets. The excellent dielectric energy storage performances make these composites promising candidates for advanced electrostatic capacitors.