A three-dimensional (3D) macroscopic network of manganese oxide (MnO2) sheets was synthesized by an easily scalable solution approach, grafting the negatively charged surfaces of the MnO2 sheets with an aniline monomer by electrostatic interactions followed by a quick chemical oxidizing polymerization reaction. The obtained structure possessed MnO2 sheets interconnected with polyaniline chains, producing a 3D monolith rich in mesopores. The MnO2 sheets had almost all their reactive centers exposed on the electrode surface, and combined with the electron transport highways provided by polyaniline and the shortened diffusion paths provided by the porous structure, the deliberately designed electrode achieved an excellent capacitance of 762 F g–1 at a current of 1 A g–1 and cycling performance with a capacity retention of 90% over 8000 cycles. Furthermore, a flexible asymmetric supercapacitor based on the constructed electrode and activated carbon serving as the positive and negative electrodes, respectively, was successfully fabricated, delivering a maximum energy density of 40.2 Wh kg–1 (0.113 Wh cm–2) and power density of 6227.0 W kg–1 (17.44 W cm–2) in a potential window of 0–1.7 V in a PVA/Na2SO4 gel electrolyte.Keywords: 3D network; electrostatic interaction; flexible devices; manganese oxide; two-dimensional sheets;

•A novel three-phase Ag-NBCTO-PVDF composite was prepared.•Three-phase composites showed better thermal stability.•High permittivity of 222.4 at 1 kHz was obtained when the Ag content was 5 vol%.•A percolation threshold of fAg=5.9 vol% was calculated.Three-phase composites with enhanced dielectric permittivity and low dielectric loss were prepared by incorporating the giant dielectric permittivity material Na0.5Bi0.5Cu3Ti4O12 (NBCTO) and conductive Ag nanoparticles in Poly(vinylidene fluoride) (PVDF) polymer matrix by melt mixing and hot pressing process, in which the filler content (volume fraction) of Ag nanoparticles and NBCTO powders was set at 50 vol% and PVDF was set at 50 vol%. The structure and thermal stability of the composites were characterized using X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA). Studies on the dielectric properties of composites in the frequency range from 10 to 106 Hz showed that the Ag-NBCTO-PVDF composite exhibited high dielectric permittivity of 222.4 and low loss tangent of 0.32 at 1 kHz when the content of Ag was 5 vol%. A percolation threshold of fAg=5.9 vol% was calculated through the percolation theory.

Na0.5Bi0.5Cu3Ti4O12 (NBCTO)/poly(vinylidene fluoride) (PVDF) composites with various NBCTO volume fractions were prepared via solution mixing and hot pressing process. The structure, morphology, and dielectric properties of the composites were characterized with X-ray diffraction (XRD), thermal-gravimetric analysis (TGA), scanning electron microscope (SEM), and broadband dielectric spectrometer. The dielectric constant (ε) and dielectric loss (tan δ) of the composites were both found to increase with increasing NBCTO volume fraction within the frequency range of 1–106 Hz at room temperature. Relatively high dielectric constant of 79.8 and low loss of 0.21 at 1 kHz were obtained for the NBCTO/PVDF composite with 50 vol% NBCTO. Additionally, theoretical models like Logarithmic mixture rule, Maxwell–Garnet, Effective medium theory, and Yamada model were also employed to predict the dielectric constant of these composites. The values obtained by the EMT model are in close agreement with the experimental values.