Significantly enhanced energy storage properties in sandwich-structured polymer composites with self-assembled boron nitride layers

Electrostatic capacitors have attracted tremendous attention in modern electron systems. Herein, we report a new design of sandwich-structured composite boron nitride-poly(vinylidene fluoride-co-hexafluoropropylene)/barium titanate-boron nitride (BN-P(VDF-HFP)/BT-BN) via interfacial self-assembly combined with the solution casting method. In this composite, the outer layers are the self-assembled BN films with high insulation to provide high breakdown strength (E_b) and resist the charge injection, whereas the middle layer contains the high permittivity (ε_r) BaTiO₃ nanoparticles to provide high electrical polarization. Experimental results show that the E_b and discharged energy density (U_e) of BN-P(VDF-HFP)/BT-BN composites can be significantly improved with BN layer. The sandwich-structured composites of BN-3-BN show a high U_e of 19.4 J/cm³ at 550 MV/m, which is much greater than the corresponding single-layer composite. Further, the finite element results indicate that the designed sandwich-structure was contributing to improved E_b and U_e. Therefore, this study provides a novel strategy to enhance energy density in dielectric materials, which has great potential in high-performance electrostatic capacitor.