Interface‐Tailored Relaxor Ferroelectric Nanocomposites with Ultrahigh‐Insulation Shell of Fluorinated Aromatic Polythiourea for High‐Capacitance Energy Storage Applications

Abstract The strategy of interface engineering plays a prominent role in obtaining desirable dielectric performance of polymer nanocomposites. In this study, ultrahigh‐insulation BaTiO3@fluorinated aromatic polythiourea (BT@ArPFTU) nanoparticles (NPs), which are successfully synthesized via microwave‐initiated polymerization, are served as novel nanofillers to prepare poly(vinylidenefluoride‐trifluoroethylenechlorotrifuoroethylene)‐based (P(VDF‐TrFE‐CTFE)‐based) nanocomposites for capacitor applications. The ArPFTU coating shell forms a strong interface with 30‐nm thickness between BT and the matrix. It not only contributes to the suppression of current density at the interfaces, the regulation of interfacial charge distribution and tolerating high electric‐field strength, but also favors the improvement in dielectric constant and electric polarization due to interfacial polarization, as confirmed by finite element simulations and experimental results. In addition, the direct observation of electric‐polarization enhancement at the interfaces in the P(VDF‐TrFE‐CTFE)/BT@ArPFTU nanocomposites is well probed by piezoelectric force microscopy. Remarkably, with small loading of BT@ArPFTU NPs, relaxor ferroelectric nanocomposites display an unprecedented discharged energy density of 23.1 J cm−3 and the charge–discharge efficiency of 65%, which is much larger than that of other types of BT‐based polymer nanocomposites and commercial biaxially oriented polypropylene of 0.71 J cm−3. This systematic study further paves a new avenue to design high‐performance polymer nanocomposites by interfacial architecture for capacitor application.