Improved Energy Storage Property of Sandwich-Structured Poly(vinylidene fluoride)-Based Composites by Introducing Na_0.5Bi_0.5TiO₃@TiO₂ Whiskers

In recent years, high-energy-density polymer-based capacitors have received extensive attention because of their potential applications in advanced power systems and electronic equipment. However, their development is severely hampered by the inherent features of polymers such as low polarization and low charge–discharge efficiency (η). In this study, a new strategy for core–shell Na0.5Bi0.5TiO3(NBT)@TiO2(TO) whiskers combined with sandwich-structured poly(vinylidene fluoride) (PVDF)-based dielectric composites is proposed, in which the middle layer is the PVDF-based composites filled with different fractions of NBT@TO whiskers and the outer layers are pristine PVDF. The experimental results show that the loading of NBT@TO whiskers can simultaneously optimize electrical displacement and breakdown strength of the sandwich-structured composite due to the additional interfacial polarization and the contribution of the barrier effect between adjacent layers. Thus, a significantly improved electric displacement of ∼13.99 μC cm–2, a maximum discharge energy density (Ud) of ∼15.42 J cm–3 at a low electric field of 314 MV m–1, and a high charging–discharging efficiency (η ∼ 66.12%) can be obtained from the composite with the middle layer containing 6 wt % NBT@TO whiskers. This research provides a strategy for the preparation of advanced polymer-based composites with a superior discharge energy density in the future.