A detailed overview on interface design and control in polymer based composite dielectrics for energy storage applications.

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An ultra-high discharged energy density P(VDF-HFP) capacitor is achieved by introducing a small fraction of Na0.5Bi0.5TiO3 nanofibers.

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Thermal-stable dielectric capacitors with high energy density and power density have attracted increasing attention in recent years. In this work, (1 – x)­Bi0.5Na0.5TiO3–xNaTaO3 [(1 – x)­BNT–xNT, x = 0–0.30] lead-free relaxor ferroelectric ceramics are developed for capacitor applications. The x = 0.20 ceramic exhibits superior thermal stability of discharged energy density (W D) with a variation of less than 10% in an ultrawide temperature range of −50 to 300 °C, showing a significant advantage compared with the previously reported ceramic systems. The W D reaches 4.21 J/cm3 under 38 kV/mm at room temperature. Besides, a record high of power density (P D ≈ 89.5 MW/cm3) in BNT-based ceramics is also achieved in x = 0.20 ceramic with an excellent temperature insensitivity within 25–160 °C. The x = 0.20 ceramic is indicated to be an ergodic relaxor ferroelectric with coexisted R3c nanodomains and P4bm polar nanoregions at room temperature, greatly inducing large maximum polarization, maintaining low remnant polarization, and thus achieving high W D and P D. Furthermore, the diffuse phase transition from R3c to P4bm phase on heating is considered to be responsible for the superior thermal stability of the high W D and P D. These results imply the large potential of the 0.80BNT–0.20NT ceramic in temperature-stable dielectric capacitor applications.

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The interfacial region plays a critical role in determining the electrical properties of dielectric nanocomposites. The current state-of-the-art interfacial modification is predominantly based on utilizing flexible organic molecules, which are random polymer coils and generally collapse on the surface of any modified nanoparticles. This work focused on engineering the interfacial region between Na 2 Ti 3 O 7 nanofibers and polymer matrix and, for the first time, utilized the liquid-crystalline polymer poly{2,5-bis[(4methoxyphenyl)oxycarbonyl]styrene} (PMPCS) to modulate the interface where the rigid polymer was forced to form a straight conformation. Owing to the rigidity and orientation of PMPCS, a series of core−shell structured Na 2 Ti 3 O 7 @PMPCS nanofibers with finely tuned shell thickness were prepared. The prepared Na 2 Ti 3 O 7 @PMPCS/P(VDF-HFP) nanocomposites showed significantly different permittivity from 10.7 to 69.6 at 1 kHz with the gradient thicknesses of PMPCS shell. These results effectively proved that modulating the interfacial layer thickness in the dielectrics nanocomposites is also a method to modulating the dielectric property.

The ability to tune the interfacial layer in nanocomposites is attracting increasing interest due to its wide application in the field of nanoscale energy storage materials. However, most of the current interfacial modifiers are flexible coils collapsing on the surface of fillers. The interfacial layer thickness cannot be readily tailored. This work demonstrates an inspiring approach to design the interfacial layer of BaTiO3 nanowires and nanoparticles with poly­{5-bis­[(4-trifluoro-methoxyphenyl)­oxycarbonyl]­styrene} (PTFMPCS). The PTFMPCS is a kind of fluoric-liquid-crystalline polymer (LCPs) that possesses polymer-chain rigidity and an orientated structure, which is useful to design the interfacial layer thicknesses of fillers. Four types of BaTiO3@PTFMPCS nanostructures are prepared and incorporated into a polymer matrix for capacitor applications. The experimental results show that the PTFMPCS interfacial layer thicknesses are precisely controlled and in good agreement with the theoretically predicted thicknesses. In addition, the performance of the nanocomposites are obviously affected by the PTFMPCS interfacial layer thickness, e.g., the discharge energy density of the nanocomposites with a 14.8 nm thickness of the PTFMPCS layer increased by 8.5% than with 9.2 nm, which reaches to 14.64 J/cm3. The findings provide an innovative way to design the interfacial layer thickness in various nanostructured materials for applications related to energy storage.