This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area.

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Interface design for high energy density polymer nanocomposites

Reversible-deactivation radical polymerization (Controlled/living radical polymerization): From discovery to materials design and applications

Electromagnetic microwave absorption theory and recent achievements in microwave absorbers

High-k polymer nanocomposites with 1D filler for dielectric and energy storage applications

Z.L., T.L., R.W., and Y.L. thank the Australian Research Council (ARCDP160104780) for financial support in the form of ARC Discovery Project. Z.L., J.Y., G.W., and X.D. thank the financial support of the National Natural Science Foundation of China (NSFC No. 11774366) and International Partnership Project of Chinese Academy of Science. Z.L. also acknowledges the support of Shanghai Sailing Program (No. 17YF1429700).

Antiferroelectrics for Energy Storage Applications: a Review

Ceramic/polymer nanocomposites are attractive for energy storage applications due to their ability to exploit the high permittivity of ceramic fillers and high breakdown strength of the polymer matrix. One challenge for the development of high performance nanocomposites based on ceramic particulates or fibers in a polymer matrix is that they often require a high volume fraction (>50%) to achieve a high permittivity, which is often at the expense of a reduction in dielectric strength and mechanical flexibility. In this paper we demonstrate by both experiment and finite element simulation that high aspect ratio nanofiber fillers offer an effective approach to achieve high energy density and dielectric strength. Lead-free ferroelectric Na0.5Bi0.5TiO3 (BNT) nanofibers with a high aspect ratio (>200) are synthesized by a hydrothermal method and dispersed in a poly(vinylidene difluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix. The increased fraction of β-phase and the alignment of BNT nanofibers perpendicular to the direction of the applied electric field lead to an enhanced dielectric strength, compared to spherical BNT/P(VDF-FHP) nanoparticles and pure P(VDF-HFP), and experimental measurements are compared with numerical simulations. The results demonstrate that the nanofiber nanocomposites exhibited an ultra-high discharged energy density (12.7 J cm−3) and provide an innovative approach to produce high-energy storage density materials.

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Ultra-high discharged energy density capacitor using high aspect ratio Na0.5Bi0.5TiO3 nanofibers

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 Na2Ti3O7 nanofibers and polymer matrix and, for the first time, utilized the liquid-crystalline polymer poly{2,5-bis[(4-methoxyphenyl)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 Na2Ti3O7@PMPCS nanofibers with finely tuned shell thickness were prepared. The prepared Na2Ti3O7@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...

Interfacial Design in Dielectric Nanocomposite Using Liquid-Crystalline Polymers

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 t...

Core–Shell Nanostructure Design in Polymer Nanocomposite Capacitors for Energy Storage Applications

A series of side-chain liquid crystal polymers (SCLCPs), named poly[ω-(4′-n-alkyloxybiphenyl-4-oxy) hexyl methacrylates] (P6biCm, m = 1, 2, 4, 6, 8, 10, 12, 14, 16 and 18), have been synthesized. Novel SCLCP/paraffin composite form-stable phase change materials (FSPCMs) were prepared by introducing P6biCm into paraffin. The minimum gelation concentration (MGC) and gel-to-sol transition temperature (TGS) properties were tested by a “tube-testing method”. It was found that P6biCm (m = 1, 2, 4, 6, 8, 10) were insoluble in paraffin, while P6biCm (m = 12, 14, 16, 18) exhibited a low MGC (≤6 wt%) and high TGS (TGS of P6biC12/paraffin is 140 °C). The structure and morphology of FSPCMs were systematically investigated by FT-IR, POM, 1D WXAD and SEM. The experimental results revealed that paraffin was restricted in the three-dimensional P6biCm network, leading to the FSPCM without leakage even above its melting point. The thermal properties were studied by DSC and TG. The research showed that the P6biCm/paraffin exhibited excellent thermal stability and high heat storage density. The shape stability was assessed by rheological measurements, indicating that solid ↔ hard gel ↔ soft gel ↔ liquid was observed with the increase of temperature. This work is useful in comprehending the physical mechanism of shape stability and in the meanwhile provides a novel method for synthesis of FSPCMs.

Sheng Chen

Papers

Interface design for high energy density polymer nanocomposites

Ultra-high discharged energy density capacitor using high aspect ratio Na0.5Bi0.5TiO3 nanofibers

Interfacial Design in Dielectric Nanocomposite Using Liquid-Crystalline Polymers

Core–Shell Nanostructure Design in Polymer Nanocomposite Capacitors for Energy Storage Applications

Preparation and characterization of side-chain liquid crystal polymer/paraffin composites as form-stable phase change materials