High Energy Density Polymer Dielectrics Interlayered by Assembled Boron Nitride Nanosheets

Abstract

terms of a graceful failure. [1] These devices have been applied in many high-tech fields such as hybrid electric vehicles, electrical defibrillators, pulsed power systems, and power grids. Nevertheless, the inferior energy density of the polymer dielectrics significantly restrains the development of film capacitors in the future applications. For instance, the commercial benchmark poly mer dielectric biaxially oriented polypropylene (BOPP) only possesses an energy density of <4 J cm −3 , [2] which leads to the cumbrous volume and cost in the practical applications. For example, film capacitors occupy ≈35% the volume and ≈40% the cost of the power inverters in hybrid electric vehicles. [3] The energy density (U e ) of dielectric materials can be derived from U e = ∫EdD , where E is the applied electric field and D denotes the electrical displacement. For linear dielectrics, the formula evolves into U e = 1/2ε 0 ε r E b 2 , where ε 0 is the vacuum permittivity, and ε r and E b are the dielectric constant and breakdown strength of dielectrics, respectively. Clearly, U e depends on the dielectric constant and breakdown strength of dielectrics, where E b is more important because of its quadratic relationship to U e .Boron nitride nanosheets (BNNSs), a 2D nanomaterial with a wide bandgap (≈6 eV), have proved to be an intriguing dopant in dielectric polymer nanocomposites for the interest of enhancing dielectric strength and energy efficiency, because they are of high intrinsic breakdown voltage, can serve as efficient scattering centers for charge carriers, and possess large electrical resistance, in addition to their great thermal conductivity and mechanical strength. [4] To make use of the exceptional effects of BNNSs on dielectric polymers, a straightforward approach is to homogeneously disperse such nanosheets in the polymer matrices to impede charge conduction. In princi ple, with increasing the population density of BNNSs in the polymer matrices, the transport of charge carriers becomes increasingly constrained by these 2D topological barriers, leading to better dielectric performance. A strain forced orientation (i.e., mechanical stretching) of the BNNSs along the film direction is usually applied as an extra step to further enlarge the coverage of the embedded nanofillers in the transverse plane direction, and hence improve the dielectric performance of the composite film. [5] However, with increasing the feed Polymer dielectrics such as poly(vinylidene fluoride) (PVDF) have drawn tremendous attention in high energy density capacitors because of their high dielectric constant and ease of processing. However, the discharged energy density attained with these materials is restrained by the inferior breakdown strength and electric resistivity. Herein, PVDF composite films with a nanosized interlayer of assembled boron nitride nanosheets (BNNSs) that is aligned along the in-plane direction are prepared through a simple layer-by-layer solution-casting process. Compared to the pristine PVDF, the composite films ...

Theoretical Study of Nanocomposite Permittivity with a Tunable Clustering of Inclusions

“…This result implicitly explains the experimental observations reported in refs. [96,104,106–113] showing the permittivity of high‐aspect‐ratio nanocomposites strongly depends on the filler orientation.…”

“…This prediction correlates with the FEM based and experimental findings that the inclusion shape and/or its clustering in a given direction greatly affect energy storage capacities of the composite. [ 96,104–115 ] In the current study, however, we deal with the clustering of spherical inclusions, and thus assume that γ only depends on the preferred clustering orientation of inclusions. In experimental studies such clustering can be engineered using the dielectrophoretic assembly effect.…”

“…Therefore, it is natural to expect that the inclusion's shape, i.e., the aspect ratio of the filler, determines how much energy can be stored in the nanocomposite. Indeed, lately much attention has been given to the storage capacities of nanocomposites with high‐aspect‐ratio fillers such as nanofibers, nanosheets, nanobelts, and oriented clusters of nanofillers [ 96,104–113 ] or their mixtures. [ 114,115 ] These studies mostly focus on the question of how the filler orientation relative to the applied field alters the stored energy density in the material.…”

Tuning Nanofillers in In Situ Prepared Polyimide Nanocomposites for High‐Temperature Capacitive Energy Storage

“…[ 4,5 ] While dielectric ceramics are traditional materials for high‐temperature capacitors, [ 6 ] they are severely limited by scalability, weight, fracture toughness, and breakdown strength in comparison to their polymer counterparts. [ 7–17 ] Biaxially oriented polypropylene film (BOPP), the state‐of‐the‐art commercially available polymer dielectric, however, shows largely degraded high‐field dielectric properties when operating at temperatures above 100 °C. [ 18 ]…”

3D printing of anisotropic polymer nanocomposites with aligned BaTiO3 nanowires for enhanced energy density

“…High performance dielectric capacitors have been widely applied in electrical and electronic systems, such as electric vehicles, wind generators and aerospace power conditioning, due to their merits of super high power density and ability to withstand high operating voltage. [1][2][3][4][5][6][7] The dielectric materials used in commercially available capacitors are mainly based on biaxially oriented polypropylenes (BOPP), which exhibit energy densities of only 1-1.2 J cm À3 at high applied electric field (B640 kV mm À1 ). 8 In this case, the low energy density of the dielectric becomes a limitation to their applications.…”