Largely enhanced energy storage capability of a polymer nanocomposite utilizing a core-satellite strategy

Improved Energy Density and Energy Efficiency of Poly(vinylidene difluoride) Nanocomposite Dielectrics Using 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 Nanofibers

In modern electronic and power systems, it is essential to develop advanced dielectric materials with high energy density. One-dimensional ferroelectric ceramic nanofibers were proved to be a feasible strategy for improving the permittivity and energy density of nanocomposites. In this paper, to overcome the high loss issue of Na_0.5Bi_0.5TiO₃ (NBT), a kind of novel nanofibers 0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃ (NBT-BT) with large aspect ratio are synthesized by the electrospinning method and used as the dielectric fillers in trilayer structured poly(vinylidene difluoride) (PVDF) nanocomposites for energy storage applications. The finite element analysis is performed to evaluate the electric field distribution in the nanocomposites. The results showed that the trilayer structured nanocomposite loaded with 6 wt % NBT-BT nanofibers in the middle layer achieved the highest discharge energy density of 19.21 J cm^-3 at 527 kV mm^-1, which is 87.2% higher than that of pure PVDF (10.26 J cm^-3 at 420 kV mm^-1). Owing to the contribution of the barrier effect and interface polarization between adjacent layers, the energy density of the trilayer structured nanocomposites is significantly higher than that of the single-layer nanocomposites. This work provides a kind of novel one-dimensional ceramic fillers for obviously improving the energy density of polymer-based dielectrics.

Two-Dimensional Fillers Induced Superior Electrostatic Energy Storage Performance in Trilayered Architecture Nanocomposites

Dielectric capacitors with ultrahigh power densities and fast charging/discharging rates are of vital relevance in advanced electronic markets. Nevertheless, a tradeoff always exists between breakdown strength and polarization, which are two essential elements determining the energy storage density. Herein, a novel trilayered architecture composite film, which combines outer layers of two-dimensional (2D) BNNS/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) with high breakdown strength and an intermediate layer made of blended 2D MoS₂ nanosheets/P(VDF-HFP) with large polarization, is fabricated using the layer-by-layer casting method. The insulating BNNS with a wide band gap is able to largely alleviate the distortion of the local electric field, thereby suppressing the leakage current and effectively reducing the conductivity loss, while the 2D MoS₂ nanosheets act as microcapacitors in the polymer composites, thus significantly increasing the permittivity. A finite element simulation is carried out to further analyze the evolution process of electrical treeing in the experimental breakdown of the polymer nanocomposites. Consequently, the nanocomposites possess an excellent discharged energy density of 25.03 J/cm³ accompanied with a high charging/discharging efficiency of 77.4% at 650 MV/m, which greatly exceeds those of most conventional single-layer films. In addition, the corresponding composites exhibit an outstanding reliability of energy storage performance under continuous cycling. The excellent performances of these polymer-based nanocomposite films could pave a way for widespread applications in advanced capacitors.

Enhanced Energy Storage Performance of Polymer/Ceramic/Metal Composites by Increase of Thermal Conductivity and Coulomb-Blockade Effect

Polymer-based dielectrics have attracted considerable attention for a wide range of applications as energy storage devices with high power. However, high loss from low thermal conductivity (K) and leaky current may limit their practical utilization greatly. To overcome these issues, two-dimensional hexagonal boron nitride (h-BN) modified with polydopamine (PDA) and metal palladium nanoparticles (h-BN@PDA@Pd NPs) are introduced into a poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) copolymer matrix. The PDA coating improves the compatibility between the ceramic h-BN filler and the polymer matrix. Contrary to the general idea, the metallic Pd NPs enhance the breakdown strength of the polymer nanocomposites through the Coulomb-blockade effect. The nanocomposite film filled with 6 vol % h-BN@PDA@Pd NPs exhibits significantly improved recoverable energy density (U_rec) of 58.6 J cm^-3, which is increasedby 496% compared to pure P(VDF-HFP) film, maintaining an efficiency of 65%, even under a high voltage of 500 MV m^-1. The in-plane thermal conductivity of the nanocomposites was improved from 0.21 to 1.02 W m^-1 K^-1 with increasing ceramic h-BN content. This study suggests that a dielectric polymer with surface-engineered ceramic h-BN fillers through a Coulomb-blockade effect of metal Pd NPs might be a promising strategy for high energy storage devices.

MgAl LDH nanosheets loaded with Ni nanoparticles: a multifunctional filler for improving the energy storage performance of PVDF-based nanocomposites

The dielectric constant and breakdown strength of the PVDF-based nanocomposites can be increased simultaneously by adding multifunctional Ni–MgAl LDH nanosheets, thus the nanocomposites can exhibit excellent energy storage performance.

Enhanced energy density of PVDF-based nanocomposites via a core-shell strategy

In recent years, high energy density polymer capacitors have attracted a lot of scientific interest due to their potential applications in advanced power systems and electronic devices. Here, core-shell structured TiO₂@SrTiO₃@polydamine nanowires (TiO₂@SrTiO₃@PDA NWs) were synthesized via a combination of surface conversion reaction and in-situ polymerization method, and then incorporated into the poly(vinylidene fluoride) (PVDF) matrix. Our results showed that a small amount of TiO₂@SrTiO₃@PDA NWs can simultaneously enhance the breakdown strength and electric displacement of nanocomposite (NC) films, resulting in improved energy storage capability. The 5 wt% TiO₂@SrTiO₃@PDA NWs/PVDF NC demonstrates 1.72 times higher maximum discharge energy density compared to pristine PVDF (10.34 J/cm³ at 198 MV/m vs. 6.01 J/cm³ at 170 MV/m). In addition, the NC with 5 wt% TiO₂@SrTiO₃@PDA NWs also demonstrates an excellent charge-discharge efficiency (69% at 198 MV/m). Enhanced energy storage performance is due to hierarchical interfacial polarization among their multiple interfaces, the large aspect ratio as well as surface modification of the TiO₂@SrTiO₃ NWs. The results of this study provide guidelines and a foundation for the preparation of the polymer NCs with an outstanding discharge energy density.

Improved polarization and energy density in boron nitride nanosheets/poly(vinylidene fluoride-chlorotrifluoroethylene) nanocomposite with trilayered architecture regulation

A polymer film capacitor with high energy density has attracted great attention in recent decades to fulfil the requirements of miniaturization and light weight for electronics and energy storage systems. The multi-layered nanocomposite exhibits an effective route for developing polymer film with large energy capability due to the advantage of each layer. Here, two sandwich constructions of boron nitride nanosheets (BNNSs)/poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite film were designed to investigate the effects of architecture regulation on energy storage performance, i.e. the nanocomposite serving as an inner layer with pristine films as outer layers, in which the nanocomposite film delivers a strongly polarized behavior and the pristine polymer provides a high breakdown strength. The BNNSs were liquid exfoliated from boron nitride bulk assisted with fluoro hyperbranched copolymer that was adsorbed on the surface of nanosheets via CH-π non-covalent interactions. The presence of fluoro segments improves the compatibility between the nanosheets and the P(VDF-CTFE) matrix. The maximum polarization of 7.9 μC cm^-2 at 300 MV m^-1 is achieved in the tailored sandwich film, and the discharged energy density of 9.1 J cm^-3 is obtained in the current nanocomposite, which benefits from the barrier effect between adjacent layers induced by the redistribution of electric field and emerging charge traps at the interfaces. This sandwich BNNSs/P(VDF-CTFE) nanocomposite provides an insightful prospect for structural design with respect to the advanced application of the polymer film capacitor.

Tunable dielectric polarization and breakdown behavior for high energy storage capability in P(VDF-TrFE-CFE)/PVDF polymer blended composite films

Polymer dielectrics with high dielectric performances and superior discharge energy capability are highly desirable for advanced electrostatic capacitor applications. However, the paradoxical relationship between dielectric polarization and electric breakdown behavior generally hinder their further enhancement in energy storage performances. Herein, polymer blended composite films with high energy storage capability were successfully fabricated by blending together poly(vinylidene fluoride) (PVDF) polymer and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer. The P(VDF-TrFE-CFE) terpolymer has a high dielectric constant to provide a large electric displacement under an applied electric field far below its breakdown field, which is anticipated to modulate the dielectric polarization behavior of PVDF polymer when blended in different proportions. Consequently, the polymer blended composite film consisting of 20 wt% (P(VDF-TrFE-CFE)) terpolymer exhibits a high discharge energy density of 13.63 J cm^-3 at an enhanced breakdown strength of 480 MV m^-1. This obtained high discharge energy density is 84% higher than the pure PVDF film and 582% higher than a commercialized biaxially oriented polypropylene (BOPP). Large interfacial polarization and strong interaction of polymer chains between the PVDF polymer and P(VDF-TrFE-CFE) terpolymer may contribute to the tunable dielectric constant and electric breakdown strength, thus promoting the energy storage capability. This work establishes a facile, but effective approach to achieve the high energy storage capability of PVDF polymer-based flexible composite films for capacitive energy storage applications.

Optimizing electric field distribution via tuning cross-linked point size for improving the dielectric properties of polymer nanocomposites

Polymer nanocomposites containing high K ceramics have been developed for boosting the energy density of dielectric capacitors. However, there are numerous challenges in the research about how to optimize the electric field distribution and improve the interfacial structure of nanocomposites for overcoming dielectric mismatches between high K nanofillers and low K polymers. Herein, all-chemical bonding cross-linked nanocomposites were designed and nano-BT with different sizes were regarded as cross-linked points rather than a free dispersed phase in polymers. In addition, the cross-linking degree could be controlled by changing the nano-BT sizes. 60 nm BT-BCB@DPAES nanocomposites possess the most excellent mechanical and thermal properties as well as the highest theoretical breakdown strength. In fact, 100 nm BT-BCB@DPAES nanocomposites have the most perfect dielectric performance combined with the experimental data and finite element simulation, particularly at 150 °C, the highest breakdown strength of 442 MV m^-1 and greatest discharged energy density of 3.1 J cm^-3 were obtained. This is attributed to the proper cross-linking degree and uniform electric field distribution. Overall, this kind of cross-linked structure can effectively enhance dielectric performance, particularly at elevated temperatures. This provides an idea for developing high temperature polymer nanocomposites for dielectric energy storage applications.

Multilayer Structured Poly(vinylidene fluoride)-Based Composite Film with Ultrahigh Breakdown Strength and Discharged Energy Density

Poly(vinylidene fluoride)-based (PVDF) composites with high discharged energy density (U_e) have been considered as advanced dielectric materials for pulsed power systems and electrical weapon systems. However, further improvement of the U_e of PVDF-based composites with higher breakdown strength (E_b) is of utmost importance. Based on the principle of voltage distribution in the multilayer structure, the multilayer structure (five-layer structure) ceramic/polymer composite films consisting of pristine PVDF layers with high breakdown strength and PVDF layers doped with one-dimensional 0.15SrTiO₃-0.85Na_0.5Bi_0.5TiO₃ (1D SNBT) fibers where the two kinds of layers stacked alternately has been designed and fabricated. Accordingly, a series of analyses of the dielectric properties and energy storage performances are presented, and the related results are tentatively explained by finite element simulation. The energy storage characteristics of the composite films are greatly improved due to the newly designed structure. An excellent U_e of 20.82 J cm^-3 is achieved at an ultrahigh electric field of 640 MV m^-1 with the PVDF layers containing 6 vol % SNBT fibers. Therefore, this work provides a new strategy to design and fabricate advanced polymer-based energy storage materials.

Enhanced interfacial polarization in poly(vinylidene fluoride-chlorotrifluoroethylene) nanocomposite with parallel boron nitride nanosheets

The miniaturization of electronics provides an opportunity for the polymer film capacitor due to its lightweight and flexibility. In order to improve energy density and charge-discharge efficiency of the film capacitor, the development of a polymer nanocomposite is one of the effective strategies, in which the distribution of the fillers plays a key role in the enhancement of the electrical energy capability. In this work, the few-layer boron nitride nanosheets (BNNSs) was exfoliated with assistance of the fluoro hyperbranched polyethylene-graft-poly(trifluoroethyl methacrylate) (HBPE-g-PTFEMA) copolymer as stabilizer, which was adsorbed on the surface of the nanosheets via a CH-π non-covalent interaction. The morphological results confirm the lateral size of ∼0.4 μm for resultant nanosheets with the intact crystal structure. The loading of 0.5 vol% BNNSs was embedded into poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) matrix by solution casting method, and then the nanocomposite film was uniaxial stretched to achieve the orientation of nanosheets in polymer host. The dielectric constant of stretching nanocomposite with ratio of 4 at 50 mm min^-1 reaches 51.1 at 100 Hz with low loss as 0.016, while the energy density of 7.0 J cm^-3 at 250 MV m^-1 with charge-discharge efficiency of 56% is obtained in current nanocomposite film, which is attributed to the interfacial polarization as well as parallel nanosheets blocking the growth of electrical treeing branches. This strategy of the aligned nanosheets/polymer nanocomposite establishes a simple route to construct heterogeneity in polymer films with enhanced electrical energy capability for flexible capacitors.

The role of PN-like junction effects in energy storage performances for Ag2O nanoparticle dispersed lead-free K0.5Na0.5NbO3-BiMnO3 films

This work designs a PN-like junction structure by introducing Ag₂O nanoparticles into lead-free 0.92K_0.5Na_0.5NbO₃-0.08BiMnO₃ solid solution films to investigate the role of PN-like junction effects in energy storage performances. It is shown that the energy storage performances are obviously improved with the energy density increasing to 65.1 J cm^-3 from 20.1 J cm^-3 and the efficiency to 62.6% from 50.7%. The enhancement is attributed to the formation of the depletion layer with high resistance derived from a PN-like junction structure at the interface between Ag₂O nanoparticles and matrices. The rectification effect of the high resistance region in PN-like junction improves the insulation and breakdown strength, and the internal local field derived from the high resistance region divides the macroscopic domains, which are attributed to the enhancement of energy storage performances. This work provides an alternative strategy to improve the energy storage performances by designing a PN-like junction structure.

Ultrahigh Energy Efficiency and Large Discharge Energy Density in Flexible Dielectric Nanocomposites with Pb0.97La0.02(Zr0.5SnxTi0.5-x)O3 Antiferroelectric Nanofillers

Flexible dielectric capacitors have been widely studied recently on account of their fast charge-discharge speed, high power density, and superior wearable characteristics. Inorganic ferroelectric fillers/polymer matrix composites combining large maximum electric displacement (D_max) of ferroelectric materials with good flexibility and high electric breakdown strength (E_b) of the polymer are regarded as the most promising materials for preparing flexible dielectric capacitors with superior energy storage properties. However, simultaneously achieving large discharge energy density (W_d) and high energy efficiency (η) in these composites remains challenging on account of a large remnant electric displacement (D_r) and low D_max - D_r values of ferroelectric fillers. In contrast, antiferroelectrics (AFEs) exhibit near zero D_r and larger D_max - D_r values and are thus attractive composite fillers to simultaneously achieve large W_d and high η. On the basis of these factors, in this report, we design and prepare Pb_0.97La_0.02(Zr_0.5Sn_xTi_0.5-x)O₃ (PLZST) AFE nanoparticles (NPs)/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposites and investigate the effects of the Sn and AFE NPs contents on the energy storage capacity of the nanocomposites. Through reasonable adjustment of the Sn content and the PLZST AFE fillers content, because of the large D_max - D_r value of 7.75 μC/cm² and small D_r value of 0.26 μC/cm² at the E_b as high as 3162 kV/cm, the Pb_0.97La_0.02(Zr_0.5Sn_0.38Ti_0.12)O₃ AFE NPs/P(VDF-HFP) polymer nanocomposite with 7 wt % fillers exhibits the most superior energy storage properties with an ultrahigh η of 93.4% and a large W_d of 12.5 J/cm³. These values are superior to those of the recently reported dielectric nanocomposites with a single-layer structure containing ferroelectric nanowires, nanofibers, nanobelts, nanotubes, and nanosheets or core-shell structure fillers, which are prepared via a very complicated method. This work not only shows that, in principle, the polarization characteristics of the composites depend mainly on those of the inorganic fillers but also demonstrates a convenient, effective, and scalable way to fabricate dielectric capacitors with superior flexibility and energy storage capacities.

Polymer Matrix Nanocomposites with 1D Ceramic Nanofillers for Energy Storage Capacitor Applications

Recent developments in various technologies, such as hybrid electric vehicles and pulsed power systems, have challenged researchers to discover affordable, compact, and super-functioning electric energy storage devices. Among the existing energy storage devices, polymer nanocomposite film capacitors are a preferred choice due to their high power density, fast charge and discharge speed, high operation voltage, and long service lifetime. In the past several years, they have been extensively researched worldwide, with 0D, 1D, and 2D nanofillers being incorporated into various polymer matrixes. However, 1D nanofillers appeared to be the most effective in producing large dipole moments, which leads to a considerably enhanced dielectric permittivity and energy density of the nanocomposite. As such, this Review focuses on recent advances in polymer matrix nanocomposites using various types of 1D nanofillers, i.e., linear, ferroelectric, paraelectric, and relaxor-ferroelectric for energy storage applications. Correspondingly, the latest developments in the nanocomposite dielectrics with highly oriented, surface-coated, and surface-decorated 1D nanofillers are presented. Special attention has been paid to identifying the underlying mechanisms of maximizing dielectric displacement, increasing dielectric breakdown strength, and enhancing the energy density. This Review also presents some suggestions for future research in low-loss, high energy storage devices.

Interface design for high energy density polymer nanocomposites

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.

Simultaneously enhanced discharge energy density and efficiency in nanocomposite film capacitors utilizing two-dimensional NaNbO3@Al2O3 platelets

With rapid developments in the consumer electronics market, electrostatic capacitors need to store as much energy as possible within a rather restricted space. In this work, nanocomposite films combining two-dimensional core-shell NaNbO3@Al2O3 platelets (2D NN@AO Ps) and poly(vinylidene-fluoride hexafluoropropylene) (P(VDF-HFP)), featuring excellent energy storage capability, high efficiency, and ultrafast discharge performance, are designed and fabricated. Both the experimental results and finite element simulations confirm the superiority of these 2D NN@AO Ps nanocomposite films in improving the breakdown strength (Eb) and energy storage capability. In particular, the introduction of 3 vol% 2D NN@AO Ps results in much enhanced discharge energy density of 14.59 J cm-3 and outstanding discharge efficiency of 70.1% in NN@AO Ps/P(VDF-HFP) nanocomposite films, which is much greater than that of pure P(VDF-HFP) (7.74 J cm-3). The corresponding nanocomposite films exhibit excellent reliability in energy storage performance under consecutive cycling. Therefore, this research could reveal a new chapter in the study and application of polymer nanocomposites in energy-storage dielectric capacitors.