High-Energy-Density Polymer Nanocomposites Composed of Newly Structured One-Dimensional BaTiO3@Al2O3 Nanofibers

Enhancing Energy Density of BaTiO3-Bi(M)O3@SiO2/PVDF Nanocomposites via Filler Component Modulation and Film Structure Design

The low energy density (Ud) of polymeric dielectrics is unfavorable for the integration and miniaturization of electronics, thus limiting their application prospects. Introducing high-εr (dielectric constant) ceramic nanofillers to polymer matrices is the most common strategy to enhance their εr, and hence their Ud. By comparison, enhancing breakdown strength (Eb) is a more effective strategy to enhance Ud. Herein, 0.6BaTiO3-0.4Bi(Mg0.5Ti0.5)O3 and 0.85BaTiO3-0.15Bi(Mg0.5Zr0.5)O3 nanofibers coated with SiO2 were utilized as fillers in PVDF-based nanocomposites. The combination of experimental and simulation results suggests that the intrinsic properties of nanofillers are the determining factor of the Eb of polymer-based nanocomposites, and SiO2 coating and film structure design are effective strategies to enhance their Eb, and consequently their Ud. As a result, the sandwich-structured PVDF/6 wt% 0.85BaTiO3-0.15Bi(Mg0.5Zr0.5)O3@SiO2 nanofiber within PVDF/PVDF nanocomposite films achieved a maximum Ud of 11.1 J/cm3 at an Eb of 458 MV/m, which are 2.15 and 1.40 times those of pristine PVDF, respectively.

Enhanced energy storage performance in polyetherimide composites via oriented one-dimensional BZCT@BT core-shell filler

The development of dielectric capacitors toward high voltage and high power density requires materials with excellent insulation and energy storage performances. In this work, a polymer dielectric with polyetherimide (PEI) as the matrix and calcium barium zirconate titanate (BZCT) coated by barium titanate fiber (BT) as the filler (BZCT@BT) was constructed. The (0.5%-10% BZCT@BT/PEI) polymer dielectric has an excellent discharge energy density (Ue) of 6.66 J/cm3 and maintains an advanced charge/discharge efficiency (η) of 93.29% when the BT content was 0.5% and the BZCT particle content was 10%. The addition of BZCT endows the polymer dielectric with a higher relative dielectric constant (εr), while BT, maintaining a lower εr than BZCT, could reduce the electric field (E) distortion caused by the dielectric mismatch between PEI and BZCT. Oriented fiber fillers increase the breakdown strength of the polymer dielectric, ultimately increasing the performance of energy storage. A new strategy for the design of energy storage polymer dielectrics was provided by this work.

Electrospun PVDF-Based Polymers for Lithium-Ion Battery Separators: A Review

Lithium-ion batteries (LIBs) have been widely applied in electronic communication, transportation, aerospace, and other fields, among which separators are vital for their electrochemical stability and safety. Electrospun polyvinylidene fluoride (PVDF)-based separators have a large specific surface area, high porosity, and remarkable thermal stability, which significantly enhances the electrochemistry and safety of LIBs. First, this paper reviewed recent research hotspots and processes of electrospun PVDF-based LIB separators; then, their pivotal parameters influencing morphology, structures, and properties of separators, especially in the process of electrospinning solution preparation, electrospinning process, and post-treatment methods were summarized. Finally, the challenges of PVDF-based LIB separators were proposed and discussed, which paved the way for the application of electrospun PVDF-based separators in LIBs and the development of LIBs with high electrochemistry and security.

Constructing Deep Traps to Achieve Excellent Dielectric Properties in Crystal-Based HfO2/PEI Nanocomposite Films with Ultralow Filler Loadings

Mixing fillers featured with wide band gaps in polymers can effectively meet the requirement of higher energy storage densities. However, the fundamental relationship between the crystal structures of fillers and the dielectric properties of the corresponding nanocomposites is still unclear. Accordingly, we introduced ultralow contents of the synthesized cubic Hafnium dioxide (c-HfO2) or monoclinic Hafnium dioxide (m-HfO2) as deep traps into poly(ether imide) (PEI) to explore their effects on dielectric properties and the charge-blocking mechanism. m-HfO2/PEI showed better charge trapping due to the higher electron affinity and deeper trap energy. At room temperature, the 0.4 vol % m-HfO2/PEI maintains an ultralow dielectric loss of 0.008 while obtaining a dielectric constant twice that of pure PEI at 1 kHz, simultaneously outperforming in terms of leakage current density, breakdown strength (452 kV mm-1), discharge energy density (Ud, 5.03 J cm-3), charge-discharge efficiency (η, 92%), and dielectric thermal stability. At 125 °C, it exhibits a considerable Ud of 2.48 J cm-3 and a high η of 85% at 300 kV mm-1, surpassing the properties of pure PEI. This promising work opens up a new path for studying HfO2-derived dielectrics with unique crystal structures.

Linear and nonlinear optical parameters of biodegradable chitosan/polyvinyl alcohol/sodium montmorillonite nanocomposite films for potential optoelectronic applications

Innovations in sophisticated optoelectronic devices have increased interest in high-refractive index polymers. Herein, we report innovative nanocomposite films with high linear and nonlinear refractive indices prepared by casting chitosan (Cs) with polyvinyl alcohol (PVA) (50:50 wt%) along with different concentrations (10-50 wt%) of sodium montmorillonite (NaMMT) nanoclay. The refractive indices in addition to other optical parameters of homopolymers and hybrid materials were investigated by UV-Vis. spectroscopy and optical modeling to assess their potential applications in optics. Besides, the structure, morphology, and thermal stability of the prepared films were investigated by a multitude of experimental techniques including X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), and thermogravimetric analysis (TGA/DTG). The ATR-FTIR, XRD, SEM, and AFM measurements confirmed the complete exfoliation of NaMMT nanolayers in the Cs/PVA matrix. The TGA/DTG revealed an increase in the thermal stability of Cs/PVA film with increasing clay content. The UV-Vis. measurements revealed a decrease in the optical energy gap (Eg) and a substantial increase in the linear (nD) and nonlinear (n2) refractive indices as clay content increased. Additionally, the nanohybrids displayed low UV transmission and reflected about 80 % of UV rays, making them excellent candidates for UV protection. For the first time, the dissipation factor (tanδ) in the UV/Vis. region has been calculated and fitted with the Drude-Lorentz model to predict the plasma frequency (ωp), resonance frequency (ω0), and electron lifetime (τ) of pristine polymers and nanocomposites.

Toward Excellent Energy Storage Performance via Well-Aligned and Isolated Interfaces in Multicomponent Polypropylene-Based All-Organic Polymer Dielectric Films

Polypropylene (PP) serves as an excellent commercialized polymer dielectric film owing to its high breakdown strength, excellent self-healing ability, and flexibility. However, its low dielectric constant causes the large volume of the capacitor. Constructing multicomponent polypropylene-based all-organic polymer dielectric films is a facile strategy for achieving high energy density and efficiency simultaneously. Thereinto, the interfaces between the components become the key factors that determine the energy storage performance of the dielectric films. In this work, we propose to fabricate high-performance polyamide 513 (PA513)/PP all-organic polymer dielectric films via the construction of abundant well-aligned and isolated nanofibrillar interfaces. Laudably, a significant enhancement in the breakdown strength is achieved from 573.1 MV/m of pure PP to 692.3 MV/m with 5 wt % of PA513 nanofibrils. Besides, a maximum discharge energy density of about 4.4 J/cm² is realized with 20 wt % of PA513 nanofibrils, which is about 1.6-folds higher than pure PP. Simultaneously, the energy efficiency of samples with modulated interfaces maintains higher than 80% up to 600 MV/m, which is much higher than pure PP of about 40.7% at 550 MV/m. This work provides a new strategy to fabricate high-performance multicomponent all-organic polymer dielectric films on an industrial scale.

Improved Energy Density Obtained in Trilayered Poly(vinylidene fluoride)-Based Composites by Introducing Two-Dimensional BN and TiO2 Nanosheets

Dielectric capacitors with an ultrahigh power density have received extensive attention due to their potential applications in advanced electronic devices. However, their inherent low energy density restricts their application for miniaturization and integration of advanced dielectric capacitors. Herein, a novel composite entirely incorporated with two-dimensional (2D) nanosheets with a topological trilayered construction is prepared by a solution casting and hot-pressing method. The 2D boron nitride nanosheets (BNNS) with a wide band gap that are oriented in a poly(vinylidene fluoride) (PVDF) matrix to form the upper and bottom outer layers would efficiently suppress the leakage current in composites, thus significantly improving the overall breakdown strength. Meanwhile, the 2D anatase-type TiO₂ nanosheets (TONS) uniformly distributed in the middle layer can enhance their interfacial compatibility and polarization with the PVDF matrix, leading to a synergistic improvement in both the breakdown strength and dielectric constant of the composite. In particular, a significantly improved dielectric constant of ∼11.42, a reduced dielectric loss of 0.03 at 100 Hz, and a maximum discharge energy density (U_dis) of 10.17 J cm^-3 at an electric field of 370.1 MV m^-1 can be obtained from the trilayered composite containing 3 wt % 2D TONS in the middle layer and 2 wt % 2D BNNS on the outer layer. The finding of this research offers an effective strategy for the preparation of advanced polymer-based composites with an outstanding discharge energy density performance.

Role of Microstructures in the Dielectric Properties of PVDF-Based Nanocomposites Containing High-Permittivity Fillers for Energy Storage

Polymer-based nanocomposites containing inorganic ferroelectric inclusions, typically ABO₃ perovskites, have emerged as innovative dielectric materials for energy storage and electric insulation, potentially coupling the high breakdown strength (BDS) and easy processing of polymers with the enhancement of dielectric constant provided by the ferroelectric phase. In this paper, experimental data and three-dimensional finite element method (3D FEM) simulations were combined to shed some light on the effect of microstructures on the dielectric properties of poly(vinylidene fluoride) (PVDF)-BaTiO₃ composites. The existence of particle aggregates or touching particles has a strong effect on the effective dielectric constant and determines an increase of the local field in the neck region of the ferroelectric phase with a detrimental effect on the BDS. The distribution of the field and the effective permittivity are very sensitive to the specific microstructure considered. The degradation of the BDS can be overcome by coating the ferroelectric particles with a thin shell of an insulating oxide with a low dielectric constant, such as SiO₂ (ε_r = 4). The local field is highly concentrated on the shell, while the field in the ferroelectric phase is reduced almost to zero and that on the matrix is close to the applied one. The electric field in the matrix becomes less homogeneous with increasing the dielectric constant of the shell material, as happens with TiO₂ (ε_r = 30). These results provide a solid background to explain the enhanced dielectric properties and the superior BDS of composites containing core-shell inclusions.

High-Energy-Density and High Efficiency Polymer Dielectrics for High Temperature Electrostatic Energy Storage: A Review

Polymer dielectrics are key components for electrostatic capacitors in energy, transportation, military, and aerospace fields, where their operation temperature can be boosted beyond 125 °C. While most polymers bear poor thermal stability and severe dielectric loss at elevated temperatures, numerous linear polymers with linear D-E loops and low dielectric permittivity exhibit low loss and high thermal stability. Therefore, the broad prospect of electrostatic capacitors under extreme conditions is anticipated for linear polymers, along with intensive efforts to enhance their energy density with high efficiency in recent years. In this article, an overview of recent progress in linear polymers and their composites for high-energy-density electrostatic capacitors at elevated temperatures is presented. Three key factors determining energy storage performance, including polarization, breakdown strength, and thermal stability, and their couplings are discussed. Strategies including chain modulation, filler selection, and design of topological structure are summarized. Key parameters for electrical and thermal evaluations of polymer dielectrics are also introduced. At the end of this review, research challenges and future opportunities for better performance and industrialization of dielectrics based on linear polymers are concluded.

Improved Energy Storage Property of Sandwich-Structured Poly(vinylidene fluoride)-Based Composites by Introducing Na0.5Bi0.5TiO3@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 Na_0.5Bi_0.5TiO₃(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 (U_d) 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.

High Conduction Band Inorganic Layers for Distinct Enhancement of Electrical Energy Storage in Polymer Nanocomposites

Dielectric polymer nanocomposites are considered as one of the most promising candidates for high-power-density electrical energy storage applications. Inorganic nanofillers with high insulation property are frequently introduced into fluoropolymer to improve its breakdown strength and energy storage capability. Normally, inorganic nanofillers are thought to introducing traps into polymer matrix to suppress leakage current. However, how these nanofillers effect the leakage current is still unclear. Meanwhile, high dopant (> 5 vol%) is prerequisite for distinctly improved energy storage performance, which severely deteriorates the processing and mechanical property of polymer nanocomposites, hence brings high technical complication and cost. Herein, boron nitride nanosheet (BNNS) layers are utilized for substantially improving the electrical energy storage capability of polyvinylidene fluoride (PVDF) nanocomposite. Results reveal that the high conduction band minimum of BNNS produces energy barrier at the interface of adjacent layers, preventing the electron in PVDF from passing through inorganic layers, leading to suppressed leakage current and superior breakdown strength. Accompanied by improved Young's modulus (from 1.2 GPa of PVDF to 1.6 GPa of nanocomposite), significantly boosted discharged energy density (14.3 J cm-3) and charge-discharge efficiency (75%) are realized in multilayered nanocomposites, which are 340 and 300% of PVDF (4.2 J cm-3, 25%). More importantly, thus remarkably boosted energy storage performance is accomplished by marginal BNNS. This work offers a new paradigm for developing dielectric nanocomposites with advanced energy storage performance.

Multiscale Characterization of the Influence of the Organic-Inorganic Interface on the Dielectric Breakdown of Nanocomposites

Nanoscale engineered materials such as nanocomposites can display or be designed to enhance their material properties through control of the internal interfaces. Here, we unveil the nanoscale origin and important characteristics of the enhanced dielectric breakdown capabilities of gold nanoparticle/polymer nanocomposites. Our multiscale approach spans from the study of a single chemically designed organic/inorganic interface to micrometer-thick films. At the nanoscale, we relate the improved breakdown strength to the interfacial charge retention capability by combining scanning probe measurements and density functional theory calculations. At the meso- and macroscales, our findings highlight the relevance of the nanoparticle concentration and distribution in determining and enhancing the dielectric properties, as well as identifying this as a crucial limiting factor for the achievable sample size.

Enhanced dielectric properties of PVDF-based composite film with BaTiO3@SrTiO3 nanoparticles

(a) SEM image and (c) TEM image of BT particles before coating. (b) SEM image and (d) TEM image of BT@ST nanoparticles.

"Toolbox" for the Processing of Functional Polymer Composites

The processing methods of functional polymer composites (FPCs) are systematically summarized in “Toolbox”. The relationship of processing method-structure-property is discussed and the selection and combination of tools in processing among different FPCs are analyzed. A promising prospect is provided regarding the design principle for high performance FPCs for further investigation.

ABSTRACT

Functional polymer composites (FPCs) have attracted increasing attention in recent decades due to their great potential in delivering a wide range of functionalities. These functionalities are largely determined by functional fillers and their network morphology in polymer matrix. In recent years, a large number of studies on morphology control and interfacial modification have been reported, where numerous preparation methods and exciting performance of FPCs have been reported. Despite the fact that these FPCs have many similarities because they are all consisting of functional inorganic fillers and polymer matrices, review on the overall progress of FPCs is still missing, and especially the overall processing strategy for these composites is urgently needed. Herein, a “Toolbox” for the processing of FPCs is proposed to summarize and analyze the overall processing strategies and corresponding morphology evolution for FPCs. From this perspective, the morphological control methods already utilized for various FPCs are systematically reviewed, so that guidelines or even predictions on the processing strategies of various FPCs as well as multi-functional polymer composites could be given. This review should be able to provide interesting insights for the field of FPCs and boost future intelligent design of various FPCs. [Image: see text]

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-021-00774-5.

Enhanced crystallization behaviors and dielectric performance of poly(vinylidene fluoride) film induced by polyamide-1

Poly(vinylidene fluoride) (PVDF)-based composites attract tremendous attention as dielectric materials. However, their development has been limited due to the raised problem in the in-homogeneous polymer composites. In this work, a novel PVDF-based film incorporated with polyamide-1, containing the highest density of dipole among all polyamides, was prepared to improve the crystallization behaviors and dielectric properties. The results showed that the optimal concentration of polyamide-1 in PVDF was 6 wt.%. The crystallization rate of PVDF was improved in the presence of polyamide-1. Interestingly, the polyamide-1 was conductive to the formation of β form crystal of PVDF, which exhibited great electric performance. The dielectric constant of PVDF increased sharply and loss tangent still kept at a low level of 0.03@100 Hz when the concentration of polyamide-1 was 6 wt.%. This work may provide a new direction to design dielectric materials for PVDF blends.

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.

Modulation of the interfacial architecture enhancing the efficiency and energy density of ferroelectric nanocomposites via the irradiation method

Flexible dielectric materials such as poly(vinylidene fluoride)-based nanocomposites with high energy density are employed for applications in modern electronic and electric systems. In this study, we improve traditional methods by optimizing the interfacial structure, achieving a 34% increase in energy density without reduced discharge efficiency. Herein, a simple solution-cast method is used to prepare poly(vinylidene fluoride-co-trifluoroethylene) nanocomposites filled by γ-methacryloyl-propyltrimethoxysilane (MPMS) grafting barium titanate nanoparticles, forming a class of cross-linking networks by irradiation. More additional interfaces arising from irradiation cross-linking give rise to high discharge energy density, and the small crystalline domain and cross-linking network enhance the charge-discharge efficiency. Furthermore, we find two types of cross-linking centers on the network. One is more beneficial to energy density, and the other is more beneficial to efficiency. Regulating two types of cross-linking centers can balance efficiency and energy density. In summary, this work provides a promising strategy for exploiting advanced flexible dielectric materials to meet application requirements.

Cellulose/BaTiO3 nanofiber dielectric films with enhanced energy density by interface modification with poly(dopamine)

Flexible electrostatic capacitors have many potential applications in modern electric power systems. In this study, flexible cellulose-based dielectric films were prepared by compositing regenerated cellulose (RC) and one-dimensional BaTiO₃ nanofiber (BTNF) via a simple and environmentally friendly process. To improve compatibility and distributional homogeneity of the fillers/matrix, BTNF was surface modified by dopamine to prepare the poly(dopamine) modified BTNF (PDA@BTNF). The obtained RC/PDA@BTNF composite films (RC-PDA@BTNF) possessed higher dielectric constant and breakdown strength than those of the RC and RC/BTNF composite films. In particular, RC/PDA@BTNF composite films with 2 vol% PDA@BTNF (RC-2PDA@BTNF) exhibited a high discharged energy density of 17.1 J/cm³ at 520 MV/m, which exceeded 40 % compared with that of RC-2BTNF at 460 MV/m. Meanwhile, RC-2PDA@BTNF could continuously work for more than 10,000 times with a high efficiency of 91 %. Furthermore, the composite films could maintain good dielectric properties for a long time when stored in vacuum condition (under 0.3 atm). Therefore, these flexible cellulose-based dielectric materials are promising in the field of novel high-performance film dielectric capacitors.

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.

Multifunctional composite membrane based on BaTiO3@PU/PSA nanofibers for high-efficiency PM2.5 removal

In this study, a new barium titanate@polyurethane/polysulfonamide (BaTiO₃@PU/PSA) composite nanofibrous membrane with comprehensive properties for high temperature filtration and robust PM2.5 removal was successfully fabricated through the blending spinning of PU and PSA and the introduction of BaTiO₃. As a consequence, the BaTiO₃@PU/PSA membrane achieved the high capture efficiency of 99.99 % for fine particulates, low pressure drop of 39.4 ± 0.2 Pa, good mechanical property (13.27 MPa), sufficient flexibility, high thermal stability (up to 300 °C), favorable flame-retardancy as well as superior chemical resistance against acid and alkali. Especially, to intuitively reveal the relationship between the fiber structure, high temperature environment, gas velocity and filtration performance of the composite membrane, the filtration processes were carefully investigated through the analog simulation. More importantly, the BaTiO₃@PU/PSA membrane exhibited high-efficiency PM2.5 purification capacity, and the removal efficiency kept stable after high temperature, acid or alkali treatment, ascribing to the advantageous structure of PSA, PU and BaTiO₃. Overall, the BaTiO₃@PU/PSA nanofiber membranes with versatility are a promising high-efficiency candidate for dust removal, particularly in harsh conditions.

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.

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.

High dielectric thin films based on barium titanate and cellulose nanofibrils

A series of composite films based on tetragonal barium titanate (BTO) and cellulose nanofibrils (CNF) with high dielectric constant are prepared using a casting method in aqueous solution. No organic solvent is involved during the preparation, which demonstrates the environmental friendliness of the novel material. With less than 30 wt% of filler loading, the excellent distribution of BTO nanoparticles within the CNF matrix is revealed by the FE-SEM images. The dielectric constant of the CNF/BTO (30 wt%) composite film reaches up to 188.03, which is about seven times higher than that of pure CNF (25.24), while the loss tangent only rises slightly from 0.70 to 1.21 (at 1 kHz). The thin films kept their dielectric properties on an acceptable level after repeatedly twisting or rolling 10 times. The improvement of thermal stability is observed with the presence of BTO. The outstanding dielectric properties of the CNF/BTO composite film indicates its great potential to be utilized in energy storage applications.

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.

Ferroelectric nanocomposite networks with high energy storage capacitance and low ferroelectric loss by designing a hierarchical interface architecture

Nanoscale design of nanofillers and interfacial architecture are vital to achieve high-capacity and high-energy-conversion efficiency poly(vinylidene fluoride) [(PVDF)-based] nanocomposite materials for vast potential applications in modern electronic devices and electric power systems. Using traditional methods, the addition of ceramic nanoparticles can only produce one type of interface between the nanoparticles and this matrix, achieving an enhanced dielectric constant and energy density at the expense of the charge-discharge efficiency. Herein, we demonstrate a novel class of cross-linking nanofiller system, poly(vinylidene fluoride-chlorotrifluoroethylene)/γ-methacryloylpropyl trimethoxysilane@BaTiO₃ [P(VDF-CTFE)/MPS@BT]. This novel approach can not only provide the interfaces between the nanoparticle and the matrix, but also scale down the size of crystalline domains, which results in producing more additional interfaces between the crystalline and amorphous phases to achieve an improved discharged energy density. Remarkably, the smaller crystalline domains, which were characterized by XRD and FTIR spectroscopy, could be beneficial for improving the dipole switchability from the polar phases to non-polar phases during the charge-discharge cycles, leading to unprecedented charge-discharge efficiency. Furthermore, the addition of MPS@BT NPs can regulate two stages of the discharge rate. The early discharge process can be accelerated, while the following stage is obviously delayed. The simplicity of the hierarchical interfacial engineering method provides a promising path to design ferroelectric polymer nanocomposites for dielectric capacitor applications.

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.

Significantly Enhanced Energy Density by Tailoring the Interface in Hierarchically Structured TiO2-BaTiO3-TiO2 Nanofillers in PVDF-Based Thin-Film Polymer Nanocomposites

Dielectric polymer nanocomposites with a high breakdown field and high dielectric constant have drawn significant attention in modern electrical and electronic industries due to their potential applications in dielectric and energy storage systems. The interfaces of the nanomaterials play a significant role in improving the dielectric performance of polymer nanocomposites. In this work, polydopamine (dopa)-functionalized TiO₂-BaTiO₃-TiO₂ (TiO₂-BT-TiO₂@dopa) core@double-shell nanoparticles have been developed as novel nanofillers for high-energy-density capacitor applications. The hierarchically designed nanofillers help in tailoring the interfaces surrounding the polymer matrix as well as act as individual capacitors in which the core and outer TiO₂ shell function as a capacitor plate because of their high electrical conductivity while the middle BT layer functions as a dielectric medium due to high dielectric constant. Detailed electrical characterizations have revealed that TiO₂-BT-TiO₂@dopa/poly(vinylidene fluoride) (PVDF) possesses a higher relative dielectric permittivity (ε_r), breakdown strength ( E_b), and energy density as compared to those of PVDF, TiO₂/PVDF, TiO₂@dopa/PVDF, and TiO₂-BT@dopa/PVDF polymer nanocomposites. The ε_r and energy density of TiO₂-BT-TiO₂@dopa/PVDF were 12.6 at 1 kHz and 4.4 J cm^-3 at 3128 kV cm^-1, respectively, which were comparatively much higher than those of commercially available biaxially oriented polypropylene having ε_r of 2.2 and the energy density of 1.2 J cm^-3 at a much higher electric field of 6400 kV cm^-1. It is expected that these results will further open new avenues for the design of novel architecture for high-performance polymer nanocomposite-based capacitors having core@multishell nanofillers with tailored interfaces.

Barium titanate at the nanoscale: controlled synthesis and dielectric and ferroelectric properties

The current trend in the miniaturization of electronic devices has driven the investigation into many nanostructured materials. The ferroelectric material barium titanate (BaTiO3) has garnered considerable attention over the past decade owing to its excellent dielectric and ferroelectric properties. This has led to significant progress in synthetic techniques that yield high quality BaTiO3 nanocrystals (NCs) with well-defined morphologies (e.g., nanoparticles, nanorods, nanocubes and nanowires) and controlled crystal phases (e.g., cubic, tetragonal and multi-phase). The ability to produce nanoscale BaTiO3 with controlled properties enables theoretical and experimental studies on the intriguing yet complex dielectric properties of individual BaTiO3 NCs as well as BaTiO3/polymer nanocomposites. Compared with polymer-free individual BaTiO3 NCs, BaTiO3/polymer nanocomposites possess several advantages. The polymeric component enables simple solution processibility, high breakdown strength and light weight for device scalability. The BaTiO3 component enables a high dielectric constant. In this review, we highlight recent advances in the synthesis of high-quality BaTiO3 NCs via a variety of chemical approaches including organometallic, solvothermal/hydrothermal, templating, molten salt, and sol-gel methods. We also summarize the dielectric and ferroelectric properties of individual BaTiO3 NCs and devices based on BaTiO3 NCs via theoretical modeling and experimental piezoresponse force microscopy (PFM) studies. In addition, viable synthetic strategies for novel BaTiO3/polymer nanocomposites and their structure-composition-performance relationship are discussed. Lastly, a perspective on the future direction of nanostructured BaTiO3-based materials is presented.

Fabrication of Morphologically Controlled Composites with High Thermal Conductivity and Dielectric Performance from Aluminum Nanoflake and Recycled Plastic Package

Polymer composites with high thermal conductivity are highly desirable for modern electronic and electrical industry because of their wide range of applications. However, conventional polymer composites with high thermal conductivity usually suffer from the deterioration of electrical insulation and high dielectric loss, whereas polymer composite materials with excellent electrical insulation and dielectric properties usually possess low thermal conductivity. In this study, combining surface-oxidized aluminum (Al) nanoflake and multilayer plastic package waste (MPW) by powder mixing technique, we report a novel strategy for polymer composites with high thermal conduction, high electrical insulation, and low dielectric loss. The resultant MPW/Al, MPW/Al₄₀₀, and MPW/Al₅₀₀ composites exhibited the maximum thermal conductivity of 4.8, 3.5, and 1.4 W/mK, respectively, which exceeds those of most of the corresponding composites reported previously. In addition, all the composites still have high insulation (<10^-13 S/cm) and maintain dielectric loss at a relatively low level (<0.025). Such a result is ascribed to the formation of an insulating Al₂O₃ shell and the continuous three-dimensional filler network, which is revealed by Agari model fitting coefficient. The model of effective medium theory qualitatively demonstrates that the lower interfacial thermal resistances of the MPW/Al composite can also benefit the high thermal conduction. This interfacial engineering strategy provides an effectively method for the fabrication of polymer materials with high-performance thermal management.

Optimizing sandwich-structured composites based on the structure of the filler and the polymer matrix: toward high energy storage properties

Polymer-based energy storage materials have been widely applied in the energy storage industry, such as in the hybrid electric vehicle and power-conditioning equipment, due to their moderate energy density and ultrafast charging/discharging speed. Accordingly, the improvement of the energy storage density of polymer matrix composites has become the focus of current research. In this study, different fillers (e.g., 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ nanofibers (BCZT NFs), BCZT + Ag NFs and BCZT + Ag@Al₂O₃ NFs) were synthesized via electrospinning and were added to the poly(vinylidene fluoride) (PVDF) matrix as a middle layer in sandwich-structure composites. The PVDF polymer-containing PMMA was prepared as the outer layer in the sandwich structure composites. These sandwich-structured composites have low loss, low current density, better breakdown strength and higher efficiency. In particular, 40% PMMA/PVDF/3 vol% BCZT + Ag@Al₂O₃/PVDF/40% PMMA/PVDF composites have an energy density of 7.23 J cm⁻³ and efficiency above 75.8% at 370 kV mm⁻¹. This article could open up a convenient and effective means for the practical application of power-pulsed capacitors by tuning the filler nanostructure and polymer nanocomposites.

Inorganic composite fillers and sandwich-structured composite films have been designed for further increasing the energy storage density.

Enhancement of Dielectric Performance of Polymer Composites via Constructing BaTiO3-Poly(dopamine)-Ag Nanoparticles through Mussel-Inspired Surface Functionalization

We demonstrate the synthesis of a novel core-satellite-structured BaTiO₃-poly(dopamine)-silver (BT-PDA-Ag) nanoparticle for improving dielectric properties of nitrile-butadiene rubber (NBR) nanocomposites. The BT-PDA-Ag nanoparticles are synthesized by dopamine oxidative polymerization and electroless plating of silver. The Ag nanoparticles decorated on the BT nanoparticles enhanced the dielectric constant of NBR nanocomposites due to the increased conductivity of the filler/matrix interlayer and nanocapacitor structure. In addition, the incorporation of the BT nanoparticles prevented the continuous connection of Ag nanoparticles and suppressed the formation of a conductive path in the NBR matrix. Moreover, the ultrasmall Ag nanoparticles trapped the carriers by Coulomb blockade and quantum confinement effects, which results in low dielectric loss and electrical conductivity of nanocomposites. The proposed method with simplicity and scalability can be adapted to process high-dielectric polymer nanocomposites.

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

The development of new generation dielectric materials toward capacitive energy storage has been driven by the rise of high-power applications such as electric vehicles, aircraft, and pulsed power systems. Here we demonstrate remarkable improvements in the energy density and charge-discharge efficiency of poly(vinylidene fluoride) (PVDF) upon the incorporation of core-satellite structures, namely NaNbO3(NN)@polydopamine (PDA)@Ag nanowires. As compared to the NN NWs/PVDF and NN@PDA NWs/PVDF nanocomposites, the NN@PDA@Ag NWs/PVDF nanocomposites exhibit greatly enhanced energy density and significantly suppressed energy loss. As a result, the NN@PDA@Ag NWs/PVDF nanocomposite films with optimized filler content exhibit an excellent discharge energy density of 16.04 J cm-3 at 485 MV m-1, and maintain a high discharge efficiency of 62.8%. Moreover, the corresponding nanocomposite films exhibit a superior power density of 2.1 MW cm-3 and ultra-fast discharge speed of 153 ns. Ultimately, the excellent dielectric and capacitive properties of the polymer nanocomposites could pave the way for widespread applications in modern electronics and power modules.

Achieving High Energy Density and Low Loss in PVDF/BST Nanodielectrics with Enhanced Structural Homogeneity

Poor compatibility of polymer/ceramic composites used as high-pulse capacitors with high permittivity suffers from the reduced breakdown strength ( E_b) and lowered energy density ( U_e). Herein, mussel-inspired poly(dopamine) (PDA)-modified BaSrTiO₃ (mBST) nanoparticle and poly(vinylidene fluoride) (PVDF) matrix are bonded together to fabricate nanocomposites with a cross-linked network and enhanced compatibility. The significantly improved E_b of 466 MV/m and the highest U_e of 11.0 J/cm³ for PVDF-based polymer/BST composites have been obtained. By comparing the properties of the three series of composites with different structures, the contribution of ferroelectric relaxation, interface polarization, and leakage conduction to the dielectric loss has been well addressed. Notably, the surface modification of BST with PDA could remarkably enhance the compatibility of the two components and the structural homogeneity of the composite. The improved bonding between the polymer matrix and the filler chemically or physically is responsible for the reduced dielectric loss from both conduction loss and interfacial polarization, which is the key to improve the E_b, U_e, and η of the composite. It has been revealed that enhancing the homogeneity of the composites by modifying ceramics and constructing cross-linked networks between the polymer matrix and the filler might be a facile strategy to achieve high energy storage performance in polymer composites.