Interface-Strengthened Polymer Nanocomposites with Reduced Dielectric Relaxation Exhibit High Energy Density at Elevated Temperatures Utilizing a Facile Dual Crosslinked Network

Polyvinylidene Fluoride Based Piezoelectric Composites with Strong Interfacial Adhesion via Click Chemistry for Self-Powered Flexible Sensors

Achieving relatively uniform dispersion in organic-inorganic composites with overwhelming differences in surface energy is a perennial challenge. Herein, novel eliminated polyvinylidene fluoride (EPVDF)/EPVDF functionalized barium titanate nanoparticles (EPVDF@BT) flexible piezoelectric nanogenerators (PENGs) with strong interfacial adhesion are developed via thermal stretching following sequential click chemistry. Thanks to the strong interfacial adhesion, the optimal PENGs containing ultra-high β-phase content (97.2%) exhibit not only optimized mechanical and dielectric behaviors but also excellent piezoelectric properties with high piezoelectric output (V = 10.7 V, I = 216 nA), reliable durability (8000 cycles), ultrafast response time (20 ms), and good sensitivity (2.09 nA kPa-1), far outperforming most reported PVDF-based composites. Furthermore, COMSOL finite element simulations (FEM) confirm that the elevated stress transfer efficiency induced by the strong interfacial adhesion is the main driving force for enhanced piezoelectric performances. For practical applications, self-powered PENGs can simply but stably capture mechanical energy, drive tiny electronic devices, and serve as potential multifunctional and durable sensors for detecting human physiological motions. This work opens a pioneering avenue to break the trade-offs between piezoelectric and other properties, which is of great importance for developing self-powered flexible sensors.

Anisotropic Semicrystalline Homopolymer Dielectrics for High-Temperature Capacitive Energy Storage

High-temperature dielectric polymers are in high demand for powering applications in extreme environments. Here, we have developed high-temperature homopolymer dielectrics with anisotropy by leveraging the hierarchical structure in semicrystalline polymers. The lamellae have been aligned parallel to the surface in the dielectric films. This structural arrangement resembles the horizontal alignment of nanosheet fillers in polymer nanocomposites and nanosheet-like lamellae in block copolymers, which has been proven to provide the optimal topological structure for electrical energy storage. The unique ordering of lamellae in our dielectric films endue a significantly increased breakdown strength and a reduced leakage current compared to amorphous films. This novel approach of enhancing the capacitive energy storage properties by controlled orientation of lamellae in homopolymer offers a new perspective for the design of high-temperature polymer dielectrics.

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.

Scalable co-cured polyimide/poly(p-phenylene benzobisoxazole) all-organic composites enabling improved energy storage density, low leakage current and long-term cycling stability

The all-organic high-temperature polymer dielectrics with promising scale-up potential have witnessed much progress in the energy storage area, etc. However, the electron suppression trap mechanisms behind many all-organic dielectrics are still unclear, especially for high temperature resistant poly(p-phenylene benzobisoxazole) (PBO) polymers. To resolve this tough issue, we herein innovatively prepared PBO-based all-organic thin films containing sulfone-based polyimide (P(DSDA-ODA)) functioning as an electron trap phase using a facile and scalable co-curing method. The great linear dielectric properties of the prepared P(DSDA-ODA)/PBO films hold high dielectric thermal stability over the temperature range from 25 °C to 200 °C. The 60 wt% P(DSDA-ODA) systems yield the lowest leakage current (3.8 × 10-8 A cm-2). The tight structure and reduced leakage current enable an enhanced breakdown strength of 60 wt% P(DSDA-ODA)/PBO (470 kV mm-1), which is 1.7 times that of pure PBO. Meanwhile, it can reach 4.16 J cm-3 of energy density, which is 257% higher than that for pure PBO thin films while concurrently maintaining a long stable charge-discharge cycle (at least 5000 times) and high charge-discharge efficiency at 85.10%. Moreover, P(DSDA-ODA)/PBO still exhibits excellent energy storage performance at high temperature compared to PBO. This innovative strategy is further verified by replacing P(DSDA-ODA) with P(6FDA-ODA), and therefore lays a solid foundation for more investigation on scalable all-organic dielectrics.

Double-Network DNA Macroporous Hydrogel Enables Aptamer-Directed Cell Recruitment to Accelerate Bone Healing

Recruiting endogenous bone marrow mesenchymal stem cells (BMSCs) in vivo to bone defect sites shows great promise in cell therapies for bone tissue engineering, which tackles the shortcomings of delivering exogenous stem cells, including limited sources, low retention, stemness loss, and immunogenicity. However, it remains challenging to efficiently recruit stem cells while simultaneously directing cell differentiation in the dynamic microenvironment and promoting neo-regenerated tissue ingrowth to achieve augmented bone regeneration. Herein, a synthetic macroporous double-network hydrogel presenting nucleic acid aptamer and nano-inducer enhances BMSCs recruitment, and osteogenic differentiation is demonstrated. An air-in-water template enables the rapid construction of highly interconnective macroporous structures, and the physical self-assembly of DNA strands and chemical cross-linking of gelatin chains synergistically generate a resilient double network. The aptamer Apt19S and black phosphorus nanosheets-specific macroporous hydrogel demonstrate highly efficient endogenous BMSCs recruitment, cell differentiation, and extracellular matrix mineralization. Notably, the enhanced calvarial bone healing with promising matrix mineralization and new bone formation is accompanied by adapting this engineered hydrogel to the bone defects. The findings suggest an appealing material approach overcoming the traditional limitations of cell-delivery therapy that can inspire the future design of next-generation hydrogel for enhanced bone tissue regeneration.

Polyimides Physically Crosslinked by Aromatic Molecules Exhibit Ultrahigh Energy Density at 200 °C

Polymer dielectrics possess significant advantages in electrostatic energy storage applications, such as high breakdown strength (Eb ) and efficiency (η), while their discharged energy density (Ud ) at high temperature is limited by the decrease in Eb and η. Several strategies including introducing inorganic components and crosslinking have been investigated to improve the Ud of polymer dielectrics, but new issues will be encountered, e.g., the sacrifice of flexibility, the degradation of the interfacial insulating property and the complex preparation process. In this work, 3D rigid aromatic molecules are introduced into aromatic polyimides to form physical crosslinking networks through electrostatic interactions between their oppositely charged phenyl groups. The dense physical crosslinking networks strengthen the polyimides to boost the Eb , and the aromatic molecules trap the charge carriers to suppress the loss, allowing the strategy to combine the advantages of inorganic incorporation and crosslinking. This study demonstrates that this strategy is well applicable to a number of representative aromatic polyimides, and ultrahigh Ud of 8.05 J cm-3 (150 °C) and 5.12 J cm-3 (200 °C) is achieved. Furthermore, the all-organic composites exhibit stable performances during ultralong 105 charge-discharge cycles in harsh environments (500 MV m-1 and 200 °C) and prospects for large-scale preparation.

Sandwiched Polymer Nanocomposites Reinforced by Two-Dimensional Interface Nanocoating for Ultrahigh Energy Storage Performance at Elevated Temperatures

Polymer-based dielectrics are essential components in electrical and power electronic systems for high power density storage and conversion. A mounting challenge for polymer dielectrics is how to maintain their electrical insulation at not only high electric fields but also elevated temperatures, in order to meet the growing needs for renewable energies and grand electrifications. Here, a sandwiched barium titanate/polyamideimide nanocomposite with reinforced interfaces via two-dimensional nanocoatings is presented. It is demonstrated that boron nitride and montmorillonite nanocoatings can block and dissipate injected charges, respectively, to present a synergetic effect on the suppression of conduction loss and the enhancement of breakdown strength. Ultrahigh energy densities of 2.6, 1.8, and 1.0 J cm^-3 are obtained at 150 °C, 200 °C, and 250 °C, respectively, with a charge-discharge efficiency >90%, far outperforming the state-of-the-art high-temperature polymer dielectrics. Cyclic charge-discharge tests up to 10 000 times verify the excellent lifetime of the interface-reinforced sandwiched polymer nanocomposite. This work provides a new pathway to design high-performance polymer dielectrics for high-temperature energy storage via interfacial engineering.

Excellent Energy Storage Performance in Epoxy Resin Dielectric Polymer Films by a Facile Hot-Pressing Method

Epoxy resin (EP), as a kind of dielectric polymer, exhibits the advantages of low-curing shrinkage, high-insulating properties, and good thermal/chemical stability, which is widely used in electronic and electrical industry. However, the complicated preparation process of EP has limited their practical applications for energy storage. In this manuscript, bisphenol F epoxy resin (EPF) was successfully fabricated into polymer films with a thickness of 10~15 μm by a facile hot-pressing method. It was found that the curing degree of EPF was significantly affected by changing the ratio of EP monomer/curing agent, which led to the improvement in breakdown strength and energy storage performance. In particular, a high discharged energy density (U_d) of 6.5 J·cm^-3 and efficiency (η) of 86% under an electric field of 600 MV·m^-1 were obtained for the EPF film with an EP monomer/curing agent ratio of 1:1.5 by hot pressing at 130 °C, which indicates that the hot-pressing method could be facilely employed to produce high-quality EP films with excellent energy storage performance for pulse power capacitors.

Side-Chain-Type High Dielectric-Constant Dipolar Polyimides with Temperature Resistance

Innovative dielectric materials with high-temperature resistance and outstanding dielectric properties have attracted tremendous attention in advanced electronical fields. Polyimide(PI) is considered a promising candidate for the modern electronic industry due to its excellent dielectric properties and comprehensive properties. However, the limited-adjustable range of dielectric constant and the difficulty to obtain a high dielectric constant restrict the application of PI as high dielectric materials. Herein, a novel diamine monomer (2,2'-bis((methylsulfonyl)methyl)-[1,1'-biphenyl]-4,4'-diamine (BSBPA)) containing a rigid biphenyl structure and high dipolar sulfonyl pendant groups is designed for high dielectric polyimides. The rigid biphenyl and polar sulfonyl pendant groups can reasonably optimize the molecular structure and orientational polarization of polyimides to improve their dielectric properties and thermal properties. Moreover, the effect of different bridge linkages on the dielectric properties is studied by using the different dianhydrides. Thus, the PI-BSBPA films especially the DSDA-BSBPA film (DSDA: 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride) achieve great thermal properties (T_5%d of 377 °C and T_g of 358 °C) and excellent dielectric properties (6.95 at 1 kHz) along with high discharged energy density of 5.25 J cm^-3 and charge-discharge efficiency of 90%. The collaborative control of main-chain and side-chain engineering is effective to endow the polyimides with high-temperature tolerance and high dielectric performance.

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.

Ultrahigh energy storage performance of all-organic dielectrics at high-temperature by tuning the density and location of traps

Improving the tolerance of flexible polymers to extreme temperatures and electrical fields is critical to the development of advanced electrical and electronic systems. Suppressing carrier movement at high temperatures is one of the key methods to improve the high-temperature charging and discharging efficiency. In this work, a molecular semiconductor (ITIC) with high electron affinity energy is blended into the promising polymer polyetherimide (PEI). This molecular semiconductor will introduce traps in the dielectric that can trap carriers, thus achieving the effect of inhibiting carrier movement. Changing the concentration and position of the molecular semiconductor by electrospinning technology also means changing the density of the trap and the position of the trap layer. The effects of trap density and trap layer location on the high-temperature breakdown strength and energy storage properties of composite dielectrics are studied successively, and the structure of a composite with optimal high temperature energy storage properties is obtained. That is, the dielectric S-15-28 has an energy storage density (U) of 6.37 J cm^-3 at a temperature of 150 °C with a charge-discharge efficiency (η) of 90%; it also has a U of 4.3 J cm^-3 at a temperature of 180 °C with the η of 90%. A mechanism based on Mott and Gurney's law is proposed to explain the effect of trap parameters on leakage current. This work provides a new structural design idea to regulate the dielectric properties of all-organic dielectrics through trap distribution parameter optimization.

Polymer Nanocomposite Dielectrics: Understanding the Matrix/Particle Interface

Polymer nanocomposite dielectrics possess exceptional electric properties that are absent in the pristine dielectric polymers. The matrix/particle interface in polymer nanocomposite dielectrics is suggested to play decisive roles on the bulk material performance. Herein, we present a critical overview of recent research advances and important insights in understanding the matrix/particle interfacial characteristics in polymer nanocomposite dielectrics. The primary experimental strategies and state-of-the-art characterization techniques for resolving the local property-structure correlation of the matrix/particle interface are dissected in depth, with a focus on the characterization capabilities of each strategy or technique that other approaches cannot compete with. Limitations to each of the experimental strategy are evaluated as well. In the last section of this Review, we summarize and compare the three experimental strategies from multiple aspects and point out their advantages and disadvantages, critical issues, and possible experimental schemes to be established. Finally, the authors' personal viewpoints regarding the challenges of the existing experimental strategies are presented, and potential directions for the interface study are proposed for future research.

Multilayer Dielectric Nanocomposites with Cross-Linked Dielectric Transition Interlayers for High-Temperature Applications

In energy storage and transportation systems, polymer dielectrics are widely applied in smart grids, electric vehicles, and power conditioning owing to their incomparable power density and high reliability. However, the dielectric constant (ε) and breakdown strength (E_b) normally cannot be increased simultaneously, which results in insufficient discharged energy density especially at high temperatures. In this work, enhanced E_b and high energy density are archived in multilayer polymer nanocomposites by introducing cross-linked dielectric transition layers. Specifically, the sandwiched composite achieves a huge discharge energy density of 4.64 J cm^-3 with a charged-discharged efficiency of 84% at 150 °C and 500 MV m^-1. The formation of cross-linked dielectric transition layers between layers of the multilayer nanocomposite could effectively restrain the growth of the electrical tree and greatly increase the E_b. This work presents a strategy for designing high-performance multilayered dielectric polymer nanocomposites by introducing cross-linked dielectric transition layers to reduce the loss from interlayer interfaces.

Polyimide Nanodielectrics Doped with Ultralow Content of MgO Nanoparticles for High-Temperature Energy Storage

Advanced polymer dielectrics with high energy density at elevated temperatures are highly desired to meet the requirements of modern electronic and electrical systems under harsh conditions. Herein, we report a novel polyimide/magnesium oxide (PI/MgO) nanodielectric that exhibits high energy storage density (U_e) and charge–discharge efficiency (η) along with excellent cycling stability at elevated temperatures. Benefiting from the large bandgap of MgO and the extended interchain spacing of PI, the composite films can simultaneously achieve high dielectric constant and high breakdown strength, leading to enhanced energy storage density. The nanocomposite film doped with 0.1 vol% MgO can achieve a maximum U_e of 2.6 J cm⁻³ and a η of 89% at 450 MV m⁻¹ and 150 °C, which is three times that of the PI film under the same conditions. In addition, embedding ultralow content of inorganic fillers can avoid aggregation and facilitate its large-scale production. This work may provide a new paradigm for exploring polymer nanocomposites with excellent energy storage performance at high temperatures and under a high electric field.

Prediction of Energy Storage Performance in Polymer Composites Using High-Throughput Stochastic Breakdown Simulation and Machine Learning

Polymer dielectric capacitors are widely utilized in pulse power devices owing to their high power density. Because of the low dielectric constants of pure polymers, inorganic fillers are needed to improve their properties. The size and dielectric properties of fillers will affect the dielectric breakdown of polymer-based composites. However, the effect of fillers on breakdown strength cannot be completely obtained through experiments alone. In this paper, three of the most important variables affecting the breakdown strength of polymer-based composites are considered: the filler dielectric constants, filler sizes, and filler contents. High-throughput stochastic breakdown simulation is performed on 504 groups of data, and the simulation results are used as the machine learning database to obtain the breakdown strength prediction of polymer-based composites. Combined with the classical dielectric prediction formula, the energy storage density prediction of polymer-based composites is obtained. The accuracy of the prediction is verified by the directional experiments, including dielectric constant and breakdown strength. This work provides insight into the design and fabrication of polymer-based composites with high energy density for capacitive energy storage applications.

Scalable Polyimide-Poly(Amic Acid) Copolymer Based Nanocomposites for High-Temperature Capacitive Energy Storage

The developments of next-generation electric power systems and electronics demand for high temperature (≈150 °C), high energy density, high efficiency, scalable, and low-cost polymer-based dielectric capacitors are still scarce. Here, the nanocomposites based on polyimide-poly(amic acid) copolymers with a very low amount of boron nitride nanosheets are designed and synthesized. Under the actual working condition in hybrid electric vehicles of 200 MV m^-1 and 150 °C, a high energy density of 1.38 J cm^-3 with an efficiency higher than 96% is achieved. This is about 2.5 times higher than the room temperature energy density (≈0.39 J cm^-3 under 200 MV m^-1 ) of the commercially used biaxially oriented polypropylene, the benchmark of dielectric polymer. Especially, the energy density and efficiency at 150 °C show no sign of degradation after 20 000 cycles of charge-discharge test and 35 days' high-temperature endurance test. This research provides an effective and low-cost strategy to develop high-temperature polymer-based capacitors.

Based On Confined Polymerization: In Situ Synthesis of PANI/PEEK Composite Film in One-Step

Confined polymerization is an effective method for precise synthesis, which can further control the micro-nano structure inside the composite material. Polyaniline (PANI)-based composites are usually prepared by blending and original growth methods. However, due to the strong rigidity and hydrogen bonding of PANI, the content of PANI composites is low and easy to agglomerate. Here, based on confined polymerization, it is reported that polyaniline /polyether ether ketone (PANI/PEEK) film with high PANI content is synthesized in situ by a one-step method. The micro-nano structure of the two polymers in the confined space is further explored and it is found that PANI grows in the free volume of the PEEK chain, making the arrangement of the PEEK chain more orderly. Under the best experimental conditions, the prepared 16 µm-PANI/PEEK film has a dielectric constant of 205.4 (dielectric loss 0.401), the 75 µm-PANI/PEEK film has a conductivity of 3.01×10-4 S m-1 . The prepared PANI/PEEK composite film can be further used as electronic packaging materials, conductive materials, and other fields, which has potential application prospects in anti-static, electromagnetic shielding materials, corrosion resistance, and other fields.

High loading BaTiO3 nanoparticles chemically bonded with fluorinated silicone rubber for largely enhanced dielectric properties of polymer nanocomposites

Integrating high-loading dielectric nanoparticles into polar polymer matrices potentially can profit the intrinsic polarization of each phase and allow for greatly enhanced dielectric properties in polymer nanocomposites. It is however challenging to achieve desirable highly filled polar polymer composites because of the lack of efficient approaches to disperse nanoparticles and maintain interfacial compatibility. Here, we report a versatile route to fabricate highly filled barium titanate/fluorinated silicone rubber (BT/FSR) nanocomposites by "thiol-ene click" and isostatic pressing techniques. The loaded BT nanoparticles (from 82 wt% to 90 wt%) are chemically bonded with FSR in the nanocomposites. The existence of the polar group (-CH₂CF₃) of the polymer matrix does not affect the uniform dispersion of the nanoparticles or the good interfacial compatibility. The 90 wt% BT/FSR nanocomposite shows the highest dielectric constant of 57.8 at 10³ Hz, while the loss tangent can be kept below 0.03. Besides, BT/FSR nanocomposites display higher breakdown strength than BT/SR nanocomposites. This work offers a facile strategy towards superior dielectric properties of polymer nanocomposites.

Ultrahigh Energy Storage Performance of Layered Polymer Nanocomposites over a Broad Temperature Range

To reach the full potential of polymer dielectrics in advanced electronics and electrified transportation, it calls for efficient operation of high-energy-density dielectric polymers under high voltages over a wide temperature range. Here, the polymer composites consisting of the boron nitride nanosheet/polyetherimide and TiO₂ nanorod arrays/polyetherimide layers are reported. The layered composite exhibits a much higher dielectric constant than the current high-temperature dielectric polymers and composites, while simultaneously retaining low dielectric loss at elevated temperatures and high applied fields. Consequently, the layered polymer composite presents much improved capacitive performance than the current dielectric polymers and composites over a temperature range of 25-150 °C. Moreover, the excellent capacitive performance of the layered composite is achieved at an applied field that is about 40% lower than the typical field strength of the current polymer composites with the discharged energy densities of >3 J cm^-3 at 150 °C. Remarkable cyclability and dielectric stability are established in the layered polymer nanocomposites. This work addresses the current challenge in the enhancement of the energy densities of high-temperature dielectric polymers and demonstrates an efficient route to dielectric polymeric materials with high energy densities and low loss over a broad temperature range.