Search

The great development potential of polymer dielectric capacitors in harsh environments urgently requires enhancing capacitive performance at high temperatures. However, the exponentially increased conduction loss at high temperature and high field results in a drastic drop in energy density and charge-discharge efficiency. Here, a bilayer-structured polyimide (PI) composite film containing a wide-band gap inorganic layer as a charge blocking layer is designed. The inorganic layer improves the charge trapping ability and regulates the charge mobility at the electrode/dielectric interface. The charge injection mechanism in the interface-optimized PI/boron nitride nanosheet (BNNS) composite films is investigated by finite element simulation, and the effect of the BNNS layer on high temperature conduction is further understood. An appropriate thickness of the charge blocking layer establishes an effective energy barrier. Therefore, the composite films exhibit significantly suppressed conduction loss and excellent capacitive performance at a high temperature. A high energy density of 4.37 J cm

Self-healing of damage is a common phenomenon in organisms but is hardly ever encountered in rigid polymer materials. For next-generation electricals and electronics, it is crucial to accurately mimic organisms to detect and heal mechanical/electrical damage. Herein, disulfide bond exchange is designed to introduce the self-healing ability in a copolymerized polyimide (copolyimide). A copolyimide insulation film with two diamine monomers is successfully prepared, which also possesses good self-healing ability after being mechanical/electrical damaged. Furthermore, the self-healing copolyimide film still maintains its good Young's modulus (E) >4 GPa, high thermal stability with glass transition temperature (Tg) >190 °C, and excellent insulation property with breakdown strength (Eb) >300 kV mm−1. The combination of the simple copolymerization and unique self-healing ability is suitable for high Tg polyimide to make this an ideal method for insulation field.

The high operating temperature of dielectric capacitors applied in electric vehicles, aerospace and underground exploration require dielectric materials with high temperature resistance and high energy density. Polyimide (PI) turns out to be a potential dielectric material for capacitors applications at high temperature. In this review, the key parameters related to high temperature resistance and energy storage characteristics were introduced and recent developments in all-organic PI dielectrics and PI-matrix dielectric nanocomposites were discussed. Synthetic strategies of new functional PI via modification at the molecular level together with the design engineering of nanofillers and multilayer structures of PIs were also analysed. Finally, a systematic summary of the current challenges and future developments for capacitor materials used at high temperatures were presented.

There is a great demand for low dielectric materials as insulating interlayers in large-scale integrated circuit development. However, it is still a huge challenge to reduce the dielectric permittivity of polymers while maintaining excellent thermal stability and mechanical properties. In this work, the fluorinated polyimides (PIs) in combination with a micro-branched crosslinking structure were prepared successfully by introducing different amounts of 1,3,5-tris(4-aminophenyl) benzene (TAPB) to obtain ultra-low dielectric permittivity. The results revealed that PI film containing 2 mmol TAPB had the lowest dielectric permittivity (2.47) and dielectric loss (0.008) at 1 MHz due to the fluorine atoms and the micro-branched crosslink structure, which not only decreased the molecular polarizability but also increased the free fractional volume. In addition, PI film containing 2 mmol TAPB had the highest tensile strength of 106.02 MPa with an elongation at a break of 15.1% because the presence of TAPB effectively promoted the connection between PI molecular chains, resulting in the inhibition of the molecular mobility. The incorporation of TAPB also enhanced the thermal stability and ultraviolet light-shielding performance of PI films. This method paves the way for the development of PIs with ultra-low dielectric permittivity for the electronic industry.

The interchain space of polyimide is optimized to hinder charge carrier transport, thus improving the energy storage performance at high temperatures.

The introduction of CA effective combines the self-healing and fluorescence characteristics, and provides a reliable method for the development of multifunctional PDMS.

Dielectric polyimides (PIs) are ubiquitous as insulation in electrical power systems and electronic devices. Generally, dynamic polyimide is required to solve irreversible failure processes of electrical or mechanical damage, for example, under high temperature, pressure, and field strength. The challenge lies in the design of the molecular structure of rigid polyimide to achieve dynamic reversibility. Herein, a low-molecular-weight polyimide gene unit is designed to crosslink with polyimide ligase to prepare the smart film. Interestingly, due to the variability of gene unit and ligase combinations, the polyimide films combining hardness with softness are designed into three forms via a "Mimosa-like" bionic strategy to adapt to different application scenarios. Meanwhile, the films have good degradation efficiency, excellent recyclability, and can be self-healable, which makes them reuse. Clearly, the films can be used in the preparation of ultrafast sensors with a response time ≈0.15 s and the application of corona-resistant films with 100% recovery. Furthermore, the construction of polyimide and carbon-fiber-reinforced composites (CFRCs) has been verified to apply to the worse environment. Nicely, the composites have the property of multiple cycles and the non-destructive recycle rate of carbon fiber (CF) is as high as 100%. The design idea of preparing high-strength dynamic polyimide by crosslinking simple polyimide gene unit with ligase could provide a good foundation and a clear case for the sustainable development of electrical and electronic polyimides, from the perspective of Mimosa bionics.

Polymer nanocomposites have attracted increased attention for use in the field of high‐voltage direct current (HVDC) cable insulation. To study the use of polymer nanocomposites for this purpose, 3D flower‐like MgO (flower‐MgO) particles with hierarchical surface morphology are first synthesised. Polypropylene (PP) was simultaneously mixed with styrene‐(ethylene‐co‐butylene)‐styrene triblock copolymer (SEBS) and flower‐MgO to obtain PP/SEBS/flower‐MgO composites. The microstructural, thermal, electrical, and mechanical properties of the obtained nanocomposites were then studied in detail. The results showed that flower‐MgO particles loaded at low concentration were well dispersed in the PP/SEBS matrix. The incorporation of flower‐MgO particles has been found to significantly suppress the injection of homocharges and strengthen the ability to release the charge, thus containing accumulation of the space charge. The DC breakdown strength of PP/SEBS/flower‐MgO composites was increased to 323 MV/m. Meanwhile, the tensile strength and elongation at break of the obtained composites was improved by loading 0.5 phr flower‐MgO because of the synergistic toughening effects of SEBS and MgO. The investigation demonstrates the immense potential to replace nonrecyclable cross‐linked polyethylene as an HVDC cable insulating material.

Polymer dielectrics have been widely used in electrical energy storage devices. However, the relatively low operating temperature hinders their applications in harsh environments. Herein, the molecular structure of polyimide (PI) is optimized by adjusting the reaction kinetics of polyamic acid, which improves the energy storage performance of PI at elevated temperature. The PI film with an optimal imidization degree achieves a simultaneous increase in dielectric permittivity (ϵ r) and breakdown strength (E b), resulting in a maximum discharged energy density (U e) of 6.9 J cm −3 with a charge-discharge efficiency of 90.0% at room temperature and a high U e of 3.9 J cm −3 at 150 °C. The introduced -COOH/-CN-OH- polar groups increase the ϵ r through the enhancement of dipole polarization. Moreover, an appropriate number of -COOH/-CN-OH- groups as deep traps reduce the mobility of carriers, thereby increasing the E b. Finite element simulation reveals that PI with an appropriate imidization degree exhibits suppressed space charge accumulation and improved electric field distortion. This method reduces the PI processing temperature, which effectively reduces the production energy consumption. For verifying the universality of the design strategy, two other PIs prepared from different monomers are also demonstrated to have simultaneous improvement in ϵ r and E b.Finally, this production process of only reducing the preparation temperature without adjusting the original commercial PI production equipment is crucial for the practical application of capacitor films in the future.

High-performance epoxy (EP) composites with excellent thermal conductivity and dielectric properties have attracted increasing attention for effective thermal management. In this work, three-dimensional (3D) structural functional fillers were prepared by an electrostatic self-assembly approach. The negatively charged carbon nanotubes (nCNTs) prepared by carboxylation on the surface of CNTs were attached to the positively charged boron nitride (pBN) to form the 3D pBN@nCNTs functional fillers. The morphological characterizations of the formed 3D pBN@nCNTs fillers and epoxy composites were established, illustrating that nCNTs were linearly overlapped between the BN sheets, thus forming a 3D heat conduction network in the epoxy matrix. The synergistic effect of pBN with nCNTs on the enhancement of thermal conductivity and dielectric properties of composites was systematically studied. The experimental results demonstrated that the thermal conductivity of pBN@nCNTs/EP composites could reach 1.986 W m−1K−1 with the loading of 50 wt% fillers at 10:1 mass ratio of pBN:nCNTs, which is 464% and 124% higher than that of pure EP and BN/EP, respectively. Simultaneously, the dielectric permittivity was successfully increased to 15.14. Moreover, the thermal stability of the composites was synchronously enhanced. This study provides a facile path to fabricate thermosetting polymer composites with high thermal conductivity and dielectric properties.

High-voltage direct current (HVDC) power cables have been paid more attention due to the big issue concerning the main insulation materials. The residues in the industrial production process will cause space charge generation and accumulation in the materials, which has become one bottleneck to limit the development of power cables up to higher voltage levels. In this paper, the LDPE matrix was modified by three types of ethylene-butyl acrylate (EBA) copolymers (1.0 wt%) with different polarities (BA content) via melt blending to optimize the space charge behavior of the LDPE insulation. The micromorphology and structure of the blends are examined by polarized light microscope and differential scanning calorimetry. The space charge distribution is tested by the pulsed electroacoustic method. The trap level is studied by the thermally stimulated current. The results show that EBA introduces more deep traps and decreases the shallow traps. The medium-polar EBA (16% BA content) can effectively suppress charge accumulation, and have the same suppressed effect on XLPE/EBA blends. This study will provide important insights into the design and development of advanced HVDC power cable applications.

International audience; This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

With the increasing demand for safe operation in harsh environments, polymer dielectric capacitors with high energy density ( Ue) and charge-discharge efficiency (η) operating at high temperatures are urgently needed. In this work, the sulfone group-containing polyimide (SO2PI) film with optimal imidization degree is prepared by regulating the kinetics of imidization reaction. The functional groups obtained by partial imidization enable polyimide to achieve excellent energy storage performance, and it is found that the presence of sulfone groups is beneficial for the further improvement of η. The optimal SO2PI film achieves a Ue of 2.40 J cm−3 at 400 MV m−1 and 150 °C, while it maintains a high η of 92%. Moreover, its preparation process without any additional modification steps matches commercial production equipment, indicating a simple and effective strategy for fabrication of a high-performance dielectric film. Thus, this work exhibits great potential in the field of high temperature energy storage.

Polymer-based composites with ceramic fillers could combine the advantages of both, which can be potentially used in electrical and electronic technology. In this work, the barium titanate (BaTiO 3 ) nanofibres and the core-shell structured BaTiO 3 @Al 2 O 3 nanofibres with Al 2 O 3 insulation layer coated on the BaTiO 3 surface were both prepared via the electrospinning method. The appropriate incorporation of the ceramic nanofibres effectively improves the dielectric properties and energy density of the polymer. Moreover, the poly(vinylidene fluoride- co -hexafluoropropylene)-based composite films with the three-layer sandwich structure were fabricated to further promote the dielectric properties. The results show that the outer two layers with a higher content of BaTiO 3 nanofibres can make more contribution to the improved permittivity of the composites. In addition, the introduction of the interlayer with low loading of BaTiO 3 @Al 2 O 3 nanofibres promotes the breakdown strength. This work gives rise to the potential in high energy storage applications.

The dielectric elastomers have been widely studied in last decades due to their excellent electromechanical conversion ability. Herein, two kinds of polyurethanes (PU) with different molecular weights were used and the results demonstrated that incorporating low molecular weight (MW) PU into high MW PU not only caused the decrease in elastic modulus but also induced a high elongation at break. The optimal performances of PU mixture were observed when the content of low MW PU was 20 wt% and the PU mixture with 20 wt% low MW PU was used as the matrix in this work. In order to achieve a high electromechanical conversion performance, the surface modification of BaTiO3 (BT) nanoparticles by 4,4′-diphenylmethane diisocyanate (MDI) was carried out and the obtained BT products (BT-MDI) were used as fillers for the PU nanocomposites. The permittivity of BT-MDI/PU nanocomposites with 6 wt% fillers increased to 8.6 at 1 kHz and the elongation at break of nanocomposites at this filler loading still remained as high as 1070%. Because of the enhanced properties, the achieved energy-conversion density reached 2.88 mJ/cm3 at 900 V, and the conversion efficiency was up to 1.56 %. The results reveal that an effective surface modification of nanoparticles is beneficial for the improvement of electromechanical conversion behavior of composite dielectric elastomers due to both the excellent dispersion of BT-MDI nanofillers and the improved compatibility between BT-MDI nanoparticles and PU matrix.

Solid polymer electrolytes (SPEs) have drawn considerable attention owing to their reliable safety performance, electrochemical stability and exceptional flexibility, which make them superior to conventional liquid electrolytes. Here, we report a novel composite electrolyte which is composed of homogeneously dispersed Li ion-conducting Li0.33La0.557TiO3 (LLTO) nanowires in a poly(ethylene oxide) (PEO)/LiClO4 matrix. It is demonstrated that only 3 wt% LLTO nanofibers are needed for the optimal performance of SPEs. The PEO-based composite electrolyte shows an excellent Li ion conductivity of 4.01 × 10−4 S cm−1 at 60 °C. In addition, it is worth mentioning that the all-solid-state lithium battery based on this composite electrolyte exhibits a specific capacity of 140 mA h g−1 and an excellent capacity retention of 92.4% after running 100 cycles at a rate of 1C and 60 °C. The study offers a superior alternative for the design of PEO-based solid composite electrolytes.

The availability of high-temperature dielectrics is key to develop advanced electronics and power systems that operate under extreme environmental conditions. In the past few years, many improvements have been made and many exciting developments have taken place. However, currently available candidate materials and methods still do not meet the applicable standards. Polyimide (PI) was found to be the preferred choice for high-temperature dielectric films development due to its thermal stability, dielectric properties, and flexibility. However, it has disadvantages such as a relatively low dielectric permittivity. This chapter presents an overview of recent progress on PI dielectric materials for high-temperature capacitive energy storage applications. In this way, a new molecular design of the skeleton structure of PI should be performed to balance size and thermal stability and to optimize energy storage property for high-temperature application. The improved performance can be generated via incorporation of inorganic units into polymers to form organic-inorganic hybrid and composite structures.

Polyimide (PI) film is considered to be an ideal packaging material due to its excellent comprehensive properties. However, the traditional PI has a relatively high dielectric permittivity ( $k=3.0\sim 3.4$ ), which cannot meet the current requirements in the field of microelectronic packaging ( $k ). In this work, Tris(4-aminophenyl) amine (TPA) was used the cross-linking agent to combine with biphenyl-3,3′,4,4′-tetracarboxylic dianhydride (BPDA) and 1,4-Bis(4-amino-2-trifluoromethylphenoxy) benzene (6FAPB) by in-situ polymerization for the purpose of obtaining cross-linked low-dielectric polyimide. And the influences of cross-linking agent ratio on the comprehensive properties of PI were studied. The results showed that under a certain loading of TPA, the dielectric permittivity of the PI gradually decreased with the incremental crosslinking agent content. When the molar ratios of amino groups in TPA and 6FAPB was 1:9, the dielectric properties of the cross-linked PI can be minimized, with the lowest value of 1.86 (107 Hz). In addition, the obtained cross-linked polyimide had good thermal stability. It has broad development prospects in the field of microelectronic packaging and integrated circuits in the future.

High-voltage direct current (HVDC) transmission plays an important role in the development of sustainable transmission networks and the conversion of energy systems. As an important medium in the transmission system, HVDC cables have become a hot research topic. Flexible DC transmission using HVDC plastic cables is the mainstream direction advocated by the international power grid. Therefore, the demand for high-performance HVDC plastic cables is increasing. Aiming at the development process of thermoplastic environmental polypropylene insulation materials for HVDC cables, the development status and technical bottlenecks of HVDC cable insulation materials were summarized. This chapter discussed the research progress of polypropylene insulation materials from the perspective of the basic structure of polypropylene, intrinsic modification, and its nanocomposite, etc. The necessity and urgency of research and development of insulation materials for HVDC cables were clarified. Finally, the future development direction of HVDC cables was summarized and prospected.

Ceramic spheres and fibers co-filled nanocomposite has shown great potential in the field of high energy density dielectrics. In this work, finite element simulation was adopted to investigate the dielectric property of the nanocomposite with ceramic spheres and fibers co-filled configuration. A three-dimensional model with random distribution of fillers was built to study the effect of filler parameters on the dielectric performance of nanocomposites. The effect of the co-filled particles with different shape and distribution on the dielectric properties of composites has been systematically studied. The aspect ratio of fiber is found to have great effect on the dielectric performance of the composites. The size of sphere fillers affects their distribution in composites, which leads to the variation of the composite permittivity.