Enhanced thermal conductivity of epoxy resin by incorporating three-dimensional boron nitride thermally conductive network.

Packaging insulation materials with high thermal conductivity and excellent dielectric properties are favorable to meet the high demand and rapid development of third generation power semiconductors. In this study, we propose to improve the thermal conductivity of epoxy resin (EP) by incorporating a three-dimensional boron nitride thermally conductive network. Detailedly, polyurethane foam (PU) was used as a supporter, and boron nitride nanosheets (BNNSs) were loaded onto the PU supporter through chemical bonding (BNNS@PU). After immersing BNNS@PU into the EP resin, EP-based thermally conductive composites were prepared by vacuum-assisted impregnation. Fourier transform infrared spectrometer and scanning electron microscope were used to characterize the chemical bonding and morphological structure of BNNS@PU, respectively. The content of BNNS in BNNS@PU/EP composites was quantitatively analyzed by TGA. The results show that the thermal conductivity of the BNNS@PU/EP composites reaches 0.521 W/m K with an enhancement rate η of 30.89 at an ultra-low BNNS filler content (5.93 wt. %). Additionally, the BNNS@PU/EP composites have excellent dielectric properties with the frequency range from 101 to 106 Hz. This paper provides an interesting idea for developing high thermal conductivity insulating materials used for power semiconductor packaging.

Research on molecular dynamics and electrical properties of high heat-resistant epoxy resins.

In order to prepare highly heat-resistant packaging insulation materials, in this paper, bismaleimide/epoxy resin (BMI/EP55) composites with different contents of BMI were prepared by melt blending BMI into amino tetrafunctional and phenolic epoxy resin (at a ratio of 5:5). The microstructures and thermal and electrical properties of the composites were tested. The electrostatic potential distribution, energy level distribution, and molecular orbitals of BMI were calculated using Gaussian. The results showed that the carbonyl group in BMI is highly electronegative, implying that the carbonyl group has a strong electron trapping ability. The thermal decomposition temperature of the composites gradually increased with the increase of BMI content, and the 20% BMI/EP55 composites had the highest heat-resistance index, along with a glass transition temperature (Tg) of >250 °C. At different test temperatures, with increase in the BMI content, the conductivity of epoxy resin composites showed a tendency to first decrease and then increase, the breakdown field strength showed a tendency to first increase and then decrease, and the dielectric constant was gradually decreased. Two trap centers were present simultaneously in the composites, where the shallow trap energy level is the deepest in 20% BMI/EP composites and the deep trap energy level is the deepest in 10% BMI/EP55 composites. Correspondingly, the 10% BMI/EP55 composite had a slower charge decay rate, while the 20% BMI/EP55 had a faster charge decay rate. In summary, the BMI/EP55 composites with high heat resistance and insulating properties were prepared in this study, which provided ideas for preparing high-temperature packaging insulating materials.

Study of the Dielectric and Corona Resistance Properties of PI Films Modified with Fluorene Moiety/Aluminum Sec-Butoxide.

With the policy tilt and increased investment in research and development in the world, new energy vehicle technology continues to progress and the drive motor power density continues to improve, which puts forward higher requirements for the comprehensive performance of the core insulating material enameled wire enamel for drive motors. Polyimide (PI) has excellent electrical insulation properties, and heat resistance is often used to drive the motor winding insulation. To further improve the corona resistance and insulating properties of PI wire enamel varnish, in this paper, firstly, fluorene groups with a rigid conjugated structure were introduced into the molecular chain of the PI film by molecular structure modulation, and then uniformly dispersed alumina nanoclusters (AOCs) were introduced into the PI matrix by using an in situ growth process to inhibit the migration of high-energy electrons. The quantum size effect of the alumina nanoclusters was exploited to synergistically enhance the suppression and scattering of energetic moving electrons by PI-based composite films. The results show that the breakdown field strength of the PI-based composite film (MPI/1.0 vol% AOC) reaches 672.2 kV/mm, and the corona resistance life reaches 7.9 min, which are, respectively, 1.55 and 2.19 times higher than those of the initial PI film. A PI-based composite film with excellent insulating and corona resistance properties was obtained.

Achieving synergistic improvement in dielectric and energy storage properties at high-temperature of all-organic composites via physical electrostatic effect.

In response to the increasing demand for miniaturization and lightweight equipment, as well as the challenges of application in harsh environments, there is an urgent need to explore the new generation of high-temperature-resistant film capacitors with excellent energy storage properties. In this study, we report an all-organic composite system based on two polymers with similar densities and high glass transition temperatures, achieving a synergistic effect of dielectric constant and breakdown strength. The preparation of the composite is simple, overcoming the challenge of dispersing nanoparticles in traditional organic-inorganic systems. The high polarity of polyethersulfone can modulate the polarization properties of the composites and, through a physical electrostatic effect, inhibit dipole relaxation, further reducing the current density of the composite dielectric at high temperatures, resulting in a significant improvement in insulating properties. The 9 : 1 composite dielectric at 150 °C demonstrates an energy storage density of up to 6.4 J cm-3 and an efficiency of 82.7%. This study offers a promising candidate material and development direction for the next-generation energy storage capacitors with broad application prospects.

Improvements in the Magnesium Ion Transport Properties of Graphene/CNT-Wrapped TiO2 -B Nanoflowers by Nickel Doping.

Magnesium-ion batteries are widely studied for its environmentally friendly, low-cost, and high volumetric energy density. In this work, the solvothermal method is used to prepare titanium dioxide bronze (TiO2 -B) nanoflowers with different nickel (Ni) doping concentrations for use in magnesium ion batteries as cathode materials. As Ni doping enhances the electrical conductivity of TiO2 -B and promotes magnesium ion diffusion, the band gap of TiO2 -B host material can be significantly reduced, and as Ni content increases, diffusion contributes more to capacity. According to the electrochemical test, TiO2 -B exhibits excellent electrochemical performance when the Ni element doping content is 2 at% and it is coated with reduced graphene oxide@carbon nanotube (RGO@CNT). At a current density of 100 mA g-1 , NT-2/RGO@CNT discharge specific capacity is as high as 167.5 mAh g-1 , which is 2.36 times of the specific discharge capacity of pure TiO2 -B. It is a very valuable research material for magnesium ion battery cathode materials.

Advances in Polymer Dielectrics with High Energy Storage Performance by Designing Electric Charge Trap Structures.

Dielectric capacitors have been developed for nearly a century, and all-polymer film capacitors are currently the most popular. Much effort has been devoted to studying polymer dielectric capacitors and improving their capacitive performance, but their high conductivity and capacitance losses under high electric fields or elevated temperatures are still significant challenges. Although many review articles have reported various strategies to address these problems, to the best of current knowledge, no review article has summarized the recent progress in the high-energy storage performance of polymer-based dielectric films with electric charge trap structures. Therefore, this paper first reviews the charge trap characterization methods for polymeric dielectrics and discusses their strengths and weaknesses. The research progress on the design of charge trap structures in polymer dielectric films, including molecular chain optimization, organic doping, blending modification, inorganic doping, multilayered structures, and the mechanisms of the charge trap-induced enhancement of the capacitive performance of polymers are systematically reviewed. Finally, a summary and outlook on the fundamental theory of charge trap regulation, performance characterization, numerical calculations, and engineering applications are presented. This review provides a valuable reference for improving the insulation and energy storage performance of dielectric capacitive films.

Utilizing Linear Polymers to Optimize Remanent Polarization and Construct Multilayer Interfaces to Obtain High-Efficient Poly(vinylidene fluoride)-Based Energy-Storage Composites.

Polyvinylidene fluoride (PVDF) has been widely studied as a ferroelectric polymer for energy dielectric applications. However, high-polarization PVDF has a low-efficiency issue, owing to high residual polarization. This study introduces highly insulating, low-loss linear polycarbonate (PC) into PVDF-based dielectrics. The PC layer optimizes the remanent polarization (Dr) of PVDF and maintains it within a small range, thus achieving a high charge-discharge efficiency. The multilayer structural design of PVDF-based dielectrics adjusts the interlayer electric field distribution. We have thoroughly studied the influence of the number and proportion of PC layers on the polarization and breakdown of the multilayer films as well as achieved collaborative regulation of dual parameters. Our results indicate that three layers of PC-PVDF-PC (CPC) films containing a large proportion of PC can polarize under high electric fields and maintain excellent charge-discharge efficiency, achieving an energy density and efficiency of 11.48 J/cm3 and 92.4%, respectively, under 610 kV/mm. The PVDF-based dielectrics prepared in this work are all organic films, and their flexibility and foldability are conducive to the preparation of flexible devices.

Improvements in the Electrochemical Performance of Sodium Manganese Oxides by Ti Doping for Aqueous Mg-Ion Batteries.

In recent times, the research on cathode materials for aqueous rechargeable magnesium ion battery has gained significant attention. The focus is on enhancing high-rate performance and cycle stability, which has become the primary research goal. Manganese oxide and its derived Na-Mn-O system have been considered as one of the most promising electrode materials due to its low cost, non-toxicity and stable spatial structure. This work uses hydrothermal method to prepare titanium gradient doped nano sodium manganese oxides, and uses freeze-drying technology to prepare magnesium ion battery cathode materials with high tap density. At the initial current density of 50 mA g-1 , the NMTO-5 material exhibits a high reversible capacity of 231.0 mAh g-1 , even at a current density of 1000 mA g-1 , there is still 122.1 mAh g-1 . It is worth noting that after 180 cycles of charging and discharging at a gradually increasing current density such as 50-1000 mA g-1 , it can still return to the original level after returning to 50 mA g-1 . Excellent electrochemical performance and capacity stability show that NMTO-5 material is a promising electrode material.

Innovative all-organic dielectric composite for dielectric capacitor with great energy storage performance based on thermodynamic compatibility.

In modern electronics and power systems, good-performance dielectric capacitors have an essential function. Polymer-based dielectrics are widely used in the field of dielectric capacitors because of their large dielectric constant, flexibility, low density, and ease of processing. At present, ferroelectric polymers suffer from low breakdown field strength and high dielectric losses. How to improve the performance of dielectric materials in capacitors is still a promising research. This paper chooses the ferroelectric polymer poly(vinylidene fluoride) (PVDF) that worked as the matrix, and the linear polymers polyimide, cyanoethyl pullulan (CR-S), polyethersulfone, and cyanoethylated cellulose served as fillers. This all-organic dielectric composite produced as films working in electrostatic energy storage devices is prepared by using a casting method. Analyzing the test results, the composite film exhibited excellent electrical properties when the CR-S doping content was 5 wt. %. The organic composite dielectric based on CR-S/PVDF has a breakdown field strength of 450 MV/m, a discharge energy storage density (Ue) of 10.3 J/cm3, a high dielectric constant of 10.9, and a low dielectric loss of 0.004 at 1 kHz, which is a significant improvement compared with other dielectric composites. This all-organic dielectric composite strategy offers a new approach to achieve better-performance dielectric energy storage materials.

Enhancement of Energy Storage Performance of PMMA/PVDF Composites by Changing the Crystalline Phase through Heat Treatment.

In today's contemporary civilization, there is a growing need for clean energy focused on preserving the environment; thus, dielectric capacitors are crucial equipment in energy conversion. On the other hand, the energy storage performance of commercial BOPP (Biaxially Oriented Polypropylene) dielectric capacitors is relatively poor; hence, enhancing their performance has drawn the attention of an increasing number of researchers. This study used heat treatment to boost the performance of the composite made from PMAA and PVDF, combined in various ratios with good compatibility. The impacts of varying percentages of PMMA-doped PMMA/PVDF mixes and heat treatment at varying temperatures were systematically explored for their influence on the attributes of the blends. After some time, the blended composite's breakdown strength improves from 389 kV/mm to 729.42 kV/mm at a processing temperature of 120 °C. Consequently, the energy storage density is 21.12 J/cm3, and the discharge efficiency is 64.8%. The performance has been significantly enhanced compared to PVDF in its purest state. This work offers a helpful technique for designing polymers that perform well as energy storage materials.

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.

High Energy Storage Performance of All-Inorganic Flexible Antiferroelectric-Insulator Multilayered Thin Films.

With the increasingly high requirements for wearable and flexible devices, traditional inorganic capacitors cannot meet the flexible demand of next-generation electronic devices. In this work, the energy storage property of all-inorganic flexible films has been systematically studied. PbZrO3 (PZO) and Al2O3 (AO) are selected as the antiferroelectric layer and insulating layer, respectively. The heterostructured films are prepared on the fluorphlogopite (F-Mica) substrate by chemical solution deposition. The microstructure, polarization behavior, and energy storage performances are investigated. The results demonstrate that the AO/PZO/AO/PZO/AO (APAPA) multilayered thin film possesses a greatly improved energy storage density (Wrec) of 28.1 J/cm3 with an excellent energy storage efficiency (η) of 80.1%, which is ascribed to the enhanced breakdown strength and large difference in polarization. Furthermore, the capacitive films exhibit good stability under a wide working temperature range of 25-140 °C and an electric fatigue endurance of 107 cycles. Besides, the energy storage performances are almost unchanged after 104 bending cycles, demonstrating an excellent mechanical bending endurance. This work sheds light on the preparation technology and improvement of the dielectric energy storage performance for all-inorganic flexible multilayered thin films.

Polymer dielectric films exhibiting superior high-temperature capacitive performance by utilizing an inorganic insulation interlayer.

With the rapid development of next-generation electrical power equipment and microelectronics, there is an urgent demand for dielectric capacitor films which can work efficiently under extreme conditions. However, sharply increased electrical conduction and drastically degrading electric breakdown strength are inevitable at elevated temperatures. Herein, a facile but effective method is proposed to improve high temperature capacitive performance. We report that utilizing an inorganic insulation interlayer can significantly increase the discharge energy density with a high efficiency above 90% at 150 °C, i.e., a discharged energy density of 4.13 J cm-3 and an efficiency of >90% measured at 150 °C, which is superior to the state-of-the-art dielectric polymers. Combining the experimental results and computational simulations reveals that the remarkable improvement in energy storage performance at high temperature is attributed to the blocking effects that reduce the leakage current and maintain the breakdown strength. The proposed facile method provides great inspiration for developing polymer dielectric films with high capacitive performance under extreme environments.

Excellent Energy Storage Performance of Ferroconcrete-like All-Organic Linear/Ferroelectric Polymer Films Utilizing Interface Engineering.

Ferroelectric polymers are regarded as the preferred material in dielectric energy storage devices because of their high dielectric constant. However, their relatively low breakdown strength and efficiency restrict their practical application. This work combines coaxial spinning and hot pressing to compound the highly insulating linear poly(methyl methacrylate) (PMMA) and ferroelectric poly(vinylidene fluoride) (PVDF) to obtain a PMMA/PVDF all-organic film with a ferroconcrete-like structure. Further, improvements in the energy storage performance over those of the pristine polymer were achieved via modulation of the PMMA to PVDF ratio. The 45% PMMA/PVDF film had an energy storage density of 17.7 J/cm3 and an energy efficiency of 73% at 640 kV/mm. Moreover, 51% PMMA/PVDF exhibited the best energy storage density (U = 20.7 J/cm3, η = 63% at 630 kV/mm). This work, therefore, provides a new idea for the design of all-organic polymer films for the field of energy storage.

Improved Energy Storage Performance of All-Organic Composite Dielectric via Constructing Sandwich Structure.

Improving the energy storage density of dielectrics without sacrificing charge-discharge energy storage efficiency and reliability is crucial to the performance improvement of modern electrical and electronic systems, but traditional methods of doping high-dielectric ceramics cannot achieve high energy storage densities without sacrificing reliability and storage efficiency. Here, an all-organic energy storage dielectric composed of ferroelectric and linear polymer with a sandwich structure is proposed and successfully prepared by the electrostatic spinning method. Additionally, the effect of the ferroelectric/linear volume ratio on the dielectric properties, breakdown, and energy storage is systematically studied. The results show that the structure has good energy storage characteristics with a high energy storage density (9.7 J/cm3) and a high energy storage efficiency (78%). In addition, the energy storage density of the composite dielectric under high energy storage efficiency (90%) is effectively improved (25%). This result provides theoretical analysis and experience for the preparation of multilayer energy storage dielectrics which will promote the development and application of energy storage dielectrics.

Designing coexisting multi-phases in PZT multilayer thin films: an effective way to induce large electrocaloric effect.

Coexisting multi-phases in PbZr x Ti1-x O3 multilayer thin films were successfully fabricated using the sol-gel method. The microstructure and electrical of the multilayer films with different growth sequences, including the up multilayer films and down multilayer films, have been systematically investigated. The results indicate that a large electrocaloric effect (ECE) is obtained at the temperatures much below the Curie temperature. At room temperature (25 °C), the change in temperature (ΔT) values of the up multilayer and down multilayer thin films are 20.2 K with the applied electric field E = 826 kV cm-1 and 46.3 K with the E = 992 kV cm-1, respectively. In addition, both the films exhibit outstanding ECE of around 145 °C, and ΔT values of 28.9 K and 14.8 K have been obtained for the up multilayer and down multilayer thin films. The results indicate that the antiferroelectric/ferroelectric (AFE/FE), ferroelectric/ferroelectric (FE/FE) phase transition and the synergistic effect of the AFE/FE and FE/FE phase transition are as effective as the FE/PE phase transition. In particular, the multilayer thin films are endowed with refrigeration ability at multi-temperature zones due to the coexistence of multi-phases.

Efficacy and safety of clopidogrel only vs. clopidogrel added proton pump inhibitors in the treatment of patients with coronary heart disease after percutaneous coronary intervention: A systematic review and meta-analysis.

BACKGROUND: Controversy still exists that whether clopidogrel should add proton pump inhibitors (PPIs) in patients with coronary heart disease after percutaneous coronary intervention (PCI). The aim of this study was to evaluate the efficacy and safety of clopidogrel added proton pump inhibitors (PPIs) vs. clopidogrel for the treatment of patients with coronary heart disease after percutaneous coronary intervention (PCI). METHODS AND RESULTS: We systematically searched PubMed, EMBASE, Web of Science, the Chinese Biomedical Medical Literature database, and the Cochrane Library for all clinical trials that were published on this topic through October 2018. We specifically selected the clinical trials that evaluated the efficacy and safety of clopidogrel added proton pump inhibitors vs. clopidogrel in the treatment of patients with coronary heart disease after PCI. RevMan 5.0 software was used for quantitative data analyses.15 randomized controlled trials including 50,366 patients were included. The meta-analysis results showed that compared with the clopidogrel added PPI group, the non-PPI group had significantly less risk of MACE[RR = 0.82,95%CI:0.77-0.88], myocardial infarction recurrence[RR = 0.72,95%CI:0.57-0.90], stent thrombosis[RR = 0.71,95%CI:0.56-0.92], Target vessel revascularization (TVR)[RR = 0.77,95%CI:0.63-0.93] and stroke [RR = 0.72,95%CI:0.67-0.76]. The risks of all cause death [RR = 1.14,95%CI:0.85-1.51], cardiovascular death [RR = 1.14, 95% CI: 0.85-1.52], bleedings events [RR = 1.60,95%CI:0.53-4.81] were similar in the two groups. CONCLUSIONS: The patients in the non-PPI group were observed to be associated with less risk of MACE, myocardial infarction recurrence, stent thrombosis, target vessel revascularization (TVR) and stroke. And the two groups had similar all cause death, cardiovascular death, bleedings events.

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(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)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.

Study on Nonlinear Conductivity of CCTO/EPDM Rubber Composites.

Researches of the theories and application of polymer composites with nonlinear conductivity are useful for dealing with the nonuniform electrical fields widely existing in the cable accessory insulation. In the present work, we fabricated CCTO (CaCu3Ti4O12)/EPDM (Ethylene Propylene Diene Monomer) composites and investigated their breakdown strength, dielectric and nonlinear conductivity properties in detail; the microstructures of fillers and composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction. CCTO particles are uniformly dispersed in CCTO/EPDM composites, and the composites showed nonlinear conductivity with electric field changes. When the CCTO particle content is low, the conductivity of CCTO/EPDM composites does not present obvious nonlinearity. However, when CCTO content exceeds 2 vol %, the conductivity experiences a nonlinear change with increasing electric field strength and the threshold field (Eth) of nonlinear conductivity declines with the increase of CCTO contents. In addition, it can be found from experiment and simulation results that 8 vol % CCTO/EPDM exhibit significant nonlinear conductivity and dielectric properties as expected, and homogenizing the electrical field much more effectively. Therefore, this paper offers a preliminary discussion about the variation trend of nonlinear conductivity CCTO/EDPM composites, providing an effective reference to solve the application of nonlinear conductivity materials for cable accessories.