All-organic Composites Research Articles

Enhanced breakdown strength and corona aging life in PI dielectric based on heterogeneous all-organic design

The high-speed train is developing towards higher speed and greater load capacity. As an important part of this, inverter-fed traction motors need higher power. As the turn-to-turn insulating material for inverter-fed traction motors, polyimide (PI) does not satisfy the requirements for breakdown strength and corona aging life with higher power. In this paper, the heterogeneous all-organic composite is designed with polyimide as matrix and acrylic elastomer (DE) as reinforcing material. When the load of DE is 0.5 wt%, the breakdown strength of the thermosetting DE/PI composites is up to 740 kV/mm, which is 60 % higher than PI (462 kV/mm) and the corona aging life is up to 70.4 h which is increased by about 340 % compared with PI (16 h). The synergy of free volume and trap makes comprehensive properties enhanced in the thermosetting DE/PI composite. This work provides a new design for turn-to-turn insulation with a high voltage level and a high operating frequency.

High-throughput phase field simulation and machine learning for predicting the breakdown performance of all-organic composites

All-organic dielectric polymers are materials of choice for modern power electronics and high-density energy storage, and their performance can be significantly improved by doping trace amounts of organic molecular semiconductors with strong electron-affinity energy to suppress charge conduction losses. Insight into the breakdown mechanism of polymers/organic molecular semiconductor composites is essential for the design of high-performance dielectric polymers. This study investigates the impact of the doping concentration of organic molecular semiconductors, dielectric constants, and trap depths on the breakdown performance of dielectric polymers under high temperature and electric fields. A modified phase-field model, incorporating deep traps and carriers’ coulomb capture radius, has been developed to facilitate high-throughput simulations of electrical breakdown in polymer/organic molecular semiconductor composites. This work accurately predicted the breakdown strength of all-organic composites using high-throughput phase-field simulation data as input for machine learning, which provides crucial theoretical support for designing all-organic composite dielectric polymers for energy storage capacitors under extreme conditions.

High energy storage performance in poly(vinylidene fluoride)-based all-organic composites via optimizing the structure of semiconductive filler

The great demand for miniaturization and lightweight energy equipment stimulates the fast development of polymer-based dielectrics with low density and easy processability. Unfortunately, the low energy density puts barriers to the development of polymer dielectrics in the new energy industry. In this work, poly(vinylidene fluoride) (PVDF)-based blending films are prepared and the energy storage properties are explored by regulating the content and structure of semiconductive polymer fillers. The experiment results show that when poly{2-((3,6,7,10,11-pentakis(hexyloxy)triphenylene-2-yl)oxy)ethyl methacrylate} (P6) filler is added, 0.25 wt%-P6/PVDF film attains the maximal discharge energy density (Ud) of 19.1 J cm−3 at 624 MV m−1. Compared with poly{2-((3,6,7,10,11-pentabutoxytriphenylen-2-yl)oxy)ethyl methacrylate} (P4) filler, the P6 filler possesses better compatibility with PVDF and creates deeper traps to suppress the carrier migration and achieve the higher breakdown strength. This research offers useful references for the design of polymer-based composites with excellent energy density through blending triphenylene semiconductive fillers.

Superior electric displacement and energy storage density in dielectric polymer via inserting thermoplastic polyurethane

Dielectric polymers have been broadly applied in film energy storage capacitors owing to their excellent insulating characteristics. However, low electric displacement (D) and available energy densities (Ue) of existing polymer systems restrict them for miniaturized and integration applications. Herein, thermoplastic polyurethane (TPU) is utilized as the central layer to provide high D, and poly (methyl methacrylate) (PMMA) is used as the coating layer to maintain insulating characteristics. The electric displacement difference (Dmax-Dr) value and Ue values of the all-organic composites were optimized by modifying the relative ratios of the intermediate layer TPU. Notably, the all-organic composites with optimized relative ratio (26.13 vol%) of the TPU layer exhibits the largest Dmax-Dr of 8.27 μC/cm2 at highest breakdown strength of 450 MV/m, which is 89 % higher than that of PMMA at 4.37 μC/cm2, and thus a maximum Ue of 16.23 J/cm3 is obtained, far exceeding the values for advanced polymer and their composites. This strategy provides an effective approach for the development of dielectric polymer with high energy storage capabilities.

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.

Tri-layer high-temperature all-organic films with superior energy-storage density and thermal stability

Tri-layered all-organic composites exceed the upper energy-storage-density limits of commercial bench-mark BOPP (∼1.4 J cm−3) and representative ferroelectric polymer-based composites (<4 J cm−3) at elevated temperature.

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.

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 8.05Jcm-3 (150°C) and 5.12Jcm-3 (200°C) is achieved. Furthermore, the all-organic composites exhibit stable performances during ultralong 105 charge-discharge cycles in harsh environments (500MVm-1 and 200°C) and prospects for large-scale preparation.

Achieve High Dielectric and Energy-Storage Density Properties by Employing Cyanoethyl Cellulose as Fillers in PVDF-Based Polymer Composites.

Fluoropolymer/inorganic nanofiller composites are considered to be ideal polymer dielectrics for energy storage applications because of their high dielectric constant and high breakdown strength. However, these advantages are a trade-off with the unavoidable aggregation of the inorganic nanofillers, which result in a reduced discharge of the energy storage density. To address this problem, we developed polyvinylidene fluoride (PVDF) graft copolymer/cellulose-derivative composites to achieve high-dielectric and energy-storage density properties. An enhanced dielectric constant and improved energy density were achieved with this structure. The optimal composites exhibited a high discharge energy density of 8.40 J/cm3 at 300 MV/m. This work provides new insight into the development of all-organic composites with bio-based nanofillers.

Enhanced energy density at elevated temperature in polyetherimide based all-organic dielectrics via UV irradiation

The rapid development of electrostatic capacitors puts forward more stringent requirements for the use of polymer dielectrics, that is, to maintain high energy storage density and efficiency under extreme environments of high temperature and high electric field. In this work, all-organic composites comprising polyetherimide (PEI) blended with high-electron-affinity polymer dots (PDs) have been fabricated and modified by UV irradiation. It is found that the UV irradiated all-organic composites exhibit high energy density (4.1 J cm−3), far outperforming pristine PEI. The energy level diagram and electric conduction results prove that PDs capture free electrons via electrostatic attraction and the wide bandgap forms a barrier to electron transport, which inhibits the electric conduction, leading to the substantial performance improvements. This work demonstrates an effective modification method for the improvement of high-temperature electronics and energy storage devices.

Enhanced energy density and efficiency of all-organic composites by designing a multilayer gradient structure

Dielectric capacitors have bright application prospects in the field of pulse power devices due to their extremely high power density.

Simulation-aided studies on the superior thermoelectric performance of printable PBDTT-FTTE/SWCNT composites

Quasi one-dimensional (1D) carbon nanostructures hybridized with π-conjugated polymeric systems are vastly explored for their unique heat/carrier transport beneficial for thermoelectric (TE) applications. We present the TE response of all-organic composites fabricated with poly[4,8-bis(5-(2-ethylyhexyl)thiophene-2-yl)benzo[1,2-b; 4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)3-fluorothieno[3,4-b']thiophene-)-2-carboxylate-2-6-diyl)] (PBDTT-FTTE) and single-walled carbon nanotube (SWCNT). SWCNTs form strong π-π interfacial interactions with the polymer, and their TE performance is improved through p-doping with ferric chloride (FeCl3). Investigation of the electrical conductivity (σ) and Seebeck coefficient (α) reveals a characteristic mechanism arising from low-energy carrier filtering and Fermi-level pinning. DIGIMAT-MF© material modeling platform simulates σ and thermal conductivity (κ) and indicates a CNT aspect ratio distribution in the system. The doped composite with 55 wt% SWCNT exhibits the maximum ZT value of 0.044 at 303 K using the simulated κ value. A flexible TE generator (TEG) consisting of 21 legs is dispenser printed that produces ∼32.7 nW power output with a 65 K temperature gradient across 15 kΩ load resistance. COMSOL Multiphysics® simulation is used to optimize TEG design for maximum extractable output power.

Scalable Ultrathin All-Organic Polymer Dielectric Films for High-Temperature Capacitive Energy Storage.

The miniaturization of electronic devices and power systems for capacitive energy storage under harsh environments requires scalable high-quality ultrathin high-temperature dielectric films. To meet the need, ultrasonic spray-coating (USC) can be used. Novel polyimides with a dipolar group, CF3 (F-PI), and all-organic composites with trace organic semiconductor can serve as models. These scalable high-quality ultrathin films (≈2.6 and ≈5.2µm) are successfully fabricated via USC. The high quality of the films is evaluated from the micro-millimeter scale to the sub-millimeter and above. The high glass transition temperature Tg (≈340 °C) and concurrent large bandgap Eg (≈3.53eV) induced by weak conjugation from considerable interchain distance (≈6.2 Å) enable F-PI to be an excellent matrix delivering a discharge energy density with 90% discharge efficiency Uη90 of 2.85 J cm-3 at 200 °C. Further, the incorporation of a trace organic semiconductor leads to a record Uη90 of ≈4.39 J cm-3 at 200 °C due to the markedly enhanced breakdown strength caused by deep charge traps of ≈2eV. Also, a USC-fabricated multilayer F-PI foil capacitor with ≈85nF (six layers) has good performance at 150 °C. These results confirm that USC is an excellent technology to fabricate high-quality ultrathin dielectric films and capacitors.

An all-organic spatial structure composed of perylene diimide/mesoporous graphitic carbon nitride for high efficiency photocatalysis

The development of semiconductor photocatalytic technology is still limited to low carrier separation efficiency and secondary contamination of metal ions. The construction of bandgap-matched all-organic semiconductor materials is environmentally friendly and can achieve directional carrier migration and efficient separation. Herein, a series of perylene diimide/mesoporous graphitic carbon nitride (PDI/mpg-C3N4) all-organic composites with spatial stereostructure were successfully fabricated via in-situ electrostatic assembly. The spatial structure composed of perylene diimide/mesoporous graphitic carbon nitride exhibit outstanding light absorption properties and rapid separation and migration abilities of photocarriers, which greatly enhance solar energy utilization. The experiment results exhibit that the bisphenol A (BPA) degradation rate of the 20% perylene diimide/mesoporous graphitic carbon nitride (20% PDI/mpg-C3N4) composite attained to 3.4 and 7.3 times than that of the self-assembled perylene diimide (self-assembled PDI) and mesoporous graphitic carbon nitride (mpg-C3N4). This work provides ideas for constructing organic catalysts with high photocatalytic performance.

Significantly improved high-temperature charge-discharge efficiency of all-organic polyimide composites by suppressing space charges

In order to satisfy the miniaturization trends of power electronic devices and safe operation in harsh environments, high-temperature dielectric polymers with excellent energy density and great reliability are desired in advanced electronic and power systems as electrostatic capacitors. Herein, the all-polymer dielectric composite films, consisting of ferroelectric polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as filler and linear polymer polyimide (PI) as matrix, were fabricated by in situ polymerization method for electrostatic energy storage scenarios. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results indicated that the P(VDF-HFP) was successfully compounded into the PI matrix. The dielectric permittivity of PI/P(VDF-HFP) energy storage composites was enhanced, while the breakdown strength and electrical resistivity values were wrecked slightly with enhancive mass fraction of P(VDF-HFP). Consequently, the discharged energy density (Ud) of PI-10, PI-20 and PI-30 were 2.60, 2.90, and 3.16 J/cm3 at 30 ℃ and 400 MV/m, respectively, which were 1.05, 1.17 and 1.27 times than those of neat PI film (2.48 J/cm3). Notably, an interesting phenomenon was observed that the charge-discharge efficiency (η) of all-organic composites was dramatically improved situated in high-temperature conditions. When the mass ratio of P(VDF-HFP) to PI was 1:4, the corresponding Ud and η of PI-20 could be significantly improved to 2.25 J/cm3 and 76.9% at 382 MV/m and 150 ℃, which were 6.7 and 10.5 times than those of neat PI film (0.336 J/cm3 and 7.3%) at 300 MV/m, respectively. Impressively, PI-30 film delivers an enhanced Ud of 1.81 J/cm3 and η of 71% at 200 ℃ and 308 MV/m. The significant improvement in the efficiency of composites under high-temperature environment is attributed to the suppression of space charges, which was verified by the TSDC results. In addition, the all-polymer composites exhibited outstanding cycling stability under harsh conditions of high temperature and high electric field. Our fabricated PI/P(VDF-HFP) composite films present potential energy storage applications in the high temperature environments with demand for flexible dielectric materials with upgraded permittivity, excellent energy density as well as reliable cycling stability.

Ultrahigh-energy-density dielectric materials from ferroelectric polymer/glucose all-organic composites with a cross-linking network of hydrogen bonds

Polymer dielectrics have been widely used for capacitive energy storage. However, the volumetric energy density of polymer dielectrics is generally low, which falls short of the need for high-power and compact-size electronic devices and electrical systems. Here, a scalable all-organic composite based on a ferroelectric polymer incorporated with an abundant, cost-effective organic molecule, i.e., glucose is reported, exhibiting record dischargeable energy density (37.7 J/cm3) that outperforms the state-of-the-art dielectric polymer composites. The glucose molecules rich in hydroxyl groups are found to facilitate the formation of a physically cross-linking network of hydrogen bonds within the polymer matrix, which is responsible for the remarkable performance improvement. Both simulation and experimental results show that the hydrogen bonds serve as the trapping sites of charge carriers and suppress conduction loss. The hydrogen bond network is also found to account for the increased crystallinity, reduced crystallite size, and stabilized γ phase in the polymer, which leads to enhanced electric displacement and reduced hysteresis loss. In combining the advantages of extraordinary energy storage performance, abundant raw materials, ease of preparation, this approach is viable for large-scale production of polymer-based high-energy-density dielectric materials.

Research Advances in Hierarchically Structured PVDF-Based All-Organic Composites for High-Energy Density Capacitors.

Polymer film capacitors have been widely applied in many pulsed power fields owing to their fastest energy-released rates. The development of ferroelectric polyvinylidene fluoride (PVDF)-based composites has become one of the hot research directions in the field of high-energy storage capacitors. Recently, hierarchically-structured all-organic composites have been shown to possess excellent comprehensive energy storage performance and great potential for application. In this review, most research advances of hierarchically-structured all-organic composites for the energy storage application are systematically classified and summarized. The regulating strategies of hierarchically structured all-organic composites are highlighted from the perspective of preparation approaches, tailored material choices, layer thicknesses, and interfaces. Systematic comparisons of energy storage abilities are presented, including electric displacement, breakdown strength, energy storage density, and efficiency. Finally, we present the remaining problems of hierarchically structured all-organic composites and provide an outlook for future energy storage applications.

Enhanced energy storage density of all-organic fluoropolymer composite dielectric via introducing crosslinked structure.

Polymer-based dielectrics have been attracted much attention to flexible energy storage devices due to their rapid charge–discharge rate, flexibility, lightness and compactness. Nevertheless, the energy storage performance of these dielectric polymers was limited by the weak dielectric breakdown properties. Crosslinked structure has been proven efficient to enhance breakdown strength (Eb) and charge–discharge efficiency (η) of polymer film capacitors. However, crosslinked networks usually lead to low electric displacement of dielectric capacitors, which greatly restrict their energy storage density (Ud). In this work, we present a tri-layered composite via layer-by-layer casting technology, where crosslinked polyvinylidene fluoride (c-PVDF) was used as the inter-layer to offer high breakdown strength, and the outer ternary fluoropolymer layers with high dielectric constant could provide high electric displacement. The optimal tri-layered composites exhibit an ultrahigh discharge energy density of 18.3 J cm−3 and a discharge efficiency of 60.6% at 550 kV mm−1. This energy density is much higher than that of the PVDF terpolymer and commercially biaxially oriented polypropylene (BOPP, 1–2 J cm−3). The simulation results prove that the enhanced energy density originates from the effectively depressed charge transport in crosslinked structure at high applied electric field. Moreover, this work provides a feasible method for developing flexible all-organic high-energy-density composites for polymer capacitors.

All-organic composites with strong photoelectric response over a wide spectral range

2-hydroxynaphthylidene-1′-naphthylamine (HNAN) and −NO2 modified HNAN (HNAN-NO2) Schiff base compounds were synthesized and exhibited strong visible light absorption (<650 nm). These compounds were added to poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric polymer, obtaining composites with high photoelectric response under visible and infrared light. It was found that the modification of HNAN by the nitro group and the poling of the composites under a high electric field can greatly enhance the photoelectric response of the composites. The composites can generate high photovoltages of 1386 and 352.7 mV under irradiation with near-infrared light (915 nm) and green light (532 nm). The mechanism of the photoelectric response of the composites under green light was explored and it was found that the response originates mainly from the coupling effect of the photothermal effect of the Schiff base and the pyroelectric effect of the ferroelectric polymer. The composites, which can be utilized as photodetector materials, are promising for next-generation artificial retina applications and the sensing capability of retina can be extended in a wide wavelength range from visible to infrared light.

Polymer/molecular semiconductor all-organic composites for high-temperature dielectric energy storage

Dielectric polymers for electrostatic energy storage suffer from low energy density and poor efficiency at elevated temperatures, which constrains their use in the harsh-environment electronic devices, circuits, and systems. Although incorporating insulating, inorganic nanostructures into dielectric polymers promotes the temperature capability, scalable fabrication of high-quality nanocomposite films remains a formidable challenge. Here, we report an all-organic composite comprising dielectric polymers blended with high-electron-affinity molecular semiconductors that exhibits concurrent high energy density (3.0 J cm−3) and high discharge efficiency (90%) up to 200 °C, far outperforming the existing dielectric polymers and polymer nanocomposites. We demonstrate that molecular semiconductors immobilize free electrons via strong electrostatic attraction and impede electric charge injection and transport in dielectric polymers, which leads to the substantial performance improvements. The all-organic composites can be fabricated into large-area and high-quality films with uniform dielectric and capacitive performance, which is crucially important for their successful commercialization and practical application in high-temperature electronics and energy storage devices.