Device junctions as in metal-insulator, metal-insulator-semiconductor, and solid-gas interfaces are critical to the performance and reliability of modern electronic and electrical systems ranging from micro-electronics to mega-voltage power grids, as they govern the electromagnetic fields and thus the flow of power and information, constituting the backbone of our modern infrastructures. However, with ever-increasing demands in power and payload efficiency, these interfaces are subjected to exceedingly high fields approaching gigavolt per meter and, concurrently, harsh environmental and thermal stresses. These adverse interfacial processes—namely hot-carrier injection at metal-insulator interface, dielectric surface flashover, and discharge erosion—culminate ultimately to the aging and system failure. Due to the complexity and magnitude of these challenges, no single, unified solution exists today. Here, we disclose a conformal, self-assembled 2D nanocoating formed through the co-assembly of hundreds of highly oriented organic-inorganic nanolayers—collectively confined within ∼300 nm—that can be readily applied via scalable spray coating to effectively impede and dissipate hot carriers through anisotropic, multi-phonon-assisted scattering, thereby forming defect-tolerant hot-carrier “rectifiers.” We further demonstrate that this surface re-engineering solution also suppresses surface flashover and corona discharge aging in outdoor mega-voltage power grids, with promise of generative design and holistic, multifunctional barrier properties for future large-scale electrification.

Dielectric materials with superior high-temperature energy storage capability are of critical importance for the development of modern power electronic systems. However, polymer dielectrics generally suffer from rapid performance degradation at high temperature and under a strong electric field due to charge injection, which is particularly severe for highly aromatic, high-temperature-resistant polymers such as polyimide. Owing to their intrinsically low bandgap and limited charge-injection barriers, pronounced conductive losses can occur even under moderate electric fields. Conventional methods to address this issue involve coating the polymer surface with highly insulating nanomaterials; while this can suppress charge injection, it simultaneously triggers space charge accumulation and local electric-field distortion. To address these challenges, a novel bilayer nanocoated polyimide (Kapton PI)-based multilayer architecture is designed in this work to synergistically integrate charge-blocking and charge-dissipation functionalities. The boron nitride nanosheets (BNNSs) layer adjacent to the electrodes effectively increases the charge-injection barrier, while the montmorillonite (MMT) nanosheets layer near the polymer substrate facilitates in-plane charge dissipation and alleviates local electric-field distortion. Plasma treatment is strategically employed to optimize the interfacial chemistry, further enhancing interfacial polarization and interfacial interactions to ensure a robust synergistic effect. Benefiting from this comprehensive interfacial engineering, the bilayer nanocoatings simultaneously achieve suppressed electrical breakdown and enhanced polarization at elevated temperatures. Remarkably, they deliver a high discharged energy density (Ue) of 1.6 J cm-3 with an outstanding charge-discharge efficiency (eta) of 90.1% at 200 degrees C under a low electric field of 250 MV m-1. This work demonstrates an effective strategy based on bilayer nanocoatings for improving the high-temperature energy storage performance of polymer films, showing great potential for harsh environment applications.

The self-assembled anisotropic coating modifies the surface defects of amorphous polymers, inhibiting charge injection and greatly improving the breakdown strength and storage efficiency.

This study examines the morphological evolution of melt-cast Poly (ethylene terephthalate) (PET) thin films under nonlinear deformation strategies, specifically stretching and cycling, to analyze their structural, mechanical, and electrical properties. Capacitor-grade thin films were melt-cast and subjected to uniaxial deformation using an instrumented stretching machine that applied programmable deformations. During deformation, real-time mechano-optical data, including birefringence, true strain, and true stress, were collected above the glass transition temperature (Tg).Stress-induced crystallization emerged as the primary mechanism during stretching, as thermally induced crystallization was suppressed due to high viscosity in the rubbery temperatures near Tg. Strain oscillations after steady deformations at various strain levels promoted crystallization and relaxed oriented amorphous chains. This process enhanced crystalline orientation and crystallinity, particularly in stretching and oscillation tests compared to stretching and holding tests. At higher deformation levels, the orientation of amorphous domains transitioned to oriented crystalline structures. Increased crystallinity and crystalline and amorphous chain orientation enhanced electrical breakdown. The strain oscillation played a crucial role in promoting crystallinity enhancement while minimizing amorphous chain orientation, leading to lower electrical breakdown. These results highlight the substantial influence of the amorphous phase and its chain orientation on the electrical breakdown of PET films.

Biaxially oriented polypropylene (BOPP) thin film is the predominant dielectric material used in film capacitive energy storage for pulsed power engineering and power conversions due to its remarkable high dielectric strength and low conduction loss. However, the design rating of BOPP film capacitors in high power density conversion systems operated also under high temperature is still based on the empirical criteria due to the lack of systematic mechanism studies at elevated temperature. In this work, the temperature‐dependent electrical conduction in tenter and bubble BOPP films up to their breakdown strength was systematically studied using a specialised circuitry featuring dynamic gain‐controlled capacitive current cancellation. Both tenter and bubble BOPP films exhibit an extended trap‐limited conduction region at the high electric field, followed subsequently with a trap‐filled limited conduction until breakdown. This trap‐filled‐limited conduction presents characteristics of carriers transport with detrimental high mobility and soaring conduction loss. Overall, the shallow localised states revealed by the Arrhenius analysis, the large bandgap, and high barrier height of BOPP film together render its exceptional electrical integrity. In comparison, the enhanced crystallinity and larger crystallite sizes in tenter BOPP produced by the sequential stretching result in a higher upper operational temperature and slightly higher breakdown strength than bubble BOPP, suggesting the important role of processing induced enhancements to intrinsic properties of molecular origin. This study provides insights into the high‐field characteristics of BOPP films at elevated temperature with promising learning outcomes useful to the expedited designs of the next generation polymer films for capacitive energy storages.

Next-generation electrical and power electronic systems necessitate polymer dielectrics with high energy densities and high-temperature applicability. However, such ever-increasing performance demands result in exponential increases of leakage electrical conduction, which is fundamentally associated with thermally and electrically assisted charge injection and transport mechanisms. Here, we report a substantial improvement in high-temperature energy storage properties for polymer dielectrics with a bilayer nanocoating. Two-dimensional boron nitride and montmorillonite nanosheets were coated on the polymer surface, showing a synergetic effect on trapping and dissipating the hot carriers injected from electrodes. We obtain an ultrahigh discharged energy density of 5.5 J/cm3 with an efficiency exceeding 90 % at 150 degrees C. This bilayer nanocoating strategy provides a generalizable approach for designing high-performance polymer dielectrics via interfacial engineering.

This work proposes to combine the functionality benefits of power electronics with the power density benefits of medium-voltage cables to create a streamlined, high-density power electronics solution that seamlessly integrates with medium-voltage cables. Located at the ends of a medium- or high-voltage line, the proposed converter uses a cascade of coaxial power conversion cells to gradually step down the voltage, and excels in high step-down applications. By mimicking the coaxial geometry of medium-voltage cables, the converter preserves the axisymmetric electric field of the cable which, when combined with a solid insulating dielectric, provides a voltage scaling advantage over conventional planar and PCB-based converter solutions. Similar to medium voltage cables, the converter is fully passively cooled. A passive cooling strategy allows for combined installation with existing medium voltage cable systems without the added cost, maintenance needs, infrastructure, and reliability concerns associated with active cooling systems. The scalability of the modular structure in combination with the integration benefits provide a flexible power electronics system that can adapt to the evolving demands of the grid.

The electronic band structure, especially the defect states at the conduction band tail, dominates electron transport and electrical degradation of a dielectric material under an extremely high electric field. However, the electronic band structure in a dielectric is barely well studied due to experimental challenges in detecting the electrical conduction to an extremely high electric field, i.e., prebreakdown. In this work, the electronic band structure of polymer dielectric films is probed through an in situ prebreakdown conduction measurement method in conjunction with a space-charge-limited-current spectroscopic analysis. An exponential distribution of defect states at the conduction band tail with varying trap levels is observed in accordance with the specific morphological disorder in the polymer dielectric, and the experimental defect states show also a favorable agreement with the calculated density of states from the density functional theory. The methodology demonstrated in this work bridges the molecule-structure-determined electronic band structure and the macro electrical conduction behavior with a highly improved understanding of material properties that control the electrical breakdown, and paves a way for guiding the modification of existing material and the exploration of novel materials for high electric field applications.

PCB layouts with different polygon shapes and insulation distances were prepared and their surface flashover voltage subjected to different ramping rates were measured at different temperatures and different low gas pressures for emulated high-altitude conditions. The dependence of the surface flashover voltage on effects of gas pressure, surface insulation distance, temperature, and polygon shape was studied. Modulation efforts which include tailoring the local surface conductivity and local topography modification were performed to increase the flashover of PCB, and the related mechanism was studied. The results showed that the voltage ramping rate plays an important role in determining flashover voltage. The flashover voltage is lower when the sample is subjected to a rapid voltage ramping rate than with a slow ramping rate. This phenomenon is more prominent towards ambient pressure. The increase in temperature results in a decrease in flashover voltage at 100 kPa, while at 20 kPa and 10 kPa, the influence of temperature on flashover becomes less significant. Through-holes designed in the PCB have a positive role in increasing flashover voltage at lower pressures. However, at 100 kPa, the holes no longer contribute to any higher flashover voltage. Modification of local surface conductivity has no contribution in increasing the flashover voltage, while a surface coating with a surface conductivity of 10 -10 S dramatically decreases the flashover voltage. The work presented in this paper provides a reference for the design and modification of PCB layouts for use in future aerospace hybrid propulsion systems.

C4F7N [2,3,3,3-tetrafluoro-2-(trifluoromethyl)propanenitrile]/CO2 gas mixtures are being developed as an eco-friendly electrical insulator to replace SF6, the most potent greenhouse industrial gaseous dielectric. However, recent studies have reported complicated and often conflicting decomposition pathways for C4F7N/CO2 gas mixtures, which has raised concerns. In this work, the decomposition characteristics of C4F7N/CO2 gas mixtures were studied comprehensively by both designed computations and experiments. Computations were performed starting from fundamental propositions of C4F7N/CO2 decompositions, which were further experimentally verified by pyrolysis, long-term thermal aging with/without catalytic materials (industrial-grade molecular sieves 4A), and electrical decomposition by spark discharge. The results of both computations and experiments suggest that in an ideal thermal decomposition, C4F7N is likely to decompose into C2F6 and small fluoronitriles first at high temperatures. The generation of C3F6 and C2N2 from C4F7N thermal decomposition at lower temperatures appears because of the catalytic effect of incompatible materials, for example, the industrial-grade molecular sieves 4A that we tested. The electron impact dissociation of C4F7N plays an important role in C4F7N electrical decomposition, leading to additional formation of distinctive small molecules of CF4 and C2N2 of low concentrations. It was pointed out based on a real arcing test in a load disconnector that the decomposition of C4F7N gas mixtures in real applications will be at a much moderate and manageable rate than what was obtained from the highly accelerated laboratory tests presented in this work. The signatures of decomposition products extracted in this study provide invaluable guidance for developing decomposition-based diagnosis and fixation of decomposition byproducts toward SF6-free power grids.

High-temperature flexible polymer dielectrics are critical for high density energy storage and conversion. The need to simultaneously possess a high bandgap, dielectric constant and glass transition temperature forms a substantial design challenge for novel dielectric polymers. Here, by varying halogen substituents of an aromatic pendant hanging off a bicyclic mainchain polymer, a class of high-temperature olefins with adjustable thermal stability are obtained, all with uncompromised large bandgaps. Halogens substitution of the pendant groups at para or ortho position of polyoxanorborneneimides (PONB) imparts it with tunable high glass transition from 220 to 245 °C, while with high breakdown strength of 625-800 MV/m. A high energy density of 7.1 J/cc at 200 °C is achieved with p-POClNB, representing the highest energy density reported among homo-polymers. Molecular dynamic simulations and ultrafast infrared spectroscopy are used to probe the free volume element distribution and chain relaxations pertinent to dielectric thermal properties. An increase in free volume element is observed with the change in the pendant group from fluorine to bromine at the para position; however, smaller free volume element is observed for the same pendant when at the ortho position due to steric hindrance. With the dielectric constant and bandgap remaining stable, properly designing the pendant groups of PONB boosts its thermal stability for high density electrification.

With the annual global electricity production exceeding 30,000 TWh, the safe transmission of electric power has been heavily relying on SF6, the most potent industrial greenhouse gas. While promising SF6 alternatives have been proposed, their compatibilities with materials used in gas-insulated equipment (GIE) must be thoroughly studied. This is particularly true as the emerging SF6 alternatives generally leverage their relatively higher reactivity to achieve lower global warming potentials (GWPs). Here, a high-throughput compatibility screening of common GIE materials was conducted with a representative SF6 alternative, namely, C4F7N (2,3,3,3-tetrafluoro-2-(trifluoromethyl)propanenitrile)/CO2 gas mixtures. In this screening, the insulation performance of C4F7N/CO2 gas mixtures, as an indicator of the C4F7N/materials compatibility level, was periodically monitored during the thermal aging with tens of materials from SF6-insulated GIE, including desiccants/adsorbents, rubber, plastics, composites, ceramics, metals, etc. The identification of incompatible materials and the follow-up mechanism studies suggested that the acidity of materials represents the primary cause for C4F7N/materials incompatibility when C4F7N/CO2 gas mixtures are used as a drop-in replacement solution for existing SF6-insulated apparatuses. Mitigation strategies tackling the acidity of materials were then proposed and validated. Additionally, the amphoteric characteristics of C4F7N were briefly discussed. This work provides insight into the materials incompatibility of SF6 alternatives, along with validated mitigation strategies, for the selection and design of materials used in future eco-friendly GIE.

C4F7N (2,3,3,3-tetrafluoro-2-(trifluoromethyl) propanenitrile) gas mixtures have emerged as a promising ecofriendly replacement for SF6, the most global-warming-potent and widely used industrial gaseous dielectric in power grids. However, aging products of C4F7N gas mixtures with potential toxicity have also raised concerns. In this work, we demonstrate that by properly exploiting the heterogeneous characteristics of C4F7N aging, both its solid and gaseous aging products generated due to electric discharges can be effectively mitigated. With CO2 as the buffer gas to prevent carbonization, FKM fluoroelastomer rubber as the gasket to hinder the polymerization, and 4A molecular sieves as the adsorbent to further fixate the residual aging products, benign C2F6 and CO at sufficiently low concentrations become the only aging products detected after the electrical aging of C4F7N gas mixtures. This work showcases effective abatement strategies of C4F7N aging products, thus facilitating the transition toward SF6-free green power grids.

In this study, the relationship between structural hierarchy in PVDF/PMMA blends as altered by melt casting and annealing and electrical properties was investigated. PVDF was blended with PMMA in three crystallizable compositions: 50/50, 60/40 and 70/30 of PVDF/PMMA using twin screw extrusion followed by film casting. The films were characterized structurally through offline birefringence measurements as well as WAXS, SAXS, IR Dichroism and DSC to understand the processing induced structural changes and their effect on electrical properties. The addition of PMMA to PVDF suppressed crystalization during casting of films. This opened a low temperature film deformation window between T g and cold crystallization temperatures allowing for development of high preferential chain orientation in the films. Crystallinity in cast films was shown to correlate directly with breakdown strength. Systemic annealing experiments were carried out to enhance crystallinity and the effect of annealing induced structural changes on the dielectric properties were studied. It was found that upon annealing, the amorphous PMMA tends to undergo relaxation that is detrimental to the breakdown properties. As annealing progresses, the mismatch in the kinetics between crystallization/recrystallization and the amorphous relaxation causes density gradients within the bulk of the films and dictate the overall orientation levels in the films, as well as have implications on the dielectric properties.

Polymer-thin films are critical dielectric materials for capacitive energy storage in power and electronic systems. The rapid development of wide bandgap semiconductors urgently calls for polymers that can attain high energy density and high charge-discharge efficiency at elevated temperatures. However, high-temperature polymers usually suffer from compromised dielectric breakdown strength and soaring conduction loss due to the intrinsic constraint between their bandgaps and thermal stability. In this work, we propose a facile and high throughput interface engineering technique utilizing nanocoatings formed by montmorillonite (MMT) nanoclays, which can serve as an out-of-the-box solution to bypass this constraint. The highly ordered MMT-based nanocoatings with layered structure can significantly block the excessive charge injection at high electric fields and dissipate the charge carriers along the in-plane direction. The MMT-coated PI films exhibit improved breakdown strength, suppressed conduction loss, and boosted charging-discharging efficiency. This work holds the promise of improving the dielectric properties of polymers through surface engineering, enabling their application at concurrent electrical and thermal extremes.

This paper presents a data-driven design and optimization of acoustic metamaterials with three-phase materials for highly tunable wave transmission. The geometry of representative unitcell is defined by the trigonometric series function to describe an arbitrary shape with symmetry, which enables the unitcell to achieve a large sub-wavelength bandgap. We propose a lightweight and efficient algorithm, ‘decoupled gradient decent (DGD)’, to search for the optimal design and uncover the ‘best’ shape features—the interface curvature—in tuning the wave transmission. As a result, the host composite can partly overlap the individual cell’s bandgap and achieve a wide frequency gap that forbids wave transmission, namely a passive tunability. Another advantage of the trigonometric series designed shape is the high flexibility. A slight surface pressure obviously deforms the unitcell and shifts its band structure. Our simulation shows that a moderate pressure dramatically changes the frequency forbidding gap for both traversal and longitudinal wave transmissions, which indicates an active tunability. The surface deformation can be applied by either a mechanical pressure or external electric field if the composite uses a dielectric substrate. Therefore, this study opens a sandbox of manipulating wave transmission through the topology and structure optimization in applications such as seismic damping (Hz), noise insulating (kHz) and ultrasound imaging (MHz).

Exploration of novel polymer dielectrics exhibiting high electric-field stability and high energy density with high efficiency at elevated temperatures is urgently needed for ever-demanding energy-storage technologies. Conventional high-temperature polymers with conjugated backbone structures cannot fulfill this demand due to their deteriorated performance at elevated electric fields. Here, in search of new polymer structures, we have explored the effect of fluorine groups on the energy-storage properties of polyoxanorbornene imide polymers with simultaneous wide band gap and high glass transition temperature (Tg). The systematic synthesis of polymers with varying amounts of fluorine is carried out and characterized for the energy-storage properties. The incorporation of fluorine imparts flexibility to the polymer structure, and free-standing films can be obtained. An oxanorbornene copolymer with 25% fluorination exhibits a high breakdown strength of 700 MV/m and a discharged energy density of 6.3 J/cm3 with 90% efficiency. The incorporation of fluorine helps to increase the polymer band gap, as observed using UV-vis spectroscopy, but lowers the polymer Tg, as shown by differential scanning calorimetry. Both the displacement-electric field (D-E) hysteresis loop and high-field conduction measurements show increased conduction loss for polymers with higher fluorine content, despite their larger band gap. The presence of excess free volume may play a key role in increasing the conduction current and lowering the efficiency of polymers with high fluorine content. Such an improved understanding of the effect of fluorination on the polymer energy-storage properties, as revealed in this systematic molecular engineering study, broadens the basis of material-informatic proxies to enable a more targeted codesign of scalable and efficient polymer dielectrics.

In this study, the effect of organically modified clay on the orientation enhancement in Nylon 11 in melt casting was investigated. Nylon 11 was mixed with 1 and 3 wt% Cloisite 20A using twin screw extrusion and they were cast into films with varying take-up speeds. The addition of clay in Nylon 11 helped increase orientation levels substantially in melt cast films, both as a function of clay concentration as well as take-up speeds. This was primarily due to shear amplification effect caused by the movement of adjacent clay nanoparticles due to the shear flow gradient within the die. At low clay concentrations, the sub-T-m stretchability, and electrical breakdown strength improve as the presence of clay reduces inter/intrachain hydrogen bonding. At higher clay concentrations, both orientation and electrical breakdown levels decrease. The latter is primarily caused by increased percolation path of charge carriers. Nevertheless, clay nanoplatelets were very effective in their role as melt processing aids, as they enhance orientation levels of Nylon 11 thin films by shear amplification effect where they increase local chain orientation of chains trapped between clay platelets while their orientation relaxation is suppressed.

Polymer dielectrics endowed with high dielectric constant and high breakdown strength are critical for high-power systems and compact electronics to realize ultrahigh energy density. Nevertheless, the constrained energy density attainment of prevalent commercial polymers such as BOPP has been impeded by their inadequately satisfied dielectric constant. A polynorbornenes-BP (PNB-BP) is introduced in this paper, which features a rigid backbone composed of bicyclic aliphatic, while the incorporation of an electron acceptor and aromatic groups facilitates the formation of an enhanced dipole, endowing it with a satisfied dielectric constant of 3.72. Leveraging its high breakdown strength, the PNB-BP polymer achieves a notable energy density of 12.7 J/cm 3 at room temperature. Furthermore, the PNB-BP polymer exhibits commendable thermal properties, including a high glass transition temperature (Tg) of 220°C, and satisfactory thermal stability as evidenced by the observed dielectric constants. The design strategy uncovered in this work unveils the to realize the ultrahigh energy density of the capacitor by introducing the enhanced dipole.

Polymer thin films operable under concurrent electric and thermal extremes represent critical building blocks of capacitive energy storage and electrical isolator for modern power and electronic systems with ever-increasing demands for power density and payload efficiency. However, polymer dielectrics are prone to fast aging under high fields due to hot electrons injected from electrodes. Especially, performance high-heat polymers such as polyimides with high aromaticity suffer fast aging induced by non-thermalized electrons even at moderate fields due to their intrinsically low bandgap and injection barrier. Herein, a facile, low-cost, and scalable interfaceengineering approach utilizing the highly ordered organic/inorganic layered nanocoatings is reported, which serve as a retrofittable solution to break this design constraint. By probing the energetic modes of transport and aging at pre-breakdown field, we demonstrate that our 2D montmorillonite (MMT) self-co-assembly nanocoatings can effectively boost the dielectric properties of substrate polyimide (PI) film by suppressing the charge injection and shifting the fast mode of hot-electron aging to a slow, ultimately thermalized process. This agingimpeding scheme imparts PI films with an exceptional endurance capability (enhanced by 100 MV/m) and a 6x improved charge-discharge efficiency at an elevated temperature of 175 degrees C. The nanostructured interface engineering disclosed in this work thus opens a new pathway of boosting the performance of a spectrum of highheat polymer dielectrics already commercially available in thin gauges of films for applications in zero-emission electric aircraft and renewable energy integration.