Significantly enhanced high-temperature capacitive energy storage in cyclic olefin copolymer dielectric films via ultraviolet irradiation

One-step fabrication of high energy storage polymer films with a wide bandgap and high melting temperature induced by the fluorine effect for high temperature capacitor applications with ultra-high efficiency

The development of polymer dielectrics with both high energy density and low energy loss is a formidable challenge in the area of high-temperature dielectric energy storage. To address this challenge, a class of polymers (Parylene F) are designed by alternating fluorinated aromatic rings and vinyl groups in the polymer chain to confine the conjugating sequence and broaden the bandgap with the fluorine effect. The target films with desired thickness, ultra-high purity, and a wide bandgap are facilely fabricated by a one-step chemical vapor deposition (CVD) technique from monomers. The symmetric and bulky aromatic structures exhibit high crystalline performance and excellent stability at high temperature. The presence of strongly electronegative fluorine atoms effectively enhances bandgap and electron trapping capability, which effectively reduces the conduction loss as well as the possibility of breakdown at high temperatures. CVD technology avoids the post-processing film-forming process, ensuring the fabrication of thin films with high quality. These benefits allow Parylene F films to effectively store electrical energy at temperature up to 150 °C, exhibiting a record discharged energy density of 2.92 J cm-3 at charge-discharge efficiency exceeding 90%. This work provides a new idea for the design and synthesis of all-organic polymer dielectric films for high temperature applications.

Magnetic-assisted alignment of nanofibers in a polymer nanocomposite for high-temperature capacitive energy storage applications

Flexible polymer-based dielectrics with high energy storage characteristics over a wide temperature range are crucial for advanced electrical and electronic systems. However, the intrinsic low dielectric constant and drastically degraded breakdown strength hinder the development of polymer-based dielectrics at elevated temperatures. Here, we propose a magnetic-assisted approach for fabricating a polyethyleneimine (PEI)-based nanocomposite with precisely aligned nanofibers within the polymer matrix, and with Al2O3 deposition layers applied on the surface. The resulting polymer nanocomposite exhibits simultaneously increased dielectric constant and enhanced breakdown strength at high temperatures compared to pristine PEI. The enhanced dielectric constant is contributed by the depolarization effect of out-of-plane orientated nanofibers in composite films, while the surficial Al2O3 layers, with a wide bandgap, effectively prevent charge injection and transport at the electrode/dielectric interface. The optimally aligned composite films exhibit a significantly enhanced discharged energy density of 6.5 J cm-3 at 150 °C, with approximately 41% and 132% enhancement compared to random films and pristine PEI films, respectively. Additionally, a metalized multilayer polymer-based capacitor utilizing this composite film produces a high capacitance of 88 nF, while demonstrating excellent cyclability and flexibility at 150 °C. This work offers an effective strategy for developing polymer-based composite dielectrics with superior capacitive performance at elevated temperatures and demonstrates the potential of fabricating high-quality flexible capacitors.

γ-Ray Irradiation Significantly Enhances Capacitive Energy Storage Performance of Polymer Dielectric Films

Polymer dielectric capacitors are fundamental in advanced electronics and power grids but suffer from low energy density, hindering miniaturization of compact electrical systems. It is shown that high-energy and strong penetrating γ-irradiation significantly enhances capacitive energy storage performance of polymer dielectrics. γ-irradiated biaxially oriented polypropylene (BOPP) films exhibit an extraordinarily high energy density of 10.4 J cm-3 at 968 MV m-1 with an efficiency of 97.3%. In particular, an energy density of 4.06 J cm-3 with an ultrahigh efficiency of 98% is reliably maintained through 20 000 charge-discharge cycles under 600 MV m-1. At 125 °C, the γ-irradiated BOPP film still delivers a high discharged energy density of 5.88 J cm-3 with an efficiency of 90% at 770 MV m-1. Substantial improvements are also achieved for γ-irradiated cycloolefin copolymers at a high temperature of 150 °C, verifying the strategy generalizability. Experimental and theoretical analyses reveal that the excellent performance should be related to the γ-irradiation induced polar functional groups with high electron affinity in the molecular chain, which offer deep energy traps to impede charge transport. This work provides a simple and generally applicable strategy for developing high-performance polymer dielectrics.

Constructing asymmetric gradient structures to enhance the energy storage performance of PEI-based composite dielectrics

Enhancing the high electric field resistance and energy storage capacity of polymer dielectrics has been a long-standing challenge for the iterations of power equipment. Synergistic inhibition of carrier injection and transport is vital to energy storage performance improvement. Herein, promising polymer polyetherimide (PEI) was employed as a matrix and wider bandgap boron nitride nanosheets (BNNSs) were used as a reinforcing filler. Utilizing high-throughput stochastic breakdown simulations with the distribution characteristics of BNNSs as parameters, a series of topological gradient structures with the potential to enhance performance were obtained, thereby shortening the experimental cycle. Changing the BNNS distribution of symmetric/asymmetric and positive/inverse gradients, as well as the total and gradient contents of BNNSs, means that the position and condition of the surface barrier layer and central hinder layer change, which influences the energy storage performance of the polymer at room temperature and high temperature. Remarkably, the asymmetric gradient structure composite dielectrics exhibited excellent performances. Among them, the PEI-based composite dielectric with 2 vol% BNNS asymmetric inverse gradient distribution (gradient content of 1 vol%) achieved energy densities of 8.26 and 4.78 J cm-3 at room temperature and 150 °C, respectively. The asymmetric gradient structure design strategy holds great promise for optimizing the energy storage capacity of polymer dielectric capacitors.

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.

Engineering the Dielectric Constants of Polymers: From Molecular to Mesoscopic Scales

Polymers are essential components of modern-day materials and are widely used in various fields. The dielectric constant, a key physical parameter, plays a fundamental role in the light-, electricity-, and magnetism-related applications of polymers, such as dielectric and electrical insulation, battery and photovoltaic fabrication, sensing and electrical contact, and signal transmission and communication. Over the past few decades, numerous efforts have been devoted to engineering the intrinsic dielectric constant of polymers, particularly by tailoring the induced and orientational polarization modes and ferroelectric domain engineering. Investigations into these methods have guided the rational design and on-demand preparation of polymers with desired dielectric constants. This review article exhaustively summarizes the dielectric constant engineering of polymers from molecular to mesoscopic scales, with emphasis on application-driven design and on-demand polymer synthesis rooted in polymer chemistry principles. Additionally, it explores the key polymer applications that can benefit from dielectric constant regulation and outlines the future prospects of this field.

Unifying and Suppressing Conduction Losses of Polymer Dielectrics for Superior High-Temperature Capacitive Energy Storage

Superior high-temperature capacitive performance of polymer dielectrics is critical for the modern film capacitor demanded in the harsh-environment electronic and electrical systems. Unfortunately, the capacitive performance degrades rapidly at elevated temperatures owing to the exponential growth of conduction loss. The conduction loss is mainly composed of electrode and bulk-limited conduction. Herein, the contribution of surface and bulk factors is unified to conduction loss, and the loss is thoroughly suppressed. The experimental results demonstrate that the polar oxygen-containing groups on the surface of polymer dielectrics can act as the charge trap sites to immobilize the injected charges from electrode, which can in turn establish a built-in field to weaken the external electric field and augment the injection barrier height. Wide bandgap aluminum oxide (Al2 O3 ) nanoparticle fillers can serve as deep traps to constrain the transport of injected or thermally activated charges in the bulk phase. From this, at 200 °C, the discharged energy density with a discharge-charge efficiency of 90% increases by 1058.06% from 0.31 J cm-3 for pristine polyetherimide to 3.59 J cm-3 for irradiated composite film. The principle of simultaneously inhibiting the electrode and bulk-limited conduction losses could be easily extended to other polymer dielectrics for high-temperature capacitive performance.

Aromatic-Free Polymers Based All-Organic Dielectrics with Breakdown Self-Healing for High-Temperature Capacitive Energy Storage

High-temperature dielectric polymers are becoming increasingly desirable for capacitive energy storage in renewable energy utilization, electrified transportation, and pulse power systems. Current dielectric polymers typically require robust aromatic molecular frameworks to ensure structural thermal stability at elevated temperatures. Nevertheless, the introduction of aromatic units compromises electrical insulation owing to pronounced π─π interactions that facilitate electron transport and eliminate the breakdown self-healing property owing to their high carbon content. Herein, an aromatic-free polynorborne copolymer exhibiting electrical conductivity-two orders of magnitude lower than that of state-of-the-art polyetherimide-at elevated temperatures and high electric fields owing to its large bandgap (≈4.64 eV) and short hopping conduction distance (≈0.63 nm) is described. Density functional theory calculations demonstrate that the copolymer can effectively suppress the excitation of high-field valence electrons. Furthermore, the incorporation of trace semiconductors results in high discharge density (3.73 J cm-3 ) and charge-discharge efficiency (95% at 150 °C), outperforming existing high-temperature dielectric polymers. The excellent electrical breakdown self-healing capability of the copolymer film at elevated temperatures further demonstrates its potential for use in dielectric capacitors capable of continuous operation under extreme conditions.