Homogeneous/Inhomogeneous-Structured Dielectrics and their Energy-Storage Performances

Interlayer Coupling Enhanced Energy Storage Performance in a Flexible BMT-BTO/BMT Multilayer Ferroelectric Film Capacitor

Flexible ferroelectric capacitors with high energy density and storage efficiency are highly desirable in the next generation of flexible electronic devices. To develop high-performance ferroelectric capacitors, a conventional approach is chemical modification. Here, a novel approach of interlayer coupling is proposed to achieve high energy storage performance in BiMg_0.5Ti_0.5O₃-BaTiO₃/BiMg_0.5Ti_0.5O₃ (BMT-BTO/BMT)_N multilayer ferroelectric films fabricated on flexible mica substrates via a sol-gel coating method. The interlayer electrostatic coupling between the ferroelectric BMT and relaxor ferroelectric BMT-BTO layers leads to small remnant polarization and large breakdown field strength, resulting in an outstanding energy storage density of ∼106.8 J cm^-3 and a good efficiency of ∼75.6% in the multilayer thin films. Further, the energy storage performance remains stable in a wide range of temperatures (25-200 °C) and frequencies (500 Hz to 10 kHz) after 10⁸ electrical loading cycles. The energy storage performance also has no obvious deterioration when the multilayer film experiences 10⁴ mechanical bending cycles with a bending radius of 4 mm. The approach proposed in the present work should be generally implementable in other multilayer flexible ferroelectric capacitors and offers a novel avenue to enhance energy storage performance by tuning the interlayer coupling.

Simultaneous Enhancement of Energy Storage and Hardness Performances in (Na0.5Bi0.5)0.7Sr0.3TiO3-Based Relaxor Ferroelectrics Via Multiscale Regulation

For (Na_0.5Bi_0.5)_0.7Sr_0.3TiO₃-based (BNST) energy storage materials, a critical bottleneck is the early polarization saturation and low breakdown electric field (E_b), which severely limits further development in the field of advancing pulsed power capacitors. Herein, a strategy, via multiscale regulation, including synergistically manipulation of the domain configuration and microstructure evolution in BNST-based ceramics, is propounded through introducing LiTaO₃(LT). The composition-driven fine domain size, as demonstrated by macroscale (size effect and dielectric response) and mesoscale (domains relaxor behavior) analysis, provides robust evidence of delayed polarization saturation and large polarization difference. Theoretical simulations and experimental results confirm that the fine grain size, uniform grain size distribution, and insignificant secondary phase contribute to the enhancements of E_b. Further analyses of the intrinsic electronic structure reveal the intrinsic mechanism for enhancing E_b via first-principles calculations on the basis of density functional theory. Consequently, owing to improved E_b, delayed polarization saturation, and refined grain size, excellent comprehensive performances [high W_rec of 5.52 J/cm³, large η of 85.68%, high hardness H of 7.06 GPa, and broad operating temperature range (20-140 °C)] are realized. We believe that these findings can provide a thorough understanding of the origins of excellent comprehensive performances in BNST-based ceramics as well as some guidance in the exploration of materials with high-performance lead-free capacitors for application in future pulsed power systems.

Superior Energy-Storage Properties in Bi0.5Na0.5TiO3-Based Lead-Free Ceramics via Simultaneously Manipulating Multiscale Structure and Field-Induced Structure Transition

Pratical applications have put forward great challenges to the comprehensive energy-storage performance of ceramic material. Here, a novel route of simultaneously manipulating multiscale structure and the field-induced structural transformation in (Bi_0.5Na_0.5)TiO₃-based ceramics is proposed to address the above concern. The multiscale structure of 0.88(Bi_0.5Na_0.5)TiO₃-0.12BaTiO₃ solid solutions such as grain and domain size, band gap, and phase structure can be adjusted by adding antiferroelectric NaNbO₃. Simultaneously, a field-induced P4bm relaxor antiferroelectric to P4mm ferroelectric phase transformation can be obtained by constructing a P4mm-P4bm phase boundary, which is expected to require a lower energy barrier compared with the field-induced P4bm relaxor antiferroelectric to R3c ferroelectric transformation in other (Bi_0.5Na_0.5)TiO₃-based ceramics. The optimized field-induced structural transformation behavior and the formation of nanodomains enables a minimized polarization hysteresis but an enhanced maximum polarization. Moreover, the decreased grain size together with increased band gap leads to a significantly improved breakdown strength. Accordingly, a giant energy density W_rec ∼ 8.0 J/cm³, a high efficiency η ∼ 86%, a short discharging time t_0.9 ∼ 41 ns, and a good temperature stability (W_rec = 1.32 ± 0.12 J/cm³, η = 88.5% ± 2.5% @ 25-200 °C) are simultaneously obtained in 0.63(Bi_0.5Na_0.5)TiO₃-0.12BaTiO₃-0.25NaNbO₃ relaxor antiferroelectric ceramics, demonstrating large potentials for the ceramic capacitor applications.

Boosting Energy Storage Performance of Lead-Free Ceramics via Layered Structure Optimization Strategy

Owing to the current global scenario of environmental pollution and the energy crisis, the development of new dielectrics using lead-free ceramics for application in advanced electronic and energy storage systems is essential because of the high power density and excellent stability of such ceramics. Unfortunately, most of them have low breakdown strength and/or low maximum polarization, resulting in low energy density and efficiency. To overcome this limitation here, lead-free ceramics comprising a layered structure are designed and fabricated. By optimizing the distribution of the layered structure, a large maximum polarization and high applied electric field (>500 kV cm^-1 ) can be achieved; these result in an ultrahigh recoverable energy storage density (≈7 J cm^-3 ) and near ideal energy storage efficiency (≈95%). Furthermore, the energy storage performance without obvious deterioration over a broad range of operating frequencies (1-100 Hz), working temperatures (30-160 °C), and fatigue cycles (1-10⁴ ). In addition, the prepared ceramics exhibit extremely high discharge energy density (4.52 J cm^-3 ) and power density (405.50 MW cm^-3 ). Here, the results demonstrate that the strategy of layered structure design and optimization is promising for enhancing the energy storage performance of lead-free ceramics.

Excellent Energy Storage Properties Achieved in Sodium Niobate-Based Relaxor Ceramics through Doping Tantalum

Lead-free relaxor ferroelectric ceramics are potential for energy storage applications due to their comprehensive energy storage properties. However, the energy efficiency of many relaxor ceramics is not high enough, leading to high Joule heat during the charge-discharge cycles, thus lowering their energy storage performance. In this work, tantalum (Ta) dopants were introduced into sodium niobate-based relaxor ceramics to improve the resistivity and energy efficiency. The leakage current was reduced by Ta doping, especially at the high electric field. The enhanced resistivity is attributed to the increased bandgap induced by Ta doping. The impedance spectroscopy shows that both the grain and grain boundary resistivities are improved in the high temperature region. As a result, the optimal recoverable energy density and energy efficiency are 6.5 J/cm³ and 94% at 450 kV/cm, respectively. In addition, the energy storage properties exhibit satisfactory temperature stability and cycling reliability. All these merits demonstrate that the Ta modified sodium niobate-based relaxor ceramic a potential candidate for high-power energy storage applications.

Ultrahigh Energy-Storage Performances in Lead-free Na0.5Bi0.5TiO3-Based Relaxor Antiferroelectric Ceramics through a Synergistic Design Strategy

Dielectric ceramics with outstanding energy-storage performances are nowadays in great demand for pulsed power electronic systems. Here, we propose a synergistic design strategy to significantly enhance the energy-storage properties of (1 - x)(0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃)-xCaTi_0.75Ta_0.2O₃ solid solution ceramics through introducing polar nanoregions, shifting rhombohedral to tetragonal phase transition below room temperature (stable antiferroelectric characteristic), as well as increasing the band gap in the system. Ultrahigh energy-storage properties with a record value of recoverable energy-storage density W_rec ∼ 9.55 J/cm³ and a high efficiency η ∼ 88% are achieved in Na_0.5Bi_0.5TiO₃-based bulk ceramics with x = 0.24. Moreover, high W_rec (>3.4 J/cm³) and η (>90%) with a variation of less than 6% can be observed in a wide frequency and temperature frequency range of 5-200 Hz and 25-140 °C. Our research result not only indicates the great possibility of Na_0.5Bi_0.5TiO₃-based lead-free compositions to replace lead-based energy-storage ceramics but also gives an effective strategy to design ultrahigh energy-storage performances for eco-friendly ceramics.

Enhanced Energy Density at a Low Electric Field in PVDF-Based Heterojunctions Sandwiched with High Ion-Polarized BTO Films

Inorganic/organic dielectric composites with outstanding energy storage properties at a low electric field possess the advantages of low operating voltage and small probability of failure. Composites filled with two-dimensional inorganic nanosheets have attracted much attention owing to their fewer interfacial defects caused by the agglomeration of fillers. Continuous oxide films with a preferred orientation can play a significant role in enhancing energy storage. The challenge is to prepare large-sized, freestanding, single-crystal, ferroelectric oxide films and to combine them with polymers. In this work, a well-developed water-dissolvent process was used to transfer millimeter-sized (100)-oriented BaTiO₃ (BTO) films. Poly(vinylidene fluoride) (PVDF)-based heterojunctions sandwiched with the single-crystal films were synthesized via the transferring process and an optimized hot-pressing technique. By virtue of high ion displacement polarization and inhibited conductive path formation of single-crystal BTO films, the energy storage density and efficiency of BTO/PVDF heterojunctions reach 1.56 J cm^-3 and 71.2% at a low electric field of 120 MV m^-1, which are much higher than those of pure PVDF and BTO nanoparticles/PVDF composite films, respectively. A finite-element simulation was employed to further confirm the experimental results. This work provides an effective approach to enhance energy storage properties in various polymer-based composites and opens the door to advanced dielectric capacitors.

Local Atomic Configuration in Pristine and A-Site Doped Silver Niobate Perovskite Antiferroelectrics

Antiferroelectrics have attracted increasing research interests in recent years due to both their great potential in energy storage applications and intriguing structural characteristics. However, the links between the electrical properties and structural characteristics of distorted perovskite antiferroelectrics are yet to be fully deciphered. Here, we adopt local-structure methods to elucidate the nanoscale atomic structure of AgNbO₃-based antiferroelectrics and their structural evolution upon La doping. The local structural features including interatomic distance distributions and atomic displacements have been analyzed using neutron small-box pair distribution function (PDF) refinement in conjunction with large-box Reverse Monte Carlo modelling. Our results highlight the correlation of cation displacements in AgNbO₃ and its disruption by the incorporation of La, apparently in corroboration with the observed anomalous dielectric properties. Spatial ordering of cation vacancies is observed in La-doped AgNbO₃ samples, which coordinates with oxygen octahedral tilting to relieve lattice strain. These results provide renewed insights into the atomic structure and antiferroelectric phase instabilities of AgNbO₃ and relevant perovskite materials, further lending versatile opportunities for enhancing their functionalities.

Energy Storage Application of All-Organic Polymer Dielectrics: A Review

With the wide application of energy storage equipment in modern electronic and electrical systems, developing polymer-based dielectric capacitors with high-power density and rapid charge and discharge capabilities has become important. However, there are significant challenges in synergistic optimization of conventional polymer-based composites, specifically in terms of their breakdown and dielectric properties. As the basis of dielectrics, all-organic polymers have become a research hotspot in recent years, showing broad development prospects in the fields of dielectric and energy storage. This paper reviews the research progress of all-organic polymer dielectrics from the perspective of material preparation methods, with emphasis on strategies that enhance both dielectric and energy storage performance. By dividing all-organic polymer dielectrics into linear polymer dielectrics and nonlinear polymer dielectrics, the paper describes the effects of three structures (blending, filling, and multilayer) on the dielectric and energy storage properties of all-organic polymer dielectrics. Based on the above research progress, the energy storage applications of all-organic dielectrics are summarized and their prospects discussed.

Ultrahigh Temperature Lead-Free Film Capacitors via Strain and Dielectric Constant Double Gradient Design

With the development of miniaturization, lightweight and integration of electronic devices, the demand for high-temperature dielectric capacitors is becoming urgent. Nevertheless, the breakdown strength and polarization are deteriorated at high temperatures due to the thermal energy assisting the electron transport and impeding the dipole alignment. Here, a structure of capacitor with double gradients of dielectric constant gradient and strain gradient is designed to achieve high breakdown strength, high working temperature, and high energy storage density simultaneously. It is found that the designed structure of BaHf_0.17 Ti_0.83 O₃ /1mol% SiO₂ doped BaZr_0.35 Ti_0.65 O₃ /0.85BaTiO₃ -0.15Bi(Mg_0.5 Zr_0.5 )O₃ exhibits excellent energy storage performance. The energy storage density of 127.3 J cm^-3 with an energy storage efficiency of 79.6% is realized in the up-sequence multilayer with period N = 2 at room temperature. Moreover, when the working temperature varies from -100 to 200 °C, the energy storage density of the N = 4 capacitor keeps stably at 84.62 J cm^-3 with an energy storage efficiency 78.42% at 6.86 MV cm^-1 . All these properties promise great potential applications of the designed multilayer capacitors with the double gradients in harsh environments, and the design principle can be applicable to other systems to boost working temperature.

Excellent Energy Storage Performance in Bi(Fe0.93Mn0.05Ti0.02)O3 Modified CaBi4Ti4O15 Thin Film by Adjusting Annealing Temperature

Dielectric capacitors with ultrahigh power density are highly desired in modern electrical and electronic systems. However, their comprehensive performances still need to be further improved for application, such as recoverable energy storage density, efficiency and temperature stability. In this work, new lead-free bismuth layer-structured ferroelectric thin films of CaBi₄Ti₄O₁₅-Bi(Fe_0.93Mn_0.05Ti_0.02)O₃ (CBTi-BFO) were prepared via chemical solution deposition. The CBTi-BFO film has a small crystallization temperature window and exhibits a polycrystalline bismuth layered structure with no secondary phases at annealing temperatures of 500–550 °C. The effects of annealing temperature on the energy storage performances of a series of thin films were investigated. The lower the annealing temperature of CBTi-BFO, the smaller the carrier concentration and the fewer defects, resulting in a higher intrinsic breakdown field strength of the corresponding film. Especially, the CBTi-BFO film annealed at 500 °C shows a high recoverable energy density of 82.8 J·cm⁻³ and efficiency of 78.3%, which can be attributed to the very slim hysteresis loop and a relatively high electric breakdown strength. Meanwhile, the optimized CBTi-BFO film capacitor exhibits superior fatigue endurance after 10⁷ charge–discharge cycles, a preeminent thermal stability up to 200 °C, and an outstanding frequency stability in the range of 500 Hz–20 kHz. All these excellent performances indicate that the CBTi-BFO film can be used in high energy density storage applications.

Nonsolid TiOx Nanoparticles/PVDF Nanocomposite for Improved Energy Storage Performance

Nanofiller/polymer nanocomposites are promising dielectrics for energy harvesting to be applied in wearable and flexible electronics. The structural design of the nanofillers plays a vital role to improve the energy storage performance of the related nanocomposites. Here, we fabricate a flexible device based on nonsolid titanium oxide (TiO_x) nanoparticles/poly(vinylidene fluoride) (PVDF) to achieve enhanced energy storage performance at low loading. The room-temperature oxidation method is used to oxidize two-dimensional MXene (Ti₃C₂T_x) flakes to form partially hollow TiO_x nanoparticles. Taking advantage of this structure, the flexible TiO_x nanoparticles/PVDF nanocomposite with an ultralow loading content of 1 wt % nanofillers shows high energy storage performance, including a dielectric constant of ≈22 at 1 kHz, a breakdown strength of ≈480 MV m^-1, and an energy storage density of 7.43 J cm^-3. The finite element simulation further reveals that the optimization of the energy storage performance is ascribed to the lower electric potential among the partially hollow TiO_x nanoparticles, which enhances the breakdown strength of the nanocomposites. This work opens a new avenue to structurally design and fabricate low-loading polymer-based nanocomposites for energy storage applications in next-generation flexible electronics.

Ultrahigh Energy Storage Performance of Flexible BMT-Based Thin Film Capacitors

Ferroelectric thin film capacitors have attracted increasing attention because of their high energy storage density and fast charge-discharge speed, but less attention has been paid to the realization of flexible capacitors for wearable electronics and power systems. In this work, flexible xMn-BiMg_0.5 Ti_0.7 O₃ (xMn-BMT_0.7 ) thin film capacitors with ultrahigh energy storage density and good stability are deposited on mica substrate. The introduction of excess TiO₂ with an amorphous structure contributes to the forming of the polar nano regions, resulting in the reduced ferroelectric hysteresis. In order to further improve the energy storage performance, Mn doping increases the polarization by regulating chemical pressure in the lattices and inhibits the valence change of Ti⁴⁺ . Especially in the 1.5% Mn-BMT_0.7 film capacitor, an ultrahigh energy storage density of 124 J cm^-3 and an outstanding efficiency of 77% are obtained, which is one of the best energy storage performances recorded for ferroelectric capacitors. In addition, the flexible ferroelectric film capacitor also exhibits good thermal stability (25-200 °C), high frequency reliability (500 Hz-10 kHz), excellent electrical (10⁸ cycles), and mechanical (10⁴ cycles) fatigue properties. This work is expected to pave the way for the application of BMT-based thin film capacitors in flexible energy storage systems.

Recent Progress and Future Prospects on All-Organic Polymer Dielectrics for Energy Storage Capacitors

With the development of advanced electronic devices and electric power systems, polymer-based dielectric film capacitors with high energy storage capability have become particularly important. Compared with polymer nanocomposites with widespread attention, all-organic polymers are fundamental and have been proven to be more effective choices in the process of scalable, continuous, and large-scale industrial production, leading to many dielectric and energy storage applications. In the past decade, efforts have intensified in this field with great progress in newly discovered dielectric polymers, fundamental production technologies, and extension toward emerging computational strategies. This review summarizes the recent progress in the field of energy storage based on conventional as well as heat-resistant all-organic polymer materials with the focus on strategies to enhance the dielectric properties and energy storage performances. The key parameters of all-organic polymers, such as dielectric constant, dielectric loss, breakdown strength, energy density, and charge-discharge efficiency, have been thoroughly studied. In addition, the applications of computer-aided calculation including density functional theory, machine learning, and materials genome in rational design and performance prediction of polymer dielectrics are reviewed in detail. Based on a comprehensive understanding of recent developments, guidelines and prospects for the future development of all-organic polymer materials with dielectric and energy storage applications are proposed.

Decoding the Double/Multiple Hysteresis Loops in Antiferroelectric Materials

Antiferroelectric materials has become one of the most promising candidates for pulsed power capacitors. The polarization versus electric-field hysteresis loop is the key electrical property for evaluating their energy-storage performance. Here, we applied in situ biasing transmission electron microscopy to decode two representative energy-storage behaviors-namely, multiple and double hysteresis loops-in (Pb,La)(Zr,Sn,Ti)O₃ system. Simultaneous structural examination and domain/defects observation establish a direct relationship between phase transitions and hysteresis loops. Sustaining a smaller period of modulated structure to a certain applied electric field and then undergoing additional transitions among varying antiferroelectric phases with increasing modulation periods before the final antiferroelectric-ferroelectric transition leads to the favorable multiple-loop configuration that realizes a high energy-storage performance. Such phenomenon is described by a model in terms of defect-driven phase transition. The distinctive mechanisms of multiple phase transition will inspire future composition-design for high switch-fielding antiferroelectric materials.

Recent Advances in Multilayer-Structure Dielectrics for Energy Storage Application

An electrostatic capacitor has been widely used in many fields (such as high pulsed power technology, new energy vehicles, etc.) due to its ultrahigh discharge power density. Remarkable progress has been made over the past 10 years by doping ferroelectric ceramics into polymers because the dielectric constant is positively correlated with the energy storage density. However, this method often leads to an increase in dielectric loss and a decrease in energy storage efficiency. Therefore, the way of using a multilayer structure to improve the energy storage density of the dielectric has attracted the attention of researchers. Although research on energy storage properties using multilayer dielectric is just beginning, it shows the excellent effect and huge potential. In this review, the main physical mechanisms of polarization, breakdown and energy storage in multilayer structure dielectric are introduced, the theoretical simulation and experimental results are systematically summarized, and the preparation methods and design ideas of multilayer structure dielectrics are mainly described. This article covers not only an overview of the state-of-the-art advances of multilayer structure energy storage dielectric but also the prospects that may open another window to tune the electrical performance of the electrostatic capacitor via designing a multilayer structure.

Structural evolution and dielectric properties of biaxially oriented polyethylene/multiwalled carbon nanotube composite films

In modern power systems, polymer nanocomposite films have been more frequently used as dielectric materials for capacitors. However, the low energy storage density limits its application in more areas. It is a very challenging task to prepare dielectric films with high dielectric constant (ε), high energy storage density, and low dielectric loss (tan δ) at the same time. In this study, one kind of BOPE (biaxially oriented polyethylene) nanocomposite dielectric films with a very small amount of MWCNTs (multiwalled carbon nanotubes) was reported. MWCNTs with a high aspect ratio were used for conductive filler, and the formation of more micro capacitors and interfacial polarization were caused by better dispersibility of MWCNTs in polyethylene matrix by biaxial stretching. The BOPE/MWCNT composite films with high-performance were successfully prepared by achieving the requirements of low content, high dielectric constant and high energy storage density while maintaining the advantages of low dielectric loss of the polymer matrix. The dielectric constant of the BOPE/MWCNT composite films increased from 2.26 to 4.68 with the drawing ratio was 4 × 4 and the content of MWCNTs was 0.6 wt% and the energy storage density was also increased from 1.01 J cm^-3 to 1.29 J cm^-3. From our work, the achievement of low thickness, high energy density and low loss at the same time implied BOPE/MWCNT composite films were promising materials for next-generation film capacitors.

Nanocomposite and bio-nanocomposite polymeric materials/membranes development in energy and medical sector: A review

Nanocomposite and bio-nanocomposite polymer materials/membranes have fascinated prominent attention in the energy as well as the medical sector. Their composites make them appropriate choices for various applications in the medical, energy and industrial sectors. Composite materials are subject of interest in the polymer industry. Different kinds of fillers, such as cellulose-based fillers, carbon black, clay nanomaterials, glass fibers, ceramic nanomaterial, carbon quantum dots, talc and many others have been incorporated into polymers to improve the quality of the final product. These results are dependent on a variety of factors; however, nanoparticle dispersion and distribution are major obstacles to fully using nanocomposites/bio-nanocomposites materials/membranes in various applications. This review examines the various nanocomposite and bio-nanocomposite materials applications in the energy and medical sector. The review also covers the variety of ways for increasing nanocomposite and bio-nanocomposite materials features, each with its own set of applications. Recent researches on composite materials have shown that polymeric nanocomposites and bio-nanocomposites are promising materials that have been intensively explored for many applications that include electronics, environmental remediation, energy, sensing (biosensor) and energy storage devices among other applications. In this review, we studied various nanocomposite and bio-nanocomposite materials, their controlling parameters to develop the product and examine their features and applications in the fields of energy and the medical sector.

Large polarization and record-high performance of energy storage induced by a phase change in organic molecular crystals

Dielectrics that undergo electric-field-induced phase changes are promising for use as high-power electrical energy storage materials and transducers. We demonstrate the stepwise on/off switching of large polarization in a series of dielectrics by flipping their antipolar or canted electric dipoles via proton transfer and inducing simultaneous geometric changes in their π-conjugation system. Among antiferroelectric organic molecular crystals, the largest-magnitude polarization jump was obtained as 18 μC cm⁻² through revisited measurements of squaric acid (SQA) crystals with improved dielectric strength. The second-best polarization jump of 15.1 μC cm⁻² was achieved with a newly discovered antiferroelectric, furan-3,4-dicarboxylic acid. The field-induced dielectric phase changes show rich variations in their mechanisms. The quadruple polarization hysteresis loop observed for a 3-(4-chlorophenyl)propiolic acid crystal was caused by a two-step phase transition with moderate polarization jumps. The ferroelectric 2-phenylmalondialdehyde single crystal having canted dipoles behaved as an amphoteric dielectric, exhibiting a single or double polarization hysteresis loop depending on the direction of the external field. The magnitude of a series of observed polarizations was consistently reproduced within the simplest sublattice model by the density functional theory calculations of dipole moments flipping over a hydrogen-bonded chain or sheet (sublattice) irrespective of compounds. This finding guarantees a tool that will deepen our understanding of the microscopic phase-change mechanisms and accelerate the materials design and exploration for improving energy-storage performance. The excellent energy-storage performance of SQA was demonstrated by both a high recoverable energy-storage density W_r of 3.3 J cm⁻³ and a nearly ideal efficiency (90%). Because of the low crystal density, the corresponding energy density per mass (1.75 J g⁻¹) exceeded those derived from the highest W_r values (∼8–11 J cm⁻³) reported for several bulk antiferroelectric ceramics , without modification to relaxor forms.

Electric-field induced phase changes, which are promising for use in high-power electrical energy storage, can be realized in a series of organic dielectrics by flipping the antipolar or canted electric dipoles via proton transfer.

An Overview of Linear Dielectric Polymers and Their Nanocomposites for Energy Storage

As one of the most important energy storage devices, dielectric capacitors have attracted increasing attention because of their ultrahigh power density, which allows them to play a critical role in many high-power electrical systems. To date, four typical dielectric materials have been widely studied, including ferroelectrics, relaxor ferroelectrics, anti-ferroelectrics, and linear dielectrics. Among these materials, linear dielectric polymers are attractive due to their significant advantages in breakdown strength and efficiency. However, the practical application of linear dielectrics is usually severely hindered by their low energy density, which is caused by their relatively low dielectric constant. This review summarizes some typical studies on linear dielectric polymers and their nanocomposites, including linear dielectric polymer blends, ferroelectric/linear dielectric polymer blends, and linear polymer nanocomposites with various nanofillers. Moreover, through a detailed analysis of this research, we summarize several existing challenges and future perspectives in the research area of linear dielectric polymers, which may propel the development of linear dielectric polymers and realize their practical application.

Frequency stable dielectric constant with reduced dielectric loss of one-dimensional ZnO-ZnS heterostructures

The synthesis of one-dimensional heterostructures having high dielectric constant and low dielectric loss has remained a great challenge. Until now, the dielectric performance of ZnO-ZnS heterostructures was scarcely investigated. In this work, large-scale ZnO-ZnS heterostructures were synthesized by employing the chemical vapor deposition method. High resolution transmission electron microscopy (HRTEM) confirms the formation of heterostructures. X-ray photoelectron spectroscopy (XPS) shows that S atoms fill up the oxygen vacancy (V_O) in ZnO, leading to the suppression of charge carrier's movement from ZnO to ZnS; instead there is charge transfer from ZnS to ZnO. Conductivity mismatch between adjacent ZnO and ZnS materials leads to the accumulation of free charges at the interface of the heterostructure and can be considered as a capacitor-like structure. The electrical behaviors of the potential phases of ZnO, ZnS and the ZnO-ZnS heterostructure are well interpreted by a best fitted equivalent circuit model. Each heterostructure acts as a polarization node with a specific flip-flop frequency and all such nodes form continuous transmission of polarization, which jointly increase the dielectric energy-storage performance. The orientational polarization of the polarons and Zn²⁺-V_O dipoles present at the heterostructure interface contributes to the frequency stable dielectric constant at ≥10³ Hz. Our findings provide a systematic approach to tailor the electronic transport and dielectric properties at the interface of the heterostructure. We suggest that this approach can be extended for improving the energy harvesting, transformation and storage capabilities of the nanostructures for the development of high-performance energy-storage devices.

Molecular Dynamics Simulation on Structure and Dielectric Permittivity of BaTiO3/PVDF Composites

Molecular dynamics (MD) simulation was performed to investigate the structure and dielectric permittivity of poly(vinylidene fluoride)- (PVDF-) based composites with different contents of barium titanate (BT). The β-phase PVDF model with 100 structural units and the spherical BT particle model with a radius of 0.495 nm were built and applied in the initial models with three PVDF macromolecular chains and BT particles for the MD simulations of the BT/PVDF composites. The influences of BT content on the morphological structure, the free volume fraction, and glass transition temperature of the composites were explored according to the simulated results and the experimental ones of X-ray diffraction (XRD) and scanning electron microscope (SEM). A model was proposed to predict the static dielectric permittivity of the composites, the results of which were compared with the Cole-Cole fitting results of dielectric spectroscopy. Attempts were made to reveal the structure evolution and the micropolarization mechanism with the increasing content of BT.

Challenges and Opportunities of Polymer Nanodielectrics for Capacitive Energy Storage

With the modern development of power electrification, polymer nanocomposite dielectrics (or nanodielectrics) have attracted significant research attention. The idea is to combine the high dielectric constant of inorganic nanofillers and the high breakdown strength/low loss of a polymer matrix for higher energy density polymer film capacitors. Although impressively high energy density has been achieved at the laboratory scale, there is still a large gap from the eventual goal of polymer nanodielectric capacitors. In this review, we focus on essential material issues for two types of polymer nanodielectrics, polymer/conductive nanoparticle and polymer/ceramic nanoparticle composites. Various material design parameters, including dielectric constant, dielectric loss, breakdown strength, high temperature rating, and discharged energy density will be discussed from both fundamental science and high-voltage capacitor application points of view. The objective is to identify advantages and disadvantages of the polymer nanodielectric approach against other approaches utilizing neat dielectric polymers and ceramics. Given the state-of-the-art understanding, future research directions are outlined for the continued development of polymer nanodielectrics for electric energy storage applications.

Energy Storage Ceramics: A Bibliometric Review of Literature

Energy storage ceramics is among the most discussed topics in the field of energy research. A bibliometric analysis was carried out to evaluate energy storage ceramic publications between 2000 and 2020, based on the Web of Science (WOS) databases. This paper presents a detailed overview of energy storage ceramics research from aspects of document types, paper citations, h-indices, publish time, publications, institutions, countries/regions, research areas, highly cited papers, and keywords. A total of 3177 publications were identified after retrieval in WOS. The results show that China takes the leading position in this research field, followed by the USA and India. Xi An Jiao Tong Univ has the most publications, with the highest h-index. J.W. Zhai is the most productive author in energy storage ceramics research. Ceramics International, Journal of Materials Science-Materials in Electronics, and the Journal of Alloys and Compounds are the most productive journals in this field, and materials science—multidisciplinary is the most frequently used subject category. Keywords, highly cited papers, and the analysis of popular papers indicate that, in recent years, lead-free ceramics are prevalent, and researchers focus on fields such as the microstructure, thin films, and phase transition of ceramics.

Effect of the Na2O-Nb2O5-P2O5 glass additive on the structure, dielectric and energy storage performances of sodium niobate ceramics

A phosphate glass Na₂O–Nb₂O₅–P₂O₅ (NPP) is incorporated into NaNbO₃ (NN) ceramics to examine its impact on the density, rearrangement of structural units, dielectric and energy storage features of the elaborated composites. The sodium niobate ceramic (NN) is prepared using the solid state process, whereas, the Na₂O–Nb₂O₅–P₂O₅ (NPP) glasses are produced using the method of conventional melt quenching. The glass (NPP) is added to the ceramic (NN) according to the composition (100-x) NN-xNNP; (x = 0, 2.5, 5, and 7.5 %wt). The developed composites are denoted as NN-Gx where x represents the content of glass in %wt. The appropriate sintering temperature for the glass-ceramic composites was measured based on the density measurements. It was found that with the addition of glass, their density was decreased and their fritting at lower temperatures was enhanced. The obtained SST for all composites is about 900 °C. After the densification stage, Raman spectroscopy, X-ray Diffraction, Granulo-laser analysis, and scanning electron microscopy are examined to study the structural approach and the morphology of sintered NN-Gx composites. The NN-G5 composite was found to have a fine grain microstructure that was uniform. The dielectric features of the composite revealed that at ambient temperature the NN-G5 had the greatest dielectric constant. The energy storage performance of the composite was investigated from the P-E plots and the parameters of energy storage. Based on the obtained results, it was concluded that incorporating up to 5% wt. of NNP glass in sodium niobate ceramics positively affects their dielectric and energy storage performances.

Dielectric polymers for high-temperature capacitive energy storage

Polymers are the preferred materials for dielectrics in high-energy-density capacitors. The electrification of transport and growing demand for advanced electronics require polymer dielectrics capable of operating efficiently at high temperatures. In this review, we critically analyze the most recent development in the dielectric polymers for high-temperature capacitive energy storage applications. While general design considerations are discussed, emphasis is placed on the elucidation of the structural dependence of the high-field dielectric and electrical properties and the capacitive performance, including discharged energy density, charge-discharge efficiency and cyclability, of dielectric polymers at high temperatures. Advantages and limitations of current approaches to high-temperature dielectric polymers are summarized. Challenges along with future research opportunities are highlighted at the end of this article.

Electroceramics for High-Energy Density Capacitors: Current Status and Future Perspectives

Materials exhibiting high energy/power density are currently needed to meet the growing demand of portable electronics, electric vehicles and large-scale energy storage devices. The highest energy densities are achieved for fuel cells, batteries, and supercapacitors, but conventional dielectric capacitors are receiving increased attention for pulsed power applications due to their high power density and their fast charge-discharge speed. The key to high energy density in dielectric capacitors is a large maximum but small remanent (zero in the case of linear dielectrics) polarization and a high electric breakdown strength. Polymer dielectric capacitors offer high power/energy density for applications at room temperature, but above 100 °C they are unreliable and suffer from dielectric breakdown. For high-temperature applications, therefore, dielectric ceramics are the only feasible alternative. Lead-based ceramics such as La-doped lead zirconate titanate exhibit good energy storage properties, but their toxicity raises concern over their use in consumer applications, where capacitors are exclusively lead free. Lead-free compositions with superior power density are thus required. In this paper, we introduce the fundamental principles of energy storage in dielectrics. We discuss key factors to improve energy storage properties such as the control of local structure, phase assemblage, dielectric layer thickness, microstructure, conductivity, and electrical homogeneity through the choice of base systems, dopants, and alloying additions, followed by a comprehensive review of the state-of-the-art. Finally, we comment on the future requirements for new materials in high power/energy density capacitor applications.

Enhanced dielectric properties and thermostability in polyimide composites with core-shell structured polyimide@BaTiO3 nanoparticles

Polymer composites with high dielectric constant and thermal stability have shown great potential applications in the fields relating to the energy storage. Herein, core-shell structured polyimide@BaTiO3 (PI@BT) nanoparticles were fabricated via in-situ polymerization of poly(amic acid) (PAA) and the following thermal imidization, then utilized as fillers to prepare PI composites. Increased dielectric constant with suppressed dielectric loss, and enhanced energy density as well as heat resistance were simultaneously realized due to the presence of PI shell between BT nanoparticles and PI matrix. The dielectric constant of PI@BT/PI composites with 55 wt% fillers increased to 15.0 at 100 Hz, while the dielectric loss kept at low value of 0.0034, companied by a high energy density of 1.32 J·cm−3, which was 2.09 times higher than the pristine PI. Moreover, the temperature at 10 wt% weight loss reached 619°C, demonstrating the excellent thermostability of PI@BT/PI composites. In addition, PI@BT/PI composites exhibited improved breakdown strength and toughness as compared with the BT/PI composites due to the well dispersion of PI@BT nanofillers and the improved interfacial interactions between nanofillers and polymer matrix. These results provide useful information for the structural design of high-temperature dielectric materials.

Strategies to Improve the Energy Storage Properties of Perovskite Lead-Free Relaxor Ferroelectrics: A Review

Electrical energy storage systems (EESSs) with high energy density and power density are essential for the effective miniaturization of future electronic devices. Among different EESSs available in the market, dielectric capacitors relying on swift electronic and ionic polarization-based mechanisms to store and deliver energy already demonstrate high power densities. However, different intrinsic and extrinsic contributions to energy dissipations prevent ceramic-based dielectric capacitors from reaching high recoverable energy density levels. Interestingly, relaxor ferroelectric-based dielectric capacitors, because of their low remnant polarization, show relatively high energy density and thus display great potential for applications requiring high energy density properties. In this study, some of the main strategies to improve the energy density properties of perovskite lead-free relaxor systems are reviewed, including (i) chemical modification at different crystallographic sites, (ii) chemical additives that do not target lattice sites, and (iii) novel processing approaches dedicated to bulk ceramics, thick and thin films, respectively. Recent advancements are summarized concerning the search for relaxor materials with superior energy density properties and the appropriate choice of both composition and processing routes to match various applications' needs. Finally, future trends in computationally-aided materials design are presented.

Remarkable capacitive performance in novel tungsten bronze ceramics

In this study, novel lead-free Sr_1.75Ca_0.25NaNb₅O₁₅ tungsten bronze ceramics were designed for potential energy storage applications. A remarkable energy storage density (∼3.23 J cm^-3) along with a high energy storage efficiency (∼88.2%) was obtained simultaneously at an applied electric field of 290 kV cm^-1. Moreover, the ceramic also showed exceptional discharging performance including a fast discharge rate (τ_0.9 < 70 ns), an ultrahigh discharge current density (1104 A cm^-2) and a high power density (82.8 MW cm^-3). The achieved capacitive performance in this work indicates the great potential of the designed novel tungsten bronze ceramic for energy storage applications.

Mapping the Space Charge at Nanoscale in Dielectric Polymer Nanocomposites

Heterogeneous dielectric materials such as dielectric polymer nanocomposites have attracted extensive attention because of their exceptional insulating and dielectric performance, which originates from the unique space charge dynamics associated with the various interfacial regions. However, the space charge distribution and transport in polymer nanocomposites remain elusive due to the lack of analytical methods that can precisely probe the charge profile at the nanoscale resolution. Although a few studies have explored the possibility of using scanning probe techniques for characterizing the local charge distribution, the interference from induced electrical polarization of the material has been unfortunately ignored, leading to inaccurate results. In this contribution, we report an open-loop Kelvin probe force microscopy (KPFM) method with nanoscale resolution for the direct detection of the space charge profile in dielectric polymer nanocomposites. Unlike the conventional studies where a vertical direct current (DC) voltage is applied on the sample through the probe to evoke the charge injection and transport in dielectric polymer nanocomposites, the present method is established based on a delicate electrode configuration where a lateral electric field is allowed to be applied on the sample during the KPFM test. This special testing configuration enables real-time charge injection and transport without inducing the electrical polarization of material along the vertical direction, which gives rise to clean mapping of space charges and reveals the interfacial charge trapping in polymer nanocomposites. This work provides a robust and reliable method for studying the sophisticated charge transport properties associated with the various interfacial regions in heterogeneous dielectric materials.

Dielectric films for high performance capacitive energy storage: multiscale engineering

Dielectric capacitors are fundamental components in electronic and electrical systems due to their high-rate charging/discharging character and ultrahigh power density. Film dielectrics possess larger breakdown strength and higher energy density than their bulk counterparts, holding great promise for compact and efficient power systems. In this article, we review the very recent advances in dielectric films, in the framework of engineering at multiple scales to improve energy storage performance. Strategies are summarized including atomic-scale defect control, nanoscale domain and grain engineering, as well as mesoscale composite design. Challenges and remaining concerns are also discussed for further performance improvement and practical application of dielectric films.

Constructing phase boundary in AgNbO3 antiferroelectrics: pathway simultaneously achieving high energy density and efficiency

Dielectric capacitors with high energy storage density (W_rec) and efficiency (η) are in great demand for high/pulsed power electronic systems, but the state-of-the-art lead-free dielectric materials are facing the challenge of increasing one parameter at the cost of the other. Herein, we report that high W_rec of 6.3 J cm^-3 with η of 90% can be simultaneously achieved by constructing a room temperature M2-M3 phase boundary in (1-x)AgNbO₃-xAgTaO₃ solid solution system. The designed material exhibits high energy storage stability over a wide temperature range of 20-150 °C and excellent cycling reliability up to 10⁶ cycles. All these merits achieved in the studied solid solution are attributed to the unique relaxor antiferroelectric features relevant to the local structure heterogeneity and antiferroelectric ordering, being confirmed by scanning transmission electron microscopy and synchrotron X-ray diffraction. This work provides a good paradigm for developing new lead-free dielectrics for high-power energy storage applications.

Multiscale structural engineering of dielectric ceramics for energy storage applications: from bulk to thin films

Dielectric capacitors with the prominent features of ultrafast charging-discharging rates and ultrahigh power densities are ubiquitous components in modern electronics. To meet the growing demand for electronics miniaturization, dielectric capacitors with high energy storage properties are extensively researched. Here we present an overview of the recent progress in the engineering of multiscale structures of dielectric ceramics ranging from bulk to thin films. This article commences with a brief introduction of the fundamentals of dielectric ceramics, including primary parameters, a library of dielectric ceramics, and multiscale structures. Emphases are placed on the relationship between multiscale structures and energy storage properties and the rational structure design principles in dielectric ceramics. Also included are currently available multilayer ceramic capacitors based on multiscale engineered ceramic structures. Finally, challenges along with opportunities for further research and development of high-performance dielectric ceramics for electrostatic energy storage are highlighted.

Unveiling the ferrielectric nature of PbZrO3-based antiferroelectric materials

Benefitting from the reversible phase transition between antiferroelectric and ferroelectric states, antiferroelectric materials have recently received widespread attentions for energy storage applications. Antiferroelectric configuration with specific antiparallel dipoles has been used to establish antiferroelectric theories and understand its characteristic behaviors. Here, we report that the so-called antiferroelectric (Pb,La)(Zr,Sn,Ti)O₃ system is actually ferrielectric in nature. We demonstrate different ferrielectric configurations, which consists of ferroelectric ordering segments with either magnitude or angle modulation of dipoles. The ferrielectric configurations are mainly contributed from the coupling between A-cations and O-anions, and their displacement behavior is dependent largely on the chemical doping. Of particular significance is that the width and net polarization of ferroelectric ordering segments can be tailored by composition, which is linearly related to the key electrical characteristics, including switching field, remanent polarization and dielectric constant. These findings provide opportunities for comprehending structure-property correlation, developing antiferroelectric/ferrielectric theories and designing novel ferroic materials.

The large family PbZrO₃-based solid solutions are usually considered as antiferroelectric materials with specific antiparallel polarization configuration. Here, the authors demonstrate the PbZrO₃-based material has ferrielectric dipoles ordering and configure a clear structure-property relationship.

Structural Distortion and Dielectric Permittivities of KCoO2-Type Layered Nitrides Ca1-xSrxTiN2

Among the KCoO₂-type phases, the orthorhombic layered nitride CaTiN₂ is a newly reported high dielectric permittivity material (ε_r ∼ 1300-2500 within 10⁴-10⁶ Hz from 80 to 450 K) while the tetragonal SrTiN₂ is reported to display an unintentional metallic conduction property. In this work, a Ca_1-xSr_xTiN₂ solid solution was synthesized, in which the insulating SrTiN₂ end member and some Sr-doped CaTiN₂ samples were successfully obtained, and therefore, the dielectric properties of the Ca_1-xSr_xTiN₂ solid solution were investigated. The Sr substitution for Ca drove an orthorhombic-to-tetragonal phase transformation in Ca_1-xSr_xTiN₂, which reduced the dielectric permittivity significantly. The tetragonal SrTiN₂ displays a much lower dielectric permittivity (ε_r ∼ 20-70 in 10⁵-10⁶ Hz and 10-300 K) than that of CaTiN₂. The comparison on the dielectric permittivities and structures of CaTiN₂ and SrTiN₂ indicates that the structural distortion arising from the splitting of N planes between Ti layers within the TiN₂ pyramidal layers could be a plausible structural origin of the high bulk dielectric permittivity of CaTiN₂.

Ultrahigh capacitive energy density in ion-bombarded relaxor ferroelectric films

Dielectric capacitors can store and release electric energy at ultrafast rates and are extensively studied for applications in electronics and electric power systems. Among various candidates, thin films based on relaxor ferroelectrics, a special kind of ferroelectric with nanometer-sized domains, have attracted special attention because of their high energy densities and efficiencies. We show that high-energy ion bombardment improves the energy storage performance of relaxor ferroelectric thin films. Intrinsic point defects created by ion bombardment reduce leakage, delay low-field polarization saturation, enhance high-field polarizability, and improve breakdown strength. We demonstrate energy storage densities as high as ~133 joules per cubic centimeter with efficiencies exceeding 75%. Deterministic control of defects by means of postsynthesis processing methods such as ion bombardment can be used to overcome the trade-off between high polarizability and breakdown strength.

Effective Strategy to Achieve Excellent Energy Storage Properties in Lead-Free BaTiO3-Based Bulk Ceramics

Although extensive studies have been done on lead-free dielectric ceramics to achieve excellent dielectric behaviors and good energy storage performance, the major problem of low energy density has not been solved so far. Here, we report on designing the crossover relaxor ferroelectrics (CRFE), a crossover region between the normal ferroelectrics and relaxor ferroelectrics, as a solution to overcome the low energy density. CRFE exhibits smaller free energy and lower defect density in the modified Landau theory, which helps to obtain ultrahigh energy density and efficiency. The (1-x)Ba_0.65Sr_0.35TiO₃-xBi(Mg_2/3Nb_1/3)O₃ ((1-x)BST-xBMN) (x = 0, 0.08, 0.1, 0.18, 0.2) ceramic was synthesized by a solid-state reaction method. The solid solutions exhibit dielectric frequency dispersion, which suggests typical relaxor characteristics with the increasing BMN content. The crossover ferroelectrics of 0.9BST-0.1BMN ceramic possesses a high energy storage efficiency (η) of 85.71%, a high energy storage density (W) of 3.90 J/cm³, and an ultrahigh recoverable energy storage density (W_rec) of 3.34 J/cm³ under a dielectric breakdown strength of 400 kV/cm and is superior to other lead-free BaTiO₃ (BT)-based energy storage ceramics. It also exhibits strong thermal stability in the temperature range from 25 to 150 °C under an electric field of 300 kV/cm, with the fluctuations below 3% and with the energy storage density and energy efficiency at about 2.8 J/cm³ and 82.93%, respectively. The enhanced recoverable energy density and breakdown strength of BT-based materials with significantly high energy efficiency make it a promising candidate to meet the wide requirements for high power applications.