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

High energy capability in poly(vinylidene fluoride-co-chlorotrifluoroethylene) nanocomposite incorporated with Ag@polyaniline@covalent organic framework core-shell nanowire

The development of polymer film with large electrical displacement is essential for the applications of lightweight and compact energy storage. The dielectric diversity at interface of polymer composite should be addressed to realize the film capacitor with high energy density and dielectric reliability. In this work, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite was incorporated by core-shell nanowire with covalent organic framework (COF) outer coating to alleviate the dielectric mismatch at interface. After the preparation of Ag nanowire through polyol reduction, polyaniline (PANI) and COF layers were sequentially deposited to construct core-shell Ag@polyaniline@covalent organic framework (Ag@PANI@COF) nanowire. According to the unique core-shell architecture, the COF framework is utilized to suppress the remanent polarization while high electrical displacement is preserved by the center Ag nanowire. The maximum energy density of 25.0 J/cm3 at 425 MV/m is obtained in 0.1 wt% stretched Ag@PANI@COF/P(VDF-CTFE) nanocomposite. The presence of core-shell nanowire depresses the distribution distortion of electric field and the diffusion of charge carriers under high field. This work demonstrates an effective method to develop the polymer film with large electrical displacement, and sheds a light on insightful exploration of interfacial polarized mechanism in polymer dielectric composite.

Strong Local Polarization Fluctuations Enabled High Electrostatic Energy Storage in Pb-Free Relaxors

Electrostatic energy-storage ceramic capacitors are essential components of modern electrified power systems. However, improving their energy-storage density while maintaining high efficiency to facilitate cutting-edge miniaturized and integrated applications remains an ongoing challenge. Herein, we report a record-high energy-storage density of 20.3 J cm-3 together with a high efficiency of 89.3% achieved by constructing a relaxor ferroelectric state with strongly enhanced local polarization fluctuations. This is realized by incorporating highly polarizable, heterovalent, and large-sized Zn and Nb ions into a Bi0.5Na0.5TiO3-BaTiO3 ferroelectric matrix with very strong tetragonal distortion. Element-specific local structure analysis revealed that the foreign ions strengthen the magnitude of the unit-cell polarization vectors while simultaneously reducing their orientation anisotropy and forming strong fluctuations in both magnitude and orientation within 1-3 nm polar clusters. This leads to a particularly high polarization variation (ΔP) of 72 μC cm-2, low hysteresis, and a high effective polarization coefficient at a high breakdown strength of 80 kV mm-1. This work has surpassed the current energy density limit of 20 J cm-3 in bulk Pb-free ceramics and has demonstrated that controlling the local structure via the chemical composition design can open up new possibilities for exploring relaxors with high energy-storage performance.

Ceramic-Based Dielectric Materials for Energy Storage Capacitor Applications

Materials offering high energy density are currently desired to meet the increasing demand for energy storage applications, such as pulsed power devices, electric vehicles, high-frequency inverters, and so on. Particularly, ceramic-based dielectric materials have received significant attention for energy storage capacitor applications due to their outstanding properties of high power density, fast charge-discharge capabilities, and excellent temperature stability relative to batteries, electrochemical capacitors, and dielectric polymers. In this paper, we present fundamental concepts for energy storage in dielectrics, key parameters, and influence factors to enhance the energy storage performance, and we also summarize the recent progress of dielectrics, such as bulk ceramics (linear dielectrics, ferroelectrics, relaxor ferroelectrics, and anti-ferroelectrics), ceramic films, and multilayer ceramic capacitors. In addition, various strategies, such as chemical modification, grain refinement/microstructure, defect engineering, phase, local structure, domain evolution, layer thickness, stability, and electrical homogeneity, are focused on the structure-property relationship on the multiscale, which has been thoroughly addressed. Moreover, this review addresses the challenges and opportunities for future dielectric materials in energy storage capacitor applications. Overall, this review provides readers with a deeper understanding of the chemical composition, physical properties, and energy storage performance in this field of energy storage ceramic materials.

Optimization of switching charge and recoverable energy density mediated by structural transformation in Sr-substituted BaNiO3 perovskites

Because of their distinctive characteristics, ferroelectric perovskites are considered among the most potent and auspicious candidates for energy storage and pulsed power devices. But their energy storage properties and switching capabilities need to be further enhanced which can be done by substitutions of appropriate cations. Hence, a series of lead-free Ba1-xSrxNiO3 (x = 0.00, 0.33, 0.67, and 1.00) ceramics was fabricated using a sol-gel auto combustion technique. Rietveld's refinement of X-ray diffraction plots verified the complete development of the required hexagonal perovskite structure. Scanning electron microscopy images revealed a gradual increase in average grain sizes and agglomeration with the increase in Sr-content. Moreover, the existence of all the constituent elements exactly in proportion to their stoichiometric ratios was verified by energy dispersive X-ray spectroscopy. The characteristic parameters of ferroelectric materials such as ferroelectric response, electrical conductivity, and switching charge density were also determined. The P-E loops indicated that with the increase in Sr-content, the coercive field, remanent polarization, and maximum polarization all decreased gradually, but the recoverable energy density (Wrec) increased as the loops became slimmer. The maximum value of Wrec was found in the Ba0.33Sr0.67NiO3 sample. Moreover, SrNiO3 exhibited minimum energy loss with the highest efficiency of ∼47.21%. The existence of a current barrier in all the samples was proved from the low leakage current values (∼10-7 A). In addition, the pure SrNiO3 showed a low electrical conductivity and minimum value of switching charge density. All these findings make SrNiO3 a promising candidate for fast switching and energy storage applications.

Ultrahigh Energy Storage Density and Efficiency in Orthorhombic PLZST Antiferroelectric Ceramics via Composition Regulation

PbZrO3-based antiferroelectric (AFE) ceramic materials have emerged as potential candidates for the next generation of high-energy multilayer ceramic capacitors (MLCCs) because of their distinctive characteristics of double hysteresis loops. The energy storage efficiency of orthorhombic AFE ceramics with ultrahigh storage density is relatively low, which hinders their practical application. In this study, the low efficiency limit of PLZST-based orthorhombic ceramics was overcome by precisely adjusting the Sn4+ content in the (Pb0.95Ca0.02La0.02)(Zr0.99-xSnxTi0.01)O3 AFE ceramics. On one hand, the addition of Sn4+ disrupts the original long-range dipole and improves the rapid response of polarization reversal under the applied voltage. As a result, the difference in electric hysteresis under an electric field is reduced, leading to a significant improvement in energy storage efficiency. On the other hand, increasing the Sn4+ content suppresses the formation of oxygen vacancies, inhibiting grain growth and strengthening grain bonding. This results in ceramics with a high breakdown field strength. Ultimately, the resulting PLCZST ceramics reveal an expressively improved recoverable energy density of 10.2 J cm-3 together with a high energy efficiency of 91.4% under a high applied electric field of 560 kV cm-1. The present study demonstrates the tunability of performance in orthorhombic PLZST AFE ceramics, thereby introducing a ceramic material with exceptional energy storage capabilities for MLCC applications.

Significantly Enhanced Energy Density of Polyvinylidene Fluoride/Polyimide-Based Nanocomposites by Core-Shell BaTiO3@SiO2

Improving the limited energy storage capacity of dielectric materials has long been an attractive challenge. In this work, a four-phase hybridized nanocomposite was designed. The linear polymer polyimide (PI) was added to the ferroelectric polymer polyvinylidene fluoride (PVDF) and compounded with a nanoceramic BT@SiO2 with a core-shell structure. The results show that PVDF-PI/BT@SiO2 nanocomposites prepared by a straightforward spin-coating method have a significantly increased discharge energy density. The polymer blends obtain a tightly extended conformation in the amorphous region. Also, this provides an excellent matrix environment for the homogeneous dispersion of fillers. The core-shell structure, as a physical barrier, not only hinders the expansion of the breakdown path but also extends multiple polarization surfaces with gradient variations at the microscopic level. Therefore, the synergistic effect generated by polymer blending and core-shell structure effectively enhances the dielectric and stored energy characteristics of nanocomposites. The dielectric constant is stable at 11.39-18.7, and the dielectric loss is always lower than 0.136. The discharge energy density is 2.5 J/cm3, almost 110% higher than that of the BOPP films (about 1.2 J/cm3). These experimental results suggest that the composite system using core-shell structure and polymer blending is a new way to improve the energy density of dielectric materials.

Renewing Halogen Substitution Strategy for the Rational Design of High-Curie Temperature Metal-Free Molecular Antiferroelectrics

Metal-free molecular antiferroelectric (AFE) holds a promise for energy storage on account of its unique physical attributes. However, it is challenging to explore high-curie temperature (Tc) molecular AFEs, due to the lack of design strategies regarding the rise of phase transition energy barriers. By renewing the halogen substitution strategy, we have obtained a series of high-Tc molecular AFEs of the halogen-substituted phenethylammonium bromides (x-PEAB, x=H/F/Cl/Br), resembling the binary stator-rotator system. Strikingly, the p-site halogen substitution of PEA+ cationic rotators raises their phase transition energy barrier and greatly enhances Tc up to ~473 K for Br-PEAB, on par with the record-high Tc values for molecular AFEs. As a typical case, the member 4-fluorophenethylammonium bromide (F-PEAB) shows notable AFE properties, including high Tc (~374 K) and large electric polarization (~3.2 μC/cm2). Further, F-PEAB also exhibits a high energy storage efficiency (η) of 83.6 % even around Tc, catching up with other AFE oxides. This renewing halogen substitution strategy in the molecular AFE system provides an effective way to design high-Tc AFEs for energy storage devices.

Field-Induced Antiferroelectric-Ferroelectric Transformation in Organometallic Perovskite Displaying Giant Negative Electrocaloric Effect

Antiferroelectric materials with an electrocaloric effect (ECE) have been developed as promising candidates for solid-state refrigeration. Despite the great advances in positive ECE, reports on negative ECE remain quite scarce because of its elusive physical mechanism. Here, a giant negative ECE (maximum ΔS ∼ -33.3 J kg-1 K-1 with ΔT ∼ -11.7 K) is demonstrated near room temperature in organometallic perovskite, iBA2EA2Pb3I10 (1, where iBA = isobutylammonium and EA = ethylammonium), which is comparable to the greatest ECE effects reported so far. Moreover, the ECE efficiency ΔS/ΔE (∼1.85 J cm kg-1 K-1 kV-1) and ΔT/ΔE (∼0.65 K cm kV-1) are almost 2 orders of magnitude higher than those of classical inorganic ceramic ferroelectrics and organic polymers, such as BaTiO3, SrBi2Ta2O9, Hf1/2Zr1/2O2, and P(VDF-TrFE). As far as we know, this is the first report on negative ECE in organometallic hybrid perovskite ferroelectric. Our experimental measurement combined with the first-principles calculations reveals that electric field-induced antipolar to polar structural transformation results in a large change in dipolar ordering (from 6.5 to 45 μC/cm2 under the ΔE of 18 kV/cm) that is closely related to the entropy change, which plays a key role in generating such giant negative ECE. This discovery of field-induced negative ECE is unprecedented in organometallic perovskite, which sheds light on the exploration of next-generation refrigeration devices with high cooling efficiency.

Engineering Phase Separation in Niobate Glass through Ab Initio Molecular Dynamics for Enhanced Energy Storage Performance and Unprecedented Thermal Stability in Niobate-Based Glass Ceramics

The advancement of lead-free glass ceramics (GCs) possessing appropriate energy storage characteristics is crucial for the renewable energy and electronics industry. In this study, we synthesized lead-free GCs predominantly composed of the tungsten bronze phase, Ba3.3Nb10O28.3. Ab initio molecular dynamics initially reveal nonuniform distribution within the Ba/Nb-O regions in niobite glassy melts, offering valuable insights for the subsequent crystallization process. The proposal of a B-site engineering strategy is suggested, which entails the concurrent reduction of grain size and augmentation of the band gap in tungsten bronze GCs doped with Ta. This approach results in a substantial enhancement of the dielectric breakdown strength (BDS). Phase-field simulations have indicated that the refinement of grain sizes plays a pivotal role in augmenting the local electric field distribution and breakdown path, thereby contributing to the enhancement of BDS. As a consequence of these modifications, a notably high recoverable energy density (Wrec) of 5.23 J/cm3 can be achieved, accompanied by an ultrahigh efficiency (η) of 94%, and superior thermal stability in energy storage. These outcomes are particularly evident in the case of 2 mol % Ta2O5-doped P2O5-K2O-BaO-Bi2O3-TeO2-Nb2O5 (PKBBTN-T) GCs, where the Wrec and η can be determined to be 2.87 ± 3% J/cm3 and 95.46 ± 4%, respectively, over a temperature range spanning from 20 to 150 °C. Additionally, this specimen exhibits an exceptionally high discharge energy density (Wdis) of 4.01 J/cm3. This comprehensive investigation, comprising experimental and theoretical analyses, establishes an effective pathway and paradigm for the development of dielectric materials with ultrahigh energy storage properties.

Manipulating Cis-Trans Copolymer Chain Conformation to Simultaneously Improve Permittivity and DC Breakdown Strength in Polythiourea

Polythioureas (PTUs) show great potentials for applications in the new generation of film capacitors due to their excellent dielectric properties. Herein, the cis-trans copolymer chain of PTU is successfully tailored by employing cis and trans cyclohexyl spacers. The relationship between the copolymer chain conformation, microstructure, and dielectric properties is carefully explored by a series of analysis. Compared with cis conformation, the trans with less steric hindrance can promote the formation of H-bonds. The enhanced H-bonding interactions not only reduce the molecular inter-chain spacing, but also drive the self-assembly of molecular chains to form cylindrical and droplet nano-morphologies. The phase separation between cis and trans PTUs is confirmed by combining the experimental results of TEM and DSC, and the CT64-PTU with the most two-phase interface thus obtains the highest permittivity of 5.5 (@10 Hz). The reduced molecular inter-chain spacing is accompanied by a decreased hopping distance of charges, which improves breakdown strength by 17% from 498 MV/m to 580 MV/m. Therefore, the cis-trans copolymer chain conformation in PTU provides a simultaneous high permittivity and breakdown strength. This research offers a strategy to further design high-performance dielectrics via regulation of copolymer chain conformation.

Ultrahigh Energy Storage Density and Efficiency of Lead-Free Dielectrics with Sandwich Structure

Lead-free dielectric capacitors have attracted significant research interest for high-power applications due to their environmental benefits and ability to meet the demanding performance requirements of electronic devices. However, the development of lead-free ceramic dielectrics with outstanding energy storage performance remains a challenge. In this study, environmentally friendly ceramic dielectrics with sandwich structures are designed and fabricated to improve energy storage performance via the synergistic effect of different dielectrics. The chemical compositions of the outer and middle layers of the sandwich structure are 0.35BiFeO3 -0.65SrTiO3 and Bi0.39 Na0.36 Sr0.25 TiO3 , respectively. The experimental and theoretical simulation results demonstrate that the breakdown strength is over 700 kV cm-1 for prepare sandwich structure ceramics. As a result, an ultrahigh recoverable energy storage density of 9.05 J cm-3 and a near-ideal energy storage efficiency of 97% are simultaneously achieved under 710 kV cm-1 . Furthermore, the energy storage efficiency maintains high values (≥ 96%) within 1-100 Hz and the power density as high as 188 MW cm-3 under 400 kV cm-1 . These results indicate that the designed lead-free ceramics with a sandwich structure possess superior comprehensive energy storage performance, making them promising lead-free candidates in the energy storage field.

High Energy Density Achieved in Novel Lead-Free BiFeO3-CaTiO3 Ferroelectric Ceramics for High-Temperature Energy Storage Applications

The development of high-performance electrostatic energy storage dielectrics is essential for various applications such as pulsed-power technologies, electric vehicles (EVs), electronic devices, and the high-temperature aviation sector. However, the usage of lead as a crucial component in conventional high-performance dielectric materials has raised severe environmental concerns. As a result of this, there is an urgent need to explore lead-free alternatives. Ferroelectric ceramics offer high energy density but lack stability at high temperatures. Here we present a lead-free (1 - x)BiFeO3-xCaTiO3 (x = 0.6, 0.7, and 0.8; BFO-CTO) ceramic capacitor with low dielectric loss, high thermal stability, and high energy density up to ∼200 °C. The introduction of CTO (x = 0.7) to the BFO matrix triggers a transition from the normal ferroelectrics to the relaxor ferroelectrics state, resulting in a high recoverable energy density of 1.18 J cm-3 at 190 °C with an ultrafast dielectric relaxation time of 44 μs. These results offer a promising, environmentally friendly, high-capacity ceramic capacitor material for high-frequency and high-temperature applications.

Moderate Fields, Maximum Potential: Achieving High Records with Temperature-Stable Energy Storage in Lead-Free BNT-Based Ceramics

The increasing awareness of environmental concerns has prompted a surge in the exploration of lead-free, high-power ceramic capacitors. Ongoing efforts to develop lead-free dielectric ceramics with exceptional energy-storage performance (ESP) have predominantly relied on multi-component composite strategies, often accomplished under ultrahigh electric fields. However, this approach poses challenges in insulation and system downsizing due to the necessary working voltage under such conditions. Despite extensive study, bulk ceramics of (Bi0.5Na0.5)TiO3 (BNT), a prominent lead-free dielectric ceramic family, have seldom achieved a recoverable energy-storage (ES) density (Wrec) exceeding 7 J cm-3. This study introduces a novel approach to attain ceramic capacitors with high ESP under moderate electric fields by regulating permittivity based on a linear dielectric model, enhancing insulation quality, and engineering domain structures through chemical formula optimization. The incorporation of SrTiO3 (ST) into the BNT matrix is revealed to reduce the dielectric constant, while the addition of Bi(Mg2/3Nb1/3)O3 (BMN) aids in maintaining polarization. Additionally, the study elucidates the methodology to achieve high ESP at moderate electric fields ranging from 300 to 500 kV cm-1. In our optimized composition, 0.5(Bi0.5Na0.4K0.1)TiO3-0.5(2/3ST-1/3BMN) (B-0.5SB) ceramics, we achieved a Wrec of 7.19 J cm-3 with an efficiency of 93.8% at 460 kV cm-1. Impressively, the B-0.5SB ceramics exhibit remarkable thermal stability between 30 and 140 °C under 365 kV cm-1, maintaining a Wrec exceeding 5 J cm-3. This study not only establishes the B-0.5SB ceramics as promising candidates for ES materials but also demonstrates the feasibility of optimizing ESP by modifying the dielectric constant under specific electric field conditions. Simultaneously, it provides valuable insights for the future design of ceramic capacitors with high ESP under constraints of limited electric field.

Outstanding Energy-Storage Density Together with Efficiency of above 90% via Local Structure Design

Dielectric ceramic capacitors with high recoverable energy density (Wrec) and efficiency (η) are of great significance in advanced electronic devices. However, it remains a challenge to achieve high Wrec and η parameters simultaneously. Herein, based on density functional theory calculations and local structure analysis, the feasibility of developing the aforementioned capacitors is demonstrated by considering Bi0.25Na0.25Ba0.5TiO3 (BNT-50BT) as a matrix material with large local polarization and structural distortion. Remarkable Wrec and η of 16.21 J/cm3 and 90.5% have been achieved in Bi0.25Na0.25Ba0.5Ti0.92Hf0.08O3 via simple chemical modification, which is the highest Wrec value among reported bulk ceramics with η greater than 90%. The examination results of local structures at lattice and atomic scales indicate that the disorderly polarization distribution and small nanoregion (∼3 nm) lead to low hysteresis and high efficiency. In turn, the drastic increase in local polarization activated via the ultrahigh electric field (80 kV/mm) leads to large polarization and superior energy storage density. Therefore, this study emphasizes that chemical design should be established on a clear understanding of the performance-related local structure to enable a targeted regulation of high-performance systems.

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.

Ultrahigh Energy Storage in Tungsten Bronze Dielectric Ceramics Through a Weakly Coupled Relaxor Design

Dielectric energy-storage capacitors, known for their ultrafast discharge time and high-power density, find widespread applications in high-power pulse devices. However, ceramics featuring a tetragonal tungsten bronze structure (TTBs) have received limited attention due to their lower energy-storage capacity compared to perovskite counterparts. Herein, a TTBs relaxor ferroelectric ceramic based on the Gd0.03 Ba0.47 Sr0.485-1.5 x Smx Nb2 O6 composition, exhibiting an ultrahigh recoverable energy density of 9 J cm-3 and an efficiency of 84% under an electric field of 660 kV cm-1 is reported. Notably, the energy storage performance of this ceramic shows remarkable stability against frequency, temperature, and cycling electric field. The introduction of Sm3+ doping is found to create weakly coupled polar nanoregions in the Gd0.03 Ba0.47 Sr0.485 Nb2 O6 ceramic. Structural characterizations reveal that the incommensurability parameter increases with higher Sm3+ content, indicative of a highly disordered A-site structure. Simultaneously, the breakdown strength is also enhanced by raising the conduction activation energy, widening the bandgap, and reducing the electric field-induced strain. This work presents a significant improvement on the energy storage capabilities of TTBs-based capacitors, expanding the material choice for high-power pulse device applications.

Novel Polyetherimide Dielectrics: Molecular Design, Energy Storage Property, and Self-Healing Performance

The development of high-temperature resistant dielectrics with excellent dielectric properties and self-healing behavior is crucial for the application of metallized film capacitors. In this work, a series of polyetherimide (PEI) dielectric films are designed and fabricated. The introduction of polar groups is in favor to the increase of permittivity, and the flexible connection such as the ether group will facilitate the reduction of dielectric loss. Moreover, the oxygen elements are beneficial to the "self-healing" of metallized film capacitors. Consequently, the permittivity of 3.53-4.00, dissipation factor of 0.281-0.517%, and Weibull breakdown strength of 347-674 MV m-1 are obtained for the PEI dielectrics. In addition, PEI-4 (BPADA-BAPP) and PEI-8 (BPADA-MDA) are selected to further investigate dielectric breakdown (150 °C), electrical displacement-electric filed (D-E) loop (at room temperature and 150 °C) as well as self-healing performance, which will evaluate their potential in practical applications. The results show that PEI-8 has stable breakdown field strength and high charge-discharge efficiency at elevated temperatures. Metallized film capacitor based on PEI-8 exhibits excellent self-healing performance, with pleasing self-clear morphology, high breakdown voltage, and reduced self-healing energy. Therefore, PEI-8 is considered as a potential candidate for metallized film capacitors applied under harsh conditions.

Enhanced Thermal and Dielectric Properties of Polyarylene Ether Nitrile Nanocomposites Incorporated with BN/TiO2-Based Hybrids for Flexible Dielectrics

Outstanding high-temperature resistance, thermal stability, and dielectric properties are fundamental for dielectric materials used in harsh environments. Herein, TiO2 nanoparticles are decorated on the surface of BN nanosheets by internal crosslinking between polydopamine (PDA) and polyethyleneimine (PEI), forming three-dimensional novel nanohybrids with a rough surface. Then, an ether nitrile (PEN) matrix is introduced into the polyarylene to form polymer-based nanocomposite dielectric films. Meanwhile, the structure and micromorphology of the newly prepared nanohybrids, as well as the dielectric and thermal properties of PEN nanocomposites, are investigated in detail. The results indicate that TiO2 nanoparticles tightly attach to the surface of BN, creating a new nanohybrid that significantly enhances the comprehensive performance of PEN nanocomposites. Specifically, compared to pure PEN, the nanocomposite film with a nanofiller content of 40 wt% exhibited an 8 °C improvement in the glass transition temperature (Tg) and a 162% enhancement in the dielectric constant at 1 kHz. Moreover, the dielectric constant-temperature coefficient of the nanocomposite films remained below 5.1 × 10-4 °C-1 within the temperature range of 25-160 °C, demonstrating excellent thermal resistance. This work offers a method for preparing highly thermal-resistant dielectric nanocomposites suitable for application in elevated temperature environments.

Energy Storage Performance of Polymer-Based Dielectric Composites with Two-Dimensional Fillers

Dielectric capacitors have garnered significant attention in recent decades for their wide range of uses in contemporary electronic and electrical power systems. The integration of a high breakdown field polymer matrix with various types of fillers in dielectric polymer nanocomposites has attracted significant attention from both academic and commercial sectors. The energy storage performance is influenced by various essential factors, such as the choice of the polymer matrix, the filler type, the filler morphologies, the interfacial engineering, and the composite structure. However, their application is limited by their large amount of filler content, low energy densities, and low-temperature tolerance. Very recently, the utilization of two-dimensional (2D) materials has become prevalent across several disciplines due to their exceptional thermal, electrical, and mechanical characteristics. Compared with zero-dimensional (0D) and one-dimensional (1D) fillers, two-dimensional fillers are more effective in enhancing the dielectric and energy storage properties of polymer-based composites. The present review provides a comprehensive overview of 2D filler-based composites, encompassing a wide range of materials such as ceramics, metal oxides, carbon compounds, MXenes, clays, boron nitride, and others. In a general sense, the incorporation of 2D fillers into polymer nanocomposite dielectrics can result in a significant enhancement in the energy storage capability, even at low filler concentrations. The current challenges and future perspectives are also discussed.

Achieving Ultrahigh Energy Storage Performance for NaNbO3-Based Lead-Free Antiferroelectric Ceramics via the Coupling of the Stable Antiferroelectric R Phase and Nanodomain Engineering

NaNbO3(NN)-based lead-free eco-friendly antiferroelectric (AFE) ceramics with an extremely high maximum polarization (Pm) are believed to be a promising alternative to traditional lead-based ceramics. Nevertheless, the high energy dissipation resulting from the large polarization hysteresis, which arises from the AFE-ferroelectric (FE) phase transition, poses a great challenge to the application of this promising ceramic. Herein, an excellent recoverable energy storage density (Wrec) was attained by intentionally designing a (0.86 - x) NaNbO3-0.14CaTiO3-xBiMg2/3Nb1/3O3 (NN-CT-xBMN) relaxor antiferroelectric ceramic, attributed to the synergistic effect of the stable AFE R phase and nanodomain engineering to overcome the bottleneck. The obtained results illustrate that the inclusion of BMN causes the transition from AFE microdomains to nanodomains and stabilizes the relaxor AFE orthorhombic R phase, which generates a highly stable polarization field response with low hysteresis and delays the AFE-FE phase transition, thus improving energy storage density. As a consequence, a high Wrec of 5.41 J cm-3 with an excellent conversion efficiency η of 86.7% was obtained in the NN-CT-0.08BMN ceramic. Moreover, the NN-CT-0.08BMN ceramic exhibits superior stability in temperature (25-150 °C), frequency (1-600 Hz), and fatigue behavior (10°-104 cycles) together with a large current density (CD = 810 A cm-2), ultrahigh power density (PD = 118 MW cm-3), and ultrafast discharge rate (t0.9 < 0.7 μs). This superior energy storage density, coupled with outstanding stability, suggests that the NN-CT-0.08BMN ceramic has the potential to be a promising candidate for pulsed power applications and power electronics.

AgNbO3-Based Multilayer Capacitors: Heterovalent-Ion-Substitution Engineering Achieves High Energy Storage Performances

The demand for miniaturization and integration in next-generation advanced high-/pulsed-power devices has resulted in a strong desire for dielectric capacitors with high energy storage capabilities. However, practical applications of dielectric capacitors have been hindered by the challenge of poor energy-storage density (Urec) and efficiency (η) caused by large remanent polarization (Pr) and low breakdown strength (BDS). Herein, we take a method of heterovalent ion substitution engineering in combination with the multilayer capacitor (MLCC) technology and thus achieve a large maximum polarization (Pmax), zero Pr, and high BDS in the AgNbO3 (AN) system simultaneously and obtain excellent Urec and η. The substitution of Sm3+ for Ag+ in SmxAN+Mn MLCCs at x ≥ 0.01 decreases the M1-M2 phase transition temperature, and the antiferroelectric (AFE) M2 phase appears at room temperature, which is beneficial to achieving a low Pr value. Due to the low Pr value and high BDS ∼ 1300 kV·cm-1, an excellent Urec ∼9.8 J·cm-3 and PD,max ∼ 34.8 MW·cm-3 were achieved in SmxAN+Mn MLCCs at x = 0.03. The work suggests a paradigm that can enhance the energy storage capabilities of AFE MLCCs to meet the demanding requirements of advanced energy storage applications.

Investigation of the Fabrication of Diamond/SiC Composites Using α-Si3N4/Si Infiltration

Diamond/SiC (Dia/SiC) composites possess excellent properties, such as high thermal conductivity and low thermal expansion coefficient. In addition, they are suitable as electronic packaging materials. This study mainly optimized the diamond particle size packing and liquid-phase silicon infiltration processes and investigated a method to prevent the adhesion of the product to molten silicon. Based on the Dinger-Funk particle stacking theory, a multiscale diamond ratio optimization model was established, and the volume ratio of diamond particles with sizes of D20, D50, and D90 was optimized as 1:3:6. The method of pressureless silicon infiltration and the formulas of the composites were investigated. The influences of bedding powder on phase composition and microstructure were studied using X-ray diffraction and scanning electron microscopy, and the optimal parameters were obtained. The porosity of the preform was controlled by regulating the feeding amount through constant volume molding. Dia/SiC-8 exhibited the highest density of 2.73 g/cm3 and the lowest porosity of 0.6%. To avoid adhesion between the sample and buried powder with the bedding silicon powder, a mixed powder of α-Si3N4 and silicon was used as the buried powder and the related mechanisms of action were discussed.

Enhancing High-Temperature Energy Storage Performance of PEI-Based Dielectrics by Incorporating ZIF-67 with a Narrow Bandgap

Polymer dielectrics are crucial for use in electrostatic capacitors, owing to their high voltage resistance, high energy storage density, and ultrahigh reliability. Furthermore, high-temperature-resistant polymer dielectrics are applied in various emerging fields. Herein, poly(ether imide) (PEI)-based polymer dielectrics prepared by adding a low loading of dimethylimidazolium cobalt (ZIF-67) with a narrow bandgaps are investigated. The results show that the composites exhibit considerably increased Young's modulus, suppressed conductivity loss, and improved breakdown strength compared with pure PEI. Consequently, a stable energy storage performance is realized for ZIF-67/PEI composites. Particularly, at 150 °C, 1 wt % ZIF-67/PEI composite affords an excellent energy storage density of 4.59 J/cm3 with a discharge energy efficiency of 80.6%, exhibiting a considerable increase compared with the values obtained for PEI (2.58 J/cm3 with a discharge energy efficiency of 68.8%). The results of this study reveal a feasible pathway to design polymer dielectrics with the potential for use in capacitive applications in harsh environments.

Local Chemical Clustering Enabled Ultrahigh Capacitive Energy Storage in Pb-Free Relaxors

Designing Pb-free relaxors with both a high capacitive energy density (Wrec) and high storage efficiency (η) remains a remarkable challenge for cutting-edge pulsed power technologies. Local compositional heterogeneity is crucial for achieving complex polar structure in solid solution relaxors, but its role in optimizing energy storage properties is often overlooked. Here, we report that an exceptionally high Wrec of 15.2 J cm-3 along with an ultrahigh η of 91% can be achieved through designing local chemical clustering in Bi0.5Na0.5TiO3-BaTiO3-based relaxors. A three-dimensional atomistic model derived from neutron/X-ray total scattering combined with reverse Monte Carlo method reveals the presence of subnanometer scale clustering of Bi, Na, and Ba, which host differentiated polar displacements, and confirming the prediction by density functional theory calculations. This leads to a polar state with small polar clusters and strong length and direction fluctuations in unit-cell polar vectors, thus manifesting improved high-field polarizability, steadily reduced hysteresis, and high breakdown strength macroscopically. The favorable polar structure features also result in a unique field-increased η, excellent stability, and superior discharge capacity. Our work demonstrates that the hidden local chemical order exerts a significant impact on the polarization characteristic of relaxors, and can be exploited for accessing superior energy storage performance.

Synthesis and Characterization of Core-Double-Shell-Structured PVDF-grafted-BaTiO3/P(VDF-co-HFP) Nanocomposite Films

Core-double-shell-structured nanocomposite films consisting of polyvinylidene fluoride-grafted-barium titanate (PVDF-g-BT) incorporated into a P(VDF-co-hexafluoropropylene (HFP)) copolymer matrix were produced via a solution mixing method for energy storage applications. The resulting films were thoroughly investigated via spectroscopic, thermal, and morphological analyses. Thermogravimetric data provided an enhancement of the thermal stability, while differential scanning calorimetry indicated an increase in the crystallinity of the films after the addition of PVDF-g-BT. Moreover, broadband dielectric spectroscopy revealed three dielectric processes, namely, glass-rubber relaxation (α_a), relaxation associated with the polymer crystalline phase (α_c), and slower relaxation in the nanocomposites resulting from the accumulation of charge on the interface between the PVDF-g-BT filler and the P(VDF-co-HFP) matrix. The dependence of the dielectric constant from the composition was analyzed, and we found that the highest permittivity enhancement was obtained by the highest concentration filler added to the largest concentration of P(VDF-co-HFP). Mechanical analysis revealed an improvement in Young's modulus for all nanocomposites versus pristine P(VDF-co-HFP), confirming the uniformity of the distribution of the PVDF-g-BT nanocomposite with a strong interaction with the copolymer matrix, as also evidenced via scanning electron microscopy. The suggested system is promising for use in high-energy-density storage devices as supercapacitors.

Enhanced Energy Storage Performance and Efficiency in Bi0.5(Na0.8K0.2)0.5TiO3-Bi0.2Sr0.7TiO3 Relaxor Ferroelectric Ceramics via Domain Engineering

Dielectric materials are highly desired for pulsed power capacitors due to their ultra-fast charge-discharge rate and excellent fatigue behavior. Nevertheless, the low energy storage density caused by the low breakdown strength has been the main challenge for practical applications. Herein, we report the electric energy storage properties of (1 - x) Bi_0.5(Na_0.8K_0.2)_0.5TiO₃-xBi_0.2Sr_0.7TiO₃ (BNKT-BST; x = 0.15-0.50) relaxor ferroelectric ceramics that are enhanced via a domain engineering method. A rhombohedral-tetragonal phase, the formation of highly dynamic PNRs, and a dense microstructure are confirmed from XRD, Raman vibrational spectra, and microscopic investigations. The relative dielectric permittivity (2664 at 1 kHz) and loss factor (0.058) were gradually improved with BST (x = 0.45). The incorporation of BST into BNKT can disturb the long-range ferroelectric order, lowering the dielectric maximum temperature T_m and inducing the formation of highly dynamic polar nano-regions. In addition, the T_m shifts toward a high temperature with frequency and a diffuse phase transition, indicating relaxor ferroelectric characteristics of BNKT-BST ceramics, which is confirmed by the modified Curie-Weiss law. The rhombohedral-tetragonal phase, fine grain size, and lowered T_m with relaxor properties synergistically contribute to a high P_max and low P_r, improving the breakdown strength with BST and resulting in a high recoverable energy density W_rec of 0.81 J/cm³ and a high energy efficiency η of 86.95% at 90 kV/cm for x = 0.45.

Structure, Antiferroelectricity and Energy-Storage Performance of Lead Hafnate in a Wide Temperature Range

Lead hafnate (PbHfO₃) has attracted a lot of renewed interest due to its potential as antiferroelectric (AFE) material for energy storage. However, its room temperature (RT) energy-storage performance has not been well established and no reports on the energy-storage feature of its high-temperature intermediate phase (IM) are available. In this work, high-quality PbHfO₃ ceramics were prepared via the solid-state synthesis route. Based on high-temperature X-ray diffraction data, the IM of PbHfO₃ was found to be orthorhombic, Imma space group, with antiparallel alignment of Pb²⁺ ions along the [001]_cubic directions. The polarization-electric field (P-E) relation of PbHfO₃ is displayed at RT as well as in the temperature range of the IM. A typical AFE loop revealed an optimal recoverable energy-storage density (W_rec) of 2.7 J/cm³, which is 286% higher than the reported data with an efficiency (η) of 65% at 235 kV/cm at RT. A relatively high W_rec value of 0.7 J/cm³ was found at 190 °C with an η of 89% at 65 kV/cm. These results demonstrate that PbHfO₃ is a prototypical AFE from RT up to 200 °C, making it a suitable material for energy-storage applications in a wide temperature range.

Texture Engineering Modulating Electromechanical Breakdown in Multilayer Ceramic Capacitors

Understanding the electromechanical breakdown mechanisms of polycrystalline ceramics is critical to texture engineering for high-energy-density dielectric ceramics. Here, an electromechanical breakdown model is developed to fundamentally understand the electrostrictive effect on the breakdown behavior of textured ceramics. Taking the Na_0.5 Bi_0.5 TiO₃ -Sr_0.7 Bi_0.2 TiO₃ ceramic as an example, it is found that the breakdown process significantly depends on the local electric/strain energy distributions in polycrystalline ceramics, and reasonable texture design could greatly alleviate electromechanical breakdown. Then, high-throughput simulations are performed to establish the mapping relationship between the breakdown strength and different intrinsic/extrinsic variables. Finally, machine learning is conducted on the database from the high-throughput simulations to obtain the mathematical expression for semi-quantitatively predicting the breakdown strength, based on which some basic principles of texture design are proposed. The present work provides a computational understanding of the electromechanical breakdown behavior in textured ceramics and is expected to stimulate more theoretical and experimental efforts in designing textured ceramics with reliable electromechanical performances.

Machine Learning-Enabled Superior Energy Storage in Ferroelectric Films with a Slush-Like Polar State

Heterogeneities in structure and polarization have been employed to enhance the energy storage properties of ferroelectric films. The presence of nonpolar phases, however, weakens the net polarization. Here, we achieve a slush-like polar state with fine domains of different ferroelectric polar phases by narrowing the large combinatorial space of likely candidates using machine learning methods. The formation of the slush-like polar state at the nanoscale in cation-doped BaTiO₃ films is simulated by phase field simulation and confirmed by aberration-corrected scanning transmission electron microscopy. The large polarization and the delayed polarization saturation lead to greatly enhanced energy density of 80 J/cm³ and transfer efficiency of 85% over a wide temperature range. Such a data-driven design recipe for a slush-like polar state is generally applicable to quickly optimize functionalities of ferroelectric materials.

Chemical Design of Pb-Free Relaxors for Giant Capacitive Energy Storage

Dielectric capacitors have captured substantial attention for advanced electrical and electronic systems. Developing dielectrics with high energy density and high storage efficiency is challenging owing to the high compositional diversity and the lack of general guidelines. Herein, we propose a map that captures the structural distortion (δ) and tolerance factor (t) of perovskites to design Pb-free relaxors with extremely high capacitive energy storage. Our map shows how to select ferroelectric with large δ and paraelectric components to form relaxors with a t value close to 1 and thus obtaining eliminated hysteresis and large polarization under a high electric breakdown. Taking the Bi_0.5Na_0.5TiO₃-based solid solution as an example, we demonstrate that composition-driven predominant order-disorder characteristic of local atomic polar displacements endows the relaxor with a slushlike structure and strong local polar fluctuations at several nanoscale. This leads to a giant recoverable energy density of 13.6 J cm^-3, along with an ultrahigh efficiency of 94%, which is far beyond the current performance boundary reported in Pb-free bulk ceramics. Our work provides a solution through rational chemical design for obtaining Pb-free relaxors with outstanding energy-storage properties.

Enhanced Interfacial and Dielectric Performance for Polyetherimide Nanocomposites through Tailoring Shell Polarities

Polyimide (PI) and its derivative polyetherimide (PEI) have been widely investigated as promising candidates for dielectric energy storage due to their excellent intrinsic features. However, most of the current research for PI- or PEI-based dielectric nanocomposites only focuses on a certain polar group contained in a dianhydride monomer, while there are very few studies on exploring the effect of a series of polar groups derived from various dianhydride monomers on the dielectric properties of nanocomposites. To fill this gap, we herein fabricated and investigated a series of novel hyperbranched polyimides grafted on barium titanate nanoparticles (HBPI@BT) using different dianhydride monomers and their nanocomposites with the PEI matrix. The results showed that sophisticated hyperbranched structures effectively alleviated the incompatibility between fillers and the matrix, thus significantly improving the bonding energy of nanocomposites, especially for HBPI-S@BT/PEI (797.7 kJ/mol). The U_d of HBPI-S@BT/PEI reached 8.38 J/cm³, which is 3.3 times higher than that of pure PEI. The HBPI-F@BT/PEI nanocomposites achieved high breakdown strength (∼500 MV/m) and low dielectric loss (0.008) simultaneously. The dielectric constants of HBPI@BT/PEI nanocomposites remained at a stable level from 25 to 150 °C. This work provides us promising hyperbranched structured materials for potentially advanced dielectric applications such as field effect transistors.

Reversible electric-field-induced phase transition in Ca-modified NaNbO3 perovskites for energy storage applications

Sodium niobate (NaNbO₃) is a potential material for lead-free dielectric ceramic capacitors for energy storage applications because of its antipolar ordering. In principle, a reversible phase transition between antiferroelectric (AFE) and ferroelectric (FE) phases can be induced by an application of electric field (E) and provides a large recoverable energy density. However, an irreversible phase transition from the AFE to the FE phase usually takes place and an AFE-derived polarization feature, a double polarization (P)-E hysteresis loop, does not appear. In this study, we investigate the impact of chemically induced hydrostatic pressure (p_chem) on the phase stability and polarization characteristics of NaNbO₃-based ceramics. We reveal that the cell volume of Ca-modified NaNbO₃ [(Ca_xNa_1-2xV_x)NbO₃], where V is A-site vacancy, decreases with increasing x by a positive p_chem. Structural analysis using micro-X-ray diffraction measurements shows that a reversible AFE-FE phase transition leads to a double P-E hysteresis loop for the sample with x = 0.10. DFT calculations support that a positive p_chem stabilizes the AFE phase even after the electrical poling and provides the reversible phase transition. Our study demonstrates that an application of positive p_chem is effective in delivering the double P-E loop in the NaNbO₃ system for energy storage applications.

Superior Capacitive Energy-Storage Performance in Pb-Free Relaxors with a Simple Chemical Composition

Chemical design of lead-free relaxors with simultaneously high energy density (W_rec) and high efficiency (η) for capacitive energy-storage has been a big challenge for advanced electronic systems. The current situation indicates that realizing such superior energy-storage properties requires highly complex chemical components. Herein, we demonstrate that, via local structure design, an ultrahigh W_rec of 10.1 J/cm³, concurrent with a high η of 90%, as well as excellent thermal and frequency stabilities can be achieved in a relaxor with a very simple chemical composition. By introducing 6s² lone pair stereochemical active Bi into the classical BaTiO₃ ferroelectric to generate a mismatch between A- and B-site polar displacements, a relaxor state with strong local polar fluctuations can be formed. Through advanced atomic-resolution displacement mapping and 3D reconstructing the nanoscale structure from neutron/X-ray total scattering, it is revealed that the localized Bi enhances the polar length largely at several perovskite unit cells and disrupts the long-range coherent Ti polar displacements, resulting in a slush-like structure with extremely small size polar clusters and strong local polar fluctuations. This favorable relaxor state exhibits substantially enhanced polarization, and minimized hysteresis at a high breakdown strength. This work offers a feasible avenue to chemically design new relaxors with a simple composition for high-performance capacitive energy-storage.

Heterovalent-doping-enabled atom-displacement fluctuation leads to ultrahigh energy-storage density in AgNbO3-based multilayer capacitors

Dielectric capacitors with high energy storage performance are highly desired for next-generation advanced high/pulsed power capacitors that demand miniaturization and integration. However, the poor energy-storage density that results from the low breakdown strength, has been the major challenge for practical applications of dielectric capacitors. Herein, we propose a heterovalent-doping-enabled atom-displacement fluctuation strategy for the design of low-atom-displacements regions in the antiferroelectric matrix to achieve the increase in breakdown strength and enhancement of the energy-storage density for AgNbO₃-based multilayer capacitors. An ultrahigh breakdown strength ~1450 kV·cm^-1 is realized in the Sm_0.05Ag_0.85Nb_0.7Ta_0.3O₃ multilayer capacitors, especially with an ultrahigh U_rec ~14 J·cm^-3, excellent η ~ 85% and P_D,max ~ 102.84 MW·cm^-3, manifesting a breakthrough in the comprehensive energy storage performance for lead-free antiferroelectric capacitors. This work offers a good paradigm for improving the energy storage properties of antiferroelectric multilayer capacitors to meet the demanding requirements of advanced energy storage applications.

Alternating [1.1.1]Propellane-(Meth)Acrylate Copolymers: A New Class of Dielectrics with High Energy Density for Film Capacitors

Polymer dielectrics with high energy density are of urgent demand in electric and electronic devices, but the tradeoff between dielectric constant and breakdown strength is still unsolved. Herein, the synthesis and molar mass control of three alternating [1.1.1]propellane-(meth)acrylate copolymers, denoted as P-MA, P-MMA, and P-EA, respectively, are reported. These copolymers exhibit high thermal stability and are semi-crystalline with varied glass transition temperatures and melting temperatures. The rigid bicyclo[1.1.1]pentane units in the polymer backbone promote the orientational polarization of the polar ester groups, thus enhancing the dielectric constants of these polymers, which are 4.50 for P-EA, 4.55 for P-MA, and 5.11 for P-MMA at 10 Hz and room temperature, respectively. Moreover, the high breakdown strength is ensured by the non-conjugated nature of bicyclo[1.1.1]pentane unit. As a result, these copolymers show extraordinary energy storage performance; P-MA exhibits a discharge energy density of 9.73 J cm^-3 at 750 MV m^-1 and ambient temperature. This work provides a new type of promising candidates as polymer dielectrics for film capacitors, and offers an efficient strategy to improve the dielectric and energy storage properties by introducing rigid non-conjugated bicyclo[1.1.1]pentane unit into the polymer backbone.

High Energy Storage Performance of PZO/PTO Multilayers via Interface Engineering

Antiferroelectric thin-film capacitors with ultralow remanent polarization and fast discharge speed have attracted extensive attention for energy storage applications. A multilayer heterostructure is considered to be an efficient approach to enhance the breakdown strength and improve the functionality. Here, we report a high-performance multilayer heterostructure (PbZrO₃/PbTiO₃)_n with a maximum recoverable energy storage density of 36.4 J/cm³ due to its high electric breakdown strength (2.9 MV/cm) through the heterostructure strategy. The positive effect of interfacial blockage and the negative effect of local strain defects competitively affect the breakdown strength, showing an inflection point at n = 3. The atomic-scale characterizations reveal the underlying microstructure mechanism of the interplay between the heterointerface dislocations and the decreased energy storage performance. This work offers the potential of well-designed multilayers with high energy storage performance through heterostructure engineering.

Improving the Energy Storage Performance of All-Polymer Composites By Blending PVDF and P(VDF-CTFE)

Organic film capacitors have incredibly high power density and have an irreplaceable position in pulsed power systems, high-voltage power transmission networks and other fields. At present, the energy storage density and energy storage efficiency of organic film capacitors are relatively low, resulting in excessive equipment volume. The performance of organic film capacitors is determined by polymer materials, so it is crucial to develop a polymer composite with high energy storage density and high charge-discharge efficiency. Poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) is incorporated into the polyvinylidene fluoride (PVDF) matrix by solution blending. The successful preparation of the all-polymer composite material solves the problems of low breakdown electric field strength, low discharge energy density, and low charge-discharge efficiency of high-dielectric ferroelectric materials. The discharge energy density of the PVDF/P(VDF-CTFE) (70/30) film is more than twice that of pure PVDF due to the increase of phases α and γ and the decrease of crystallinity. Under the breakdown electric field (380 kV mm^-1 ), PVDF/P(VDF-CTFE) (70/30) film also has an ultrahigh energy storage efficiency of 64%. The relationship between the structure and properties of composite materials is investigated in this study, which has important implications for the development of capacitors with high energy storage density.

Lead-Free Relaxor Ferroelectric Ceramics with Ultrahigh Energy Storage Densities via Polymorphic Polar Nanoregions Design

One of the long-standing challenges of current lead-free energy storage ceramics for capacitors is how to improve their comprehensive energy storage properties effectively, that is, to achieve a synergistic improvement in the breakdown strength (E_b ) and the difference between maximum polarization (P_max ) and remnant polarization (P_r ), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO₃ into Bi_0.5 Na_0.5 TiO₃ is proposed to construct the morphotropic phase boundary with coexisting structures of micrometer-size domains and polymorphic nanodomains, enhance the electric field-induced polarization response (increase P_max ). Then Sr(Al_0.5 Ta_0.5 )O₃ (SAT)-doped 0.94 Bi_0.5 Na_0.5 TiO₃ -0.06BaTiO₃ (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease P_r ). Finally, a large recoverable energy density (W_rec ) of 8.33 J cm^-3 and a high energy efficiency (η) of 90.8% under 555 kV cm^-1 are obtained in the 0.85BNBT-0.15SAT ceramic prepared by repeated rolling process method (enhance E_b ), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (W_rec > 5.0  cm^-3 , η > 90%) at 400 kV cm^-1 . This strategy provides a new conception for the design of other-based multifunctional energy storage dielectrics.

High strength and biodegradable dielectric film with synergistic alignment of chitosan nanofibrous networks and BNNSs

The development of biodegradable and robust dielectric capacitors with high breakdown strength and energy density are indispensable. Herein, the high strength chitosan/edge hydroxylated boron nitride nanosheets (BNNSs-OH) dielectric film was fabricated via combining the dual chemically-physically crosslinking and the drafting orientation strategy, which could induced BNNSs-OH and chitosan crosslinked network alignment within the film via covalent and hydrogen bonding interaction, leading to the comprehensive reinforcement of tensile strength from 126 to 240 MPa, the E_b from 448 to 584 MV m^-1, the in-plane thermal conductivity from 1.46 to 5.95 W m^-1 K^-1 and energy storage density from 7.22 to 13.71 J cm^-1, superior than the comprehensive evaluation of the reported polymer dielectrics. The dielectric film could be completely degraded in soil in 90 days, which opened a new path for the development of next-generation environment-friendly dielectrics with excellent mechanical and dielectric properties.

Study on the Automatic Identification of ABX3 Perovskite Crystal Structure Based on the Bond-Valence Vector Sum

Perovskite materials have a variety of crystal structures, and the properties of crystalline materials are greatly influenced by geometric information such as the space group, crystal system, and lattice constant. It used to be mostly obtained using calculations based on density functional theory (DFT) and experimental data from X-ray diffraction (XRD) curve fitting. These two techniques cannot be utilized to identify materials on a wide scale in businesses since they require expensive equipment and take a lot of time. Machine learning (ML), which is based on big data statistics and nonlinear modeling, has advanced significantly in recent years and is now capable of swiftly and reliably predicting the structures of materials with known chemical ratios based on a few key material-specific factors. A dataset encompassing 1647 perovskite compounds in seven crystal systems was obtained from the Materials Project database for this study, which used the ABX3 perovskite system as its research object. A descriptor called the bond-valence vector sum (BVVS) is presented to describe the intricate geometry of perovskites in addition to information on the usual chemical composition of the elements. Additionally, a model for the automatic identification of perovskite structures was built through a comparison of various ML techniques. It is possible to identify the space group and crystal system using just a small dataset of 10 feature descriptors. The highest accuracy is 0.955 and 0.974, and the highest correlation coefficient (R2) value of the lattice constant can reach 0.887, making this a quick and efficient method for determining the crystal structure.

Ultrahigh Polarization Response along Large Energy Storage Properties in BiFeO3-BaTiO3-Based Relaxor Ferroelectric Ceramics under Low Electric Field

BiFeO₃-BaTiO₃ (BF-BT) dielectric ceramics are receiving more and more concern for advanced energy storage devices owing to their excellent ferroelectric properties and environmental sustainability. However, the energy density and efficiency are limited in spite of the large remanent polarization. Herein, we proposed a multiscale optimization strategy via a local compositional disorder with a Birich content and nanodomain engineering by introducing the Sr_0.7Bi_0.2Ca_0.1TiO₃ (SBCT) into BF-BT ceramics. Interestingly, an extraordinary energy storage property (ESP) with a high reversible energy storage density (W_rec) of ∼3.79 J/cm³ and an ultrahigh polarization discrepancy (ΔP) of ∼58.5 μC/cm² were obtained in the SBCT-modified BF-BT ceramics under 160 kV/cm. The boosted ESP should be attributed to the fact that the replacement of A/B-sites cations could transform the long-range ferroelectric order of the BF-BT system into polar nanoregions (PNRs) along with the refined grain size, decreased leakage current, and broadened energy band gap. Moreover, good frequency (1-10³ Hz) and temperature (25-125 °C) stabilities, high fatigue resistance (× 10⁵), large power density (∼31.1 MW/cm³), and fast discharge time (∼97 ns) were also observed for the optimized ceramics. These results illustrate a potentially effective method for creating high ESP lead-free ceramics at a low electric field.

Correlating the Interfacial Polar-Phase Structure to the Local Chemistry in Ferroelectric Polymer Nanocomposites by Combined Scanning Probe Microscopy

Ferroelectric polymer nanocomposites possess exceptional electric properties with respect to the two otherwise uniform phases, which is commonly attributed to the critical role of the matrix-particle interfacial region. However, the structure-property correlation of the interface remains unestablished, and thus, the design of ferroelectric polymer nanocomposite has largely relied on the trial-and-error method. Here, a strategy that combines multi-mode scanning probe microscopy-based electrical characterization and nano-infrared spectroscopy is developed to unveil the local structure-property correlation of the interface in ferroelectric polymer nanocomposites. The results show that the type of surface modifiers decorated on the nanoparticles can significantly influence the local polar-phase content and the piezoelectric effect of the polymer matrix surrounding the nanoparticles. The strongly coupled polar-phase content and piezoelectric effect measured directly in the interfacial region as well as the computed bonding energy suggest that the property enhancement originates from the formation of hydrogen bond between the surface modifiers and the ferroelectric polymer. It is also directly detected that the local domain size of the ferroelectric polymer can impact the energy level and distribution of charge traps in the interfacial region and eventually influence the local dielectric strength.

High-Energy-Density and High Efficiency Polymer Dielectrics for High Temperature Electrostatic Energy Storage: A Review

Polymer dielectrics are key components for electrostatic capacitors in energy, transportation, military, and aerospace fields, where their operation temperature can be boosted beyond 125 °C. While most polymers bear poor thermal stability and severe dielectric loss at elevated temperatures, numerous linear polymers with linear D-E loops and low dielectric permittivity exhibit low loss and high thermal stability. Therefore, the broad prospect of electrostatic capacitors under extreme conditions is anticipated for linear polymers, along with intensive efforts to enhance their energy density with high efficiency in recent years. In this article, an overview of recent progress in linear polymers and their composites for high-energy-density electrostatic capacitors at elevated temperatures is presented. Three key factors determining energy storage performance, including polarization, breakdown strength, and thermal stability, and their couplings are discussed. Strategies including chain modulation, filler selection, and design of topological structure are summarized. Key parameters for electrical and thermal evaluations of polymer dielectrics are also introduced. At the end of this review, research challenges and future opportunities for better performance and industrialization of dielectrics based on linear polymers are concluded.

A room-temperature antiferroelectric in hybrid perovskite enables highly efficient energy storage at low electric fields

Molecular antiferroelectrics (AFEs) have taken a booming position in the miniaturization of energy storage devices due to their low critical electric fields. However, regarding intrinsic competitions between dipolar interaction and steric hindrance, it is a challenge to exploit room-temperature molecular AFEs with high energy storage efficiency. Here, we present a new 2D hybrid perovskite-type AFE, (i-BA)₂(FA)Pb₂Br₇ (1), which shows ultrahigh energy storage efficiencies at room temperature. Most strikingly, the typical double P-E hysteresis loops afford an ultrahigh storage efficiency up to ∼91% at low critical electric fields (E _cr = 41 kV cm^-1); this E _cr value is much lower than those of state-of-the-art AFE oxides, revealing the potential of 1 for miniaturized energy-storage devices. In terms of the energy storage mechanism, the dynamic ordering and antiparallel reorientation of organic cations trigger its AFE-type phase transition at 303 K, thus giving a large spontaneous electric polarization of ∼3.7 μC cm^-2, while the increasement of steric hindrance of the organic branched-chain i-BA⁺ spacer cations stabilizes its antipolar sublattices. To the best of our knowledge, this exploration of achieving ultrahigh energy storage efficiency at such a low critical electric field is unprecedented in the AFE family, which paves a pathway for miniaturized energy storage applications.

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.