With the increasingly severe environmental pollution and global warming, developing green and sustainable energy storage devices with high power density, energy storage density, and good stability becomes a research hotspot. Compared with batteries and electrochemical capacitors, lead-free ceramic dielectric capacitors exhibit eco-friendly, high power density, fast charge/discharge speed and excellent reliability, which are promising candidates for advanced pulse power systems. In general, the energy storage density of ceramic dielectric capacitors can be evaluated via measuring the polarization versus electric field hysteresis loops (i.e., P-E loops). Large maximum polarization (P_max), small remnant polarization (P_r) and high breakdown strength (E_b) are critical parameters to achieve a high recoverable energy storage density (W_rec) and an energy storage efficiency (η). Although some previous work reported a higher energy storage density at higher electric field (>200 kV/cm), the high electric field could restrict the application in some fields. It is thus crucial to develop ceramic dielectric capacitors with a superior energy storage performance at a lower electric field (<200 kV/cm). In this paper, we designed and prepared a series of (1-x)(0.94Bi_0.55Na_0.45TiO₃-0.06BaTiO₃)-xSr_0.7Bi_0.2TiO₃ (x=0, 0.10, 0.20, 0.30, 0.40) lead-free relaxor ferroelectric ceramics to achieve a high energy storage performance and a superior stability at a low electric filed. In addition, the energy storage properties were also investigated.

TiO₂ (98%), SrCO₃ (99%), Bi₂O₃ (99%), Na₂CO₃ (99.8%) and BaCO₃ (99%) were used as raw materials for the synthesis of (1-x)BNBT-xSBT lead-free ceramics. According to the stoichiometric ratio, these raw materials were weighed. The materials were mixed with alcohol and ground in nylon jars for 12 h. After drying, the powders were calcined at 950 ℃ for 4 h. Subsequently, the calcined powders with alcohol were further ground in nylon jars for 12 h. Afterwards, the obtained powders were mixed with binders and pressed uniaxially into disk-shaped samples with 1 mm in thickness and 10 mm in diameter. Finally, the samples were sintered at 1 150-1 250 ℃ for 2 h after removing the binders at 600 ℃ for 8 h.

The phase structure of the ceramics was analyzed by a model D8-Advance X-ray diffractometer (XRD, Germany). The Raman spectra were collected by a model Jobin-Yvon HR800 Raman spectroscope (Horiba Co., France). The microstructure of the ceramics was determined by a model APERO HIVAC scanning electron microscope (SEM, USA). In order to test the electrical properties of the (1-x)BNBT-xSBT ceramics, the silver paste was coated on the surface of the samples and fired at 580 ℃ for 10 min to form silver electrodes. The temperature-dependent dielectric constant and loss were measured by a model Agilent E4980A impedance analyzer. The ferroelectric performance was determined by a model Precision Premier II ferroelectric analyzer (Radiant Co., USA) with 2 mm in electrode diameter.

The microstructure analysis indicates that all the ceramics samples have a slight porosity. Although some secondary phases appear in the ceramics due to the non-stoichiometric ratio of Bi and Na elements, the ceramics maintain a main perovskite structure. The difference of peak intensity between v₂, v₃ and v₄, v₅ reduces gradually with increasing the SBT content due to the enhancement of structural symmetry. Meanwhile, the peaks of dielectric constant shift towards a lower temperature along with the improvement of temperature stability of dielectric constant as the SBT content increases. At 25-343.9 ℃, the variation of dielectric constant is less than ±10% for (1-x)BNBT-xSBT ceramics when x=0.40. At 10 Hz and 120 kV/cm, the P_max decreases with increasing the SBT content, but the P-E loops become slimmer, which is beneficial to achieving a higher energy storage efficiency. Meanwhile, four peaks appear in current versus electric field curves (I-E curves) and the current peak shifts towards zero electric field along with the decrement of current intensity when the SBT content increases, indicating the enhancement of response speed for domains after removing the external voltage. The ceramic with the composition of x=0.30 exhibits slim P-E loops at different electric fields and a recoverable energy storage density of 2.16 J/cm³ along with a high energy storage efficiency of 90% at a low electric field of 192 kV/cm. In addition, the energy storage performance shows superior frequency and cycle stability. The variation of recoverable energy storage density and energy storage efficiency is less than ±8% within 1-200 Hz and 1-10⁵ cycles.

(1-x)BNBT-xSBT lead-free ceramics were prepared by a solid-state reaction method. The effect of SBT content on the microstructure, dielectric, ferroelectric, energy storage properties and stability of (1-x)BNBT-xSBT ceramics were investigated. The temperature stability of dielectric constant was improved and the variation of dielectric constant was less than ±10% at 25-343.9 ℃ for the composition of 0.60BNBT-0.40SBT. The superior energy storage performance with a recoverable energy storage density of 2.16 J/cm³ and an energy storage efficiency of 90% was achieved at a low electric field (<200 kV/cm) and an optimized SBT content. In addition, the energy storage performance of (1-x)BNBT-xSBT ceramics showed a superior frequency and cycle stability. This study demonstrated that the addition of SBT could be beneficial to optimizing the energy storage performance of BNT-based lead-free ceramics and the (1-x)BNBT-xSBT ceramics could be promising candidates for advanced pulse power systems application.

The pulse power capacitors can be used in military, medical, and aerospace fields due to their high power density and rapid charge-discharge capabilities. Despite these advantages, limited energy storage capacity and efficiency become challenges in achieving miniaturization and high-power performance. Among dielectric energy storage materials, antiferroelectric materials are regarded as promising for high-performance pulse power capacitors due to their distinctive double hysteresis loops, lower residual polarization, and higher energy storage efficiency. However, the breakdown strength decreases due to non-uniform electric field when the resistance of ceramic grain is equal to that of grain boundary, resulting in a decrease of energy storage density. Therefore, the enhancement of grain boundary impedance plays a key role in improving the dielectric breakdown strength of the system. In this paper, (Pb_(1-1.5x)Tm_x)(Zr_0.55Sn_0.44Ti_0.01)O₃ (x=0.00, 0.02, 0.04, 0.06) antiferroelectric ceramics were prepared via tape casting. The strategy of grain boundary impedance was constructed via enhancing the grain boundary quantity.

Powders of Pb₃O₄, Tm₃O₂, ZrO₂, SnO₂, and TiO₂ as raw materials were precisely weighed according to their chemical formulae after drying. The powders were mixed with alcohol and then ground in a ball mill for 24 h. Afterwards, the mixture was dried and pre-sintered at 850 ℃, and further ground in a ball mill for 24 h. The ground powders were mixed with toluene ethanol as a solvent, polyvinyl alcohol as an adhesive and butyl phthalate as a plasticizer. After 24 h milling, the mixture underwent degassing for 40 min, resulting in a slurry with an optimal fluidity. A flexible film with a thickness of 0.02 mm was produced via casting at a linear speed of 40 cm/min, and dried for 6 h. This film was then compressed into a block with the sizes of 10.0 mm×10.0 mm×0.5 mm. The samples were sintered in a muffle furnace via increasing the temperature from room temperature to 600 ℃ for 12 h to firstly remove the adhesive and then at 1 300 ℃. The sintered samples were cooled to room temperature.

The crystal structure of PTZST ceramics at room temperature was determined by X-ray diffraction. The ion vibration mode and the degree of disorder in the local structure were characterized by Raman spectroscopy. The surface morphology and grain size of the ceramic samples were analyzed by scanning electron microscopy. The particle sizes were determined by a software named Nano Measure. The dielectric temperature spectra were analyzed. The hysteresis curves were measured at various electric fields and temperatures as well as at a constant electric field intensity of 10 Hz, by a ferroelectric testing system. The test samples had a thickness of 0.1 mm and an electrode diameter of 2 mm. The impedance data were recorded by a high-temperature dielectric test system and subsequently analyzed by a software named ZView to evaluate the electrical performance of the samples.

All the PTZST ceramics exhibit a pronounced perovskite structure without elemental distortion, as evidenced by X-ray diffraction analysis. The orthogonal antiferroelectric phase of these ceramics is confirmed through superlattice diffraction and component selection analysis. The scanning electron microscopy images reveal that the grain size of the ceramics decreases with increasing Tm³⁺ content. This phenomenon is attributed to the formation of lead ion vacancies induced by the substitution of high valence Tm³⁺ for Pb²⁺, subsequently inhibiting oxygen vacancy formation and grain growth. Moreover, this modification increases the number of grain boundaries, enhancing the effectiveness of the grain boundary impedance strategy. However, excessive Tm³⁺ doping deteriorates the sample properties. The analysis of the P-E loops indicates a change in the energy storage density of PTZST ceramics. The PT4ZST ceramics demonstrate the maximum energy storage density (i.e., W_rec=9.37 J/cm³) and efficiency (i.e., η=77%). There is little variation in energy storage density at 30-120 ℃.

The impedance spectrum transformation from two semicircles to a single semicircle indicates the effective implementation of the grain boundary impedance strategy. This alteration enhances the dielectric breakdown strength of PTZST ceramics, thereby augmenting the energy storage density.

In exploring practical applications, charge-discharge tests were conducted. The discharge energy density of PT4ZST ceramics increases with increasing applied electric field, having the maximum value at a discharge energy density (i.e., W_dis=5.5 J/cm³) and a discharge rate (i.e., t_0.9=199.85 ns).

The original long-range ordered structure was disrupted via doping Tm³⁺ in the A-site to replace Pb²⁺, reducing a tolerance factor and stabilizing an antiferroelectric phase. Consequently, this led to an improved dielectric breakdown and an enhanced energy storage capability. The results indicated that the PT4ZST ceramics achieved a high dielectric breakdown (i.e., E_b=490 kV/cm) and a significant energy storage density (i.e., W_rec=9.37 J/cm³). These ceramics exhibited a high energy storage efficiency (i.e., 77%) and a substantial discharge energy density (i.e., W_dis=5.5 J/cm³), coupled with a rapid discharge rate (i.e., t_0.9=199.85 ns). Furthermore, the PT4ZST ceramic had a superior temperature stability at 30~120 ℃. The results indicated that the PT4ZST ceramic could be used as an effective material for high-temperature pulse power capacitors.

Antiferroelectric ceramic and multilayer ceramic capacitors have the advantages of high energy storage density, fast discharge speed, high discharge current, etc., which can improve the energy storage density of pulse power device and effectively suppress ripple in power electronic system, etc. Unlike ferroelectrics, antiferroelectric materials adjacent to the lattice of dipoles reverse parallel, and therefore do not show a macroscopic spontaneous polarization phenomenon. In a certain external electric field, the dipoles redirect, the antiferroelectric phase converts to a ferroelectric phase, the polarization intensity increases abruptly after the withdrawal of the external electric field, and it returns to an antiferroelectric phase. This polarization/phase transition behavior can be characterized by the hysteresis loop. In the hysteresis loop, antiferroelectric material shows a double loop, and it is divided into two kinds, i.e., "Square" and "Slant" according to the different shapes of the antiferroelectric hysteresis loop. The polarization effect of the antiferroelectric capacitor gives it the better energy storage characteristics and discharge performance, thus having an advantage in practical applications. General capacitors are polarized under a certain period of time and voltage in the factory. However, changes of external conditions (i.e., temperature, voltage, time, etc.) can depolarize the antiferroelectric capacitor. Also, some antiferroelectric capacitors need to consider the effect of polarity. As a result, the practical application of antiferroelectric MLCCs is different from that of conventional Class I or Class II MLCCs. Therefore, in this paper, antiferroelectric ceramics with hysteresis loop shapes of "square" and "slant" were prepared by a conventional solid-phase reaction method to investigate the polarization effect of antiferroelectric ceramics and capacitors, and provide a guidance for the application of antiferroelectric MLCCs.

For the preparation of the antiferroelectric ceramic, the raw materials were weighed according to the chemical formula. The excess Pb₃O₄ was used to compensate for lead loss in sintering. The weighed raw materials were mixed in a mass ratio of 1.0∶1.0∶1.5 and ground in anhydrous alcohol by grinding in a ball mill with zirconium balls at 300 rpm for 20 h. After ball-milling, the slurry was pre-fired at 850 ℃ for 3 h. The film was formed, and heated at 1 280 ℃ for 2 h. The samples were prepared after polished with sandpaper to a certain thickness (less than or equal to 0.1 mm) and sputtered with gold electrodes. The micro-morphology of the samples was measured by a model JSM-6390A scanning electron microscope (SEM, JOEL Co., Japan). The crystalline phase composition was determined by a model D/Max-2400 X-ray diffractometer (XRD, Rigaku Co., Japan), using Cu K_α rays, with a scanning range of 20°-70°. The hysteresis loops and polarization current curves of the samples were examined by a model TF Analyzer 2000 ferroelectric test system (aix-ACCT Co., Germany). The basic principle of the test was based on the Sawyer-Tower circuit. The test frequency was 1 Hz, and the voltage waveform was a triangular wave. The pulse discharge test used a self-built platform.

From the SEM images of the samples, the grains are uniform and have a good densification. From the XRD patterns of the samples, the prepared samples have a quadrilateral phase structure. The prepared samples have a typical double hysteresis loop, and the shapes of hysteresis loops for sample S1 and S2 are "square" and "slant". The hysteresis loops of the samples after and before polarization indicate that for the unpolarized ceramic sample, the transition field is higher, the stored energy density and energy conversion efficiency are lower. This phenomenon is also related to the shape of the hysteresis loops, so the polarization has a certain impact on the practical application of antiferroelectric ceramics. The electric hysteresis loop nearby transition field shows that for capacitors with antiferroelectric ceramic dielectrics, the antiferroelectric capacitor is unpolarized (or is depolarized) if the operating voltage is set nearby the transition field, thus leading to a weakening of its performance. To analyze whether high temperature should have an effect on the degree of polarization of antiferroelectric ceramics, the capacitances of the antiferroelectric ceramics are tested after depolarization at different temperatures, and the pulse discharge currents of the antiferroelectric MLCCs after depolarization at different temperatures are tested. The results show that if the antiferroelectric capacitor is overheated and warmed up, and although the temperature is recovered after using, the temperature still has a certain effect on the performance of antiferroelectric capacitor, especially at a lower applied voltage. To study the effect of polarity on the antiferroelectric material, the hysteresis loops of antiferroelectric ceramics in positive and negative electric fields were tested, and the pulse discharge of antiferroelectric MLCCs in different polarity electric fields was tested. The results show that the antiferroelectric domains are preferentially oriented, and the antiferroelectric domains have a memory effect after a certain direction of the electric field polarization, preventing its entry into the opposite direction of the ferroelectric domains. And this effect is more serious on the antiferroelectric ceramics with a "square" hysteresis loop.

The antiferroelectric polarization and polarity characteristics had dominant effects on their applications. Those effects above were lower although antiferroelectric capacitors were generally made of materials with "slant" hysteresis loops. However, since antiferroelectric materials were in an electric field that was slightly higher than the E_AFE-FE phase transition field, their depolarization and polarity characteristics still affected their performance. In addition, a slight attenuation of the antiferroelectric MLCCs performance still adversely affected the reliability of the whole system since some applications required an extremely high reliability. In practice, antiferroelectric MLCCs were bound to depolarize after soldering, and their performance could be greatly degraded if the applied electric filed was lower than the transition field.

Flexible and stretchable electronics have attracted much attention due to their potential applications in wearable devices, robotics, and healthcare. Among various materials, barium titanate (BTO) is a promising candidate for flexible and stretchable electronics because of its high dielectric constant, piezoelectric property, and superior thermal stability. However, the brittle nature of BTO restricts its application in flexible and stretchable devices. Polymer composites such as polydimethylsiloxane (PDMS) can be used, providing a flexibility and a stretchability for BTO-based devices. In this paper, flexible BTO/PDMS composites with a hierarchical microstructure were prepared and their dielectric performance was optimized. The hierarchical microstructure could enhance the mechanical properties, electrical conductivity, and dielectric performance of the composites. This study could provide valuable insights into the design and fabrication of flexible and stretchable electronic devices based on BTO/PDMS composites.

A piece of foam nickel was prepared, cleaned with acetone under ultrasound for 10 min and then washed with deionized water for several times to remove impurities on the surface. An isopropanol was used as a solvent, an appropriate amount of phenolic resin was used as a stabilizer, and an appropriate amount of aluminum nitrate nonahydrate was added to make the BTO positively charged. Little precipitation occurred after mechanical stirring and ultrasonic treatment. A uniform and stable barium titanate suspension was formed. A layer of BTO coating was deposited on the pore walls of the pretreated foam nickel by an electrophoretic deposition (EPD) process. Two copper plates were used as the poles of the electrophoretic deposition. A nickel metal foam template was fixed on a negative pole, immersing it into the EPD tank with the stable BTO suspension To prepare the samples with different BaTiO₃ contents, the diameter of the BTO framework pore was controlled via adjusting the electrophoresis time. The sample was sintered in an argon atmosphere at 1 200 ℃ for 2 h, and then immersed in a 1 mol/L FeCl₃ solution to completely remove the foam nickel. Finally, the sample was sintered in air at 700 ℃ for 2 h to remove carbon, forming a BTO framework. To determine the mass fraction of BTO, a barium titanate framework was weighed before and after penetration by epoxy resin. The PDMS (with curing agent) was filled into the porous structure and cured at room temperature for 24 h to obtain the BTO/PDMS dielectric composite material.

The results indicate that when the BTO content reaches 10.16% (in mass), the relative permittivity of the composite increases up to 85 at 1 000 Hz (compared to only 2.75 for pristine PDMS). Also, the dielectric permittivity increases as the mass fraction of BTO increases from 5% to 20% (in mass). For the BTO with an ordered morphology, the dielectric permittivity value increases, improving the dielectric strength performance in specific directions. Adding PVDF slightly increases the dielectric permittivity, while reducing the difference between the dielectric properties of filler and substrate, thereby enhancing the dielectric strength performance via combining PVDF with PDMS to form a core-shell structure and optimizing the dielectric properties by a finite element method. The hierarchical microstructure of the composites plays an important role in enhancing the dielectric properties. The uniform distribution of BTO particles and the interconnected porous structure of PDMS matrix provide a continuous path for the movement of charge carriers, which contributes to a high dielectric constant and a low dielectric loss of the composites. In addition, the flexible nature of PDMS matrix also makes the BTO/PDMS composites suitable for various applications, such as flexible electronic devices, sensors, and actuators.

The BTO/PDMS flexible dielectric composites with a hierarchical microstructure were prepared by a template method and an electrophoresis deposition method with BTO as a filling material and PDMS as a matrix. The influences of filler morphology and content on the dielectric constant and dielectric strength of the composites were investigated via finite element simulation analysis. Two kinds of ordered network structures of the composites, i.e., tetrahedral network structure and honeycomb network structure, were designed. This provides a theoretical guidance for the preparation of high-quality dielectric composite materials with superior energy storage density. The main conclusions were as follows: (1) Compared to the particle-filled composites, the BTO/PDMS composites with a hierarchical microstructure have an improved dielectric constant at a low filler content. For instance, the relative dielectric constant of the sample with 10.16% BTO could reach 85 at 1 kHz, which was 31 times higher than that of pure PDMS; (2) The morphology of filler had an impact on the dielectric performance of composites. In the case of a low filler content, the composites with a hierarchical microstructure had a higher dielectric constant rather than those with a solid network structure; (3) PVDF was used to form a nuclear shell structure (PVDF@BTO/PDMS) to improve the relative dielectric constant of the composites to a limited extent and the breakdown performance of composites; (4) The orderly network structures were designed. The ordered network structures with a tetrahedral network structure and a honeycomb network structure could improve the dielectric constant of composites to a certain extent and had the anisotropic characteristics.

Global energy crisis has sparked unprecedented momentum for renewable energy sources. Energy storage systems such as electrochemical capacitors, batteries, fuel cells, and dielectric capacitors are considered as the most important technologies to address rapidly growing energy demands and environmental concerns. In comparison with batteries or fuel cells, dielectric capacitors possess high power density resulting from their faster charging/discharging characteristics, which are advantageous for power electronics and pulse power applications. The majority of materials used for fabrication of dielectric capacitors consist of linear dielectrics, ferroelectrics, relaxor ferroelectrics, and anti-ferroelectrics. Among these materials, relaxor ferroelectrics are the most popular choice for capacitor applications because of their lack of long-range order ferroelectric domains. (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) as the typical representative of relaxor ferroelectrics, which possesses small remanent polarization and low coercive electric field, enjoys promising prospects in dielectric capacitor application. Nevertheless, limited by its low E_b, the energy storage density and efficiency for pure PMNT film are not yet ideal. Moreover, it is difficult for traditional PMNT film to be bendable due to limitations of rigid substrates, which lead to descend of flexibility and cannot meet modern flexible electronic production requirements. In this paper, to overcoming the bottlenecks of inflexibility and inferior energy storage performance of the pure PMNT films, rare-earth element of Sm and promising LaNiO₃ (LNO) buffer layer were introduced into PMNT thin film. To obtain extraordinary flexibility, two-dimensional mica substrate was used to prepare the modified PMNT film via a simple sol-gel method. The microstructure, dielectric, ferroelectric and energy storage properties of the flexible Pb_0.99Sm_0.01(Mg_1/3Nb_2/3)_0.68Ti_0.32O₃ (PSMNT) film were studied systematically.

The PSMNT and LNO films were prepared using a sol-gel method. First, niobium ethoxide (Nb(OC₂H₅)₅) was dissolved in 2-methoxyethanol at room temperature. And tetrabutyl titanate (Ti(OC₄H₉)₄) was stabilized in acetylacetone. Second, lead (Ⅱ) acetate trihydrate (Pb(CH₃COO)₂·3H₂O) with 10% excess Pb, samarium (Ⅲ) nitrate hexahydrate (Sm(NO₃)₃·6H₂O), and magnesium (Ⅱ) acetate tetrahydrate (Mg(CH₃COO)₂·4H₂O) were dissolved together in a mixed solvent of glacial acetic acid and 2-methoxyethanol (volume ratio of 2∶1) at room temperature. Then, the solutions above were mixed to obtain the PSMNT precursor. To prepare the LNO precursor, the lanthanum (Ⅲ) nitrate hexahydrate (La(NO₃)₃·6H₂O) and nickel (Ⅱ) acetate tetrahydrate (Ni(CH₃COO)₂·4H₂O) were dissolved in 2-methoxyethanol. The concentration of the PSMNT and LNO precursors were 0.2 mol·L^-1 and 0.1 mol·L^-1, respectively.

The flexible mica substrate was separated from the bulk fluorphlogopite mica crystal by mechanical exfoliation using a razor blade in deionized water. When the thickness of the mica substrate was reduced to ~15 μm, good flexibility could be realized. The LNO precursor solution was firstly spin-coated onto the mica substrate, followed by an annealing process at 750 ℃ for 2 min. Then, the PSMNT precursor was spin-coated on the surface of the freshly prepared LNO layer and then the wet film was annealed at 700 ℃. The spin-coating and annealing process was repeated to achieve a desirable film thickness. Finally, Au top electrodes, ~200 μm in diameter, were sputtered on the film surface through a shadow mask for electrical properties measurements.

PSMNT and PMNT thin films were directly deposited on LaNiO₃ buffered mica substrate via simple one-step fabrication process. X-ray diffraction (XRD) results indicated that the crystal structure of PSMNT film was pure perovskite phase without detectable secondary phases. Scanning electron microscope (SEM) measurement revealed that the film exhibited compact microstructure with uniform crystal grain distribution, indicating that the PSMNT film can be successfully grown on the LaNiO₃ buffered mica substrate. In terms of polarization characteristics, slim hysteresis loop with a large maximum polarization P_max (~74.5 μC/cm²) and a small remnant polarization P_r (~16.4 μC/cm²) was observed in the PSMNT film under the electric field of 2 468 kV/cm, while fatted P-E loop was observed in the PMNT film. The leakage current density in the PSMNT film is almost an order of magnitude lower than the pure PMNT sample, indicating the success of the introduction of Sm in improving of electric resistance. The recoverable energy storage density for the PSMNT film capacitor at the maximum electric field was 40.7 J/cm³, and the corresponding energy-storage efficiency was 70% due to its high breakdown strength and strong relaxor dispersion. The PSMNT film capacitor also exhibits excellent stability in energy storage performance in a wide operating frequency (1-20 kHz) and broad temperature (25-120 ℃) ranges. With the assistance of a mica substrate, the all-inorganic PSMNT/LNO/mica capacitor possesses an outstanding mechanical-bending resistance without obvious deterioration in its energy storage performance even down to a bending radius of 2 mm or repeated bending for 10³ cycles.

The main conclusions of this paper are summarized as following. Flexible Pb_0.99Sm_0.01(Mg_1/3Nb_2/3)_0.68Ti_0.32O₃ (PSMNT) film was successfully deposited on LaNiO₃ buffered mica substrate by a simple sol-gel method. A high recoverable energy density of 40.7 J/cm³ and efficiency of 70% were realized in the fabricated film capacitor. The energy storage performance was quite stable in a wide temperature (25-120 ℃) and frequency (1-20 kHz) ranges. Meanwhile, the designed PSMNT film capacitor exhibited superior mechanical-bending resistance since it is attached on the bendable mica substrate, and its energy storage behavior did not show obvious deterioration even under a small bending radius of R=2 mm and 1 000 mechanical bending cycles (R=4 mm). This study showed that flexible PSMNT thin film on mica platform has bright prospects in future flexible electronics application for energy storage.

As a core energy storage device of high energy pulse power supply, dielectric energy storage materials have the characteristics of high-power density, fast charging and discharging rate, good temperature stability, and intense aging resistance. They are widely used in power and electronic systems such as hybrid electric vehicles, oil exploration, directional weapons, etc., especially in high energy pulse power technology, having irreplaceable application prospects. With the rapid development of pulse power electronic systems, higher requirements are placed on the energy storage density, discharge current and time of dielectric capacitors in pulse power systems. These advanced devices are used in scenarios such as 100 kA current or 100 kV high voltage. This becomes some challenges for the energy storage density of dielectric capacitors. In addition, a problem of low energy storage density of dielectric capacitors also makes the pulse power system too large and cumbersome to meet the requirements of practical equipment platforms for small and lightweight high-tech weapons. Dielectric energy storage materials are key materials for pulse power devices, but their low energy storage density severely limits the miniaturization of dielectric capacitors. Further improving the breakdown field strength and increasing the dielectric constant to obtain high energy storage density dielectric materials remain a major challenge. It is necessary to develop new technologies that can improve the energy density of dielectric capacitors or explore new material systems with a high energy storage density. Doping rare-earth oxides into glass ceramics can enhance their dielectric and energy storage properties. The rare-earth element La³⁺ has a unique 4f electron layer structure, large ion radius and a high coordination number. Incorporating La³⁺ into the glass ceramics has an impact on their phase structure, dielectric properties, and energy storage performance. It is thus expected that the energy storage performance of glass ceramics can be improved via doping the rare-earth element La³⁺.

Strontium barium niobate glass ceramics doped with different mole fractions of La³⁺ were prepared via high-temperature melting and subsequent temperature-controlled crystallization. The strontium barium niobate glass ceramic had a composition of 20SrO-20BaO-20Nb₂O₅-33.5SiO₂-5Al₂O₃-1.5B₂O₃. Different mole fractions (i.e., 0.5%, 1.0% and 1.5%, in mole) of La³⁺ elements were doped into the galss ceramics. The raw materials were weighed according to the stoichiometric ratio and evenly mixed/ground in a ball mill. The mixed raw materials were sintered in a high-temperature glass furnace at 1 550 ℃ for 2.5 h. The molten material was quickly poured into a preheated metal mold to create a bulk glass. The glass was then held at 650 ℃ for 3 h to remove any remaining stresses. The transparent glass was cut into flakes with the sizes of 1.5 mm×6.0 mm×6.0 mm and heated to 1 100 ℃ for 3 h. Finally, strontium barium niobate glass ceramics with varying mole fractions of La³⁺ doping were prepared.

The phase structure and content of La³⁺ doped strontium barium niobate-based glass ceramics were analyzed by a model D8 Advanced X-ray diffractometer. The crystal size and microstructure of glass ceramics were determined by a model XL30-FEG scanning electron microscope. The dielectric constant and dielectric loss of glass ceramics at different temperatures were measured by a model E4980A LCR meter. The breakdown strength of glass ceramics was evaluated by a model ET2671B breakdown resistance tester. The P-E polarization curve of glass ceramics was tested by a model Premier-II ferroelectric tester.

The impact of doping mole fractions of La³⁺ on the phase structure, microstructure, and dielectric constant, loss, breakdown field strength, and energy storage performance of strontium barium niobate glass ceramics was investigated via experiments and theoretical simulation to reveal the mechanism of enhancing the energy storage performance of strontium barium niobate glass ceramics. The results show that La³⁺ doping can improve the crystallinity and the content of tungsten bronze structure Ba_0.5Sr_0.5Nb₂O₆ of the glass ceramics, thereby increasing the dielectric constant of strontium barium niobate glass-ceramics. At doping mole fractions of 0.5%, 1.0%, and 1.5% for La³⁺, the room-temperature dielectric constants of strontium barium niobate glass ceramics are 76.3, 96.3, and 88.1, respectively. These values are all greater than the dielectric constant of undoped strontium barium niobate glass ceramics (i.e., 65.7). La³⁺ doped strontium barium niobate glass ceramics have a superior temperature stability and a low loss. The optimum La³⁺ doping mole fraction can improve the microstructure and reduce the interface activation energy of glass ceramics, thus enhancing the breakdown strength of glass ceramics. When the doping mole fraction of La³⁺ is 1.0%, the breakdown strength of the glass ceramics reaches 1 458 kV/cm, and the dielectric constant is 96.3. The maximum energy storage density reaches 9.36 J/cm³, which is 2.25 times greater than that of undoped strontium barium niobate glass ceramics.

In the controlled doping amount of La³⁺ of glass ceramics, the phases and microstructure of glass ceramics could be effectively controlled. This improved the dielectric properties and breakdown strength of the glass ceramics. The increase in energy storage density of strontium barium niobate glass ceramic with an appropriate doping amount of La³⁺ was attributed to the increase in crystallinity and decrease in interfacial activation energy of the glass ceramics. This study could provide a reference for the development of high energy storage density glass-ceramics.

Polymer-based dielectrics with ultrahigh power density, good flexibility and easy-processing have attracted much attention in powering electronics such as capacitor, power transmission, pulsed power systems and microelectronic systems. However, the low energy density affects the application in electronics industry. Recently, introducing the ferroelectric ceramic fillers with a high dielectric constant into the polymer matrix can improve the dielectric constant of polymer composite dielectric materials. In general, the microscopy of fillers has a great influence on the energy storage performance of polymer-based dielectric capacitors. One-dimensional nanomaterials are potential to fabricating the high-performance polymer-based dielectric capacitors due to their quantum size effect, surface effect and macroscopic quantum tunneling effect. When one-dimensional nano-ferroelectric materials are introduced into the composites, a high length-diameter ratio can reduce the specific surface area and enhance the dispersion in the polymer matrix. Also, the composites can obtain better energy storage properties with a lower filler content due to its large electric dipole. In this paper, KNbO₃ nanofibers with a good crystalline and a high length-diameter ratio were firstly synthesized via hydrothermal reaction. Polymer-based dielectric capacitors were then fabricated with KNbO₃ nanofibers and poly(vinylidene fluoride-co-hexafluoropropylene) & polymethyl methacrylate (P(VDF-HFP)&PMMA) polymers. The recoverable energy storage density and energy storage efficiency were analyzed.

For the synthesis of KNbO₃ nanofibers, 36 g KOH and 1 g Nb₂O₅ were mixed in a 60 mL beaker and then were stirred for 1 h. Afterwards, the solution was transferred to a 100 mL reactor for hydrothermal reaction at 180 ℃ for 12 h. The particles were washed using deionized water and ethanol for several times and dried at 60 ℃ for 12 h. Finally, the composite films were prepared through a solution-casting method. 0.9 g P(VDF-HFP) and 0.1 g PMMA were dissolved in 10 mL N,N-Dimethylacetamide (DMAC) at 80 ℃. KNbO₃ nanofibers with different mass fractions (x=0, 2.5%, 5.0%, 7.5%, and 10.0%) were dispersed in the DMAC solution under magnetically stirring to obtain the mixture, and then the mixture was added into the P(VDF-HFP)&PMMA solutions. The composite films were prepared by a tape casting and subsequently dried at 90 ℃. The thickness of the prepared films was 20 μm. Au electrodes (2 mm in diameter) were sputtered on the composite films for the coming electrical measurements.

Based on the crystal structure of the KNbO₃ nanofibers detected by XRD, the nanofibers exhibit a pure orthorhombic perovskite structure in coincidence with the standard JCPDS 32-0822. A high diffraction intensity reflects a good crystallinity of KNbO₃ nanofibers. In addition, the widen diffraction peaks show the small size of KNbO₃ nanofibers. From the TEM and SEM images, KNbO₃ nanofibers have a uniform microscopy with a diameter of 10-20 nm and the length of ~500 nm. The distinct lattice fingers and selected area electron diffraction patterns confirm a good crystallinity of KNbO₃ nanofibers. Besides, all the elements uniformly distribute for KNbO₃ nanofibers.

The frequency-dependent dielectric constants of composite films with x of 0, 2.5%, 5.0%, 7.5%, and 10.0% are 2.8, 5.2, 6.1, 8.2, and 11.5, respectively. KNbO₃ nanofibers enhance the dielectric properties of composite films because of the intense ferroelectricity and the Maxwell-Wagner-Sillars interface effect. In addition, all the films exhibit a low dielectric loss, indicating the superior breakdown strength.

The polarization intensity at the same external electric field increases with the increase of KNbO₃ nanofiber fillers. Besides, the breakdown electric field reduces as the KNbO₃ nanofibers increases because a severe electric field deformation nearby KNbO₃ nanofiber fillers generates a high local electric field distribution. Therefore, the energy storage density firstly increases and then decreases, achieving an optimal value of 14.3 J/cm³ when 7.5% (in mass fraction) KNbO₃ nanofibers are doped in the composite films. Also, the energy storage efficiency of the optimized composites is 72%.

The ferroelectric nano-materials were filled into the polymers to enhance the energy storage performance of composite capacitors. KNbO₃ nanofibers prepared by a hydrothermal method exhibited a high aspect ratio and a good crystallinity. KNbO₃ nanofibers were mixed with P(VDF-HFP)&PMMA polymers to prepare KNbO₃/P(VDF-HFP)&PMMA composite films. The polarization strength of composite films was enhanced. Meanwhile, the breakdown strength of composite films slightly degraded. Therefore, the optimum energy storage density of 14.3 J/cm³ and efficiency of 72% were achieved when 7.5% KNbO₃ nanofibers were doped in the composite films. The results indicated that KNbO₃ nanofibers could effectively enhance the energy storage performance of composite capacitors.

Environmental pollution and energy shortage become more serious. How to effectively store energy and reduce energy loss is a recent challenge. Dielectric ceramic capacitors have some advantages such as long lifespan, fast charging and discharging speed, high power density, and good temperature stability. Na_0.5Bi_0.5TiO₃ (NBT) is a ferroelectric material with an A-site composite ABO₃ perovskite structure. The Curie temperature of NBT is 320 ℃, with a large maximum polarization (P_max) (40-50 μC/cm²) and a wide sintering temperature range. NBT is one of the hot research topics in energy storage ceramics. However, a high remanent polarization (P_r) (~38 μC/cm²) results in low recyclable energy storage density (W_rec) and efficiency (η) for NBT. Introducing a low P_r component into NBT to form a solid solution can refine the polarization-electric field (P-E), and improve the material breakdown strength (BDS) to achieve a high W_rec. In this paper, Ti⁴⁺ was replaced in Sr_0.7Bi_0.2TiO₃ by Zr⁴⁺. The introduction of Sr_0.7Bi_0.2ZrO₃ (SBZ) could enhance the degree of disorder in the A-site and B-site in the NBT, respectively. The ferroelectric long-range ordered structure was effectively break, further enhancing the relaxor ferroelectricity of NBT ceramics. Zr⁴⁺ was chosen instead of Ti⁴⁺ because Zr⁴⁺ was more stable chemically, and the properties of the material were further improved via introducing ionic radius difference and oxygen vacancies, leading to the lattice distortion. Also, ZrO₂ with a larger band gap was conducive to improving BDS and achieving a high energy storage performance.

The (1-x) Na_0.5Bi_0.5TiO₃-xSr_0.7Bi_0.2ZrO₃ (NBT-SBZ, x=0.1, 0.2, 0.3, 0.4) ceramics were synthesized by a solid-phase method. Na₂CO₃ (99.8%, in mass fraction, the same below), Bi₂O₃ (99.9%), ZrO₂ (99.0%), SrCO₃ (99.0%), and TiO₂ (98.0%) (National Pharmaceutical Group Chemical Reagent Co., China) were used as raw materials. The raw materials were mixed with alcohol and ground in a ball mill for 24 h. After drying, the powder was calcined at 850 ℃ for 4 h. The green body with a diameter of 12 mm was pressed by cold isostatic pressing at 200 MPa for 3 min. The green body was sintered in air at 1 090-1 150 ℃ for 4 h.

The phase structure of NBT-SBZ ceramic samples was characterized by a model D8 Advance X-ray diffractometer (XRD, Bruker Co., Germany) at 20°-80°. The microstructure was determined by a model S4800 scanning electron microscope (SEM, RIGAKU Co., Japan). The dielectric properties were measured by a model 4980A precision LCR (Agilent Co., USA). The thickness of the dielectric properties sample was 0.6 mm, and a silver electrode was fired at 850 ℃. The P-E loops were tested by a model Premier II ferroelectric analyzer (Radiant Co., USA). The P-E test sample thickness was 0.1 mm and a diameter of 2.0 mm for a gold electrode. The charging and discharging characteristics were determined from a model CFD-003 charging/discharging system (Gogo Co., China). The sample thickness was 0.3 mm, and a silver electrode was fired at 850 ℃.

The XRD pattern of NBT-SBZ ceramics indicates that all the samples exhibit a NBT pseudocubic perovskite structure. ZrO₂ and Bi₂Ti₂O₇ second phase appear as the SBZ content increases. A peak at 46.5° (200) shifts towards a lower angle as the SBZ content increases, indicating an increase in the spacing between ceramic crystal planes. The SEM images indicate that the grain size distribution of all the samples is uniform and presents a normal distribution. The average grain size decreases from 1.57 μm for the sample with x of 0.10 μm to 1.06 μm for the sample with x of 0.4 with the increase of SBZ content. The substitution of larger radius ions increases the lattice strain energy and hinders the grain boundary movement, leading to a grain refinement. The grain refinement and reduction of pores are beneficial to obtaining a larger BDS. The dielectric constant (ε_r) decreases from 870.5 for the sample with x of 0.1 to 668.5 for the sample with x of 0.4 with increasing the frequency due to a decrease in polarization mechanism. As the SBZ content increases, the dielectric loss (tanδ) at 1 kHz decreases from 0.041 for the sample with x of 0.100 to 0.029 for the sample with x of 0.4. All the samples exhibit obvious relaxor ferroelectric characteristics. The P-E loops also change from a typical ferroelectric shape to a thin and elongated shape of a relaxor ferroelectric, and the current density (J)-E current peak becomes rectangular, indicating that the relaxor ferroelectricity of NBT-SBZ ceramics increases with the addition of SBZ. BDS increases from 189.7 kV/cm for the sample with x of 0.1 to 298.1 kV/cm for the sample with x of 0.4, which is consistent with the decrease in average grain size and leakage current density, indicating that small grain size and dense microstructure are important reasons for achieving a high BDS. 0.8NBT-0.2SBZ ceramic with x of 0.2 at 265 kV/cm obtains W_rec of 3.15 J/cm³ and η of 76.05%. 0.8NBT-0.2SBZ ceramics exhibit a superior frequency/temperature stability in energy storage performance. C_D and P_D of 0.8NBT-0.2SBZ ceramics are 188.54 A/cm² and 11.31 MW/cm³ at 120 kV/cm, with an extremely fast t_0.9 of 52.6 ns.

NBT-SBZ relaxor ferroelectric ceramics were prepared via introducing SBZ to improve the relaxor ferroelectricity and energy storage properties of NBT ceramics. 0.8NBT-0.2SBZ ceramic achieved the optimum energy storage properties (i.e., W_rec=3.15 J/cm³, η=76.05%) at 265 kV/cm, as well as a superior stability of the energy storage performance at 1-100 Hz) and 20-140 ℃. The C_D and P_D of 0.8NBT-0.2SBZ ceramic were 188.54 A/cm² and 11.31 MW/cm³ at 120 kV/cm, respectively, with a fast t_0.9 of 52.6 ns. The 0.8NBT-0.2SBZ ceramic had a superior temperature/frequency stability, a super high power density, and extremely fast discharge time, having a great potential for application in pulse power supply equipment.

Lead-free dielectric capacitors have attacted recent attention due to the super power density, fast charge-discharge rate and outstanding thermal stability. However, the recoverable energy density of lead-free ferroelectric ceramic is relatively lower, compared to ceramics containing lead. The introduction of strong relaxor ferroelectrics can realize the excellent energy storage performance via decreasing remanent polarization as well as enhancing impedance. Bi_0.5K_0.5TiO₃ (BKT) is a promising candidate for dielectric capacitor due to the unique lone pair electronic 6s² configuration about Bi, leading to a large spontaneous polarization (i.e., P = 52 μC/cm²). Nevertheless, the energy storage properties of BKT-based ceramics are poor (i.e., W_rec < 3 J/cm³, η < 80%) because of the large remanent polarization and negative breakdown strength. Chen et al. reported that the recoverable energy storage density reached 7.5 J/cm³ through adding the BaTiO₃ and NaNbO₃ into BKT, indicating that BKT-based ceramics had a substantial prospect. The long-range ferroelectric order is broken to obtain a slim hysteresis loop, which can improve the energy storage performance. Simultaneously, the uniform small grain and compact microstructure of ceramic are essential, which can upgrade the breakdown strength for ferroelectric material. Thus, reducing grain size and breaking ferroelectric long-range order to generate polar nano-regions (PNRs) could improve the BKT-based specimens energy storage properties. In this paper, a relaxor ferroelectric material of Na_0.73Bi_0.09NbO₃ (NBN) was induced into 0.75Bi_0.5K_0.5TiO₃-0.25BiFeO₃(0.75BKT-0.25BF) to reinforce the ESP of ceramics. BF and NBN were selected to optimize ESP. The morphotropic phase boundary (MPB) of BKT-BF binary system was constructed.

For the synthesis of BKT-BF-xNBN (x=0, 0.1, 0.2, 0.3 and 0.4) ceramics, Bi₂O₃ (99.5%, in mass fraction, the same below), K₂CO₃ (99.5%), TiO₂ (99.5%), Fe₂O₃ (99.5%), Na₂CO₃ (99.8%) and Nb₂O₅ (99.5%) were used as raw materials. The dried oxides were weighted and mixed according to stoichiometric ratios in a polyethylene container, and then the mixed materials with alcohol were ground in a ball mill for 12 h. After drying, the mixture was calcined at 850 ℃ for 5 h, and the powder was further ground under the same condition. Sequentially, the dried powder with 0.5% (in mass fraction) polyvinyl alcohol (PVA) was pressed into discs with a thickness of 0.8 mm and a diameter of 12 mm. Finally, the green plates were sintered at 1 000-1 035 ℃ for 3 h.

The results show that an optimum recoverable energy storage density (W_rec) of 4.23 J/cm³ and an improved energy storage efficiency (η) of 81.2% at 380 kV/cm are achieved. The microstructure of the specimens is compact due to the refined size of grain, leading to a boosted breakdown strength (E_b). In addition, an enhanced efficiency of the specimen with x of 0.3 can be obtained, which arose from the negligible remanent polarization (P_r). Based on the analysis of dielectric relaxation, the dispersion coefficient (γ) of the BKT-BF-0.3NBN is 2.2, implying a short-range ferroelectric order, which can increase the polar nanometer regions. To better understand the reason for the decreased P_r, the first order reversal curve (FORC) distribution of ceramics was measured. The optimized composition has a distinguished dielectric thermal stability and a superior charge-discharge performance (i.e., t_0.9 (the time for releasing 90% of all storage energy) < 75 ns, current density (C_D) of 757.9 A/cm² and power density (P_D) of 94.7 MW/cm³), indicating a promising prospect in the applications for high-power dielectric capacitors. These results illustrate that the composition design for BKT-BF-xNBN is effective to refine the energy storage performance of ceramic.

Lead-free BKT-BF-xNBN ceramics with x of 0, 0.1, 0.2, 0.3 and 0.4 were synthesized. The introduction of Na_0.73Bi_0.09NbO₃ improved the microstructure of ceramics, boosted the breakdown strength, enhanced the ceramics relaxtion and resulted in the appearance of PNRs. As a result, the BKT-based ceramic with x of 0.3 had the optimum properties (i.e., W_rec of 4.23 J/cm³ and η of 81.2%). Moreover, the superior dielectric thermal stability as well as charge-discharge performance (i.e., t_0.9<75 ns, C_D=757.9 A/cm², P_D=94.7 MW/cm³) were achieved. This work indicated that BKT-BF-0.3NBN ceramic could have a promising application potential in cutting-edge performance dielectric capacitor.

Dielectric ceramic capacitors are essential components in next-generation advanced pulse power systems due to their ultra-fast charging/discharging rates and remarkable power density. As a typical lead-free perovskite material, Sr_0.7Bi_0.2TiO₃ (SBT) has a larger permittivity rather than SrTiO₃ because Bi modification favors producing a high polarization due to the intense hybridization between the 6s² orbitals of Bi³⁺ and O 2p orbitals. Moreover, it also has a superior ferroelectric relaxor behavior with a diffused maximum dielectric constant in a wide temperature range, benefiting from Bi³⁺ off centering and Sr site vacancies. However, SBT ceramic still has a critical challenge for improving dielectric breakdown strength (E_b). Some previous studies indicate that adding some oxides can effectively inhibit grain growth and increase E_b. In this paper, the SBT ceramics were synthesized by a conventional solid-state sintering method with ZrO₂ as an additive. A part of Zr⁴⁺ was deposited on the grain boundary in the form of oxides to inhibit grain growth. The breakdown strength and the energy storage density of the ceramics with different ZrO₂ contents were analyzed.

Bi₂O₃(99.5%, in mass. The same below), SrCO₃(99.5%), TiO₂(99.8%), and ZrO₂(99.9%) were used as raw materials. The raw materials were weighed according to the stoichiometric ratio. The materials were mixed with anhydrous ethanol and ground in a ball mill with zirconium balls for 12 h. The slurry was dried in an oven. After pre-firing at 850 ℃ for 5 h, the powder was further ground for 24 h according to the corresponding mass ratio Sr_0.7Bi_0.2TiO₃+xZrO₂ (SBT-xZr, x= 0, 0.5%, 1.0%, 2.0%, 5.0%, in mass fraction). The dried ground powder was pressed into sheets with a thickness of 0.8 mm and a diameter of 12 mm, and then sintered at a rate of 4 ℃/min at 1 200-1 250 ℃ for 3 h, and then cooled down naturally.

Based on the XRD patterns and mapping energy spectra, element Zr partially dissolves in the SBT lattice in the form of Zr⁴⁺, and the rest exists in the form of ZrO₂ on the grain boundary and surface, showing the formation of a 0-3 type composite structure. The dielectric constant of SBT-2%Zr ceramic consistently exhibits a high value, while the low dielectric loss mitigates excess waste heat, which is beneficial to the energy storage performance. The heightened energy storage density primarily stems from the increased E_b value. With the augmentation of ZrO₂ content, the E_b value of the SBT-2%Zr increases, reaching a peak of 580 kV/cm, which is 27.6% higher than that of pure SBT ceramic. Consequently, the recoverable energy storage density (W_rec) experiences an elevation from 4.07 J/cm³ for the ceramic without x to 5.57 J/cm³ for the ceramic with x of 2%, while energy efficiency (η) maintains 88.97%. However, for the ceramic with x of 5%, despite achieving a high E_b value, the introduction of excessive ZrO₂ leads to a notable reduction in maximum polarization (P_max), preventing the attainment of the maximum W_rec value. The average grain size decreases from 2.30 μm to 1.31 μm, facilitating the attainment of more highly insulated grain boundaries. Also, the band gap energy (E_g) increases from 2.94 eV for the SBT ceramic to 3.02 eV for the SBT-5%Zr ceramic. This signifies that electrons require a larger applied electric field to achieve the valence band and conduction band transition. The expansion of the impedance circle indicates a higher resistivity of the material, and the elevated activation energy (E_a) effectively restrains the transmission of charged carriers. These interrelated mechanisms are crucial factors contributing to the substantial enhancement of E_b. In addition, SBT-2%Zr ceramic also shows an excellent fatigue stability (i.e, 5×10⁴ cycles, W_rec change <1%) and a good charge-discharge performance (i.e., discharge energy density W_d=2.15 J/cm³, current density C_D=1 060.51 A/cm² and power density P_D=169.68 MW/cm³).

A lead-free 0-3 type relaxation ferroelectric ceramic based on SBT was prepared by a stable solid-state reaction method. The ceramics doped with different concentrations of ZrO₂ exhibited an original crystal structure with some Zr⁴⁺ in the lattice. The remaining Zr⁴⁺ existed in the form of a second phase, predominantly appearing at the boundaries and surfaces of grains. The increase of energy storage density mainly depended on the increase of E_b, and the possible physical mechanisms (i.e., grain size, band gap, impedance and activation energy) cooperated to promote the increase of E_b. SBT-2%Zr ceramic had the optimum energy storage performance, i.e., recoverable energy storage density (W_rec=5.57 J/cm³) and energy efficiency (η=88.97%). After 5×10⁴ cycles, SBT-2%Zr ceramic with a good performance stability (i.e., W_rec change amplitude <1%) could be used as a promising candidate material for pulse power energy storage capacitors.