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The 0.95K0.42Na0.58Nb0.96Sb0.04O3–0.02BaZrO3–0.03Bi0.5K0.5HfO3 ceramic was fabricated via a conventional solid-state reaction. This ceramic exhibits the diffuse polymorphic phase boundary (PPB) near room temperature. The dielectric, ferroelectric, electromechanical, electrocaloric, and dielectric energy storage properties were studied systemically. The normalized large signal d33* values are approximately 400–600 pm/V at measured temperatures and electric fields, which are larger than or comparable with the values reported in other lead-free compositions. The electrocaloric strength is enhanced at the broad region of PPB provided by the indirect and direct measurements. At low field of 30 kV/cm, the dielectric energy storage is ∼0.12–018 J/cm3 at relative broad temperature range due to the diffuse nature of polymorphic phase boundary. Theoretical simulations reveal that multi-element dopants, such as Sb5+, Hf4+, Zr4+, and Bi3+ ions, could induce the breaking of local structure symmetry in the orthorhombic phase to form the PPB. In addition, the charge distribution may also break the long-range ferroelectric order through the analysis of Bader charge. Our study suggests that the K0.5Na0.5NbO3-based ceramic exhibits improved performance and good thermal stability in piezoelectric, electrocaloric, and dielectric energy storage characteristics in terms of the design of multi-element dopants to form the PPB and it will benefit the promising applications in electronic devices. [ABSTRACT FROM AUTHOR]

0.8(Bi 0.5 Na 0.5 )TiO 3 −0.2(Bi 0.5 K 0.5 )(Hf x Ti 1−x )O 3 (abbreviated as BNT-BKH x T 1−x ) lead-free ceramics are prepared using a solid state reaction method and their dielectric, field-induced strain and energy storage properties have been systemically investigated. It was found that the largest strain induced by an external electric field occurs for x=0.02. For the x=0.02 sample, S 33 =0.41%, S max /E max =683 pm/V. However, the energy storage density is optimized at the x=0.03 sample, for which W 1 =0.51 J/cm 3 . Those results may originate from the field-induced transition between a relaxor-ferroelectric mixture phase and a ferroelectric phase. [ABSTRACT FROM AUTHOR]

AgNbO3 (AN)-based lead-free antiferroelectric ceramics are widely studied for their use as dielectric capacitor materials. In this study, Eu3+-doped AN ceramics were prepared and the results show that Eu3+ diffused into the AN lattice. The ceramics were formed by M1 and M2 phases coexisting at room temperature, as distinct from the M1 (M: monoclinic) phase of pure AN. Electrical properties and structural characterization showed that the antiferroelectric stability of the ceramics increases with the increase in Eu3+ levels. At room temperature, Ag0.94Eu0.02NbO3 ceramic exhibited a good energy storage density of 5.3 J/cm3 and a high efficiency of 71.9%. When the temperature rises from room temperature to 140 °C, the efficiency of the sample decreases from 80.4% to 67.1% and Wr decreases from 2.1 to 2.0 J/cm3, which indicates that the sample has good temperature stability. The time constant (t0.9) of this sample was less than 60 ns and the power density (PD) was 51.3 MW/cm3, indicating excellent charge–discharge capabilities. This novel ceramic is expected to be used as a new dielectric capacitor material for pulsed power supplies. [ABSTRACT FROM AUTHOR]

The lead-free Ba 0.53 Sr 0.47 TiO 3 (BST) thin films buffered with La 0.67 Sr 0.33 MnO 3 (LSMO) bottom electrode of different thicknesses were fabricated by pulsed laser deposition method on a (001) SrTiO 3 substrate. It was found that the roughness of electrode decreases and substrate stress relaxes gradually with the increase of LSMO thickness, which is beneficial for weakening local high electric field and achieving higher E b. Therefore, the recoverable energy density (W rec) of BST films can be greatly improved up to 67.3 %, that is, from 30.6 J/cm3 for the LSMO thickness of 30 nm up to 51.2 J/cm3 for the LSMO thickness of 140 nm after optimizing the LSMO thickness. Furthermore, the thin film capacitor with a 140 nm LSMO bottom electrode shows an outstanding thermal stability from 20 °C to 160 °C and superior fatigue resistance after 108 electrical cycles with only a slightly decrease of W rec below 1.6 % and 3.7 %, respectively. Our work demonstrates that optimizing bottom electrodes thickness is a promising way for enhancing energy storage properties of thin-film capacitors. [ABSTRACT FROM AUTHOR]

Dielectric capacitors are widely used in pulsed power electronic devices due to their ultrahigh power densities and extremely fast charge/discharge speed. To achieve enhanced energy storage density, maximum polarization (Pmax) and breakdown strength (Eb) need to be improved simultaneously. However, these two key parameters are inversely correlated. In this study, order–disorder transition induced polar nanoregions have been achieved in PbZrO3 thin films by making use of the low-energy ion implantation, enabling us to overcome the trade-off between high polarizability and breakdown strength, which leads to the tripling of the energy storage density from 20.5 to 62.3 J/cm3 as well as the great enhancement of breakdown strength. This approach could be extended to other dielectric oxides to improve the energy storage performance, providing a new pathway for tailoring the oxide functionalities. [ABSTRACT FROM AUTHOR]

Lead‐based antiferroelectric (AFE) ceramics have attracted increasing interest in pulse power systems owing to their high‐energy storage and power densities. However, the single AFE–ferroelectric (FE) phase transition in conventional AFE materials usually leads to premature polarization saturation and low breakdown strength, which are disadvantageous to energy storage performance. In this study, high energy storage performance was achieved in Pb0.94−xLa0.04Cax[Nb0.02(Zr0.99Ti0.01)0.975]O3 (PLCNZT) AFE ceramics by constructing electric‐field‐induced multiple phase transitions. A maximum recoverable energy storage density of 12.15 J/cm3 and a high energy efficiency of 85.4% were obtained for the PLCNZT ceramic with x = 0.03 at 420 kV/cm. These excellent properties are attributed to the AFE–FE Ⅰ‐FE Ⅱ multiple phase transitions induced by Ca2+ doping, which effectively enhances the breakdown strength. This result indicates that field‐induced multiple phase transitions significantly improve the energy storage of AFE materials. [ABSTRACT FROM AUTHOR]

Dielectric capacitors, as one of the important electronic devices, are widely used in various fields. However, most ferroelectric capacitors with high energy storage density require excessively high electric fields. In this work, we have prepared 0.9(Bi0.5Na0.5)0.7Sr0.3TiO3-0.1 Bi(Mg2/3Nb1/3)O3 relaxor ferroelectric ceramics with different BaZrO3 doping levels. A high energy storage (Wr) of 4.07 J/cm3 and efficiency (η) of 91% are simultaneously obtained in 0.94[0.9(Bi0.5Na0.5)0.7Sr0.3TiO3-0.1 Bi(Mg2/3Nb1/3)O3]-0.06BaZrO3 ceramic under a medium electric field of 260 kV/cm. Additionally, the ceramic also exhibits excellent temperature and frequency stability. Furthermore, the phase field simulation is used to simulate the evolution of domain structure and hysteresis loops of the ceramics with different doping levels. The results of phase field simulation explicitly explain the influence of different relaxation degrees on energy storage density and efficiency of the ceramics. We believe that the ceramic prepared in this work is one of the most promising candidate materials for some miniaturized energy storage devices operating under low or medium electric fields. [ABSTRACT FROM AUTHOR]

• A high W r of 4.97 J/cm3 and an η of 84.4% are obtained in BNT-based ceramics. • The W r of 2.73 J/cm3 with η of 80.6% are obtained at 140 ℃. • A superior temperature performance compared with other typical dielectric materials. • A strategy of precisely adjusting the relaxation and ferroelectricity states. Dielectric energy storage materials have attracted much attention because of their wide applications in the electronics industry. However, low energy storage density and poor thermostability limit their application. In this work, a strategy was proposed to prepare lead-free relaxor ferroelectric ceramics with ultra-high energy storage properties and superior temperature stability by precisely adjusting the relaxation and ferroelectricity states and increasing the electric field intensity. An ultra-high recoverable energy storage density (W r) of 4.97 J/cm3 and an efficiency (η) of 84.4% are simultaneously obtained for the 0.95(0.9Bi 0.5 Na 0.5 TiO 3 -0.1Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3)-0.05BaSnO 3 ceramic. Moreover, a high W r of 2.73 J/cm3 with brilliant η of 80.6% are obtained in the ceramic at 140 ℃ and there is almost no thermal degradation of energy storage properties from 25 ℃ to 140 ℃. The W r and η have decreased by 2.2% and 1.9% after 105 cycles under 200 kV/cm, respectively, which demonstrates the good cycle stability of the sample. A discharge power density of up to 99.0 MW/cm3 is obtained in the 0.95(0.9Bi 0.5 Na 0.5 TiO 3 -0.1Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3)-0.05BaSnO 3 ceramic and the good charge and discharge performance of this sample is important for practical applications. [ABSTRACT FROM AUTHOR]

Tetragonal tungsten bronze structure (TTB) compounds have attracted tremendous interest for their applications in energy storage, especially as dielectric capacitor mediums. However, constrained by the inverse correlation of polarization and electric breakdown field in relaxor ferroelectrics, there is still a major challenge in improving energy density. To addresse this challenge, a viable strategy of constructing relaxor behavior with robust electrical insulation in TTB-type Sr 0.485 Ba 0.47 Gd 0.03 Nb 2- x Zr x O 6 (SBN-Gd-Zr x) by introducing ZrO 2 during the preparation process was proposed. By introducing Zr4+ in the B-site, we have revealed how Zr4+ affects the dielectric and ferroelectric characteristics to explore the intrinsic relaxation. Based on the analysis of Rietveld refinement against synchrotron X-ray powder diffraction and Raman results, the substitution of Gd3+ and Zr4+ for Sr2+ and Nb5+ in Sr 0.53 Ba 0.47 Nb 2 O 6 caused a decline in tetragonality and a shrinkage of the unit cell due to the lattice defect of [Gd Sr ]• and [Zr Nb ] ' , which mutually compensates effectively alleviate the distortion of BO 6 and then favors the balance of polarization and dielectric constant. The accrual of additional ZrO 2 at grain boundaries significantly enhances electrical insulation characteristics, as validated by complex impedance spectroscopy. At near room temperature, all Zr-doped SBN-Gd compounds of the series exhibit heightened relaxation and undergo a phase transition from ferroelectric to paraelectric. As a result, in tandem with the synchronous augmentation in breakdown electric field (E B) and saturation polarization (P m), optimal energy storage characteristic is realized in the SBN-Gd-Zr0.2 sample. It attains a remarkable W rec of 2.67 J/cm3 and an efficiency ƞ of 91.21 %, showcasing excellent suitability in terms of different frequencies and temperatures, which far exceeds that of Gd-modified SBN ceramics and pure SBN ceramics. These results exemplify an efficacious strategy for designing novel TTB dielectrics by coupling relaxor modulation with electrical insulation, and position them competitively for implementation in dielectric storage capacitors utilized in pulsed power devices. [ABSTRACT FROM AUTHOR]

Recently, dielectric energy storage materials and devices attracted much research interest due to its high-power density and the resulted applications. In this work, relaxor ferroelectric (Pb 1-x ,La x)(Zr 0.65 ,Ti 0.35)O 3 (abbreviated as PLZT100X, X = 0.06, 0.08, 0.10 and 0.12) thin films are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel method, and temperature stability of relative dielectric constant as well as energy storage density of the PLZT thin films with different level of La doping are studied. The relative dielectric constant of the PLZT10 thin films is 873 at 1 kHz at 30°C, with maximum of variation of 7.6% in the temperature range from 30–200 °C, which indicates very high temperature stability. The energy storage density of the PLZT thin films is 38.8 J/cm3, 42.2 J/cm3, 33.5 J/cm3 and 36.0 J/cm3 with the La doping of 0.06, 0.08, 0.10 and 0.12, respectively, under the applied electric field of 2840 kV/cm. The energy efficiency of the PLZT thin films is above 70%. In addition, the energy storage density of the PLZT thin films shows good temperature stability, with about 20 J/cm3around the electric field of 1800 kV/cm in the temperature range from 30–150 °C. [ABSTRACT FROM AUTHOR]

• A W r of 4.6 J/cm3 under 430 kV/cm and η of 62.5% are achieved in Ag 0.97 Nd 0.01 NbO 3. • Ag 0.97 Nd 0.01 NbO 3 ceramics demonstrate excellent temperature stability from 25 ℃ up to 125 ℃. • Outstanding power density of 54.0 MW/cm3 and ultrafast discharge speed (t 0.9) of 59.2 ns were also obtained. Lead-free dielectric capacitors for energy storage device have attracted increasing attention recently because of their high-power density and superior temperature stability. In this work, Nd-doped silver niobate (AgNbO 3 , abbreviated as AN) lead-free antiferroelectric ceramics were prepared by utilizing traditional solid state reaction method. A large energy storage density of 4.6 J/cm3 and an efficiency of 62.5% were simultaneously obtained in the 1% Nd-doped AN sample with an outstanding power density of 54.0 MW/cm3 and an ultrafast discharge speed (t 0.9) of 59.2 ns. Additionally, the 1% Nd-doped AN ceramic demonstrates a good temperature stability from 25 ℃ to 130 ℃. The excellent energy storage properties of the 1% Nd-doped ceramic is ascribed to the enhanced breakdown electric field induced by grain size engineering and the construction of phase structure via heterovalent substitution at the A-site of the lattice structure at room temperature. Our present work suggests that the 1% Nd-doped AN ceramic show promise for energy storage application in miniaturized mobile electronic devices and high-power equipment. [ABSTRACT FROM AUTHOR]

• Large recoverable energy storage density of 2.9 J/cm3 is obtained in BNT-BST-CZ ceramic. • The ceramic shows excellent dielectric permittivity stability at 44-483 °C. • The ceramic owns a fast charge-discharge speed of 110 ns. In the 0.9(0.65Bi 0.5 Na 0.5 TiO 3 -0.35Bi 0.2 Sr 0.7 TiO 3)-0.1CaZrO 3 ceramic, superior energy storage performance and excellent dielectric stability have been achieved, along with a higher discharge rate. Our finding suggests that the ceramic has great potential applications in pulsed power systems and high-temperature capacitors. [Display omitted] Novel (1− x)(0.65Bi 0.5 Na 0.5 TiO 3 -0.35Bi 0.2 Sr 0.7 TiO 3)- x CaZrO 3 (BNT-BST- x CZ, x = 0–0.15) ceramics were manufactured through a solid phase sintering process and their structural and electrical performance have been systematically investigated. By doping CaZrO 3 , a higher recoverable energy storage density of 2.9 J/cm3 and energy storage efficiency of 80% at 330 kV/cm can be simultaneously obtained in BNT-BST-0.1CZ ceramic. Further analysis with the aid of finite element simulation indicates that the improvement of energy storage performance lies in the refined grain size and reduced defects, which are both conductive to improve the dielectric breakdown strength. More importantly, incorporating CaZrO 3 gives slimmer hysteresis loops as well as excellent temperature (20–150 °C) and frequency (5–200 Hz) stability of energy storage properties. Moreover, a stable dielectric permittivity of in an ultra-wide range from 44 °C to 483 °C was achieved in BNT-BST-0.10CZ ceramic. Our findings suggest that the BNT-BST-0.1CZ ceramic has great potential applications in pulsed power systems and high-temperature capacitors. [ABSTRACT FROM AUTHOR]

Dielectric capacitors with high energy storage and dielectric properties at high temperatures have significantly practical application in many fields. Lead-free ceramics of (1- x)(0.65Bi 0.5 Na 0.5 TiO 3 -0.35Bi 0.2 Sr 0.7 TiO 3)- x BaSnO 3 were prepared by a solid-state reaction method. It was found that the 0.8(0.65Bi 0.5 Na 0.5 TiO 3 -0.35Bi 0.2 Sr 0.7 TiO 3)-0.2BaSnO 3 ceramic shows a large recoverable energy storage density (W r) of 3.75 J/cm3 and efficiency (η) of 84.8% under 380 kV/cm along with outstanding power density of 38.73 MW/cm3 under 130 kV/cm at room temperature. Additionally, a high W r of 3.21 J/cm3 and η of 77% are achieved under a high electric field of 300 kV/cm at 100 °C. When the temperature reaches 140 °C, it still has a high W r of 3.1 J/cm3 and η of 72%. The outstanding energy storage performance at high temperatures can be explained by the enhancement of breakdown strength and the constructing of polar phase stability caused by the introduction of BaSnO 3. [ABSTRACT FROM AUTHOR]

The urgent requirement of environment-friendly materials with excellent energy storage performance for pulse power systems has sparked considerable research on lead-free ceramics. In this work, a new lead-free 0.90(0.80NaNbO3–0.20Sr0.7Bi0.2TiO3)–0.10BaSnO3 ceramic with high recoverable energy storage density (Wr = 3.51 J/cm3) and decent energy storage efficiency (η = 70.85%) has been obtained. In particular, these ceramics exhibit an ultrahigh breakdown strength of 402 kV/cm due to the dense microstructure and small grain size. The impedance analysis also reveals that the incorporation of BaSnO3 is conducive to the enhancement of insulation ability and breakdown strength. Additionally, great thermal stability (ΔWr < 10% over 20–120 °C at 200 kV/cm) and fatigue resistance (ΔWr < 1% after 120,000 electrical cycles at 200 kV/cm) are observed, indicating that the 0.90(0.80NaNbO3–0.20Sr0.7Bi0.2TiO3)–0.10BaSnO3 ceramics have promising application prospect for high-temperature energy storage devices in pulse power applications. [ABSTRACT FROM AUTHOR]

• A comprehensive strategy of hybridizations of Bi3+ orbitals and relaxor was adopted. • Relaxor behavior was analyzed via Raman spectroscopy and the Curie-Weiss law. • BNT-0.40ST-0.02FN composition exhibits high W (3.36 J/cm3) and η (81%) under a low electric field of 170 kV/cm. • BNT-0.40ST-0.02FN ceramic shows superior thermal stability (25–200 °C). • The BNT-0.40ST-0.02FN ceramic possesses potential to be employed in pulsed power devices under extreme conditions. Dielectric ceramics are highly favorable for pulsed power applications owing to their ultra-fast charge-discharge speed and excellent reliability. However, their low energy density under low electric fields remains as a bottleneck for them to be employed in integrated electronic devices with shrinking dimensions. In this work, we have designed a comprehensive strategy to synthesize lead-free (Bi 1/2 Na 1/2) 1−x Sr x Ti 0.98 (Fe 1/2 Nb 1/2) 0.02 O 3 (BNT-xST-2FN, x = 0.30, 0.35, 0.40 and 0.45) ceramics via traditional solid-state method. On one hand, the hybridizations of Bi3+ orbitals and the displacement of B-site cations under the applied electric field lead to a high polarization. On the other hand, the (Fe 1/2 Nb 1/2)4+ complex-ion and SrTiO 3 were introduced to improve the relaxor behavior of the system, resulting in a high energy-storage efficiency. In this way, an excellent energy density of 3.36 J/cm3 and a high energy efficiency of 81% are simultaneously achieved in the BNT-0.40ST-0.02FN composition under a low electric field of 170 kV/cm, which is superior to other BNT-based materials under similar electric fields. Moreover, the ceramic exhibits a superior thermal stability (25–200 °C). This work provides a promising approach for designing high-performance lead-free energy storage ceramics under low electric fields. [ABSTRACT FROM AUTHOR]

• BNT-(BCT-BZT) ceramics with large strain and without negative strain were prepared • A large field-induced strain of 0.42% and large d 33 * of 547 pm/V are obtained • Large strain is mainly due to the crossover of relaxor nonpolar state to ferroelectric polar state Piezoelectric ceramics with high strain can convert electrical energy and mechanical energy into each other for a wide range of applications. (1- x)Bi 0.5 Na 0.5 TiO 3 - x (0.5Ba 0.7 Ca 0.3 TiO 3 -0.5BaTi 0.8 Zr 0.2 O 3) (BNT- x (BCT-BZT)) lead-free piezoelectric ceramics were prepared through solid-state reaction methods. The structural, dielectric, field-induced strain and energy storage properties of the ceramics were investigated systematically by various characterization techniques. A large field-induced strain of 0.42% with negligible negative strain and large reverse piezoelectric coefficient of 547 pm/V are obtained in BNT-9(BCT-BZT) ceramics. A large recoverable energy storage of 3.49 J/cm3 under 360 kV/cm and high energy storage efficiency of 64.9% are achieved in the BNT-10(BCT-BZT) ceramics. It believes that the large strain with negligible negative strain is mainly due to the crossover of relaxor nonpolar state to ferroelectric polar state. We believe that the BNT- x (BCT-BZT) ceramics are favorable for the practical applications in the mobile electronic devices. [ABSTRACT FROM AUTHOR]

Dielectric energy-storage capacitors are of great importance for modern electronic technology and pulse power systems. However, the energy storage density (W rec) of dielectric capacitors is much lower than lithium batteries or supercapacitors, limiting the development of dielectric materials in cutting-edge energy storage systems. This study presents a single-phase BaTiO 3 -based high-entropy (BT-H) ceramic, which is synthesized using a conventional solid-state reaction method. It is found that the BT-H ceramic exhibits a remarkable energy storage performance, with a W rec of 5.18 J/cm3 and an ultrahigh η of 93.7% at 640 kV/cm electric field. Moreover, it also features wide temperature stability and excellent frequency stability. It is proposed that the introduction of high entropy enhances the random electric field and stress field, leading to lattice distortion and reduction of nanometer domain size, which in turn reduces remnant polarization and increases electric breakdown strength. This research provides a novel approach to improve the energy storage performance of ceramics through the high-entropy strategy. • High-entropy engineering could enhance the energy storage performance of dielectric capacitors. • An ultrahigh W rec of 5.18 J/cm3 and η of 93.7% at 640 kV/cm electric field were achieved in the BT-H (Mg) ceramics. • The BT-H ceramics exhibit remarkable energy storage performance stability. [ABSTRACT FROM AUTHOR]

• High-entropy engineering. • The activation energy. • Thermal stability. The utilization of a high entropy approach for the design of high-performance perovskite dielectric capacitors has been gaining much attention for the development of next-generation pulse power capacitors. Despite this, there are still challenges to further enhance their energy storage density and efficiency. To address this, a high-entropy strategy is proposed to significantly improve the energy storage characteristics of ceramics by increasing the configurational entropy and delaying saturation polarization. This approach has resulted in an ultra-high recoverable energy storage density (W rec) of 7.16 J/cm3 and a high efficiency (η) of 93.3 % for 0.8[0.65(Bi 0.5 Na 0.5)TiO 3 -0.35SrTiO 3)]-0.2[Ba(Zr 0.2 Ti 0.2 Sn 0.2 Hf 0.2 Nb 0.2)O 3 ] (abbreviated as 0.8BNST-0.2Ba(5 M)O) ceramic. The inclusion of Ba(5 M)O high entropy oxides has resulted in slender polarization–electric field hysteresis loops with delayed polarization saturation. The increase in atomic configuration entropy, degree of atomic disorder and lattice distortion due to the Ba(5 M)O high entropy oxides, has led to an increase in breakdown field, improved energy storage density and efficiency. Furthermore, excellent thermal stability (30–150 ℃), superior frequency stability (5–1000 Hz), and robust fatigue (100–105 cycles) endurance were achieved. The high entropy strategy has been demonstrated to be an effective method for the design of novel capacitors with superior energy storage performance. [ABSTRACT FROM AUTHOR]

Lead-free (0.70- x)BiFeO 3 -0.30BaTiO 3 - x AgNbO 3 +5‰mol CuO (abbreviated as BF-BT- x AN) ceramics were fabricated using a modified thermal quenching technique. BF-BT- x AN ceramics are of a perovskite structure with morphotropic phase boundary (MPB) and show strong relaxor properties. Remarkably, the high recoverable energy storage density of 2.11 J/cm3 is obtained for BF-BT- x AN with x = 0.14. For the x = 0.14 ceramics, its energy storage efficiency is as high as 84 % at relative low field of 195 kV/cm, together with an outstanding thermal stability in a broad temperature range from 25 °C to 150 °C. In addition, this ceramic maintains superior energy storage performance even after 8 × 104 electrical cycles due to its high densification after doping Ag 2 O and Nb 2 O 5. The result suggests that lead-free BF-BT- x AN ceramics may be promising candidate for dielectric energy storage application. [ABSTRACT FROM AUTHOR]

(Pb 0.92 La 0.08)(Zr 0.65 Ti 0.35)O 3 (PLZT), PbZrO 3 (PZO) films, and type A and type B PLZT/PZO multilayer thin films were deposited on Pt(111)/TiO x /SiO 2 /Si substrates by sol-gel method, where type A and type B films stand for PLZT/PZO/PLZT/PZO/PLZT/PZO and PLZT/PZO/PLZT/PLZT/PZO/PLZT multilayer thin film, respectively. Compared to the PLZT and PZO film, enhanced breakdown field strength and improved energy storage density were obtained in type A and B multilayer thin films. A superior energy storage density of 29.7 J/cm3 with the energy storage efficiency of 50.8% was achieved in type B multilayer thin film, corresponding to 81% enhancement compared with the energy storage density of PLZT films (16.4 J/cm3). Additionally, the type B multilayer thin film exhibits a good thermal stability up to 160 °C and excellent fatigue endurance after 107 charging-discharging cycles. The enhanced energy storage performance of type B multilayer thin film shows promise and may stimulate further researches on energy storage applications of multilayer dielectric thin films. [ABSTRACT FROM AUTHOR]

• High-entropy design strategy was adopted in this work. • The W rec of 7.6 J/cm3 and η of 90% were obtained in fabricated high-entropy ceramic. • The ceramic displayed good thermal/frequency/fatigue-resistance stability. Dielectric capacitors have gained much attention in next-generation advanced pulse power systems owing to their ultrafast charging/discharging rate. However, the early polarization saturation and large hysteresis hinder the enhancement of recoverable energy-storage density (W rec) with increasing electric field. Here, we design (Bi 0.5 Na 0.5)TiO 3 -based high-entropy dielectric capacitors to modulate polarization behavior and maximize the energy storage capacity. An ultrahigh W rec of 7.6 J/cm3, together with a high η of 90% is simultaneously obtained, showing great competitiveness among the (Bi 0.5 Na 0.5)TiO 3 -based energy storage ceramics. On the one hand, the linear-like P - E loops induced by enhanced random field, which is achieved by increasing the atomic configurational entropy, delay the polarization saturation and ensure the rapid enhancement of W rec under higher electric fields. On the other hand, the high efficiency (η) is assured due to the existence of polar nanoregions (PNRs) and the absence of relaxor ferroelectric to ferroelectric transition. Noticeably, the ceramic also exhibits excellent thermal stability (Δ W rec < 4.4%, Δ η < 10.3%, −50–200 °C), cycling stability (Δ W rec < 0.085%, Δ η < 0.12%, 1–105) and frequency stability (Δ W rec < 7.08%, Δ η < 3.79%, 1–200 Hz). This work reveals that regulating the entropy is an effective method to design high-performance dielectric capacitors. [ABSTRACT FROM AUTHOR]

Abstract Core-shell nanoparticles used as blocks to construct composite ceramics can exhibit high energy storage density, but the effects of original tunable shell thickness on the microstructures and energy storage property of finally sintered bulk ceramics has not been clarified, thus how to achieve the full potential of this technology to improve the energy storage density of ferroelectric-based ceramics remains to be solved. In this study, as precursors to fabricate bulk ceramics, BaTiO 3 @SiO 2 core-shell nanoparticles were successfully synthesized by a wet-chemical method and they were used as models to investigate the effect of the core-shell nanostructured precursors on the energy storage property of the bulk composite ceramics. The original BaTiO 3 nanoparticles coated with various homogenous SiO 2 shells were acquired by controlling the concentration of tetraethyl orthosilicate (TEOS). The surface microstructure of the bulk composite ceramics observed by scanning electron microscope (SEM) revealed that the SiO 2 outer shell of BaTiO 3 @SiO 2 nanoparticles plays an important role in constructing the microstructure of the ceramics. The remodeled microstructure has a great impact on leakage current density and dielectric property, and it makes a leading contribution to the energy storage performance of ceramics. As a result, the optimum SiO 2 loading range was confirmed and the maximum energy storage density obtained from BaTiO 3 @20 wt%SiO 2 was ∼4.799 J/cm3 at 370 kV/cm, demonstrating that nanoscale core-shell architecture is an effective strategy to improve the energy storage performance of ferroelectric-based composite ceramics. Highlights • BaTiO 3 @SiO 2 core-shell nanoparticles are used as blocks to construct composite ceramics for energy storage. • Tunable shell plays an important role in remodeling the microstructure of the ceramics. • The remodeled microstructure has a great impact on leakage current density, dielectric property and energy storage density. • The maximum energy storage density obtained from BaTiO 3 @20 wt%SiO 2 was ∼4.799 J/cm3 at 370 kV/cm. [ABSTRACT FROM AUTHOR]

Abstract The piezoelectric, electrocaloric and energy storage properties were systemically investigated in lead-free Bi 0.5 (Na 1-x K x) 0.5 TiO 3 ceramics from room temperature to high temperature region. These ceramics can be poled completely to obtain large piezoelectric coefficient (104–153 pC/N) at low electric field of ~30 kV/cm. The piezoelectric property shows good thermal stability due to high depolarization temperature (T d). For BNKT 20 , a large low electric field-induced strain of 0.36% is obtained at 120 °C under 50 kV/cm, the corresponding normalized strain coefficient is up to 720 pm/V, which is larger than other BNT-based ceramics at high temperature region. The electrocaloric properties of these ceramics are studied via indirect and direct methods. Large EC value (~1.08 K) in BNKT 20 ceramic is obtained at 50 kV/cm using indirect calculation. Above 100 °C, the dielectric energy storage density and efficiency of BNKT 20 is still up to ~0.85 J/cm3 and 0.75, respectively. The BNKT x ceramics may become promising candidates in the fields of actuators, electrocaloric cooling and energy storage at high temperature region. [ABSTRACT FROM AUTHOR]

The electrocaloric effect and energy storage property are tuned in the Ba 1-x Ce x Ti 0.99 Mn 0.01 O 3 ceramics prepared by the solid state reaction method. The ceramics with lower Ce content (x = 0.005, 0.015) show a better ΔT and ΔT/ΔE response. The ceramics with higher Ce content (x = 0.030, 0.040, 0.045) represent the broader ΔT peaks (50 K–60 K), and the higher energy storage density and efficiency. The largest electrocaloric response (ΔT max  = 1.22 K, ΔT/ΔE = 0.41 K mm/kV) is found in the Ba 0.995 Ce 0.005 Ti 0.99 Mn 0.01 O 3 ceramics, which is comparable or even higher than that of the most isovalent substituting BaTiO 3 -based ceramics reported before. The maximum energy storage density 0.11 J/cm 3 ( E  = 30 kV/cm) is obtained for the Ba 0.970 Ce 0.030 Ti 0.99 Mn 0.01 O 3 ceramics, with high efficiency of 65–88% over a wide temperature range of 72 K. This work may open more opportunities to design high electrocalaric and energy storage performance lead-free systems from the viewpoint of the heterovalent and size mismatch substitution. [ABSTRACT FROM AUTHOR]

Fast development of electrostatic capacitors requires dielectric materials to perform large energy storage densities with high efficiency over a wide temperature range. Although antiferroelectric materials hold great potentials for achieving superior energy storage effect due to the field-induced antiferroelectric-ferroelectric transition, the strongly first-order transition is inevitably accompanied with a low energy storage efficiency and inferior thermal stability. Here, we found that a high polarization change and low hysteresis can be simultaneously achieved in a crossover composition between antiferroelectric and relaxor antiferroelectric states. As a result, a large recoverable energy storage density (W rec ∼ 8.6 J/cm3) with high efficiency (η ∼ 85%) is obtained in lead-free Ag 1-3 x La x Nb 0.9 Ta 0.1 O 3 (x =0.03) ceramics under 460 kV/cm. The x =0.03 ceramics also exhibit excellent energy storage properties (W rec > 6.8 J/cm3 with ultrahigh η ∼ 90%) in the temperature range of 20-120°C. This promising energy storage effect of the antiferroelectric crossover composition arises from the coexistence of micro- and nano-antiferroelectric domains, which can persist over a wide temperature range. Our work may push forward the development of high-performance lead-free antiferroelectric dielectrics for energy storage devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Numerous electrode materials have been studied in supercapacitors for next-generation energy storage applications. As a paramagnetic metal with low resistivity, NiSe 2 has received much attention and been used extensively in many applications, including energy storage, electrocatalysts, and high temperature superconductors, etc. However, the capacitive properties of NiSe 2 are rarely investigated. In the present work, truncated cube-like NiSe 2 single crystals are synthesized by a facile hydrothermal approach and further used as electrode material in supercapacitors. The effects of different loading mass of electrode material on electrochemical capacitive behaviors are also investigated. Experimental results demonstrate that under a mass loading of 3.90 mg cm −2 , the as-prepared NiSe 2 electrode exhibits a high specific capacitance of 1044 F g −1 at 3 A g −1 (or an areal capacitance of 4.07 F cm −2 ), along with an excellent rate capability (601 F g −1 at 30 A g −1 ). Besides, the morphology change and the impedance increasement are responsible for the worse cycling performance of NiSe 2 electrode in the three-electrode system. Meanwhile, the practical electrochemical energy storage behavior of as-synthesized NiSe 2 is investigated in an asymmetric supercapacitor. The NiSe 2 //activated carbon (AC) asymmetric device possesses an outstanding cycle life (87.4% after 20,000 successive cycles), a high energy density of 44.8 Wh kg −1 at 969.7 W kg −1 and a higher power density of 17.2 kW kg −1 at 17.4 Wh kg −1 , showing attractive potential in practical applications. This work opens avenue for utilizing single crystal NiSe 2 as electrode material and providing important guidance to the further investigation of nickel selenides for advanced supercapacitors. [ABSTRACT FROM AUTHOR]

• Grain tuning and relaxor construction strategy was adopted in this work. • The W rec of 5.5 J/cm3 and W t of 6.4 J/cm3 were achieved in 0.6BNT-0.4SBTH ceramic. • The ceramic displayed good thermal stability and frequency insensitivity. Relaxor ferroelectrics have become competitive candidates in energy storage applications owing to their relatively high maximum polarization, high breakdown strength, and relatively low remnant polarization. Here, Bi 0.5 Na 0.5 TiO 3 (BNT) with large polarization was selected as the base composition, and Sr 0.7 Bi 0.2 Ti 0.8 Hf 0.2 O 3 (SBTH), as a dopant, was added into BNT to improve its relaxor behavior and decrease the grain size. A series of (1- x)Bi 0.5 Na 0.5 TiO 3 - x Sr 0.7 Bi 0.2 Ti 0.8 Hf 0.2 O 3 (abbreviated as (1- x)BNT- x SBTH, x = 0.1, 0.2, 0.3 and 0.4) ceramics were synthesized. The addition of SBTH resulted in the increase in structural disorder, as confirmed by the red-shift in Raman spectra, the enhancement of the relaxor characteristic and the fast response of the domains in local poling measurements. As a result, excellent energy storage properties (with the recoverable energy storage density of 5.5 J/cm3 and efficiency of 85.9 % at 410 kV/cm) were realized in the 0.6BNT-0.4SBTH sample. Moreover, the sample also exhibited excellent thermal stability (20 °C to 200 °C) and frequency insensitivity (0.5–500 Hz). These results suggest that BNT-based relaxor ferroelectric ceramics modulated by SBTH possess great potential in dielectric energy-storage capacitors. [ABSTRACT FROM AUTHOR]

To meet the booming demands for advanced pulse power systems, developing dielectric ceramics with excellent energy storage performance is extremely urgent. In this work, a composition modulation strategy was adopted for designing Bi 0.5 K 0.5 TiO 3 -based ceramics. That is, incorporating Bi(Mg 0.5 Hf 0.5)O 3 into 0.6Bi 0.5 K 0.5 TiO 3 -0.4Sr 0.7 Bi 0.2 TiO 3 matrix (abbreviated as (1- x)(BKT-SBT)- x BMH, x = 0.00, 0.04 and 0.08). The energy storage performance of the (1- x)(BKT-SBT)- x BMH ceramics was enhanced by increasing the breakdown strength. Ultimately, a recoverable energy density (W rec) of 4.25 J/cm3 together with an efficiency (η) of 87 % was achieved for the x = 0.04 ceramic at 360 kV/cm. Furthermore, excellent energy storage properties (W rec ≥ 2.71 J/cm3, η ≥ 85 %) were obtained over a wide range of temperatures (20–200 ℃), frequencies (0.5–100 Hz) and cycle numbers (105) under 260 kV/cm, indicating good thermal stability, frequency-independent character and fatigue-resistance behavior. Our work would open up a new avenue for preparing BKT-based dielectric ceramics. • Composition modulation was adopted to design Bi 0.5 K 0.5 TiO 3 -based ceramics. • An excellent W rec of 4.25 J/cm3 along with η of 87 % at 360 kV/cm was achieved. • The ceramic displayed good thermal, frequency and cycle stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxygen-doped solid solution Ti 3 AlC 2-δ O δ MAX is synthesized. • The Ti 3 C 2-δ O δ T x MXene is obtained by etching the forming solid solution. • Ti 3 C 2-δ O δ T x electrodes show a capacity of 306.0 C g−1 (216.8 C g−1 for Ti 3 C 2 T x). • Improved diffusion-controlled capacitance is owed to the higher Ti active center. • Enhanced interface capacitance is owed to the improved quantum capacitance. Heteroatom doping has been proven to be an effective strategy to improve the electrochemical energy storage capacity of two-dimensional MXenes. However, the heteroatom for MXenes is mainly focused on the N atoms, while the effects and underlying mechanisms of O substituted partial C atoms of MXene have not been explored so far. Herein, comprehensive research is firstly performed to reveal the oxygen doping mechanism in Ti 3 C 2 T x MXene by the experimental characterization and the density functional theory simulation. The in situ oxygen doped Ti 3 C 2 T x nanosheets, in which oxygen atoms substitute partial carbon atoms in the titanium octahedron, are synthesized by etching the oxygen doped Ti 3 AlC 2 MAX phase, which is more facile than the complex post-doped process. The introduction of appropriate oxygen atoms can effectively improve the interlayer space, electronic conductivity, and interface charge transfer of the Ti 3 C 2 T x MXene as a supercapacitor electrode. Further, the electrochemical performances demonstrate that the oxygen doped MXene (O-Ti 3 C 2 T x -0.05) film electrode can deliver a higher capacity of 306.0 C g−1 compared to the pristine Ti 3 C 2 T x electrode (216.8 C g−1). Besides, the quantitative analysis results imply that the enhanced capacitance is mainly attributed to the diffusion-controlled capacitance and interface capacitance, which result from the higher Ti metal active center, the enhanced quantum capacitance, and the higher adsorption energy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of ST and BMH doping in BNT on energy storage properties were studied. • By modifying composition, good energy storage properties are obtained in BNST-BMH. • Ultrahigh W rec of 5.59 J/cm3 and η of 85.3% are realized in BNST-BMH ceramic. • BNST-BMH ceramic exhibits excellent thermal stability from 20 °C to 140 °C. • A superior fatigue resistance over 105 cycles was achieved in BNST-BMH ceramic. Dielectric ceramic capacitors with high energy density are one of the great bright energy storage devices. Here, the Bi 0.5 Na 0.5 TiO 3 , 0.75Bi 0.5 Na 0.5 TiO 3 -0.25SrTiO 3 , 0.65Bi 0.5 Na 0.5 TiO 3 -0.35SrTiO 3 and 0.88(0.65Bi 0.5 Na 0.5 TiO 3 -0.35SrTiO 3)-0.12Bi(Mg 0.5 Hf 0.5)O 3 , (abbreviated as BNT, BNT-25ST, BNT-35ST and BNST-BMH, respectively) ceramics were produced by solid state sintering method. The influence of solid solution of SrTiO 3 and Bi(Mg 0.5 Hf 0.5)O 3 doping in Bi 0.5 Na 0.5 TiO 3 on crystal structure, microstructure, electrical and energy storage performance were evaluated systematically. By optimizing ceramics composition, high breakdown field and slim hysteresis loops were simultaneously realized due to enhanced band gap, refined grain size and nano-domains formed, which can be verified by the transmission electron microscope (TEM), piezoelectric force microscope (PFM) and ultraviolet–visible spectrum. Therefore, an ultrahigh recoverable energy density of 5.59 J/cm3 with brilliant efficiency of 85.3% is realized in BNST-BMH ceramic. Besides, the BNST-BMH also exhibits prominent temperature stability at 20–140 °C, superior fatigue resistance beyond 105 cycles and outstanding frequency stability at 1–200 Hz. Our work offers a novel way for designing dielectric capacitors and also proves that BNST-BMH is indeed a great hopeful dielectric energy storage material in pulse power electronics. [ABSTRACT FROM AUTHOR]

[Display omitted] • 0.9NBST-0.1BMS lead-free ceramics with W rec = 6.68 J/cm3 and η = 89.1 % were designed and fabricated. • Small grain size and high activation energy of grain boundary leads to high breakdown field (405 kV/cm). • The energy storage potential (W rec /E b) is up to 0.01649 μC/cm2. • Excellent fatigue endurance over 105 electrical cycles (the W rec variation is less than 1.5%). Ferroelectric ceramics, as a potential candidate for high-power energy storage capacitors, lies in their excellent recoverable energy storage density (W rec) and outstanding efficiency (η) in practical applications. Herein, a new type of lead-free ceramics (1- x)(Na 0.5 Bi 0.5) 0.65 Sr 0.35 TiO 3 - x BiMg 0.5 Sn 0.5 O 3 or (1- x)NBST- x BMS was prepared with the aim of enhancing the breakdown strength (E b) and reducing the energy storage loss through grain refinement. It was found that E b of 0.9NBST-0.1BMS reaches 405 kV/cm due to the reduction in the grain size of ceramic and thus the extremely high ratio of grain boundary resistance to grain resistance. Besides, a remarkable energy-storage performance was obtained, that is, W rec and η are ∼ 6.68 J/cm3 and 89.1% at 405 kV/cm, respectively, along with excellent stability in terms of frequency, temperature, and fatigue endurance. The outstanding energy-storage performance is resulted from modulating the grain size via doping the moderate content of Bi3+ and Mg2+/Sn4+, which is beneficial to increase the breakdown field by increasing resistivity under high electric field while increasing the grain boundary activation energy and promote the formation of a relaxor state at the same time. More importantly, energy storage potential (defined as W rec /E b) is up to 0.01649 μC/cm2, being the highest value reported so far for BNT-based ceramics in energy-storage application. Our results pave the way for practical applications of NBST-based ferroelectric capacitors with excellent energy storage performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Utilize an average ionic polarizability design strategy to balance W rec and η. • The high-polarization gene is maintained and the polar order is disrupted. • Achieve excellent energy-storage properties both in low-field and moderate-field. • The existence of dynamic PNRs is confirmed by PFM measurements. • The temperature-dependent Raman spectra reveal the variation of local structure. Electrostatic capacitors are promising candidates in the application of pulse-power systems due to their high power density and fast charge-discharge rate. However, the insufficient recoverable energy density (W rec) and energy efficiency (η) under low/moderate electric field is still the bottleneck for their applications in miniaturized equipment and portable devices. In this work, we utilize an average ionic polarizability design strategy to enhance W rec by sustaining the high-polarization gene of the system and simultaneously improve η by disrupting the polar order in (1- x)[0.7Bi 0.5 Na 0.5 TiO 3 -0.3Sr 0.7 Bi 0.2 TiO 3 ]- x Sr(Zn 1/3 (Nb 0.85 Ta 0.15) 2/3)O 3 ceramics. As a result, excellent energy-storage properties have been achieved both in low-field (W rec ∼ 2.7 J/cm3 and high η ∼ 93% at 200 kV/cm) and moderate-field (W rec ∼ 5.2 J/cm3 and η ∼ 91% at 330 kV/cm) for x = 0.12 sample. Additionally, the x = 0.12 sample exhibits good thermal stability (−50 ∼ 200 ℃), frequency stability (0.5 ∼ 500 Hz) and cycle stability (105 cycles). Hence, the current work may provide some novel perspectives for improving the W rec and η of dielectric capacitors under low/moderate electric fields. [ABSTRACT FROM AUTHOR]

• Through modifying Sn4+ content, the breakdown strength is increased by 112.3%. • The recoverable energy density enhanced by 276.2% via incorporation of Sn4+. • The doping of Sn4+ inhibits the migration of grain boundary and refines grains. • The delayed polarization saturation result from Sn4+ with d10 substitutes Ti4+ with d0. [Display omitted] High-performance dielectric ceramic capacitors is a promising candidate in energy storage devices. In this work, the energy storage performance of Ba 0.94 Ca 0.06 Ti 1−x Sn x O 3 (x = 0.04, 0.08, 0.12, 0.16) ceramics was systematically studied. Through modifying Sn4+ doping content, the breakdown strength of the ceramics is enhanced by 112.3% from 133.4 kV/cm (Ba 0.94 Ca 0.06 Ti 0.96 Sn 0.04 O 3) to 283.2 kV/cm (Ba 0.94 Ca 0.06 Ti 0.84 Sn 0.16 O 3). Accordingly, the recoverable energy density is greatly increased by 276.2%, that is, from 0.42 J/cm3 grow to 1.58 J/cm3. The enhanced energy storage properties could be ascribed to the following aspects: (1) the doping of Sn4+ with a larger ionic radius inhibits the migration of grain boundaries and therefore refines grains, resulting in a higher activation energy and a larger E b ; (2) the long range polar order is broke and polar nano-regions are formed, giving rise to lower energy barrier and smaller P r ; (3) the weakened ferroelectricity and delayed polarization saturation lead to higher W rec owing to the fact that Sn4+ with d10 electronic configurations substitutes Ti4+ with d0. Our work provides a novel approach for enhancing energy storage performance in dielectric ceramic capacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Moderate Bi3+ content is helpful to enhance activation energy and breakdown field. • Through introducing A-site defect, the slim loop and high Δ P are received in SBT2. • Ultrahigh W rec of 4.77 J/cm3 and η of 85.7% were obtained in Sr 0.7 Bi 0.2 TiO 3 ceramic. • Sr 0.7 Bi 0.2 TiO 3 ceramic shows good temperature stability at 20–160 °C. • An outstanding fatigue resistance after 105 cycles was achieved in Sr 0.7 Bi 0.2 TiO 3. The application of dielectric capacitors with high energy density is very important to solve the increasingly serious energy crisis. However, the further improvement of energy density is seriously confining by their poor breakdown fields. In this work, outstanding energy storage performance is achieved in Sr 0.7 Bi x TiO 3 (x = 0.1, 0.2, 0.3 and 0.4) ceramics via A-site defect and grain size tuning. It was found that the moderate Bi3+ content is helpful to reduce sintering temperature and refine grain size, which lead to higher activation energy and breakdown field. Besides, moderate Bi3+ doping in A-site enhances polarity owing to the hybridizations between 6p orbital of Bi and 2p orbital of O. Thus, a high recoverable energy density of 4.77 J/cm3 with prominent efficiency of 85.7% at 570 kV/cm is realized in Sr 0.7 Bi 0.2 TiO 3 ceramic. Moreover, the Sr 0.7 Bi 0.2 TiO 3 ceramic also displays superior thermal stability from 20 °C to 160 °C and excellent fatigue endurance over 105 cycles. Our results in this work offer a better understanding and design methodology for developing novel high-performance dielectric capacitors. [ABSTRACT FROM AUTHOR]

Nickel-phosphorus semimetallic compounds with an open-framework structure have attracted increasing interests as electrode materials for supercapacitor applications. In this work, ultrafine Ni–P@Ni nanotubes (NTs) with a novel three-dimensional network are synthesized by using a one-pot hydrothermal method under different temperatures to form the electrode material for hybrid supercapacitors. The energy storage performances of the Ni–P@Ni NTs electrodes are systematically investigated, and the results demonstrate that the Ni–P@Ni NTs possess a superior specific capacity of 771.8 C g−1 at 1 A g−1 in a three-electrode cell. Remarkably, a specific capacity of 350.2 C g−1 can still be maintained when the current density increases up to 30 A g−1. The energy storage performance of the as-prepared Ni–P nanowires (NWs) and Ni 11 (HPO 3) 8 (OH) 6 @Ni nanoparticles (NPs) also are evaluated for comparison. Furthermore, a hybrid supercapacitor (HSC) is assembled with the Ni–P@Ni NTs as the positive electrode and activated carbon (AC) as the negative electrode. The as-assembled HSCs show a high energy density of 58.7 Wh kg−1 at a relatively high-power density of 945 W kg−1, outweighing most of the hybrid supercapacitors reported in the literature. Furthermore, such a hybrid supercapacitor displays an excellent cycling stability (91.2% after 6000 cycles at 5 A g−1) under a voltage of 1.6 V. • The first report on the Ni–P@Ni NTs with a 3D porous network by a facile hydrothermal method and calcination. • The loaded mass of the Ni–P@Ni NTs electrode is around 8 mg cm−2, comparable with the commercial supercapacitors. • The as-fabricated Ni–P@Ni NTs//AC device shows a energy density of 58.7 Wh kg−1 at a power density of 945 W kg−1. [ABSTRACT FROM AUTHOR]