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

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

Compared with fuel cells and electrochemical capacitors, dielectric capacitors are regarded as promising devices to store electrical energy for pulsed power systems due to their fast charge/discharge rates and ultrahigh power density. Dielectric materials are core components of dielectric capacitors and directly determine their performance. Over the past decade, extensive efforts have been devoted to develop high-performance dielectric materials for electrical energy storage applications and great progress has been achieved. Here, we present an overview on the current state-of-the-art lead-free bulk ceramics for electrical energy storage applications, including SrTiO3, CaTiO3, BaTiO3, (Bi0.5Na0.5)TiO3, (K0.5Na0.5)NbO3, BiFeO3, AgNbO3 and NaNbO3-based ceramics. This review starts with a brief introduction of the research background, the development history and the basic fundamentals of dielectric materials for energy storage applications as well as the universal strategies to optimize their energy storage performance. Emphases are placed on the design strategies for each type of dielectric ceramic based on their special physical properties with a summary of their respective advantages and disadvantages. Challenges along with future prospects are presented at the end of this review. This review will not only accelerate the exploration of higher performance lead-free dielectric materials, but also provides a deeper understanding of the relationship among chemical composition, physical properties and energy storage performance.

High-performance lead-free bulk ceramics for electrical energy storage applications: design strategies and challenges

Lead-free antiferroelectric (AFE) ceramics have attracted increasing attention in recent years for application in high-power capacitors owing to both environmental friendliness and high energy density. However, the relevant research progress has been seriously restricted by the limited amount of AFE candidate materials with low cost and excellent properties, which significantly rely on the AFE phase stability and crystal symmetry. In this work, NaNbO3–Bi(Mg0.5Ti0.5)O3 (NN–BMT) perovskite solid solutions were reported to obviously exhibit AFE phase structure dependent energy-storage performances, evolving from Wrec ∼ 1.08 J cm−3 and η ∼ 19% at x = 0.05 with an orthorhombic P phase (Pbam) under 25 kV mm−1 to 3.12 J cm−3 and 74%, respectively, at x = 0.08 with an orthorhombic R phase (Pnma) under 30 kV mm−1 owing to the transition of square-like double hysteresis loops into slim and double-like ones and the increased testable electric fields. Most interestingly, doping 0.5 mol% transition-metal oxides (CuO, CeO2 and MnO2) was found to evidently improve the sintering behaviour, bulk resistivity and defect structure, thus leading to largely enhanced dielectric breakdown strength. In particular, the MnO2 doped 0.92NN–0.08BMT sample exhibits a large Wrec of ∼ 5.57 J cm−3 and a high η of ∼ 71% as well as excellent charge–discharge performance (CD = 636.7 A cm−2, PD = 63.7 MW cm−3 and t0.9 ∼ 85 ns), determined by means of the detailed analysis of the grain size distribution, impedance and X-ray photoelectron spectra. The results demonstrate that NN–BMT bulk ceramics could be very competitive lead-free AFE materials for energy-storage capacitors in pulsed power devices.

Large energy-storage density in transition-metal oxide modified NaNbO3–Bi(Mg0.5Ti0.5)O3 lead-free ceramics through regulating the antiferroelectric phase structure

The development and use of high-performance and environmentally friendly energy storage capacitors are urgently demanded. Despite extensive research efforts, the performance of existing lead-free dielectric ceramics is barely satisfactory. In this work, a novel lead-free 0.78NaNbO3–0.22Bi(Mg2/3Ta1/3)O3 (0.22BMT) linear-like relaxor ferroelectric with ultrahigh energy storage capability and ultrahigh efficiency was designed and synthesized via a local random field strategy. To our satisfaction, an ultrahigh recoverable energy density (Wrec, 5.01 J cm−3) and an ultrahigh energy efficiency (η) of 86.1% were achieved simultaneously, which are superior to those of other reported lead-free systems. In addition, excellent temperature, frequency and fatigue stabilities (variation of Wrec < 8% over 20–200 °C, Wrec < 3% after 1–100 Hz and 104 cycles) were observed. More importantly, the 0.22BMT ceramic exhibited a large current density (CD ∼ 537.9 A cm−2), an extremely high power density (PD ∼ 37.7 MW cm−3), and an ultrafast discharge time (t0.9 ∼ 23 ns). The impedance analysis demonstrated that the introduction of BMT was beneficial for the improvement of the insulation ability and breakdown strength (Eb) of the 0.22BMT ceramic. Additionally, nonisovalent Mg2+ and Ta5+-filled Nb5+ on the B-site with low average electronegativity generated a random local field, which enhanced the ion bonding, destroyed the long-range order and led to decreased remnant polarization (Pr). These results indicate that this new strategy is a feasible and efficacious means to simultaneously achieve ultrahigh Wrec, superior η and excellent thermal stability in NN-based lead-free ceramics. Furthermore, this work has further broadened the scope of research and the application of the NN-based ceramics.

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Realizing ultrahigh recoverable energy density and superior charge–discharge performance in NaNbO3-based lead-free ceramics via a local random field strategy

Relaxor ferroelectric (FE) ceramic capacitors have attracted increasing attention for their excellent energy-storage performance. However, it is extremely difficult to achieve desirable comprehensive energy-storage features required for industrial applications. In this work, very high recoverable energy density W-rec approximate to 8.73 J cm(-3), high efficiency eta approximate to 80.1%, ultrafast discharge rate of

NaNbO3-(Bi0.5Li0.5)TiO3 Lead-Free Relaxor Ferroelectric Capacitors with Superior Energy-Storage Performances via Multiple Synergistic Design

High energy storage density and power density achieved simultaneously in NaNbO3-based lead-free ceramics via antiferroelectricity enhancement

Simultaneously achieving ultrahigh energy storage density and energy efficiency in barium titanate based ceramics

NaNbO3-based (NN) energy storage ceramics exhibit high breakdown electric field strength (Eb) with large recoverable energy storage density (Wrec). However, due to their large energy loss density (Wloss) under strong electric fields, maintaining high energy storage efficiency (η) is a challenge. In this study, to produce a dielectric ceramic with both high Wrec and η, a ternary system was designed. By the addition of (Bi0.5Na0.5)0.7Sr0.3TiO3 (BNST), the grain size of 0.90NaNbO3–0.10Bi(Mg0.5Ta0.5)O3 (0.10BMT) was effectively reduced, and the long-range ordered structure was broken, providing an easily turned over dielectric domain to inhibit Wloss. The activation energy of the grain boundary increased with the increase in resistivity, indicating that the concentration of free vacancies at the grain boundary was low. The jump barrier of oxygen vacancies in the grain boundary increased, making up for the grain boundary defects, thus increasing Eb. When the BNST concentration increased, the Eb and Wrec of the dielectric ceramics increased. Optimum performance was obtained with the 0.75[0.90NaNbO3–0.10Bi(Mg0.5Ta0.5)O3]–0.25(Bi0.5Na0.5)0.7Sr0.3TiO3 (0.25BNST) ceramic, which exhibited an exceptionally high Eb (800 kV cm−1) and Wrec (8 J cm−3), while maintaining a relatively high η (90.4%). The ceramics developed in this study showed excellent temperature and frequency stability over 20–200 °C and 1–160 Hz, respectively. In addition, the dielectric properties of the ceramics were maintained after 10 000 hysteresis cycles. The 0.25BNST ceramic showed an exceptionally fast t0.9 (∼32 ns) and a high CD (614.5A cm−2). This study demonstrates that the energy storage performance and stability of the fabricated 0.25BNST ceramic are superior to those of previously reported dielectric ceramics.

Excellent energy storage properties and stability of NaNbO3–Bi(Mg0.5Ta0.5)O3 ceramics by introducing (Bi0.5Na0.5)0.7Sr0.3TiO3

Lead-free ceramic capacitors are widely applied for novel pulse power supply systems owing to their environmental friendliness, high power density and fast charge/discharge characteristics. Neverth...

Feihong Pang

Papers

Realizing ultrahigh recoverable energy density and superior charge–discharge performance in NaNbO3-based lead-free ceramics via a local random field strategy

High energy storage density and power density achieved simultaneously in NaNbO3-based lead-free ceramics via antiferroelectricity enhancement

Simultaneously achieving ultrahigh energy storage density and energy efficiency in barium titanate based ceramics

Excellent energy storage properties and stability of NaNbO3–Bi(Mg0.5Ta0.5)O3 ceramics by introducing (Bi0.5Na0.5)0.7Sr0.3TiO3

Ultrahigh Energy Storage Characteristics of Sodium Niobate-Based Ceramics by Introducing a Local Random Field