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

Dielectric energy-storage capacitors have received increasing attention in recent years due to the advantages of high voltage, high power density, and fast charge/discharge rates. Here, a new environment-friendly 0.76NaNbO3–0.24(Bi0.5Na0.5)TiO3 relaxor antiferroelectric (AFE) bulk ceramic is studied, where local orthorhombic Pnma symmetry (R phase) and nanodomains are observed based on high-resolution transmission electron microscopy, selected area electron diffraction, and in/ex situ synchrotron X-ray diffraction. The orthorhombic AFE R phase and relaxor characteristics synergistically contribute to the record-high energy-storage density Wrec of ≈12.2 J cm−3 and acceptable energy efficiency η ≈ 69% at 68 kV mm−1, showing great advantages over currently reported bulk dielectric ceramics. In comparison with normal AFEs, the existence of large random fields in the relaxor AFE matrix and intrinsically high breakdown strength of NaNbO3-based compositions are thought to be responsible for the observed energy-storage performances. Together with the good thermal stability of Wrec (>7.4 J cm−3) and η (>73%) values at 45 kV mm−1 up to temperature of 200 °C, it is demonstrated that NaNbO3-based relaxor AFE ceramics will be potential lead-free dielectric materials for next-generation pulsed power capacitor applications.

Ultrahigh Energy‐Storage Density in NaNbO3‐Based Lead‐Free Relaxor Antiferroelectric Ceramics with Nanoscale Domains

Achieve ultrahigh energy storage performance in BaTiO3–Bi(Mg1/2Ti1/2)O3 relaxor ferroelectric ceramics via nano-scale polarization mismatch and reconstruction

Dielectric ceramics are highly desired for electronic systems owing to their fast discharge speed and excellent fatigue resistance. However, the low energy density resulting from the low breakdown electric field leads to inferior volumetric efficiency, which is the main challenge for practical applications of dielectric ceramics. Here, we propose a strategy to increase the breakdown electric field and thus enhance the energy storage density of polycrystalline ceramics by controlling grain orientation. We fabricated high-quality -textured Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 (NBT-SBT) ceramics, in which the strain induced by the electric field is substantially lowered, leading to a reduced failure probability and improved Weibull breakdown strength, on the order of 103 MV m−1, an ~65% enhancement compared to their randomly oriented counterparts. The recoverable energy density of -textured NBT-SBT multilayer ceramics is up to 21.5 J cm−3, outperforming state-of-the-art dielectric ceramics. The present research offers a route for designing dielectric ceramics with enhanced breakdown strength, which is expected to benefit a wide range of applications of dielectric ceramics for which high breakdown strength is required, such as high-voltage capacitors and electrocaloric solid-state cooling devices. The energy density of dielectric ceramic capacitors is limited by low breakdown fields. Here, by considering the anisotropy of electrostriction in perovskites, it is shown that -textured Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 ceramics can sustain higher electrical fields and achieve an energy density of 21.5 J cm−3.

Grain-orientation-engineered multilayer ceramic capacitors for energy storage applications.

Superior comprehensive energy storage properties in Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics

Grain size engineered lead-free ceramics with both large energy storage density and ultrahigh mechanical properties

Although tremendous achievements have been made in enhancing recoverable energy storage density (Wrec) of lead-free dielectric ceramics for electrical energy storage applications in recent years, these ceramics with high Wrec still have two disadvantages: complex chemical composition and difficult preparation process. In this work, we selected NaNbO3 (NN)-based ceramics as base materials and used Bi2O3 as a sintering aid to reduce porosity and enhance dielectric breakdown strengths. Encouragingly, high Wrec, simple chemical composition and facile preparation process were simultaneously realized in 0.77NaNbO3-0.23BaTiO3 (0.77NN-0.23BT) ceramics. A large Wrec of 1.5 J cm−3 at 175 kV cm−1 and excellent thermal stability (variation of Wrec

A new family of sodium niobate-based dielectrics for electrical energy storage applications

Converting electrical into thermal energy in ferroelectrics paves the way for a novel cooling technology, to open up new fields of applications. For electrocaloric refrigeration, a large temperature change (ΔT) and excellent temperature stability are highly desired. Unfortunately, a large room temperature ΔT in lead-free bulk ceramics is usually obtained at the expense of temperature stability, and vice versa, limiting their practical applications. In this work, composition engineering is carried out as an important strategy to tune the phase transition to room temperature and simultaneously induce a diffuse phase transition to achieve excellent temperature stability. A large room temperature ΔT is realized by the application of large electric fields, possibly due to the optimization of sintering process in sodium niobate based ceramics. The 0.78NaNbO3–0.22BaTiO3 ceramic is found to exhibit both a large room temperature ΔT (∼0.70 K) and superior temperature stability (±1.4% variation in ΔT from 300 K to 380 K). Those properties are superior to previously reported lead-free bulk ceramics. This work provides a guide for the development of high-performance ceramic materials such as NaNbO3–ABO3 (A = Ba, Sr and Ca; and B = Ti and Zr) for electrocaloric refrigeration. Most importantly, this work expands the applications of NaNbO3-based ceramics from electric energy storage, electrostrictive and piezoelectric applications, to a new field, i.e. solid-state refrigeration. This makes NaNbO3-based ceramics very promising multifunctional materials for device integration.

Ying Yu

Papers

Grain size engineered lead-free ceramics with both large energy storage density and ultrahigh mechanical properties

A new family of sodium niobate-based dielectrics for electrical energy storage applications

Significantly enhanced room temperature electrocaloric response with superior thermal stability in sodium niobate-based bulk ceramics

Investigation of the discharging behaviors of different doped silicon nanowires in alkaline Si-air batteries

First-principles study of ZIF-8 as anode for Na and K ion batteries