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

We have observed size effects in the structural phase transition of submicron vanadium dioxide precipitates in silica. The VO 2 nanoprecipitates are produced by the stoichiometric coimplantation of vanadium and oxygen andsubsequent thermal processing. The observed size dependence in the transition temperature and hysteresis loops of the semiconductor-to-metal phase transition in VO 2 is described in terms of heterogeneous nucleation statistics with a phenomenological approach in which the density of nucleating defects is a power function of the driving force.

Size effects in the structural phase transition of VO2 nanoparticles

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 ceramic capacitors play an important role in electrical energy storage devices because of their ultrafast charge/discharge rates and high power density. However, simultaneously obtaining large energy storage capability, high efficiency and superior temperature stability has been a huge challenge for practical applications of ceramic capacitors. Here, the relaxor ferroelectric (1-x)[0.8Bi0.5Na0.5TiO3-0.2Ba(Zr0.3Ti0.7)O3]-xSr0.7La0.2TiO3 ((1-x)(BNT-BZT)-xSLT) ceramics are prepared through solid-state reaction method to obtain excellent comprehensive energy storage performances. Particularly, high recoverable energy density (Wrec ∼ 2.6 J/cm3) as well as superior efficiency (η ∼ 92.2 %) can be achieved simultaneously under 210 kV/cm with composition of x = 0.3. Meanwhile, the corresponding ceramic shows excellent temperature (20−140 °C), frequency (1−200 Hz) and cycle stabilities (106 st). Additionally, the 0.7(BNT-BZT)-0.3SLT ceramic also displays high power density (PD ∼ 38.8 MW/cm3) and extremely short discharge time (τ0.9 ∼ 0.11 μs). Therefore, this study provides a useful guideline for designing novel BNT-based ceramics with superior comprehensive energy storage performances.

Realizing high comprehensive energy storage performances of BNT-based ceramics for application in pulse power capacitors

Local Structure Engineered Lead-Free Ferroic Dielectrics for Superior Energy-Storage Capacitors: A Review

High energy density and efficiency in (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics with high La3+ content and optimized Sn4+ content

High-temperature energy storage performances in (1-x)(Na0.50Bi0.50TiO3)-xBaZrO3 lead-free relaxor ceramics

In order to enhance the visible-light transmittance while reducing the insulator–metal transition (IMT) temperature, Hf–W co-doping is designed for modification of VO2. We grow high-quality HfxWyV1−x−yO2 (HfWVO2) alloy films on c-plane sapphire substrates by pulsed laser deposition, and test structural, electrical, and optical properties of the films by various techniques. The Hf–W co-doped VO2 films exhibit outstanding thermochromic performances with a high luminous transmittance up to 41.1%, a fairly good near-infrared modulation capacity of 13.1%, and a low phase transition temperature of 38.9 °C. The enhanced luminous transmittance along with reduced IMT temperature in HfWVO2 is attributed to the co-doping synergetic effect of Hf and W, which effectively improves the optical bandgap and donates extra electrons into the system, respectively, while largely retaining the near-infrared modulation capacity of VO2. Our work provides an effective strategy in tailoring VO2 toward practical smart-coating applications by Hf–W co-doping.

Enhancing visible-light transmittance while reducing phase transition temperature of VO2 by Hf–W co-doping

Nb-doped VO2 thin films with enhanced thermal sensing performance for uncooled infrared detection

The invention discloses a Ru V O alloy semiconductor thin-film material with an adjustable phase-transition temperature and a preparation method thereof, and application of the Ru V O alloy semiconductor thin-film material to smart windows. The Ru V O alloy semiconductor thin-film material provided by the invention is a three-membered solid solution composed of ruthenium, vanadium and oxygen in a certain atomic ratio. According to the invention, Ru ions are selected to partially replace V ions and used for preparing a replacement Ru V O alloy system, therebyrealizing the adjustment of the phase-transition temperature of VO . The Ru V O alloy semiconductor thin-film material provided by the invention has metal-insulator transition characteristics, with an MIT phase-transition temperature being 43-65 DEG C; resistivity changes in a range of 3-5 orders of magnitude before and after metal-insulator transition; and the capacity of a smart window prepared from the thin-film material in modulation of infrared light in a wavelength range of 780-2500 nm is 12.7-21.4%. In addition, the method of the invention is simple, and the requirements ofthin-film growth on the environment are low; so the method is suitable for large-scale production.

Ru V O alloy semiconductor thin-film material with adjustable phase-transition temperature and preparation method thereof, and application of Ru V O alloy semiconductor thin-film material to smart windows

Hao Li

Papers

High energy density and efficiency in (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics with high La3+ content and optimized Sn4+ content

High-temperature energy storage performances in (1-x)(Na0.50Bi0.50TiO3)-xBaZrO3 lead-free relaxor ceramics

Enhancing visible-light transmittance while reducing phase transition temperature of VO2 by Hf–W co-doping

Nb-doped VO2 thin films with enhanced thermal sensing performance for uncooled infrared detection

Ru V O alloy semiconductor thin-film material with adjustable phase-transition temperature and preparation method thereof, and application of Ru V O alloy semiconductor thin-film material to smart windows