Perovskite lead-free dielectrics for energy storage applications
Introduction
As the world population keeps growing and the global economy developing, worldwide energy consumption is increasing at a high rate. The total final energy consumption of the whole world has gone up from 54,207 TWh in 1973 to 111,125 TWh in 2016 [1]. Due to the problems caused by global warming, air pollution, and the depletion of fossil fuel resources, exploiting various clean and renewable energy sources is the obvious solution [2], [3], [4], [5]. Although more than half of our consumed energy is generated from fossil fuels, renewable energy sources, such as solar, wind, or geothermal, are becoming more dominant [1]. Even so, most renewable energy is intermittent in nature, which poses challenges for harnessing these sources of energy. Converting the renewable energy to other forms (mainly electricity) is a good solution, where efficient and reliable electrical energy storage solutions are keys to effective implementation of the electricity generated from these renewable sources [2], [6], [7], [8], [9], [10]. Chemical energy storage devices (batteries), solid oxide fuel cells (SOFCs), flywheels, superconducting magnetic energy storage (SMES) systems, electrochemical capacitors (ECs), and electrostatic capacitors (dielectric capacitors) represent the majority of electrical storage technologies today. The batteries and fuel cells possess high energy density but low power density, while the dielectric capacitors exhibit the opposite features. Meanwhile, the electrochemical capacitors possess medium energy density and power density. Compared with dielectric capacitors, electrochemical capacitors suffer from low operating voltage (<3 V), large leakage current (∼mA), and high cost (9500 USD/kWh) [11], [12], while dielectric capacitors are more suitable for high-voltage, low-cost, and large-scale applications.
The Ragone plot is important for benchmarking energy and power densities for energy storage devices (ESDs), being widely used for comparisons of their performance. As shown in Fig. 1, no one individual ESD can possess high energy density and high power density simultaneously. The usage of each ESD can be determined by its own characteristic time [13], i.e., based on its energy-to-power ratio or charge/discharge rate, which is represented by the straight dashed lines in Fig. 1. It should be noted that the practical charge/discharge time of the ESD is impacted by external factors such as the load resistance. As can be observed from Fig. 1, capacitors possess higher charge/discharge rates and higher power density than batteries and SOFCs. This is because capacitors store energy by displacement of bound charged elements while batteries and SOFCs store energy by chemical reactions. Capacitors have been widely used in numerous fields, such as electronic circuits with various functions (filtering, coupling, decoupling, etc.), microwave communications, hybrid electrical vehicles, distributed power systems, renewable energy storage, and high-power applications such as fusion applications, as shown in Fig. 2. Different applications require different kinds of capacitors with different characteristics. For example, the capacitors used in microwave communications applications should possess a very high quality factor (very low dielectric loss), while the capacitors used in decoupling circuits are required to possess large capacitance per unit volume. Of particular importance, the high charge/discharge rates of dielectric capacitors, corresponding to their small characteristic time in Fig. 1, make them suitable for high-power/pulse-power systems and efficient capture of energy from intermittent renewable sources [14]. The energy density of dielectric capacitors is relatively low, however, as shown in Fig. 1 [15]. High energy density dielectrics will significantly reduce the device volume (increase the volumetric efficiency), thus benefiting many applications where miniaturization, light weight, low cost, and easy integration are desirable, e.g. consumer electronics, pulsed power applications, and commercial defibrillators, to name a few [12], [15], [16], [17], [18]. In addition, if the energy density of dielectric capacitors can be improved and made comparable to those of electrochemical capacitors or even batteries, the application range of dielectric capacitors in the energy storage field will be greatly expanded [12].
Early dielectric capacitors (capacitors for short) are based on the dielectrics such as wax-impregnated paper and mica. Currently, commercially available solid-state capacitors for high-power applications are dominated by polymer and dielectric ceramics, but they usually possess limited energy density of less than 2 J/cm3 [17], [18]. Generally, ceramics possess high permittivity but low breakdown strength (BDS), while polymers exhibit high BDS but low permittivity. As polymers possess low permittivity, they are usually fabricated into film form with thickness in the micron or submicron range and are stacked into multilayer structures to achieve relatively high capacitance in real applications. Under very high electric fields, the leakage current of polymer-based film capacitors increases rapidly due to their trap-filled space charge, or due to the Schottky or Poole-Frenkel mechanisms [19]. As a result, polymer-based film capacitors cannot maintain high energy efficiency at high applied electric fields, where the high-field conduction may act as a limiting factor for energy density [20]. In addition, although biaxially orientated polypropylene (BOPP)-based capacitors have been widely used as high-power capacitors in recent decades, they are being challenged by alternatives in some applications such as deep-well drilling and aerospace industries, where the electronic equipment is required to work in a high-temperature environment (>150 °C) [21], [22]. This is due to the fact that the BDSs of many polymer films decrease sharply in association with increased conduction and losses at elevated temperature [19], [23], [24], [25]. On the contrary, the ceramics possess high permittivity and can tolerate relatively high temperature, but the BDSs are usually low. This may be partially due to the negative correlation between permittivity and BDS [26], [27], [28], [29], [30], [31], [32], [33], as shown in Fig. 3, i.e., higher permittivity leads to lower breakdown strength due to the electrostrictive effect. The factors affecting BDS will be discussed in Section 2.2.
Based on the fabrication method and material thickness, the dielectric materials in capacitors can be categorized into thin films, thick films, and bulk materials. Thin films (<1 μm) and thick films (1–10 μm) can tolerate higher applied electric field (>1000 kV/cm) due to their smaller volume associated with less defects and impurities [34]. Therefore, they usually possess much higher energy density [35], [36], [37], [38], [39], [40]. Due to their small volume and low capacity, however, the total energy that can be stored in film materials is less than for their bulk counterparts. Lead-based materials have been extensively studied for bulk dielectrics, exhibiting good energy-storage performance. For example, a large recoverable energy density of 6.4 J/cm3 has been achieved in lead-based antiferroelectric ceramics [41]. The toxicity of lead-based derivatives, however, raises great environmental and human health concerns. Thus, numerous efforts have been made to explore lead-free materials to circumvent this issue [35], [42], [43], [44], including barium-based and bismuth-based dielectrics.
In this review, the fundamentals of energy storage capacitors are first introduced to highlight the basic requirements for high-energy-storage applications. In particular, the approaches to increase BDS are briefly summarised. Then, recent progress on actively studied dielectric materials is surveyed, namely, linear dielectrics, paraelectrics, ferroelectrics (FEs), and antiferroelectrics (AFEs). The multilayer ceramic capacitors and polymer-ceramic composites are also introduced. Lastly, the pros and cons of each category of material and the challenges of energy-storage dielectric capacitors are discussed, and future prospects for them based on our understanding are proposed.
Section snippets
Fundamentals of energy storage capacitors
A dielectric capacitor is usually constructed in a parallel-plate form, consisting of two conductive electrodes and a dielectric layer filled in between them. Their energy-storage capability is called capacitance (C), which can be described by the following equation:where ε0 is the dielectric permittivity in vacuum (∼8.85 × 10−12 F/m), εr is the dielectric constant (or relative dielectric permittivity) of the dielectric layer, A is the overlapping area of the two electrodes, and d is
Linear dielectrics
Linear dielectrics usually possess low permittivity, low dielectric loss, and high BDS. The permittivity of an ideal linear dielectric is independent of the electric field. In other words, its polarization increases linearly with increasing electric field, without hysteresis, as shown in Fig. 4(a). All of the stored energy in the charging process can be released from the dielectric in the discharging process. The recoverable energy density can be calculated using Eq. (5). Linear dielectrics are
Summary and perspectives
The demand for exploiting and harnessing renewable energy is the driving force for the research on energy storage devices. Among these devices, electrostatic capacitors possess unique benefits, such as high charge/discharge rates, high operating voltage, and high-temperature stability, making them suitable to store the electricity harvested from intermittent renewable energy sources. One of the important figures of merit for dielectric capacitors is energy density. According to the physical
Acknowledgments
S.Z. thanks the Australian Research Council for financial support through the Future Fellowship Scheme (FT140100698). F. Li. thanks to the National Natural Science Foundation of China (Grant No. 51572214). H.H. and H.X.L. acknowledge support from the National Natural Science Foundation of China-Guangdong Joint Funds (No. U1601209), the Major Program of the National Natural Science Foundation of China (51790490), and the Technical Innovation Special Program of Hubei Province (2017AHB055). J.F.L.
References (418)
- et al.
Role of renewable energy sources in environmental protection: a review
Renew Sustain Energy Rev
(2011) - et al.
Classification and assessment of energy storage systems
Renew Sustain Energy Rev
(2017) - et al.
Energy storage systems—characteristics and comparisons
Renew Sustain Energy Rev
(2008) - et al.
Energy storage: applications and challenges
Sol Energy Mater Sol Cells
(2014) - et al.
Progress in renewable energy
Environ Int
(2003) Renewable energy and sustainable development: a crucial review
Renew Sustain Energy Rev
(2000)- et al.
Energy-storage technologies and electricity generation
Energy Policy
(2008) - et al.
Progress in electrical energy storage system: a critical review
Prog Nat Sci
(2009) - et al.
Theory of Ragone plots
J Power Sources
(2000) - et al.
Size-dependence of the dielectric breakdown strength from nano- to millimeter scale
J Mech Phys Solids
(2014)
Enhanced energy storage performance in (Pb0.858Ba0.1La0.02Y0.008)(Zr0.65Sn0.3Ti0.05)O3–(Pb0.97La0.02)(Zr0.9Sn0.05Ti0.05)O3 anti-ferroelectric composite ceramics by Spark Plasma Sintering
J Alloys Compd
Temperature induced high charge–discharge performances in lead-free Bi0.5Na0.5TiO3-based ergodic relaxor ferroelectric ceramics
Scr Mater
The role of Co in the BaTiO3-Na0.5Bi0.5TiO3 based X9R ceramics
Ceram Int
Dielectric behavior and impedance spectroscopy in lead-free BNT–BT–NBN perovskite ceramics for energy storage
Ceram Int
Advanced materials for energy storage
Adv Mater
Stored energy - short-term and long-term energy storage methods
IEEE Ind Appl Mag
Nonlinear dielectric thin films for high-power electric storage with energy density comparable with electrochemical supercapacitors
IEEE Trans Ultrason Ferroelectr Freq Control
High to ultra-high power electrical energy storage
Phys Chem Chem Phys
Materials challenges facing electrical energy storage
MRS Bull
High energy and power density capacitors from solution-processed ternary ferroelectric polymer nanocomposites
Adv Mater
A review on the dielectric materials for high energy-storage application
J Adv Dielectr
Homogeneous/inhomogeneous-structured dielectrics and their energy-storage performances
Adv Mater
Electrical degradation and breakdown in polymers
High field tunneling as a limiting factor of maximum energy density in dielectric energy storage capacitors
Appl Phys Lett
The changing automotive environment: high-temperature electronics
IEEE Trans Electron Packaging Man IEEE Electrical Insulation Mag Manuf
High-temperature electronics - a role for wide bandgap semiconductors?
Electrical breakdown and ultrahigh electrical energy density in poly(vinylidene fluoride-hexafluoropropylene) copolymer
Appl Phys Lett
Energy and power densities of capacitors and dielectrics
Flexible high-temperature dielectric materials from polymer nanocomposites
Nature
Proposed universal relationship between dielectric breakdown and dielectric constant
Trends in the ultimate breakdown strength of high dielectric-constant materials
IEEE Trans Electron Devices
Embedded thin film capacitors - theoretical limits
IEEE Trans Adv Pack.
Comparison of paraeletric and ferroelectric materials for applications as dielectrics in thin film integrated capacitors
Int J Microcircuits Electron Packag
Structural and electrical properties of rf magnetron-sputtered Ba1−xSrxTiO3 thin films on indium-tin-oxide-coated glass substrate
J Appl Phys
Structural and electrical properties of Ba0.5Sr0.5TiO3 thin films with conductive SrRuO3 bottom electrodes
Appl Phys Lett
Thickness-dependent electrical characteristics of lead zirconate titanate thin films
J Appl Phys
On why dielectric breakdown strength reduces with dielectric thickness
Proceedings of the IEEE international reliability physics symposium (IRPS)
A lead-free and high-energy density ceramic for energy storage applications
J Am Ceram Soc
Giant electric energy density in epitaxial lead-free thin films with coexistence of ferroelectrics and antiferroelectrics
Adv Electron Mater
Fabrication and energy-storage performance of (Pb, La)(Zr, Ti)O3 antiferroelectric thick films derived from polyvinylpyrrolidone-modified chemical solution
J Appl Phys
Large enhancement of the recoverable energy storage density and piezoelectric response in relaxor-ferroelectric capacitors by utilizing the seeding layers engineering
Appl Phys Lett
Dielectric properties and energy storage capability of antiferroelectric Pb0.92La0.08Zr0.95Ti0.05O3 film-on-foil capacitors
J Mater Res
Anti-ferroelectric ceramics for high energy density capacitors
Materials
Perspective on the development of lead-free piezoceramics
J Am Ceram Soc
Lead-free piezoceramics
Nature
Lead-free relaxor ferroelectrics
J Am Ceram Soc
Antiferroelectric ceramics with field-enforced transitions: a new nonlinear circuit element
Proc IRE
A dielectric polymer with high electric energy density and fast discharge speed
Science
Antiferroelectric thin-film capacitors with high energy-storage densities, low energy losses, and fast discharge times
ACS Appl Mater Interf
Cited by (1175)
Entropy regulation enhanced superior energy storage density and high temperature stability in lead-free relaxors
2024, Journal of the European Ceramic SocietyLow-field energy storage enhancement in ferroelectric/paraelectric PbTiO<inf>3</inf>/SrTiO<inf>3</inf> nanocomposites near antiferroelectric–ferroelectric transition region
2024, Journal of Science: Advanced Materials and Devices
- 1
Authors contributed to this paper equally.