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

Abstract

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.

Figure 1

(a) Applications for energy storage capacitors. *EMP: electromagnetic pulse. (b) Number of annual publications on lead-based ceramics, lead-free ceramics, ceramic multilayers, and ceramic films for energy storage capacitors from 2010 to 2020. (Collected from Web of Science, search “energy storage/density lead-based ceramic, lead-free ceramic, multilayer ceramic, ceramic capacitor, ceramic films but NOT polymer”). Reproduced with permission from PixaBay, Creative Commons License.

Figure 2

Schematic representation of an electrostatic capacitor, where D, P, and ε₀ are electric displacement, polarization, and electric permittivity of free space (electric constant), respectively.

Figure 3

Four distinctive P–E hysteresis loops and their energy storage behavior: (a) linear, (b) FE, (c) relaxor-ferroelectric (with the schematic of energy storage calculation), and (d) antiferroelectric materials. *W_loss is loss energy density.

Figure 4

(a) Comparison of the E_g among dielectric perovskites and a schematic of electronic breakdown. (b) Variation of average grain size and E_g as a function of NN concentration. (c) P–E loops and dP/dE under different E, (d) W_rec and η values, and (e) pulsed overdamped discharging energy density (W_D) of the BF–BT–0.10NN ceramic. (a) Reproduced with permission from ref (42). Copyright 2019 John Wiley and Sons. (b-e) Reproduced with permission from ref (43). 2020 John Wiley and Sons.

Figure 5

Scanning electron microscopy (SEM) images of the 0.9KNN-0.1BMN-x mol % CuO ceramics with (a) x = 0.25; (b) x = 0.5; (c) x = 1.0; (d) x = 1.5, as liquid phase is circled in red. (e) Unipolar P–E hysteresis loops and (f) Calculated W and W_rec under different E of 0.9KNN-0.1BMN-1 mol % CuO ceramics. Reproduced with permission from ref (66). Copyright 2017 John Wiley and Sons.

Figure 6

Relationship between energy storage properties of ceramics and G: (a) G vs E_max and (b) G vs W_rec. *AN: AgNbO₃.

Figure 7

SEM images of x mol % Nd-doped BF–BT with different Nd concentrations: (a) BF–BT, (b) 2.5 mol % Nd–BF–BT, (c) 5 mol % Nd–BF–BT, (d) 7.5 mol % Nd–BF–BT, (e) 10 mol % Nd–BF–BT, (f) 15 mol % Nd–BF–BT, (g) 20 mol % Nd–BF–BT, (h) 30 mol % Nd–BF–BT, and (i) 40 mol % Nd–BF–BT; the G distributions of Nd-doped BF–BT are shown in the insets of the SEM images. (j) G, density and (k) energy storage performance at 170 kV cm^–1, as a function of x(Nd) mol % in BF–BT ceramics. Reproduced with permission from ref (90). Copyright 2017 Royal Society of Chemistry.

Figure 8

W_rec of 0.2PMN–0.8PS_xT_1–x ceramics with different Sn (x) contents at 70 kV cm^–1. The insets show the mechanism of enhanced energy storage due to coexistent-phase structure and the W_rec for PMN–PS_xT_1–x ceramics under different electric fields. Reproduced with permission from ref (111). Copyright 2018 Elsevier.

Figure 9

Phase diagram of PLZT at room temperature. Reproduced with permission from ref (139). Copyright 2014 Elsevier.

Figure 10

Effect of Zr/Ti ratio on P–E loops and energy storage properties of PLZT. Reproduced with permission from ref (115). Copyright 2019 Elsevier.

Figure 11

Phase diagram of (Pb_0.97La_0.02)(Zr,Sn,Ti)O₃, where T, R, and O represent the tetragonal, rhombohedral, and orthorhombic structure, respectively, and HT and LT represent high and low temperature, respectively. Reproduced with permission from ref (167). Copyright 2005 John Wiley and Sons.

Figure 12

AFE-type P–E hysteresis loops of Pb_0.97La_0.02(Zr_0.5Sn_0.5–xTi_x)O₃ with x = (a) 0.10, (b) 0.08, (c) 0.06, and (d) 0.04. Reproduced with permission from ref (118). Copyright 2016 Elsevier.

Figure 13

(a) Bipolar P–E hysteresis loops and (b) energy storage properties of (Pb_0.98La_0.02)(Zr_0.55Sn_0.45)_0.995O₃ ceramics under different applied fields. (c) Unipolar P–E hysteresis loops of the (Pb_0.94La_0.02Sr_0.04)(Zr_0.9Sn_0.1)_0.995O₃ ceramic under different applied fields. (d) W_rec of (Pb_0.98-xLa_0.02Sr_x)(Zr_0.9Sn_0.1)_0.995O₃ with Sr concentration (x = 0–0.06) as a function of the E. (a, b) Reproduced with permission from ref (131). Copyright 2019 John Wiley and Sons; (c, d) Reproduced with permission from ref (130). Copyright 2019 Royal Society of Chemistry.

Figure 14

(a) Unipolar P–E loops under E_max and (b) calculated W_rec and η at different electric field for BT–0.06B_2/3MN ceramics. (c) Z* plots of (c) BT at 400 °C and (d) BT–0.06B_2/3MN at 550 °C. Reproduced from ref (209). Copyright 2020 American Chemical Society.

Figure 15

(a) Unipolar P–E loops and (b) W, W_rec, and η of 0.9(Sr_0.7Bi_0.2)TiO₃–0.1Bi(Mg_0.5Hf_0.5)O₃ ceramic as functions of E. (c) Unipolar P–E loops and (d) W_rec and η of 0.9(Sr_0.7Bi_0.2)TiO₃–0.1Bi(Mg_0.5Hf_0.5)O₃ ceramic as functions of cycle numbers up to 10⁵. (e) Unipolar P–E loops, with the inset shows the P_max and P_r as functions of temperature, and (f) W_rec and η of 0.9(Sr_0.7Bi_0.2)TiO₃–0.1Bi(Mg_0.5Hf_0.5)O₃ ceramics as a function of temperature. Reproduced with permission from ref (242). Copyright 2019 John Wiley and Sons.

Figure 16

(a) Unipolar P–E hysteresis loops and (b) calculated W and W_rec and (c) W_loss and η for 0.90KNN–0.10BMN ceramics under different E. Reproduced with permission from ref (91). Copyright 2017 Royal Society of Chemistry.

Figure 17

Combined Z′′ and M′′ spectroscopic plots at 275 °C for (a) BF–BT and (b) BF–BT–0.08NZZ. Unipolar P–E loops of BF–BT–0.08NZZ (c) bulk ceramics and (e) ceramic MLs, with cross-section SEM image as shown in inset figure. Calculated energy storage properties of BF–BT–0.08NZZ (d) bulk ceramic and (e) ceramic MLs. Reproduced from ref (34). Copyright 2019 Royal Society of Chemistry.

Figure 18

(a) Z* plots and (b) Combined Z′′ and M′′ spectroscopic plots of 0.54BF–0.4ST–0.06BMN–xNb (x = 0); (c) Z* plots and (d) Combined Z′′ and M′′ spectroscopic plots of x = 0.01–0.05; (e) Arrhenius plots, (f) Seebeck coefficients, and (g) unipolar P–E loops under E_max of x = 0.01–0.05. (h) W_rec and η of (0.6–y)BF–0.4ST–0.03Nb–yBMN. Reproduced from ref (45). Copyright 2020 Royal Society of Chemistry.

Figure 19

(a) Unipolar P–E loop and the current–E curve for NBT–0.45SBT bulk ceramics. (b) W_rec and η for NBT–0.45SBT ceramic MLs; inset SEM image of the ceramic MLs (c) Bipolar P–E loops and (c) calculated W_rec and η of 0.78NBT–0.22NN ceramic.^, (a, b) Reproduced with permission from ref (222). Copyright 2018 John Wiley and Sons; (c, d) Reproduced with permission from ref (297). Copyright 2019 Royal Society of Chemistry.

Figure 20

(a) Tolerance factor and average ionic polarizability per unit cell of NBT–SBT–xBMN as a function of BMN concentration. (b) Combined Z′′ and M′′ spectroscopic plots for NBT–SBT–0.08BMN ceramics at 660 °C. (c) P–E loops at the E_max, and (d) W_rec and η for NBT–SBT–xBMN ceramics. Reproduced with permission from ref (337). Copyright 2021 Elsevier.

Figure 21

(a) Bipolar P–E loops of AN and Ag(Nb_0.85Ta_0.15)O₃ ceramics. (b) Energy storage performance of Ag(Nb_1–xTa_x)O₃ ceramics prior to their breakdown. (c) Schematic of the underlying principles for enhancing energy storage property in AN-based materials. (a, b) Reproduced with permission from ref (357). Copyright 2017 John Wiley and Sons; (c) Reproduced with permission from ref (359). Copyright 2019 Royal Society of Chemistry.

Figure 22

(a) Bipolar P–E loops with corresponding current density-field (J–E) curves and (b) W_rec and η values of under different E for the 0.76NN–0.24BNT ceramic at 10 Hz (c) a comparison of W_rec, η, and E_max among the recently reported bulk ceramics; (d) temperature-dependent P–E hysteresis, (e) temperature- and frequency-dependent ε_r and (f) W_rec and η as a function of temperature for the 0.76NN-0.24NBT ceramic at 450 kV cm^–1. Reproduced with permission from ref (42). Copyright 2019 John Wiley and Sons.

Figure 23

Schematic of the processing step of glass-ceramics.

Figure 24

(a) X-ray diffraction (XRD) patterns of BPNN-AS glass ceramics annealed from 850 to 1000 °C; (b) ε_r and M₂NaNb₅O₁₅ + NN phase proportion with increasing annealing temperature; (c) BDS Weibull distribution plots; (d) W_rec of 900 °C annealed BPNN-AS glass ceramics, compared with other kinds of ferroelectric glass ceramics. Reproduced with permission from ref (384). Copyright 2018 Royal Society of Chemistry.

Figure 25

(a) Dielectric properties, (b) XRD patterns, and (c) BDS of SNN-Si glass ceramics as a function of SiO₂ concentration (β). Reproduced with permission from ref (392). Copyright 2017 Elsevier.

Figure 26

SEM images of BST-BBAS samples annealed at 950 °C by (a) conventional method and (b) microwave treatment. SEM images of BNNS samples annealed at 1000 °C by (c) conventional method and (d) microwave treatment. (e, f) Temperature dependence of dielectric properties of BNNS samples. The BDS plot is inset in (f). (a, b) Reproduced with permission from ref (408). Copyright 2014 Elsevier; (c−f) Reproduced with permission from ref (409). Copyright 2017 Elsevier.

Figure 27

Comparison of (a) E_max vs W_rec; (b) ΔP vs W_rec; and (c) W_rec vs η for lead-based/lead-free bulk ceramics. *t of the bulk ceramics is commonly >0.1 mm.

Figure 28

(a) Temperature-^,,,,,,,,,,, and (b) frequency-dependent W_rec for some reported electroceramic materials for high energy density capacitors.^,,,,

Figure 29

Ceramic MLs fabrication process (MLs cofire technology). Reproduced with permission from ref (18). Copyright 2010 IEEE.

Figure 30

(a) P–E loops under electric field up to E_max (b) calculated W_rec and η values for Pb_0.98La_0.02(Zr_0.7Sn_0.3)_0.995O₃ ceramic ML. Reproduced with permission from ref (436). Copyright 2020 Royal Society of Chemistry.

Figure 31

(a) Bipolar P–E loops and (b) calculated W_rec and η of 0.87BT−0.13Bi[Zn_2/3(Nb_0.85Ta_0.15)_1/3]O₃ MLs under different electric fields. (c) Unipolar P–E loop, with inset SEM micrograph of ceramic MLs, and (d) calculated W_rec and η of NBT–0.45SBT–0.08BMN ceramic MLs under different E. (a, b) Reproduced with permission from ref (438). Copyright 2019 John Wiley and Sons; (c, d) Reproduced with permission from ref (337). Copyright 2021 Elsevier.

Figure 32

(a) Backscattering electron (BSE) cross section micrographs of BF–BT–0.13BLN ceramic MLs; (b) energy dispersive X-ray (EDX) mapping of all elemental distribution (c) transmission electron microscopy (TEM) micrograph obtained from an interface between a BF–BT–0.13BLN grain and a Pt grain (electrode); inset shows a high resolution TEM (HRTEM) image (filtered) obtained from the grain at a higher magnification. (d) Unipolar P–E loops and (e) calculated energy storage properties for BF–BT–0.13BLN ceramic MLs. Reproduced from ref (276). Copyright 2020 Royal Society of Chemistry.

Figure 33

(a) Unipolar P–E loops, inset image is cross-section SEM image of ceramic film deposited on the substrate, and (b) W_rec and η of Pb_0.97La_0.02Zr_0.66Sn_0.23Ti_0.11O₃ ceramic film under various E. (c) Temperature and (d) cyclic unipolar P–E loops, W_rec, and η of Pb_0.97La_0.02Zr_0.66Sn_0.23Ti_0.11O₃ ceramic film under E∼ 2200 kV cm^–1. Reproduced with permission from ref (453). Copyright 2018 Elsevier.

Figure 34

(a) Comparative display of Landau energy profiles and P–E loops of an FE with micrometer-size domains, an RFE with nanodomains, and an RFE with polymorphic nanodomains. Phase-field-simulated three-dimensional domain structures of (b) 0.45BF-0.55ST with rhombohedral nanodomains and (c) 0.20BF-0.25BT–0.55ST with coexisting rhombohedral and tetragonal nanodomains. (d) Simulation of the two-dimensional multiple nanodomain structure of 0.20BF-0.25BT–0.55ST in the cubic matrix. Contour plots of the simulated (e) W_rec and (f) η of BF–BT–ST solid solutions. Reproduced with permission from ref (452). Copyright 2019 The American Association for the Advancement of Science.

Figure 35

(a) E_max vs W_rec, (b) ΔP vs W_rec, (c) W_rec vs η, and (d) t vs W_rec and E_max between bulk ceramics, ceramic MLs and ceramic films.

Figure 36

(a) XRD patterns with representative peaks and (b) Bipolar P–E loops for xB_2/3MN–BT ceramics with x = 0.00–0.10. (c) BSE surface micrographs of Ag–Pd cofired 0.06B_2/3MN–BT ceramics. (d) EDX mapping distribution of Ag, Pd, Ba, and Ti elements. Reproduced from ref (209). Copyright 2020 American Chemical Society.

Figure 37

(a) TEM images of the domain structure in BF–BT, 5 mol % Nd–BT–BT and 10 mol % Nd–BF–BT. (b) The changes of W_rec as a function of electric field for x mol % Nd–BF–BT ceramics. (d) W, W_rec, and η for 15 mol % Nd–BF–BT MLs, with ceramic MLs microstructure as inset figure. Reproduced with permission from ref (90). Copyright 2018 Royal Society of Chemistry.

Figure 38

(a) E_max vs W_rec, (b) ΔP vs W_rec and (c) W_rec vs η for FEs and RFEs bulk ceramics to demonstrate the relaxor optimization.

Figure 39

(a) Schematic illustrating how W_rec is optimized through doping in AN. Gray, yellow, green, dark green, and red spheres represent Ag, Nd, Nb, Ta, and O atoms, respectively. The W_rec and η of (b) AN and (c) Nd_0.01Ta_0.20 codoped AN under the respective electric fields.

Figure 40

TEM [210]_c (c = cubic) zone axis diffraction patterns and corresponding dark field images obtained using (001) reflections from (a) and (b) AN and (c) and (d) Ag_0.91Nd_0.03NbO₃ (e) [210]_c zone axis diffraction pattern of Ag_0.97Nd_0.01Ta_0.20Nb_0.80O₃. (f) Bright field TEM image of domains in a grain of Ag_0.97Nd_0.01Ta_0.20Nb_0.80O₃.

Figure 41

Schematic contour diagrams of the free energy difference (ΔG) for (a) AN- and (b) Nd/Ta-codoped AN without electric field. Schematic contour diagrams of GLD phenomenological theory of AFE-to-FIE phase transition for (c) AN- and (d) Nd/Ta-codoped AN under application of electric field.

Figure 42

(a) E_max vs W_rec and (b) ΔP vs W_rec and (c) W_rec vs η for AFEs and stabilized AFEs bulk ceramics to demonstrate the AFE stabilized optimization.

Figure 43

(a–c) TEM micrographs of BTnanoparticles coated with SiO₂: (a) BT@10 wt %SiO₂; (b) BT@15 wt %SiO₂; (c) BT@20 wt %SiO₂. The shell region is defined by red arrows and dash lines. Bipolar P–E loops of BT with (d) 10 wt % (e) 15 wt % (f) 20 wt % SiO₂ composite ceramics at the highest applied electric field, measured at 10 Hz and room temperature. Reproduced with permission from ref (88). Copyright 2019 Elsevier.

Figure 44

(a) Bipolar P–E loops of the ST+Li₂O₃, NBT–0.06BT and ST + Li₂O₃/NBT–0.06BT ceramic MLs. (b) Comparison of W_rec and electric field between the ST + Li₂O₃/NBT–0.06BT ceramic MLs and some recently reported lead-free ceramics. (c) Distribution of the electric field at 200 kV cm^–1, model of electrical tree propagation simulated using the finite element method for the ST + Li₂O₃/NBT–0.06BT MLs ceramic under (d) 200 kV cm^–1 and (e) 250 kV cm^–1. Reproduced with permission from ref (442). Copyright 2018 Royal Society of Chemistry.