Perovskite lead-free dielectrics for energy storage applications

Antiferroelectric materials that display double ferroelectric hysteresis loops are receiving increasing attention for their superior energy storage density compared to their ferroelectric counterparts. Despite the good properties obtained in antiferroelectric La-doped Pb(Zr,Ti)O3 -based ceramics, lead-free alternatives are highly desired due to the environmental concerns, and AgNbO3 has been highlighted as a ferrielectric/antiferroelectric perovskite for energy storage applications. Enhanced energy storage performance, with recoverable energy density of 4.2 J cm-3 and high thermal stability of the energy storage density (with minimal variation of ≤±5%) over 20-120 °C, can be achieved in Ta-modified AgNbO3 ceramics. It is revealed that the incorporation of Ta to the Nb site can enhance the antiferroelectricity because of the reduced polarizability of B-site cations, which is confirmed by the polarization hysteresis, dielectric tunability, and selected-area electron diffraction measurements. Additionally, Ta addition in AgNbO3 leads to decreased grain size and increased bulk density, increasing the dielectric breakdown strength, up to 240 kV cm-1 versus 175 kV cm-1 for the pure counterpart, together with the enhanced antiferroelectricity, accounting for the high energy storage density.

Lead-Free Antiferroelectric Silver Niobate Tantalate with High Energy Storage Performance.

The utilization of antiferroelectric (AFE) materials is thought to be an effective approach to enhance the energy density of dielectric capacitors. However, the high energy dissipation and inferior reliability that are associated with the antiferroelectric-ferroelectric phase transition are the main issues that restrict the applications of antiferroelectric ceramics. Here, simultaneously achieving high energy density and efficiency in a dielectric ceramic is proposed by combining antiferroelectric and relaxor features. Based on this concept, a lead-free dielectric (Na0.5 Bi0.5 )TiO3 -x(Sr0.7 Bi0.2 )TiO3 (NBT-xSBT) system is investigated and the corresponding multilayer ceramic capacitors (MLCCs) are fabricated. A record-high energy density of 9.5 J cm-3 , together with a high energy efficiency of 92%, is achieved in NBT-0.45SBT multilayer ceramic capacitors, which consist of ten dielectric layers with the single-layer thickness of 20 µm and the internal electrode area of 6.25 mm2 . Furthermore, the newly developed capacitor exhibits a wide temperature usage range of -60 to 120 °C, with an energy-density variation of less than 10%, and satisfactory cycling reliability, with degradation of less than 8% over 106 cycles. These characteristics demonstrate that the NBT-0.45SBT multilayer ceramic is a promising candidate for high-power energy storage applications.

Multilayer Lead-Free Ceramic Capacitors with Ultrahigh Energy Density and Efficiency.

The development of lead-free bulk ceramics with high recoverable energy density (Wrec) is of decisive importance for meeting the requirements of advanced pulsed power capacitors toward miniaturization and integration. However, the Wrec (<2 J cm−3) of lead-free bulk ceramics has long been limited by their low dielectric breakdown strength (DBS < 200 kV cm−1) and small saturation polarization (Ps). In this work, a strategy (compositions control the grain size of lead-free ceramics to submicron scale to increase the DBS, and the hybridization between the Bi 6p and O 2p orbitals enhances the Ps) was proposed to improve the Wrec of lead-free ceramics. (K0.5Na0.5)NbO3–Bi(Me2/3Nb1/3)O3 solid solutions (where Me2+ = Mg and Zn) were designed for achieving large Ps, and high DBS and Wrec. As an example, (1 − x)(K0.5Na0.5)NbO3–xBi(Mg2/3Nb1/3)O3 (KNN–BMN) ceramics were prepared by using a conventional solid-state reaction process in this study. Large Ps (41 μC cm−2) and high DBS (300 kV cm−1) were obtained for 0.90KNN–0.10BMN ceramics, leading to large Wrec (4.08 J cm−3). The significantly enhanced Wrec is more than 2–3 times larger than that of other lead-free bulk ceramics. The findings in this study not only provide a design methodology for developing lead-free bulk ceramics with large Wrec but also could bring about the development of a series of KNN-based ceramics with significantly enhanced Wrec and DBS in the future. More importantly, this work opens a new research and application field (dielectric energy storage) for (K0.5Na0.5)NbO3-based ceramics.

Potassium–sodium niobate based lead-free ceramics: novel electrical energy storage materials

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

Ceramic-based dielectric materials are regarded as the best candidates for advanced pulsed power capacitors because of their excellent mechanical and thermal properties. Nevertheless, lead-free bulk ceramics show relatively low recoverable energy storage density (Wrec < 2 J cm−3) owing to their low dielectric breakdown strength (DBS < 200 kV cm−1). In order to significantly increase Wrec, we proposed a strategy (compositions drive the grain size to submicrometer) to improve the DBS of lead-free ceramics. In this work, (1 − x)(K0.5Na0.5)NbO3–xSrTiO3 (KNN–ST) ceramics were chosen as a representative to verify the validity of this strategy. The (1 − x)KNN–xST ceramics (x = 0.15 and 0.20) with submicrometer grains (about 0.3 μm) were prepared using pressureless solid state sintering. A large Wrec (4.03 J cm−3) and DBS (400 kV cm−1 with a thickness of 0.2 mm) were achieved for 0.85KNN–0.15ST ceramics. The value of 4.03 J cm−3 is superior to all other Wrec in lead-free bulk ceramics and 2–3 times larger than that of other lead-free bulk ceramics. A large Wrec (3.67 J cm−3) and energy storage efficiency (72.1%) were simultaneously achieved for 0.80KNN–0.20ST ceramics. The results confirm that the (1 − x)KNN–xST ceramics (x = 0.15 and 0.20) are desirable materials for advanced pulsed power capacitors. The findings in this study could push the development of a series of KNN-based ceramics with enhanced DBS and Wrec in the future. On the other hand, this work could broaden the applications of KNN materials in a new field.

Significantly enhanced recoverable energy storage density in potassium–sodium niobate-based lead free ceramics

The invention discloses a double-passband frequency selective surface based on a high-dielectric low-loss all-dielectric metamaterial The double-passband frequency selective surface comprises two layers of microwave ceramic structures and an air layer clamped between the two layers of microwave ceramic structures Each microwave ceramic structure is composed of a microwave ceramic substrate of an etched cross-shaped flower-type pore structure and a cylindrical dielectric resonator, wherein the cylindrical dielectric resonator is installed in the center of the cross-shaped flower-type pore structure, and the thickness of the cylindrical dielectric resonator is the same as that of the microwave ceramic substrate The microwave ceramic substrate is made of high-dielectric low-loss microwave ceramic materials A pore opening period unit is of a cross-shaped flower-type pore structure, and the band-pass characteristics of the FSS can be expanded and optimized by adjusting the dielectric resonator in the center of the unit structure By the adoption of the all-dielectric microwave ceramic design, the double-passband frequency selective surface contains no metal materials and has the advantages of being low in loss, high in power capacity, resistant to high temperature and the like; the dual-band gating characteristics within the Ku wave band can be achieved, and the double-passband frequency selective surface has the polarization insensitivity and the good angle stability

Double-passband frequency selective surface based on high-dielectric low-loss all-dielectric metamaterial

The invention discloses a ceramic material with high energy storage density and energy storage efficiency and a preparation method thereof. The chemical formula of the ceramic material is (1-x)(KyNal-y)NbO3-xBi(Mg2/3Nb1/3)O3, wherein x is greater than or equal to 0.08 and less than or equal to 0.5, and y is greater than or equal to 0.2 and less than or equal to 0.8. By adding Bi(Mg2/3Nb1/3)O3, the breakdown strength of the (KyNal-y)NbO3-based ceramic is enhanced remarkably, reaching 240kV/cm, and the effective energy storage density is 0.59J/cm to 1.66J/cm , and the energy storage efficiency is 49.4 to 95 percent; by batching, drying, grinding, secondary presintering, granulation, forming, sintering, grinding and silvered electrode sintering, the ceramic material is obtained, and the preparation process is simple; the cost is low; no pollution is produced, and the ceramic material has the advantages of high energy storage density, high energy storage efficiency, simple preparation process, low preparation cost and high practicability.

Ceramic material with high energy storage density and energy storage efficiency and preparation method thereof

Based on dielectric resonators, the theory, design and implementation of planar magnetic metamaterials made of dielectric blocks were investigated. By etching simple metallic patterns on surface of the dielectric blocks, fleld distributions of the desired resonance modes can be enhanced while those of the undesired suppressed. In this way, the resonance frequency of the desired mode can be tuned down to lower frequency range. A wide-angle polarization- independent planar magnetic metamaterial based on short cylindrical dielectric resonators was proposed and analyzed. Due to its polarization-independence, wide incident angle, the magnetic metamaterial is ready to be used in various microwave components, such as antenna radomes, microwave fllters and frequency selective surfaces.

Hua Ma

Papers

Potassium–sodium niobate based lead-free ceramics: novel electrical energy storage materials

Significantly enhanced recoverable energy storage density in potassium–sodium niobate-based lead free ceramics

Double-passband frequency selective surface based on high-dielectric low-loss all-dielectric metamaterial

Ceramic material with high energy storage density and energy storage efficiency and preparation method thereof

Wide-angle Polarization-independent Planar Magnetic Metamaterials Based on Dielectric Resonators