Ultrahigh Energy Storage Density and Efficiency of Lead-Free Dielectrics with Sandwich Structure.

Lead-free dielectric capacitors have attracted significant research interest for high-power applications due to their environmental benefits and ability to meet the demanding performance requirements of electronic devices. However, the development of lead-free ceramic dielectrics with outstanding energy storage performance remains a challenge. In this study, environmentally friendly ceramic dielectrics with sandwich structures are designed and fabricated to improve energy storage performance via the synergistic effect of different dielectrics. The chemical compositions of the outer and middle layers of the sandwich structure are 0.35BiFeO3 -0.65SrTiO3 and Bi0.39 Na0.36 Sr0.25 TiO3 , respectively. The experimental and theoretical simulation results demonstrate that the breakdown strength is over 700 kV cm-1 for prepare sandwich structure ceramics. As a result, an ultrahigh recoverable energy storage density of 9.05 J cm-3 and a near-ideal energy storage efficiency of 97% are simultaneously achieved under 710 kV cm-1 . Furthermore, the energy storage efficiency maintains high values (≥ 96%) within 1-100 Hz and the power density as high as 188 MW cm-3 under 400 kV cm-1 . These results indicate that the designed lead-free ceramics with a sandwich structure possess superior comprehensive energy storage performance, making them promising lead-free candidates in the energy storage field.

Gradient-Structured Ceramics with High Energy Storage Performance and Excellent Stability.

Owing to the high power density, eco-friendly, and outstanding stability, the lead-free ceramics have attracted great interest in the fields of pulsed power systems. Nevertheless, the low energy storage density of such ceramics is undoubtedly a severe problem in practical applications. To overcome this limitation, the lead-free ceramics with gradient structures are designed and fabricated using the tape-casting method herein. By optimizing the composition and distribution of the gradient-structured ceramics, the energy storage density, and efficiency can be improved simultaneously. Under a moderate electric field of 320 kV cm-1 , the value of recoverable energy storage density (Wrec ) is higher than 4 J cm-3 , and the energy storage efficiency (η) is of ≥88% for 20-5-20 and 20-10-20. Furthermore, the gradient-structured ceramics of 20-10-0-10-20 and 20-15-0-15-20 possess high applied electric field, large maximum polarization, and small remnant polarization, which give rise to ultrahigh Wrec and η on the order of ≈6.5 J cm-3 and 89-90%, respectively. In addition, the energy storage density and efficiency also exhibit excellent stability over a broad range of frequencies, temperatures, and cycling numbers. This work provides an effective strategy for improving the energy storage capability of eco-friendly ceramics.

Synergistic Optimization of Energy Storage Density of PYN-Based Antiferroelectric Ceramics by Composition Design and Microstructure Engineering.

PbYb0.5 Nb0.5 O3 (PYN)-based ceramics, featured by their ultra-high phase-switching field and low sintering temperature (950 °C), are of great potential in exploiting dielectric ceramics with high energy storage density and low preparation cost. However, due to insufficient breakdown strength (BDS), their complete polarization-electric field (P-E) loops are difficult to be obtained. Here, to fully reveal their potential in energy storage, synergistic optimization strategy of composition design with Ba2+ substitution and microstructure engineering via hot-pressing (HP) are adopted in this work. With 2 mol% Ba2+ doping, a recoverable energy storage density (Wrec ) of 10.10 J cm-3 and a discharge energy density (Wdis ) of 8.51 J cm-3 can be obtained, supporting the superior current density (CD ) of 1391.97 A cm-2 and the outstanding power density (PD ) of 417.59 MW cm-2 . In situ characterization methods are utilized here to reveal the unique movement of the B-site ions of PYN-based ceramics under electric field, which is the key factor of the ultra-high phase-switching field. It is also confirmed that microstructure engineering can refine the grain of ceramics and improve BDS. This work strongly demonstrates the potential of PYN-based ceramics in energy storage field and plays a guiding role in the follow-up research.

Composition and Structure Optimized BiFeO3 -SrTiO3 Lead-Free Ceramics with Ultrahigh Energy Storage Performance.

Dielectric ceramic capacitors have attracted increasing attention as advanced pulsed power devices and modern electronic systems owing to their fast charge/discharge speed and high power density. However, it is challenging to meet the urgent needs of lead-free ceramics with superior energy storage performance in practical applications. Herein, a strategy for the composition and structural modification is proposed to overcome the current challenge. The lead-free ceramics composed of BiFeO3 -SrTiO3 are fabricated. A low hysteresis and high polarization can be achieved via composition optimization. The experimental results and finite element simulations indicate that the two-step sintering method significantly influences the decrease in the grain size and improvement in the breakdown strength (EBDS ). A high EBDS of ≈750 kV cm-1 accompanied by a large maximum polarization (≈40 µC cm-2 ) and negligible remanent polarization (<2 µC cm-2 ) contribute to the ultrahigh energy density and efficiency values of the order of 8.4 J cm-3 and ≈90%, respectively. Both energy density and efficiency exhibit excellent stability over the frequency range of 1-100 Hz and temperatures up to 120 °C, along with the superior power density of 280 MW cm-3 , making the studied BiFeO3 -SrTiO3 ceramics potentially useful for high-power energy storage applications.

Boosting Energy Storage Performance of Lead-Free Ceramics via Layered Structure Optimization Strategy.

Owing to the current global scenario of environmental pollution and the energy crisis, the development of new dielectrics using lead-free ceramics for application in advanced electronic and energy storage systems is essential because of the high power density and excellent stability of such ceramics. Unfortunately, most of them have low breakdown strength and/or low maximum polarization, resulting in low energy density and efficiency. To overcome this limitation here, lead-free ceramics comprising a layered structure are designed and fabricated. By optimizing the distribution of the layered structure, a large maximum polarization and high applied electric field (>500 kV cm-1 ) can be achieved; these result in an ultrahigh recoverable energy storage density (≈7 J cm-3 ) and near ideal energy storage efficiency (≈95%). Furthermore, the energy storage performance without obvious deterioration over a broad range of operating frequencies (1-100 Hz), working temperatures (30-160 °C), and fatigue cycles (1-104 ). In addition, the prepared ceramics exhibit extremely high discharge energy density (4.52 J cm-3 ) and power density (405.50 MW cm-3 ). Here, the results demonstrate that the strategy of layered structure design and optimization is promising for enhancing the energy storage performance of lead-free ceramics.

Achieving Ultrahigh Electrocaloric Response in (Bi0.5Na0.5)TiO3-Based Ceramics through B-Site Defect Engineering.

Lead-free electrocaloric (EC) ferroelectrics are considered ideal for the next generation of environmentally friendly solid-state refrigeration materials. However, their inferior performance compared to lead-based materials significantly restricts their potential application. According to phase-field simulations, it is predicted that the pinning effect of a moderate number of defects can effectively enhance the reversible polarization response associated with the entropy change. Herein, sodium-bismuth titanate (BNT) ceramics with high spontaneous polarization are selected to construct B-site defects by introducing Li+ and Nb5+. Under an electric field of 6 kV mm-1, ultrahigh EC temperature changes of ΔTpos = 1.77 and ΔTneg = 1.49 K are achieved at 65 °C by direct measurement (ΔTneg > 1 K over 55-120 °C). Furthermore, ΔTneg remains above 0.70 K in the temperature range from 25 to 130 °C, exhibiting immense potential for practical applications. This study offers a promising direction for optimizing the EC response in defect systems.

Multiscale reconfiguration induced highly saturated poling in lead-free piezoceramics for giant energy conversion.

The development of high-performance lead-free K0.5Na0.5NbO3-based piezoceramics for replacing commercial lead-containing counterparts is crucial for achieving environmentally sustainable society. Although the proposed new phase boundaries (NPB) can effectively improve the piezoelectricity of KNN-based ceramics, the difficulty of achieving saturated poling and the underlying multiscale structures resolution of their complex microstructures are urgent issues. Here, we employ a medium entropy strategy to design NPB and utilize texture engineering to induce crystal orientation. The developed K0.5Na0.5NbO3-based ceramics enjoys both prominent piezoelectric performance and satisfactory Curie temperature, thus exhibiting an ultrahigh energy harvesting performance as well as excellent transducer performance, which is highly competitive in both lead-free and lead-based piezoceramics. Comprehensive structural analysis have ascertained that the field-induced efficient multiscale polarization configurations irreversible transitions greatly encourages high saturated poling. This study demonstrates a strategy for designing high-performance piezoceramics and establishes a close correlation between the piezoelectricty and the underlying multiscale structures.

High Piezoelectricity in Eco-Friendly NaNbO3-Based Ferroelectric Relaxor Ceramics via Phase and Domain Engineering.

To meet the requirements of environmental friendliness, high-performance lead-free piezoelectric materials have become important materials for next-generation electronic devices. Here, lead-free and potassium-free NaNbO3 (NN)-based ceramics with high piezoelectric (d33 = 361 ± 10 pC/N) and dielectric (εr = 4500) properties were obtained by tolerant preparation techniques. The excellent piezoelectric and dielectric properties can be attributed to the relaxor morphotropic phase boundaries (R-MPB) and coexisting domain regions, which are beneficial in lowering the free energy and greatly improving the dielectric response and domain switching capability. Furthermore, the d33 of NaNbO3-10Ba(Ti0.7Sn0.3)O3-1.5NaSbO3 (NN-10BTS-1.5NS) ceramics can be maintained at 350 pC/N over the range of 25-80 °C with a change rate of less than 10%, exhibiting excellent temperature stability. Based on a series of in situ characterizations, the variations of the phase and domain structures of NN-based relaxor piezoelectric ceramics with temperature are clearly demonstrated. This work not only proposes new materials for sensors and actuators but also provides an excellent strategy for designing high-performance piezoelectric ceramics through phase and domain engineering.

Morphotropic Relaxor Boundary Construction Highly Boosts the Piezoelectric Properties of Bi-Based Lead-Free Thin Films.

To achieve large electrostrain and low hysteresis, we further optimized a morphotropic phase boundary (MPB) by modulating its local polar symmetries. The construction of a morphotropic relaxor boundary (MRB) in thin films can be achieved by suitable introduction of Bi(Fe0.95Mn0.03Ti0.02)O3 into (Bi0.5Na0.5)TiO3-SrTiO3 to form a solid solution. The designed thin film achieves surprising piezoelectric properties with an inverse piezoelectric coefficient of 179.7 pm V-1 and negligible hysteresis. The composition of two relaxors with different local polar symmetries (tetragonal nanoregions and rhombohedral nanoregions), namely, an MRB, and the coexistence of multiscale domain structures can greatly weaken the anisotropy of polarization, degrade the energy barrier, attenuate the discontinuity of polarization, and achieve a large electrostrain and low hysteresis. The domain dynamics of the PNRs under the action of an external excitation field are analyzed to clarify the enhancement mechanism. This construction of MRBs is feasible for producing lead-free piezoelectric films with high-voltage electrical properties and low hysteresis, and various experimental design and theoretical references are provided.

Tunable Domain Switching Features of Incommensurate Antiferroelectric Ceramics Realizing Excellent Energy Storage Properties.

An incommensurate modulated antiferroelectric phase is a key part of ideal candidate materials for the next generation of dielectric ceramics with excellent energy storage properties. However, there is less research carried out when considering its relatively low polarization response. Here, the incommensurate phase is modulated by stabilizing the antiferroelectric phase and the energy storage performance of the incommensurate phase under ultrahigh electric field is studied. The tape-casting method is applied to construct dense and thin ceramics. La3+ doping induces a room-temperature incommensurate antiferroelectric orthorhombic matrix. With little Cd2+ , the extremely superior energy storage performances arose as follows: when 0.03, the recoverable energy storage density reaches ≈19.3 J cm-3 , accompanying an ultrahigh energy storage efficiency of ≈91% (870 kV cm-1 ); also, a giant discharge energy density of ≈15.4 J cm-3 emerges during actual operation. In situ observations demonstrate that these superior energy storage properties originate from the phase transition from the incommensurate antiferroelectric orthorhombic phase to the induced rhombohedral relaxor ferroelectric one. The adjustable incommensurate period affects the depolarization response. The revealed phase-transition mechanism enriches the existing antiferroelectric-ferroelectric transition. Attention to the incommensurate phase can provide a reference for the selection of the next generation of high-performance antiferroelectric materials.

High Energy Storage Performance and Large Electrocaloric Response in Bi0.5Na0.5TiO3-Ba(Zr0.2Ti0.8)O3 Thin Films.

With regard to the global energy crisis and environmental pollution, ferroelectric thin films with unique polarization behavior have garnered considerable attention for energy storage and electrocaloric refrigeration. Herein, a series of (1 - x)Bi0.5Na0.5TiO3-xBa(Zr0.2Ti0.8)O3 (x = 0.3-0.9; (1 - x)BNT-xBZT) films were fabricated on Pt(111)/Ti/SiO2/Si substrates. Incorporating BZT can tune the polarization behavior and phase transition temperature of BNT. A high recoverable energy density ≈ 82 J cm-3 and optimized efficiency ≈ 81% were realized for the (1 - x)BNT-xBZT thin film with x = 0.7. The thin film exhibits excellent stability in energy storage performance, a wide working frequency range (0.5-20 kHz), a broad operating temperature window (20-200 °C), and reduplicative switching cycles (107 cycles). In addition, the 0.5BNT-0.5BZT film exhibits a desirable electrocaloric effect with a large adiabatic temperature change (ΔT ≈ -22.9 K) and isothermal entropy change (ΔS ≈ 33.4 J K-1 kg-1) near room temperature under a moderate applied electric field of 2319 kV cm-1. These remarkable performances signify that the (1 - x)BNT-xBZT system is a promising multifunctional electronic material for energy storage and solid-state cooling applications.

Cu-Doped Alloy Layer Guiding Uniform Li Deposition on a Li-LLZO Interface under High Current Density.

Li7La3Zr2O12(LLZO)-based ceramics as promising solid-state electrolytes (SSEs) have received much attention for use in high-energy lithium (Li) metal batteries. However, the Li growth through the solid garnet electrolyte under a low current density hinders its practical application. In this work, the Cu doped Li3Zn was designed to guide uniform Li deposition by magnetron cosputtering and an in situ alloying reaction on Li6.5La3Zr1.5Ta0.5O12 (LLZTO) pellets. After introducing the composite layer, a small interfacial area specific resistance (∼30 Ω·cm2) can be obtained. Improved lithium plating/stripping performance, including a long-life span of 450 h (under a current density of 0.8 mA cm-2 without short circuit) and a high critical current density (CCD) of 2.8 mA cm-2 is performed by the composite interlayer with a Zn:Cu ratio of 10:1. And the Li/Cu-Li3Zn SSEs/LFP full cell exhibits good electrochemical performance. Accordingly, the Li deposited behavior in the Li plating/stripping process at the intermediate layer is discussed in detail. This work provides a new sight for the alloy interface designed on the solid-state garnet SSEs for high performance lithium metal batteries under high current density.