High Breakdown Strength Research Articles

Janus composite film comprising metal–organic framework/polyimide and BNNSs/polyimide as high energy storage dielectrics

AbstractIn order to prepare polymer dielectric materials with high energy storage density, a series of polyimide (PI) based Janus composite films were prepared by metal–organic frameworks (MOFs) material (UiO‐66) with high dielectric constant (ɛr) and boron nitride nanosheets (BNNSs) with high breakdown strength (Eb). As reported, the UiO‐66 can significantly improve the ɛr of the composites. The ɛr of 20 wt% UiO‐66/PI film is 10.51 at 103 Hz, which is 3.1 times that of pure PI film (3.39 at 103 Hz). However, the Eb of 20 wt% UiO‐66/PI is only 58 MV m−1, which is only 16.51% of pure PI (352 MV m−1). The sharp decline in Eb reduces the energy storage capacity of the composites. To solve this problem, first, BNNSs with an average diameter of 2 μm and a thickness of 1.36 nm (about 4–5 layer) were obtained by hydrothermal reflux stripping. BNNSs/PI//UiO‐66/PI Janus composite films with double‐layer structure were prepared by directly casting BNNSs/PI on the surface of UiO‐66/PI. For 0.3 wt% BNNSs/PI//10 wt% UiO‐66/PI, the calculated energy storage density (Ue) is 5.75 J cm−3 at 140 MV m−1, which is 3.57 times that of pure PI film (1.61 J cm−3 at 140 MV m−1). Meanwhile, the charge discharge efficiency is 82.55% (at 140 MV m−1).Highlights BNNSs prepared by hydrothermal reflux stripping have fewer layers. BNNSs/PI composites improve the Eb of UiO‐66/PI composites by Janus structure. The Ue of BP‐0.3//UP‐10 composites with Janus structure was 5.75 J cm−3.

Energy storage enhancement of sandwich-structured nanocomposites with mono/adjacent-layer design and their synergistic effect optimization

Currently, advanced electronic devices demand capacitors with superior discharge energy density (U d) and charge–discharge efficiency (η). Sandwich-structured nanocomposites have been extensively studied to significantly enhance U d through the synergistic effect of each component layer and their interfacial effects. Herein, sandwich-structured x wt.% Ni(OH)2 BPB nanocomposites are prepared, where upper and lower high breakdown strength (E b, B) layers are composed of 3 wt.% Ni(OH)2 and blended PMMA/P(VDF-HFP), while middle high polarization (P) layer is composed by various weight fraction (x wt.%) of Ni(OH)2 and P(VDF-HFP). Interestingly, 3 wt.% Ni(OH)2 BPB achieves improvements in U d of 22.2 J cm−3 as well as η of 81.7% at 586 MV m−1 simultaneously. Improved energy storage performances are mainly attributed to the individual B and P layer design, as well as their synergistic coupling effects in the sandwich-structured nanocomposites. The results of experiment and simulation have concurrently demonstrated Ni(OH)2, PMMA and the functionalized sandwiched structured design could enhance U d and descend remanent polarization and leakage current to increase η, which helps to obtain a satisfactory energy storage performance. This study offers a valid strategy for nanocomposites possessing high energy storage performances designing.

Effect of controlled solvent evaporation on the electroactive phase content of P (VDF-HFP) films

Poly (vinylidene fluoride)-based dielectric materials have attracted much attention in the field of high power density electric energy storage due to their ferroelectric properties, high dielectric breakdown strength and superior processability. However, it is a key challenge how to obtaining high content electroactive phases with ferroelectric and piezoelectric properties in PVDF. Up till now, researchers have prepared PVDF films with high content of electroactive phase via irradiation with high-energy electron-beam or γ-ray radiations and pressing-and-folding process. In this paper, P(VDF-HFP) films were prepared by controlled solvent evaporation method at different ambient temperature. The results showed that the morphologiy of the film showed insignificant changes with the increase of ambient temperature. Total contents of β and γ phases were nearly 100 % in the PVDF films prepared at ambient temperature below 110 °C. The microcrystals in P(VDF-HFP) was more and more perfect with the increase of the ambient temperature under the condition of controlled solvent evaporation. The films prepared at 70 °C showed a dielectric constant of 12.76 under the test condition of 100 Hz with the remnant polarization of 0.54 μC/cm2. All of these results demonstrated that the formation of the electroactive phase of P(VDF-HFP) thin films was related to the evaporation process and evaporate rate of the solvent.

Evaluation of ferroelectricity in a distorted wurtzite-type structure of Sc-doped LiGaO2.

Since the discovery of ferroelectricity in a wurtzite-type structure, this structural type has gathered much attention as a next-generation ferroelectric material due to its high polarization value combined with its high breakdown strength. However, the main targets of wurtzite-type ferroelectrics have been limited thus far to simple nitride/oxide compounds. The investigation of new ferroelectric materials with wurtzite-type structures is important for understanding ferroelectricity in such structures. We therefore focus on β-LiGaO2 in this study. Although AlN and ZnO possess well-known wurtzite-type structures (P63mc), β-LiGaO2 has a distorted wurtzite-type structure (Pna21), and there are no reports of ferroelectricity in LiGaO2. In this study, we have revealed that LiGaO2 exhibits relatively high barrier height energy for polarization switching, however, Sc doping effectively reduces that energy. Then, we conducted thin film preparation and evaluation for Sc-doped LiGaO2 to observe its ferroelectric properties. We successfully observed ferroelectric behavior by using piezoresponse force microscopy measurements for LiGa0.8Sc0.2O2/SrRuO3/(111)SrTiO3.

Enhancing the high-temperature energy storage properties of PEI dielectrics by constructing trap-rich covalently cross-linked networks via POSS-functionalized BNNS.

Polymer films are ideal dielectric materials for energy storage capacitors due to their light weight and flexibility, but lower energy density and poor heat resistance greatly limit their application in high-temperature energy storage. Unlike the traditional method of solely adding wide-bandgap inorganic fillers to enhance energy density, in this study we constructed trap-rich hybrid covalently cross-linked networks in polyetherimide (PEI) via reactive polyhedral oligomeric silsesquioxane (POSS)-functionalized boron nitride nanosheets (BNNS@POSS), which not only serve as interfacial layers for dielectric transitions and insulating barriers but also create deeper traps and higher energy barriers in the region of cross-linked chains. This strategy based on the co-modulation of interfaces and traps achieved the compatibility of high polarization and high breakdown strength and improved energy storage performance. Therefore, the composite film BNNS@POSS/PEI with the addition of 5 wt% BNNS@POSS achieved a maximum discharge energy density and charge-discharge efficiency at 150 °C of 6.16 J cm-3 and 89.92%, and maintained high values at 200 °C of 4.12 J cm-3 and 88.38%, respectively. Moreover, the glass transition temperature (Tg) of the composite dielectrics increased by 20.2 °C. This work provides a promising candidate material and development directions for research in the field of high-temperature energy storage capacitors.

Heterostructured n-ZnO@p-CuO nanosheets filled in a polymer matrix for enhanced electrostatic energy storage performance.

Metallized film capacitors use plastic films as the dielectric spacer, and these polymer films generally have low dielectric constants. To boost the electrostatic energy storage density of a film capacitor, advanced high-k films with high electrical breakdown strength and low dielectric loss are highly desired. Herein, polymer nanocomposite films were made by filling ZnO@CuO nanosheets into poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)]. The n-type ZnO nanosheets are synthesized in an aqueous solution. Through a calcination process, thin layers of p-type CuO are coated over the ZnO nanosheets. Compared to pure P(VDF-HFP) and ZnO/P(VDF-HFP) films, the ZnO@CuO/P(VDF-HFP) films exhibit higher dielectric constant and higher breakdown strength. The optimal content of ZnO@CuO nanosheet in the polymer matrix is determined to be 3 wt%, which leads to a dielectric constant of 15.6 at 1 kHz and the highest energy density of 5.6 J cm-3. The efficacy of ZnO@CuO nanosheets in enhancing the dielectric performance of the polymer nanocomposite is elucidated in detail. This research provides a scalable and low-cost strategy to produce polymer nanocomposite films with high capacitive energy storage performance.

Room-temperature ferromagnetic semiconductor Fe-doped β-Ga2O3 thin films with high saturation magnetization and low coercivity.

Emergent ferromagnetism in β-Ga2O3 with an ultra-wide bandwidth and high electrical breakdown strength offers exciting opportunities for fabricating robust spintronic devices. One pertinent obstacle in the material has been the low saturation magnetization, which precludes its practical application in magnetic devices. In this work, large-scale Fe-doped β-Ga2O3 diluted magnetic semiconductor (DMS) films are synthesized using a polymer-assisted deposition method, and the effect of Fe doping on their structural and magnetic properties is investigated. Remarkably, the optimal sample exhibits a high saturation magnetization (70 emu cm-3 at 300 K), much larger than those in previously reported stable oxide DMS films, as well as a low coercivity (12 Oe at 300 K). Further analysis shows that our samples manifest a typical bound magnetic polaron (BMP) model and the high saturation magnetization originates from the strong ferromagnetic coupling between the BMPs which is enhanced by Ga vacancies. The Fe-doped β-Ga2O3 thin films with high saturation magnetization and low coercivity may provide a promising platform for related semiconductor spintronics.

Enhanced dielectric properties of Sr2+ and Zr4+ doped BaTiO3 colossal permittivity metamaterials

BaTiO3, as one of the most important functional materials of perovskite structure, is widely used in the electronic industry. However, the dielectric permittivity of BaTiO3 remains relatively low, which greatly limits its practical application in metamaterials with colossal dielectric permittivity. In this work, (Ba100−xSrx)(Ti100−yZry)O3 composite ceramics are fabricated via the solid sintering method. Surprisingly, the dielectric properties of (Ba100−xSrx)(Ti100−yZry)O3 composite ceramic materials are strongly dependent on the occupancy of Sr2+ and Zr4+ at the A-sites and B-sites, respectively. Consequently, via adjusting the doping amount of SrTiO3 and BaZrO3, a greatly enhanced dielectric permittivity of 28287 (65 °C, 1 kHz), along with a high breakdown strength of 84.47 kV/cm is achieved in (Ba90Sr10)(Ti90Zr10)O3 composite ceramics, which are 2144% and 13 % higher than those of (Ba99Sr1)(Ti99Zr1)O3 composite ceramics, respectively. Moreover, the reasons for the significant increase in dielectric permittivity are identified through finite element simulations, and the breakdown mechanism of composite ceramic materials is explored. This work provides a facile approach to constructing high dielectric permittivity composite ceramics, the (Ba100−xSrx)(Ti100−yZry)O3 composite ceramics have broad application prospects in electronics and electrostatic energy storage capacitors.

Enhanced dielectric constant and breakdown strength of sandwiched polymer nanocomposite film for excellent energy storage.

Enhanced dielectric constant and high breakdown strength offers immense promise for excellent energy storage performance, which is of critical significance in modern electronics and power systems. However, polymer nanocomposites with traditional routes have to balance between dielectric constant and breakdown strength, hence hindering substantive increases in energy density. Herein, a sandwiched polymer nanocomposite film has been constructed to take full advantage of the individual component layers. BaTiO3 nanoparticles are coated with a fluoropolymer to form core-shell structures and then introduced into a polymer as the top and the bottom layers of a sandwich film for enhancing polarization. Moreover, boron nitride nanosheets (BNNSs) in the middle layer of the sandwich film exert positive effects on the inhibition of current leakage for high breakdown resistance. The breakdown strength increases from 480 MV m-1 of the neat polymer to 580 MV m-1 of the sandwiched film. Additionally, the film exhibits a higher dielectric constant in comparison with the neat polymer. The sandwiched film displays a superior energy density (15.75 J cm-3), which is about 1.9 times that of the neat polymer. This work proposes a feasible route to achieve excellent energy storage of polymer dielectrics by synergistically introducing insulating fillers and additional dipoles in a sandwiched polymer nanocomposite film.

High energy storage of PbZrO3 antiferroelectric thin films via constructing phase composition

In this paper, we fabricated PbZrO3 (PZ) thin films by the way of sol–gel spin on LaNiO3 buffered SiO2/Si substrates, and annealed them at different given temperatures by rapid thermal annealing (RTA). By controlling annealing temperature, PZ thin films showed different microstructures and phase compositions, whose impact of electrical properties and energy storage performance were researched. According to the research findings, the phase composition of film presents a general rule with the decrease of annealing temperature: PZ thin films crystallize into perovskite phase, pyrochlore phase, and amorphous phase. The films annealed at 620 °C crystallized into a state of coexistence of pyrochlore phase and perovskite phases, which also show moderate recoverable energy density and the highest energy storage efficiency (8.7 J cm−3 and 93.1%). This energy storage performance can be attributed to the synergistic effect of high electric breakdown strength of dense pyrochlore phase structure and high maximum polarization of perovskite phase. The findings of this paper help to explain the influence of pyrochlore phase on the energy storge performance of thin films. Thus, it is useful way to improve the energy storage performance of thin films.

Ultrahigh efficiency and enhanced discharge energy density at low loading of nanofiller in trilayered polyvinylidene fluoride‐Ba0.8Sr0.2TiO3 nanocomposites

AbstractPoly(vinylidene)fluoride‐Ba0.8Sr0.2TiO3 (PVDF‐BST) trilayered nanocomposites (with different vol% loading of BST nanoparticles, i.e. 0.75%, 1.50%, 2.25% and 3.00%) has been processed by the tape casting technique. The upper and lower layers of the nanocomposites are casted in the same direction, whereas the middle layer is casted in the opposite direction. The trilayered PVDF‐BST nanocomposite consisting of 3.00 vol% of BST nanoparticles exhibited high dielectric permittivity (~25), low tangent loss (~0.03) and moderately high breakdown strength (BDS ~282 MV/m). Moreover, it also possesses a high discharge energy density (~7.8 J/cc at 1400 kV/cm) and efficiency (~93%). A mechanism for the excellent energy storage behavior and dielectric properties has been proposed. Where, moderately high BDS and low tangent loss are associated with the spatial distribution of the local electric field at interlayer interfaces of PVDF‐BST trilayered nanocomposites, which restricts the conduction of charge carriers at high electric field. The ultrahigh efficiency and enhanced discharge energy density is attributed to the formation of interfacial dipoles at various interfaces such as interlayer, intralayer (PVDF/PVDF), and PVDF/BST interfaces. These investigations would be adopted as a futuristic strategy for developing excellently efficient polymer‐ceramic nanocomposites for the high energy density capacitors used in pulsed power applications.Highlights PVDF‐BST trilayered nanocomposites exhibit high ε′ ~25 and low tanδ ~0.03. Nanocomposite shows ultra‐high energy efficiency ~93% and enhanced UD ~ 7.8 J/cc. Mechanism for the excellent energy storage and dielectric properties Relies on the interfacial dipoles and distribution of the local electric field.

Design of voltage stabilizers for high breakdown strength materials

AbstractHigh breakdown strength material in the cable insulation layer is a key enabler for high voltage power transmission. In this work, we seek to design high‐performance voltage stabilizers to be compounded into polyethylene to improve its breakdown strength. We hypothesize that electron affinity (EA) and HOMO‐LUMO gap are two key factors that affect the performance of voltage stabilizers. To achieve larger EA and smaller HOMO‐LUMO gap, we propose to use aromatic molecules decorated with electron acceptors and donors. A search of an internal chemical database narrows down to 529 molecules using structure, ClogP, and H‐phrases (hazard statement) as criteria. The EA and HOMO‐LUMO gap of these molecules are then calculated and experiments are carried out to measure the performance of 20 molecules. The performance improvement does not show a significant correlation with either EA or HOMO‐LUMO gap. However, the best performers have an EA of 1.3–2.3 eV and HOMO‐LUMO gap of 3.2–5.2 eV. The experimental study shows that adding side groups to voltage stabilizers will typically degrade their performance because side groups will generally increase the distance between the HOMO‐LUMO orbitals and polyethylene backbone, and therefore decrease the electron/hole tunneling effectiveness.

Nonpolar sub-10 nm TiO2 nanocrystal for high energy density polypropylene nanocomposites

Film capacitors have shown great potential in high-power energy storage devices due to their high breakdown strength and low dielectric loss. However, the state-of-the-art commercial capacitor dielectric, biaxially oriented polypropylene (BOPP), exhibits limited energy storage density below 2 J cm−3 because of its low dielectric constant (approximately 2.2 at 103 Hz). In this work, we present a novel PP-based nanocomposites by incorporating nonpolar sub-10 nm sized TiO2 nanoparticles into the PP matrix for the first time. The nonpolar TiO2 nanoparticles are functionalized with Trioctylphosphine oxide (TOPO) ligands, ensuring excellent compatibility and dispersion of the TiO2 fillers in the PP matrix, resulting in a homogeneous dielectric PP nanocomposite. Moreover, the TOPO ligand, with lower LUMO energy level and higher HOMO level than that of PP matrix, serves as an energy trap to capture carriers upon their occurrence. Furthermore, the well-dispersed sub-10 nm sized TiO2 nanoparticles enlarges the interfacial area, thereby increasing the interfacial polarization and the dielectric constant. The resultant PP nanocomposites exhibit a high discharged energy density of 4.19 J cm−3 at 600 MV m−1, representing a remarkable 74.9% increase compared to that of the pure PP films. This work provides a brand-new strategy for constructing homogeneous PP nanocomposite dielectrics by incorporating nonpolar sub-10 nm sized TiO2 nanoparticles as fillers. And this approach is critical for the design of high energy density PP-based nanocomposites.

High discharge energy density in rationally designed graphene oxide@zinc oxide/polymer blend-polyetherimide heterostructured bilayer nanocomposites

The advancement of new dielectric materials exhibiting greater discharge energy density is crucial for current power systems and electronic devices. In this work, various weight percentages of graphene oxide@zinc oxide (GO@ZO) nanofillers were incorporated inside a polymer blend of poly(vinylidene fluoride-hexafluoropropylene)/polyetherimide (P(VDF-HFP)/PEI; shortened as BP) and used as a high dielectric top layer. In contrast, linear-type PEI (L) was used as a bottom insulation layer to achieve a high breakdown strength (Eb) in bilayer nanocomposites. As a result, the 2BP-L composite demonstrated a high discharged energy density of 12.63 J/cm3 at an electric field of 527 MV/m with only 2 wt% GO@ZO nanofillers addition in the top layer. Such a high discharge energy density with minimal nanofiller loading is attributed to the utilization of novel surface-decorated GO@ZO nanofillers and new bilayer-heterostructured linear/ferroelectric-linear polymer. In comparison to its counterparts (i.e., PEI, P(VDF-HFP) and 0BP-L), the 2BP-L nanocomposite showed ∼426.3 %, 92.5 %, and 9.8 % enhancement in discharge energy density, respectively. The discharge rate and stability analysis revealed a significantly higher power density of 0.55 MW/cm3, indicating its high potential to be used as a pulsed power system. Finite element simulation revealed that the effective internal electric field distribution and higher dielectric displacement in 2BP-L resulted in such enhancement over its counterparts. This study presents a new model to maximize the energy storage capability of flexible energy storage devices and advances knowledge of the polarization mechanisms and breakdown of bilayer nanocomposite dielectric materials.

BN6BT ceramics via cold‐sintering with annealing: Effects of grain size of precursor powders and annealing temperature

AbstractIn this work, (Bi0.5Na0.5)0.94Ba0.06TiO3 (BN6BT) lead‐free ceramics were prepared via cold‐sintering followed by annealing, and effects of grain size of precursor powders and annealing temperature on microstructure, dielectric, and ferroelectric properties of the ceramics were studied. The precursor powders for cold sintering were obtained by mixing the powders with sub‐micrometer (average grain size, AGS = 0.26 μm) and nanometer (AGS = 73 nm) grains in various mass ratios (1:0, 1:1, 1:2, and 1:4). The precursor powders were mixed with deionized water and cold sintered at 180°C for 1 h under 500 MPa. The cold‐sintered samples were then annealed at temperatures between 800 and 1000°C for 2 h. For the ratios of 1:2 and 1:4, the corresponding ceramics annealed at 950°C exhibit dielectric and ferroelectric properties similar to those of the BN6BT ceramics sintered at 1170°C via the solid‐state sintering method. The present BN6BT ceramics exhibit dense microstructure with finer grains with AGS = 280 nm, higher breakdown strength (BDS = 160 kV· cm−1) compared to the solid‐state sintered BN6BT ceramics with AGS = 1.6 μm and BDS = 75 kV· cm−1. The results demonstrate that the cold‐sintering followed by annealing is effective in preparing BN6BT ceramics with fine grains and excellent dielectric and ferroelectric properties at relatively low temperatures.

Stepwise-design activated high capacitive energy storage in lead-free NaNbO3-based relaxor antiferroelectric ceramics

Although comparable energy storage performance (ESP) has been realized in NaNbO3 (NN)-based antiferroelectric (AFE) ceramics, how to simultaneously realize large energy density (Wrec), large storage efficiency (η), and outstanding thermal stability still remains a remarkable challenge. Herein, by progressively substituting BiFeO3 (BF) and CaTiO3 (CT), we propose a stepwise-design strategy to activate comprehensive exceptional ESP in NN-based relaxor AFE ceramics. The substitution of BF with high spontaneous polarization and CT with high breakdown strength (Eb) into NN generates stabilized AFE R phase, strong tilt distortions of oxygen octahedron, ultrasmall and highly dynamic polar nanoregions, and refined grains, thus manifesting enhanced high-field polarizability, significantly delayed polarization saturation, and ultrahigh Eb macroscopically. With the deliberate stepwise-design route, we realize an optimal overall ESP in 0.6(0.96NN-0.04BF)-0.4CT relaxor AFE ceramics, featuring a high Wrec of 6.84 J/cm3, a large η of 81.5 %, along with super temperature/frequency/fatigue stabilities, which shows great performance merits compared with previous reports. This work demonstrates that stepwise-design engineering approach by manipulating the crucial structures exerts a positive size effect on the polarization and breakdown response of dielectrics, and can be exploited for designing more high-performance energy storage ceramics.

P(VDF-HFP)-based nanocomposites with elaborative PN-junction nanofillers displaying high energy storage performance

Given its wide application ranges, dielectric capacitors have garnered extensive attentions. However, due to the excessive premature agglomeration of free electrons, capacitors with nanocomposites as dielectrics fail to attain high breakdown strength (Eb), and thereby constrain their ability to achieve superior energy storage performances. To alleviate the effects of free electrons and secondary impact-ionized electrons (SIE) on Eb and leakage currents, here, a novel organic-inorganic core–shell Ni(OH)2@PDI (N@P) nanofiller with opposite double-PN-junction was well-designed and successfully synthesized by coating p-typed Ni(OH)2 nanosheets with n-typed perylene diimide (PDI). It could reduce free electron kinetic energy and mitigate SIE amounts regardless of the applied electric field direction. Furthermore, PDI, as an organic compound, can uniformly and densely coat onto surfaces of 2D Ni(OH)2, as well as enhance compatibilities between Ni(OH)2 and matrix, and thereby reducing structure defects at their interfaces. Last but not the least, Ni(OH)2 nanosheets also contribute to Eb improvement via acting as scattering centers. Experimental and simulation results concurrently affirmed positive influences of organic-inorganic N@P nanofillers on discharge energy density (Ud) and efficiency (η) of P(VDF-HFP)-based (PVH-based) nanocomposites. Remarkably, 1.3 vol% N@P/PVH achieves a high Ud of 21.7 J/cm3 and η of 81.2 % under 569.0 MV/m. More importantly, it maintains an excellent energy storage performance throughout 104 cyclic tests. This study presents a valid strategy for concurrently improving Ud and η of polymer-based nanocomposites.

Epitaxial Stabilization of Perovskite ATeO3 Thin Films

Tellurium oxides of the ATeO3 form typically do not crystallize in perovskite structures. Here, we show that perovskite-like ATeO3 (A = Ca, Sr, Ba) thin films can be grown on perovskite single-crystal substrates via epitaxial stabilization. These films are stable with high optical bandgaps, low dielectric losses, and a high electric breakdown strength. Hysteretic dielectric behavior found in SrTeO3 and BaTeO3 strongly suggests the presence of antiferroelectricity and ferroelectricity, respectively. These properties make perovskite tellurium oxides possibly appealing candidates for thin film coating or insulator materials in advanced microelectronics. Tellurium oxides constitute a largely unexplored class of materials that might show new and interesting functionalities in epitaxial thin-films. Our work encourages new work within this field.

Superior energy storage performance of BNT-based ferroelectric ceramics based on maintaining high polarization and breakdown strength

Bi[Formula: see text]Na[Formula: see text]TiO3 (BNT)-based lead-free ceramics with superior ferroelectric properties are considered to be extremely advantageous in energy storage capacitors for future green technologies. Here, we demonstrate an approach to achieve both ultrahigh energy density [Formula: see text] and efficiency [Formula: see text] by regulating the multiscale electropolar structures and microstructure. A satisfactory energy storage performance of a high [Formula: see text] of [Formula: see text], and a decent [Formula: see text] of 80% under [Formula: see text] are attained in the 0.5(BNT-CS)-0.5SB[Formula: see text]T ceramic (abbreviated as BNT-0.2SBT). Moreover, BNT-0.2SBT exhibits superior power density ([Formula: see text]), ultrafast discharge time ([Formula: see text][Formula: see text]ns) at [Formula: see text], and good temperature stability. The findings in this work not only demonstrate that a valid candidate, but also provide a new idea of how to achieve both high-energy storage density and efficiency in lead-free ferroelectric materials.

Enhanced thermal conductivity and electrical insulation by patterned self-assembly of electrospun nanofibers

Low intrinsic thermal conductivity (TC) of polymer materials has severely limited their further applicability in electronic and electrical products. To enhance the TC, a strategy for constructing nanofiller-based thermal conductive networks by patterned self-assembly of electrospun nanofibers was first proposed in this paper. By selecting a regular metal mesh as the collector, the electrostatic field-induced directional deposition of nanofibers was achieved, thereby constructing interconnected heat transfer paths aligned in at least four directions. The in-plane TC of heat-pressed electrospun polyvinylidene fluoride (PVDF) nanofibers with 20 wt% loading of boron nitride nanosheets (BNNSs) can reach 7.27 W/(m·K). Electrical insulation of the PVDF/BNNS composites has also been confirmed, showing high volume resistivity and breakdown strength, which have increased by 460.0 % and 26.6 %, respectively, compared to pure PVDF. Finally, a double-layer composite film with waterproof and easy-cleaning characteristics was prepared for electronic device packaging. This simple and efficient preparation strategy for thermal conductive networks may bring new perspectives to thermal management applications.