Search

Sodium‐ion batteries (SIBs) have rapidly risen to the forefront of energy storage systems as a promising supplementary for Lithium‐ion batteries (LIBs). Na3V2(PO4)2F3 (NVPF) as a common cathode of SIBs, features the merits of high operating voltage, small volume change and favorable specific energy density. However, it suffers from poor cycling stability and rate performance induced by its low intrinsic conductivity. Herein, we propose an ingenious strategy targeting superior SIBs through cross‐linked NVPF with multi‐dimensional nanocarbon frameworks composed of amorphous carbon and carbon nanotubes (NVPF@C@CNTs). This rational design ensures favorable particle size for shortened sodium ion transmission pathway as well as improved electronic transfer network, thus leading to enhanced charge transfer kinetics and superior cycling stability. Benefited from this unique structure, significantly improved electrochemical properties are obtained, including high specific capacity (126.9 mAh g−1 at 1 C, 1 C = 128 mA g−1) and remarkably improved long‐term cycling stability with 93.9% capacity retention after 1000 cycles at 20 C. The energy density of 286.8 Wh kg−1 can be reached for full cells with hard carbon as anode (NVPF@C@CNTs//HC). Additionally, the electrochemical performance of the full cell at high temperature is also investigated (95.3 mAh g−1 after 100 cycles at 1 C at 50 °C). Such nanoscale dual‐carbon networks engineering and thorough discussion of ion diffusion kinetics might make contributions to accelerating the process of phosphate cathodes in SIBs for large‐scale energy storages. [ABSTRACT FROM AUTHOR]

The µW‐level power density of flexible piezoelectric energy harvesters (FPEHs) restricts their potential in applications related to high‐power multifunctional wearable devices. To overcome this challenge, a hierarchical design strategy is proposed by forming porous piezoceramics with an optimum microstructure into an ordered macroscopic array structure to enable the construction of high performance FPEHs. The porous piezoceramic elements allows optimization of the sensing and harvesting Figure of merit, and the array structure causes a high level of effective strain under a mechanical load. The introduction of a network of polymer channels between the piezoceramic array also provides increased device flexibility, thereby allowing the device to attach and conform to the curved contours of the human body. The unique hierarchical piezoceramic array architecture exhibits superior flexibility, a high open circuit voltage (618 V), high short circuit current (188 µA), and ultrahigh power density (19.1 mW cm−2). This energy density value surpasses previously reported high‐performance FPEHs. The ultrahigh power flexible harvesting can charge a 0.1 F supercapacitor at 2.5 Hz to power high‐power electronic devices. Finally, the FPEH is employed in two novel applications related to fracture healing monitoring and self‐powered wireless position tracking in extreme environments. [ABSTRACT FROM AUTHOR]

Electrostatic capacitors attract great interest in energy storage fields due to their advantages of high power‐density, fast charge/discharge speed, and great reliability. Intensive efforts have been placed on the development of high‐energy‐density of capacitors. Herein, a novel supercapacitor with Hf0.2Zr0.8O2/xAl2O3/Hf0.2Zr0.8O2 (HAHx) is designed to improve the breakdown strength (Eb) through optimizing Al2O3 (AO) film thickness. Low‐temperature annealing is first proposed to enhance the polarization difference (Pm−Pr) due to the formation of dispersed polar nanoregions, which is called "superparaelectric‐like" similar to previous super‐paraelectric behavior of perovskite structures. As results, both large Eb and Pm−Pr values are obtained, leading to an ultrahigh energy storage density of 87.66 J cm−3 with a high efficiency of 68.6%, as well as a reliable endurance of 107 cycles. This work provides a feasible pathway to improve both the polarization difference and breakdown strength of HfO2‐based films by the combination of insulation insertion layer and low‐temperature annealing. The proposed strategy can contribute to the realization of high‐performance electrostatic supercapacitors with excellent microsystem compatibility. [ABSTRACT FROM AUTHOR]

In this work, (1 − x)(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–xKTaO3 (x = 0–0.30) ceramics are developed for dielectric capacitor applications. The introduction of KTaO3 from x = 0 to 0.30 increases the tolerance factor t from 0.984 to 1.005 and causes the decrease of ferroelectric rhombohedral phase in the ceramics. Besides, a gradual structural change toward a higher symmetry can be detected, accompanied by the obvious domain refinement. In the aspect of electrical property, the strengthened dielectric relaxation leads to the greatly enhanced thermal stability of dielectric response. The decline in Ts from 98 to −96°C causes a significant widening of the low‐temperature region with temperature‐stable dielectric constant εr and low dielectric loss tan δ. The x = 0.30 ceramic shows a high εr (25°C) of 1094 with the temperature coefficient of capacitance ≤±15% over −70 to 200°C, which exceeds the X9R standard. Meanwhile, tan δ is less than 0.02 in a wide temperature range of −35 to 300°C. In addition, the ultrafine grain size of 290 nm, large bandgap of 3.22 eV, and high resistance of the x = 0.30 ceramic contribute to its electrical breakdown strength. A linear‐like P–E loop with the large discharged energy density WD ∼ 3.50 J/cm3 and high energy efficiency η ∼ 90.1% is obtained under 28 kV/mm at room temperature. The thermal stability of the energy storage performance is also satisfactory with the variation of WD less than 15% over −40 to 200°C, and the η is higher than 85%. [ABSTRACT FROM AUTHOR]

Polymer dielectrics are attracting increasing attention for electrical energy storage owing to their advantages of mechanical flexibility, corrosion resistance, facile processability, light weight, great reliability, and high operating voltages. However, the dielectric constants of most dielectric polymers are less than 10, which results in low energy densities and limits their applications in electrostatic capacitors for advanced electronics and electrical power systems. Therefore, intensive efforts have been placed on the development of high‐energy‐density polymer dielectrics. In this perspective, the most recent results on the all‐organic polymer dielectrics are summarized, including molecular structure design, polymer blends, and layered structured polymers. The challenges in the field and suggestions for future research on high‐energy‐density polymer dielectrics are also presented. [ABSTRACT FROM AUTHOR]

Dielectric composites based on ferroelectric ceramics nanofibers are attracting increasing attention in capacitor application. In this work, the sol–gel method and electrospinning technology are utilized to prepare one-dimensional Na0.5Bi0.5TiO3 (NBT) nanofibers, and the influence of electrospinning process parameters such as spinning voltage, liquid supply rate, and collector speed on the morphology and structure of nanofibers are systematically explored. The final optimized parameters include the applied voltage of 20 kV, the solution flow rate of 1 mL/h, and the collector's rotation speed of 1500 rpm. The optimized NBT nanofibers are introduced into the PVDF polymer matrix for energy storage application. Owing to the enhanced interfacial polarization between PVDF matrix and NBT nanofibers with a high aspect ratio, the NBT–PVDF nanocomposites achieve a high discharge energy density of 14.59 J cm−3 and an energy efficiency of 53.69% at 490 kV mm−1, which are higher than those of pure PVDF, i.e., 10.26 J cm−3 and 48.17% at 420 kV mm−1, respectively. The results demonstrate that the strategy of synthesizing NBT nanofibers using the electrospinning method is of great potential for high-performance dielectric capacitor application. [ABSTRACT FROM AUTHOR]

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area. [ABSTRACT FROM AUTHOR]

Dielectric polymer-based nanocomposites have attracted significant attention in recent years for energy storage applications because of their potential high permittivity and breakdown strength. The coupling effect of a nanofiller/matrix interface plays a crucial role in the dielectric and electric properties of polymer-based nanocomposites. In this paper, three kinds of side-chain liquid crystalline fluoric-polymers, denoted as P-nF (n = 3, 5 or 7, which is the number of terminal fluoric groups), were grafted on the surface of BaTiO3 nanoparticles by a surface-initiated reversible-addition–fragmentation chain transfer polymerization method. The nanocomposite films were prepared via core–shell BaTiO3 nanoparticles dispersed in a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) P(VDF-TrFE-CTFE) polymer matrix. The frequency dependent dielectric properties and energy storage capability of the polymer nanocomposites were studied. The results showed that the permittivity and energy densities of the polymer nanocomposites depended on the molecular structure of the modifier, especially the number of electron-rich fluoric groups. Firstly, all modified BaTiO3 nanoparticles were homogeneously dispersed in the polymer matrix, resulting in the polymer nanocomposites presenting a higher breakdown strength compared with the unmodified BaTiO3 nanoparticles. Secondly, the changes in the nanocomposites’ permittivity exhibited diversity for three modifiers due to many influential factors. Thirdly, compared with neat P(VDF-TrFE-CTFE), the discharge energy densities of the polymer nanocomposites are all significantly improved. The highest discharge energy densities of nanocomposites with 5 vol% P-3F@BT reached 14.5 J cm−3. These findings suggest that the optimal interfacial modifier should be carefully decided by combining various properties of the nanocomposites for energy storage. [ABSTRACT FROM AUTHOR]

Dielectric composites are of great demand in the micro-electronics industry. To enhance the energy storage density of the composites, TiO2 nanowire clusters was synthesized by a hydrothermal method and incorporated into the P(VDF-HFP) polymer matrix in this work. The microstructure, dielectric properties of the prepared film were discussed and the effects of TiO2 loading on the energy density were investigated. The results shows that the TiO2 clusters were tightly blended to the P(VDF-HFP) matrix owing to the dopamine-modified interface. The dielectric constant increased with the loading of TiO2, the maximum dielectric constant reached 12.04 with 7.5 vol% TiO2 loading at 1 kHz, as compared to 5.01 for the neat P(VDF-HFP). The enhanced dielectric constant was attributed to the interface polarization originated from the large interface area between the TiO2 nanowire and polymer matrix. The discharged energy density of the composite significantly increased to 1.35 J/cm3 with 7.5 vol% TiO2 nanowire clusters, which was two times higher than that of the neat P(VDF-HFP) at the same condition. The findings of this work can shed a light on improving the energy density of energy storage device via morphology modification. [ABSTRACT FROM AUTHOR]

Dielectric materials with high energy storage density are attracting scientific and commercial interest due to the prospect of application in advanced electronic devices and electric power systems. Ceramic/polymer composite is one of the most promising materials to obtain high energy density because it combines high permittivity from ceramic and high breakdown strength as well as flexibility from polymer matrix. However, the homogeneous dispersion and compatibility of nanoparticles in polymers matrix are still of great challenges due to the different surface energy between inorganic fillers and organic polymer matrix. Interfaces modification for ceramic fillers is an effective way to ease the mentioned problems. Herein, we proposed a low-cost and environmentally friendly route to prepare a core–shell structure by paraffin engineer the BaTiO 3 nanoparticles. The modified BaTiO 3 nanoparticles exhibited homogeneous dispersion in the ferroelectric polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix and strong interfacial adhesion with the polymer matrix. The nanocomposites prepared in this work showed notably enhanced energy storage density. The maximum storage energy density of the nanocomposite with 50 vol% BaTiO 3 increased to 21.1 J/cm 3 at 150 kV/mm. These results indicate that paraffin is an effective modifier to prepare high energy storage density capacitor. [ABSTRACT FROM AUTHOR]

Low energy densities of polymer-based composites restrict their application in miniaturization and integration of dielectric capacitors. Recently, multilayered hierarchical polymer composite is emerging as a promising route to address the aforementioned challenges. In most cases, high loading (>10 wt%) of ceramic nanoparticles were incorporated into polymer matrix to act as a hard layer for high permittivity. In fact, high-loading filler will inevitably cause agglomerations and deteriorate electric breakdown strength due to the poor dispersion and compatibility between the fillers and matrix. One-dimension nanowires exhibit obvious superiority to increase the permittivity of the nanocomposites due to large dipole moments from its high aspect ratios. In this work, a novel strategy of designing sandwich structured PVDF nanocomposites with low-loading BaTiO 3 nanowires was proposed. The motivation is to maintain high breakdown strength by the contribution of barrier effect from the sandwich structure and low-loading of BaTiO 3 nanowire fillers. Two sandwich structures including ″3-0-3″ and ″0-3-0″ (the digit representing BaTiO 3 nanowires mass fraction in each layer) and single-layered BaTiO 3 /PVDF nanocomposites are fabricated for optimization and comparison. The results revealed that due to the contribution of interfacial polarization and barrier effect between adjacent layers, sandwich-structured BaTiO 3 /PVDF nanocomposites deliver greatly improved polarization, enhanced electric breakdown strength, and limited leakage current density, which significantly outperform single-layered films. For instance, a high breakdown strength of 519 kV mm−1 with a high maximum polarization of 12.1 μC cm−2, and an impressive discharged energy density of 19.1 J cm−3 accompanied with energy efficiency of 68.6% were achieved even at a very low filler loading of 3 wt% BaTiO 3 nanowires. In addition, the potential applications of the nanocomposites for energy storage have been further demonstrated by keeping stable performance after 106 charge-discharge cycles. ga1 • BaTiO 3 nanowires with high aspect ratio were empolyed in sandwich-structured nanocomposite. • Enhanced E b and D max were achieved in the sandwich-structured nanocomposite. • High energy density of 19.1 J cm 3 was achieved by 3 wt% BaTiO 3 nanowires. [ABSTRACT FROM AUTHOR]

There is still a problem of low energy storage density in dielectric capacitors which is a core component of power systems. For the improvement of the energy storage density, the linear dielectric material CaTiO 3 (CT) was introduced in Na 0.5 Bi 0.5 TiO 3 (NBT) ceramics in this paper. By modifying the A site, a new relaxor ferroelectric ceramic was successfully synthesized and attained a recoverable density (W rec) of 2.34 J/cm3 at x = 0.18. Moreover, the preparation process was optimized in this paper. Through the viscous polymer process (VPP) route, the energy density (W A) of 82NBT-18CT VPP ceramic further reaches 6.45 J/cm3 at 340 kV/cm, with efficiency (η) up to 75% and a W rec of 4.82 J/cm3. At the same time, the change of W rec is small at temperature (30–150 °C) and frequency (1 Hz–300 Hz), which demonstrates its excellent stability. The discharge power density reaches about 180 MW/cm3 and the discharge time is 0.117 μs, which indicates its excellent pulse discharge performance. The results show that 82NBT-18CT lead-free relaxation ferroelectric material is expected to become ideal for high-energy storage applications. [ABSTRACT FROM AUTHOR]

• The density and depth of traps are improved attributed to the incorporation of F4-TCNQ with high electron affinity. • Physical interaction between F4-TCNQ and PEI endows composites with dense chain packing and increased Young's modulus. • At 150 °C, a high discharged energy density of 7.84 J/cm3 is achieved under 670 kV/mm. High temperature resistance is essential for electrostatic capacitors, for example, the operating temperature of capacitors used in inverters for hybrid electric vehicles is around 140–150 °C. However, the reliability of current commercial dielectrics, such as biaxial stretched polypropylene (BOPP), significantly degrades when the operating temperature exceeds 105 °C. In this work, an all-organic dielectric utilizing two mechanisms—high electron affinity and physical interaction—is designed to enhance the capacitive performance. Specifically, the molecular semiconductor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), with ultra-high electron affinity (5.24 eV) and peripheral electronegativity, is incorporated with polyetherimide (PEI). Deep electron traps are successfully constructed to capture free electrons due to the incorporation of high-electron-affinity F4-TCNQ. Moreover, it is difficult for the captured electrons to escape because of the Coulomb force between electrons in the low unoccupied molecular orbital (LUMO) of F4-TCNQ and holes in the highest occupied molecular orbital (HOMO) of PEI. From another point of view, physical interaction is formed between the peripherally electronegative groups of F4-TCNQ and the positively charged phenyls of PEI, improving the packing density among polymer chains and the Young's modulus. Consequently, the electromechanical breakdown strength is enhanced. These two mechanisms play their part simultaneously, realizing significantly suppressed conductivity loss and increased breakdown electric field. Accompanied by an improved dielectric constant, the discharged energy density of F4-TCNQ/PEI composites is significantly increased over a wide temperature range. Especially at 150 °C, the discharged energy density (U e) of 0.6 wt% F4-TCNQ/PEI reaches 7.84 J/cm3 at 670 kV/mm, which is 123 % higher than that of PEI (3.52 J/cm3). The U e is still as high as 5.12 J/cm3 even when the discharged efficiency (η) is over 90 %. This work exhibits a promising prospect of all-organic dielectrics in capacitive application at high temperature. [ABSTRACT FROM AUTHOR]

Low-grade heat conversion is one of the most promising strategies to realise carbon-neutral electricity production. Here we present a study on a hierarchically structured porous pyroelectric barium strontium titanate (BST) ceramic with a low Curie temperature and improved thermal energy harvesting performance. The aligned porous structure is beneficial to achieve a greatly reduced permittivity and heat capacity, combined with a high degree of polarisation to maintain a high pyroelectric coefficient. These characteristics contributed to significantly improved sensing and harvesting pyroelectric figures-of-merit, where the thermal energy harvesting figure-of-merit (F E ′) increased by 510% when the porosity reached to 54 vol%, compared to that of the dense BST ceramic. After rectification of the AC pyroelectric current to a DC current, the electric output was stored on a 1 μF capacitor whose voltage after 20 s increased with increasing volume fraction of porosity; namely 5.8 V (dense, 3 vol% porosity), 6.9 V (30 vol%), 7.5 V (43 vol%) and 9.2 V (54 vol%). A maximum energy density of 4.26 μJ/mm3 was obtained from the BST with 54 vol% porosity, which was 1.6 times higher than that of the dense counterpart (2.71 μJ/mm3). This aligned porous structure therefore represents a new and promising architecture for facile harvesting and conversion of low-grade waste heat into electrical power. [ABSTRACT FROM AUTHOR]

In this work, fine-grained (0.95- x)(Bi 0.5 Na 0.5)TiO 3 -0.05BaTiO 3 - x Bi(Zn 2/3 Nb 1/3)O 3 (abbreviated as BNT-BT- x BZN, x = 0∼0.20) lead-free ceramics are successfully prepared, showing a high energy storage performance. The addition of BZN results in decreased grain size, enhanced breakdown strength and stronger relaxor behavior with polar nanoregions. Slimmer P - E loops are thereby achieved, leading to the improvement of energy density and efficiency. As a result, a high W D of ∼2.83 J/cm3 is achieved under a relatively low electric field of 18 kV/mm in the x = 0.125 ceramic with submicron-sized grains (∼0.4 μm). The W D value is larger than that of x = 0 ceramic by ∼800%. Furthermore, the x = 0.125 ceramic possesses excellent frequency stability and strong fatigue endurance. The BNT-BT- x BZN lead-free ceramics show promising potential for application in high energy density ceramic capacitors. [ABSTRACT FROM AUTHOR]

Abstract It is challenging to achieve high energy density in conductive fillers/polymer nanocomposites due to their extremely low breakdown strength. In this paper, a novel multi-component and multilayer-structured nanocomposite was designed and investigated, consisting of Ba 0.8 Sr 0.2 TiO 3 decorated graphene (BST @ RGO)/poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer (P(VDF-CTFE)) composites (R-Layer) as interlayer, and BaTiO 3 /P(VDF-CTFE) composites (B-Layer) as surface layer. The multilayer-structured nanocomposites were prepared through layer-by-layer solution casting method. Enhanced breakdown strength, energy density, dielectric constant and low dielectric loss were simultaneously obtained in the nanocomposites by the multilayer structure. The maximum dielectric constant of the composites with multi-layered structure was approximately 14, which was increased by 16.67% compared to the pure P(VDF-CTFE) layer, and the dielectric loss was as low as 0.047 at 1 kHz, even lower than pure P(VDF-CTFE) in frequency range from 10 kHz to 1 MHz. The breakdown strength and energy storage density of BRB-3 nanocomposites with 3 R-Layers reached to 220 kV mm−1 and 6.49 J cm−3, respectively. These results demonstrated that designing multi-component and multilayer-structured nanocomposites was an effective approach to fabricate high performance dielectric nanocomposites. [ABSTRACT FROM AUTHOR]

Dielectric capacitors are of urgently demand in modern micro-electric industry. The surface modified inorganic filler introduced to polymer matrix represents a promising avenue for the dielectric material's enhancement of energy storage density. To ease the electric field concentration of the composite induced by permittivity difference between ceramic fillers and polymer matrix, the specific dielectric fillers of TiO 2 nanowires modified BT particles were synthesized in this study. Gradient dielectric composite consisting of poly(vinylidene fluoride-co-hexafluoropylene) [P(VDF-HFP)] matrix ( ε r ∼10), TiO 2 shell ( ε r ∼40), and BaTiO 3 (BT) core ( ε r ∼1000) were focused to investigate the electric field contribution and interface polarization. The results revealed that the permittivity of the composites increased as a result of large interfacial polarization induced by the large specific surface area of the nanowires as compared to the composite with randomly mixed TiO 2 /BT fillers. The breakdown strength of the composite was slightly improved with 20 vol% fillers, attributed to the fact that the electric field intensification was weakened by the BT@TiO 2 /Dop gradient dielectric fillers. The composite could endure up to 10 6 times of field cycling at the applied cycling field and the leakage current density was rather low. The composites with 20 vol% fillers exhibited a discharged energy density of 2.8 J/cm 3 at a low electric field, which was much higher than that of the neat P(VDF-HFP). The findings of this research introduced a new inorganic particle with large specific surface area and gradient dielectric permittivity as filler in composite for energy storage application. [ABSTRACT FROM AUTHOR]

[Display omitted] • High performance nitrated polystyrene can be prepared on a large scale. • Nitrated polystyrene shows high permittivity and high breakdown strength. • The mechanism of polarization and breakdown was investigated. • The discharge energy density of 6.32 J cm−3 was achieved in nitrated polystyrene. It is a great challenge to achieve ultrahigh discharge energy density (U e) via improving simultaneously permittivity and breakdown strength of polymer dielectrics. In this work, it is first found that nitrated polystyrene films possess excellent dielectric and energy storage properties. The mechanism for the permittivity and breakdown strength of nitrated polystyrene were investigated. On one hand, substituent group of dipolar nitro can increase the glass transition temperature and permittivity of polystyrene. On the other hand, nitro substituent group can not only construct charge traps to reduce the carrier mobility under high fields, but also effectively destroy the carrier channel formed by the accumulation of pi-pi between the benzene rings under high field, both which favor the enhancive breakdown strength of polystyrene. As a results, the maximum U e of 6.32 J cm−3 at 640 MV m−1 was obtained in nitrated polystyrene with a substitution degree of 15%, which is 2.38 times than that of neat polystyrene. Furthermore, at 200 MV m−1 and 100 °C, nitrated polystyrene with a substitution degree of 66% produced U e of 1.1 J cm−3 with 88% efficiency. This study demonstrates that the nitration can significantly promote permittivity and breakdown strength of polystyrene, and provides a guidance for preparing high-performance and large-scale polymer dielectrics. [ABSTRACT FROM AUTHOR]

Our research provides a potential avenue for preparing high-performance all-organic polymer dielectrics via optimizing sequential structure of polystyrene-based copolymers. [Display omitted] • All organic P(St-co-CBMA) dielectrics with high-performance are synthesized. • Improved permittivity and breakdown strength are achieved in the copolymer. • An outstanding U e of 8.94 J/cm3 and high η of 87.4% at 476 MV/m are achieved in the designed copolymer. It is a great challenge to improve simultaneously the permittivity (ε r) and breakdown strength of polymer dielectrics. The linear polystyrene (PS) has the advantages of low cost, easy processing and high charge-discharge efficiency (η). However, the low ε r and low breakdown strength result in the low discharge energy density (U e) of PS. For polar liquid crystalline polymer poly[11-((4′-cyano-[1,1′-biphenyl]-4-yl)oxy)undecyl methacrylate] (PCBMA), it shows the merit of high ε r , low band gap width and good film-forming property. In this paper, random copolymers P(St-co-CBMA) and block copolymers PS-b-PCBMA were synthesized by radical polymerization and reversible addition-breaking chain transfer polymerization, respectively. The effect of sequential structure on the dielectric behaviors and energy storage properties of polystyrene copolymers is investigated in detail. The experimental results indicate that a high ε r value of 5.2 (±0.049), an outstanding U e of 8.94 J/cm3 and high η of 87.4% at 476 MV/m are achieved in random copolymer P(St-co-CBMA) with the 92 mol% content of CBMA unit because of the strong orientation polarization, deep traps and good film-forming property. This work demonstrates that it is a feasible strategy to obtain high performance polystyrene copolymer dielectrics via tailoring sequential structure between functional monomer and styrene monomer. [ABSTRACT FROM AUTHOR]

In this work, polyimide-based (PI) nanocomposites containing two-dimensional oxidized MXenes as filler exhibit obviously enhanced capacitive performances at elevated temperature. To decrease the aggregation, Ti 3 C 2 T X colloidal solution was directly introduced into PI matrix via in-situ polymerization method. Because of the strong electrostatic attraction to electrons, the charge can be captured by oxidized MXenes, resulting in suppressed leakage current and greatly improved breakdown strength. Therefore, the largest discharged energy density (U d) of 8.67 J/cm3 and the efficiency of 84.1% are achieved at 648 kV/mm in 0.5-wt% oxidized MXenes/PI nanocomposites at room temperature, which is more than twice than that of pure PI. In high temperature, significantly increased U d of 5.46 J/cm3 at 100 °C and U d of 2.05 J/cm3 at 150 °C are obtained compared with the pure PI (1.28 J/cm3@100 °C). This research contributes to broadening the application of oxidized MXene in flexible dielectrics and providing an effective way for the preparation of high-performance dielectric polymer-based composites over a broad temperature range. [Display omitted] • The oxidized Ti 3 C 2 T x is proposed to construct polyimide-based dielectric composites. • The oxidized MXenes can capture charges to improve breakdown strength. • The superior discharge energy density is achieved at elevated temperature. [ABSTRACT FROM AUTHOR]

• BaTiO 3 nanowire array and BN nanosheet are integrated in PVDF based nanocomposite. • The synergy ascension of ε r and E b is yield by optimizing BN nanosheet contents. • BaTiO 3 -3wt.%BN/PVDF nanocomposite shows a high U e of 16.1 J/cm3 at 500.3 kV/mm. • This novel spatial structure design is applicable to wide range of energy fields. Polymer based dielectric nanocomposites with high energy density are highly desirable to satisfy the lightweight and integration of electrostatic capacitors in electronic and electrical equipment. Recently, it is proved that polymer incorporated with aligned nanowire array represents an effective strategy for significantly improving the permittivity due to largely enhanced space charge and orientation polarization. Nevertheless, it is still a great challenge to overcome the contradictory relationship between permittivity and electric breakdown strength. In this work, a unique spatial design in bilayer structured PVDF based nanocomposites are proposed by incorporating BaTiO 3 nanowire array with high-permittivity and BN nanosheets with wide-band gap, respectively. The bottom BaTiO 3 /PVDF layer and upper BN/PVDF layer are constructed for the synergy ascension of permittivity and breakdown strength by the optimization of BN nanosheet content. As a consequence, the dielectric permittivity of BaTiO 3 /BN-PVDF nanocomposite reaches 35.3 at 1 kHz, which is higher than that of 33.9 for BaTiO 3 /PVDF nanocomposite and 9.1 for pristine PVDF film, respectively. Also, the significantly increased electric displacement, e.g., 12.1 μC cm−2, enhanced E b , e.g., 500.3 kV mm−1 and suppressed leakage current density are obtained in BaTiO 3 /BN-PVDF nanocomposites. The highest discharged energy density reaches 16.1 J cm−3, which shows a great improvement comparing to that of commercial biaxially oriented polypropylene (BOPP) film. This work demonstrates a unique design of spatial structure integrating various anisotropic nanofillers in polymer-based nanocomposite, whose outstanding energy storage performance makes it as a promising candidate for high-performance electrostatic capacitors application. [ABSTRACT FROM AUTHOR]

• Ferroelectric HZO-NFs was fabricated via electrospinning technique. • Continuous interface was built between HZO-NFs with low ɛ r and P(VDF-HFP). • Ultrahigh E b of 706.71 kV/mm was obtained due to the existence of multi-interfaces. • Enhanced U d of 21.63 J/cm3 was achieved in P-3 wt% HZO/P-P sandwich structures. Ceramic/polymer composites with high energy density attract great interest due to their application in micro-electric power systems. However, the large permittivity mismatch between ceramic fillers and polymer matrix will largely decrease the breakdown strength and energy density of nanocomposites. Herein, one-dimensional Hf 0.5 Zr 0.5 O 2 nanofibers (HZO-NFs) with very low permittivity were proposed as the loading fillers in poly (vinylidene fluoride - hexafluoro propylene) (P(VDF-HFP)) copolymer for energy-storage applications for the first time via a simple scalable method of electrospinning technique. P(VDF-HFP) nanocomposites with 3 wt% HZO-NFs (3 wt% HZO/P) showed a high discharged energy density (U d) of 13.68 J/cm3 with a high breakdown strength (E b) of 508.66 kV/mm. Sandwich-structured P-3 wt% HZO/P-P nanocomposite achieved an excellent U d of 21.63 J/cm3 and a high η of ∼ 65.68% at ultrahigh E b of 706.71 kV/mm, which are much higher than those of the commercial BOPP, i.e. 2 J/cm3 at 640 kV/mm. Moreover, the COMSOL simulations revealed that the introduction of 1D nanofibers and charge traps could effectively improve the local distribution of electric field, and finally increased the breakdown strength. The major contribution to the improved U d originates from the large breakdown strength (4 ∼ 8 MV/cm), because of the large band width of HZO and the existence of multi-interfaces. This work can provide a new perspective for promoting the performance of polymer nanocomposites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Functionalized CQDs were synthesized, which showed monodispersity in solvent. • Coulomb-blockade effect of CQDs was utilized to increase the E b of PEI matrix. • The composite with 0.5 wt% CQDs exhibited a high U e of 10.66 J/cm3 at 600 kV/mm. There is an urgent need for dielectric capacitors with high energy density and efficiency with the rapid progress of power electronic devices. Inorganic/organic composites were once considered as a potential candidate for dielectrics. However, the inevitable defects induced by the inorganic fillers always lead to the decreased breakdown strength and limited energy density and efficiency. In this work, carbon quantum dots (CQDs) with abundant functional groups were synthetized and introduced into linear dielectric polyethyleneimine (PEI) matrix. Due to the unique Coulomb-blockade effect of quantum dots, the movement of carriers can be hindered under the applied electric field, leading to the improvement of breakdown strength. Compared with most of the reported nanocomposites with high loading of fillers, the nanocomposites in this work with extremely low loading of CQDs exhibit obviously enhanced performance. The nanocomposite with 0.5 wt% CQDs exhibits a high discharge energy density of 10.66 J/cm3 and efficiency of 88.3% at 600 kV/mm, corresponding to a 62.3% improvement over that of PEI (6.57 J/cm3 at 490 kV/mm). This work provides an effective strategy to break down the long-standing contradiction between the enhancement of dielectric constant and the reduced in breakdown strength. The film dielectrics with extremely low loading of fillers contributing to enhanced energy density and high energy efficiency is very important for practical applications. [ABSTRACT FROM AUTHOR]

• KTaO 3 modified Na 0.5 Bi 0.5 TiO 3 ceramics are synthesized for dielectric and energy storage capacitors. • The dielectric constant variation of the 0.90NBT-0.10KT ceramic is less than 15% in the range of 29–390 °C. • A large discharge energy density W D of 2.8 J/cm3 and energy efficiency of η 80.4% are achieved for 0.80NBT-0.20KT ceramic. Nowadays, it remains a challenge to achieve a simultaneous improvement of dielectric constant, energy density, and temperature stability in dielectric ceramics. In this work, it was found that such drawback could be effectively resolved by using KTaO 3 to substitute Na 0.5 Bi 0.5 TiO 3. In (1- x)Na 0.5 Bi 0.5 TiO 3 - x KTaO 3 ceramics, the temperature coefficient of capacitance (TCC) of x = 0.10 composition is lower than 15% in the temperature range of 25–390 °C, with a high dielectric constant of 2008 and a low dielectric loss of 0.0044 at 150 °C. Meanwhile, a large discharged energy density of ~2.50 J/cm3 with the variation less than± 3% in 5–190 °C was obtained under a low electric field of 18 kV/mm in x = 0.20 composition, accompanied with a high energy efficiency of> 80%. These results reveal that this ceramic system is a promising candidate for temperature-stable dielectric and energy storage capacitors applications. [ABSTRACT FROM AUTHOR]

• Low-cost natural-sepiolite was used to develop large-scale production of high performance dielectrics. • Organophilic-sepiolites nanofibers possessed well dispersion in the PVDF matrix. • The maximal U e of 7.2 J·cm−3 was achieved in 2.5%-APTES@Sepiolites/PVDF nanocomposites. The preparation of large-aspect-ratio nanofillers is challenging due to the complicated and expensive artificial processing procedures and low yields, obstructing scale-up production of 1D nanofillers/polymer dielectric nanocomposites. In this paper, a kind of natural sepiolite nanofiber was utilized to fabricate scale-up of PVDF-based dielectric nanocomposites. The sepiolite nanofibers were modified by aminopropyltriethoxysilane (denoted as APTES@Sep) and 1H,1H,2H,2H-perfluoroheptadecane trimethysiloxane (denoted as PFDTES@Sep), respectively, before being incorporated into PVDF. The effect of nanfibers loading and modifiers on the dielectric behaivor and energy stroage properties of nanocomposites was investigated. As results, the nanocomposites with 7.5 vol% PFDTES@Sep exhibited highest permittivity of 16.4 at 103 Hz originating from well dispersibility, strong interfacial polarization and orientation polarization. The nanocomposites with 2.5 vol% APTES@Sep displayed maximal discharged energy density of 7.2 J·cm−3 owing to highest breakdown strength. This work provides a simple and cheap strategy for developing high performance flexible dielectric nanocomposites, which is suitable for large-scale preparation. [ABSTRACT FROM AUTHOR]