Achieving High Energy Density and Low Loss in PVDF/BST Nanodielectrics with Enhanced Structural Homogeneity

Bioinspired Dielectric Nanocomposites with High Charge-Discharge Efficiency Enabled by Superspreading-Induced Alignment of Nanosheets

High-performance dielectric nanocomposites are promising candidates for thin-film dielectric capacitors for high-power pulse devices. However, the existing nanocomposites suffer from low charge-discharge efficiency (η), which results in severe generation and accumulation of Joule heat and subsequently the failure of the devices. In this work, we report nacre-inspired dielectric nanocomposites with outstanding η, which are enabled by superspreading shear flow-induced highly aligned two-dimensional (2D) nanofillers. Taking boron nitride nanosheets (BNNS) as an example, the highly aligned BNNS in the poly(vinylidene fluoride) (PVDF)-based nanocomposites contributes to a highly efficient Coulomb blockade effect for the injected charge carriers. Therefore, the bioinspired nanocomposites with highly aligned BNNS show significantly reduced dielectric loss (tan δ) (63.3%) and improved η (144.8%), compared to the ones with partially aligned nanosheets fabricated by solution casting. Furthermore, the optimized loading content of BNNS is as low as 3.6 wt %. The resulting nanocomposites exhibit reduced tan δ (0.018) and enhanced Eb (687 kV/mm), η (71%), and Ue (16.74 J/cm3). Our work demonstrates that the realization of high alignment of 2D nanofillers enabled by the superspreading shear flow is a promising way for the development of high-performance dielectric nanocomposites.

Crosslinking modification and hydrogen bonding synergy to achieve high breakdown strength and energy density of PMMA-co-GMA/PVDF dielectric composite films

Polymer-based dielectric materials have been used in film capacitors due to their rapid charge-discharge rate, lightness, and low cost. Nevertheless, the energy storage properties of these dielectric films were limited by their weak polarization ability and low discharge energy density. Herein, the solution casting method was used to prepare all-organic crosslinked composite films using linear methyl methacrylate-co-glycidyl methacrylate (MG) as the matrix and ferroelectric poly(vinylidene fluoride) (PVDF) as the organic filler. The crosslinked MG networks can enhance the breakdown strength, restrain dielectric loss, and keep high discharge efficiency. What's more, the presence of PVDF can compensate for the low electrical displacement, improve the permittivity, and overcome the brittleness of the crosslinked films. The optimal all-organic crosslinked dielectric film exhibited an ultrahigh breakdown strength of 800 MV m-1 and a high efficiency of 77.4%. The maximum energy density of the composite film reached up to 12.1 J cm-3, which was nearly 120% higher than the energy density of 5.6 J cm-3 of the pure MG film. The enhancement in energy storage properties is ascribed to the synergistic effects of chemical crosslinking and hydrogen bonding. This study offers a feasible method for all-organic polymer films to fabricate energy storage equipment.

Perspective on interface engineering for capacitive energy storage polymer nanodielectrics

Polymer nanodielectrics with high breakdown strength (E_b), high energy density (U_e) and low energy loss have great potential to be used as capacitive energy storage materials of high-voltage film capacitors in modern electrical and electronic equipment, such as smart grids, new energy vehicles and pulse powered weapons. Usually, inorganic nanoparticles with high dielectric constant (ε_r) are added into a high E_b polymer matrix to achieve simultaneously enhanced ε_r and E_b, thus leading to nanodielectrics with high U_e. However, this strategy was seriously hampered by the uneven distribution of electric fields and inhomogeneous microstructures of the multi-phased nanodielectrics until increasing research work was focused on interface engineering. Recent progress in nanocomposites suggests that interface engineering plays a critical role in regulating the polarization and breakdown behaviors of the nanodielectrics, such as balancing ε_r and E_b, enhancing U_e and energy discharge efficiency (η). This article highlights the recent advances in the interface engineering of polymer nanodielectrics, including theoretical models, interface engineering strategies, and the latest characterization and fabrication techniques of high performance nanodielectrics. Finally, the challenges and opportunities in the interface engineering of the nanodielectrics in film capacitors are discussed and predicted from a practical point of view.

High Conduction Band Inorganic Layers for Distinct Enhancement of Electrical Energy Storage in Polymer Nanocomposites

Dielectric polymer nanocomposites are considered as one of the most promising candidates for high-power-density electrical energy storage applications. Inorganic nanofillers with high insulation property are frequently introduced into fluoropolymer to improve its breakdown strength and energy storage capability. Normally, inorganic nanofillers are thought to introducing traps into polymer matrix to suppress leakage current. However, how these nanofillers effect the leakage current is still unclear. Meanwhile, high dopant (> 5 vol%) is prerequisite for distinctly improved energy storage performance, which severely deteriorates the processing and mechanical property of polymer nanocomposites, hence brings high technical complication and cost. Herein, boron nitride nanosheet (BNNS) layers are utilized for substantially improving the electrical energy storage capability of polyvinylidene fluoride (PVDF) nanocomposite. Results reveal that the high conduction band minimum of BNNS produces energy barrier at the interface of adjacent layers, preventing the electron in PVDF from passing through inorganic layers, leading to suppressed leakage current and superior breakdown strength. Accompanied by improved Young's modulus (from 1.2 GPa of PVDF to 1.6 GPa of nanocomposite), significantly boosted discharged energy density (14.3 J cm^-3) and charge-discharge efficiency (75%) are realized in multilayered nanocomposites, which are 340 and 300% of PVDF (4.2 J cm^-3, 25%). More importantly, thus remarkably boosted energy storage performance is accomplished by marginal BNNS. This work offers a new paradigm for developing dielectric nanocomposites with advanced energy storage performance.

Enhanced Energy Storage Performance of PVDF-Based Composites Using BN@PDA Sheets and Titania Nanosheets

With the rapid development of modern electrical and electronic applications, the demand for high-performance film capacitors is becoming increasingly urgent. The energy density of a capacitor is dependent on permittivity and breakdown strength. However, the development of polymer-based composites with both high permittivity (εr) and breakdown strength (Eb) remains a huge challenge. In this work, a strategy of doping synergistic dual-fillers with complementary functionalities into polymer is demonstrated, by which high εr and Eb are obtained simultaneously. Small-sized titania nanosheets (STNSs) with high εr and high-insulating boron nitride sheets coated with polydopamine on the surface (BN@PDA) were introduced into poly(vinylidene fluoride) (PVDF) to prepare a ternary composite. Remarkably, a PVDF-based composite with 1 wt% BN@PDA and 0.5 wt% STNSs (1 wt% PVDF/BN@PDA−STNSs) shows an excellent energy storage performance, including a high εr of ~13.9 at 1 Hz, a superior Eb of ~440 kV/mm, and a high discharged energy density Ue of ~12.1 J/cm3. Moreover, the simulation results confirm that BN@PDA sheets improve breakdown strength and STNSs boost polarization, which is consistent with the experimental results. This contribution provides a new design paradigm for energy storage dielectrics.

Enhanced Energy Density at a Low Electric Field in PVDF-Based Heterojunctions Sandwiched with High Ion-Polarized BTO Films

Inorganic/organic dielectric composites with outstanding energy storage properties at a low electric field possess the advantages of low operating voltage and small probability of failure. Composites filled with two-dimensional inorganic nanosheets have attracted much attention owing to their fewer interfacial defects caused by the agglomeration of fillers. Continuous oxide films with a preferred orientation can play a significant role in enhancing energy storage. The challenge is to prepare large-sized, freestanding, single-crystal, ferroelectric oxide films and to combine them with polymers. In this work, a well-developed water-dissolvent process was used to transfer millimeter-sized (100)-oriented BaTiO₃ (BTO) films. Poly(vinylidene fluoride) (PVDF)-based heterojunctions sandwiched with the single-crystal films were synthesized via the transferring process and an optimized hot-pressing technique. By virtue of high ion displacement polarization and inhibited conductive path formation of single-crystal BTO films, the energy storage density and efficiency of BTO/PVDF heterojunctions reach 1.56 J cm^-3 and 71.2% at a low electric field of 120 MV m^-1, which are much higher than those of pure PVDF and BTO nanoparticles/PVDF composite films, respectively. A finite-element simulation was employed to further confirm the experimental results. This work provides an effective approach to enhance energy storage properties in various polymer-based composites and opens the door to advanced dielectric capacitors.

Epoxy-Based/BaMnO4 Nanodielectrics: Dielectric Response and Energy Storage Efficiency

Compact capacitive energy storing/harvesting systems could play a key role in the urgent need for more energy-efficient technologies to address both energy and environmental issues. Therein, the purpose of the present work is to develop and investigate epoxy/BaMnO4 nanocomposites at various filler concentrations, which could be applicable as compact materials systems for energy storage and harvesting. Broadband dielectric spectroscopy was used for studying the dielectric properties and the relaxation processes of the examined nanodielectrics. The energy storing/retrieving ability of the nanocomposites was also evaluated via DC charge–discharge experiments. The coefficient of energy efficiency (neff) was found for all prepared nanocomposites to evaluate the energy performance of the systems. Dielectric data divulge the existence of two matrix-related relaxations, i.e., α-mode and β-mode, attributed to the glass-to-rubber transition of the polymer matrix and re-orientation of polar side groups, respectively. Interfacial polarization was also identified in the low-frequency and high-temperature region. The 7 phr BaMnO4 nanocomposite exhibits the best performance in terms of the stored and harvested energies compared to all systems. On the other hand, the 5 phr, 3 phr and 1 phr nanocomposites display optimum energy performance, reaching high values of neff.

On the Temperature Dependence of the Piezoelectric Response of Prepoled Poly(vinylidene fluoride) Films

There is growing interest in integrating piezoelectric materials with complementary metal-oxide-semiconductor (CMOS) technology to enable expanded applications. A promising material for ultrasound transducer applications is polyvinylidene fluoride (PVDF), a piezoelectric polymer. One of the challenges with PVDF is that its piezoelectric properties can deteriorate when exposed to temperatures in excess of 70 °C for extended periods of time during fabrication. Here, we report on the effects of both shortening annealing times and providing this heating non-uniformly, as is characteristic of some processing conditions, on the piezoelectric coefficient (d ₃₃) of PVDF films for various thicknesses. In this case, no degradation in the d ₃₃ was observed at temperatures below 100 °C for anneal times of under one minute when this heating is applied through one side of the film, making PVDF compatible with many bonding and photolithographic processing steps required for CMOS integration. More surprisingly, for one-sided heating to temperatures between 90 °C and 110 °C, we observed a transient enhancement of the d ₃₃ by nearly 40% that lasted for several hours after these anneals. We attribute this effect to induced strain in these films.

Frequency dependent energy storage and dielectric performance of Ba-Zr Co-doped BiFeO3 loaded PVDF based mechanical energy harvesters: effect of corona poling

Bi0.95Ba0.05Fe0.95Zr0.05O3 (BBFZO) nanoparticles were synthesized by a sol-gel technique to develop a filler material with lower leakage current and oxygen vacancies compared to the host BiFeO3. In this work, we report the enhanced dielectric, ferroelectric, energy storage and energy harvesting performance of BBFZO incorporated PVDF composites. 15 wt% BBFZO loaded PVDF (15BBFZO) exhibited improved polarity (F(EA) = 77.42%) compared to neat PVDF (F(EA) = 37.01%). At an applied field of ∼14 kV cm-1 (1 Hz), this film (15BBFZO) exhibited a maximum energy storage density of 151.18 μJ cm-3 (at 1 Hz). Upon repeated human finger tapping, an average open circuit peak to peak a.c. voltage (VOC) ∼ 20 V was obtained from 15BBFZO. A comprehensive study of frequency dependent D-E loops and an extensive study of the effect of electrical poling on the output performance of the developed composite films have been performed. An improvement of the dipolar polarization was established through a frequency dependent D-E loop study of unpoled and poled 15BBFZO and from other experiments. After poling the energy storage density and VOC of 15BBFZO were 154.66 μJ cm-3 (at 1 Hz) and ∼30 V, respectively. After rectification this output electrical signal was able to charge a 10 μF commercial capacitor up to ∼5.5 V. After poling, the energy storage efficiency (η) of 15BBFZO also improved from 52.49% to 67.85% (at 1 Hz). The frequency dependence of the storage efficiency for all the samples has also been extensively investigated here. At 1 kHz, η improved to 93.30% for poled 15BBFZO.

Chitin/MoS2 Nanosheet Dielectric Composite Films with Significantly Enhanced Discharge Energy Density and Efficiency

High-performance dielectric nanomaterials have received increasing attention due to their important applications in the field of energy storage. Among various dielectric materials, polymer nanocomposite is one of the most promising candidates. However, the problems of environmental pollution caused by polymer-based dielectric materials have been extensively studied in recent years, which need to be solved urgently, leading to the search for new biodegradable dielectric materials. Herein, we report composite materials based on biodegradable and renewable chitin and molybdenum disulfide (MoS₂) nanosheets for the first time. The MoS₂ nanosheets were first fabricated by glycerol/urea system and then KOH/urea aqueous solution was used to directly dissolve chitin at low temperature together with the dispersion of the MoS₂ nanosheets in a simple green process. The two-dimensional MoS₂ nanosheets possess high polarization strength, and a large specific surface area can enhance the interfacial polarization with chitin; meanwhile, it can serve as a charge breakdown barrier to hinder the propagation of electrical tree branches. The results also show that the dielectric constant and breakdown strength of the chitin/MoS₂ nanocomposites were increased, while the dielectric loss remained low. When the MoS₂ content was 5 wt %, the charge and discharge efficiencies of the composite film were more than 80%, and the breakdown strength also reached 350 MV m^-1, thus resulting in a high discharge energy density of 4.91 J cm^-3, which was more than twice of the neat chitin (2.17 J cm^-3). Furthermore, the nanocomposite films exhibited good thermal stability. Therefore, these chitin-based nanocomposite films are promising as high-performance biomass-based dielectric capacitors.

Tunable dielectric polarization and breakdown behavior for high energy storage capability in P(VDF-TrFE-CFE)/PVDF polymer blended composite films

Polymer dielectrics with high dielectric performances and superior discharge energy capability are highly desirable for advanced electrostatic capacitor applications. However, the paradoxical relationship between dielectric polarization and electric breakdown behavior generally hinder their further enhancement in energy storage performances. Herein, polymer blended composite films with high energy storage capability were successfully fabricated by blending together poly(vinylidene fluoride) (PVDF) polymer and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer. The P(VDF-TrFE-CFE) terpolymer has a high dielectric constant to provide a large electric displacement under an applied electric field far below its breakdown field, which is anticipated to modulate the dielectric polarization behavior of PVDF polymer when blended in different proportions. Consequently, the polymer blended composite film consisting of 20 wt% (P(VDF-TrFE-CFE)) terpolymer exhibits a high discharge energy density of 13.63 J cm^-3 at an enhanced breakdown strength of 480 MV m^-1. This obtained high discharge energy density is 84% higher than the pure PVDF film and 582% higher than a commercialized biaxially oriented polypropylene (BOPP). Large interfacial polarization and strong interaction of polymer chains between the PVDF polymer and P(VDF-TrFE-CFE) terpolymer may contribute to the tunable dielectric constant and electric breakdown strength, thus promoting the energy storage capability. This work establishes a facile, but effective approach to achieve the high energy storage capability of PVDF polymer-based flexible composite films for capacitive energy storage applications.

Ultrahigh Energy Efficiency and Large Discharge Energy Density in Flexible Dielectric Nanocomposites with Pb0.97La0.02(Zr0.5SnxTi0.5-x)O3 Antiferroelectric Nanofillers

Flexible dielectric capacitors have been widely studied recently on account of their fast charge-discharge speed, high power density, and superior wearable characteristics. Inorganic ferroelectric fillers/polymer matrix composites combining large maximum electric displacement (D_max) of ferroelectric materials with good flexibility and high electric breakdown strength (E_b) of the polymer are regarded as the most promising materials for preparing flexible dielectric capacitors with superior energy storage properties. However, simultaneously achieving large discharge energy density (W_d) and high energy efficiency (η) in these composites remains challenging on account of a large remnant electric displacement (D_r) and low D_max - D_r values of ferroelectric fillers. In contrast, antiferroelectrics (AFEs) exhibit near zero D_r and larger D_max - D_r values and are thus attractive composite fillers to simultaneously achieve large W_d and high η. On the basis of these factors, in this report, we design and prepare Pb_0.97La_0.02(Zr_0.5Sn_xTi_0.5-x)O₃ (PLZST) AFE nanoparticles (NPs)/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposites and investigate the effects of the Sn and AFE NPs contents on the energy storage capacity of the nanocomposites. Through reasonable adjustment of the Sn content and the PLZST AFE fillers content, because of the large D_max - D_r value of 7.75 μC/cm² and small D_r value of 0.26 μC/cm² at the E_b as high as 3162 kV/cm, the Pb_0.97La_0.02(Zr_0.5Sn_0.38Ti_0.12)O₃ AFE NPs/P(VDF-HFP) polymer nanocomposite with 7 wt % fillers exhibits the most superior energy storage properties with an ultrahigh η of 93.4% and a large W_d of 12.5 J/cm³. These values are superior to those of the recently reported dielectric nanocomposites with a single-layer structure containing ferroelectric nanowires, nanofibers, nanobelts, nanotubes, and nanosheets or core-shell structure fillers, which are prepared via a very complicated method. This work not only shows that, in principle, the polarization characteristics of the composites depend mainly on those of the inorganic fillers but also demonstrates a convenient, effective, and scalable way to fabricate dielectric capacitors with superior flexibility and energy storage capacities.

Enhanced Dielectric Performance of P(VDF-HFP) Composites with Satellite-Core-Structured Fe2O3@BaTiO3 Nanofillers

Polymer dielectric materials are extensively used in electronic devices. To enhance the dielectric constant, ceramic fillers with high dielectric constant have been widely introduced into polymer matrices. However, to obtain high permittivity, a large added amount (>50 vol%) is usually needed. With the aim of improving dielectric properties with low filler content, satellite–core-structured Fe₂O₃@BaTiO₃ (Fe₂O₃@BT) nanoparticles were fabricated as fillers for a poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix. The interfacial polarization effect is increased by Fe₂O₃ nanoparticles, and thus, composite permittivity is enhanced. Besides, the satellite–core structure prevents Fe₂O₃ particles from directly contacting each other, so that the dielectric loss remains relatively low. Typically, with 20 vol% Fe₂O₃@BT nanoparticle fillers, the permittivity of the composite is 31.7 (1 kHz), nearly 1.8 and 3.0 times that of 20 vol% BT composites and pure polymers, respectively. Nanocomposites also achieve high breakdown strength (>150 KV/mm) and low loss tangent (~0.05). Moreover, the composites exhibited excellent flexibility and maintained good dielectric properties after bending. These results demonstrate that composite films possess broad application prospects in flexible electronics.

Effects of the Particle Size of BaTiO₃ Fillers on Fabrication and Dielectric Properties of BaTiO₃/Polymer/Al Films for Capacitor Energy-Storage Application

BaTiO₃/polymer/Al (BPA) composite films for energy storage were fabricated by way of a roll coating and thermal curing process. The coating slurry consisted of silicon-containing heat-resistant resin (CYN-01) and BaTiO₃ particles with various particle sizes obtained from commercial BaTiO₃ powders processed at different durations of wet sand grinding in the presence of silane coupling agent (KH550), which not only improves the dielectric performance of the BPA films but also facilitates its production in a large scale. The major influence factors, such as the ratio between BaTiO₃ and resin and the size of BaTiO₃ particles, were investigated and their related mechanisms were discussed. The results show that modifying BaTiO₃ particles (D₉₀ = 0.83 μm) with the silane coupling agent of KH550 enhances the dielectric properties of the BPA films. The typical BPA films obtained exhibit a high dielectric constant of 32, a high break strength of 20.8 V/μm and a low dielectric loss of 0.014. The present work provides a simple and convenient way to prepare high-quality ceramic/polymer composite films for energy-storage application in a large scale.

Improved Energy Storage Performance of Linear Dielectric Polymer Nanodielectrics with Polydopamine coated BN Nanosheets

Polymer-based nanodielectrics have been intensively investigated for their potential application as energy storage capacitors. However, their relatively low energy density (U_e) and discharging efficiency (η) may greatly limit their practical usage. In present work, high insulating two-dimensional boron nitride nanosheets (BNNS), were introduced into a linear dielectric polymer (P(VDF-TrFE-CTFE)-g-PMMA) matrix to enhance the energy storage performance of the composite. Thanks to the surface coating of polydopamine (PDA) on BN nanosheets, the composite filled with 6 wt% coated BNNS (mBNNS) exhibits significantly improved breakdown strength (E_b) of 540 MV/m and an energy density (U_e) of 11 J/cm³, which are increased by 23% and 100%, respectively as compared with the composite filled with the same content of pristine BNNS. Meanwhile, η of both composites is well retained at around 70% even under a high voltage of 400 MV/m, which is superior to most of the reported composites. This work suggests that complexing polymer matrix with linear dielectric properties with surface coated BNNS fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency.