Charge-discharge Efficiency Research Articles

Improving the Energy Storage Performance of All-Polymer Composites By Blending PVDF and P(VDF-CTFE).

Organic film capacitors have incredibly high power density and have an irreplaceable position in pulsed power systems, high-voltage power transmission networks and other fields. At present, the energy storage density and energy storage efficiency of organic film capacitors are relatively low, resulting in excessive equipment volume. The performance of organic film capacitors is determined by polymer materials, so it is crucial to develop a polymer composite with high energy storage density and high charge-discharge efficiency. Poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) is incorporated into the polyvinylidene fluoride (PVDF) matrix by solution blending. The successful preparation of the all-polymer composite material solves the problems of low breakdown electric field strength, low discharge energy density, and low charge-discharge efficiency of high-dielectric ferroelectric materials. The discharge energy density of the PVDF/P(VDF-CTFE) (70/30) film is more than twice that of pure PVDF due to the increase of phases α and γ and the decrease of crystallinity. Under the breakdown electric field (380kV mm-1 ), PVDF/P(VDF-CTFE) (70/30) film also has an ultrahigh energy storage efficiency of 64%. The relationship between the structure and properties of composite materials is investigated in this study, which has important implications for the development of capacitors with high energy storage density.

Radical change in the Spanish grid: Renewable energy generation profile and electric energy excess

The National Integrated Energy and Climate Plan 2021–2030 presented by Spain expected to increase the installed power of renewable energy in 62 GW by 2030. However, the electricity operator system (Red Eléctrica Española (REE)) foresees a different scenario, in which the new approved power generation plants (non-synchronous generation i.e.: wind and photovoltaic), for the peninsular system, will reach 84 GW. Moreover, the total power of the request forms, which have license to access the grid, rise up to 143 GW. This scenario leads to a new era of power generation in which the generation patterns differ from the current ones diverting the consumption profiles or making imperative new ways of energy storage to be able to reach the expected Renewable Energy share or prevent massive curtailments. The analysis presented in this work is based on the modelling and simulation of the wind and solar energy generation for several scenarios. The results of this analysis show a lack of energy balance (an excess of energy between 92 and 168 TWh with overgeneration during more than 3500 h after balancing mechanisms) due to the non-integrated technologies and due to the (over expected) future installed power derived from REE reports. In addition, the energy available for charging will be higher than the hypothetical discharge to the grid. This allows low charge–discharge efficiencies. Two energy storage technologies: thermal storage for thermal plants retrofitting and reversible hydrogen systems are proposed for analysis. These novel energy balancing technologies are economically modelled and assessed for this specific energy scenario and present moderate paybacks. Even with a high investment in storage facilities, and taking into account the exported energy, the in-excess energy will be very high. This will lead to massive curtailments of renewables (between 35% and 40%) or to a paradigm shift on the energy consumption behaviours.

Achieving ultra-high discharge energy density of dielectric polymer nanocomposites by in situ synthesis

Polymer dielectrics are promising dielectric materials for high-energy-density dielectric capacitors owing to their facile processability and high breakdown strength. Currently, the primary method used to prepare nanocomposites involves the combination of polymers and nanoparticles and utilises the high insulation abilities of nanoparticles to limit the migration of carriers to obtain a high breakdown strength and charge–discharge efficiency. However, the dispersion of nanofillers in nanocomposites prepared using traditional methods is unsatisfactory, which not only leads to unsatisfactory energy-storage performance but also limits their applications owing to inconsistent batch-to-batch performance. Herein, nanocomposites with high energy densities are prepared through the in situ synthesis of nanoparticles in polymer solutions. Owing to the uniform dispersion and excellent insulation performance of the nanoparticles, the nanocomposites demonstrated a discharge energy density of 26.5 J/cm3 with a charge–discharge efficiency of 68% at the optimal composition. Additionally, amorphous nanoparticles have a higher energy barrier than crystalline nanoparticles, which can inhibit the carrier transport more effectively to obtain a lower leakage current. Compared with traditional preparation approaches, the as-proposed method for preparing nanocomposites is simple, and the resulting materials exhibit high performance, which is critical for the application of nanocomposites in capacitors.

Cycloolefin copolymer dielectrics for high temperature energy storage

Cycloolefin copolymer (COC) could be a best promising commercial polymer dielectric for metallized film capacitors at elevated temperature according to the molecular structure, but the dielectric energy storage about COC remains a huge challenge due to the lack of processing strategies of its ultrathin films. Herein, we demonstrate that COC dielectric film of around 10 μm can be fabricated by solution casting followed by uniaxial stretching and steadily service at 140 °C. Excitedly, the charge-discharge efficiency (η) of COC film is up to 97.8 % at 600 MV/m at 25 °C, which is superior to the commercially available biaxially oriented polypropylene (BOPP). Remarkably, at 140 °C, COC film exhibits a maximum discharge energy density (Ue) of 2.32 J/cm3 and a η of 85.7 %, far outperforming the heat-resistant polyimide (PI) with a maximum Ue of 1.00 J/cm3 and a η of 24.1 %. Our work provides a novel strategy for the manufacture of ultrathin COC film and could promote the commercialization of high-temperature polymer capacitor films for the energy storage.

Side-Chain-Type High Dielectric-Constant Dipolar Polyimides with Temperature Resistance.

Innovative dielectric materials with high-temperature resistance and outstanding dielectric properties have attracted tremendous attention in advanced electronical fields. Polyimide(PI) is considered a promising candidate for the modern electronic industry due to its excellent dielectric properties and comprehensive properties. However, the limited-adjustable range of dielectric constant and the difficulty to obtain a high dielectric constant restrict the application of PI as high dielectric materials. Herein, a novel diamine monomer (2,2'-bis((methylsulfonyl)methyl)-[1,1'-biphenyl]-4,4'-diamine (BSBPA)) containing a rigid biphenyl structure and high dipolar sulfonyl pendant groups is designed for high dielectric polyimides. The rigid biphenyl and polar sulfonyl pendant groups can reasonably optimize the molecular structure and orientational polarization of polyimides to improve their dielectric properties and thermal properties. Moreover, the effect of different bridge linkages on the dielectric properties is studied by using the different dianhydrides. Thus, the PI-BSBPA films especially the DSDA-BSBPA film (DSDA: 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride)achieve great thermal properties (T5%d of 377°C and Tg of 358°C) and excellent dielectric properties (6.95 at 1kHz) along with high discharged energy density of 5.25Jcm-3 and charge-discharge efficiency of 90%. The collaborative control of main-chain and side-chain engineering is effective to endow the polyimides with high-temperature tolerance and high dielectric performance.

Optimizing high-temperature capacitive energy storage performance by constructing crosslinked structure in self-crosslinkable polyetherimides

Crosslinking is a proven method for effectively improving the high-temperature energy storage performance of polymer dielectrics. In this work, the relationship between crosslinked structure and energy storage performance was demonstrated by crosslinked polyetherimide films with various degree of crosslinking. Specifically, the maximum weight average molecular weight (Mw) of soluble parts and proper gel content favors the formation of an optimal crosslinked structure with an optimal energy density (∼3.6 J/cm3) and charge–discharge efficiency (≥ 95%) at 150 °C. Furthermore, the energy storage performance of the crosslinked films obtained by the longtime treatment under relatively low temperatures is equivalent to that obtained by the short-time treatment under relatively high temperatures. This work provides a reference model for designing high-temperature crosslinked polymer dielectrics.

Interface‐Tailored Relaxor Ferroelectric Nanocomposites with Ultrahigh‐Insulation Shell of Fluorinated Aromatic Polythiourea for High‐Capacitance Energy Storage Applications

AbstractThe strategy of interface engineering plays a prominent role in obtaining desirable dielectric performance of polymer nanocomposites. In this study, ultrahigh‐insulation BaTiO3@fluorinated aromatic polythiourea (BT@ArPFTU) nanoparticles (NPs), which are successfully synthesized via microwave‐initiated polymerization, are served as novel nanofillers to prepare poly(vinylidenefluoride‐trifluoroethylenechlorotrifuoroethylene)‐based (P(VDF‐TrFE‐CTFE)‐based) nanocomposites for capacitor applications. The ArPFTU coating shell forms a strong interface with 30‐nm thickness between BT and the matrix. It not only contributes to the suppression of current density at the interfaces, the regulation of interfacial charge distribution and tolerating high electric‐field strength, but also favors the improvement in dielectric constant and electric polarization due to interfacial polarization, as confirmed by finite element simulations and experimental results. In addition, the direct observation of electric‐polarization enhancement at the interfaces in the P(VDF‐TrFE‐CTFE)/BT@ArPFTU nanocomposites is well probed by piezoelectric force microscopy. Remarkably, with small loading of BT@ArPFTU NPs, relaxor ferroelectric nanocomposites display an unprecedented discharged energy density of 23.1 J cm−3 and the charge–discharge efficiency of 65%, which is much larger than that of other types of BT‐based polymer nanocomposites and commercial biaxially oriented polypropylene of 0.71 J cm−3. This systematic study further paves a new avenue to design high‐performance polymer nanocomposites by interfacial architecture for capacitor application.

High-energy-density ferroelectric polymer nanocomposites utilizing the Coulomb-blockade effect

Ferroelectric polymers have been regarded as promising dielectric materials for high volumetric energy density dielectric capacitors due to their high dielectric constant and facile processability. However, ferroelectric dielectric polymers suffer from high intrinsic loss, resulting in low charge-discharge efficiency and insufficient breakdown strength. Here, a sandwich-structured ferroelectric polymer nanocomposite with high energy density is fabricated by sandwiching an array of ultra-small metal particles grown in-situ between two layers of ferroelectric polymers. Due to the unique Coulomb-blockade effect of the ultra-small metal particles, the nanocomposites with suitable distribution density of metal particles exhibit significantly suppressed leakage current density and superior breakdown strength. Compared with Au and Ag, the Pt particle with the highest work function is more effective in improving the capacitive performance of the polymer. In addition, it is revealed that within the theoretical particle size range where the Coulomb-blockade takes effect, the nanocomposite with larger metal particles exhibits better capacitive performance. The optimal composition with an extremely low fraction (0.07 vol%) of 10-nm-size Pt nanoparticles shows a remarkable discharge energy density of 28.6 J/cm3 and a charge-discharge efficiency of 76%. This method effectively suppresses the energy loss of ferroelectric polymers, and bypasses the dispersion issues in the traditional polymer nanocomposites, providing a new paradigm for fabricating high-energy-density and high-efficiency polymer dielectrics.

Dielectric and energy storage properties of all-organic sandwich-structured films used for high-temperature film capacitors

Dielectric polymers with ultrahigh power density are widely utilized in the fields of modern electronics and power systems. This article proposes the all-organic sandwich-structured films with ferroelectric polymer poly (vinylidene fluoride-hexafluoropropylene) and linear polymer poly (ethylene terephthalate) (PET) as the energy storage dielectrics for film capacitors. The morphological characterizations, thermal, dielectric, and energy storage performances have been investigated to evaluate the comprehensive properties of the sandwich-structured films. Excellent interlaminar interfaces are observed between poly(vinylidene fluoride-hexafluoropropylene) and PET layers. Compared with pure PET films, the sandwich-structured films exhibit improved thermal stability and dielectric constant, but some degradation in loss factor and breakdown strength. With the increase of ambient temperature, the sandwich-structured films still show improved and stable dielectric properties and insulating strength up to 125 °C. The sandwiched all-organic film shows an improved energy density (Ud) as high as 8.2 J/cm3 and concurrently an immense charge-discharge efficiency of 86.4%. This strategy offers a feasible idea to enhance the thermal, dielectric, and energy storage capability of dielectric films with a layered architecture, which facilitates the evolution of flexible film capacitors.

Tunable BaxSr1-xTiO3 nanoparticles induced high energy storage density in layer-structured asymmetric polymer-based nanocomposites

In order to solve the problem of low charging and discharging energy density of dielectric capacitors, the structure design of layered polymer matrix composites is carried out in this paper. Ba0.7Sr0.3TiO3, Ba0.8Sr0.2TiO3 and Ba0.9Sr0.1TiO3 nanoparticles were successfully prepared by the oxalate coprecipitation method. The surface of BaxSr1-xTiO3 was successfully coated with dopamine, which promoted the dispersion of the polymer matrix of the ceramic powder. Monolayer BaxSr1-xTiO3/PVDF composites containing BaxSr1-xTiO3 with different Ba/Sr ratios were successfully prepared by the casting method. Three-layer asymmetric composites with different fillers were successfully prepared by layer-by-layer casting. The phase and microstructure of the as-prepared materials were analyzed by XRD and SEM. The dielectric, electrical conductivity, ferroelectric and energy storage properties of the composites were tested. The effects and laws of the design of the three-layer asymmetric structure on the dielectric properties and energy storage properties of the layered composites are mainly studied. When the structure of the three-layer asymmetric composite is 1-2-3, the breakdown field strength reaches 330 kV/mm, the discharge energy density reaches 8.51 J/cm3, and the charge-discharge efficiency is 67%. This work demonstrates that layered composites with asymmetric properties can facilitate the development of electrical energy storage.

High performances of polyimide/boron nitride nanosheets composites via integrative interfacial decoration strategy

With the rapid development of electrical equipment and integrated circuits, packaging materials with high heat dissipation capability are in great demand. Reducing the interfacial thermal resistance is still a great challenge in polymeric composites. Herein, surface-induced polyamide acid (PAA) polymerization on boron nitride nanosheets (BNNSs) was firstly achieved, and then the BNNS@PAA was introduced into the polymerization system of polyimide (PI). The dependence of microstructures and performances of the composites on imidization degree of BNNS@PAA was systematically investigated. The results show that there is an appropriate imidization temperature (120 °C), at which the composite with only 10 wt% BNNS@PAA exhibits high thermal conductivity (2.11 W/m·K), excellent mechanical properties (with tensile strength of 97.2 MPa and elongation at break of 19.8%), and good dielectric properties (with a discharged energy density of 3.67 J/cm3 and a charge-discharge efficiency of 87.4% at the field of 300 MV/m).

Improved Energy Storage Property of Sandwich-Structured Poly(vinylidene fluoride)-Based Composites by Introducing Na0.5Bi0.5TiO3@TiO2 Whiskers.

In recent years, high-energy-density polymer-based capacitors have received extensive attention because of their potential applications in advanced power systems and electronic equipment. However, their development is severely hampered by the inherent features of polymers such as low polarization and low charge-discharge efficiency (η). In this study, a new strategy for core-shell Na0.5Bi0.5TiO3(NBT)@TiO2(TO) whiskers combined with sandwich-structured poly(vinylidene fluoride) (PVDF)-based dielectric composites is proposed, in which the middle layer is the PVDF-based composites filled with different fractions of NBT@TO whiskers and the outer layers are pristine PVDF. The experimental results show that the loading of NBT@TO whiskers can simultaneously optimize electrical displacement and breakdown strength of the sandwich-structured composite due to the additional interfacial polarization and the contribution of the barrier effect between adjacent layers. Thus, a significantly improved electric displacement of ∼13.99 μC cm-2, a maximum discharge energy density (Ud) of ∼15.42 J cm-3 at a low electric field of 314 MV m-1, and a high charging-discharging efficiency (η ∼ 66.12%) can be obtained from the composite with the middle layer containing 6 wt % NBT@TO whiskers. This research provides a strategy for the preparation of advanced polymer-based composites with a superior discharge energy density in the future.

Enhanced energy storage properties and dielectric stabilities in BNT-based ceramics via multiphase and dielectric peak broadening engineering

Recently, lead-free energy storage ceramics have attracted considerable research interests due to their fast charge/discharge rate, environmental friendliness and high-power density. However, there also exist the problems of low energy density (W) and poor charge-discharge efficiency (η) for most of lead-free ceramics. Herein, novel ceramics of (1-x)(Bi0.5Na0.5)0.94Ba0.06]TiO3-xLa[Zn2/3(Nb0.5Ta0.5)1/3]O3 (BNBT-xLZNT) have been developed and synthesised by an ordinary sintering technique, and their microstructures and electrical properties have been researched systematically. The tetragonal (T) and rhombohedral (R) phases coexist in the BNBT-xLZNT ceramics. After the doping of La[Zn2/3(Nb0.5Ta0.5)1/3]O3 (LZNT), the ferroelectric long-range order is effectively destroyed and the remanent polarization (Pr) of the materials is significantly reduced, leading to the shift of the shoulder dielectric peak at Ts towards room temperature and the broadening of the maximum dielectric peak at Tm. Consequently, the ceramic with x = 0.04 (BNBT-4LZNT) possesses the highest maximum polarization (Pmax) of 31.82 μC/cm2 and the lowest Pr of 2.57 μC/cm2. According to above advantages, the optimum effective energy storage density (Wrec) of 1.66 J/cm3 and η of 73.97% are gained under a relatively low dielectric breakdown strength (DBS) of 139 kV/cm. In addition, the BNBT-4LZNT ceramic exhibits excellent temperature (25–250 °C), frequency (1–100 Hz) and fatigue resistant stabilities (10-104 cycles). Our study indicates that the energy storage properties of BNT-based ceramics can be significantly enhanced via multiphase and dielectric peak broadening engineering.

Experimental investigations on the thermal performance and phase change hysteresis of composite phase change material Na2HPO4·12H2O/SiO2

Integrating hydrated salt phase change material (PCM) into building envelopes is a promising method for achieving building energy saving. However, the hydrated salt suffers from the issues of supercooling, phase separation, leakage and phase change hysteresis. In this work, a novel form-stable composite phase change material (CPCM) with mesoporous silica (SiO2) encapsulating Na2HPO4·12H2O(DHPD) was synthesized by porous matrix composite technology. Thereinto, Na4P2O7·10H2O(TPD) used as the nucleating agent suppressed the supercooling phenomenon, 3 % sucrose can solve the issue of the water molecules loss of DHPD and phase separation.18 % SiO2 was favored for preventing leakage. The modified CPCM exhibited good chemical compatibility, higher charge-discharge efficiency, and good thermal stability via DSC, SEM, XRD, FT-IR and TG tests. According to experimental results, the surface area and pore volume of CPCM decreased, and the weight loss rate was lower than that of pure DHPD. The FT-IR and XRD tests indicated that only physical interaction occurred between the DHPD core and the SiO2 shell. Moreover, it displayed excellent thermal reliability after 500 melting-freezing cycles. Furthermore, the phase change onset temperature, supercooling, and hysteresis degree of CPCM at different melting states during partial melting phase transition were studied. It was found that the hysteresis degree of CPCM decreases with the increase in melting ratio, which may be related to the volume-free energy of PCM.

Optimal Configuration of Fire-Storage Capacity Considering Dynamic Charge-Discharge Efficiency of Hybrid Energy Storage

The combination of thermal power and hybrid energy storage is an effective way to improve the response ability of automatic generation control (AGC) command in thermal power plants. Notably, the configuration of hybrid energy storage capacity is directly related to improvement of the frequency modulation ability of thermal power plants and the coordination of economic benefits. However, the constant efficiency model adopted in capacity configuration will misjudge the actual operating status of each energy storage unit, resulting in unreasonable capacity allocation. In this context, a fire-storage capacity optimization configuration model considering the dynamic charge–discharge efficiency of hybrid energy storage is established. The model presents the functional relationship between charge and discharge power and the efficiency of different types of energy storage. Simulation proves that the proposed strategy can meet the tracking demand of area control error signal in thermal power plants and reduce the planning and operation cost of energy storage.

Concurrent Enhancement of Breakdown Strength and Dielectric Constant in Poly(vinylidene Fluoride) Film with High Energy Storage Density by Ultraviolet Irradiation.

Polyvinylidene fluoride (PVDF) film with high energy storage density has exhibited great potential for applications in modern electronics, particle accelerators, and pulsed lasers. Typically, dielectric/ferroelectric properties of PVDF film have been tailored for energy storage through stretching, annealing, and defect modification. Here, PVDF films were prepared by the solution casting method followed by an ultraviolet (UV) irradiation process, with special emphasis on how such treatment influences their dielectric and energy storage properties. Upon UV irradiation, the dielectric constant and breakdown strength of the PVDF film were enhanced simultaneously. A high energy density of 18.6 J/cm3, along with a charge–discharge efficiency of 81% at 600 MV/m, was achieved in PVDF after exposure to UV for 15 min. This work may provide a simple and yet effective route to enhance energy storage density of PVDF-based polymers.

Polyimide Nanodielectrics Doped with Ultralow Content of MgO Nanoparticles for High-Temperature Energy Storage.

Advanced polymer dielectrics with high energy density at elevated temperatures are highly desired to meet the requirements of modern electronic and electrical systems under harsh conditions. Herein, we report a novel polyimide/magnesium oxide (PI/MgO) nanodielectric that exhibits high energy storage density (Ue) and charge–discharge efficiency (η) along with excellent cycling stability at elevated temperatures. Benefiting from the large bandgap of MgO and the extended interchain spacing of PI, the composite films can simultaneously achieve high dielectric constant and high breakdown strength, leading to enhanced energy storage density. The nanocomposite film doped with 0.1 vol% MgO can achieve a maximum Ue of 2.6 J cm−3 and a η of 89% at 450 MV m−1 and 150 °C, which is three times that of the PI film under the same conditions. In addition, embedding ultralow content of inorganic fillers can avoid aggregation and facilitate its large-scale production. This work may provide a new paradigm for exploring polymer nanocomposites with excellent energy storage performance at high temperatures and under a high electric field.

Dielectric film with high energy density based on polypropylene/maleic anhydride-grafted polypropylene/boron nitride nanosheet ternary system

With the development of advanced power system, high energy storage polymer film capacitors have attracted more and more attention. Polypropylene (PP) membrane is the most commonly used polymer based membrane, accounting for 70% of the total market share of products. Due to its low dielectric loss, it has a high charge-discharge efficiency (η). However, its inherently low dielectric constant (2.2 at 1 kHz) seriously hinders the increase of energy storage density (1–2 J/cm3). In this study, a ternary PP nanocomposite are prepared by melting blending and die pressing crosslinking, which greatly improved the capacitive properties of PP films. The discharge energy density (Ue) of PP nanocomposite films increased from 1.63 J/cm3 to 4.11 J/cm3 by adding a small amount (1 wt%) of BNNSs into PP matrix. Ue increased significantly (152.1%). By utilizing the special layered structure provided by BNNSs, the energy storage capacity of PP/ PP-g-MAH /BNNSs is significantly improved.

Improving the Rotational Freedom of Polyetherimide: Enhancement of the Dielectric Properties of a Commodity High-Temperature Polymer Using a Structural Defect

Dielectric polymers that can withstand harsh conditions of simultaneous high electric field and elevated temperature are widely used in electrical and electronic systems. However, traditionally, the thermal stability of polymers is engineered based on highly conjugated aromatic molecular structures, giving rise to soring charge transport and thus poor charge–discharge efficiency under concurrent high electric field and elevated temperature. Here, we locally improved the rotational flexibility of the phenylenediamine linkage structure in polyetherimide (PEI) to decouple the conjugation of the organic molecule. p-Phenylenediamine (5 mol %) as a low-energy rotation repeat unit within PEI significantly optimized its dielectric properties, exhibiting substantially suppressed electrical conduction (more than 1 order of magnitude lower) and polarization loss (<1%). The new PEI has a largely improved charge–discharge efficiency of 91% at 400 MV/m 200 °C, outperforming the best-reported polymer-based dielectrics without any modification of the cost of goods. The high-throughput facile processing of the new PEI provides a potential candidate for energy storage applications under elevated temperatures. This work unveils a scalable approach to exploring polymer dielectrics by introducing a small amount of local structural modifications.

Kalman-Filter-Based Learning of Characteristic Profiles of Lithium-Ion Batteries.

The main analyzed aspect of lithium-ion battery (LIB) degradation so far has been capacity fading. On the other hand, interest in efficiency degradation has also increased in recent years. Battery aggregation, which is expected to absorb the surplus of variable renewable energies such as photovoltaic energy, is affected by efficiency degradation in terms of the decreases in the economic gain and renewable energy use. Reusable LIBs could be used as aggregation components in the future; naturally, the variety of charge–discharge efficiencies might be more complex. To improve the operation efficiency of aggregation, including that obtained using reusable LIBs, we propose the Kalman-filter-based quasi-unsupervised learning of the characteristic profiles of LIBs. This method shows good accuracy in the estimation of charge–discharge energy. It should be emphasized that there are no reports of charge–discharge energy estimation using the Kalman filter. In addition, this study shows that the incorrect open-circuit voltage function for the state of charge, which is assumed in the case of a reused battery, could be applied as the reference for the Kalman filter for LIB state estimation. In summary, it is expected that this diagnosis method could contribute to the economic and renewable energy usage improvement of battery aggregation.