Discharge Energy Research Articles

Significantly enhanced energy storage performance in multi-layer polyimide films with nano dielectric layer

Polymer-based composites with multilayer structure were emerging as an effective way to solve the contradiction between high breakdown strength and large permittivity in past decades. However, the incorporating layers in conventional multilayer composite films are usually inorganic thick films, which is not beneficial for the retention of excellent mechanical properties of the polymer matrix. In this work, the multilayer films consisting of micrometer polyimide (PI) and nanoscale TiO2 layer were prepared by spin-coating and atomic layer deposition (ALD), respectively. Carrier migration in PI-TiO2 multilayer films was hindered effectively by the interfacial barrier, as indicated by the results of the Pulsed Electro-Acoustic (PEA) tests. Compared to pure PI, both the permittivity, dielectric loss and breakdown strength were optimized in the PI-TiO2 multilayer films. A satisfactory discharge energy density of 6.77 J cm−3 (efficiency >90 %) was obtained in the multilayer films, which is about 5 times higher than that of pure PI. The strategy of constructing heterogeneous interfaces by incorporated nanoscale TiO2 layers is promising for designing high performance capacitors in practical application.

Evaluating the bio-functionalities of Ti-6Al-7Nb alloy after surface modification using electrical discharge machining

The present work evaluates the influence of surface modification on the bio-functionalities of Ti-6Al-7Nb alloy in terms of apatite formation, metal ion release rate and anti-bacterial activities. The surface modification in the form of change in surface integrity, and increases in the exposed surface area, has been achieved using wire-electrical discharge machining (WEDM) and electrical discharge μ-drilling(EDD). Due to high discharge energies, molten material will deposit on the parent material (recast layer), which increases the surface roughness (parent surface 0.5 μm to 2.34 μm) and hardness (patent material 304VH to 385VH) after subsequent re-solidification and quenching. Surface roughness and hardness near the micro-drilled hole are observed to increase. After surface modification, the apatite formation is increased on Ti-6Al-7Nb alloy with increasing immersion time and the ion released rate was found lowest on the WEDMed surface as compared to micro drilled and polished surface. Field-emission electron scanning microscopy (FESEM) and energy dispersive x-ray spectroscopy (EDAX) observations confirmed the presence of phosphate and calcium ions on the WEDMed surface and nearby the micro-drilled surface. The variation in colour of the simulated body fluid (SBF) after the immersion of WEDMed, EDD, and polished samples indicates the variable effecton pH levels of the SBF solution for three types of samples.The anti-bacterial bioactivity of Ti-6Al-7Nb was found to be better on the WEDMed surface as compared to polished surfaces, which is due to the formation of a rutile-TiO2 layer on WEDMed surface.

Influences of single-pulse energy distribution on WEDM cutting efficiency

ABSTRACT In wire electrical discharge machining (WEDM), cutting efficiency is a significant process index whose improvement has always been the research focus. Among the many factors affecting cutting efficiency, discharge energy is the most important factor. Different energy distribution form pulses were obtained by changing the peak currents at single-pulse different discharge stages. Through single-pulse discharge experiments, pulse energy distribution how to impact discharge channel motion characteristics was studied. When the energy distribution is changed through gradually increasing the peak current, an outward-pointing pressure difference will be formed inside the channel, which provides a driving force for the channel to move faster, accelerating the material erosion rate and increasing the discharge crater surface size. The cutting results reveal consistent variations in the cutting efficiency and surface size of individual discharge crater with the pulse energy distribution form. Through changing single-pulse energy distribution, the cutting efficiency can be improved by about 21%.

Microstructure evolution and mechanical behavior of foamed cement-based tail backfills under varying fiber types and concentrations.

Industrial solid waste (mine tailings) management has emerged as the key universal ecological challenge as a result of the unceasing creation of rising waste by-products. Employing tailings makes mine fill production economical and assists resolve disposal problems. Foamed cement-based tailings backfill (FCTB) is a mine fill consisting of tailing, cement, water, and foaming agents. It provides certain advantages such as lightweight, good fluidity, and thermal insulation yet is relatively weak in strength. Additionally, FCTB's strength properties can be intensely improved by adding fibers. A total of three diverse fibers: polypropylene (PP), glass (G), and basalt (B) as well as dodecyltrimethylammonium bromide (DTAB) as a foaming agent were used to prepare fiber-reinforced foamed cementitious tailings backfill (FR-FCTB). The mechanical properties, energy evolution, ductility, and microstructure of FR-FCTB were elaborately investigated by uniaxial compression tests (UCS) and SEM. Laboratory findings demonstrate the reinforcing effect of three fibers on FCTB specimens: glass > polypropylene > basalt. FR-FCTB showed the best strength features as a fiber content of 0.3% was adopted in FCTB. At this time, the UCS performance of glass fiber-reinforced FCTBs was 0.85MPa increased by 18.1%. The addition of fibers can increase the fill's energy storage limit, slow down the discharge of elastic strain energy within the backfill, and enhance the fill's ductility and toughness. The ductility factor evaluates the degree of deterioration of filling in terms of post-peak drop, with all FR-FCTB values being greater than CTB. FR-FCTB's chief hydration product is the C-S-H gel. Fiber's bridging effect significantly rallies crack extension and thus fill's strength features. Lastly, the study's main results are instructive for the industrial application of FR-FCTB used in metallic mines.

Underwater surface discharge characteristics and multi-physical effects with conductive coating load under fast electric pulse

Abstract Underwater pulsed discharges, where intense reactions between ionized gas and condensed-state water exist, can be a joint problem of both physics and chemistry. The study tries to build a comprehensive visualization of nanosecond-risetime discharge initiated by a conductive coating and its successive multi-physical effects. The scenario is established via a pair of thin-plate electrodes positioned on both sides of the coating, and diagnosed using high-speed backlight photography synchronized with electrical and optical measurements. For the sprayed Cu/Ag composite coating, the current density can achieve 20 A/mm2 which is high enough to induce the surface “electrical explosion” and breakup the conductive matrix within 500 ns. By increasing the discharge energy from 0.5 to 10 J, the explosion of coating can exhibit different discharge types as exploding wires. Adopting a thicker carbon foil or cermet sheet can reduce the current density and energy deposition rate, which converts the global explosion to partial ones, significantly increasing the lifetime. With the aid of the conductive coating, the breakdown delay diminishes, and hot plasma spots form in 100 ns due to non-uniform Joule heating of the pulsed current, which gradually evolve to a plasma bubble cluster above the lower-conductive coating (bypassing branch). Once the high-conductive plasma channel bridges two electrodes, it will be intensively heated (MW-level energy deposition rate) and rapidly expand, accompanied by underwater shock wave (102 kPa @30 cm) and bubble/cavity generation (20 mm maximum). Finally, microscopic characterization has been made, and the erosion morphology suggests typical arc erosion features (pits, cracks, etc.) and nanoparticles condensation from evaporated materials.

Experimental study of ECDM using a porous electrode containing internal micropores

ABSTRACT In electrochemical discharge machining (ECDM), continuous renewal of electrolyte between the tool electrode and the workpiece guarantees stable discharge machining. Proposed in this paper is Porous-electrode ECDM (p-ECDM) using a tool electrode made of porous material containing micrometer pores. The rough surface of the porous electrode promotes electrolyte regeneration between the electrodes to produce a stable and relatively thin gas film. At the same time, the internal connected micropores are used to provide controlled gas flow to the processing area, reduce the energy consumption of electrolytic bubbles, and improve the discharge energy to achieve efficient ECDM processing. Experimental results indicate that compared with a solid electrode, the porous electrode has faster electrolyte renewal, smaller bubble volume, more-stable voltage characteristics, 22.55% less overcut, a 4.7% smaller heat-affected zone, and better deep hole processing ability. Experimental results for p-ECDM assisted by controlled airflow demonstrate a 54.23% increase in the material removal rate.

HBN/PVDF‐HFP and BNNS/PVDF‐HFP nanocomposites as flexible and lightweight dielectric capacitors: High energy storage performance via electrically insulating nanoparticles

AbstractAs the energy demand continuously increases, polymer‐based materials have attracted much attention for energy storage systems as dielectric capacitors due to their higher power density and charge–discharge rate than lithium‐ion batteries and supercapacitors. However, it is necessary to increase the energy density of dielectric capacitors. In this context, poly(vinylidene fluoride‐co‐hexafluoropropylene), PVDF‐HFP, matrix nanocomposites are produced by solution casting method reinforced with hexagonal boron nitride (hBN) nanoparticles and silane‐modified boron nitride nanosheets ‐BNNSs‐ (BNNS‐VTS) up to 10 wt.% filler content. The effects of filler content and surface modification of hBN/BNNSs on PVDF‐HFP matrix nanocomposites' microstructure, phase evolution, crystalization behavior, dielectric properties, and energy storage performance are discussed. 4% hBN/PVDF‐HFP nanocomposite demonstrates 641 MV·m−1 of breakdown strength and 23.2 J·cm−3 of discharged energy density due to hexagonal boron nitride's excellent electrical insulating behavior. The achieved values are 3.0 and 10.5 times superior to the values of the neat thin film, respectively, and they are noteworthy among hBN‐ or BNNS‐reinforced PVDF‐based nanocomposites, even in multi‐layered structures. Furthermore, 4% hBN/PVDF‐HFP presents a giant charge–discharge energy efficiency (92%). It is thus demonstrated that hBN/PVDF‐HFP nanocomposites hold a great potential to be used in energy storage applications as flexible and lightweight dielectric capacitors.Highlights PVDF‐HFP matrix nanocomposites for electrical energy storage as flexible dielectric capacitors hBN NPs and silane‐modified BNNSs are reinforced into the matrix by 0–10 wt.%. The effects of filler content and surface modification of hBN/BNNSs are discussed. 4% hBN loading results in 23.2 J·cm−3 energy density and 92% efficiency at 641 MV·m−1 breakdown strength. Those metrics are relatively high in hBN‐ or BNNS‐reinforced PVDF‐based nanocomposites.

A novel multi-spot structure for joining aluminum and steel dissimilar thin-walled tubes by magnetic pulse crimping

Lightweight manufacture for dissimilar thin-walled tube structures without additional liner support has always been a challenge. A novel magnetic pulse multi-spot joining structure was proposed for the non-weight gain mechanical connection of 6061 aluminum to SPCC (Steel Plate Cold-rolled Common) steel thin-walled tubes. Mechanical properties, microscopic features, and joining mechanism of the magnetic pulse crimping (MPC) joints were explored based on simulation and experiments. Under the geometric conditions of flyer tube with an outer diameter of 30 mm and a thickness of 1 mm, the optimal preformed groove depth and discharge energy for the MPC joints were 2 mm and 16 kJ, respectively. The corresponding maximum tensile and torsional strength were 10.6 kN and 131.2 N m, respectively. The corresponding relative thinning rate of aluminum outer tube was 13 %. The failure forms of the MPC joints were all pull out and torsion out failures. During the high-speed joining of aluminum tube to steel tube, stress concentration phenomena occurred successively at the circumferential bottom fillet, axial bottom fillet, and axial upper edge of the groove. This was due to a certain height difference between the circumferential and axial directions of the groove. It was related to induction distance, discharge energy, skin effect, proximity effect, and tip effect in the coupled field. The yielding and instability of the groove in the steel inner tube would lead to a decrease in the fitting area of the aluminum outer tube filled groove and the relative thinning rate of the aluminum outer tube. This caused a decrease in the mechanical interlocking force at the groove, which was detrimental to the mechanical properties of the MPC joints. This article provides a new approach and data support for the lightweight manufacture of dissimilar thin-walled tube structures.

An Analytical Model for Predicting the Rate Performance of Battery Cells Under Mixed Kinetic Control

The prediction of battery performance conventionally relies on resource-intensive numerical simulations based on the porous electrode theory. For computational speedup, simplified physics-based models have proven attractive as they still capture the underlying reaction mechanisms to a certain degree. In this class of models, physical complexity is usually reduced by assuming a single rate-limiting reaction. For example, the single particle model describes battery cells limited only by the solid diffusion pathway [1]. On the flipside, our previous analytical model exploited inefficiency of electrolyte transport, particularly in thick electrodes [2]. With advancement in both electrode and electrolyte technologies, however, it becomes challenging for these models to handle more realistic batteries.In this work, we propose an improved physics-based analytical model that enables mixed control of both kinetic processes, reflecting both salt depletion and particle size effect. An extension to our uniform reaction (UR) model, the new model uses salt distribution in electrolyte to probe the accessible lithium in the electrode level. The added solid diffusion module calculates the equilibrium potential at particle surface, lithium concentration at particle surface (Cs), and in turn the particle-level depth of discharge. We refer to the model as the URCs model, recognizing its two components. The model features higher tunability as it now accepts function-valued electrode and electrolyte properties. It also allows for prediction of discharge voltage curves and energy output of the cell.The model is compared with numerical simulation over a wide range of cell parameters. It shows good agreement with simulated results in rate performance test, specific energy output test, and discharge voltage curves. Better alignment is observed for the NMC/Li half cell than the NMC/Gr full cell, likely due to mixed reaction type in the graphite anode. Figure 1 shows the comparison of voltage curves across various C rates for a half cell with 70um NMC electrode and particles of 4um radius. Additionally, the cells are optimized for their specific capacity against electrode thickness and porosity. The optimal parameters predicted by the model lie closely to the global optimum from numerical simulation. Figure 2 shows the optimization results for a full cell with particles of 4um radius, overlaid on contour lines generated from the URCs model.The model offers a speed up of over 500 times compared with state-of-art P2D solvers [3]. Furthermore, its compatibility with gradient-based optimization algorithms opens possibilities for more efficient global optimization schemes, in which the number of function calls can be reduced. The high efficiency and the analytical nature of the URCs model render it a powerful tool for both on-board applications and battery cell design.[1] Doyle, M. and Newman, J., 1997. Analysis of capacity–rate data for lithium batteries using simplified models of the discharge process. Journal of Applied Electrochemistry, 27, pp.846-856.[2] Wang, F. and Tang, M., 2020. A quantitative analytical model for predicting and optimizing the rate performance of battery cells. Cell Reports Physical Science, 1(9).[3] Sulzer, V., Marquis, S.G., Timms, R., Robinson, M. and Chapman, S.J., 2021. Python battery mathematical modelling (PyBaMM). Journal of Open Research Software, 9(1). Figure 1

Significantly enhanced high-temperature energy storage performance for polymer composite films with gradient distribution of organic fillers

Film capacitors as one of the most important electronic devices are heading in large capacity, heightened integration and excellent extreme-condition tolerance, which faces the challenges in maintaining outstanding performance under harsh conditions of high temperature and large electric field. Nonetheless, polymer capacitive films, which are renowned for their exceptional thermal stability, experience an escalation in conduction losses at elevated temperatures, resulting in degradation of energy storage performance. This study presents the gradient distribution of organic fillers content in all-organic polymer capacitive films utilizing electrospinning technique, the significantly improved high-temperature energy storage performance has been achieved. Glucose (GLC), a weak polar molecule rich in hydroxyl groups, is blended with the most promising polyetherimide (PEI). Experimental and theoretical calculations confirm that the formed hydrogen bond between GLC and PEI acts as a trapping site for capturing carriers and suppressing conduction losses. Furthermore, the spatial distribution of organic fillers was designed on the basis of direct mixing. The results demonstrate that the gradient composite film introduces interlayer interfacial polarization, while the dielectric mismatch between adjacent layers increases the height of potential barriers for the charge carriers across the interfaces, thereby achieving a synergistic enhancement of dielectric response and insulation strength. The maximum discharge energy density of 6.52 J/cm3 with an efficiency of 85.6 % has been achieved at 150℃ for the modified capacitive films. This work establishes a decoupling relationship between permittivity and electric breakdown strength, offering insights for the advancement of polymer films with outstanding energy storage capabilities in extreme environments.

Dissolved gas analysis comparison of electrically stressed methyl ester and mineral oil

Methyl ester is considered one of the alternative substitutes to mineral oil as an insulating liquid. This study investigates the dissolved gas analysis (DGA) of the methyl ester derived from palm oil, under low energy discharge faults. The aims are to understand the gas composition and evaluate the applicability of the well-established fault interpretation methods for mineral oil to the methyl ester. Experimental procedures were conducted based on the International Electrotechnical Commission (IEC) standards. It involved simulating electrical breakdowns in laboratory conditions as per IEC-156 standard and analyzing gas samples using gas chromatography based on IEC-567. Results show that methyl ester oils produce similar types of gases as mineral oils but at higher concentrations. The interpretation of DGA results using fault identification methods such as Duval Triangle, Duval Pentagon, and IEC ratio indicates an overestimation of fault severity in methyl ester oils, and categorizing the faults as high energy discharge. However, the key gas method correctly identifies the discharge in both methyl ester and mineral oils. These findings suggest the need for adjustments in existing DGA methods to account for the higher gas concentrations in methyl ester oils, for effective condition monitoring and maintenance of transformers if it was filled with methyl ester oil.

SOC and SOH state estimation of lithium battery based on ffrls and kalman filter

Abstract In the energy storage System, the Battery Management System (BMS) is responsible for the charge and discharge control and energy balance control of the lithium battery, and the accuracy of lithium battery state estimation is directly affected by the control effect of BMS. In order to ensure the normal operation of lithium batteries, this paper selects the State of Charge (SOC) and State of Health (SOH) of lithium batteries as the research object and accurately estimates the SOC and SOH of lithium batteries as the research goal. The equivalent circuit model based on lithium battery is established, and the identification model parameters are based on the recursive least squares method with forgetting factor. Based on the Thevenin equivalent circuit model, the Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) are used to estimate the SOC of the battery, respectively. FFRLS and Double Extended Kalman Filter (DEKF) are used to estimate the ohm internal resistance in the equivalent model based on lithium battery, and then the SOH is estimated.

Nutritional gap after transfer from the intensive care unit to a general ward – A retrospective quality assurance study

BackgroundAdequate nutrition is important for recovery after critical illness. Even so, our knowledge of patients' nutritional intake after intensive care unit (ICU) discharge is scarce. ObjectivesWe aimed to explore nutritional planning and achieved nutritional intake in ICU patients who transfer from the ICU to general wards. MethodsA retrospective quality assurance study. Inclusion criteria: adult ICU patients transferring to a general ward at Copenhagen University Hospital-Herlev from May to August 2021. Primary outcomes were as follows: having a nutritional plan on the day of ICU transfer. A nutritional plan was defined as follows: (i) individual assessment of energy and protein requirement; (ii) intake, documented as achieved percentage of energy and protein requirements; (iii) prescribed type of nutrition. If using enteral or parenteral nutrition; (iv) the prescribed doses; and (v) the prescribed product. Secondary outcomes were as follows: achieved percentage of energy and protein requirements from day -1 before ICU transfer until day +1 and day +3 after ICU transfer. ResultsWe included 57 patients; the mean age was 64 years (±11.1); 43 (75%) patients were male; the median ICU stay was 6 days (interquartile range: 3–11). One (2%) patient had a full nutritional plan according to listed criteria. Patients' median percentage of requirements met declined significantly from the day before to the day after ICU discharge (energy: from 94% to 30.5%; p = 0.0051; protein: from 73% to 27.5%; p = 0.0117). The decline in percentage of requirements met remained unchanged from day 1 to 3 after ICU transfer. ConclusionsIn conclusion, few patients had a nutritional plan when transferring from the ICU to a general ward. After ICU discharge, percentage of energy and protein requirements met declined significantly and remained insufficient during the first 3 days at the general ward.

Optimal regulation strategy of energy storage combined with new energy stations participating in power market

Abstract Energy storage systems can efficiently address the challenges of inadequate power grid regulation capabilities and the escalating complexity of maintaining frequency stability due to a significant integration of renewable energy sources. Under the background of power marketization reform, it is highly important to establish a perfect power market mechanism and incorporate energy storage into it to stimulate energy storage advancements. Consequently, this paper proposes an optimization model for energy storage in conjunction with new energy stations participating in the power market, following the introduction of new energy storage technologies. It effectively verifies the optimization energy storage charge and discharge duration with examples. It achieves the realignment of output curves for coordinating the operation of new energy stations and energy storage facilities, enabling peak shaving and load shifting to minimize the peak-to-valley differential in the system load. It makes the overall output more ‘stable’ and improves the efficiency of the comprehensive operation of wind, solar, and energy storage. In the future, the engagement of energy storage will be essential in the market, and it is crucial to propose practical suggestions to enhance its participation.

Significantly improved energy storage performance of Na0.5Bi0.5TiO3–BaTiO3 ferroelectric ceramics with a wide temperature range via high-entropy doping

The emergence of high-entropy perovskite materials provides a new research idea to solve the problem of high remnant polarization and low recoverable energy storage density (Wrec) of relaxor ferroelectrics. In this study, barium-based high-entropy perovskite oxides Ba(Zr0.2Sn0.2Hf0.2Nb0.2Ti0.2)O3 (BZSHNT) were introduced into the 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-6BT) ceramic by the conventional solid state sintering method. The 0.2BZSHNT doped BNT-6BT ceramic demonstrates significantly improved Wrec of 3.57 J/cm3 and a high efficiency of 81.6 % compared to those of the BNT-6BT ceramic, which is only 0.5 J/cm3 and 60 % respectively. The doped BZSHNT refines the hysteresis loops and drastically reduces the remnant polarization, which lead to the increase of the polarization difference. The 0.8(BNT-6BT)-0.2BZSHNT ceramics show high discharge energy density, good temperature stability (25–200 °C), excellent frequency stability (10–300 Hz) and superior discharge rate (t0.9 = 83 ns) because of its increased TiO6 lattice distortion, atomic disorder, relaxation degree and band gap, as well as the disruption of the long-range ordered ferroelectric domains. Our findings make BNT-6BT doped BZSHNT based ceramics one of the most promising lead-free dielectric energy storage candidates.

Surface characteristics and machining rate of SS 316L coating developed using hydroxyapatite-mixed EDM process

Hydroxyapatite (HA) or bioceramic-based coatings on stainless steel (SS) 316L significantly enhance the biofunctionality of the base material's surface. However, HA's low thermal conductivity and brittleness limit its effectiveness as a coating material. This study investigates HA coating on SS 316L using electric discharge machining (EDM) with varying discharge energies and powder concentrations. Surface morphology, elemental composition, and phase analysis of untreated and coated samples were characterised using field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD). The results demonstrate that the HA-assisted EDM process creates a coating comprising biocompatible oxides, phosphates, carbides, and intermetallic compounds. The coating exhibits a thin resolidified layer of 10.74 μm, characterised by redeposited spherical debris, shallow cavities, and a surface texture of 2.688 μm. The layer's hydrophilic nature is confirmed by a minimum contact angle of 47.68°. Taguchi analysis indicates that the machining rate is optimised at an HA powder concentration of 16 g/l, with peak current and HA powder concentration being the most influential parameters affecting resolidified layer thickness, surface texture, and wetting angle. The research intends to motivate SS 316L medical device manufacturers to implement the HA-assisted EDM process for bioimplant's dual machining and coating.

Enhancing machining efficiency in hybrid metal matrix composites through EDM parameter optimization via grey relational analysis

In summary, this study utilized stir casting to develop three distinct aluminium hybrid composites incorporating boron carbide and alumina. These composites were identified as Al7075 + 12%B4C + 6%Al2O3, Al7075 + 6%B4C + 6%Al2O3, and Al7075 + 6%B4C + 12%Al2O3. The novelty of this research lies in the unique combination of materials and their proportions, offering enhanced properties yet unexplored in this specific configuration. The research focused on machining these composite materials using EDM and employed a Taguchi L27 orthogonal array design to plan the machining tests. Key process parameters considered were gap voltage (V), duty cycle (%), current (A), and different percentages of reinforcement content. This aspect adds a significant novel dimension to the study, as the impact of EDM machining parameters on hybrid composites with this particular composition has not been extensively explored previously. The study applied Grey Relational Analysis to evaluate the impact of EDM machining process parameters on critical output responses, specifically material removal rate (MRR) and tool wear rate (TWR). SEM images revealed redeposited molten material, craters, and surface cracks, emphasizing the importance of controlling discharge energy and current levels for desired surface quality. An optimal configuration was identified peak current 2 A, pulse duration 100 μs, duty factor 20%, Composition 2 for improved surface attributes. These qualitative and quantitative insights inform process optimization strategies for EDM machining of aluminium hybrid composites.

Preparation and characterization of nano‐filled polypropylene dielectric films

AbstractModified copper calcium titanate (MCCTO) or functional activated carbon (FANC) particles were added to functional polypropylene (FPP) or heat‐treated polypropylene (HTFPP) matrix to improve the performance of FPP as dielectric films. By testing and characterizing the prepared FPPwxMCCTOy, FPPwxFANCz, FPPwxMCCTOyFANCz and HTFPPwxMCCTOy, HTFPPwxFANCy and HTFPPwxMCCTOyFANCz films, It is found that the dielectric constant and discharge energy density of each FPPwxMCCTOy, FPPwxFANCz, HTFPPwxFANCz and HTFPPwxFANCz films reach the maximum when the MCCTO and FANC loads are close to 8 and 6 wt% respectively. FPPwxMCCTO8FANCz and HTFPPwxMCCTO8FANCz series films also obtain the maximum dielectric constant and discharge energy density at FANC load approaching 6 wt%. The discharge energy density of HTFPPw86MCCTO8FANC6 film prepared properly is 3.2 J/cm3, which is more than 3 times higher than that of FPP. When MCCTO and FANC loads are ≦8 and 6 wt% respectively, with the increase of additive content, More dense distribution of MCCTO and FANC was observed in FPPwxMCCTOy(or HTFPPwxMCCTOy), FPPwxFANCz(or HTFPPwxFANCz) and FPPwxMCCTO8FANCz(or HTFPPwxMCCTO8FANCz) series film sections. In this paper, we propose possible explanations for the apparent improvement in dielectric constant, discharge energy density and heat resistance of capacitive films after appropriate heat treatment or addition of appropriate MCCTO and/or FANC loads.

High energy storage performance in BTO-based ferroelectric films

Dielectric capacitors play an increasingly important role in modern electronic power systems due to their ultrahigh charging and discharging speeds and power density. Much research has focused on enhancing dielectric breakdown strength to achieve better energy storage performance; however, this increases the potential for heat generation and unexpected insulation failures, thereby affecting the stability and lifespan of devices. This study introduces a small amount of Na+ dopants at the A-site of BaTiO3, inducing lattice distortions and enhancing local polarization to increase energy storage density rather than through enhancing breakdown strength. The introduction of Na+ enhances the ferroelectric properties, with polar nano-regions (PNRs) gradually evolving into long-range ordered large domains. In the Ba0.985Na0.015TiO3 films, the coexistence and coupling of abundant PNRs with a few long-range ordered ferroelectric domains result in high saturation polarization and low residual polarization. At a moderate electric field of 2.3 MV cm−1, an ultrahigh energy density of 44.3 J cm−3 and a high energy storage efficiency of 78.6 % were obtained. Additionally, the film exhibits excellent frequency stability (100 Hz-20 kHz), temperature stability (30–180 °C), fatigue resistance (107 cycles), and high pulsed discharge energy density, along with great thermal stability. This work provides new insights into achieving exceptional energy storage performance in single-phase films.

A wireless-feeding capacitive electrode mechanism for achieving massive nanosecond parallel-discharge EDM for large-size wafer flattening

The single-crystal silicon carbide (SiC) wafer diameter is increasing beyond 8 in posing significant challenges to conventional mechanical wafer-processing methods. This study presents an innovative capacitive electrode method for electrical discharge flattening (EDF) of as-sliced large 4H-SiC wafers. The capacitive electrode can be divided into near-infinite units, which significantly reduces the working gap capacitance and enables the generation of a mass of parallel discharges with a nanosecond pulse duration (< 200 ns). This approach offers significant advantages in achieving high efficiency and surface finish simultaneously, regardless of the increase in wafer size. This novel electrode design allows wireless electricity feeding via electrostatic induction, which significantly facilitates the integration of parallel electrode units. Furthermore, a sinusoidal voltage is demonstrated for the first time to identify and promote a parallel discharge state. A model was devised to quantitatively describe the overall process. Using this model, the relationship between the gap voltage, discharge energy, and capacitive electrode properties was predicted, revealing a parallel discharge mechanism. The capacitive electrode mechanism was validated via EDF experiments on a 4H-SiC wafer. Notably, >33 parallel discharges within 6 μs were achieved in a single pulse, resulting in a minimum discharge energy of 0.312 μJ (peak current: 0.18 A, duration: 160 ns) and a surface roughness of Ra 42 nm. Moreover, a machining speed of 0.5 μm/min was achieved on a 4 in wafer, representing an improvement of an order of magnitude compared to conventional non-parallel discharge methods.