Uneven Electric Field Distribution Research Articles

Stretchable Zn‐Ion Hybrid Capacitor with Hydrogel Encapsulated 3D Interdigital Structure

AbstractTo enhance the areal energy density of current flexible energy storage devices, hybrid capacitors combining the advantages of supercapacitors and batteries are proposed and further enhanced by incorporating the 3D interdigital structure design. However, uneven electric field distribution and hindered ion diffusion kinetics due to the non‐electroactive components in these devices limit the enhancement of areal electrochemical performances when expanding the electrodes longitudinally. Herein, hydrogels with high ionic conductivity and high mechanical stability are designed to accommodate Zn2+‐containing electrolytes and integrated with Ti3C2Tx‐MXene electrodes to assemble flexible Zn‐ion hybrid capacitors (ZIHCs). Fully encapsulated by ionic conductive hydrogels, 3D interdigital electrodes enable omnidirectional ion transport and unimpeded ionic accessibility, facilitating adequate electrode reactions, rapid energy storage, and uniform energy distribution. Hence, the all‐hydrogel‐encapsulated ZIHC achieved a 50‐fold increase in capacitance with a quadrupled electrode thickness, exhibiting a large areal capacitance of 1432 mF cm−2 and an energy density of 389.7 µWh cm−2 without sacrificing power density and rate performance. Finite element simulations further illustrate the uniform distribution of potential, electric field intensity, and energy density in this structure. In addition, the device shows great stability under deformation, excellent adhesion, and underwater workability, demonstrating great promise for next‐generation wearable energy storage devices.

Preparation of anode by MOF pyrolysis enabled long-life rechargeable zinc nickel batteries

Water-induced parasitic reaction and zinc dendrite growth caused by uneven electric field distribution on the surface of the zinc anode are the most controversial problems in the practical application of zinc-nickel rechargeable batteries in large-scale energy storage. Herein, Bi2O3/In2O3 doped ZnO@C synthesized by MOF pyrolysis with good cycle stability. The ability to inhibit hydrogen evolution and achieve uniform deposition of zinc is characterized by CV, Tafel, and scanning electron microscopy (SEM). Benefiting from the high hydrogen evolution overpotential and high electrical conductivity, Bi2O3 doped ZnO@C (BCZ) and In2O3 doped ZnO@C (ICZ) electrodes deliver high capacity of 640 mA h g−1 and 580 mA h g−1 at 10 C after 1200 and 3400 cycles, respectively, and reveals long-term cyclic stability with capacity retention over 90%. This work provides new ideas for the anode synthesis of aqueous rechargeable zinc metal batteries and other batteries.

Study of electrical properties and detection mechanism of a practical novel 3D-Spherical Electrode Detector

Among the 3D electrode Si detectors for high energy particle and X-ray detection, the traditional 3D-Trench electrode Si detector is a semiconductor detector that is widely used and discussed. Aiming at removing the shortcomings of the traditional 3D-Trench electrode Si detectors such as uneven electric field distribution, asymmetric electric potential, and the existence of some dead zone, we propose a new type 3D-Spherical Electrode Detectors and carry out extensive and systematic studies of their physical properties. We simulated detector electric field, electric potential, electron concentration distribution, full depletion voltage, leakage current, capacitance, the incident particle induced transient current and the weighting field. We systematically studied and analyzed detector’s electrical characteristics. By comparing with the traditional 3D-Trench electrode Si detectors, the new detector structure has more uniform electric field and potential, and less depletion voltage, leakage current and capacitance.

Few-layer Graphene Lithiophilic and Sodiophilic Diffusion Layer on Porous Stainless Steel as Lithium and Sodium Metal Anodes.

In order to subdue the obvious problem of uneven electric field distribution on regularly used copper/aluminum current collectors for alkali metal batteries, graphene on porous stainless steel (pSS_Gr) was fabricated using the ion etching technique that is employed as an effective host for lithium and sodium metal anodes. The binder-free pSS_Gr demonstrated stable Li plating and stripping at areal current and capacity of 6 mA cm-2 and 2.54 mAh cm-2 , respectively, for over 1000 cycles with 98% coulombic efficiency (C.E.). Also, in the case of Na metal anode, the host has shown stable performance at 4 mA cm-2 and 1 mAh cm-2 over 1000 cycles with ∼100% C.E.. Further, a full cell composed of Li-plated pSS_Gr as an anode and LiFePO4 as a cathode is electrochemically tested at 50 mA g-1 current density with stable 100 cycles.

Multi-mesa photodiodes with uneven electric field distribution designed for 100-Gbits 4-level pulse amplitude modulation applications

The influence of a multi-mesa structure on a pin photodiode (pin-PD) was carefully studied. It was found that PDs with multi-mesa structures form an uneven electric field in the device under the working voltage, and the electron obtains the overshoot velocity in the uneven electric field. The device that adopts the multi-mesa structure can also reduce the capacitance. The introduction of multi-mesa structures provides another way to improve the performance of the pin-PD. Compared with the one-mesa structure, the multi-mesa structure improved the bandwidth of 5.5 GHz and reduced the capacitance from 26 to 19 fF. The modified pin-PD with a multi-mesa structure can be used in 100-Gbits optical communication systems.

Scaled-Up Multi-Needle Electrospinning Process Using Parallel Plate Auxiliary Electrodes.

Electrospinning has gained much attention in recent years due to its ability to easily produce high-quality polymeric nanofibers. However, electrospinning suffers from limited production capacity and a method to readily scale up this process is needed. One obvious approach includes the use of multiple electrospinning needles operating in parallel. Nonetheless, such an implementation has remained elusive, partly due to the uneven electric field distribution resulting from the Coulombic repulsion between the charged jets and needles. In this work, the uniformization of the electric field was performed for a linear array of twenty electrospinning needles using lateral charged plates as auxiliary electrodes. The effect of the auxiliary electrodes was characterized by investigating the semi-vertical angle of the spun jets, the deposition area and diameter of the fibers, as well as the thickness of the produced membranes. Finite element simulation was also used to analyze the impact of the auxiliary electrodes on the electric field intensity below each needle. Implementing parallel lateral plates as auxiliary electrodes was shown to help achieve uniformization of the electric field, the semi-vertical angle of the spun jet, and the deposition area of the fibers for the multi-needle electrospinning process. The high-quality morphology of the polymer nanofibers obtained by this improved process was confirmed by scanning electron microscopy (SEM). These findings help resolve one of the primary challenges that have plagued the large-scale industrial adoption of this exciting polymer processing technique.

Synthesis of inherently helical nanofibers: Effects of solidification of electrified jet during electrospinning

AbstractIn this paper, a helical fiber was fabricated through electrospinning by increasing the vapor pressure of the solvent, increasing the conductivity of the polymer solution and forming an uneven electrical field distribution around the jet. Fiber morphology during electrospinning of a dielectric polymer solution was observed to dramatically change from straight to helical due to rapid solidification of the jet as vapor pressure of the solvent increased. A similar effect was observed with conductive solutions prepared by adding large amounts of metal ion to the polymer solution. The addition of metal ion induced strong electrical stresses, causing the electrified jet to rapidly solidify in the early stage of electrospinning. Simulations revealed that the jet near the nozzle tip was subject to a strong electrical field due to increased charge density. The thickness of the emerging fiber was rapidly reduced with fast and simultaneous solidification, resulting in helical nanofibers. In addition, by using the asymmetric spinnerets, an uneven electric field distribution around jet was generated, maximizing the fiber curvature and increasing the helical fiber ratio.

High energy density of ferroelectric polymer nanocomposites utilizing PZT@SiO2 nanocubes with morphotropic phase boundary

Polymer-based nanocomposites embedded high dielectric-constant (high-εr) ceramic fillers in high breakdown-strength (high-Eb) polymer matrix are extensively studied as the flexible dielectrics for high discharged-energy–density (high-Ue) film capacitors. Ferroelectric ceramics composition lying on the morphotropic phase boundary (MPB) show ultrahigh dielectric and polarization response, which as ceramic fillers, have great promise to enhance the Ue of polymer/ceramic composites. Herein, high-εr Pb(Zr0.52Ti0.48)O3 (PZT) nanocubes (NCs) with MPB composition are prepared successfully via an improved hydrothermal reaction. Based on this, core–shell structured PZT@SiO2 nanofillers are designed to reduce the uneven electric field distribution and leakage current in P(VDF-CTFE)-based nanocomposites for high Eb. We demonstrate that the PZT@SiO2 nanofillers with MPB composition can effectively resolve the paradox between εr and Eb. The prepared P(VDF-CTFE)/PZT@SiO2 nanocomposites can display a high Ue of 16.8 J/cm3 at Eb of 491 MV/m, which is substantially improved by 107% over the pristine P(VDF-CTFE). Plus, high discharging efficiency of 70% is also achieved. The superiority of the PZT@SiO2 NCs with MPB in improving the capacitive energy density of film capacitors will be expected to provide a design paradigm for advanced polymer composites with high energy storage performance.

Facile and effective repair of Pt/Nafion IPMC actuator by dip-coating of PVP@AgNPs

Ionic polymer metal composite (IPMC) always takes big risks of electrode cracking and peeling, which lead to energy wasting, waterloss, and uneven electric field distribution, thus hamper its commercial applications. To address this issue, we propose a facile and effective technique to repair the electrode fatigue by coating polyvinylpyrrolidone (PVP) encapsulated Ag nanoparticles (PVP@AgNPs) on the long-term used IPMC surface. To improve the electrochemical stability, the silver nanoparticles (Ag NPs) with a diameter of ∼34 nm are encapsulated by a 1.3 nm thick PVP film, thus forming a shell–core structure to resist corrosion from the electrolyte solution. Physiochemical investigations reveal that, PVP@AgNPs closely attach to the interior and exterior surfaces of the original Pt nanograin electrode, thus refreshing its electronic conductivity; the repaired IPMC actuator exhibits better electromechanical properties compared to its precursor actuator: 7.62 folds in displacement output, 9.38 folds in force output, and 9.73 folds in stable working time.

High Energy Storage Performance of PMMA Nanocomposites Utilizing Hierarchically Structured Nanowires Based on Interface Engineering.

To overcome the inherent high hysteresis loss of ferroelectric polymer-based nanocomposites, non-ferroelectric linear dielectric poly(methyl methacrylate) (PMMA) is adopted as the polymer matrix for high discharge efficiency. At the same time, slender ferroelectric BaTiO3 nanowires (BT NWs) with a high dielectric constant are selected as the nanofiller for high energy density. To avoid the agglomeration of BT NWs and enhance the strength of interfaces, dopamine is used as organic coatings to tailor the interface. The BT@dopa NWs/PMMA nanocomposites exhibit excellent interface compatibility between the BT NWs and PMMA matrix and a very good microstructure uniformity. Based on this, hierarchically structured BT@SiO2@dopa NWs are designed and prepared to overcome the uneven electric field distribution at the interface, resulting from the dielectric constant mismatch. The discharged energy density (Ue) can be largely enhanced from 3.76 J/cm3 for pure PMMA films to 11.78 J/cm3 for PMMA-based nanocomposites by incorporating 5.0 wt % BT@SiO2@dopa NWs. In addition, a high discharging efficiency (η) of 91% is obtained simultaneously in the nanocomposites. Both experimental and theoretical simulations demonstrate that the double core-shell structure nanowire fillers can effectively alleviate the local field distortion, inhibit leakage current, and suppress remnant electric displacement, leading to the high Ue and η. These findings are significant in facilitating the development of high-performance film dielectric capacitor materials using PMMA-based nanocomposites toward high energy storage density.

Visualization of Mossy Zinc Electroplating Structure Evolution Via Operando Nanotomography

Dendrite growth during electrodeposition is a critical challenge faced by high-energy metallic electrodes (e.g. Li, Zn) in rechargeable batteries. Under typical battery operation conditions, mossy structure forms on Li and Zn anode surface, which may be described as colonies of intertwined and branched filaments with diameters of ~ 100 nm. Compared to the well-known diffusion-limited dendritic growth, which occurs at much higher current density, the mossy growth process is vaguely described as “kinetically limited” in literature and its mechanism remains poorly understood. Recent study shows that the detachment of mossy filaments from substrate during electrostripping, which forms “dead lithium”, is a major cause of the battery capacity fading. A better understanding of the structure evolution of mossy deposits during cycling is therefore of considerable importance for developing successful strategies to improve the cycling life of metallic anodes.In this study, we performed operando tomography of mossy zinc structure growth on Cu substrate during electrodeposition with nanoscale resolution at the National Synchrotron Light Source II. Zinc electroplating was carried out at a constant overpotential of 50mv in an in-situ electrodeposition cell made of a capillary tube with the working (Cu wire) and counter (Zn wire) electrodes inserted from opposite ends. Tomography datasets were collected every 2 minutes with an effective voxel size of 43 nm. The 3D structure of zinc deposits was reconstructed from the datasets using open-source code TomoPy.Three different nucleation sites were observed, and the Zn mossy structure was divided into three groups according to these sites for a more detailed analysis. The calculated average porosity of the three mosses was ~35% and this was supported by ex-situ analysis. These three groups were separated into shells from their cores, and the most significant growth was occurring at the outermost shell. Further, the porosity and the volume of the inner shell and the core reached a steady state after a certain amount of time of electrodeposition. This result showed the penetration of the electrolyte to the inner parts of the mossy Zn was limited. All three mossy structure showed the same growth pattern without a preferred growth direction; however, there was an apparent difference of volume growth rate between them, indicating a possible diffusion limitation or uneven electric field distribution, which was in contrast with the previous studies. From ex-situ focus-ion beam scanning electron microscopy examination, it was shown that the moss structure was comprised of individual filaments, which repeatedly branched and entangled to form a mossy Zn. Figure 1

Influence of zirconia and ceria nanoparticles on structure and properties of electrodeposited Ni-W nanocomposites

Ni-W-ZrO2-CeO2 nanocomposites were prepared by pulse electrodeposition for high wear and corrosion resistance as a protective coating. The structure (morphology, phase composition, roughness, crystallite size, surface feature) and properties (hardness, wear and corrosion resistance) of the nanocomposites were evaluated by various methods. The formation mechanism of the nanocomposites were proposed. The results show that the nanocomposite coatings are dense with nodular-like structure. The cauliflower-like protrusion clusters were formed due to the ‘tip discharge effect’ in the uneven distribution of electric field. It demonstrated that these nanoparticles were homogeneously distributed in the Ni-W matrix. The presence of the nanoparticles in Ni-W matrix improved the hardness, wear and corrosion resistance. The combination of ceramic particles and rare earth oxide particles was an excellent reinforcement phase for Ni-W matrix. The sample obtained at 1000 Hz has the optimal hardness and wear resistance, as well as the satisfying corrosion resistance. The nanocomposite deposited for 10 min owns the superior corrosion resistance in the initial stage of immersion. Ni-W-ZrO2-CeO2 nanocomposites own excellent performance and exhibit potential application values in harsh conditions.

The Auxiliary Electrode Can Improve the Electric Field Distribution of the Roller Electrostatic Spinning

Although needle-free roller electrostatic spinning technology has the advantages of higher output than traditional needle electrostatic spinning, it has the problem of uneven distribution of electric field and poor quality of filaments. The emphasis of this study is to solve the non-uniform distribution of the electric field of roller electrostatic spinning so that it can produce high-quality nanofibers. The electric field analysis shows that the electric field distribution is most uniform when (1) ring electrode is connected to 5kv and parallel electrode is connected to 11kv, and (2) auxiliary electrode is connected to -700v. The finite element analysis of the electric field shows that the auxiliary electrode increases the electric field intensity in the spinneret area. The auxiliary electrode in needleless roller electrostatic spinning technology can be used to develop high efficiency and low energy consumption nano-fiber production system.

Breakage features of coal treated by cyclic single pulse electrical disintegration

AbstractHigh‐voltage electrical pulse (HVEP) technology, a potential method for degassing coal seam in the future, has made great progress in field application. However, the previous studies mainly concentrated on the coal‐crushing effect of the action of single pulse, ignoring the influence of cyclic single pulse on the fracture structure of coal. In this paper, Huaibei anthracite coal and Inner Mongolia bituminous coal were taken as the experimental objects to study the effect of cyclic single pulse on the fracture structure of coal. The results show that the uneven distribution of electric field in the coal causes the crack to break along the interface between the mineral and the coal. Besides, the characteristics of cracks and functional groups of coal before and after electrical breakdown were investigated through scanning electron microscope and Fourier transform infrared spectroscopy. The results suggest that the relative contents of oxygen‐containing functional groups are reduced after electrical breakdown, which promotes the gas desorption from the surfaces of coal samples. Moreover, changes in CH4 adsorption capacity of HVEP‐treated coal were studied through a high‐pressure adsorption instrument, with the adsorption temperature set from 40 to 120°C. The results show that the adsorption amount of electrically broken coal is smaller than that of raw coal, which proves that temperature and current exert similar influences on the adsorption capacity of coal sample. Additionally, current waveforms indicate that the peak current increases with the number of cycle, whereas the breakdown time decreases with it. However, the peak current and breakdown time will eventually become stable as the number of cycles grows, demonstrating that electrical properties of coal are changed in the process of breakdown, which thus affects the next discharge.

Eliminating Tip Dendrite Growth by Lorentz Force for Stable Lithium Metal Anodes

AbstractLithium metal anodes are deemed as the “Holy Grail” for next generation high energy density batteries, due to the reported highest specific capacity (3860 mAh g−1) and the lowest negative electrochemical potential (−3.04 V vs the standard hydrogen electrode). However, the notorious tip‐induced dendrite growth leads to low Coulombic efficiency, restricted lifespan, and even catastrophic short‐circuits, blocking the roadmap of their commercialization. Here, a magnetic field is introduced into the lithium plating process. The Li+ concentrated around the tips by the uneven electric field distribution can be taken off the hotpots by the Lorentz force and the tip dendrite growth can be eliminated. The relationship between current density and magnetic flux intensity is established by monitoring the deposited lithium morphology as well as the electrochemical performance, which is confirmed by mathematic modeling and COMSOL Multiphysics simulation. It is also demonstrated that the Lorentz force–induced tip dendrite elimination can be utilized practically by assembling permanent magnet‐containing prototype coin cell. It is anticipated that this physical approach can be applied to other high energy density systems as well.

Porous equipotential body with heterogeneous nucleation sites: A novel 3D composite current collector for lithium metal anode

Lithium metal is an ideal anode material for lithium battery thanks to its ultra-high specific capacity and lowest redox potential. However, uncontrollable growth of lithium dendrites hinders its application due to local aggregation of lithium ions and anisotropic growth of lithium metal driven by uneven electric field distribution. Here a strategy is proposed to address this issue via utilizing porous equipotential body decorated with heterogeneous nucleation sites as advanced three-dimensional current collector. The conductive network of carbon nanofibers is recognized as a porous equipotential body, where the interior electric filed is zero due to the well-defined electric field shielding effect. In addition, copper nanoparticles as heterogeneous nucleation sites are uniformly anchored on carbon nanofibers, which guide lithium deposition evenly. As a result, lower impedance and higher Coulombic efficiency (∼97%) are achieved in modified lithium-copper cell. In particular, the cycling lifetime of modified symmetric lithium-lithium cell is expanded up to 500 cycles at extremely large current density of 50 mA cm−2.

Electrohydrodynamic assisted droplet alignment for lens fabrication by droplet evaporation

Lens fabrication by droplet evaporation has attracted a lot of attention since the fabrication approach is simple and moldless. Droplet position accuracy is a critical parameter in this approach, and thus it is of great importance to use accurate methods to realize the droplet position alignment. In this paper, we propose an electrohydrodynamic (EHD) assisted droplet alignment method. An electrostatic force was induced at the interface between materials to overcome the surface tension and gravity. The deviation of droplet position from the center region was eliminated and alignment was successfully realized. We demonstrated the capability of the proposed method theoretically and experimentally. First, we built a simulation model coupled with the three-phase flow formulations and the EHD equations to study the three-phase flowing process in an electric field. Results show that it is the uneven electric field distribution that leads to the relative movement of the droplet. Then, we conducted experiments to verify the method. Experimental results are consistent with the numerical simulation results. Moreover, we successfully fabricated a crater lens after applying the proposed method. A light emitting diode module packaging with the fabricated crater lens shows a significant light intensity distribution adjustment compared with a spherical cap lens.

Theoretical analysis and application of polymer‐matrix field grading materials in HVDC cable terminals

The distortion and uneven distribution of electric field in high-voltage direct current (HVDC) terminal insulator is the key problem for stable running of the power transmission system. Semiconducting flexible materials filled polymer-matrix composites with non-linear conductivity have also been considered to modify the distribution of electric field in cable terminal. Several factors having influence on the non-linear conductivity will be analysed in this review.

Ejection of Electrode Molten Droplet and Its Effect on the Degradation of Insulator in Gas Spark Switches

Electrode erosion is a notable issue influencing the performance and restricting the lifetime of gas switches. In the erosion process, electrode materials heated by spark channel will melt or evaporate and be driven to depart from electrode surface, contaminating the gas switch insulator, and potentially inducing flashover accidents. In this paper, sputtering spots are observed near the erosion crater in a two-electrode gas switch, which indicates the existence of molten droplet ejection. In addition, a set of polymethyl methacrylate rings are inserted in the gas switch to detect the ejection of molten droplet as well as to simulate the switch insulator for investigating the degradation of surface insulation strength. The results show that the ejection of molten droplet is along the tangent surface of electrode with a small divergent angle. After repeated discharges, the insulator surface is bombarded by the droplet ejection and forms dense cracks and embedded metal particles in a narrow band. The spatial varied droplet ejection causes a decrease in both flashover electric field and surface resistance. It also leads to different surface resistances in different regions, which can result in an uneven electric field distribution. Thus, droplet ejection increases the probability of surface flashover accidents in gas switches.

Reactor Design of Microwave Assisted Demetallization of Heavy Crude Oil

In the recent years with the deeper exploiting of world-wide crude oil, the heavy and poor trend of which is aggravating, inducing the metal contents in the oil increasing rapidly. Vanadium (V) and nickel (Ni) are the most harmful metals to petroleum processing among these metals, which mainly displays poisonous effect to the catalysts of Fluid Catalytic Cracking (FCC) and hydrogenation. The commonly used technologies to remove these metals can be classified into physical method, chemical method and catalytic hydroprocessing method. Hydrodemetallization (HDM) is widely employed in industry. However, the products of HDM reactions can accumulate in the catalyst pores, causing the formation of deposits which end up obstructing those pores irreversibly, blocking access to the catalyst sites and leading to a progressive loss of catalytic activity. Thus the removal of nickel and vanadium from crude oil has become a challenge in petrochemical processing.This work focuses on these metals removal by using microwave heating technology. A suitable reactor was first developed through numerical simulation technology using COMSOL. It was found that the reactor with a radius of 20 mm shows good coupling with microwaves, and the optimized loading height achieved is 40 mm. Experiments of demetallization were then conducted for Venezuela crude oil using this reactor, the maximum removal rate of 72.4 % and 76.8 % were obtained for Ni and V respectively. However, by using this batch reactor, the temperature distribution is non-uniform within the treated material, a continuous system were therefore developed to overcome the un-even electric field distribution. The reactor was designed as a cylinder with the length of 500 mm, and different crude oil flow rates were simulated, good demetallization rate can be achieved using the same microwave operating conditions.