Discharge Mechanism Research Articles

Hydrogen-Bond-Assisted Solution Discharge in Aprotic Li-O2 Batteries.

Surface discharge mechanism induced cathode passivation is a critical challenge that blocks the full liberation of the ultrahigh theoretical energy density in aprotic Li-O2 batteries. Herein, a facile and universal concept of hydrogen-bond-assisted solvation is proposed to trigger the solution discharge process for averting the shortcomings associated with surface discharge. 2,5-Di-tert-butylhydroquinone (DBHQ), an antioxidant with hydroxyl groups, is introduced as an exemplary soluble catalyst to promote solution discharge by hydrogen-bond-assisted solvation of O2 - and Li2 O2 (OH···O). Thus, a Li-O2 battery with 50× 10-3 m DBHQ delivers an extraordinary discharge capacity of 18945 mAh g-1 (i.e., 9.47 mAh cm-2 ), even surpassing the capacity endowed by the state-of-the-art reduction mediator of 2,5-di-tert-butyl-1,4-benzoquinone. Besides, an ultrahigh Li2 O2 yield of 97.1% is also achieved due to the depressed reactivity of the reduced oxygen-containing species (O2 - , LiO2 , and Li2 O2 ) by the solvating and antioxidative abilities of DBHQ. Consequently, the Li-O2 battery with DBHQ exhibits excellent cycling lifetime and rate capability. Furthermore, the generalizability of this approach of hydrogen-bond-assisted solution discharge is verified by other soluble catalysts that contain OH or NH groups, with implications that could bring Li-O2 batteries one step closer to being a viable technology.

Modeling the multi-step discharge and charge reaction mechanisms of non-aqueous Li-O2 batteries

The modeling study plays a critical role in understanding the reaction mechanisms and predicting the performance of lithium-oxygen (Li-O2) batteries. Although several models have successfully captured the discharge behaviors of the Li-O2 batteries, modeling the charge behaviors of the Li-O2 batteries is a challenge due to lacking a thorough understanding of the related reaction processes. This work proposes a multi-step reversible discharge/charge model for the non-aqueous Li-O2 batteries. Both the surface and solution reaction pathways of lithium peroxide (Li2O2) are taken into account. The proposed model can predict the discharge behaviors well, and more importantly, can accurately capture the charge behaviors of the Li-O2 batteries by considering the following three aspects: the effect of Li2O2 morphology on its decomposition potential, the evolution of interfacial resistance by Li2O2 film collapse, and the different desorption rates of absorbed lithium superoxide (LiO2∗) in different electrolytes. Based on this model, the discharge/charge processes of the Li-O2 batteries using dimethoxyethane(DME), tetraethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO) electrolytes, as well as a redox mediator TEMPO, are simulated and verified. The Li2O2 formation/decomposition through the surface and solution pathways are dominated by the specific surface area of the electrode and the potential, respectively. The Li2O2 generated by the solution pathway is more difficult to be decomposed during charge. The use of redox mediator TEMPO lowers the discharge capacity of the Li-O2 batteries due to the weakened solution reaction, while remarkably reduces the reversible capacity loss. The desorption time constant of LiO2∗ in electrolyte is a critical parameter that determines the degree of the reaction through the solution pathway, thus determining the discharge/charge cycling performance of the Li-O2 batteries with various electrolytes.

Interaction Simulation of Vadose Zone Water and Groundwater in Cele Oasis: Assessment of the Impact of Agricultural Intensification, Northwestern China

Agricultural intensification has boosted land productivity, but it has also created new sustainability issues. As one of the most important human habitations and agricultural farming areas in arid areas, the Cele Oasis has a very developed agricultural system. This paper studies the long-term effects of different types of agricultural intensification strategies on groundwater level fluctuations in the Cele Oasis. A soil water flow (HYDRUS-1D) and aquifer simulation (MODFLOW) coupling model were used to construct the geometric structures of the vadose zone and saturated zone in the Cele Oasis and to analyze the recharge and discharge mechanism of the oasis. The results showed that HYDRUS-1D accurately simulated soil moisture transport in the Cele Oasis, providing reliable data for calibration of the MODFLOW model. The groundwater level simulated by MODFLOW was in good agreement with the observed value. The results of the R2, RMSE, and NSE were ranges of 0.77–0.90, 0.45–0.74 m, and 0.76–0.87, respectively. The errors were acceptable limits. The coupling model predicted the responses of different agricultural types and cropping scenarios to groundwater. Predictions showed that the groundwater level in the Cele Oasis remained stable under the current cropping scenario (100% cropping intensity), and that the groundwater level decreased slightly under the cropping scenario (110% cropping intensity and 130% cropping intensity). When the cropping scenario was at 170% cropping intensity, the groundwater level decreased rapidly, and the maximum drawdown value was 7 m. Therefore, the maximum cropping intensity of the Cele Oasis in the future should be 130% of the current cropping intensity.

Electron beam-plasma discharge in GDT mirror trap: experiments on plasma start-up with electron gun

The paper describes experiments on the injection of an electron beam into a gas at the gas dynamic trap (GDT) and develops a technique for creating a starting plasma with parameters sufficient for its subsequent heating by neutral beams. It is found that a relatively thin electron beam is capable of ionizing plasma in the entire volume of the trap, and the plasma turbulence it excites is capable of accelerating some of the electrons to energies tens of times higher than the initial energy of the beam. It is shown that, in contrast to early experiments on tabletop open traps, collective beam relaxation under GDT conditions occurs in the vicinity of the entrance magnetic mirror. Since the electron cyclotron frequency in this region significantly exceeds the plasma frequency, it is necessary to study the mechanism of a beam-plasma discharge under these conditions. As a first step along this path, we measure the radial diffusion coefficient of fast particles, as well as the rate at which they gain energy.

Photo-assisted Al-air batteries based on gel-state electrolyte

The use of new concept electrochemical devices to store and release solar energy has always been a research hotspot in the society of resource shortage. In this work, we firstly introduce sunlight into the Al-air battery by CuO and Cu2O semiconductor electrode materials to improve the discharge voltage under illumination and the calcium alginate hydrogel-based electrolyte is also applied to the Al-air battery. The calcium alginate hydrogel-based electrolyte can greatly inhibit the self-corrosion of aluminum, resulting in the specific capacity of Al-air battery being significantly increased. At the current density of 1 mA cm−2, the CuO air cathode shows better performance, the maximum discharge voltage is 1.37 V and 1.23 V under illumination in aqueous sodium hydroxide solution and hydrogel, respectively, while the maximum discharge is 0.9 V and 0.78 V in the darkness. And the specific capacity in the hydrogel is about 20 times that of the aqueous sodium hydroxide solution. In addition, the semiconductor energy band structure and the discharge mechanism of the photo-assisted Al-air battery under illumination are also studied. This study provides a prospect for the conversion and application of solar energy in the photo-assisted Al-air battery.

A modified expression for breakdown voltage of Townsend discharge in a non-uniform electric field and uniform axial magnetic field

Townsend breakdown mechanism for direct current discharge in argon gas by considering the effects of the non-uniformity of electric field, the loss of electrons due to radial diffusion, and the applied axial magnetic field has been discussed and an analytical expression has been derived for the breakdown voltage. It was Shown that the non-uniformity of electric field, between two parallel disc electrodes with radius R and separation of d, significantly affects the electron multiplication for d≥2.7R and that effect was disappeared for the gas pressure higher than 0.35 Torr. The loss coefficient δ was used to quantify the effects of the electron radial diffusion and axial magnetic field and the PIC-MCC numerical simulations were used to determine it. The results show that increasing the gap size above the electrode radius leads to dramatic increase of the δ coefficient while applying an axial magnetic field can effectively decrease it.

Periodical discharge regime transitions under long-term repetitive nanosecond pulses

Intuitively, the nanosecond repetitively pulsed (NRP) corona and spark regimes are sustained successively after onsets due to the high background electron density and/or the surplus heat. In this paper, the NRP discharge unexpectedly swings among different regimes (corona → glow → spark → corona → …) in one pulse train, which is characterized by the periodical spark quench and reestablishment. We have investigated discharge regime instabilities by applying long-term repetitive high-voltage nanosecond pulses of ∼15 ns duration to needle–needle and needle–plane gaps in atmospheric-pressure N2 and N2–O2 mixtures. Pulse-sequence resolved electrical and optical diagnostics have been implemented to capture transition processes. The initial corona gradually grows into glow and then spark ‘pulse-by-pulse’, however, the spark regime was interrupted after a certain number of voltage pulses until the next reestablishment. Narrow pulse width impedes the discharge instability growth within one pulse, and a certain number of voltage pulses are required for the discharge regime transition. The addition of O2 dramatically boosts the duration length of spark regime. A lower output impedance of the power supply induces a higher deposited energy into a spark, however, not necessarily leads to a longer spark regime duration, although both the energy storage and the average electric field strength are approximate. Polarity effects, conventionally diminished in pulse-periodic discharges, are still evident during the discharge regime transition. The periodical discharge regime transition is qualitatively explained based on the plasma–source coupling and the evolution trajectory along the power transfer curve. Feedback mechanisms and residual-conductivity related screening effect in NRP spark discharges are analyzed based on a simplified 0D simulation. The periodical feature is probably caused by the insufficient average deposited energy per unit distance per one pulse cycle. In-depth understandings of ‘non-binary’ regimes (neither corona nor spark) and memory effect mechanisms of NRP discharges could be reached.

ESD HBM Discharge Model in RF GaN-on-Si (MIS)HEMTs

Gallium nitride (GaN) technologies have become an essential role in commercial advanced RF systems, which accompany emerging RF electrostatic discharge (ESD) reliability challenges. As opposed to ESD clamp transistors in <i>LV</i> CMOS technologies, a mis-correlation between standard-defined human body model (HBM) ESD robustness and commonly used TLP failure current was observed in GaN (MIS) high electron mobility transistors (HEMTs). Using transient HBM <inline-formula> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula>&#x2013;<inline-formula> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characteristics, a novel discharge model is proposed to explain the transient discharge mechanism. The TCAD and SPICE simulations confirmed that the observed mis-correlation between TLP and HBM is attributed to 2-dimensional electron gas (2DEG) resistance modulation in response to HBM ESD transient voltage waveforms. The HBM waveforms under full transient duration in terms of rising and falling edges are further discussed. Eventually, the failure mechanisms in the TLP IVs and the HBM transient IVs can be well correlated in GaN (MIS)HEMTs.

Investigation of material removal rate and surface roughness during electrical discharge machining on Al (6061)-5%SiC-10%B4C hybrid composite

Electrode Discharge Mechanism (EDM) is a manufacturing process using controlled sparks that occur between an electrically conductive workpiece and an electrode in the presence of an insulating liquid. The EDM process is commonly used to manufacture metallic matrix compounds that have wide applications in the railway sectors and the aircraft industry. Aluminum metal matrix composites (AMMCs) are one of the important kinds of metallic matrix compounds due to their advanced characteristics, such as lightweight and high strength. This lightweight material was developed and used in various manufacturing processes, like the automobile industry to reduce vehicle weight and thus reduce fuel consumption. This paper discussed the experiments of the EDM that were conducted to examine the effect of machining parameters, including peak current (10, 20, and 30 A), pulse on different times (50, 100, and 200 µsec), duty factors (4, 6, and 8) on the material removal rate, and surface roughness of the Al (6061)-5%SiC-10%B4C hybrid composite as workpiece using copper electrode tool by Box-Behnken design. The analysis data for the dependent and independent variables manifested that the influence of machine parameters whenever Ip and Pon increase, the MRR and Ra increase.

Study on Surface Discharge Characteristics of GO-Doped Epoxy Resin-LN2 Composite Insulation.

Superconducting power lead equipment for epoxy insulation, such as high-temperature superconducting DC power or liquefied natural gas energy pipelines, as well as high-temperature superconducting cables, has long been used in extreme environments, from liquid nitrogen temperatures to normal temperatures. It is easy to induce surface discharge and flashover under the action of strong electric field, which accelerates the insulation failure of current leads. In this paper, two-dimensional nano-material GO was used to control the electrical properties of epoxy resins. The DC surface discharge and flashover characteristics of the prepared epoxy resin–GO composite insulation materials were tested at room temperature with liquid nitrogen. The surface discharge mechanism of the epoxy resin–GO composite insulation materials was analyzed. The experimental results show that the insulation properties of epoxy composites doped with GO changed. Among them, the surface flashover voltage of 0.05 wt% material is the best, which can inhibit the discharge phenomenon and improve its insulation properties in extreme environments, from room temperature to liquid nitrogen temperature. It is found that the development process of surface discharge of composite insulating materials under liquid nitrogen is quite different from that under room temperature. Before critical flashover, the repetition rate and amplitude of surface discharge remain at a low level until critical flashover. Furthermore, the voltage of the first flashover is significantly higher than that of the subsequent flashover under the action of the desorption gas on the surface of the composite insulating material and the gasification layer produced by the discharge. Given that the surface flashover voltage of 0.05 wt% epoxy composite is the best, the research and analysis of 0.05 wt% composite is emphasized. In the future design of superconducting power lead insulation, the modification method of adding GO to epoxy resin can be considered in order to improve its insulation performance.

Surface Flashover Induced by Metal Contaminants Adhered to Tri-Post Epoxy Insulators under Superimposed Direct and Lightning Impulse Voltages

Metal contaminants can distort the surface electric field of the tri-post epoxy insulator and cause serious surface charge accumulation, significantly reducing the insulation performance of the insulator under the superimposed DC and lightning impulse voltage. In this paper, an experimental platform for charge accumulation and surface flashover of tri-post epoxy insulators under the superimposed DC and lightning impulse voltage was built, by surface point measurement and charge inversion calculation, the surface charge distribution characteristics of tri-post insulators with attached particles was experimentally explored and the influence law of attached metal particles on the charge accumulation was discussed. The results show that metal particles can cause a surge in the surface charge density of the tri-post epoxy insulator, forming bipolar charge spots whose polarity is opposite to that of the adjacent electrodes. The adsorbed metal dust can cause the polarity reversal of adjacent surface charges, forming a large-area unipolar charge spot. Moreover, the flashover voltage of a tri-post insulator under DC superimposed lightning impulse voltage with a clean surface and attached metal particle was measured, and the synergistic induction mechanism of charge spot accumulation and metal particle discharge on the flashover along the face of the tri-post insulator is thereby revealed. Compared with the clean insulators, the surface flashover voltages of tri-post epoxy insulators with metal contaminants adhered decrease under the superimposed voltages of different polarities, but the decline amplitude is greater under the heteropolar composite voltage. When adhered to the middle of the insulator leg, the distribution range of bipolar charge spots is the widest, and the surface flashover voltage decreases sharply, which can drop by 32% compared with the absence of particles. In addition, when the metal dust adsorbed by the tri-post epoxy insulator has a wide distribution range, the impact of metal dust on the flashover voltage is greater than that of the attached metal particles, and its hazard cannot be ignored. The research results can provide a reference for the insulation test method and optimal design of the DC tri-post epoxy insulator.

Design and Experiment of Spiral Discharge Anti-Blocking and Row-Sorting Device of Wheat No-Till Planter

Aiming at the problems of the poor passing capacity of machines and low cleaning rate of seed strip during wheat no-tillage sowing in annual double cropping areas of North China, a spiral discharge anti-blocking and row-sorting device (SDARD) was designed and is reported in this paper. After the straw was cut and chopped by the high-velocity rotating no-till anti-blocking knife group (NAKG), the straw was thrown into the spiral discharging mechanism (SDM) behind the NAKG. The chopped straw was discharged to the non-sowing area to reach the effect of seed strip cleaning through the interaction between the SDM and the row-sorting of straw mechanism (RSM). Based on a theoretical analysis for determining the parameters of crucial components, the quadratic rotation orthogonal combination test method was adopted, and the operating velocity of machines (OVM), the rotary velocity of the spiral shaft (RVSS), and the height of the holding hopper from the ground (HHHG) were selected as the test factors. The straw cleaning rate (SCR) was taken as the test index. The discrete element simulation test was carried out, the regression model of the SCR was established, and parameters optimization and field test were carried out. The results show that the significant order of the three influencing factors on the SCR was HHHG &gt; OVM &gt; RVSS. The optimal combination of operating parameters was that OVM was 5 km/h, RVSS was 80 r/min, and HHHG was 10 mm. Under the optimal parameter combination, the average SCR was 84.49%, which was 15.5% higher than the no-till planter without the device, and the passing capacity of machines was great, which met the agronomic requirements of no-tillage sowing of wheat in annual double cropping areas. This study could provide a reference for the design of no-tillage machines.

Simulation of surface flashover probability distribution with gas-solid charge transport/multiplication coupling of epoxy resin

<p indent="0mm">The insulation failure of key equipment in power systems caused by gas-solid interface flashover of basin insulators is a key scientific problem that must be solved urgently. The time and space scales of gas electron multiplication and solid-surface charge evolution span multiple orders of magnitude, resulting in an unclear physical mechanism of the gas-solid coupling interface discharge of a basin insulator. A gas-solid coupling surface flashover model was established considering three junction point charge injection, solid surface charge transport, and gas collision ionization. The violent collision ionization in the gas caused by electrons emitted from the solid was taken as the surface flashover criterion. The key parameters characterizing surface charge transport and gas collision ionization were extracted based on gas-solid coupling surface flashover, and a model considering random variables was established to simulate the flashover voltage distribution of epoxy resin. The flashover voltage obeys the Weibull distribution when the charge transport parameters are Gaussian random variables, and the simulation results are consistent with the experimental results. By comparing the simulation and experimental results, it is found that the characteristic flashover voltage and distribution parameter are mainly controlled by the gas and solid media, respectively, and each charge transport random variable has a different effect on the distribution shape parameter. The Weibull distribution of flashover voltage consistent with the experimental results can be obtained by adjusting the standard deviation of charge transport random variables. This research explains the relationship between the Weibull distribution of flashover voltage and the charge transport and gas collision ionization parameters, providing an effective method to simulate the probability distribution characteristics of flashover voltage, which can also be used to evaluate the failure probability of the gas-solid interface under a certain voltage.

Correlations between precipitation reactions and electrochemical performance of lithium-sulfur batteries probed by operando scattering techniques

<h2>Summary</h2> A comprehensive description of electrochemical processes in the positive electrode of lithium-sulfur batteries is crucial for the utilization of active material. However, the discharge mechanisms are complicated due to various reactions in multiple phases and the tortuosity of the highly porous carbon matrix. In this work, simultaneous measurements of small-angle and wide-angle scattering and cell resistance are performed on operating lithium-sulfur cells. Results indicate that precipitates grow mostly in number, not in size, and that the structure of the carbon matrix is not affected. The comparison of the small-angle and wide-angle scattering reveals the amorphous discharge products found at a low discharge rate. Further analysis demonstrates the correlation between the diffusion resistance and the compositional change of electrolyte in the mesopores at the end of discharge, which suggests that Li-ion deficiency is the limiting factor for sulfur utilization at a medium discharge rate.

Study on electric spark discharge between pantograph and catenary in electrified railway

The electric spark caused by pantograph-catenary (PC) electrical contact failure happens frequently, it is a kind of arcing phenomenon which can severely affect the current collection of PC. The theoretical analysis and modelling of PC electric spark are tried. First, the contact spots between PC and their temperature rise are analysed and derived based on the classical electrical contact theory, respectively. The mechanism of spark discharge is revealed through the analysis of PC voltage difference, and the spark discharge model is proposed combining with the spot temperature rise formula and spark discharge mechanism. Then, in order to obtain some key parameters in an electric spark discharge model, such as contact force and contact current, the structure model of PC and the circuit model of vehicle-grid are established for the calculation of the spark rate in PC. Finally, the spark rate is calculated and analysed under the different parameters in PC system. The calculation results are verified by the experiment results. Through the presentation of the correlation of electric spark discharge and factors, such as contact force, contact current and material of PC, this study can support the assessment of electrical contact quality in the PC system in future study.

Analysis of soil impulse discharge characteristics based on optical‐electrical synchronous observation

The impulse performance of grounding electrodes highly depends on soil impulse discharge characteristics. The analysis of soil discharge dynamic process images is helpful to understand the impulse discharge mechanism of grounding electrodes. This paper designed an optical-electrical synchronous observation platform for simulate soil (SiO2 crystal) discharge, and discharge dynamic process images is obtained by high-speed camera. Through analysing breakdown delay time and thermal power before breakdown, it is found that soil impulse discharge is mainly an electrical breakdown process, and soil ionization intensity is positively correlated with the light intensity emitted by whole soil sample in breakdown channel development stage. The time from voltage application to the occurrence of ionization is defined as initial ionization delay time (IIDT). Using image processing technology, the change curve of optical image average grayscale value with time in the process of soil discharge is obtained, and a calculation method of IIDT is proposed by comparing the difference between average grayscale value curve and background image average grayscale value. Experiment results show that IIDT is negatively correlated with impulse voltage, particle size and water content, but not with salt content.

Towards understanding aluminum sulfur batteries with imidazolium-based electrolytes: A phenomenological model

Aluminum sulfur batteries with ionic liquid electrolytes are promising next-generation energy storage devices due to the high abundance of both aluminium and sulfur. However, very little understanding of the discharge mechanism is currently available, which hampers their development. Herein, a mathematical model that considers the complex electrochemical reduction of the sulfide species as well as the formation of the various polysulfides is developed to describe the discharge performance and the reversibility of Al–S cells at different current densities. The model is validated with experimental data obtained from Swagelok cells composed of Al metal anode, S@CNT cathode, and EMIMCl-AlCl3 ionic liquid electrolyte. The cells exhibited different discharge mechanisms and Al2S3 precipitation routes at the different current densities. The contact resistance between the composite electrode and the current collector was the main factor limiting the discharge performance at high current densities. The reversibility of the Al–S cells based on the formation of Al2S3 precipitates strongly depends on the operating current density. The developed model will serve as a tool for other researchers to enhance the electrochemical performance of aluminum sulfur batteries.

Influence of flash ignition mechanism of high-current pulsed xenon discharge on the optical degradation of the quartz shell in the UV region of the spectrum

Influence of flash ignition mechanism of high-current pulsed xenon discharge on the optical degradation of the quartz shell in the UV region of the spectrum

Spring discharge mechanism along the southeast coast of Yonaguni Island in the southern Ryukyu forearc

Study regionSpring along the southeast coast of Yonaguni Island, located at the western end of the Ryukyu forearc. Study focusThe chemical composition of groundwater, including SF6 concentration, was investigated to clarify the mechanism of groundwater discharge around Sanninudai on the southeast coast of Yonaguni Island. New hydrological insights for the regionAccurate determination of groundwater flow paths is essential to the conservation and management of groundwater sources and their sustainable use. Other areas around the world may show similar complexity, requiring a review of past findings. This possibility indicates the need for re-examination of groundwater sources around the world. In particular, the development of novel analytical methods for chemical components may provide valuable information. The chemical composition of spring water on remote islands, where anthropogenic activities have little influence, should be investigated continuously to monitor the effects of sea-level rise caused by global warming.

Improvement of degradation of Orange G in aqueous solution by Fe2+ added in dielectric barrier discharge plasma system

As a typical azo dye, Orange G (OG) is a potential threat to human health and the safety of water environment. In this study, the effect and mechanism of dielectric barrier discharge (DBD) plasma combined with Fe2+ on the degradation of OG were explored. The removal efficiency of OG in the DBD/Fe2+ system was significantly higher than that in the sole DBD system. In the DBD/Fe2+ system, 93.6% removal efficiency of OG was achieved at an input voltage of 70 V within 10 min, which was much higher than the 56.68% in the sole DBD system. Except for high concentrations of HCO3− and PO43−, which could promote the degradation of OG in the sole DBD system, SO42−, NO3− and Cl− could all inhibit the degradation of OG in both the sole DBD and DBD/Fe2+ system. The radical quenching experiments and the variation of O3 and H2O2 showed that the addition of Fe2+ could promote the effective decomposition of H2O2 into OH, which could improve the removal efficiency of OG. OH was the main active species for OG degradation, at the same time O3 and H2O2 played important role in both the system. The TOC mineralization efficiency gradually improved with the extension of treatment time. The possible degradation pathways of OG were proposed based on UV–visible spectroscopy and liquid chromatography-tandem mass spectrometry.