Low-current Discharge Research Articles

Methods for faster estimation of the entropy profile of a lithium-ion battery: A comparison of accelerated potentiometry and the estimation of entropy through thermal signatures

The operating temperature of a lithium-ion battery (LIB) has strong effects on its electrochemical performance, safety, and lifetime. Reliable predictions of cell temperature and heat generation rate are required for the design and thermal management of battery systems. The entropy variation of a LIB has a significant influence on the heat generation and the cell temperature variation, especially at a lower C-rate. Since the entropy is a function of State-of-Charge (SoC), and may change during ageing, the entropy profile may as well be used as an indicator for battery State-of-Health diagnostics. The present experimental methods, such as potentiometric or calorimetric methods, for determining the entropy variation throughout a battery's full SoC window are time-consuming and require specialized equipment with good thermal insulation and instrumentation. Hence, faster and more convenient methods are needed. In this paper, we compare an accelerated potentiometric method with a new entropy characterization method where the entropy profile is extracted from the thermal signature of a LIB during charge and discharge at low C-rates. The accelerated potentiometric method aims to obtain the entropy from thermal cycling while the cell is still not completely relaxed to its stable OCV. The thermal signature method monitors the variations of a cell's outer surface temperature during a low constant current charge or discharge, from which the continuous variation of entropy with the SoC can be extracted. The obtained entropy profile was validated through a modeling approach that combines a P2D-electrochemical model for battery operation and a 3D-finite-element model for the thermal behavior during battery operation. Good agreement between the model predictions and experiments was achieved on the temporal variation of the cell's outer surface temperature.

Ion-Anchored Strategy for MnO2/Mn2+ Chemistry without "Dead Mn" and Corrosion.

The utilization of MnO2/Mn2+ chemistry in near-neutral pH acetate aqueous electrolytes provides an opportunity to achieve a higher energy density (theoretical capacity 616 mA h/g, discharge platform >1.5 V). However, this Zn-MnO2 aqueous battery suffers from inevitable "dead Mn" and proton corrosion. In this study, we discover that the diffusion of the cathode reaction intermediate Mn3+ is intrinsic for the generation of "dead Mn", and the accumulation of "dead Mn" increases the H+ which shuttles to the anode, inducing serious corrosion. A pH-neutral hydrogel ion-anchored strategy is proposed here not only to restrict the diffusion of Mn3+ but also to suppress the proton transference. This hydrogel ion anchor is designed by deprotonating a series of monomers undergoing in situ free radical polymerization at the cathode interface. The anionic monomer with a moderate binding energy to manganese ions is screened to anchor Mn3+, which enhances the reversibility of the MnO2/Mn2+ reaction. Simultaneously, a substantial amount of anionic groups and hydrophilic functional groups in the hydrogel effectively constrains the proton shuttle to corrode the anode. Consequently, the Zn/MnO2 battery achieves exceptional cyclic stability of the MnO2/Mn2+ reaction, sustaining 8500 cycles even at a relatively low current density and discharge current density of 1 mA/cm2. Our findings highlight the importance of anchoring Mn3+ at the cathode interface and offer valuable insights for advancing practical applications of MnO2/Mn2+ reactions.

Low-current gliding DC discharge in high-speed flows

Abstract A low-current gliding discharge (current range 1–5 A) in high-speed air flows of 100–250 m s−1 was experimentally studied. A high-voltage direct current source with a maximum voltage of 4.5 kV was used to create the discharge. The average electron concentration n e ∼ 1014 cm−3 and the plasma ionization degree were determined by measuring the Stark broadening of the hydrogen H β line (λ Hβ = 486.1 nm). The estimates of the electric field (E ∼ 100 V cm −1 ÷ 600 V cm−1) in the discharge positive column were found using time-synchronized high-speed video recordings and oscillograms. The gas rotational temperature T g = 7000–9500 K and the vibrational temperature T v = 7000–11 000 K were estimated using optical emission spectroscopy. Time-resolved spectroscopy is used to investigate the effective plasma channel spatial regions from which the N, NH, N2 +, O and OH molecules radiate. The difference of the obtained radii indicates the presence of a radial temperature gradient and inhomogeneous plasma composition in the discharge cross section. The possibility of using of gliding discharge to ignite hydrocarbon-air mixtures in the ramjet engines combustors has been experimentally demonstrated.

Study on Discharge Characteristic Performance of New Energy Electric Vehicle Batteries in Teaching Experiments of Safety Simulation under Different Operating Conditions

High-voltage heat release from batteries can cause safety issues for electric vehicles. Relevant scientific research work is carried out in the laboratory. The battery safety of laboratory experiments should not be underestimated. In order to evaluate the safety performance of batteries in the laboratory testing of driving conditions of electric vehicles, this paper simulated and compared the discharge characteristics of two common batteries (lithium iron phosphate (LFP) battery and nickel–cobalt–manganese (NCM) ternary lithium battery) in three different operating conditions. The operating conditions are the NEDC (New European Driving Cycle), WLTP (World Light Vehicle Test Procedure) and CLTC-P (China light vehicle test cycle) for normal driving of electric vehicles. LFP batteries have a higher maximum voltage and lower minimum voltage under the same initial voltage conditions, with a maximum voltage difference variation of 11 V. The maximum current of WLTP is significantly higher than NEDC and CLTC-P operating conditions (>20 A). Low current discharge conditions should be emulated in teaching simulation and experiments for safety reasons. The simulation data showed that the LFP battery had good performance in maintaining the voltage plateau and discharge voltage stability, while the NCM battery had excellent energy density and long-term endurance.

Simulation of low-current DC discharges in longitudinal flows of atmospheric-pressure air

Characteristics of low-current stationary axially symmetric discharges in longitudinal laminar flows of atmospheric-pressure air calculated in the framework of a two-dimensional model are presented. Non-equilibrium discharge regimes, in the current range from 1 to 100 mA, are considered for gas flow velocities up to 50 m s−1. It is shown that variation of the flow velocity substantially affects the discharge characteristics, such as the width of discharge column, the electric field inside the gap, the current density etc. Validity of the obtained results is confirmed by their comparison with available experimental data.

Modeling of the influence of field electron emission from a cathode with a thin insulating film on its sputtering in a gas discharge in a mixture of argon and mercury vapor

A model of the low-current gas discharge in a mixture of argon and mercury vapor in the presence of a thin insulating film on the cathode surface is proposed. The model takes into account that in such a mixture a substantial contribution to the ionization of the working gas can come from the ionization of mercury atoms during their collisions with metastable excited argon atoms. In the discharge, positive charges accumulate on the film surface, creating an electric field in the film sufficient to cause field emission of electrons from the cathode metal substrate into the insulator. Such electrons are accelerated in the film by the field and can escape from it into the discharge volume. As a result, the effective yield of ion-electron emission from the cathode increases. The temperature dependences of discharge characteristics are calculated and it is shown that, due to a rapid decrease in the concentration of mercury vapor in the mixture with decreasing temperature, the electric field strength in the discharge gap and the discharge voltage increase. The presence of a thin insulating film on the cathode can result in an improvement in its emission characteristics and a significant reduction in the discharge voltage. This causes a decrease in the energies of the ions and atoms bombarding the cathode surface, and, consequently, in the intensity of cathode sputtering in the discharge.

Reduced ionization coefficients in low-current dc discharge in freons of a new generation

Reduced ionization coefficients in low-current dc discharge in freons of a new generation

Proposal and Fundamental Investigation of Energy Storage and Hydrogen Supply System Using the Lithium

In recent years, variable renewable energy such as solar power and wind power spreads rapidly. At the same time, taking measures against output fluctuations and utilization of surplus electricity become important issues. Conversion of electricity to hydrogen is considered as one of the utilizations of surplus electricity [1]. The hydrogen is stored and can be supplied to the fuel cell vehicles according to demand, regardless of weather or time. However, the disadvantage of hydrogen is its low energy density. Although several methods have been investigated for high-density storage of hydrogen, there are still issues about safety, energy loss, cost, and durability [2].In this study, we propose a new energy storage and hydrogen supply method using lithium (Figure 1). The surplus electricity can be converted by the following reaction, and the energy is stored as the lithium.Li+ + e- → Li (-3.04 V vs. SHE) (1)4LiOH → 4Li+ + O2 + 2H2O + 4e- (0.41 V vs. SHE) (2)The lithium can be stored at room temperature and pressure, and its volumetric energy is higher than that of conventional hydrogen storage methods. When hydrogen is needed, the system can be discharged to produce hydrogen by the following reaction.Li → Li+ + e- (-3.04 V vs. SHE) (3)2Li+ + 2H2O + 2e-→ 2LiOH + H2 (-0.82 V vs. SHE) (4)Since the lithium is highly reactive, discharge reaction with water occurs, and hydrogen can be produced without energy input from the outside. As shown in Equation (2) and Equation (4), charge and discharge reactions at the cathode are different, and this system combines the characteristics of lithium-air cell [3] and lithium-water cell [4]. This system has a potential to utilize the surplus electricity; but it has not been fully evaluated from the viewpoint of hydrogen production [5]. Therefore, present study investigated the characteristics of the discharge reaction and hydrogen production behavior.Figure 2 shows experimental cell. The composite anode was water-stable and had a multilayer structure [6]. LATP (Li1+x+yAlxTi2-xSiyP3-y, Ohara Co., Kanagawa, Japan), which is a water-stable lithium-ion-conducting glass ceramic, was used, along with PEO18LiTFSI as the organic electrolyte. The lithium foil and polyethylene oxide (PEO) membrane were sealed inside the cell to prevent direct contact with water vapor and oxygen. Since the cell resistance depends on the temperature, the composite anode was kept at 70°C. For the cathode, glassy carbon rod was used.Figure 3 shows current-voltage (I-V) characteristics. The cathode potential at low-current discharge is higher than theoretical value (-0.82 V). It was caused by reaction with dissolved oxygen in the electrolyte. As the current value is increased, the cathode potential drops sharply, and many bubbles were observed on the cathode end face. It is thought that oxygen concentration overvoltage increased significantly and the discharge reaction with water (hydrogen production as shown in Equation (4)) was occurred.The volume of the produced bubble was measured with using a sealed cathode and adding a liquid level gauge (not shown in Figure 2). As a result, the measured volume showed good agreement with the theoretical hydrogen volume produced by the reaction of Equation (4). It is considered that the reaction shifts to hydrogen production and the effect of dissolved oxygen can be negligible at sufficiently low cathode potential (i.e. high current discharge).The efficiency of this system was estimated by using the obtained experimental results. Generated electricity and enthalpy of produced hydrogen was calculated. When a 20 μA discharge test was conducted by using experimental cell, the discharge efficiency and conversion rate to hydrogen were 30% and 39%, respectively. For comparison, the experimental cell was converted to the lithium-air battery mode and discharged at 20 μA. The discharge efficiency was 56%. Considering the conversion ratio of lithium to electricity and hydrogen, the proposed hydrogen supply system using the lithium can utilize the variable renewable energy.

Initiation of a Volume Glow Discharge of Atmospheric Pressure in a Cylindrical Tube Using a Low-Current Surface Discharge in Argon

Initiation of a Volume Glow Discharge of Atmospheric Pressure in a Cylindrical Tube Using a Low-Current Surface Discharge in Argon

Observation of plasma boundary induced Negative Differential Resistance (NDR) in a planar DC discharge system

Observation of Negative Differential Resistance (NDR) in the discharge characteristics of a planar DC discharge system induced by specific combination of plasma boundaries is reported. In a previous work [Barnwal et al 2022 Phys. Plasmas 29 072102] it was shown by the authors that no NDRs are triggered in enclosures that have either a fully conducting boundary (viz., an ss vacuum chamber) or a fully insulating boundary (apart from the electrodes), comprising of glass tubes/mica sheets, etc. In the present work, it is shown that an NDR is triggered when the discharge produced within a small enclosure with an insulating boundary (IB), is allowed to leak out through a small aperture into a larger volume with a conducting boundary (CB). As the plasma density increases with increasing discharge current, the Debye length (λ De), which is initially larger than the gap width at low discharge currents, decreases to become of the order of gap width, triggering the NDR. Since the plasma boundary conditions before and after the NDR are widely different (insulating versus mixed) the NDR, which is unstable electrically, connects a low-current, high-voltage state before the NDR to a high-current, low-voltage state afterward. Further, issues related to changes in the anode sheath before and after the NDR are also explored. When the electrode system is nearly symmetric, the anode sheath prior to the onset of the NDR is an ion sheath that flips into an electron sheath after the NDR. When the electrode system is highly asymmetric, the anode sheath remains an electron sheath throughout (both before and after the NDR). Reasons for such behavior are discussed in the paper.

Air Interactions of Magnetically Driven Plasma Discharges in Crossflow

Motivated by the use of magnetohydrodynamic devices in fluid dynamic flow control research, the current work experimentally studied the actuation mechanism and the resulting aerodynamic interactions of magnetically driven low-current arc-plasma discharges. The investigation was conducted in the context of boundary-layer interactions in low-speed crossflow conditions through the use of coaxial and v-shaped geometries. Time-averaged velocity field measurements showed that the toroidal region of vorticity induced by the coaxial geometry in quiescent air resulted in the formation of a horseshoe vortex in crossflow. Similarly, the v-shaped actuator resulted in the formation of streamwise vortices. The resulting boundary layers had s-shaped streamwise velocity profiles as measured in the wall-normal direction characteristic for the flow downstream of a conventional vortex generator pair, due to the three-dimensional mixing induced by coherent vortex structures. A simplified model based on intermolecular momentum transfer through collisions is proposed to explain the fundamental discharge–air interactions and the induced flowfields. These results inform the applications of various magnetically driven discharges in the field of aerodynamic flow control.

The JET hybrid scenario in Deuterium, Tritium and Deuterium-Tritium

The JET hybrid scenario has been developed from low plasma current carbon wall discharges to the record-breaking Deuterium-Tritium plasmas obtained in 2021 with the ITER-like Be/W wall. The development started in pure Deuterium with refinement of the plasma current, and toroidal magnetic field choices and succeeded in solving the heat load challenges arising from 37 MW of injected power in the ITER like wall environment, keeping the radiation in the edge and core controlled, avoiding MHD instabilities and reaching high neutron rates. The Deuterium hybrid plasmas have been re-run in Tritium and methods have been found to keep the radiation controlled but not at high fusion performance probably due to time constraints. For the first time this scenario has been run in Deuterium-Tritium (50:50). These plasmas were re-optimised to have a radiation-stable H-mode entry phase, good impurity control through edge Ti gradient screening and optimised performance with fusion power exceeding 10 MW for longer than three alpha particle slow down times, 8.3 MW averaged over 5 s and fusion energy of 45.8 MJ.

Study of trigger mechanisms of a pseudospark switch configuration with a steady-state auxiliary glow discharge

This paper presents data on investigation of the pseudospark switch whose trigger unit uses a low-current auxiliary glow discharge with hollow cathode and hollow anode. The electrode system of this unit communicates with the main high-voltage gap of the switch due to the aperture in the flat part of one of the trigger electrodes. It is shown that when the electrode with the aperture plays of role of the hollow cathode of the auxiliary discharge, a low parasitic current through the aperture is provided by the ion flow. This ion current does not practically influence on the static breakdown voltage of the main gap. Applying the trigger pulse between the trigger electrodes leads to the pulsed trigger discharge with an enhanced current. At a negative polarity of the trigger pulse, the cavity with aperture turns out into the hollow anode so that the current is able to be intercepted through the aperture to the grounded cavity of the main gap. The plasma is generated in the cavity and the switch is triggered. With the proper selection of the geometry of the trigger electrodes, the delay time to trigger at a level of several tens of nanoseconds is achievable.

Polypyrrole decorated on irregular SnSe particles: A high energy density and stable durability for asymmetric supercapacitor applications

This work reported the tin selenide (SnSe), polypyrrole (PPy), and their nanocomposite with different contents, e.g., SnSe-10%PPy, and SnSe-30%PPy and examined their electrochemical performance for supercapacitor (SCs) applications. XRD and Raman's analysis confirmed the crystalline nature and phase purity with the adequate formation of the samples. The EDS mapping results confirm the structural homogeneity of the samples in the composite matrix, while the EDX spectrum of the samples reveals the purity and the adequate formation of the compounds. The morphological investigation reveals that the SnSe and PPy are composed of irregular particle morphology covered with thin sheets, forming highly conductive pathways for the diffusion of electrolyte ions to facilitate faradaic reactions. The detailed electrochemical investigation demonstrated that the SnSe-30%PPy nanocomposite electrode outperforms the pure SnSe, and SnSe-10%PPy electrodes with a maximum charge storage capability owing to their lower ohmic resistance during fast faradaic reactions. A hybrid-type asymmetric SC was assembled using activated carbon (AC) as an anode and the SnSe-30%PPy nanocomposite as the cathode in a sandwich-type configuration in an aqueous solution. A 1.7 V SnSe-30%PPy||AC asymmetric SCs was built that simultaneously achieved a high capacitance of 140 F/g and realized a maximum energy density of 56.19 Wh/kg at the power density of 850 W/kg at a low discharge current of 1 A/g with great cyclic stability of 84.7 % after 10,000 cycles, demonstrating their promising prospect towards future alternative energy storage devices. Our work demonstrated that pairing polymers with chalcogenides seems to be one of the promising research directions to upgrade the poor charge storage properties of polymers and prevent structural collapse efficiently.

Coherent fluctuations in a partially magnetized small magnetron discharge operating on molecular nitrogen

We report experimental data on rotating plasma disturbances in a quasi-steady direct-current magnetron discharge operating with molecular nitrogen at pressures of 27, 40, 67, and 133 Pa. Experiments with a segmented anode measuring the local current flow reveal up to 12 coherent structures (“spokes”) propagating in the +E×B and −E×B azimuthal directions. The current–voltage characteristics are studied and found to follow a negative resistance profile at the lower discharge currents. The existence of coherent structures and the number of spokes observed depend on the discharge current and operating pressure. Lower pressures are more favorable to the retrograde −E×B spoke rotation, which is observed in the 27, 40, and 67 Pa discharges. The results are interpreted with a gradient-driven drift wave model, and using the dispersion relation, we show that the propagation direction depends on the orientation of the local electric field within the plasma. Using an electron fluid model, we show how experimental conditions can lead to field reversals that generate −E×B spoke rotation in the lower pressure discharges.

Transition from retrograde to prograde drift instabilities in a magnetron microdischarge

Rotating plasma structures, or “spokes,” in magnetized discharges characterized by perpendicular electric and magnetic fields have been seen in a growing number of studies and are believed to be the result of gradient-driven drift instabilities. Under certain conditions, we have shown [Ito and Cappelli, Appl. Phys. Lett. 94, 211501 (2009)] the spoke’s rotation to be opposite to the E × B direction, i.e., retrograde in its expected direction. Recently [Marcovati et al., J. Appl. Phys. 127, 223301 (2020)], we have linked such counter-intuitive rotation to a local inversion of the electric field. Here, we give further experimental evidence for this inversion and attempt to provide an explanation for a relatively distinct transition seen between retrograde and positive (prograde) drift. In the experiments, a partially magnetized plasma forms inside a magnetron device of ≈10 mm radius operated with argon. Discharge current–voltage measurements are acquired for a range of argon fill pressure and inter-electrode spacing. We find two branches of operation—a low current branch of negative resistance, coinciding with the retrograde spoke rotation, and a higher current branch of positive resistance, coincident with prograde spoke rotation. We postulate that at low discharge currents, high magnetic field confinement leads to a large density gradient, causing more electron transport to the anode than that demanded by the external circuit. At higher currents, anomalous axial electron transport (across the magnetic field lines) becomes dominant, eliminating the conditions for field inversion. The current thresholds for the field inversion are found to be sensitive to the argon pressure and inter-electrode spacing.

Simulation of glow and arc discharges in nitrogen: effects of the cathode emission mechanisms

Experimental evidence in the literature has shown that low-current direct current nitrogen discharges can exist in both glow and arc regimes at atmospheric pressure. However, modelling investigations of the positive column that include the influence of the cathode phenomena are scarce. In this work we developed a 2D axisymmetric model of a plasma discharge in flowing nitrogen gas, studying the influence of the two cathode emission mechanisms—thermionic field emission and secondary electron emission—on the cathode region and the positive column. We show for an inlet gas flow velocity of 1 m s−1 in the current range of 80–160 mA, that the electron emission mechanism from the cathode greatly affects the size and temperature of the cathode region, but does not significantly influence the discharge column at atmospheric pressure. We also demonstrate that in the discharge column the electron density balance is local and the electron production and destruction is dominated by volume processes. With increasing flow velocity, the discharge contraction is enhanced due to the increased convective heat loss. The cross sectional area of the conductive region is strongly dependent on the gas velocity and heat conductivity of the gas.

Measuring low-current discharges from grounded rods under high background electric fields

Measuring low-current discharges from grounded rods under high background electric fields

Plasma Enhanced High-Rate Deposition of Advanced Film Materials by Metal Reactive Evaporation in Organosilicon Vapors.

Dense homogeneous nanocomposite TiSiCN coatings with a thickness of up to 15 microns and a hardness of up to 42 GPa were obtained by the method of reactive titanium evaporation in a hollow cathode arc discharge in an Ar + C2H2 + N2-gas mixture with the addition of hexamethyldisilazane (HMDS). An analysis of the plasma composition showed that this method allowed for a wide range of changes in the activation degree of all components of the gas mixture, providing a high (up to 20 mA/cm2) ion current density. It is possible to widely change the chemical composition, microstructure, deposition rate, and properties of coatings obtained by this method, by changing the pressure, composition, and activation degree of the vapor-gas mixture. An increase in the fluxes of C2H2, N2, HMDS, and discharge current leads to an increase in the rate of coating formation. However, the optimal coatings from the point of view of microhardness were obtained at a low discharge current of 10 A and relatively low contents of C2H2 (1 sccm) and HMDS (0.3 g/h), exceeding which leads to a decrease in the hardness of the films and the deterioration of their quality, which can be explained by the excessive ionic exposure and the non-optimal chemical composition of the coatings.

Low-Current Discharge in a Flow of Atmospheric-Pressure Argon Under the Formation of Metal Atoms: Electric and Optical Characteristics

Low-Current Discharge in a Flow of Atmospheric-Pressure Argon Under the Formation of Metal Atoms: Electric and Optical Characteristics