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Hollow cathodes are an integral part of ion, and Hall thrusters are used for electric propulsion in deep space missions and in commercial communications satellites. Hollow cathodes are known to operate in a quiescent "spot mode" and in a noisy "plume mode" in which plasma instabilities generate erosive energetic ions. The onset of the plume mode in hollow cathodes has been defined historically as when the keeper voltage oscillation values exceed 5 Vpp (peak-to-peak). Using a LaB6 hollow cathode in a vacuum chamber setup that simulates operation in ion and Hall thrusters, a set of emissive and Langmuir probes have been used to investigate the plasma properties associated with plume mode onset as a function of discharge current and gas flow rate. We find that the plume mode onset occurs at even less than 2 Vpp of the keeper voltage for the 5–75 A hollow cathode investigated here and starts at higher gas flow rates than expected from the traditional 5 Vpp metric used by those in the field. Mode competition and coupling between three different instabilities observed in the near-cathode plume affect the overall plasma oscillation levels that are correlated to energetic ion production. We find that the plasma oscillation levels measured by in situ plasma diagnostics are more indicative of the presence of oscillations and the generation of energetic ions than indirect keeper voltage measurements. [ABSTRACT FROM AUTHOR]

The unstable plume mode of hollow cathodes should be avoided in practical applications because it severely degrades the overall cathode lifetime. In this study, we investigate the spot-plume transition and plasma stability characteristics of an unused segmented lanthanum hexaboride emitter. The expansion of the unstable plume mode region is observed during a discharge experiment. Subsequently, the segmented emitter is retrieved, the inner surface of the emitter is observed, and the work function on the surface is measured at room temperature. The emitter surface exhibits color variations with oxygen and carbon detection. The downstream edge shows the original purple color and almost no degradation in the work function. The high temperature in this region promotes the desorption of carbon and oxygen. In the spot mode, this region mainly contributes to thermionic electron emission; therefore, the discharge voltage in the spot mode does not change during the discharge experiment. Carbon or carbide is detected in the middle of the axial direction on the emitter surface, where the surface temperature is not sufficiently high to desorb carbon during discharge. Based on the surface analysis results, the dominant substance in the region where carbon is detected was lanthanum carbide. An increase in the work function is indicated in the region, which appears to increase the plasma instability. According to previous studies, an increase in the work function results in a rise in the potential in the emitter, and an increase in the electron temperature in the outside plume region induces the plasma instability. Further investigation is needed to understand the mechanism connecting the rise in the work function and the rise in the electron temperature in the plume region. [ABSTRACT FROM AUTHOR]

Laser Thomson scattering is a minimally intrusive diagnostic technique for determining electron temperature, density, and bulk velocity in plasma systems. Advances in technology have made possible the application of Thomson scattering to electric propulsion-relevant plasma systems, with reported electron number-density detection limits as low as 1 × 10 16 m − 3 , and electron temperatures from one-to-tens eV. However, the implementation of laser Thomson scattering in large vacuum testing facilities, wherein electric propulsion devices are tested, remains a challenge. This work presents the implementation of a laser Thomson scattering system in a large vacuum test facility at the Georgia Tech High Power Electric Propulsion Laboratory. The diagnostic was optimized for maximum light-collection efficiency and ease of re-alignment while the facility is at vacuum. The high light-collection efficiency allowed reduced accumulation times to achieve the target detection limit of 1 × 10 17 m − 3 . The diagnostic is used to measure axial electron property profiles in the near-field plume of a lanthanum hexaboride hollow cathode operating at 25 A on krypton at a background pressure of 1.3 × 10 − 6 Torr—Kr. The diagnostic is quantitatively compared to similar systems in the literature. The resulting axial points, collected from 2 to 8 mm downstream of the cathode keeper orifice, are qualitatively and quantitatively compared with simulations and experimental measurements made with electrostatic probes and laser-induced fluorescence. The main quantitative difference between measured values and results is the one to two order of magnitude difference in the peak electron density, being attributed to the relative size and location of the external anode with respect to the cathode keeper. [ABSTRACT FROM AUTHOR]

A layered sodium-ion battery cathode, O3/P3/P2-type NaNi1/3Mn1/3Fe1/3O2, has been systematically investigated by first-principles density functional theory to explore the detailed structural and Na-ion diffusion behavior during desodiation. Our results suggest that the (NaO6) spacing is greatest in the P3 phase and lowest in the O3 phase, with the P2 phase exhibiting intermediate spacing. During desodiation, the intermediate stages have a greater (NaO6) spacing than the initial and final stages. The great (NaO6) spacing facilitates the formation of the P3 phase, resulting in the structural evolution of NaxNi1/3Mn1/3Fe1/3O2 from the O3 to the P3 phase at x ≈ 0.59, finally reaching the O3 structure again at x ≈ 0.12. The electronic structure clearly proves that both Ni and Fe are active in O3/P3/P2-type NaxNi1/3Mn1/3Fe1/3O2. Ni2+ is oxidized to Ni3+ as Na content decreases from x = 1 to x = 0.66, then further oxidized to Ni4+ at x = 0.33, and finally, Fe3+ → Fe4+ oxidation occurs at x = 0. In the Na ion diffusion behavior, the order of the barrier is O3 (0.82 eV) > P2 (0.53 eV) > P3 (0.35 eV) at the initial stage, whereas it is O3 (0.53 eV) > P3 (0.21 eV) > P2 (0.16 eV) at a highly desodiated stage. The former can be traced back to the (NaO6) spacing, but the latter is related to the different Na sites. Our results thus provide a factor of the structural evolution and Na ion diffusion barrier by considering (NaO6) width and Na site changes during desodiation. [ABSTRACT FROM AUTHOR]

The Air-breathing Microwave Plasma CAThode (AMPCAT) has been developed for air-breathing electric propulsion in very-low Earth orbit. In this study, the standalone AMPCAT plasma characteristics are analyzed by means of several diagnostic tools and operation on xenon is compared to a conventional hollow cathode. A transition of AMPCAT extracted current from a lower (< 0.1 A) to higher-current (> --> 0.5 A) mode, triggered by increasing the negative cathode bias voltage, is accompanied by a significant rise in internal electron density and external electron temperature. The AMPCAT is coupled with a cylindrical Hall thruster in the 100–300 W power-level running on 0.5–0.7 mg/s of xenon, and the thrust is directly measured for cathode operation with both xenon and air. Stable thruster operation is demonstrated for the AMPCAT running on both propellants. For xenon, the performance is compared to a hollow cathode, which reveals matching discharge current profiles but a significantly higher thrust for the AMPCAT at low discharge voltages, approximately two times higher at 200 V. Langmuir probe measurements highlight a 30–40 V lower plasma potential in the cathode vicinity for the AMPCAT with xenon compared to both the hollow cathode and AMPCAT with air. This indicates a significantly improved coupling of cathode electrons to the thruster discharge, yielding an increased degree of ionization. Faraday probe and Wien filter results show that a larger current utilization efficiency drives the observed performance difference at low discharge voltages, rather than a significant change in ion acceleration or plume divergence. [ABSTRACT FROM AUTHOR]

Although two-dimensional (2D) transition metal oxide monolayers have shown potential for applications in metal-ion batteries, the heterostructures of this family are yet to be studied in details for energy storage applications. In this work, we have made the heterostructure by taking half-metallic ferromagnetic 2D transition metal oxide CoO 2 and semiconducting MnO 2 monolayers and demonstrated its potential application as a cathode material in lithium and sodium-ion batteries by performing first-principles calculations using density functional theory approach. We have systematically studied the electronic structure and stability of the MnO 2 / CoO 2 heterostructure. We have carefully examined the adsorption and diffusion behavior of metal ions (lithium and sodium). Our structure has offered a maximum adsorption energy of − 3.84 eV, which is greater than the adsorption energy of individual monolayers. We found that the lowest diffusion barrier is 0.4 eV for lithium ion and 0.32 eV for sodium ion. Also, our system has shown a maximum open circuit voltage of 2.18 V for lithium ion battery and 0.32 V for Na-ion battery. The specific capacity is found to be 584 mAh g − 1 for lithium ion and 529 mAh g − 1 for sodium ion battery. These findings can serve as a proof that the MnO 2 / CoO 2 heterostructure should be considered as a potential cathode for lithium- and sodium-ion batteries. [ABSTRACT FROM AUTHOR]

For plasma window (PW) applications, we developed the cascade arc discharge device with an indirectly heated hollow cathode. The 8-mm channel diameter hollow cathode made of a lanthanum hexaboride (LaB 6) was heated by the C/C composite heater surrounding the cathode to increase the thermionic electron emission. The PW developed successfully separated 2.4 kPa and 16 Pa, and the pressure separation capability was sustained for over 1 h. H- β Stark broadening measurement and the Thomson scattering measurement showed that the electron density and temperature inside the channel reached 10 19 – 10 20 m − 3 and 2.0 eV, respectively. The power balance analysis on the electron thermal energy revealed that the neutral density and temperature inside the channel were as high as 10 23 m − 3 and 4000 K, respectively. The relation between the pressure separation capability and the neutral temperature showed that the flow inside the channel of the PW had the molecular flow feature. The SEM-EDX analysis on the LaB 6 cathode showed that boron diffused to the molybdenum (Mo) shaft during plasma operation, which supported the LaB 6 cathode. Mo shaft became brittle after more than 50 h of operation, exhibiting the necessity of buffer material between the LaB 6 cathode and Mo shaft for long-duration operation. [ABSTRACT FROM AUTHOR]

A long-term sustainable tungsten cathode-solution anode glow discharge (SAGD) source for atomic emission spectrometry was developed for the determination of heavy metal elements. The tungsten cathode of this source was cooled by a compact refrigeration semiconductor, which is simple in design and able to operate at atmospheric pressure for long periods. When the equipment operates at its optimal conditions (75 mA discharge current, 2.0 mm discharge gap, 3.8 mL min−1 flow rate, and solution pH value of 2.0), the detection limits of Ag (338.24 nm), Cd (228.80 nm), Hg (253.66 nm), Pb (368.28 nm), Tl (337.52 nm), and Zn (213.79 nm) were explored, and the values were 0.030, 1.7, 7.2, 17, 0.24, and 25 μg L−1, respectively. The interference of coexisting ions in water, such as K+, Ca2+, Na+, Mg2+, and Li+, on the analytical performance of the solution anode glow discharge-atomic emission spectrometry (SAGD-AES) for Cd, Hg, Pb, and Zn were investigated. The results showed that coexisting metal ions' interferences are insignificant. The SAGD-AES system was successfully applied for analyzing water samples from the Yangtze River and Baixi River, and its accuracy and practicality were verified by comparison with inductively coupled plasma-optical emission spectrometry (ICP-OES) results. [ABSTRACT FROM AUTHOR]

In order to improve the wear and corrosion resistance of Ti6Al4V alloy, a Ti-N compound layer was formed on the alloy by plasma nitriding at a relatively low temperature (750 °C) and within an economical processing duration (4 h), in a mixture of NH3 and N2 gases with varying ratios. The influence of the gas mixture on the microstructure, phase composition, and properties of the Ti-N layer was investigated. The results indicated that the thickness of the nitrided layer achieved in a mixed atmosphere with optimal proportions of NH3 and N2 (with a ratio of 1:2) was substantially greater than that obtained in an atmosphere of pure NH3. This suggests that appropriately increasing the proportion of N2 in the nitriding atmosphere is beneficial for the growth of the nitrided layer. The experiments demonstrated that the formation of the surface nitrided layer significantly enhances the corrosion and wear resistance of the titanium alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] The simultaneous intercalation of protons and Zn2+ ions in aqueous electrolytes presents a significant obstacle to the widespread adoption of aqueous zinc ion batteries (AZIBs) for large-scale use, a challenge that has yet to be overcome. To address this, we have developed a MnO 2 /tetramethylammonium (TMA) superstructure with an enlarged interlayer spacing, designed specifically to control H+/Zn2+ co-intercalation in AZIBs. Within this superstructure, the pre-intercalated TMA+ ions work as spacers to stabilize the layered structure of MnO 2 cathodes and expand the interlayer spacing substantially by 28 % to 0.92 nm. Evidence from in operando pH measurements, in operando synchrotron X-ray diffraction, and X-ray absorption spectroscopy shows that the enlarged interlayer spacing facilitates the diffusion and intercalation of Zn2+ ions (which have a large ionic radius) into the MnO 2 cathodes. This spacing also helps suppress the competing H+ intercalation and the formation of detrimental Zn 4 (OH) 6 SO 4 ·5H 2 O, thereby enhancing the structural stability of MnO 2. As a result, enhanced Zn2+ storage properties, including excellent capacity and long cycle stability, are achieved. [ABSTRACT FROM AUTHOR]

This work is devoted to the study of a negative corona discharge in air at atmospheric pressure. To ignite it, the edge (cathode) –plane (anode) system has been used with interelectrode gap of 10–20 mm long and edge curvature radius of ≈20 μm. For the first time, it has been established that in a certain voltage range, the Trichel pulse mode after ignition becomes unstable and is periodically replaced by the glow discharge mode with a current ≲ 1 μA. It is shown that at the stage preceding the first Trichel pulse, the discharge current is not recorded within measurement error of ±0.2 nA. [ABSTRACT FROM AUTHOR]

In recent years, aqueous zinc-ion batteries (AZIBs) have been rapidly developed and are favored by the public as a future large-scale energy storage system. Manganese-based compounds with multiple valence states and high electrochemical activity have been extensively investigated as cathodes for AZIBs due to their abundant reserves and high theoretical capacity. However, some problems hinder their application in AZIBs, such as low conductivity and sluggish kinetics. Defect engineering has been verified as an effective method to alleviate the above limitations. In this work, manganese oxide with oxygen defects (Od-MnO2) was successfully constructed and characterized by XRD, SEM, XPS, and TEM. Surface oxygen defects increase ion active transfer sites and improve electronic conductivity. Compared with MnO2, Od-MnO2 produced more localized electrons which could improve the electrochemical performance as cathodes for AZIBs. The discharge specific capacity of Od-MnO2 reaches 307.9 mAh g−1 in the first cycle at a current density of 0.1 A g−1 and maintains at 100.5 mAh g−1 at a current density of 10.0 A g−1. After 1000 cycles, the discharge specific capacity can still reach 82.5 mAh g−1 and the capacity retention rate is 82.1%. [ABSTRACT FROM AUTHOR]

The commonly utilized nitriding steel 38CrMoAl is employed for components subjected to low-impact loads but high wear. In this investigation, 38CrMoAl underwent plasma nitrocarburizing using a hollow cathode plasma source, with variations in gas ratios aimed at process optimization. The findings revealed a noteworthy influence of the NH3 to CO2 ratio on the phase composition and properties of the nitrocarburizing layers. Two distinct surface types were observed: one composed of ɛ-Fe2–3(N, C) and γ'-Fe4N and the other consisting of nitrogen-containing martensite with a small quantity of nitride. The surface comprising iron nitride was formed via downslope diffusion, leading to increased surface hardness through nitride formation. Nitrogen-containing martensite was formed via uphill diffusion due to spinodal decomposition, reinforced by mechanisms including fine-grain strengthening, solid-solution strengthening, secondary hardening during tempering, and the pinning effect of metal nitrides precipitated at the grain boundaries. The spinodal structure exhibited superior properties, with a wear rate of 1.26e − 8 mm3/Nm. Thermodynamic calculations confirmed that nitrogen diffusion facilitated spinodal decomposition by expanding the spinodal gap and reducing system energy. This study successfully overcame the performance constraints associated with such nitrided layers, which holds promise for applications to other nitride materials. [ABSTRACT FROM AUTHOR]

Electrostatic–magnetic hybrid ion acceleration has been researched to realize high-thrust density and efficient thrust operations. In this study, a newly designed stagnant ring (SR) was installed in an electrostatic–magnetic hybrid thruster with the nominal anode inner radius of 40 mm to improve the thrust performance, and the effects of SR on the thruster operation of xenon propellant were analyzed. During constant-discharge-voltage operations, the discharge current increased with both electrically conductive (copper) and non-conductive (ceramic) SR materials, yet the thrust increased only with the copper SR, which was equipotential to the anode. At lower values of the radial width (H) of the copper SR, the thrust and discharge current were almost dominated by the propellant flow rate from the anode surface. However, the contribution of the propellant flow rate from the cathode tip on the thrust and discharge current became significant when H ≥ 9 mm. The thrust coefficient in electromagnetic acceleration form exhibited a maximum value at H = 9 mm, whereas that in electrostatic acceleration form monotonically increased when H ranged from 0 to 20 mm. The highest thrust efficiency was obtained at H = 12 mm. The study findings indicate that installing a conductive SR can effectively enhance the thrust performance in electrostatic–magnetic hybrid thrusters. • A stagnant ring was installed in an electrostatic–magnetic hybrid thruster. • Thrust performance was deteriorated with electrically non-conductive stagnant ring. • Thrust performance was improved with electrically conductive stagnant ring. • Propellant from the hollow cathode was utilized for thrust generation. [ABSTRACT FROM AUTHOR]

Orifice Hollow Cathodes are electric devices necessary for the functioning of common plasma thrusters for space applications. Their reliability mainly depends on the success of a spacecraft's mission equipped with electric propulsion. The development of plasma models is crucial in the evaluation of plasma properties within the cathodes that are difficult to measure due to the small dimensions. Many models, based on non-linear systems of plasma equations, have been proposed in the openiterature. These are solved commonly by means of iterative procedures. This paper investigates the possibility of solving them by means of the Particle Swarm Optimization method. The results of the validation tests confirm the expected trends for all the unknowns; the confidence bound of the discharge current as a function of mass flow rate is very narrow (2 ÷ 5) V); moreover, the results match very well the experimental data except at theowest mass flow rate (0.08 mg/s) and discharge current (1A), where the computations underpredict the discharge current to the utmost by 40%. The highest data dispersion regards the plasma density in the emitter region (±20% of the average value) and the wall temperatures (±50 K with respect to the average values) of the orifice and insert; those of the others variables are very tiny. [ABSTRACT FROM AUTHOR]

Hollow cathodes are a common type of vacuum ultraviolet (VUV) light source with a wide range of design and application. We determined the VUV (58.4 nm) intensity distribution of a hollow cathode as a function of current and pressure. Our model describes the intensity distribution of a McPherson 629-like hollow cathode helium plasma within the range of 0.50–1.00 A and 0.50–1.00 Torr as a ring with a center peak. We found that for all pressures and currents considered, the ring emits more VUV light than the center peak. We also found that the center peak has a minimum VUV light emission near 0.9 Torr. [ABSTRACT FROM AUTHOR]

The P2‐type layered transition metal oxide cathodes confront formidable challenges, including irreversible deleterious phase transitions, transition metals migration, and sluggish Na+ diffusion kinetics, which hamper their rapid commercial application in sodium ion batteries (SIB). In this work, an entropy tuning with dual‐site substitution strategy is proposed to address the aforementioned issues. In the tailored [Na0.67Zn0.05]Ni0.22Cu0.06Mn0.66Ti0.01O2 (NZNCMTO) cathodes, the strategic incorporation of Zn ions serves to occupy Na sites, intentionally disrupting the Na/vacancy ordering and establishing a reinforcing "pillar" effect within the layered framework. Furthermore, the substitution of Cu and Ti for Ni and Mn bolsters covalent bonding with the lattice oxygen, thereby impeding the migration of the transition metal ions and leading to a near‐zero strain structural evolution during charge and discharge process. Density functional theory calculations confirmed that entropy‐tuned NZNCMTO substantially lowered the migration energy barrier for Na+ ions diffusion and improved electronic conductivity. Consequently, the NZNCMTO cathode exhibits an impressive high practical capacity of 91.54 mAh g−1 at a high discharge rate of 10 C, along with outstanding cycling stability, maintaining near 100% capacity retention over 500 cycles at a current density of 10 C. This work presents an innovative blueprint for designing high‐performance sodium‐ion battery cathode materials. [ABSTRACT FROM AUTHOR]

Recently, Na2Mn3O7 has greatly attracted the attention and interest of scholars due to its small voltage hysteresis (< 0.05 V) and high theoretical specific capacity. However, its lower capacity retention and electrochemically performance limit its application. This work reports the facile surface coating of Na2Mn3O7 cathode material by electrochemically inert Al2O3 of different mass ratio for sodium ion batteries. The electrochemical test results indicate that the 5 wt% Na2Mn3O7@Al2O3 material exhibits outstanding cyclic stability and rate capability. It displays a prominent specific capacity of 115 mAh g−1 (at a current density of 50 mA g−1, 1.5–4.6 V) and a capacity retention of 61.2% after 50 cycles. A discharge-specific capacity of 52.7 mAh g−1 is also obtained at a high current density of 4C, and most notably, a high discharge-specific capacity of 117.9 mAh g−1 is still maintained when the current density returns to 0.1C. This suggests a superior structural stability of this material. The subsequent cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests also support this point. [ABSTRACT FROM AUTHOR]

A collaborative manipulation strategy of proper heat treatment and self-customized hydrofluoroether-based electrolyte design has been proposed for boosting the sodium-ion storage kinetics of Prussian white cathodes. Improved monoclinic phase stability and electrolyte-cathode compatibility are responsible for an impressive discharge capacity of 148.4 mA h g-1 and excellent electrode reversibility. [ABSTRACT FROM AUTHOR]

[Display omitted] Na superionic conductor (NASICON)-structured Na 4 MnCr(PO 4) 3 (NMCP) possessing unique three-electron transfer process renders admirable energy density for sodium ion batteries (SIBs). However, the current issues like its sluggish Na+ diffusion kinetics, deficient intrinsic conductivity, and unsatisfactory structural stability, hinder its practical application. Herein, a selective replacement of O elements in PO 4 group by Cl anions in the NMCP system was developed to significantly enhance its electrochemical performance. The results affirm that the enhanced performance of Cl doped samples can be attributed to the enlargement of cell size, the creation of Na vacancies and the weakness of Na2 O bond after Cl doping. The as-prepared Na 3.85 □ 0.15 MnCr(PO 3.95 Cl 0.05) 3 /C (NMCPC − 15/C) cathode delivers a high capacity (128.0 mAh/g at 50 mA g−1) and excellent rate performance (73.0 mAh/g at 1000 mA g−1) in contrast to NMCP/C that merely provides 105.2 mAh/g at 50 mA g−1 and reduces to 47.4 mAh/g at 1000 mA g−1. Meanwhile, NMCPC − 15/C shows a capacity retention of 60.7 % at 1000 mA g−1 after 500 cycles, while only 37.1 % for NMCP/C in the same test conditions. Moreover, the satisfactory performance and energy density of NMCPC − 15/C||hard carbon (HC) full cell confirm the potential practicality of NMCPC − 15. Therefore, chloride ions doping into NMCP has practical application prospects in the preparation of high-performance cathode materials and our work also offers new inspiration to apply anion doping strategies in promoting the performance of the other NASICON-structured cathodes for SIBs. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) is utilized to explore the effects of increasing concentrations of vanadium (V) and chromium (Cr) substitution on the discharge of α‐MnO2 cathode in hydrated zinc‐ion batteries (ZIBs). During H+‐intercalation and Zn2+‐intercalation, Cr‐substitution proves to be more effective than V‐substitution in promoting discharge behaviors. Transitioning from Mn0.875Cr0.125O2, Mn0.75Cr0.25O2 to Mn0.625Cr0.375O2 is found to consistently enhance the discharge voltage, along with improved tunnel structure retention and volume expansion suppression. In comparison, the promoting effect of increasing V‐substitution is relatively small at initial discharge stages and leads to degradation at later stages, primarily due to an increased concentration of unstable Mn2+ ion. The superior effect of Cr‐substitution is attributed to the unique atomic and electronic structures of substituted Cr4+ and reduced Cr3+ ions during discharge. These ions serve as active electron acceptors to limit the formation of Mn3+ and Mn2+ ions, and as anchors to stabilize the α‐MnO2 framework and intercalated H+/Zn2+ ions, respectively. Our study highlights fine‐tuning through substitution to enhance the performance of α‐MnO2‐based cathode materials in ZIBs. [ABSTRACT FROM AUTHOR]

The micro-discharge with a hollow cathode and a second anode with different geometries is experimentally and numerically studied. Effects of the second anode on the micro-hollow cathode sustained discharge (MCSD) in helium are investigated. Three kinds of electrodes with different geometries are used as the second anode. The results show that when needles are inserted into the plate to be used as the second anode, the formation of MCSD can be promoted, and MCSD can be obtained at a low cathode current. Moreover, the distribution of needles has an important influence on the formation of MCSD. The cathode breakdown threshold currents for the three cases of the second anode from low to high are as follows: 13 needle-plate, five needle-plate, and plate with no needles. At the same cathode current, a stronger MCSD and a higher second anode current can be obtained when needles are inserted into the second anode plate compared with that when only a plate is used as the second anode. In the present experiment, the volume of MCSD reaches approximately 10 cm3 with an electron density of 4–5 × 1017 m−3 and an electron temperature of 2–3 eV. The experimental and simulated results show that the MCSD originates from cooperative formation between the micro-hollow cathode discharge in the cavity and the discharge around the second anode. Compared with that when only a plate is used as the second anode, when needles are inserted into the second anode, the electric field, electron temperature, and electron production rates near the second anode increase, and a stronger discharge is generated near the second anode. When the needle-plate is used as the second anode, the electron density in both the axial and radial directions in the MCSD region is higher than that when the plate without needles is used as the second anode. Before the formation of MCSD, the electrons generated by the strong discharge near the second anode extend toward the first anode, thus promoting the formation of MCSD. [ABSTRACT FROM AUTHOR]

Broadened hydrogen Balmer lines are observed in a DC glow discharge sustained in Ar–SiH4–N2 gas mixture. This broadening is due to the Doppler frequency shift. H atoms' translational energy distribution is calculated in different positions between the two electrodes of the discharge along the interelectrode axis and in different gas mixtures. Three main components are observed at 0.6(±0.5) eV, 12(±3) eV, 62(±6) eV, 1(±1) eV, 28(±6) eV, and 105(±12) eV for Hα and Hβ, respectively. They correspond to hydrogen dissociation by electron impact producing H(n = 3, 4) atoms and dissociative recombination of the ion in the cathode fall or backscattered fast H atoms on the cathode surface. The density ratio nH2/nAr ranges from 44% to 13% or from 10% to 3% when a = nH/nH2 = 0.01 and 0.1, respectively, in function of the gas mixture. So, large hydrogen density could be due to hydrogen desorption from the wall and cathodes and/or to the gas recirculation within the reactor. A new low energy component is observed in the Hα line profile, when silane and nitrogen concentrations decrease and increase, respectively. It could also be due to the H atom desorbing from the reactor wall or NHx species dissociated by an electron impact within the reactor. [ABSTRACT FROM AUTHOR]

Due to its high energy density, safety and low-cost, zinc ion batteries are considered as one of the alternatives to lithium-ion batteries. The metastable phase VO 2 (B) is a highly sought-after active material due to its high discharge specific capacity, remarkable rate performance, and rapid diffusion kinetics. Herein, VO 2 (B) nanorod materials are prepared using a novel solvothermal approach coupled with mechanical force assistance. The developed VO 2 (B) nanorod synthesized at 200 rpm (V@200 rpm) exhibit a substantial specific capacity of 300 mAh g−1 at 0.1 A g−1, excellent rate capability of 171 mAh g−1 at 2 A g−1 and prolonged cyclic stability (capacity fading rate of 0.025 per cycle after 1000 cycles), providing a straightforward and efficient approach to enhancing the capacity, rate performance, and cycle stability of ZIBs. [ABSTRACT FROM AUTHOR]

Layered oxides, the most commercially promising cathode materials for sodium‐ion batteries (SIBs), are extensively investigated due to their low cost, abundant raw materials, flexible structure, and high capacity. However, although the "rotten" transition metal (TM) migration phenomenon in layered oxide cathode materials leads to unfavorable structure reconstruction, sluggish Na+ diffusion and subsequent performance degradation, TM migration has not been systematically summarized and intensively discussed. Herein, a comprehensive insight into the recent advances of TM migration in layered SIB cathodes is provided, aiming to realize the "magical" utilization of TM migration. First, the negative effects of TM migration on crystal structure and electrochemical properties are discussed. Then, the origin of TM migration is intensively analyzed, and three main mechanisms of the migration are presented, including Cr4+–Cr4+–Cr4+ triplets, Jahn–Teller Fe4+ and Na‐free layers. Additionally, the latest research findings on exploring the origin are fully discussed. Finally, the suppression and utilization of TM migration are discussed, and the further exploration of TM migration and the future directions of suppressing/utilizing TM migration are outlooked. It is believed that this perspective will provide guidelines for the design of high‐performance layered oxide cathodes involving TM migration by turning the "rotten" into the "magical." [ABSTRACT FROM AUTHOR]

Sensitive and high-throughput analysis of trace elements in biological samples with limited volume is of great significance for clinical studies. However, traditional analysis methods often require complex sampling systems, leading to large sample consumption and hindering the rapid detection of trace samples. In this study, we have developed a simple, sensitive and portable droplet cathode glow discharge (DCGD) array for the rapid analysis of micro-volume serum samples. It requires only 10 μL of sample and utilizes a pipette gun for sample introduction, eliminating the need for pumps and valves in conventional solution discharge systems. The triggering and signal acquisition of each droplet sample can be completed within 300 ms, enabling the detection of approximately 240 samples per hour using the droplet array DCGD-OES. Under optimized conditions, the detection limits for Li, Ca and K were determined to be 0.002 mg L−1 (20 pg), 0.078 mg L−1 (780 pg), and 0.005 mg L−1 (50 pg), respectively. The accuracy of the proposed DCGD-OES method was verified through the analysis of two certified standard substances (Seronorm serum L-1 and L-2 RUO) and 20 real human serum samples, and the obtained relative standard deviation (RSD) is approximately 5% (n = 5). The results demonstrate that the low-cost, low-power DCGD-OES offers a promising and reliable approach for the rapid and high-throughput detection of Li, Ca, K and other important elements in volume-limited serum samples. [ABSTRACT FROM AUTHOR]

When a hot arc spot has just formed on the cathode surface, e.g. in the course of arc ignition on a cold cathode, a significant part of the current still flows in the glow-discharge mode to the cold surface outside the spot. The near-cathode voltage continues to be high at all points of the cathode surface. The mean free path for collisions between the atoms and the ions within the plasma ball near the spot is comparable to, or exceeds, the thickness of the ionization layer, which is a part of the near-cathode non-equilibrium layer where the ion current to the cathode is generated. The evaluation of the ion current to the cathode surface under such conditions is revisited. A fluid description of the ion motion in the ionization layer is combined with a kinetic description of the atom motion. The resulting problem admits a simple analytical solution. Formulas for the evaluation of the ion current to the cathode for a wide range of conditions are derived and the possibilities of using these formulas to improve the accuracy of existing methods for modeling high-pressure arc discharges in relation to glow-to-arc transitions are discussed. [ABSTRACT FROM AUTHOR]

The development of a high specific capacity and stable vanadium-based cathode material is very attractive for aqueous zinc-ion batteries (ZIBs). Herein, an in situ electrochemically oxidized cathode is fabricated based on a V2O3@MXene cathode for Zn-ion storage. V2O3@MXene undergoes a phase transition to Zn3(OH)2V2O7·2H2O and ZnyVOz on the first charge, thus allowing for the subsequent insertion/de-insertion of zinc ions, which can be regulated by the amount of H2O in the electrolyte. The MXene in the composite was also beneficial to electron transfer and cycling stability. V2O3@MXene delivered a high capacity of 450 mA h g−1 at 0.2 A g−1, ultra-high-rate performance and cycling stability as well as high energy density. [ABSTRACT FROM AUTHOR]

LiFe1−xMnxPO4 with elevated energy density is becoming the next-generation olivine-type cathode. However, its long cycling stability and delivered capacities are far from perfect, chiefly induced by its intrinsically poor ionic/electrical conductivities, sluggish electrode kinetics and notable Jahn–Teller effects upon charge/discharge cycles. Aimed at overcoming these barriers, we herein propose an efficient synergistic fluorine (F)/indium (In) dual doping strategy. As confirmed from the XRD Rietveld refinement results, the doped electronegative F can interact with Mn, thereby shortening Mn–O bond lengths, strengthening the covalent bonding nature and inhibiting the Jahn–Teller distortion/Mn dissolution, whereas the In doping helps to increase the electronic conductivity of particle cathodes, and opens up the crystal lattice spacing for expediting Li+ diffusion. As a proof-of-concept demonstration, the developed F/In-doped LiFe0.5Mn0.5PO4 cathodes exhibit less adverse phase variations, showing a maximum output capacity of 158.5 mA h g−1 at 0.1C, a capacity retention ratio over 86.7% after 500 cycles, and a markedly improved Mn discharge plateau capacity and capacity retention rate (at 2C). This work may not only shed new light on understanding the anion/cation co-doping effects for LiFe1−xMnxPO4, but also offer an applicable concept to design other high-energy-density electrode species. [ABSTRACT FROM AUTHOR]

Using high-speed photography and shadow photography, the structure of the glow and the microstructure of the spark discharge in a 1.5 mm long "pin(cathode)-plane" gap in air in the pressure range from 300 to 760 Torr has been studied. The presence of a micro channel structure of the discharge in the indicated pressure range was established—the discharge is a aggregation of a large number of micron-diameter channels. It is shown that with decreasing pressure, the evolution of the microstructure and glow of the discharge lags behind the onset of breakdown, however, their morphology retains similarity at different pressures. [ABSTRACT FROM AUTHOR]

This study presents the synthesis and electrochemical evaluation of nitrogen-doped vanadium oxide (N−V2O3/C) as a cathode material for aqueous zinc-ion batteries (AZIBs), using a hydrothermal method. Compared to undoped V2O3/C, N−V2O3/C exhibits enhanced electrical conductivity, capacity, and electrochemical kinetics, attributed to the incorporation of pyridinic and pyrrolic nitrogen. The initial charge–discharge cycles indicate phase transitions to amorphous vanadium oxides, enhancing conductivity. N−V2O3/C shows a high specific capacity of 168.4 mAh g−1 at 10 A g−1 and remarkable reversibility, highlighted by the transient existence of intermediate species during cycling. Optimal electrochemical performance is achieved with a vanadium-to-nitrogen molar ratio of 2:3, indicating the significant impact of the nitrogen doping concentration on the material's efficiency. This work underscores the potential of N−V2O3/C as a superior cathode material for AZIBs. [ABSTRACT FROM AUTHOR]

In order to determine metal ions in aqueous solution, a millisecond pulsed solution cathode glow discharge (SCGD) source coupled with a portable spectrometer was developed for atomic emission spectrometry (AES). The millisecond pulsed SCGD source was operated with two high-voltage DC power supplies and a high-voltage pulse switch, specifically boosting the analyte excitation and sustain the glow discharge. The method to excite the plasma discharge contrasts with traditional approaches that employ a single power source. The influence of operating parameters, including pulsed voltage, pulsed frequency, duty ratio, and sample flow rate, were optimized to construct a system having good stability and improved excitation of metal ions. The optimum detection limits for Na, K, Li, Mg, Ag, Cs, Rb, and Sr were 0.17, 0.32, 0.38, 0.50, 2.65, 1.30, 0.22, and 74.02 µg·L−1, respectively. Furthermore, mountain spring, Yangtze River, and reservoir water were spiked with Ag, Rb, and Cs; the recoveries ranged from 105% to 106%, 106% to 107%, and 107% to 108% indicating that the developed system has favorable analytical performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Improving the bond energy of TM O bonds (especially that of Mn O bonds) and suppresses the formation of O O bonds. • Delaying the P2-O2 phase transition voltage from 4.2 to 4.4 V. • The Na 0.67 Ni 0.23 Cu 0.1 Mn 0.67 O 2 cathode retained specific capacity of 69.4 mAh/g (2C) even after 500 cycles. P2-type Na 0.67 Ni 0.33 Mn 0.67 O 2 has attracted considerable attraction as a cathode material for sodium-ion batteries owing to its high operating voltage and theoretical specific capacity. However, when the charging voltage is higher than 4.2 V, the Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode undergoes a detrimental irreversible phase transition of P2-O2, leading to a drastic decrease in specific capacity. To address this challenge, we implemented a Cu-doping strategy (Na 0.67 Ni 0.23 Cu 0.1 Mn 0.67 O 2) in this work to stabilize the structure of the transition metal layer. The stabilization strategy involved reinforcing the transition metal–oxygen (TM O) bonds, particularly the Mn O bond and inhibiting interlayer slip during deep desodiation. As a result, the irreversible phase transition voltage is delayed, with the threshold voltage increasing from 4.2 to 4.4 V. Ex-situ X-ray diffraction measurements revealed that the Na 0.67 Ni 0.23 Cu 0.1 Mn 0.67 O 2 cathode maintains the P2 phase within the voltage window of 2.5–4.3 V, whereas the P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode transforms entirely into O2-type Na 0.67 Ni 0.33 Mn 0.67 O 2 when the voltage exceeds 4.3 V. Furthermore, absolute P2-O2 phase transition of the Na 0.67 Ni 0.23 Cu 0.1 Mn 0.67 O 2 cathode occurred at 4.6 V, indicating that Cu2+ doping enhances the stability of the layer structure and increases the threshold voltage. The resulting Na 0.67 Ni 0.23 Cu 0.1 Mn 0.67 O 2 cathode exhibited superior electrochemical properties, demonstrating an initial reversible specific capacity of 89.1 mAh/g at a rate of 2C (360 mA g−1) and retaining more than 78 % of its capacity after 500 cycles. [ABSTRACT FROM AUTHOR]

We present a comparative study of electron density obtained in a low-temperature plasma by the cutoff probe and compare the results with data from both the hairpin and the Langmuir probes. The measurements with different probes were conducted in a DC discharge generated by an iron hollow cathode under identical experimental conditions. This comparative analysis provides insight into the reliability and consistency of electron density measurements across different probe types in this specific experimental setup. The information acquired from the cutoff and hairpin probes enables electron density measurements within the frequency range limitations of the instruments. Measurements of electron density are performed in a mixture of argon and oxygen at a low pressure of 5 Pa, in dependence on the discharge current and Ar:O2 mixture ratio. A qualitative discussion of the obtained results is provided. [ABSTRACT FROM AUTHOR]

Nickel oxide (NiO1+δ) is a versatile material used in various fields such as optoelectronics, spintronics, electrochemistry, and catalysis which is prepared with a wide range of deposition methods. Herein, for the deposition of NiO1+δ films, the reactive gas flow sputtering (GFS) process using a metallic Ni hollow cathode is developed. This technique is distinct and has numerous advantages compared to conventional sputtering methods. The NiO1+δ films are sputtered at low temperatures (100 ºC) for various oxygen partial pressures during the GFS process. Additionally, Cu‐incorporated NiO1+δ (CuxNi1−xO1+δ) films are obtained with 5 and 8 at% Cu. The thin films of NiO1+δ are characterized and evaluated as a hole‐transporting layer (HTL) in perovskite solar cells (PSCs). The NiO1+δ devices are benchmarked against state‐of‐the‐art self‐assembled monolayers (SAM) ([2‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (also known as MeO2PACz)‐based PSCs. The best‐performing NiO1+δ PSC achieves an efficiency (η) of ≈16% without a passivation layer at the HTL interface and demonstrates better operational stability compared to the SAM device. The findings suggest that further optimization of GFS NiO1+δ devices can lead to higher‐performing and more stable PSCs. [ABSTRACT FROM AUTHOR]

Aqueous zinc ion batteries (AZIBs) show great prospects in large‐scale energy storage applications, whereas this technology suffers from the lack of cathode materials with high capacity and stability. Here, a cathode material of SbO2 nanoparticles decorated onto the surface of K0.43V6O13 nanobelt is presented. The SbO2 is disclosed as proton‐phile and zinc‐phobic, which thus favors H+ intercalation. In consequence, the increase of H+ intercalation can offset the lattice shrinkage caused by Zn2+ intercalation, and contribute to excellent cyclic stability of the battery. Finally, SbO2/K0.43V6O13 delivers a reversible capacity of 414.2 mAh g−1 at 1 A g−1 after 1000 cycles with a retention of 103%, and 223.5 mAh g−1 at 20 A g−1 after 20 000 cycles with a retention of 89.3%, showing long cycling life at both low current and high current densities. This study provides new insights into the effecting factors for the performance of AZIBs cathode and an effective strategy to improve its stability. [ABSTRACT FROM AUTHOR]

Chemical presodiation (CP) is an effective strategy to enhance energy density of sodium ion batteries. However, the sodiation reagents reported so far are basically polycyclic aromatic hydrocarbons (PAHs) wth low reductive potential (~0.1 V vs. Na+/Na), which could easily cause over‐sodiation and structural deterioration of the presodiated cathodes. In this work, Aromatic ketones (AKs) are rationally designed as mild presodiating reagents by introducing a carbonyl group (C=O) into PAHs to balance the conjugated and inductive effect. As the representatives, two compounds 9‐Fluorenoneb (9‐FN) and Benzophenone (BP) manifest favorable equilibrium potential of 1.55 V and 1.07 V (vs. Na+/Na), respectively. Note that 9‐FN demonstrates versatile presodiating capability toward multiple Na uptake hosts (tunneled Na0.44MnO2, layered Na0.67Ni0.33Mn0.67O2, polyanionic Na4Fe2.91(PO4)2P2O7, Na3V2(PO4)3 and Na3V2(PO4)2F3), enabling greatly improved initial charging capacity of the cathode to balance the irrevisible capacity of the anode. Our results indicate that the Aromatic ketones are competitive presodiating cathodic reagents for high‐performance sodium‐ion batteries, and will inspire more studies and application attempts in the future. [ABSTRACT FROM AUTHOR]

High‐efficacy recycling of spent lithium cobalt oxide (LiCoO2) batteries is one of the key tasks in realizing a global resource security strategy due to the rareness of lithium (Li) and cobalt (Co) resources. However, it is of great significance to develop the innovative recycle methods for spent LiCoO2, simultaneously realizing the efficient recovery of valuable elements and the regeneration of high‐performance LiCoO2. Herein, a novel strategy of regenerating LiCoO2 cathode is proposed, which involves the preparation of micro‐spherical aluminum (Al)‐doped lithium‐lacked precursor (Li2xCo1−x−yAl2/3yCO3, remarked as "PLCAC") via ammonium bicarbonate coprecipitation. The comprehensive conditions affecting particle growth kinetics, morphology and particle size the has been investigated in detail by physical characterizations and electrochemical measurements. And the optimized Al‐doped LiCoO2 materials with high‐density sphericity (LiCo1−zAlzO2, remarked as "LCAO") shows a high initial specific capacity of 161 mAh g−1 at 0.1 C and excellent capacity retention of 99.5 % within 100 cycles at 1 C in the voltage range of 2.8 to 4.3 V. Our work provides valuable insights into the featured design of LiCoO2 precursors and cathode materials from spent LiCoO2 batteries, potentially guaranteeing the high‐efficacy recycling and utilization of strategic resources. [ABSTRACT FROM AUTHOR]

Li-rich manganese-based oxide (LRMO) cathode materials are considered to be one of the most promising candidates for next-generation lithium-ion batteries (LIBs) because of their high specific capacity (250 mAh g−1) and low cost. However, the inevitable irreversible structural transformation during cycling leads to large irreversible capacity loss, poor rate performance, energy decay, voltage decay, etc. Based on the recent research into LRMO for LIBs, this review highlights the research progress of LRMO in terms of crystal structure, charging/discharging mechanism investigations, and the prospects of the solution of current key problems. Meanwhile, this review summarizes the specific modification strategies and their merits and demerits, i.e., surface coating, elemental doping, micro/nano structural design, introduction of high entropy, etc. Further, the future development trend and business prospect of LRMO are presented and discussed, which may inspire researchers to create more opportunities and new ideas for the future development of LRMO for LIBs with high energy density and an extended lifespan. [ABSTRACT FROM AUTHOR]

Schematic illustration of the developed strategy of the P 2/O3-NLiFMNb material. In this work, we adopted a simple Li&Nb co-doping modification method to modify the layered oxide cathode material for sodium-ion batteries, achieving dual modification effects of structural control and surface modification. Compared to the pristine, the modified material exhibits excellent cycling stability and rate performance. [Display omitted] Layered sodium iron manganese oxide cathodes have attracted great interest owing to their high specific capacity and cost-effective metal resources, while the detrimental phase transitions and surface structural degradation severely limit their commercial applications. In this work, the bulk and surface structure stability of a P 2-Na 0.67 Fe 0.5 Mn 0.5 O 2 cathode can be synergically enhanced by a one-step Li/Nb co-doping strategy. Structural characterizations reveal that Li doping promotes the formation of P 2/O3 biphasic structure and makes the unfavorable P 2-OP4 phase transition convert into a smooth solid-solution reaction. Nb doping enhances the mobility of sodium ions and forms strong Nb-O bonds, thereby enhancing the stability of the TMO 2 layer structure. In particular, the Nb element induces the surface reorganization of an atomic-scale NaNbO 3 coating layer, which could effectively prevent the dissolution of metals and surface side reactions. The synergistic mechanism of enhanced electrochemical performance is proved by multiple characterizations during cycling. As a result, the as-prepared Na 0.67 Li 0.1 Fe 0.5 Mn 0.38 Nb 0.02 O 2 exhibits improved capacity retention of 85.4 % than raw material (45.7 %) after 100 cycles at 0.5C (1C = 174 mA g−1) within 2.0–4.0 V. This co-regulating strategy provides a promising approach to designing highly stable sodium-ion battery cathodes. Furthermore, a full cell of Na 0.67 Li 0.1 Fe 0.5 Mn 0.38 Nb 0.02 O 2 with hard carbon displays excellent cycling stability (85.1 % capacity retention after 100 cycles), making its commercial operation possible. This synergistic strategy of biphasic structure and surface reorganization is a critical route to accelerate the application of layer oxide cathodes. [ABSTRACT FROM AUTHOR]

This paper presents spatially resolved laser Thomson scattering measurements in a cathode presheath and describes a new approximation for the electric field at the plasma-sheath boundary that accounts for collisional and ionization effects. The approximation is derived from a 1D sheath model using asymptotic theory, and the approximation is validated against the exact solution of the 1D model. The approximation of the electric field at the plasma-sheath boundary is examined with experimentally measured profiles of electron properties in the cathode presheath and negative glow of a glow discharge. The measurements are made with a noninvasive laser Thomson scattering system applied to a 20 kV pulsed plasma with an electrode gap of 26.53 mm at neutral pressures of 2, 2.5, and 25 Torr for argon, krypton, and helium, respectively. Peak electron densities for the He, Ar, and Kr plasmas are around 9 × 1018, 2.4 × 1019, and 7.5 × 1019 m−3, respectively. For all the gases, the electrons in the negative glow are approximately isothermal at electron temperatures between 1 and 2 eV, and for He and Ar, the electrons were not isothermal in the cathode presheath. The electron density profile in the cathode presheath was nonmonotonic, and calculations of the ionization rate indicate that a sharp increase in the ionization rate may produce a nonmonotonic density profile in the cathode presheath. The insights gained from spatially-resolved noninvasive measurements of electron properties in a cathode sheath reveal the need for more detailed cathode sheath models. [ABSTRACT FROM AUTHOR]

We successfully synthesized a series of O3‐type NaNi1/3Fe1/3Mn1/3−xZrxO2 (x = 0, 0.01, 0.02, 0.04) cathode materials by the solid‐state reaction method. Energy dispersion spectroscopy, X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy results confirmed the successful incorporation of Zr elements into the lattice to substitute Mn. Due to the introduction of Zr4+, the crystal structure modulation of O3‐NaNi1/3Fe1/3Mn1/3O2 has been realized. By increasing the Zr4+ content, the width of the sodium diffusion layer expands, thereby facilitating the diffusion of sodium ions. Consequently, the material exhibits a remarkable enhancement in high‐rate capability. At the same time, increasing the Zr4+ content results in a notable decrease in both the average bond length of TM−O and the thickness of the TMO6 octahedron in the transition metal layer, resulting in a significant improvement in the cycling performance and structural stability of the cathode material. Additionally, the in‐situ XRD results demonstrate that the optimized cathode composition of O3‐NaNi1/3Fe1/3Mn1/3–0.02Zr0.02O2 (NFMZ2) undergoes a reversible phase transition of O3 → O3 + P3 → P3 → O3 + P3 → O3 during the charge–discharge process. [ABSTRACT FROM AUTHOR]

In this study, the authors investigate the erosive effects of iodine plasma on molybdenum. By exposing molybdenum samples to three different test cases of iodine vapor, iodine plasma, and argon plasma, the plasma enhancement of erosion was characterized. A roughly exponential behavior with respect to temperature was found in iodine plasma at hollow cathode conditions and erosion rates as high as 70.1 ± 7.7 μm/h. Despite an oxygen content of <1%, evidence of oxidation was found in all test cases. Behavior consistent with preferential oxidation based on grain orientation was found in the iodine test cases. [ABSTRACT FROM AUTHOR]

A statistical analysis is conducted to identify which physically relevant non-dimensional parameters influence the total (neutral, ion, and electron) static pressure inside thermionic orificed hollow cathodes. It is critical to uncover and order the importance of the physical mechanisms that affect the pressure inside hollow cathodes because it influences the plasma attachment length, the electron temperature, and the sheath potential. These plasma parameters, in turn, affect the emitter lifetime. A principal component analysis of total pressure data obtained from the literature reveals that four non-dimensional variables can account for most of the variation in the total-to-magnetic pressure ratio over five orders of magnitude. The relevant variables are identified with a backward stepwise selection process and an exhaustive grid search and include, by order of importance: the gasdynamic-to-magnetic pressure ratio, the ratio of the mass flow rate to the discharge current, the orifice-to-insert diameter ratio, and the orifice Reynolds number. It is also shown, using various models and regression analyses, that empirical, Poiseuille, or isentropic flow models should not be used for predictive cathode design work. The data-driven study suggests that, while viscous effects may be important, the variation in those effects between cathodes is negligible compared to the effects of the modification of the gas constant due to the plasma, the transitional flow, the flux of heavy species on the orifice plate, and the Lorentz force. [ABSTRACT FROM AUTHOR]

Low‐temperature vanadium‐based zinc ion batteries (LT‐VZIBs) have attracted much attention in recent years due to their excellent theoretical specific capacities, low cost, and electrochemical structural stability. However, low working temperature surrounding often results in retarded ion transport not only in the frozen aqueous electrolyte, but also at/across the cathode/electrolyte interface and inside cathode interior, significantly limiting the performance of LT‐VZIBs for practical applications. In this review, a variety of strategies to solve these issues, mainly including cathode interface/bulk structure engineering and electrolyte optimizations, are categorially discussed and systematically summarized from the design principles to in‐depth characterizations and mechanisms. In the end, several issues about future research directions and advancements in characterization tools are prospected, aiming to facilitate the scientific and commercial development of LT‐VZIBs. [ABSTRACT FROM AUTHOR]

The sodium extraction/insertion in layered transition‐metal oxide (TMO) cathode materials are typically accompanied by slab sliding and lattice changes, leading to microstructure destruction and capacity decay. Herein, negative lattice expansion is observed in an O3 type Ni‐based layered cathode of Na0.9Ni0.32Zn0.08Fe0.1Mn0.3Ti0.2O2 upon Na+ extraction. It is attributed to the weak Zn2+−O2− orbital hybridization and increased electron density of the surrounding oxygen for reinforced interlayer O−O repulsive force. This enables gliding of TMO slabs for the intergrowth phase transition of P3→OP2 to alleviate lattice strain with moderate lattice shrinkage, which exhibits general interslab spacings and volume changes as low as 2.4 % and 1.9 %, respectively. The strong Ti−O bonds accommodate the internal distortion of TMO6 octahedra due to the flexibility of TiO6 octahedra during cycling. These endow a high specific capacity of 144.9 mAh g−1 and excellent cycling performance of pouch‐type sodium‐ion batteries with 93 % capacity retention after 3600 cycles. [ABSTRACT FROM AUTHOR]

P2-Na0.67Ni0.33Mn0.67O2 (NNMO) is regarded as a promising cathode candidate for sodium-ion batteries due to its high energy density. However, the electrochemical performance is hindered by Na+/vacancy order, irreversible P2–O2 phase transition at high voltage (>4.2 V), and harmful oxygen evolution. Herein, a synergetic Zn and Ti co-incorporation tactic is proposed for designing a Na0.67Ni0.29Zn0.04Mn0.63Ti0.04O2 (NNZMTO) cathode to overcome the above-mentioned challenges. First, the incorporated Ti heteroatom could break down Na+/vacancy order of NNMO by taking advantage of a similar ionic radius and substantially different Fermi levels with host Mn atom. Subsequently, the introduced Zn heteroatom could induce local Na–O–Zn configurations, buffer interlayer O2−–O2− electrostatic repulsion, as well as inhibit unfavorable phase transition. Moreover, the d10 band of Zn is lower than the oxygen states, and the Zn behaves like an s/p metal with oxygen, thus avoiding O2 release. Notably, in comparison with highly oxidized (Ni4+/Mn4+O6)δ− octahedron, the partial Na+ for charge neutrality in alkali metal layers could be well maintained in the as-designed (Zn2+/Ti4+O6)δ′−, which could be served as "pillars" to avoid layer gliding and structural collapse in the c-direction. As a result, an excellent electrochemical performance with high specific capacity of 90.9 mA h g−1 at 7 C could be retained for NNZMTO thanks to the synergetic effect from Ti and Zn incorporation. This study provides deep insights for designing superior layered cathode via conducting a rational cations co-incorporation strategy. [ABSTRACT FROM AUTHOR]

Aqueous zinc ion batteries (AZIBs) are garnering significant attention as a promising energy storage system owing to their high safety, low cost, and environmental friendliness. Among various cathode materials, one-dimensional (1D) tunnel vanadium-based cathode materials have been extensively studied for their excellent electrochemical performance. In this mini review, we present a summary of recent research progress on 1D tunnel VO2(B) cathode materials for AZIBs. Specifically, we delve into their crystal structure, morphology, and charge–discharge mechanism, and the impact of various synthesis and modification methods on their morphology and electrochemical performance. Additionally, we provide insights into key strategies employed to enhance the electrochemical performance of VO2(B). Furthermore, we underscore both the opportunities and challenges in this domain while also discussing the future prospects for the development of 1D tunnel VO2(B) cathode materials in AZIBs. [ABSTRACT FROM AUTHOR]

The high‐entropy approach is applied to monoclinic Prussian White (PW) Na‐ion cathodes to address the issue of unfavorable multilevel phase transitions upon electrochemical cycling, leading to poor stability and capacity decay. A series of Mn‐based samples with up to six metal species sharing the N‐coordinated positions was synthesized. The material of composition Na1.65Mn0.4Fe0.12Ni0.12Cu0.12Co0.12Cd0.12[Fe(CN)6]0.92□0.08 ⋅ 1.09H2O was found to exhibit superior cyclability over medium/low‐entropy and conventional single‐metal PWs. We also report, to our knowledge for the first time, that a high‐symmetry crystal structure may be advantageous for high‐entropy PWs during battery operation. Computational comparisons of the formation enthalpy demonstrate that the compositionally less complex materials are prone to phase transitions, which negatively affect cycling performance. Based on data from complementary characterization techniques, an intrinsic mechanism for the stability improvement of the disordered PW structure upon Na+ insertion/extraction is proposed, namely the dual effect of suppression of phase transitions and mitigation of gas evolution. [ABSTRACT FROM AUTHOR]