Main Cathode Research Articles

Invited Presentation: On the Frontier of Li Ion Batteries and the Horizon Beyond Them

In this presentation we will review first, the frontier in Li ion battery technology. Starting with current state-of-the-art systems which include graphite anodes and catode materials such as LiCoO2, LiFePO4 or Li[MnNiCo]O2 (around 150-160 mAh/gr), we intend to move further to increase as much as possible the energy density of Li ion batteries, not on the account of safety. If we mention electric-vehicle applications as the most challenging direction of Li ion batteries , indeed in term of safety and cycle life considerations, we can use today only systems with a moderate performance, such as graphite-Li[MnNiCo]O2 or graphite-LiFePO4 batteries. Conventional full EVs powered by battery modules based on these chemistries can drive no more than 150 km between charges. The eectrodes materials that can take us further are silicon for the anode side and 3 types of cathode materials: high voltage LiMn1.5Ni0.5O4 and LiCoPO4 or high capacity Li & Mn rich layered compounds with an initial structure - xLi2MnO3-(1-x)LiMn1/3Ni1/3Co1/3O2. We will discuss which type of silicon electrodes can provide prolonged cycle life. Monolithic Si electrodes with columnar or nano-wire morphology are advantageous. The choice of potential regime and the nature of the electrolyte solutions are critically important in order to obtain really stable reversible Si anodes. LiCoPO4 suffers from severe instability problems in standard electrolyte solutions (based on LiPF6). This can be overcome. However a more severe problem is the practical capacity of these electrodes, that cannot reach more than 120-130 mAh/g (out of 165 mAh/g theoretical). LiMn1.5Ni0.5O4 maybe an excellent electrode material, even in standard electrolyte solutions. A main problem arises in full cells, vs. graphite anodes at elevated temperatures (even at 45 0C), due to transition metal ions dissolution. This phenomenon, even when occuring at a low scale, affects very badely the passivation of graphite electrodes. We will discuss approaches to mitigate these detrimental situations. xLi2MnO3-(1-x)LiMn1/3Ni1/3Co1/3O2 cathodes can really demonstrate very high capacity, approaching 300 mAh/g. It is possible to ensure their reversibility and capacity retention during prolonged cycling. Their main problem is a gradual voltage shift towards lower values during cycling, due to an irreversible phase transition to a spinel type structure. It is hard to see how this everage voltage decay, which is a bulk effect, can be avoided. Being realistic: considering the most advanced electrodes materials, the energy density of Li ion battery technology can be increased beyond the state of the art level by no more than 50%. The use of sulfur as a main cathode material brings with it a better chance to increase the energy density of Li batteries, due to the high theoretical capacity of Li-S electrodes (1675 mAh/g for a full conversion to Li2S). We will discuss the options to develop highly stable Li-S cathodes. However, what may be not less important is to develop anodes suitable for Li-S athodes. Li metal cannot really serve as an anode material in practical rechargeable batteries. The most promising option to close the gap between Li batteries and internal combustion engines is by development of Li-oxygen batteries. The problem is that the moieties formed by reduction of oxygen in the presence of Li ions are too basic and nucleophilic, thus attacking any polar-aprotic solvents that might be relevant for electrolyte solutions in Li-O2 cells. The feith of these systems and their chance to emerge as secondary battery systems will be thoroughly discussed. Another direction beyond the horizon on Li batteries are magnesium batteries. Work in this direction became intensive in recent years. We will review progress, but the way to practicality is still very long. Finally, we will mention the chance of Li ion battery technology to contribute for load leveling applications.

The thrust generated by a T6 ion engine hollow cathode

The thrust produced by a T6 ion engine main discharge hollow cathode was characterized using different propellants with a target-based measurement system, for discharge current values of 5–25A and a wide range of mass flow rates. The calculated values of specific impulse are far in excess of those that could be attributed to the heating of a gas to thermal equilibrium with the walls, as in a resistojet. This would suggest an operation mechanism more similar to that of an arcjet. The main scaling parameter for the specific impulse appears to be the discharge power per unit mass flow rate (specific power).

A Novel Process for Solar Hydrogen Production Based on Water Electrolysis in Alkali Molten Carbonates

High temperature water electrolysis has a tremendous potential in enabling a cost-effective and sustainable production of synthetic fuels like hydrogen by using renewable heat and electricity from concentrating solar thermal (CSP) plants [1]. Most efforts in this research area are currently directed towards investigating solid oxide electrolysis cells (SOECs) based on fuel cell technology [2,3], although this approach is not optimal for integration with CSP plants because of electrolysis temperatures (i.e., above 800°C) significantly exceeding those of most solar heat storage systems. In order to improve thermal matching with current solar thermal fluids, development of electrolysis processes within the 500-600°C range would be a desirable option. In this context, molten salts could be seen as an ideal medium to lower process temperatures with respect to solid oxide electrolyzers since overall ionic conductivity and transport numbers of liquid salts are usually higher than solid-type electrolytes. Recently, alkali molten carbonate salts have gained a return of attention as a promising and attractive electrolyte for electrochemical conversion processes of mineral ores and CO2 gas at moderate temperatures [4,5]. At the same time, water electrolysis in alkali molten carbonates has been recently mentioned as a feasible process [2], although no systematic studies on this process are available in literature. The overall electrolysis reactions can be written as: cathode, H2O+CO2 + 2e = H2+CO3 2- (1)anode, CO3 2- = CO2 +0.5O2 +2e (2) The anode gas mixture made of 33 % O2 + 67% CO2 is ideal for oxy-combustion processes. Thus, a zero CO2 emission system could be realized by integrating a molten carbonate electrolysis with an oxycombustion process. The combined process could enable a CO2 closed-loop recycling scheme with CO2 capture. Part of the post-combustion CO2 could be, in fact, re-injected to the cathode, whereas the excess CO2 could be easily captured.From a mechanistic point of view, the exact cathode reduction reaction is not well understood. Although the cathode reaction can be interpreted in terms of a conventional water reduction process (eq. (1)), there are indications in literature that bicarbonate anions are likely the reactive species rather than dissolved water according to [6]: 2HCO3 - + 2e =H2+2CO3 2- (3) The presence of bicarbonate is possible because, in presence of a water-containing atmosphere, molten carbonates cannot be considered as a pure solvent, but rather as a mixture of three anionic constituents, namely carbonate, bicarbonate and hydroxide ions, according to the following chemical equilibrium: H2O+CO3 2- = HCO3 - + OH- (4) Thermodynamic calculations indicate that bicarbonate concentration is lower than hydroxide, but it is not negligible below 600°C. Initial lab-scale work has confirmed the effective presence of hydrogen as main cathode reaction product in a electrolysis conducted in ternary alkali carbonate eutectic mixture Li2CO3-Na2CO3-K2CO3 (43.5-31.5-25.0 mol %) despite the relatively low values of steady-state current density observed within the 525-600°C range (see Fig.1). Cyclic voltammetry experiments are also underway to study in more detail kinetics and mechanisms of the cathodic reaction, which is an essential aspect for interpreting and modeling the overall electrolysis process. Detailed results of these exploratory investigations will be shown at the time of Conference.

Hydrothermal Synthesis of Nickel Disulfide and Its Application in Thermal Battery

Thermal batteries work at 450-550°C with molten salts as electrolytes, which have high power density and reliability. They are widely applied in military weapons[1] as activating power source. At present, pyrite from natural minerals are the main cathode materials for thermal batteries due to its low cost, fine compatibility with molten electrolytes and stable discharging stages[2]. However, when the battery discharging at large current density (>0.5Acm-2), the discharging time and discharging voltages drop greatly, which will enhance the difficult of the designability of the thermal battery. Compared with FeS2, NiS2 has been less investigated in spite of its smaller electrical resistivity[3] and higher decomposition temperature [ 4]. Hydrothermal method is an efficient way to synthesize NiS2 with high purity and small particle sizes. Compared with other routes such as solvothermal method[5], solid-state reaction[6] or ultrasonic spray pyrolysis[7]method, this method features simple operation and low cost for scaling up. In this work, cubic phase Vaesite has successfully prepared by hydrothermal method via the reactants of NiSO4, S and FeSO4. Fig. 1 shows that the NiS2 particles reuniting together and the average diameter of the synthetic NiS2 is about 2.8μm according to the laser particle analysis. Fig. 2 shows that the synthetic NiS2 is cubic phase vaesite. Fig. 3 shows the polarization cures of the synthetic NiS2 and natural FeS2 single cell thermal batteries. Before 1000As g-1, the resistance of the NiS2 thermal battery is stable and 0.08Ω smaller than that of the natural FeS2 one; after 1000 As g-1, the resistance of the NiS2 thermal battery rising rapidly and at 1300As g-1. The resistance of the NiS2 thermal battery is larger than that of the FeS2 one. The resistivity of NiS2 is smaller than that of the FeS2 [ 3] which will enhance the electrical conductivity of the cathode of the thermal battery. The larger specific surface area contacting with the electrolytes will reduce the contacting resistance and the concentration polarization between the interface of the NiS2 and the electrolytes. As a result, the resistance of the NiS2 thermal battery is smaller than that of the FeS2 thermal battery. When discharging at 0.5 A cm-2 constant current density, the voltage between AB region of the NiS2 thermal battery is 120 mv higher than that of the FeS2 one due to its larger surface contacting with the molten electrolytes. Selecting 1.5 V as cutoff voltage, the specific capacity and power density of the NiS2 thermal battery is 1174 As g-1 and 0.58 Wh g-1 respectively, which are 1.1 and 1.3 times larger than those of the FeS2 thermal batteries.Fig.5 show the pulse current discharging of the thermal batteries. Compared with FeS2, the voltage drops of the NiS2 thermal batteries were 0.05V and 0.08V smaller when 0.5 A cm-2 and 1 A cm-2 were loaded (Fig.4). The small voltage drop and the high discharging voltage is beneficial to improve the reliability and designability of the thermal battery. The NiS2 single cell thermal battery shows better electrochemical performance than that of the natural FeS2 at the condition of large and pulse current density discharging, which offer a better solution for the high power density thermal battery technology. the electrochemical performance of the packed NiS2thermal batteries should be further investigated. Figure Captions Fig.1a , NiS2 SEM images; b, particle distributions of the NiS2 Fig.2. XRD patterns of (a)NiS2(b)Natural FeS2 Fig.3 Polarization of the thermal cells: a, NiS2; b, FeS2. Constant current density: 0.5Acm-2; Pulse current density (0.3s):1Acm-2 Fig.4 Discharge curves of NiS2 and FeS2 thermal batteries under 500°C at 0.5 A cm-2 Fig.5 Pulse current discharging curves of the thermal cells: a, NiS2; b, FeS2. Constant current density: 0.2 A cm-2. AB region pulse current density: 0.5 A cm-2 ; EF region pulse current density: 1 A cm-2 References [1]R. A.Guidotti, P. Masset. J. Power Sources, 161, 1443, (2006)[2]P.J. Masset, R. A.Guidotti.J. Power Sources, 177, 595, (2008)[3] C. I. Pearce, A.D.Pattrick, D. J.Vaughan. Reviews in Mineralogy & Geochemistry, 61, 127, (2006)[4]Patrick J.Masset, R. A.Guidotti. J. Power Sources, 178, 456, (2008)[5]X. F. Qian, Y. D. Li, Y. Xie et al. Materials Chemistry and Physics, 66, 97, (2000)[6] G. J. An, C. G. Liu,Y. D. Hou et al. Materials Letters 62, 2643, (2008)[7]Q.F. Shen, X.F. Zhou, S.Y. Wang. Journal of NanjingNormal University, 8, 59, (2008)

Localized Electrochemical Corrosion Characteristics of Carbon Steel in Seawater

The galvanic and potential distributions of carbon steel immersed in seawater were studied by wire beam electrode (WBE) technique. Results indicated that the corrosion of carbon steel in seawater tended to local corrosion. With immersion time increasing, local corrosion was more and more serious. During the initial immersion period, the top of the coupon near the water surface was main cathode. With the corrosion extended, corrosion products gradually gathered on the surface of the carbon steel. Potential differences between cathode and anode gradually became small. Cathode and anode redistributed on the surface of carbon steel. At last, the top and the bottom were cathode while the middle was anode. The areas of anode first increased and then decreased. The areas of cathode were in contrast.

Effect of the configuration of the discharge chamber of the plasma focus on the neutron yield

Preliminary probe experiments on the Filippov-type plasma focus with the energy E = 70 kJ and a current of about 1 MA show significant stray currents flowing near the insulator. To suppress them and optimize the discharge circuit, the main discharge chamber elements, i.e., the insulator, anode and cathode liner, were changed. As a result, a 30-fold increase in the setup neutron yield to Yn = 5· 1010 neutrons per pulse was detected.

Electrochemical removal of nitrate using ZVI packed bed bipolar electrolytic cell

The present study investigates the performance of the zero valent iron (ZVI, Fe0) packed bed bipolar electrolytic cell for nitrate removal. The packing mixture consists of ZVI as electronically conducting material and silica sand as non-conducting material between main cathode and anode electrodes. In the continuous column experiments for the simulated groundwater (initial nitrate and electrical conductivity of about 30mgL−1 as N and 300μScm−1, respectively), above 99% of nitrate was removed at the applied potential of 600V with the main anode placed on the bottom of reactor. The influx nitrate was converted to ammonia (20% to maximum 60%) and nitrite (always less than 0.5mgL−1 as N in the effluent). The optimum packing ratio (v/v) of silica sand to ZVI was found to be 1:1–2:1. Magnetite was observed on the surface of the used ZVI as corrosion product. The reduction at the lower part of the reactor in acidic condition and adsorption at the upper part of the reactor in alkaline condition are the major mechanism of nitrate removal.

Potential distribution characteristics of mild steel in seawater

Potential distribution of mild steel immersed in seawater for various periods was investigated by SMRE (scanning micro-reference electrode). For the coupons immersed horizontally, the edge was cathode while the middle was anode. When immersed vertically, the top of the coupon was the main cathode. After a period of immersion, the bottom became the main cathode. No matter how the coupons were placed, the composition of corrosion products in the cathodic area was β-FeOOH and Fe3O4 while in the anodic area was mainly γ-FeOOH. Relationship between potential distribution and corrosion products was discussed and the reasons for this phenomenon were analysed.

Realization of High Luminous Efficacy at Low Voltages in the Plasma Display Panel With SrO–MgO Double Layer

We have applied a double protecting layer consisting of SrO and MgO to a plasma display panel. The top MgO layer protects the underlying SrO from contamination by H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O or CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> when exposed to air and enables it to function as the main cathode material after the aging process, which partially removes the MgO layer. We have confirmed that the adoption of a double SrO-MgO layer results in a considerable reduction in driving voltage and improvement in luminous efficacy simultaneously.

Improved plasma uniformity in a discharge system with electron injection

We present the results of experiments leading to improvement in bulk plasma uniformity of a constricted-arc discharge system with electron injection. The steady-state discharge was in argon, at a gas pressure of 0.5 mTorr, and operated with a main discharge voltage between 20 and 100 V and current between 3 and 15 A. The radial plasma distribution was measured with a movable Langmuir probe. We find that geometric modification of the intermediate electrode exit aperture and the main discharge cathode add little to the plasma uniformity. Improved bulk plasma uniformity is observed when a special distributing grid electrode is used and the main discharge voltage is less than 20-30 V. The application of a weakly divergent magnetic field in the region of the intermediate electrode exit aperture decreases the plasma nonuniformity from 20% to 14% over a radial distance of 30 cm. The plasma uniformity was further improved by compensating the magnetic self-field of the injected electron beam by a reverse magnetic field produced with a special electrode compensator. It is shown that an increase in discharge current causes a proportional increase in back current in the distributing electrode. The approach allows a decrease in plasma nonuniformity from 20% to 13% over a radial distance of 30 cm.

Study on Radio Frequency Cathode for Ion Engines

A new cathode with inductively coupled plasma for ion engines was designed and then evaluated experimentally in this study. The fabricated cathode, which named “ICP/C (Inductively Coupled Plasma Cathode)”, employed electromagnetic fields induced by RF (Radio Frequency) current at 13.56 MHz, and had the new ignition method that spark discharge occurred by induced voltage was used. Through the experimental investigations, the new method using “C-shaped” type electrode enabled the ICP/C to ignite instantaneously without other electron source. And the cathode achieved high neutralization performance, which was over 1700 mA of extracted electron current at 80 W of RF input power, and 3.0 sccm of Xe flow rate, when target voltage simulating ion beam was 20 V. Additionally, the application of ICP/C as a main cathode of direct current ion thruster was confirmed. As these results, ICP/C may permit instantaneous ignition and simple handling to ion engines, and it may even allow a longer lifetime of ion engines.

Study of the emission properties of a W-Cs3Sb field-emission cathode

A new field-emission cathode based on the W-Cs2Sb metal-semiconductor system is produced. The emission current of this cathode is one and one-half orders of magnitude higher than that of a tungsten cathode, and the FWHM of the energy spectrum is about 0.3 eV. An energy model of the given emitter is proposed. Using it, one can obtain theoretical values of the main cathode parameters which are in good agreement with the experimental ones.

Overview and research status of the JAXA 150-mN ion engine

The research and development of the JAXA 150-mN ion engine are in progress. The objective of this activity is to establish the ion propulsion technology for future applications, which require high thrust levels, such as orbit raising and deep space exploration. Current efforts are directed to improvement in endurance of the thruster, power conditioner development, and test facility improvement because sufficiently high thruster performance has already been achieved. An endurance test of a main hollow cathode is being conducted. Back sputtering characteristics of a test facility were improved for a coming thruster endurance test. Wide range operation of the thruster, neutralizer characterization tests, and basic study on power processing units were also conducted.

Self-protection functions in direct light-triggered high-power thyristors

Direct light-triggered thyristors with integrated protection functions were fabricated and investigated. It is shown that the simultaneous integration of the light-trigger function and a reliable overvoltage self-protection can be achieved by integrating a diode into the centre of the thyristor. In addition, a dV/dt self-protection function can be integrated by a proper adjustment of the dV/dt capability of the amplifying gates and the main cathode area, ensuring a safe turn-on of the thyristor when a voltage pulse with a dV/dt value exceeding the maximum dV/dt value is applied to the device. Thyristors with different breakdown voltages ranging from 5 to 8kV on 2-, 4- and 5-inch wafers have been realised.

Performance of the Xenon Feed System on Deep Space One

Propulsion for the Deep Space One (DS1) spacecraft is provided by a xenon ion engine. Xenon is stored in a supercritical state and is delivered as a low-pressure gas to the thruster and two cathodes (called the main cathode and neutralizer) by a xenon feed system (XFS). This mission requires tight constraints on thruster performance, which in turn requires separate and very accurate throttling of the thruster and cathode  ows; the DS1 spacecraft is the Ž rst of its type to utilize a xenon ion engine that can be throttled. Flow is regulated separately to the thruster and cathodes to an accuracy of § 3% using three calibrated  ow control devices that are each fed by a dedicated plenum tank. Bang–bang regulators are used to control the set pressures in the plena. The resulting XFS control algorithms are quite complex. The XFS is controlled by a digital control interface unit and the control algorithm for achieving steady-state xenon  ow is presented. The worst-case error in  ow is shown to be less than § 3%, accounting for random and systematic errors. At the time of writing, the individual components are in excellent health and the performance of the XFS is as expected.

Alkali metal cell having main and alternate electrodes

An electrochemical cell including an alkali metal anode and a cathode, one of the anode or cathode being connected to a structure for making electrical connection from a load to the cell, the other of the anode or cathode having main and alternate portions, a main terminal connected to the main anode or cathode portion for making electrical connection between a load and the cell, and an alternate terminal connected to the alternate anode or cathode portion for making electrical connection between a load and the cell, so that the main anode or cathode portion first is discharged with the alternate portion held in reserve, whereupon when the main portion reaches end of life the alternate anode or cathode portion is discharged. The main and alternate anode or cathode portions are insulated from each other, and the anode preferably is of lithium. There is also provided a voltage responsive switch means in combination with the cell and connected electrically between a load and the main and alternate terminals for connecting the main terminal initially to the load and then disconnecting the main terminal and connecting the alternate terminal to the load when the main portion reaches end of life. The cell can be provided with a casing of electrically conductive material with one of the anode or cathode being connected to the casing for making electrical connection to the load through the casing.

亜鉛浸出液の浄液に関する研究 亜ヒ酸，銅イオン，亜鉛末によるコバルト浄液法の反応機構

Cobalt precipitation by zinc dust with co-addition of arsenious oxide and copper ion in a practical operation was simulated by the experiments using a galvanic cell with a diaphragm and this mechanism for removal of cobalt was explained as follows; a galvanic cell was formed between zinc dust and copper particles, which were precipitated first by zinc dust, and cobalt is deposited on copper particles by this galvanic cell and arsenious oxide in a solution accelerated the rate of precipitation of cobalt by co-deposition of As-Co. The anode side reaction of this galvanic cell is Zn=Zn2++2e-and a main cathode reaction is 2H++2e-=H2 (g). Cobalt is difficult to be precipitated on copper without arsenious oxide. The galvanic current between zinc and copper becomes higher by addition of arsenious oxide. The over potential of the cathode reaction sifts the cathode potential to belower potential than the deposition potential of Co-As, and this Co-Aseasily deposits on copper cathode with hydrogen.

Investigations about triggering of coaxial multichannel pseudospark switches

A fundamental problem of pseudospark switches is erosion in the borehole area. One way to reduce erosion is to distribute the current to several discharge channels. Essential for multichannel operation is a reliable ignition of all these channels. The aim of this work was to find out the requirements for a trigger for multichannel pseudospark switches and to develop a suitable trigger device. The investigations were made with a three channel pseudospark switch. The developed trigger is a pulsed hollow cathode discharge with a 3 mA dc-preionization. A trigger voltage of 4 kV results in a current of about 6 A in the hollow cathode of the trigger-section. This hollow cathode discharge causes a trigger current into the hollow cathodes of the pseudospark chambers. The trigger current which is necessary to ignite an equally distributed discharge has to be at least 3 mA into each main switch hollow cathode. A jitter of 2 ns was achieved for the coaxial multichannel pseudospark switch.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The properties of triggered vacuum gaps

The reaction of the trigger plasma of triggered vacuum gaps (TVGs) to the main gap voltage changes with the main gap polarity. The trigger polarity has no influence when the main gap voltage exceeds a certain value. The high current-chopping instability in positive TVG mode is investigated in detail, with the influence of the loop parameters and electrode contamination. In the negative mode, a history effect is found in TVG triggering, associated with the surface condition of the main gap cathode. The trigger delay time in the negative mode depends on the trigger plasma density and the plasma buildup. The general TVG triggering is explained, and the reaction of the trigger plasma to the main gap polarity determines the main-gap polarity dependence of TVG.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A trigger power supply for vacuum arc ion sources

Arc initiation plays a key role in the operation of pulsed metal vapor vacuum arc (MEVVA) ion sources. The favored triggering method in most sources is a surface discharge across an insulator inserted between an auxiliary trigger electrode and the main gap cathode. The trigger power supply must be capable of meeting specific requirements. As part of an ongoing program to develop such a power supply the authors have designed, constructed, and tested several simple units. The most successful of these is a design employing a resonant 1/2-cycle capacitor discharge which generates peak voltages to 10 kV. The maximum current and duration of the output pulse in the present configuration are 40 A and 50 mu s, respectively. The trigger unit has been tested on a MEVVA II ion source equipped with a tungsten cathode. For the trigger pulse parameters given, a misfire rate of >