Journal of Power Sources

Published by Elsevier
The objective of this work was to develop a hydrogen storage module for onboard electrical power sources suitable for use in micro power systems and micro-electro-mechanical systems (MEMS). Hydrogen storage materials were developed as thin-film inks to be compatible with an integrated manufacturing process. Important design aspects were (a) ready activation at sub-atmospheric hydrogen pressure and room temperature and (b) durability, i.e. capable of hundreds of absorption/desorption cycles and resistance to deactivation on exposure to air. Inks with palladium-treated intermetallic hydrogen storage alloys were developed and are shown here to be compatible with a thin-film micro-fabrication process. These hydrogen storage modules absorb hydrogen readily at atmospheric pressure, and the absorption/desorption rates remained fast even after the ink was exposed to air for 47 weeks.
Recently, we have shown silver vanadium phosphorous oxide (Ag(2)VO(2)PO(4), SVPO) to be a promising cathode material for lithium based batteries. Whereas the first reported preparation of SVPO employed an elevated pressure, hydrothermal approach, we report herein a novel ambient pressure synthesis method to prepare SVPO, where our chimie douce preparation is readily scalable and provides material with a smaller, more consistent particle size and higher surface area relative to SVPO prepared via the hydrothermal method. Lithium electrochemical cells utilizing SVPO cathodes made by our new process show improved power capability under constant current and pulse conditions over cells containing cathode from SVPO prepared via the hydrothermal method.
As a part of our on-going study on silver vanadium phosphorous oxides (Ag(x)V(y)O(z)PO(4)), we report here the first study of the electrochemical reduction of a low Ag/V ratio silver vanadium phosphorous oxide, Ag(0.48)VOPO(4)·1.9H(2)O. Reminiscent of Ag(2)VO(2)PO(4) reduction, in-situ formation of silver metal nanoparticles along with an associated increase in conductivity were observed after reduction of Ag(0.48)VOPO(4)·1.9H(2)O with 0.37 electron equivalents. However, in contrast to our lithium / Ag(2)VO(2)PO(4) cells, our lithium / Ag(0.48)VOPO(4)·1.9H(2)O cells displayed an even higher voltage on discharge and a characteristic multi-plateau voltage profile, where vanadium reduction was the first reduction step.
This report details the chemical and associated electrical resistance changes of silver vanadium phosphorous oxide (Ag(2)VO(2)PO(4), SVPO) incurred during electrochemical reduction in a lithium based electrochemical cell over the range of 0 to 4 electrons per formula unit. Specifically the cathode electrical conductivities and associated cell DC resistance and cell AC impedance values vary with the level of reduction, due the changes of the SVPO cathode. Initially, Ag(+) is reduced to Ag(0) (2 electrons per formula unit, or 50% of the calculated theoretical value of 4 electrons per formula unit), accompanied by significant decreases in the cathode electrical resistance, consistent with the formation of an electrically conductive silver metal matrix within the SVPO cathode. As Ag(+) reduction progresses, V(5+) reduction initiates; once the SVPO reduction process progresses to where the reduction of V(5+) to V(4+) is the dominant process, both the cell and cathode electrical resistances then begin to increase. If the discharge then continues to where the dominant cathode reduction process is the reduction of V(4+) to V(3+), the cathode and cell electrical resistances then begin to decrease. The complex cathode electrical resistance pattern exhibited during full cell discharge is an important subject of this study.
Sn based anodes allow for high initial capacities, which however cannot be retained due to the severe mechanical damage that occurs during Li-insertion and de-insertion. To better understand the fracture process during electrochemical cycling three different nanopowders comprised of Sn particles attached on artificial graphite, natural graphite or micro-carbon microbeads were examined. Although an initial capacity of 700 mAh g(-1) was obtained for all Sn-C nanopowders, a significant capacity fade took place with continuous electrochemical cycling. The microstructural changes in the electrodes corresponding to the changes in electrochemical behavior were studied by transmission and scanning electron microscopy. The fragmentation of Sn observed by microscopy correlates with the capacity fade, but this fragmentation and capacity fade can be controlled by controlling the initial microstructure. It was found that there is a dependence of the capacity fade on the Sn particle volume and surface area fraction of Sn on carbon.
In this work Substrate Induced Coagulation (SIC) was used to coat the cathode material LiCoO(2), commonly used in Li-ion batteries, with fine nano-sized particulate titania. Substrate Induced Coagulation is a self-assembled dip-coating process capable of coating different surfaces with fine particulate materials from liquid media. A SIC coating consists of thin and rinse-prove layers of solid particles. An advantage of this dip-coating method is that the method is easy and cheap and that the materials can be handled by standard lab equipment. Here, the SIC coating of titania on LiCoO(2) is followed by a solid-state reaction forming new inorganic layers and a core-shell material, while keeping the content of active battery material high. This titania based coating was designed to confine the reaction of extensively delithiated (charged) LiCoO(2) and the electrolyte. The core-shell materials were characterized by SEM, XPS, XRD and Rietveld analysis.
A sub-atmospheric pressure nickel hydrogen (Ni-H(2)) battery with metal hydride for hydrogen storage is developed for implantable neuroprosthetic devices. Pressure variations during charge and discharge of the cell are analyzed at different states of charge and are found to follow the desorption curve of the pressure composition isotherm (PCI) of the metal hydride. The measured pressure agreed well with the calculated theoretical pressure based on the PCI and is used to predict the state of charge of the battery. Hydrogen equilibration with the metal hydride during charge/discharge cycling is fast when the pressure is in the range from 8 to 13 psia and slower in the range from 6 to 8 psia. The time constant for the slower hydrogen equilibration, 1.37h, is similar to the time constant for oxygen recombination and therefore pressure changes due to different mechanisms are difficult to estimate. The self-discharge rate of the cell with metal hydride is two times lower in comparison to the cell with gaseous hydrogen storage alone and is a result of the lower pressure in the cell when the metal hydride is used.
A low pressure nickel-hydrogen battery using either a metal hydride or gaseous hydrogen for H(2) storage has been developed for use in implantable neuroprosthetic devices. In this paper, pressure variations inside the cell for the gaseous hydrogen version are analyzed and correlated with oxygen evolution side reaction at the end of charging, the recombination of oxygen with hydrogen during charging and a subsequent rest period, and the self-discharge of the nickel electrode. About 70% of the recombination occurred simultaneously with oxygen evolution during charging and the remaining oxygen recombined with hydrogen during the 1(st) hour after charging. Self-discharge of the cell varies linearly with hydrogen pressure at a given state of charge and increased with increasing battery charge levels. The coulometric efficiency calculated based on analysis of the pressure-time data agreed well with the efficiency calculated based on the current-time data. Pressure variations in the battery are simulated accurately to predict coulometric efficiency and the state of charge of the cell, factors of extreme importance for a battery intended for implantation within the human body.
Electrochemical studies of three types of CF(x) (F - Fiber based, C - Petroleum coke based, G - Graphite based) have demonstrated different electrochemical performances types in previous work, with fiber based CF(x) delivering superior performance over those based on petroleum coke and graphite. (13)C and (19)F MAS (Magic Angle Spinning) NMR techniques are employed to identify the atomic/molecular structural factors that might account for differences in electrochemical performance among the different types of CF(x). Small quantitative variations of covalent CF and LiF are noted as a function of discharge and sp(3) bonded carbons are detected in discharged F type of CF(x).
The objective of this work was to demonstrate a micro-fabricated hydrogen storage module for micro-power systems. Hydrogen storage materials were developed as thin-film inks to be compatible with an integrated manufacturing process. Performance and durability of storage modules were evaluated. Further, applications were demonstrated for a nickel-hydrogen battery and a micro-fabricated hydrogen-air PEM fuel cell. The ink making process, in which polymer binders and solvents were added to the palladium-treated alloys, slightly decreased the storage capacities, but had little effect on the activation properties of the treated alloys. After 5000 absorption/desorption cycles under hydrogen, the hydrogen storage capacities of the thin-film inks remained high. Absorption/desorption behavior of the ink was tested in the environment of a new type nickel-hydrogen battery, in which it would in contact with 26wt% KOH solution, and the ink showed no apparent degradation. Storage modules were used as the successfully as hydrogen source for PEM fuel cell.
Two incidents concerning copper contamination associated with uninterruptible power systems (UPS) were observed. Valve regulated lead-acid (VRLA) batteries used in the UPSs for back-up powering were diagnosed as the possible source of the contamination. One of the VRLA batteries from the damaged UPS unit was subjected to overcharge in the laboratory, to simulate the incident. Overcharge currents greater than 10 amperes, coupled with battery temperatures over 60°C, can cause a VRLA battery to release significant amounts of hydrogen sulfide and sulfur dioxide. Under extreme conditions, hazardous levels of hydrogen sulfide could be generated. The authors conclude that the contamination was due to copper sulfide, Cu<sub>2</sub>S, and copper oxide, Cu<sub>2 </sub>O, formed on copper surfaces as a consequence of hydrogen sulfide evolution and the high humidity inside the UPS enclosure resulting from battery venting
The current status of sodium-sulphur technology in CSPL is outlined. 350 W h cells have now been developed with energy densities of 0.36 W h/cc and 0.16 W h/g, and much of the R & D effort is now being directed towards battery design. Because it must be thermally insulated, the shape of the battery and the thickness of the insulation are significant, and it is possible to realise gross battery energy densities of between 0.1 W h/cc and 0.25 W h/cc, volumetric energy density normally being the more critical. These are some three times greater than for conventional lead-acid batteries, and combined with operating characteristics which differ markedly from conventional batteries, they could offer a number of interesting applications in addition to road transport and load levelling.
The various load profile characteristics most commonly encountered in photovoltaic installations are analyzed in conjunction with solar array and battery performance data and used to generate battery specifications with respect to operating characteristics and cycle life requirements. The design of lead-acid batteries for photovoltaic applications is discussed and illustrated with both operating, maintenance, and cycle life data. Other performance characteristics of lead-acid photovoltaic batteries are described including the effects of operating temperature and the correct choice of charging method for various operational requirements.
A cylindrical, pure lead, lead-acid cell was designed specifically for float service applications. Unique design features, including concentric, pure lead, circular grids, provide long life, reduced maintenance and improved safety. In excess of 150 000 cells are currently in use in a variety of Bell System applications. The cylindrical cells are optimally installed in a fiberglass-reinforced, modular battery stand. Evolution of the new cell design from pilot plant to large scale production demonstrated sensitivity of field float behavior to subtle changes in manufacturing processes. Analysis of interrelated float behavior and PbO2 morphologies are discussed.
Rapid battery impedance techniques have become mandatory in most battery management programs. Methods available today use a one-frequency technique at relatively high frequencies 83-90 Hz Huet, F. (1998) for this type of analysis. The results so far demonstrate reasonable accuracy at determining degradation between 0-75% battery capacity Markle, G.J. (1993). However, the same data also indicates a reduced correlation when the capacity of the battery is higher than 80% Noworolski, Z., et al. (2002). According to IEEE 450, any battery below 80% must be replaced. This creates a serious problem since the detection of the replacement boundary is directly in the region where high frequency impedance techniques become least reliable. A possible solution to this problem is to lower the frequency and investigate if better correlation may be attained. This assumption is supported by the literature where Tenno et al. provides experimental evidence for greater correlation at low frequency Tenno, A., et al. (2002). However, this raises a practical dilemma since cells must be tested in reasonable timescales. If several low frequency acquisitions are performed using standard techniques, the timescale for a complete test including modeling calculations would require ∼1 minute per cell. This is approximately 6 times longer then currently available techniques and is not practically feasible. This problem may be resolved by inspecting our initial conditions and assumptions. Physically in combined solid and liquid electrochemical systems, a strong increase in nonlinearity is induced when voltages and currents increase Macdonald, J.R. (1987). However, if we choose the excitation voltage to be less than the thermal voltage, it may be demonstrated that the response will be linear.
Solid-state synthesized LiNi0.5−yMyMn1.5O4 spinels, where M=Fe, Mg, Al, or Cu, and y=0.0–0.4, have been studied as high-voltage cathode materials. Powder X-ray diffraction studies showed that all the substituents displayed a propensity for the 8a tetrahedral site at high concentrations. Cyclic voltammetric studies showed electrochemical activity around 4 V as well as above 4.4 V. While the 4-V activity was related solely to the Mn4+/Mn3+ couple, the 5-V activity was due to the redox reactions of Ni and the other transition metal ions. The co-substituents reduced the 5-V capacity and shifted the redox potentials in the 5-V region to higher values. At high concentrations, the co-substituents tended to occupy the 8a sites, which may lead to a blockage of lithium transport during the charge–discharge processes. LiNi0.4Fe0.1Mn1.5O4 registered the best performance with a first-cycle capacity of 117 mAh/g and 78% capacity retention over 60 cycles. Electrochemical impedance spectroscopic studies showed a decrease in the charge transfer resistance at high deintercalation levels.
Layered Li(Ni0.5−xMn0.5−xM2x′)O2 materials (M′=Co, Al, Ti; x=0, 0.025) were synthesized using a manganese-nickel hydroxide precursor, and the effect of dopants on the electrochemical properties was investigated. Li(Ni0.5Mn0.5)O2 exhibited a discharge capacity of 120 mAh/g in the voltage range of 2.8–4.3 V with a slight capacity fade up to 40 cycles (0.09% per cycle); by doping of 5 mol% Co, Al, and Ti, the discharge capacities increased to 140, 142, and 132 mAh/g, respectively, and almost no capacity fading was observed. The cathode material containing 5 mol% Co had the lowest impedance, 47 Ω cm2, while undoped, Ti-doped, and Al-doped materials had impedance of 64, 62, and 99 Ω cm2, respectively. Unlike the other dopants, cobalt was found to improve the electronic conductivity of the material. Further improvement in the impedance of these materials is needed to meet the requirement for powering hybrid electric vehicle (HEV, <35 Ω cm2). In all materials, structural transformation from a layered to a spinel structure was not observed during electrochemical cycling. Cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) data suggested that Ni and Mn exist as Ni2+ and Mn4+ in the layered structure. Differential scanning calorimetry (DSC) data showed that exothermic peaks of fully charged Li1−y(Ni0.5−xMn0.5−xM2x′)O2 appeared at higher temperature (270–290 °C) than LiNiO2-based cathode materials, which indicates that the thermal stability of Li(Ni0.5−xMn0.5−xM2x′)O2 is better than those of LiNiO2-based cathode materials.
The effects of tin content and annealing temperature on the transformation sequences of Pb–0.08 wt.%Ca–x wt.%Sn supersaturated alloys (with x = 0.6, 1.2 and 2.0%) have been firstly studied from TEM observations and hardness measurements. Secondly, the age-hardening kinetics of these ternary alloys during isothermal holdings have been characterized by electrical resistivity measurements. In particular, it appeared that increase of tin content both delayed the main metallurgical stages and is accompanied by suppression of the first discontinuous reactions of ageing when the Sn/Ca ratio value is above 9. Moreover, the ageing kinetics are accelerated when increasing the annealing temperature because of the solute diffusion activation.
The design of a flow-distribution system for a 0.1 kW Fe/Cr redox flow battery has been based on the application of shunt current calculation model to a 20-cell bipolar system A model to simulate the intra-stack flow distribution has also been proposed. Both shunt-current and flow distribution analysis have yielded a prototype with a 93% current efficiency with an homogenous intrastack flow distribution.
For simulating the full discharged and charged states of nickel–cadmium and nickel–hydrogen batteries, thermodynamic characteristics such as the equilibrium Ee and thermoneutral ET potentials of the cells have been calculated over wide ranges of temperatures (0°–200°C), potassium hydroxide concentrations (0.1–20 mol kg−1) and hydrogen pressures (0.1–500 bar). The effects of non-ideality of the hydrogen gas phase and potassium hydroxide aqueous solution were taken into account by using available thermodynamic and experimental data. The effect of temperature, potassium hydroxide concentration, and hydrogen pressures on Ee and ET have been analyzed.
Fabrication of YSZ films deposited on NiO–samaria-doped ceria (SDC) substrate was studied by the chemical vapor infiltration method (CVI). A NiO–SDC substrate was used as oxygen source. The main mechanism of YSZ growth was electrochemical vapor deposition (EVD), while the contribution of oxygen in the carrier gas increased with increasing NiO content of the substrate above 60.6 mol%. The YSZ film on SDC used as the anode proved effective in obtaining high cell performance. In particular, a YSZ film thickness of 1 μm yielded the highest cell performance in the temperature range from 973 to 1073 K. The CVI method was useful for preparing a dense and strong YSZ film on the complex-shaped NiO–SDC substrate.
Amorphous hydrogen storage alloys Mg0.9Ti0.1Ni1−xPdx (x = 0–0.15) were prepared by mechanical alloying (MA). The electrochemical performances of electrode alloys were studied by cyclic charge–discharge experiment, linear polarization and electrochemical impedance spectroscopy. The capacity retention rate C20th/Cmax of quaternary Mg0.9Ti0.1Ni1−xPdx (x = 0.05, 0.1, 0.15) alloys are 66.2%, 75% and 76.8%, respectively, much higher than that of Mg0.9Ti0.1Ni (31.4%). It was demonstrated that the substitution of Pd for Ni improved the cyclic stability of MgTiNi-based electrode alloy greatly. The partial substitution of Pd for Ni also led to the increase of exchange current density I0, which concluded that the reaction activity on the surface of alloys was effectively improved.
The Li3 − xCoxN (x = 0.2–0.6) system was investigated for use as an anode material for lithium rechargeable cells. The anode performance of this system was evaluated by using Li metal/Li3 − xCoxN cells. Li2.6Co0.4N in this system exhibits the highest specific capacity of 760 mAh/g in the 0–1.4 V range, and shows the best cycle performance. The capacity of the first extraction was 2 − x Li/mol, and depended on the amount (x) of substituted Co. In addition, the structure changed gradually from the crystalline phase with hexagonal symmetry to the amorphous phase as lithium was removed during the first extraction. The cycle performance of a lithium-ion cell was evaluated by using the Li1.6Co0.4N/LiNiO2 cell. This cell showed good cycleability of more than 240 cycles. This system is thus very promising for application to lithium-ion cells.
The effect of oxygen stoichiometry on the transition metal ordering and electrochemical activity of LiMn2−xNixO4 solid solutions was investigated. Temperature–oxygen-partial-pressure–composition (pO2–T–x) diagrams of ordered and disordered phases of LiMn2−xNixO4 (0.50 ≥ x ≥ 0.36) in the vicinity of order–disorder transition temperature (Tc) was constructed by means of infrared spectroscopy, thermogravimetric analysis and galvanostatic measurements. Despite their simplicity and limitations over traditional diffraction techniques, all three techniques offered near excellent capability to distinguish ordered and disordered phases. The effect of oxygen-partial-pressure (pO2) in the annealing atmosphere and nickel content of the spinel on Tc was studied. The transition temperature increased with pO2 and nickel content, except in oxygen-rich (pO2 = 1) atmosphere for the maximum nickel content spinel of LiMn1.5Ni0.5O4. An explanation for the dependence of the transition temperature on the two variables and changes induced by the post-fabrication heat treatments is provided.
In this report is described the preparation of six nanocomposite membranes of formula {Nafion/[(ZrO2)⋅(SiO2)0.67]ΨZrO2} with ΨZrO2 ranging from 0 to 1.79 based on Nafion® and [(ZrO2)·(SiO2)0.67] nanofiller. Morphology investigations carried out by SEM measurements indicate that the composition of membranes is asymmetric. Indeed, with respect to the direction of the films after casting procedure, the top side (A-side) and bottom side (B-side) present a different nanofiller concentration. The concentration of nanofiller increases gradually from A to B side. The membranes present thicknesses ranging from 170 to 350 nm and are studied by FT-IR ATR and micro-Raman measurements.The vibrational investigations permit us to reveal that: (a) the hydrophobic polytetrafluoroethylene (PTFE) domains of Nafion® are composed of a mixture of polymer chains with 157 and 103 helical conformations; (b) the concentration of chains with 103 helical conformation depends on the nanofiller concentration and is much higher in side A; (c) six different water domains are present in bulk membranes which are singled out as I, II, II, III, III and IV; (d) water uptake of membranes is correlated to the conformational transition 103 → 157 of PTFE chains occurring in hydrophobic domains of Nafion®. The conductivity of {Nafion/[(ZrO2)⋅(SiO2)0.67]ΨZrO2} was determined by analyzing the complex conductivity plots measured in the frequency and temperature range of 10−2 Hz–10 MHz and 5–155 °C, respectively. Interestingly, the {Nafion/[(ZrO2)⋅(SiO2)0.67]ΨZrO2} nanocomposite membranes with ΨZrO2=0.313 and 0.534 showed values of conductivity of 4.3 × 10−2 S cm−1 at 135 °C and of 3.5 × 10−2 S cm−1 at 115 °C, respectively.
Studies of the electrochemical behavior of K0.27MnO2·0.6H2O in K2SO4 show the reversible intercalation/deintercalation of K+-ions in the lattice. An asymmetric supercapacitor activated carbon (AC)/0.5 mol l−1 K2SO4/K0.27MnO2·0.6H2O was assembled and tested successfully. It shows an energy density of 25.3 Wh kg−1 at a power density of 140 W kg−1; at the same time it keeps a very good rate behavior with an energy density of 17.6 Wh kg−1 at a power density of 2 kW kg−1 based on the total mass of the active electrode materials, which is higher than that of AC/0.5 mol l−1 Li2SO4/LiMn2O4. In addition, this asymmetric supercapacitor shows excellent cycling behavior without the need to remove oxygen from the electrolyte solution. This can be ascribed in part to the stability of the lamellar structure of K0.27MnO2·0.6H2O. This asymmetric aqueous capacitor has great promise for practical applications due to high energy density at high power density.
Nonaqueous electrolytes play a key role in extending the operating temperature range of Li-ion batteries. In developing electrolytes for wide temperature operations, we adopted an approach of starting with thermally stable lithium tetrafluoroborate (LiBF4) and lithium bis(oxalato)borate (LiB(C2O4)2, or LiBOB) salts. We have demonstrated that the capacity of Li-ion cells fades much slower in electrolytes using LiBF4 or LiBOB than in electrolytes using LiPF6. For low temperatures applications, suitable solvent systems for LiBF4 and LiBOB were explored. We found that the charge transfer resistance (Rct) is smaller in Li-ion cells in electrolytes based on LiBF4 in selected solvent systems than that based on LiPF6 and results in better capacity utilization at low temperatures. We also found that the electrolytes based on LiBOB in PC-based solvent system would allow Li-ion cells with graphite anode to be cycled. By comparing the properties of LiBF4 and LiPF6 in the propylene carbonate and diethyl carbonate (PC–DEC) solvent system, we found that it is possible to formulate proper solvent mixtures for enhanced conductivity for LiBF4 and LiBOB salts at low temperatures. It is concluded that nonaqueous electrolytes for wide-temperature-range operations of Li-ion cells are achievable.
A three-electrode Li-ion cell with metallic lithium as the reference electrode was designed to study the charging process of Li-ion cells. The cell was connected to three independent testing channels, of which two channels shared the same lithium reference to measure the potentials of anode and cathode, respectively. A graphite/LiCoO2 cell with a C/A ratio, i.e., the reversible capacity ratio of the cathode to anode, of 0.985 was assembled and cycled using a normal constant-current/constant-voltage (CC/CV) charging procedure, during which the potentials of the anode and cathode were recorded. The results showed that lithium plating occurred under most of the charging conditions, especially at high currents and at low temperatures. Even in the region of CC charging, the potential of the graphite might drop below 0 V versus Li+/Li. As a result, lithium plating and re-intercalating of the plated lithium into the graphite coexist, which resulted in a low charging capacity. When the current exceeded a certain level (0.4C in the present case), increasing the current could not shorten the charging time significantly, instead it aggravated lithium plating and prolonged the CV charging time. In addition, we found that lowering the battery temperature significantly aggravated lithium plating. At −20 °C, for example, the CC charging became impossible and lithium plating accompanied the entire charging process. For an improved charging performance, an optimized C/A ratio of 0.85–0.90 is proposed for the graphite/LiCoO2 Li-ion cell. A high C/A ratio results in lithium plating onto the anode, while a low ratio results in overcharge of the cathode.
Conductometric studies of highly-concentrated solutions of lithium salts have been carried out in 1,2-dimethoxyethane (DME), a low dielectric and high DN (donor number) solvent. The formation constant of the triple ion has been determined and discussed with respect to that obtained from the measurement in a very dilute solution. Direct determination of the molar conductivity of the triple ion pair has been done and compared to conventionally assumed values. The reason for the increase in the conductivity of Li ion containing propylene carbonate (PC) solutions with the addition of DME is discussed. Preferential solvation of the Li ion by solvents with higher DN is proposed as one important factor. The solvation constants of Li ion by solvents with high DN have been determined.
The fabrication, thermal and proton conducting properties of complex polymer electrolytes based on poly(vinylphosphonic acid) (VPA) and poly(1-vinyl-1,2,4-triazole) (PVTri) were investigated throughout this work. The membrane materials were produced by complexation of PVPA with PVTri at various concentrations to get PVTriP(VPA)x where x designates the molar ratio of the polymer repeating units and varied from 0.25 to 4. The complexed structure of the polymers was confirmed by FT-IR spectroscopy. The TGA results verified that the presence of PVTri in the complex polymer electrolytes suppressed the formation of phosphonic acid anhydrides up to 150 °C. The DSC and SEM results demonstrated the homogeneity of the materials. Proton conductivity, activation energy and water/methanol uptake of these membranes were also measured. PVTriP(VPA)2 showed a proton conductivity of 2.5 × 10−5 S cm−1 at 180 °C in the anhydrous state. After humidification (RH = 50%), PVTri-P(VPA)4 and PVTri-P(VPA)2 showed respective proton conductivities of 0.008 and 0.022 S cm−1 at 100 °C, where the conductivity of the latter is close to Nafion 117 at the same humidity level.
The use of highly conductive LiAsF6/1,3-dioxolane (DIOX) electrolytes in rechargeable Li batteries is precluded by the ease with which this electrolyte undergoes polymerization. By adding 0.5 – 1.0 vol.% 2-methylfuran (2-MeF) to LiAsF6/DIOX electrolytes, excellent shelf and cycle life may be obtained in Li/TiS2 cells. Stability tests indicate that 2-MeF acts on the TiS2 cathode and the bulk electrolyte as well as on the Li anode.
Highly stable solutions of 1,3-dioxolane (DN) with LiClO4 or LiAsF6 may be prepared by the use of tertiary amine additives. Very high Li-cycling efficiency is obtained with stabilized LiAsF6/DN solutions. These electrolytes can be further improved by addition of alkyl carbonates as cosolvents. The correlation between Li-cycling efficiency and Li-surface chemistry in these systems was investigated using surface sensitive Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray microanalysis techniques.
The electrochemical behaviour of a graphite electrode in a 1 M LiPF6-propylene carbonate (PC)/diethyl carbonate (DEC) (1:1 in volume) electrolyte system and in the same electrolyte system with the addition of 1,3-benzodioxol-2-one (C6H4CO3) is investigated. The decomposition of PC molecules on the graphite during the first lithium intercalation is significantly reduced by the addition of 1,3-benzodioxol-2-one. A mechanism is proposed for the suppression of PC decomposition. The 1,3-benzodioxol-2-one is stable against a LiCoO2 electrode up to 4.3 V (vs. Li+/Li).
Polycrystalline metal-organic frameworks Zn4O(1,3,5-benzenetribenzoate)2 (named as MOF-177) with different morphologies have been controlled synthesized through a solvothermal route. MOF-177 electrodes for lithium storage exhibit a relatively high irreversible capacity in the first discharge process and a much lower reversible discharge–charge capacity in the following electrochemical cycles. The performance of MOF-177 is found not impressive for application in reversible lithium storage. A preliminary reaction mechanism on the basis of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) is proposed to understand the chemical behaviors of the electrode.
Nd0.6Sr0.4Co1−yMnyO3−δ (0 ≤ y ≤ 1.0) oxides have been investigated as cathode materials for intermediate temperature solid oxide fuel cells (SOFC). The samples form a single-phase solid solution with an orthorhombic perovskite structure and the lattice parameters and volume increase with increasing Mn content y. The degree of oxygen loss at high temperatures and the thermal expansion coefficient (TEC) decrease with increasing y due to a stronger MnO bond. The electrical conductivity decreases with y and the system exhibits a metal to semiconductor transition at around y = 0.2. The electrocatalytic activity and power density measured with single cell SOFC decrease with increasing y due to a decrease in oxygen exchange and mobility as well as charge transfer kinetics, arising from a decrease in the oxide ion vacancy concentration and electrical conductivity.
Detailed thermodynamic, kinetic, geometric, and cost models are developed, implemented, and validated for the synthesis/design and operational analysis of hybrid SOFC–gas turbine–steam turbine systems ranging in size from 1.5 to 10 MWe. The fuel cell model used in this research work is based on a tubular Siemens-Westinghouse-type SOFC, which is integrated with a gas turbine and a heat recovery steam generator (HRSG) integrated in turn with a steam turbine cycle. The current work considers the possible benefits of using the exhaust gases in a HRSG in order to produce steam which drives a steam turbine for additional power output. Four different steam turbine cycles are considered in this research work: a single-pressure, a dual-pressure, a triple pressure, and a triple pressure with reheat. The models have been developed to function both at design (full load) and off-design (partial load) conditions. In addition, different solid oxide fuel cell sizes are examined to assure a proper selection of SOFC size based on efficiency or cost. The thermoeconomic analysis includes cost functions developed specifically for the different system and component sizes (capacities) analyzed. A parametric study is used to determine the most viable system/component syntheses/designs based on maximizing total system efficiency or minimizing total system life cycle cost.
Effect of La/Mg ratio on the structure and electrochemical properties of LaxMg3−xNi9 (x=1.6–2.2) ternary alloys was investigated. All alloys are consisted of a main phase with hexagonal PuNi3-type structure and a few impurity phases (mainly LaNi5 and MgNi2). The increase of La/Mg ratio in the alloys leads to an increase in both the cell volume and the hydride stability. The discharge capacity of the alloys at 100 mA/g increases with the increase of La/Mg ratio and passes though a maximum of 397.5 mAh/g at x=2.0. As the La/Mg ratio increases, the high-rate dischargeability of the alloy electrodes at 1200 mA/g HRD1200 decreases from 66.7% (x=1.6) to 26.5% (x=2.2). The slower decrease of HRD1200 (from 66.7 to 52.7%) of the alloys with x=1.6–2.0 is mainly attributed to the decrease of electrocatalytic activity of the alloys for charge-transfer reaction, the more rapid decrease of HRD1200 of the alloys with x>2.0 is mainly attributed to the lowering of the hydrogen diffusion rate in the bulk of alloy. The cycling capacity degradation of the alloys is rather fast for practical application due to the corrosion of La and Mg and the large VH in the hydride phase.
The MCFC Research Association has been conducting R&D of the 1000 kW class MCFC Power Plant under contracting research with New Energy and Industrial Technology Development Organization (NEDO) as a part of the New Sunshine Program, promoted by the Agency of Industrial Science and Technology (AIST), Ministry of International Trade and Industry (MITI). The plant consists of four 250-kW stacks, a reformer, two cathode gas recycle blowers, a turbine compressor, a heat recovery steam generator (HRSG). The power plant is the first Japanese practical external reforming pressurized type MCFC power generation plant intended for large-scale commercial plant in the near future. The construction of the 1000 kW MCFC power plant started in autumn of 1995 on Kawagoe test station in Kawagoe Thermal Power Station of Chubu Electric Power, which is located in the prefecture of Mie, Japan. The construction and installation of the plant progressed very well, and process and control (PAC) testing of the power plant (not including fuel cell stacks and inverters) was carried out through March–November of 1998. After the PAC test, the cell stacks and inverters were installed in the test site; currently, the power generation test has just started. This paper describes the outline of the plant, the status of the test and the future schedule.
Gas Turbine Technologies (GTT) and Politecnico di Torino, both located in Torino (Italy), have been involved in the design and installation of a SOFC laboratory in order to analyse the operation, in cogenerative configuration, of the CHP 100 kWe SOFC Field Unit, built by Siemens-Westinghouse Power Corporation (SWPC), which is at present (May 2005) starting its operation and which will supply electric and thermal power to the GTT factory. In order to take the better advantage from the analysis of the on-site operation, and especially to correctly design the scheduled experimental tests on the system, we developed a mathematical model and run a simulated experimental campaign, applying a rigorous statistical approach to the analysis of the results.The aim of this work is the computer experimental analysis, through a statistical methodology (2k factorial experiments), of the CHP 100 performance. First, the mathematical model has been calibrated with the results acquired during the first CHP100 demonstration at EDB/ELSAM in Westerwoort. After, the simulated tests have been performed in the form of computer experimental session, and the measurement uncertainties have been simulated with perturbation imposed to the model independent variables. The statistical methodology used for the computer experimental analysis is the factorial design (Yates’ Technique): using the ANOVA technique the effect of the main independent variables (air utilization factor Uox, fuel utilization factor UF, internal fuel and air preheating and anodic recycling flow rate) has been investigated in a rigorous manner. Analysis accounts for the effects of parameters on stack electric power, thermal recovered power, single cell voltage, cell operative temperature, consumed fuel flow and steam to carbon ratio. Each main effect and interaction effect of parameters is shown with particular attention on generated electric power and stack heat recovered.
The low-temperature pack chromization, a reforming pack cementation process, is employed to modify AISI 1045 steel for the application of bipolar plates in PEMFC. The process is conducted to yield a coating, containing major Cr-carbides and minor Cr-nitrides, on the substrate in view of enhancing the steel's corrosion resistance and lowering interfacial contact resistance between the bipolar plate and gas diffusion layer. Electrical discharge machining and rolling approach are used as the pretreatment to produce an activated surface on the steel before pack chromization process to reduce operating temperatures and increase deposition rates. The rolled-chromized steel shows the lowest corrosion current density, 3 × 10−8 A cm−2, and the smallest interfacial contact resistance, 5.9 mΩ cm2, at 140 N cm−2 among all tested steels. This study clearly states the performance of 1045 carbon steel modified by activated and low-temperature pack chromization processes, which possess the potential to be bipolar plates in the application of PEMFC.
The use of Ni–MH batteries for traction applications in electric and hybrid vehicles is increasingly attractive and reliable. Besides the energy and power handling, and the cost issues, high tolerance to abuse is an important aspect of the Ni–MH technology. Thus, the ability to reduce charging time and to absorb regenerative breaking is highly desirable in these traction applications. This requires an accurate control of the charge termination. To facilitate an easy and reliable charging control and to avoid battery premature failure or ageing it is very important to know the behavior of the battery under a range of charging conditions. In this paper, we described the performance of high capacity commercial Ni–MH traction batteries (12 V, 109 Ah modules) when subjected to different charging rates (0.1, 0.2, 0.5, and 1.0 C) from 100% depth of discharge (DOD). Changes in battery voltage and temperature during charging were monitored, with a particular emphasis on the detection of the presence of hydrogen near the battery. This unique hydrogen detection outside the battery was used as the method for the end-of-charge termination to prevent overcharging of the battery. Relevant parameters, such as charge acceptance, energy efficiency, and charging time, were analyzed for comparison.
A kW class all-vanadium redox-flow battery (VRB) stack, which was composed of 14 cells each with an electrode geometric surface area of 875 cm2, with an average output power of 1.14 kW, at the charge–discharge current density of 70 mA cm−2, was successfully assembled by filter press type. Then, a 10 kW class VRB stack was manufactured with a configuration of 4 × 2 (serial × parallel) of the improved aforementioned kW class stack modules, which produced a direct output of 10.05 kW (current density 85 mA cm−2). The energy efficiency of more than 80%, at an average output power of 10.05 kW, for the 10 kW class VRB stack was achieved, indicating VRB is a promising high efficiency technology for electric storage.
The vibration response of cubic and rhombohedral (β) 10 mol%Sc2O3–1 mol%CeO2–ZrO2 (Sc0.1Ce0.01ZrO2) both at room and high-temperatures is reported. The in situ heating experiments and ex situ indentation experiments were performed to characterize the vibrational behavior of these important materials. A temperature and stress-assisted phase transition from cubic to rhombohedral phase was detected during in situ Raman spectroscopy experiments. While heating and indentation experiments performed separately did not cause the transition of the cubic phase into the rhombohedral structure under the performed experimental conditions and only broadened or strained peaks of the cubic phase could be detected, the heating of the indented (strained) surface leaded to the formation of the rhombohedral Sc0.1Ce0.01ZrO2. Both temperature range and strained zone were estimated by in situ heating and 2D mapping, where a formation of rhombohedral or retention of cubic phase has been promoted.
Attention is given to topics of advanced concepts, hydrogen-oxygen fuel cells and electrolyzers, nickel electrodes, and advanced rechargeable batteries. Papers are presented on human exploration mission studies, advanced rechargeable sodium batteries with novel cathodes, advanced double-layer capacitors, recent advances in solid-polymer electrolyte fuel cell technology with low platinum loading electrodes, electrocatalysts for oxygen electrodes in fuel cells and water electrolyzers for space applications, and the corrosion testing of candidates for the alkaline fuel cell cathode. Other papers are on a structural comparison of nickel electodes and precursor phases, the application of electrochemical impedance spectroscopy for characterizing the degradation of Ni(OH)2/NiOOH electrodes, advances in lightweight nickel electrode technology, multimission nickel-hydrogen battery cell for the 1990s, a sodium-sulfur battery flight experiment definition study, and advances in ambient-temperature secondary lithium cells.
Hydrogen peroxide generation R&D data obtained in an alkaline fuel cell-type electrochemical reactor with a dividing Nafion™ 117 membrane have been used to extract anion-conducting properties of the cation-exchange membrane. The effective diffusion coefficient of NaOH and the average transport number of OH− in the membrane were obtained by fitting a model formula for the total alkalinity of outlet catholyte to experimental alkalinities obtained with various electrolysis parameters’ values. The formula resulted from assumptions that NaOH diffuses through the membrane and OH− migrates through the membrane, and that HO2− does not penetrate the membrane. The membrane parameters extracted in this way were in good agreement with similar data reported by others for Nafion™. Hydrogen peroxide current efficiencies remained over 90% and H2O2 concentrations reached 7 wt.%, however the fuel cell reactor's electrical efficiency was strongly limited by high internal resistance.
The methanol crossover and other mass transfer phenomena have been investigated in a free-breathing direct methanol fuel cell (DMFC). The current distribution profile along the MeOH flow channel was measured and information of local concentrations of the reacting species was obtained. The DMFC with a segmented cathode was found to be very useful for a detailed analysis of the interrelated parameters, which cause the local variations of the cell current. The connections between different operating parameters were clarified in detail for two different membranes. The measurements were done for both an experimental poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membrane and the commercial Nafion® 117 membrane, which have different methanol permeabilities. The MeOH concentration and the flow rate were varied in a wide range in order to determine their optimum values. The deviations from an even current density distribution were observed to increase as a function of MeOH concentration and decrease as a function of temperature. The power production of a free-breathing DMFC was observed to be proportional to the local oxygen concentration at the cathode side and inadequate air convection together with the MeOH crossover phenomenon was observed to decrease the cell performance locally.
Fuel cell testing and standardization thematic network (FCTESTNET) was a Thematic Network funded by the European Commission under the Fifth Framework Program (FP5), which was comprised of 55 European partners. The project concluded in 2006 and the main output was the collection and compilation of agreed testing procedures for different fuel cell technologies (PEM, SOFC, MCFC), applications (stationary, portable, transport), as well as balance of plant.Experimental validation of such testing procedures is the next necessary step for obtaining reliable harmonized testing procedures. The Joint Research Centre (JRC), Institute for Energy (IE) has started the validation process on selected PEM testing procedures. One of the FCTESTNET procedures applied at JRC-IE is the polarization curve for a PEM stack. Results show that the harmonization of some parameters, such as the acquisition and equilibrium time for each value of the current density, and the control of the stack coolant temperature, is a necessary action for an objective and trustworthy comparison of the performance data.
Nafion/titania-based fillers composites are prepared by casting and tested in proton exchange membrane fuel cells (PEMFCs) operating at elevated temperatures (130 °C). Three types of titania-based fillers are studied: nanoparticles with nearly spherical shape, mesoporous particles with high surface area, and hydrogen titanate nanotubes. Properties of composites related to PEMFC operation, such as water absorption/retention and proton conductivity, are determined and correlated with microstructural data obtained by small-angle X-ray scattering. The addition of titanate nanotubes changes more markedly the physical properties of the composite electrolytes as compared to titanium oxide nanoparticles with different surface area, a feature probably related to the intrinsic hydration and proton conductivity of the nanotubes. Polarization curves of H2/O2 PEMFCs using composite electrolytes indicate that composite electrolytes contribute to a significant boost of H2/O2 PEMFC performance at 130 °C.
Open circuit voltages (OCVs) for a PEM fuel cell operating at 3.0 atm, 100% relative humidity and in the temperature range of 23–120 °C were measured. It was observed that the OCV decreased with increasing temperature. Analysis of the partial O2 and H2 pressures in the feed streams revealed that the decrease in partial pressures with temperature were largely responsible for the decrease in OCV. The difference between the theoretical and measured OCVs was analyzed based on the literature, calculations, and hydrogen crossover measurements at OCV. It was concluded that the difference in OCV is caused mainly by two factors, one is the mixed potential of the Pt/PtO catalyst surface, and the other is hydrogen crossover.
Top-cited authors
Jiujun Zhang
  • National Research Council Canada
Dirk Uwe Sauer
  • RWTH Aachen University
Minggao Ouyang
  • Tsinghua University
Shengshui Zhang
  • Army Research Laboratory
Stefano Passerini
  • Sapienza University of Rome