Determination of state-of-discharge of zinc-silver oxide button cells. II. Impedance measurements

The prediction of the state-of-discharge of numerous types of Zn-Ag₂O button cells from six international manufacturers has been investigated using the impedance technique over an extended frequency range. The frequency responses at various states-of-discharge are presented and it is shown that the changes in impedance which result from discharging provide several potential parameters for the state-ofdischarge prediction. The complex impedance plot of the undischarged cells usually shows a fairly welldefined semicircle at high frequencies and a straight line with a slope between 40 and 50° at low frequencies. As discharge proceeds, the diameter of the semicircle increases and the overlap between the semicircle and the low-frequency straight line increases. The most attractive method would be to determine a parameter such as a characteristic relaxation frequency in the complex impedance plot. Unfortunately, no unambiguous characteristic parameter can be extracted due to the non-ideal shape of the impedance response at high frequencies. The determination of the diameter of the high-frequency semicircle has been faced with the same difficulties. The most reliable test was found to be the determination of either the phase of the impedance, or a corrected phase ^– taken from the high-frequency intercept. The proposed prediction is a go/no go indication on the basis of one- or two-frequency measurements for or, ^– respectively. The selection is made at 20–40% state-of-discharge. The charge withdrawn is negligibly small and the time of the test is between 1 and 100 s depending on the type of cell. A calibration is necessary for each cell dimension and each manufacturer. Some 10–16% of the types of cells investigated could not be selected successfully, mainly because of too large a dispersion of the electrical characteristics of the cells, especially for small newly developed types, and of the similarity of the ( and values in the low and high state-of-discharge in the appropriate frequency range. The latter difficulty arises from the difference of the frequency response between the undischarged and the partly discharged cells occurring at high frequencies.This is the second of a series of papers dedicated to Professor Ernest Yeager on the ocasion of his 60th birthday.     

流动腐蚀介质中双相不锈钢的电化学阻抗谱

测定了流动氯化物体系中双相不锈钢电极的电化学阻抗谱,发现在单相流中,当流速低于临界值时,阻抗谱为直径较大的容抗弧;一旦流速超过临界值,阻抗谱特征为2个容抗弧.流动介质中加入固体颗粒之后,阻抗谱在低流速下高频区为容抗弧,低频区为直线段,而高流速下低频区则出现实部收缩现象.根据腐蚀电化学理论,提出了流动体系中双相不锈钢电极反应过程动力学模型,较好地解释了流动体系中双相不锈钢电极的电化学阻抗谱,进一步揭示了电化学腐蚀在双相不锈钢流动腐蚀过程中的主导作用机理.     

<Emphasis Type="Italic">In situ</Emphasis> analysis of high temperature characteristics of prismatic polymer lithium - ion batteries

A systematic approach to understanding the safety fundamentals of Li-ion batteries was undertaken. Firstly, we present thermal characterization experiments of charged prismatic polymer lithium-ion batteries (PLBs). These cells, at different state of charge (SOC), were tested inside an accelerated rate calorimeter (ARC) to determine the onset-of-thermal runaway (OTR) temperatures. In addition, the thermally activated components of these cells were followed by monitoring both the impedance (at 1 kHz) and the open circuit voltage (OCV) as a function of temperature. An increase in the impedance was observed at around 133 °C corresponding to the polyethylene separator shutdown. Secondly, an original in situac impedance measurement was performed over a wide range of frequencies instead of 1 kHz when the battery was heated from ambient to 130 °C. Resulting impedance spectra were modeled using an appropriate equivalent circuit. It is concluded that the high frequency and the low frequency semicircles observed in the impedance spectra are due to processes occurring the anode/electrolyte and cathode/electrolyte interfaces, respectively. The activation energy E _a was found in the ranges of 0.4–0.6 and 0.36–0.53 eV, for cathode and anode processes, respectively. In addition, it is assumed that change in the electrolyte composition is the main factor responsible for the rise in the cell impedance at high temperatures.     

AC impedance and state-of-charge analysis of alkaline zinc/manganese dioxide primary cells

Alternating current impedance data of alkaline Zn/MnO₂ cells were analysed in view of identification of suitable parameters, which depend on the state-of-charge (SOC) of the cells. The impedance of a slightly discharged cell was found to possess impedance considerably lesser than that of an undischarged cell. The data in the form of Nyquist plot contained an inductance part at very high frequencies, a capacitive semicircle at high frequencies and a diffusion linear spike at low frequencies. The low frequency linear spike gradually transformed into a capacitive semicircle with the decrease of SOC of the cell, which was attributed to the nature of the reactions at the Zn anode. Of several impedance parameters that were examined, equivalent series capacitance (C _s) was found to have a strong dependence on SOC of the alkaline Zn/MnO₂ cells. There was a continuous change in a partially discharged cell during its ageing, which was reflected by transformation of low frequency data into a clear semicircle.     

The impedance of alkaline manganese cells and their relationship to cell performance. I. Interpretation of the basic impedance spectrum

The impedance characteristics of undischarged alkaline manganese cells of various sizes (LR20, LR6 and LR03) have been investigated over the frequency range 100 kHz to 1 mHz. Specially constructed reference electrode probes have been inserted into the cells in two basic positions such as to obtain a complete analysis of the contribution to the total impedance from the individual cell components. It is shown that the impedance of standard cells is determined by the cathode-can assembly, the anode-separator impedance being negligible by comparison. The cathode-can impedance is further resolved into two components. Firstly, a component due to a nickel oxide layer present on the surface of the nickel-plated steel can. This takes the form of a high frequency semicircle in the complex plane. Secondly, a component due to the cathode itself (manganese dioxide + graphite mixture) which takes the form of a higher frequency semicircle and a low-frequency straight line of slope 32°. The latter is interpreted in terms of porous electrode behaviour involving slow proton diffusion in the solid state. Some evidence for a porous-planar transition has also been obtained at a critical frequency of 3 mHz.     

Electrochemical studies of the pitting corrosion of tin in citric acid solution containing Cl

The electrochemical behavior of a tin electrode in citric acid solutions of different concentrations was studied by electrochemical techniques. The E/I curves showed that the anodic behavior of tin exhibits active/passive transition. Passivation is due to the formation of Sn(OH)₄ and/or SnO₂ film on the electrode surface. Addition of NaCl to citric acid solution, enhances the active dissolution of tin and tends to breakdown the passivity at a certain breakdown potential. Cyclic voltammetry and galvanostatic measurements allow the pitting potential (E_pit) and the repassivation potential (E_rp) to be determined. Potentiostatic measurements showed that the overall anodic processes can be described by three stages. The first stage corresponds to the nucleation and growth of a passive oxide layer. The second stages involve pit nucleation and growth and third stage involve repassivation. The impedance spectrum of pure Sn is found to consist of three intersecting capacitive semicircles at the high and medium frequencies with an inductive loop at low frequencies. The capacitive semicircles occurring at the high and medium frequency are due to the dielectric properties of surface oxide film and dissolution of underlying metal, respectively. The inductive loop at low frequencies results from Cl⁻ adsorption at the pitting region. By increasing the potential the pitting corrosion and the fractal dimension of surface due to pitting increase.     

Measurements of electrochemical impedance on the alloy Al 2024T3: an analysis of parameters used to predict the quality of the anodic film

Using the electrochemical impedance technique, the deterioration process of the alloy Al 2024T3 was followed in the presence of NaCl and Na₂SO₄. It was verified that the resistance obtained as the extrapolation to the null frequency in the impedance diagram, even though significant, is not sufficient to characterize the protecting quality of the anodic film. This parameter is only considered as a measure of anticorrosive protection when it is preceded by a capacitive loop at high frequencies. This phenomenon in the high frequency range gives a measure of the sealing quality of the film.     

The recovery of chlorine from by-product hydrogen chloride Part 2: Molten metal cathode method

A new method of recovering chlorine from by-product hydrogen chloride is proposed and developed. According to the reaction Me+2HC1 = MeCl₂+H_o (Me = Metal) hydrogen chloride is reduced to give hydrogen and metal chloride. Gaseous hydrogen was drawn out from the reaction system and the metal chloride dissolved in the electrolyte, where it was electrolysed to give chlorine and metal using molten metal as a cathode. The metal was recovered on the cathode in a molten state and reused for the former reaction. Bench scale tests were also carried out, where zinc was used as a molten metal cathode and the cell capacity was about 50 A. The cell voltage was 6.5 V at 50 A (working temperature 560°C, distance between anode and cathode 5 mm) and in this case, the ohmic loss was about 70%. The current efficiency was about 90% (anodic current density 200 A/dm²) when the working temperature was 500°C and electrode distance between anode and cathode was 18 mm.This method seems very promising on the basis of the above-mentioned data.     

EIS study of the influence of BrCl on the behavior of electrodes in Li/SOCl<Subscript>2</Subscript> cells

The influence of BrCl on the impedance response of both the lithium anode and the carbon cathode in Li/SOCl₂ cells was studied. The impedance of the lithium anode increases with storage time while the addition of BrCl to Li/SOCl₂ cells decreases the impedance. However, the porous carbon cathode shows a small film resistance before discharge. The addition of BrCl to Li/SOCl₂ cells also decreases the impedance, especially for that part of the interface reaction resistance R₂. As a rule, the film resistance of the lithium anode decreases sharply during the early period of discharge, while that of the porous carbon cathode rises rapidly. It follows that the porous carbon cathode is the rate controlling electrode during discharge.     

Capacitive performance of an ultralong aligned carbon nanotube electrode in an ionic liquid at 60 °C

An ultralong (1.0 mm) aligned carbon nanotube (ACNT) electrode was fabricated by a cut/paste method. The electrode retains the intrinsic properties, including robust mechanical property, high surface area, and regular pore structure, of individual nanotubes. Electrochemical properties of the ACNT electrode in an ionic liquid (IL) electrolyte were studied by cyclic voltammetry, galvanostatic charge/discharge, and ac impedance spectroscopy. The ACNT electrode achieved a specific capacitance of 27 F/g, had excellent rate capability, and a long cycle life at 60 °C, indicating that an ACNT electrode/IL electrolyte electrochemical double layer capacitor is promising for high temperature (60 °C) applications. The capacitive performance of ACNT electrode is excellent, because it possesses large pores and regular pore structures, which is revealed by N₂ adsorption and scanning electron microscopy.     

An experimental study on the placement of reference electrodes in alkaline polymer electrolyte membrane fuel cells

The ability to accurately measure separate in situ anode and cathode overpotentials and impedance responses is still a source of debate when investigating fuel cells of planar configuration containing <100 μm thickness solid electrolytes and when using the common three-electrode arrangement. The results obtained in this study indicate that the overpotentials and impedances of the anode and cathode can be successfully measured when using two spatially separated reference electrodes and when the cathode and anode of alkaline membrane electrode assemblies (for alkaline polymer electrolyte membrane fuel cells) are precisely and optimally misaligned. The frequency dependent response between the two reference electrodes is attributed to the membrane response and the “crosstalk” between anode and cathode.     

Growth kinetics of passivating oxide film of Inconel alloy 600 in 0.1 M Na2SO4 solution at 25-300 °C using the abrading electrode technique and ac impedance spectroscopy

The growth kinetics of passivating oxide film of Inconel alloy 600 has been investigated in aqueous 0.1 M Na₂SO₄ solution at temperatures 25-300 °C and at pressures 0.1-8 MPa by analyses of potentiostatic current transients and ac impedance spectra. From the analysis of current transients, it was realized that the oxide film grown on the specimen has only one-layer structure below 60 °C, but it is composed of two layers with different structures, i.e. an inner layer and an outer layer, above 100 °C. In addition, ac impedance spectra exhibited one capacitive loop below 60 °C, but they exhibited two capacitive loops above 100 °C. This substantiates that the structure of the oxide film changed from one-layer structure below 60 °C to two-layer structure above 100 °C. Moreover, from the analysis of ac impedance spectra, it was found that the value of the apparent specific resistivity of the inner layer decreased with rising solution temperature, but that value of the apparent relative permittivity increased.     

AC-Impedance measurements on aluminium in chloride containing solutions and below the pitting potential

Impedance measurements were performed on aluminium in 0.5M NaCl in the frequency range 5×10^–4-10⁴ Hz and before the onset of pitting corrosion. The behaviour of the system was characterized by a high frequency capacitive loop related to the thickness of the oxide film, an inductive loop at medium frequency, which was interpreted on the basis of the dielectric relaxation model proposed by Dignam, and a second capacitive loop obtained at low frequencies which was ascribed to the film dissolution through the formation of a soluble chloride containing aluminium salt.     

Diffusion controlled inhibition of electrodeposition: impedance measurements

At low rotation speeds of a rotating disc electrode the diffusion-controlled inhibition of zinc deposition by lead acetate or tetrabutylammonium bromide emphasizes the existence of multiple steady states. With both zinc and nickel deposition, low frequency impedance measurements reveal an additional inductive loop associated with a diffusion-controlled inhibition of electrodeposition. From the relaxation time constant it has been concluded that this loop arises from a coupling between the inhibitor diffusion and interfacial processes slower than diffusion and involving, at least for zinc deposition, the slow renewal of active growth sites.     

Mechanism of nickel-molybdenum alloy electrodeposition in citrate electrolytes

The kinetics of the induced codischarge of Mo with Ni in citrate-ammonia electrolytes was investigated by means of polarization and a.c. impedance measurements. Three potential ranges were considered. At low polarization, hydrogen evolution resulting from citrate reduction is the main reaction. The impedance plots exhibit a large capacitive loop with a small high frequency inflection characteristic of the development of a porous layer and a low frequency inductive feature. At intermediate polarization, the partial currents for Ni and Mo discharge increase in the same proportion; the hydrogen evolution is first constant and then rapidly decreases. Then a large low-frequency capacitive feature is observed on the impedance plots, whose size decreases with increasing polarization. At still higher polarization, the Mo discharge becomes increasingly controlled by diffusion which generates an additional capacitive loop. A reaction scheme is proposed which accounts for the polarization data and the major impedance features.     

Impedance spectroscopy study of aluminum electrocrystallization from basic molten salt (AlCl3-NaCl-KCl)

Aluminum electrocrystallization is studied by means of electrochemical impedance spectroscopy (EIS). A model based on random birth and deterministic growth of monolayers is proposed, in which the edges are assumed to follow a propagation law. The high frequency impedance data show charge transfer reaction of AlCl₄⁻ reduction while the low frequency features signifies the growth mode of deposits. The inductive response observed in the course of polycrystalline deposition reflects the activation of electrode area while a capacitive loop appears in regular growth. Parameters of impedance model in this system can be calculated from the fitting of experimental data to the Faradaic impedance function derived theoretically. The physical parameters of this function are analyzed by means of the dependence of simulated EIS spectra on kinetic parameters.     

Study of the storage performance of a Li-ion cell at elevated temperature

A series of Li-ion cells with a LiCoO₂ cathode, artificial graphite anode and a LiPF₆-based nonaqueous electrolyte were stored at 55 °C in a series of state of charge (SoC) from 0 to 100%. After storage, all the cells except the one stored in 0% SoC exhibited capacity fade and cycling performance decline, which were aggravated by increasing storage SoC. Furthermore, storage at higher SoC increased the safety risk of the cells. The cells stored at SoC higher than 50% could not pass the 3 C/5 V overcharge test, while such a test was easy to pass for the fresh cells and those stored at 0% SoC. The above results show that the fully discharged state is a favorable storage condition to maintain good storage performance of Li-ion cells. In addition, to clarify the aging mechanisms of the cells, XRD (X-ray diffraction), SEM (scanning electron microscopy) and EIS (electrochemical impedance spectra) measurements were carried out. The results indicate that the performance fading of the stored cells is not due to the bulk structure change of the electrode materials, but instead due to the microstructure variation of the cathode, including the decrease in the crystallite dimension, the change of the micro-stress, and the precipitation of the surface films over the electrodes. According to EIS analysis, the increase of the cathode impedance may be the main contributor to the overall degradation of the Li-ion cells after storage.     

High frequency impedance measurements of sodium solid electrolytes

Solid-state sodium batteries are currently gaining enormous interest as a lower-cost and more environmentally friendly alternative to lithium batteries. They contain significantly less critical rare elements in both the electrolyte and the active material. However, to date, there is no efficient material combination of metallic anode, cathode, and solid electrolyte for room temperature applications that does not require an additional liquid electrolyte while maintaining high energy density. NaPSiO-based glass-ceramics show high ionic conductivity at room temperature, good corrosion resistance against ambient humidity and CO₂, and stability against metallic sodium. However, the conductivity mechanisms of this promising class of materials are currently poorly understood. Herein, high frequency impedance measurements up to 10⁸ Hz shed light on the contributions of grains and grain boundaries to the total impedance, including the distribution of relaxation time constants of the fully crystallized material. In addition, analysis of the temperature dependence allows separation of electrode contributions and determination of activation energies for grain and grain boundary conductivities. Our study provides the basis for fine-tuning the stoichiometry of NaPSiO-based glass-ceramics in terms of maximizing the conductive phase fraction to optimize the performance of future solid-state sodium batteries.     

Anodic dissolution of nickel in concentrated sulfuric acidic solutions

The anodic dissolution of nickel in concentrated sulfuric acidic solutions is characterized by two diffusion plateaux related to the active and transpassive regions. For the same speed of rotation of a rotating disc electrode, the two plateaux currents are almost identical. However, the less anodic one gives rise to a rough electrode surface while a polished surface is observed at the more anodic one. For nickel as-received, mass transport influences the current over the whole potential range. After heat treatment, only the current for the two plateaux were mass transport controlled. Electrochemical impedance diagrams show that the lowest frequency capacitive loop is influenced by mass transport. Electrohydrodynamic (EHD) impedance diagrams show two different regions. In the low frequency range, the results follow the theoretical curve corresponding to a uniformly accessible electrode with a very high Schmidt number around 10⁷. At high frequency, the EHD impedance may correspond to an interface covered by a gel layer formed from the products of the anodic dissolution.