Investigation of silica additive for high-rate sealed lead-acid cells

This study investigated the effects of silica (SiO₂) additive in the positive electrode on the high-rate discharge performance of sealed lead-acid cells. X-ray diffraction studies reveal that the plate's chemical composition and crystal morphology is independent of the SiO₂ additive in the positive electrodes. Cells with SiO₂ additive in the positive plates decrease the active material, causing a lower initial capacity. However, the plates with SiO₂ additive exhibit a smaller pore size, which has a good mechanical strength and retains the electrolyte in the pore during high-rate discharge causing a lower capacity loss per cycle and a higher average capacity per cycle. Apparently, the SiO₂ additive has the beneficial effect of decreasing the capacity loss during the high-rate discharge cycles. Moreover, the discharge capacity loss rate does not correlate with the amount of SiO₂ additives. Adding more SiO₂ additives to the positive electrode decreases the active material appreciably causing a lower average capacity. The optimal amount of SiO₂ additive is about 3 wt%. The phase composition of the positive electrodes at different locations was determined after the cells completed the high-rate cycle test. The results reveal that the higher utilization of electrode plates at high-rate discharge occurred through the terminal and diagonal areas.     

On the characterization of oxygen recombination in sealed lead-acid batteries

For characterizing the oxygen cycle in sealed lead-acid batteries the technological terms oxygen recombination efficiency and oxygen recombination conditions are introduced and their different meanings explained. Numerical values are calculated or estimated from plots of overpressure against time. Emphasis is placed on investigations of the influence of technological parameters on oxygen recombination conditions.Nomenclature F Faraday constant - D diffusion coefficient - L solubility coefficient - A effective surface area on the negative electrode covered with an electrolyte film - diffusion layer thickness - p _{O 2} oxygen partial pressure - p _{H 2} hydrogen partial pressure - I _OC overcharging current (defined negative) - I _{O 2red} oxygen reduction current - I _{H 2ev} hydrogen evolution current - I _{PhSO 4red} cathodic formation (recharge) current - P _{O 2}(St) steady-state P_{O 2} - p _{O 2} quasi steady-state p_{O 2} - R gas constant - T temperature - V gas space volume - (I_OC–I_{O 2red}–I_{H 2ev}) - viscosity - d electrode distance - l crack length - p electrolyte density     

Effect of state of charge on impedance spectrum of sealed cells Part I: Ni-Cd cells

Alternating current impedance spectroscopy (ACIS) was performed on commercial sealed Ni-Cd cells. A method previously developed in the literature was modified to determine the state of charge of sealed Ni-Cd cells by obtaining the impedance spectrum in a wide frequency range. The impedance parameters were sensitive to state of charge at low frequencies. A modified Randles' circuit was used to fit the impedance data. Appropriate modifications were made to account for an additional high frequency arc or a low frequency finite diffusion element. The effect of the state of charge on the equivalent circuit parameters was determined.List of symbols R ohmic resistance of battery (ohms) - C _dl double layer capacitance (F) - Q ₁ constant phase element representing double layer capacitance - Q ₂ constant phase element representing Warburg diffusion - O finite diffusion element - R _t charge transfer resistance () - R _s,R _p equivalent series and parallel resistance () - C _s,C _p equivalent series and parallel capacitance (F)     

The impedance of 23 Ah Ni-Cd cells with sintered electrodes: measurements in the range 10 kHz-0.001 Hz as an indication of residual capacity

Impedance measurements on 23 Ah Ni-Cd cells at various residual capacity levels are described. These have been made using non-inductive connections coupled directly to a potentiostat and a frequency response analyser. The capacitive reactance at 0.39 Hz provided the best residual capacity indicator.     

Effect of state of charge on impedance spectrum of sealed cells Part II: Lead acid batteries

Alternating current impedance spectroscopy (ACIS) was performed on commercial sealed lead acid batteries. A method previously developed in the literature was modified to determine the state of charge of sealed lead acid cells by obtaining the impedance spectrum in a wide frequency range. The data were sensitive to state of charge at low frequencies. A modified Randles' circuit was used to fit the impedance data. The effect of the state of charge on the equivalent circuit parameters was determined.List of symbols R ohmic resistance of battery () - C _dl double layer capacitance (F) - Q ₁ constant phase element representing double layer capacitance - Q ₂ constant phase element representing Warburg diffusion - O finite diffusion element - R _t charge transfer resistance () - R _s,R _p equivalent series and parallel resistance () - C _s,C _p equivalent series and parallel capacitance (F)     

Evaluation of flocs resistance and reflocculation capacity using the LDS technique

In a previous paper we have shown the added value of using LDS to monitor flocculation. It can supply, simultaneously, information on flocs size and structure and enlighten flocculation kinetics and mechanisms. In this paper, LDS is applied to study deflocculation and reflocculation processes of precipitated calcium carbonate (PCC) induced by cationic polyacrylamides, when different types of shear forces are applied. LDS can detect the influence of polymer characteristics and concentration as well as of the type of shearing, on flocs resistance and reflocculation degree, which depend on flocs structure and on the type of bonds between particles. As expected, flocs formed by bridging mechanism reflocculate with difficulty while flocs formed by patching reflocculate to a higher degree. Flocs resulting from reflocculation are more compact than the original ones, as assessed by the mass fractal dimension. Reflocculation is also lower when the flocs are submitted to superficial shearing than when they are submitted to sonication. Shearing induced by sonication is sufficient to break down the flocs in many fragments while the increase of pump speed only detaches particles by erosion, at the flocs surface, where bonds are weaker. Results prove that LDS is useful to monitor deflocculation and reflocculation processes and to predict floc resistance under different conditions. Moreover, the whole study demonstrates the benefit of using LDS for a complete evaluation of flocculants performance in the different stages of flocculation: aggregation, stabilization, deflocculation and reflocculation.     

Low-temperature charging behaviour of lead-acid cells

The effect of temperature on the charging behaviour of lead-acid cells was studied at a depth of discharge of 20% of their reserve capacity. As expected the charge acceptance rates dropped markedly at temperatures below 0°C. The ability to charge at these temperatures was limited by a precipitous increase in polarization at the negative plates which occurred immediately upon starting the charge. At –18°C the charge acceptance rates fell within a range of 20 to 40% of that observed at 25°C. The highest rates at –18°C were favoured where the charge followed a high-rate, low-temperature discharge, with a minimum time and temperature for the open circuit stand. We speculate that this is due to factors such as a small PbSO₄ crystal size and a non-equilibrium electrolyte concentration in the pores of the plates. Direct evidence for this is lacking, however, because of the need forin situ determination of the physical structure of the plates in the discharged condition.     

The impedance of electrical storage cells

A brief review of the theory pertaining to the impedance of electrolytic cells is presented. Differences between the operational representations of cell impedances in the fields of electrochemistry and electrical engineering are noted. The experimental data on the impedance of complete batteries, available from the literature, is critically reviewed. The results are discussed in terms of the generation of a nondestructive,in situ, state-of-charge test.     

Faradaic impedance measurements of small magnitudes encountered in high capacity electrical storage cells

Gross errors in impedance measurements of high capacity electrical storage cells can be observed when using a commercial Frequency Response Analyser (FRA) coupled with an electrochemical interface. The magnitudes of these errors are discussed and an appropriate automatic calibration procedure is described which enables the correct impedance to be recorded at any frequency.     

The cause of residual capacity in nickel oxyhydroxide electrodes

Chemical analysis, X-ray diffraction and linear sweep voltammetry have been used to examine the cause of the secondary discharge plateau associated with the inefficient reduction of sintered plate NiOOH electrodes. The techniques confirm the presence of-Ni(OH)₂,-NiOOH and-NiOOH in electrodes after failure at high rates. No evidence was obtained in support of the plateau arising from a new intrinsically less active compound. In disagreement with previous claims the-phase formed on overcharging was found to discharge as efficiently as the-phase. Inefficient discharge is considered to be caused by an insulating barrier layer of-Ni(OH)₂ between the charged active material and the current collector. The complex non-linear current-potential behaviour, exhibited by the secondary discharge plateau near –200 mV, is considered to be caused by the removal of Ni³⁺ or Ni³⁺ defects from the electronically conducting Ni(OH)₂ prior to returning it to the poorly conducting divalent state.     

Data correction technique for using common electrochemical apparatus for the measurement of crystal impedance

Crystal impedance (CI) is a well-known technique which extends the capabilities of the quartz crystal microbalance (QCMB) technique by refining the apparent mass change reported by QCMB resonance frequency measurements into a corrected mass change and an energy loss or dissipation component. In addition to mass change, the energy loss component can provide information about additional sample properties, such as surface rigidity or roughness, as well as the viscoeleastic properties of the medium in which measurements are performed. Previous reports of CI measurements involve the use of a network analyzer, an instrument not commonly found in an electrochemical research group. Here, we describe how to utilize a more common electrochemical impedance spectroscopy (EIS) system with sufficient bandwidth for the purpose of collecting CI data. Specifically, we discuss the measurement setup required to minimize impedance mismatch and a means of mathematically correcting for the impedance of the measurement system itself. We demonstrate the utility of this system using the CI response of a Pt-coated crystal to D-fructose solutions with known density and viscosity.     

Fundamentals of lead-acid cells. XVII. The a.c. impedance of lead dioxide formed in sulphuric acid on some lead alloys

The impedances of PbO₂ formed on lead and some lead alloys have been measured over a wide range of potential. Conditions were chosen so that well-defined electrode states were obtained. Considerable differences were observed in the behaviour of alloys containing antimony and bismuth. The latter alloying ingredient appears to contribute some semiconducting properties to lead sulphate films formed on PbO₂ by polarizing them at potentials negative to the reversible potential in sulphuric acid.Nomenclature C _L double-layer capacitance - C _X series capacitance - D diffusion coefficient - E potential - R _CT charge-transfer resistance - R electrolyte resistance - Z _D impedance as defined by Equation 1 - Z _F impedance as defined by Equation 2 - Z impedance as defined by Equation 3 - Warburg coefficient - angular frequency     

The effect of additives on the electrodeposition of copper studied by the impedance technique

The impedance technique has been used to study the effects of NaCl, glue, thiourea and Avitone on the elctrodeposition of copper in a 0.71M CuSO₄-1.80M H₂SO₄ solution. NaCl affects the rate of the two-step reaction and glue is a polarizer due to adsorption on the surface. The degradation of glue by hydrolysis can be followed using impedance measurements. No significant effects of thiourea and Avitone could be detected in the concentration and potential range used in electrorefining.     

Prediction of residual capacity in thin adsorbers

A simple reliable method to measure Residual Adsorption Capacity (RAC) of charcoal adsorbers on which a gas is physisorbed has been developed. The method consists of passing a pulse of weakly adsorbed gas(es) through the adsorption filter(s) and measuring the retention time. This retention time is then correlated to the residual adsorption capacity. In order to predict the retention time-RAC relationship for filters with various configurations and bulk densities, this pulse test was mathematically modeled. The numerical solution of the model involved estimating the transport rate parameters, using existing correlations and the moment technique. A perturbation analysis indicated that the accuracy of the model is closely associated with the estimates of adsorption equilibrium constant and the intraparticle diffusion coefficient of the test gas. The model is shown to be accurate in predicting the RAC of an adsorber under dry and humid conditions from a limited data set.     

扁平床离子交换技术在铅酸废水处理中的应用

介绍了树脂扁平床的结构、配套废水处理系统的工作原理及工艺流程。与传统树脂罐运行情况相比,该工艺树脂离子交换处理量更大,再生消耗更少,系统运行、维护成本较低,具有良好的经济、环保效益。     

Influence of superimposed alternating current on capacity and cycle life for lead-acid batteries

Capacity and cycle life have been measured for commercially available lead-acid batteries by superimposing an a.c. upon the charge and discharge d.c. to clarify the influence of an a.c. invasion into the d.c. system on battery performance in an electric power storage system. The current was controlled to beI=I ₀(1+sint) in all the experiments. The value ofI ₀ corresponded to 5 or 8 HR and the frequency range was 0.1 to 4000 Hz. No capacity change was observed for the a.c. superimposition on the charge current in this frequency range. When an a.c. was superimposed upon the discharge current the capacity of the battery increased by less than 1%. No effect on the cycle life caused by the a.c. superimposition on the charge and the discharge current was observed, as the inherent distribution of the cycle life of the batteries used was much greater than the change caused by the a.c. superimposition. Thus, it was clarified that the influence of the a.c. superimposition on battery capacity and cycle life is practically negligible for lead-acid batteries.     

生料磨入磨采用密封小仓加密封链板式给料机改造

<正>我公司4 000 t/d熟料生产线回转窑规格为Φ4.2 m×66 m,配套生料磨为LM48.4型立磨,受当地石灰石生料易磨性影响生产能力设计为320 t/h。当前,节能降耗、降低成本成为企业增强市场竞争力的法宝,窑尾废气氧含量控制成为现场工艺管理好坏、生产管理成本优劣一个很重要的参数,解决工艺系统外漏风及内漏风成为工艺管理的重点,而生料磨系统漏风在整个系统漏风量中所占比例很高,解     

A study of polymer-modified mortars by the AC impedance technique

Cement mortar can be regarded as a composite consisting of the cement paste, fine aggregate, and the interfacial transition zone (ITZ). In this paper, the formation and development of the ITZ of polymer-modified mortar (PMM) was studied by alternating current impedance spectroscopy (ACIS). The test results showed that the AC impedance spectra of the PMMs had the following characteristics: (1) the AC impedance spectra of the fresh PMMs were almost parallel to the imaginary axis; (2) The AC impedance spectra of the hardened PMMs showed a high-frequency part not connected to the intermediate frequency part. This characteristic was maintained over a rather long period, and then obvious changes appeared in the AC impedance spectra. The age at which the impedance spectra of the mortars changed appeared to shorten with an increase of the sand volume fractions (SVFs). These characteristics of the AC impedance spectra of the PMMs were related to the close contact, the packing, and the formation of a mechanically rigid film of the polymer particles.     

The impedance of alkaline manganese cells and their relationship to cell performance. III. Correlation with high-rate pulse discharge capacity

The extent to which the initial impedance characteristics of a batch of LR6 alkaline manganese cells determine their life and therefore capacity during a typical 2 A/10 s pulse discharge regime has been investigated, and the importance of thermodynamic factors have also been considered. It is shown that the potential drop (E-V _pulse) for the initial discharge cycle can be calculated approximately from a knowledge of the initial internal resistance value, and the recovery voltage,V _rec, can be calculated using a simple thermodynamic theory for the homogeneous phase discharge of -MnO₂. During subsequent cycles the polarization of the cathode-can assembly remains approximately constant at 300 mV while that of the anode-separator system increases progressively from 100 mV to >300 mV. The constancy of the former parameter can be attributed to constancy in the cathode contribution to the internal resistance, whereas the changes in the latter can be ascribed to increases in anode resistance polarization and anode concentration polarization. Minimization of cell internal resistance and anode polarization are therefore of primary concern if cell performance is to be maximized.Nomenclature E initial open-circuit voltage - V _pulse cell voltage att=10 s - V _pulse cell voltage att=10 s for the first pulse - V _rec open-circuit voltage at the end of a 50-s recovery period - V total polarization of the cell - V _A anode polarization (anode-separator system) - V _C cathode polarization (cathode-can assembly) - ohmic polarization - _NT charge-transfer polarization - _C concentration polarization - R _i cell internal resistance - R _e electrolyte resistance - R _part ^cath contact resistance between cathode particles or within the particles themselves - R ^cath effective resistance of cathode-can assembly - R _i ^cath contact resistance at the interface between the nickel oxide phase and the cathode (MnO₂ + graphite mixture) - R _phase ^cath resistance of the nickel oxide phase on the surface of the nickel-plated steel positive current collector (cell can) - R ₂ ^cath contact resistance at the interface between the nickel oxide layer on the can surface and the can itself - R high frequency intercept on complex plane impedance diagram - R diameter of the complex plane impedance semicircle - f ^* characteristic frequency at the top of the complex plane semicircle - C effective parallel capacitance in the equivalent circuit for a cell attributed to the cathode-can assembly - c _MnO2 concentration of MnO₂ at any point in the discharge - cMnO ₂ ⁰ maximum MnO₂ concentration at 100% efficiency - c _MnOOH concentration of MnOOH at any point in the discharge - c _MnOOH ⁰ maximum MnOOH concentration at 100% efficiency - proton-electron spatial correlation coefficient - I total current - i _R current through resistanceR - i _c current through capacitor - V _p voltage drop across parallel R-C circuit - A anode - C cathode - obs observed - calc calculated