Valve-regulated lead-acid batteries

Valve-regulated lead-acid (VRLA) batteries with gelled electrolyte appeared as a niche market during the 1950s. During the 1970s, when glass-fiber felts became available as a further method to immobilize the electrolyte, the market for VRLA batteries expanded rapidly. The immobilized electrolyte offers a number of obvious advantages including the internal oxygen cycle which accommodates the overcharging current without chemical change within the cell. It also suppresses acid stratification and thus opens new fields of application. VRLA batteries, however, cannot be made completely sealed, but require a valve for gas escape, since hydrogen evolution and grid corrosion are unavoidable secondary reactions. These reactions result in water loss, and also must be balanced in order to ensure proper charging of both electrodes. Both secondary reactions have significant activation energies, and can reduce the service life of VRLA batteries, operated at elevated temperature. This effect can be aggravated by the comparatively high heat generation caused by the internal oxygen cycle during overcharging. Temperature control of VRLA batteries, therefore, is important in many applications.     

Influence of measurement procedure on quality of impedance spectra on lead-acid batteries

Many battery simulation models, but also electrochemical interpretations are based on impedance spectroscopy. However, the impedance of a battery is influenced by various factors, e.g. in the case of a lead-acid battery: state of charge (SOC), charging or discharging, superimposed dc current, short-term history or homogeneity of the electrolyte. This paper analyses the impact of those factors on impedance spectra of lead-acid batteries. The results show that very detailed information about the conditions during the measurement is crucial for the correct interpretation of a spectrum.     

Recovery of discarded sulfated lead-acid batteries

The aim of this research is to recover discarded sulfated lead-acid batteries. In this work, the effect of two methods (inverse charge and chemical charge) on the reactivation of sulfated active materials was investigated. At the inverse charge, the battery is deeply discharged and the electrolyte of battery is replaced with a new sulfuric acid solution of 1.28 g cm⁻³. Then, the battery is inversely charged with constant current method (2 A for the battery with the nominal capacity of 40 Ah) for 24 h. At the final stage, the inversely charged battery is directly charged for 48 h. Through these processes, a discarded battery can recover its capacity to more than 80% of a similar fresh and non-sulfated battery.At the chemical charge method, there are some effective parameters that including ammonium persulfate [(NH₄)₂S₂O₈] concentration, recovery temperature and recovery time. The effect of all parameters was optimized by one at a time method. The sulfated battery is deeply discharged and then, its electrolyte was replaced by a 40% ammonium persulfate solution (as oxidant) at temperature of 50 °C. By adding of oxidant solution, the chemical charging of positive and negative plates was performed for optimum time of 1 h. The chemically charged batteries were charged with constant voltage method (2.66 V for the battery with nominal voltage and nominal capacity of 2 V and 10 Ah, respectively) for 24 h. By performing of these processes, a discarded battery can recovers its capacity to more than 84% of the similar fresh and non-sulfated battery. Discharge and cyclelife behaviors of the recovered batteries were investigated and compared with similar healthy battery. The morphology and structure of plates was studied by scanning electron microscopy (SEM) before and after recovery.     

The partial state-of-charge cycle performance of lead-acid batteries

Negative plate lugs of flooded lead-acid battery were corroded during partial state-of-charge (PSoC) pattern cycle life tests simulated from stop and go vehicle driving.     

Sodium sulfate as an efficient additive of negative paste for lead-acid batteries

This paper is devoted to the effect of sodium sulfate as negative paste additive on the performance of the lead-acid battery. Six different percentages of sodium sulfate were added to negative paste. The effect of sodium sulfate on discharge capacity, cycle life and cold cranking ability of the sealed lead-acid batteries were investigated. Batteries containing sodium sulfate in negative plates at low amount (0.1 wt%) showed a remarkable electrical behavior during the test. Results indicate that negative electrodes containing 0.1 wt% sodium sulfate exhibit discharge capacity of the more than 3% and 12% with respect to negative electrodes without sodium sulfate before and after cycling test, respectively. Addition of sodium sulfate also increases the time of reaching to cut off voltage of 6 V at cold cranking test more than 17%. The main effect of sodium sulfate is to increase the cycle life of the lead-acid batteries to more than 18%. Scanning electron microscopy (SEM) was used for the investigation of paste morphology.     

One-dimensional dynamic modeling and validation of maintenance-free lead-acid batteries emphasizing temperature effects

Lead acid batteries are still widely used for SLI (Starting-Lighting-Ignition) systems in vehicles because of the cost advantage. The batteries are frequently charged and discharged under different operation conditions, which continuously changes distribution of inner temperature of batteries. Variation of the temperature distributions significantly affects performance and durability of the battery. We developed a one-dimensional dynamic model based on the first principle of thermal dynamics and electrochemistry. The thermal model incorporates control volumes for each of the major constituents of the battery cells that is casing, electrolyte, and electrodes. The model was extended for a six-cell battery and used to analyze effects of discharging currents on the performances and temperature, compared with results from a three-dimensional finite element analysis and tested against experimental results obtained from a thermal chamber and using thermal imaging.     

State-of-charge estimation of lead-acid batteries using an adaptive extended Kalman filter

Lead-acid batteries are widely used in conventional internal-combustion-engined vehicles and in some electric vehicles. In order to improve the longevity, performance, reliability, density and economics of the batteries, a precise state-of-charge (SoC) estimation is required. The Kalman filter is one of the techniques used to determine the SoC. This filter assumes an a priori knowledge of the process and measurement noise covariance values. Estimation errors can be large or even divergent when incorrect a priori covariance values are utilized. These estimation errors can be reduced by using the adaptive Kalman filter, which adaptively modifies the covariance. In this study, an adaptive extended Kalman filter (AEKF) method is used to estimate the SoC. The AEKF can reduce the SoC estimation error, making it more reliable than using a priori process and measurement noise covariance values.     

Investigation on electronically conductive additives to improve positive active material utilization in lead-acid batteries

In order to adapt lead-acid batteries for use in hybrid electric vehicles, its specific energy must be improved. Specific energy is greatly dependant on active material utilization. In this study, we improve active material utilization in positive electrodes by the addition of electronically conductive additives. Titanium silicide particles (<44 μm diameter), titanium dioxide fibers (<10 μm, diameter), and titanium wire (76 μm, diameter) were incorporated into the positive electrode and each of their effects on discharge capacity and utilization of active material were examined. The percent mass of each additive was varied from 2–5%. Results indicate that titanium wire at 2.3 wt.% had the optimal effect of increasing the utilization by 12.3% (57 to 64% utilization) relative to control with no additive at a slow discharge rate (10 mA cm⁻²) without detrimental effect at fast discharge rate (50 mA cm⁻²). This additive also features reduction in weight and formation enhancement.     

Simulation of the current distribution in lead-acid batteries to investigate the dynamic charge acceptance in flooded SLI batteries

Measurements show that the dynamic charge acceptance (DCA) of flooded SLI lead-acid batteries during micro-cycling in conventional and micro-hybrid vehicles is strongly dependent on the short-term history, such as previous charge or discharge, current rate, lowest state of charge in the last 24 h and more. Factors of 10 have been reported. Inhomogeneous current distribution, especially as a result of acid stratification, has been suggested to explain the DCA variability.This hypothesis was investigated by simulation of a two-dimensional macrohomogeneous model. It provides a spatial resolution of three elements in horizontal direction in each electrode and three elements in vertical direction. For an existing set of parameters, different current profiles were analyzed with regard to the current distribution during charging and discharging.In these simulations, a strong impact of the short-term history on current, charge and acid density distribution was found as well as a strong influence of micro-cycles on both charge distribution and acid stratification.     

Increase of positive active material utilization in lead-acid batteries using diatomaceous earth additives

In this study we examined the use of diatomites to improve the discharge capacity and utilization of the positive electrode of the lead-acid battery. A large fraction of the positive electrode performance of this battery system (half-reaction shown below) is based on the ionic conduction of sulfuric acid through the plate.

PbO₂(s) + HSO₄⁻ + 3H⁺ + 2e⁻ → PbSO₄(s) + 2H₂O

Model prediction for ranking lead-acid batteries according to expected lifetime in renewable energy systems and autonomous power-supply systems

Predicting the lifetime of lead-acid batteries in applications with irregular operating conditions such as partial state-of-charge cycling, varying depth-of-discharge and different times between full charging is known as a difficult task. Experimental investigations in the laboratory are difficult because each application has its own specific operation profile. Therefore, an experimental investigation is necessary for each application and, moreover, for each operation strategy.     

Three-layered absorptive glass mat separator with membrane for application in valve-regulated lead-acid batteries

During charge and discharge of the lead-acid cell equal amounts of H₂SO₄ participate in the reactions at the two types of plates (electrodes). However, the charge and discharge reactions at the positive plates involve also 2 mol of water per every mole of reacted PbO₂. Consequently, a concentration difference appears in the electrolyte between the two electrodes (horizontal stratification), which affects the reversibility of the processes at the two electrodes and thus the cycle life of the battery. The present paper proposes the use of a three-layered absorptive glass mat (AGM) separator, the middle layer playing the role of a membrane that divides (separates) the anodic and cathodic electrolyte spaces, and controls the exchange rates of H₂SO₄, H⁺ ions, O₂ and H₂O flows between the two electrode spaces. To be able to perform this membrane function, the thinner middle AGM layer (0.2 mm) is processed with an appropriate polymeric emulsion to acquire balanced hydrophobic/hydrophilic properties, which sustain constant H₂SO₄ concentration in the two electrode spaces during cycling. Three types of polymeric emulsions have been used for treatment of the membrane: (a) polyvinylpyrollidonestyrene (MPVS), (b) polyvinylpyrrolidone “Luviskol” (MPVP), or (c) polytetrafluorethylene modified with Luviskol (MMAGM). It is established experimentally that the MMAGM membrane maintains equal acid concentration in the anodic and cathodic spaces (no horizontal stratification) during battery cycling and hence ensures longer cycle life performance.     

Estimation of the kinetic parameters of processes at the negative plate of lead-acid batteries by impedance studies

Impedance characteristics of the negative electrode of lead-acid battery were derived on the basis of fundamental interfacial processes occurring at the electrode. The solution of the governing equations was presented in terms of a simple equivalent circuit consisting of resistive and capacitive loops in which charge transfer and sulfate layer formation and also mass transfer (Warburg) elements are considered. The kinetic parameters were deduced by fitting the theoretically derived impedance to the experimental data. Impedance at various States of Charge (SoC) was also examined.     

ANN modeling of water consumption in the lead-acid batteries

Due to importance of the quantity of water loss in the life cycle of lead-acid batteries, water consumption tests were performed on 72 lead-acid batteries with low antimony grid alloy at different charge voltages and temperatures. Weight loss of batteries was measured during a period of 10 days. The behavior of batteries in different charge voltages and temperatures were modeled by artificial neural networks (ANNs) using MATLAB 7 media. Four temperatures were used in the training set, out of which three were used in prediction set and one in validation set. The network was trained by training and prediction data sets, and then was used for predicting water consumption in all three temperatures of prediction set. Finally, the network obtained was verified while being used in predicting water loss in defined temperatures of validation set. To achieve a better evaluation of the model ability, three models with different validation temperatures were used (model 1 = 50 °C, model 2 = 60 °C and model 3 = 70 °C). There was a good agreement between predicted and experimental results at prediction and validation sets for all the models.     

Influence of carbons on the structure of the negative active material of lead-acid batteries and on battery performance

It has been established that addition of carbon additives to the lead negative active material (NAM) of lead-acid batteries increase battery charge acceptance in hybrid electric vehicle mode of operation. The present work studies three types of activated carbons and two types of carbon blacks with the aim to evaluate their efficiency in improving the charge acceptance of lead-acid batteries. It has been established that the size of carbon particles and their affinity to lead are essential. If carbon particles are of nanosizes, they are incorporated into the bulk of the skeleton branches of NAM and may thus increase the latter's ohmic resistance. Their content in NAM should not exceed 0.2-0.5 wt.%. At this loading level, carbon grains are adsorbed only on the surface of NAM contributing to the increase of its specific surface area and thus improving its charge acceptance. When carbon particles are of micron sizes and have high affinity to lead, they are integrated into the skeleton structure of NAM as a structural component and act as super-capacitors, i.e. electric charges are concentrated in them and then the current is distributed along the adjacent branches of the lead skeleton with the lowest ohmic resistance. This eventually improves the charge acceptance of the negative battery plates.     

Mechanism of action of electrochemically active carbons on the processes that take place at the negative plates of lead-acid batteries

It is known that negative plates of lead-acid batteries have low charge acceptance when cycled at high rates and progressively accumulate lead sulphate on high-rate partial-state-of-charge (HRPSoC) operation in hybrid-electric vehicle (HEV) applications. Addition of some carbon or graphite forms to the negative paste mix improves the charge efficiency and slows down sulfation of the negative plates. The present investigation aims to elucidate the contribution of electrochemically active carbon (EAC) additives to the mechanism of the electrochemical reactions of charge of the negative plates. Test cells are assembled with four types of EAC added to the negative paste mix in five different concentrations. Through analysis of the structure of NAM (including specific surface and pore radius measurements) and of the electrochemical parameters of the test cells on HRPSoC cycling, it is established that the electrochemical reaction of charge Pb²⁺ + 2e⁻ → Pb proceeds at 300-400 mV lower over-potentials on negative plates doped with EAC additives as compared to the charge potentials of cells with no carbon additives. Hence, electrochemically active carbons have a highly catalytic effect on the charge reaction and are directly involved in it. Consequently, the reversibility of the charge/discharge processes is improved, which eventually leads to longer battery cycle life. Thus, charging of the negative plates proceeds via a parallel mechanism on the surfaces of both Pb and EAC particles, at a higher rate on the EAC phase. Cells with EAC in NAM have the longest cycle life when their NAM specific surface is up to 4 m² g⁻¹ against 0.5 m² g⁻¹ for the lead surface. The proposed parallel mechanism of charge is verified experimentally on model Pb/EAC/PbSO₄ and Pb/EAC electrodes. During the charge and discharge cycles of the HRPSoC test, the EAC particles are involved in dynamic adsorption/desorption on the lead sulfate and lead surfaces. Another effect of electrochemically active carbons is also evidenced namely that, above a definite concentration, some EAC forms reduce the mean pore radius of NAM. When it diminishes to less than 1.5 μm, access of sulfuric acid into the pores is impeded and PbO forms instead of PbSO₄ in the pores of NAM during discharge. Thus, it may be presumed that electrochemically active carbons change the overall electrochemical reaction of charge and discharge of lead-acid cells when operated under HRPSoC cycling conditions.     

Influence of residual elements in lead on oxygen- and hydrogen-gassing rates of lead-acid batteries

Raw lead materials contain many residual elements. With respect to setting ‘safe’ levels for these elements, each country has its own standard, but the majority of the present specifications for the lead used to prepare battery oxide apply to flooded batteries that employ antimonial grids. In these batteries, the antimony in the positive and negative grids dominates gassing characteristics so that the influence of residual elements is of little importance. This is, however, not the case for valve-regulated lead-acid (VRLA) batteries, which use antimony-free grids and less sulfuric acid solution. Thus, it is necessary to specify ‘acceptable’ levels of residual elements for the production of VRLA batteries. In this study, 17 elements are examined, namely: antimony, arsenic, bismuth, cadmium, chromium, cobalt, copper, germanium, iron, manganese, nickel, selenium, silver, tellurium, thallium, tin, and zinc. The following strategy has been formulated to determine the acceptable levels: (i) selection of a control oxide; (ii) determination of critical float, hydrogen and oxygen currents; (iii) establishment of a screening plan for the elements; (iv) development of a statistical method for analysis of the experimental results. The critical values of the float, hydrogen and oxygen currents are calculated from a field survey of battery failure data. The values serve as a base-line for comparison with the corresponding measured currents from cells using positive and negative plates produced either from the control oxide or from oxide doped with different levels of the 17 elements in combination. The latter levels are determined by means of a screening plan which is based on the Plackett-Burman experimental design. Following this systematic and thorough exercise, two specifications are proposed for the purity of the lead to be used in oxide production for VRLA technology.     

Lead-acid batteries in micro-hybrid vehicles

More and more vehicles hit the European automotive market, which comprise some type of micro-hybrid functionality to improve fuel efficiency and reduce emissions. Most carmakers already offer at least one of their vehicles with an optional engine start/stop system, while some other models are sold with micro-hybrid functions implemented by default.But these car concepts show a wide variety in detail—the term “micro-hybrid” may mean a completely different functionality in one vehicle model compared to another. Accordingly, also the battery technologies are not the same. There is a wide variety of batteries from standard flooded and enhanced flooded to AGM which all are claimed to be “best choice” for micro-hybrid applications.A technical comparison of micro-hybrid cars available on the European market has been performed. Different classes of cars with different characteristics have been identified. Depending on the scope and characteristics of micro-hybrid functions, as well as on operational strategies implemented by the vehicle makers, the battery operating duties differ significantly between these classes of vehicles.Additional laboratory investigations have been carried out to develop an understanding of effects observed in batteries operated in micro-hybrid vehicles pursuing different strategies, to identify limitations for applications of different battery technologies.     

A novel electrochemical approach on the effect of alloying elements on self-discharge and discharge delivered current density of Pb-Ca-Ag lead-acid battery plates

The aim of this research is to examine the effect of alloying elements in positive plate composition of a lead-acid battery on its self-discharge and delivered current density in discharge state performances. To elucidate, a positive and negative lead-acid battery plates of two alloys namely Pb-Ca-Ag and Pb-Sb are investigated through electrochemical measurements in battery solution. Higher delivered current density of Pb-Ca-Ag cell in compare with Pb-Sb cell is observed for 25 days of 33 measurement days. The evolution of couple potential for both cases shows that the Pb-Ca-Ag cell potential achieves a value in the potential range of water stability after 25 days while in case of Pb-Sb cell, it remains well beyond the water stability potential domain for 33 days of measurements. Further investigations demonstrate that Pb-Sb cell current density is mainly caused by Pb oxidation reaction on negative plate while both anodic and cathodic polarizations (mixed polarization) are responsible in the case of Pb-Ca-Ag cell.     

New approach to prevent premature capacity loss of lead-acid battery in cycle use

Pb–Ca foil laminated on rolled sheet for positive grid of lead-acid battery is proposed to prevent premature capacity loss (PCL) during charge–discharge cycling. Batteries with Pb–Ca foil laminated on positive grid had longer life during charge–discharge cycle than conventional battery, which failed early by PCL. PCL is a phenomenon due to the increase of the interfacial resistance between the positive grid and the positive active mass (PAM) during discharging by PbSO₄ formation in the corrosion layer. Positive plates suffered from PCL when the compression between the grid and the PAM was poor, H₂SO₄ concentration at the interface was high or the corrosion layer mainly consisted of β-PbO₂. Adhesion between the PAM and Pb–5%Sb alloy or Pb–1%Ca alloy was firmer than that between the PAM and Pb–0.06%Ca–1.5%Sn. Corrosion layer formed at the interface between grid material and the PAM during cycle included more α-PbO₂ on Pb–5%Sb and on Pb–1%Ca than on Pb–0.06%Ca–1.5%Sn. It was found out that excellent cycle life performance with Pb–1%Ca foil against PCL is due to firm adhesion between the PAM and grid material, and that α-PbO₂ is formed at the interface as a result of firm adhesion of the PAM and Pb–1%Ca grid.