Cell/dendrite transition and electrochemical corrosion of Pb-Sb alloys for lead-acid battery applications

The aim of this article is focused on a comparative experimental study of the electrochemical feature of as-cast Pb-2.2 wt.% Sb alloy with cellular/dendritic transition for applications in the manufacturing of lead-acid battery parts. A water-cooled unidirectional solidification system is used to obtain the alloy samples. Electrochemical impedance spectroscopy (EIS) plots, potentiodynamic polarization curves and equivalent circuit analysis are used to evaluate corrosion resistance in a 0.5 M H₂SO₄ solution at 25 °C. The cellular Pb-2.2 wt.% Sb alloy is found to have a current density which is of about 3 times lower than that of the dendritic Pb-2.2 wt.% Sb alloy. The Pb-2.2 wt.% Sb alloy has lower current density than both the Pb-1 wt.% Sb and the Pb-6.6 wt.% Sb alloys evidencing its potential for application as positive grid material in lead-acid batteries. It is also verified that a conventional casting with low cooling rate of about 0.6 °C s⁻¹ produces coarser cellular spacings which is more appropriate for the manufacturing of the Pb-2.2 wt.% Sb alloys grids due to its corresponding electrochemical behavior.     

Comparison of electrochemical performance of as-cast Pb-1 wt.% Sn and Pb-1 wt.% Sb alloys for lead-acid battery components

A comparative experimental study of the electrochemical features of as-cast Pb-1 wt.% Sn and Pb-1 wt.% Sb alloys is carried out with a view to applications in the manufacture of lead-acid battery components. The as-cast samples are obtained using a water-cooled unidirectional solidification system. Pb-Sn and Pb-Sb alloy samples having similar coarse cell arrays are subjected to corrosion tests in order to assess the effect of Sn or Sb segregation in the cell boundary on the electrochemical performance. Electrochemical impedance spectroscopy (EIS) diagrams, potentiodynamic polarization curves and an equivalent circuit analysis are used to evaluate the electrochemical parameters in a 0.5 M H₂SO₄ solution at 25 °C. Both the experimental and simulated EIS parameters evidence different kinetics of corrosion. The Pb-1 wt.% Sn alloy is found to have a current density which is of about three times lower than that of the Pb-1 wt.% Sb alloy which indicates that dilute Pb-Sn alloys have higher potential for application as positive grid material in maintenance-free Pb-acid batteries.     

Electrochemical corrosion of Pb–1 wt% Sn and Pb–2.5 wt% Sn alloys for lead-acid battery applications

The aim of this study was to compare the electrochemical corrosion behavior of as-cast Pb–1 wt% Sn and Pb–2.5 wt% Sn alloy samples in a 0.5 M H₂SO₄ solution at 25 °C. A water-cooled unidirectional solidification system was used to obtain the as-cast samples. Electrochemical impedance spectroscopy (EIS) diagrams, potentiodynamic polarization curves and an equivalent circuit analysis were used to evaluate the electrochemical corrosion response. It was found that a coarse cellular array has a better electrochemical corrosion resistance than fine cells. The pre-programming of microstructure cell size of Pb–Sn alloys can be used as an alternative way to produce as-cast components of lead-acid batteries with higher corrosion resistance associated with environmental and economical aspects.     

Effects of cell size and macrosegregation on the corrosion behavior of a dilute Pb–Sb alloy

The aim of this study was to examine the effect of cooling rate on the cellular growth of a Pb–0.85 wt%Sb alloy and to evaluate the influences of cell size and of the corresponding macrosegregation profile on the resultant corrosion behavior. In order to obtain the as-cast samples a water-cooled unidirectional solidification system was used. Such experimental set-up has permitted the development of a clear cellular structural array even for relative high cooling rates and has allowed a wide range of solidification conditions to be analyzed. Macrostructural and microstructural aspects along the casting were characterized by optical microscopy and scanning electron microscope (SEM) techniques. The electrochemical impedance spectroscopy technique and potentiodynamic curves (Tafel extrapolation) were used to analyze the corrosion resistance of samples collected along the casting length and immersed in a 0.5 M H₂SO₄ solution at 25 °C. It was found that the corrosion rate decreases with increasing cell spacing and that the pre-programming of microstructure cell size can be used as an alternative way to produce as-cast components of Pb–Sb alloys, such as battery grids, with better corrosion resistance.     

The interrelation between mechanical properties, corrosion resistance and microstructure of Pb-Sn casting alloys for lead-acid battery components

It is well known that there is a strong influence of thermal processing variables on the solidification structure and as a direct consequence on the casting final properties. The morphological microstructural parameters such as grain size and cellular or dendritic spacings will depend on the heat transfer conditions imposed by the metal/mould system. There is a need to improve the understanding of the interrelation between the microstructure, mechanical properties and corrosion resistance of dilute Pb-Sn casting alloys which are widely used in the manufacture of battery components. The present study has established correlations between cellular microstructure, ultimate tensile strength and corrosion resistance of Pb-1 wt% Sn and Pb-2.5 wt% Sn alloys by providing a combined plot of these properties as a function of cell spacing. It was found that a compromise between good corrosion resistance and good mechanical properties can be attained by choosing an appropriate cell spacing range.     

Microstructure and electrochemical performance of thin film anodes for lithium ion batteries in immiscible Al–Sn system

The immiscible Al–Sn alloy thin films prepared by electron-beam deposition were first investigated as possible negative electrodes for lithium ion batteries. In the complex structure of the Al–Sn thin films, tiny Sn particles dispersed homogeneously in the Al active matrix. Their electrochemical characteristics were tested in comparison with the pure Al and Sn films. Cyclic voltammetry results indicated that the Li⁺-transport rates in these Al–Sn alloy films were significantly enhanced. Charge–discharge tests showed that the Al–Sn alloy film anodes had good cycle performance. The electrode with high Al content (Al–33 wt%Sn) delivered a high initial discharge capacity of 752 mAh g⁻¹ while the electrode with high Sn content (Al–64 wt%Sn) had better cycleability with a stable specific capacity of about 300 mAh g⁻¹ under 0.8 C rate. The good performance of these immiscible Al–Sn alloy film anodes was attributed to their unique microstructure. The mechanism of lithiation and delithiation reaction had been proposed based on cyclic voltammograms and impedance response of the Al–Sn alloy thin film electrodes. Our preliminary results demonstrate that the Al–Sn immiscible alloy is a potential candidate negative material for Li-ion battery.     

Electrochemical hydrogen storage characteristics of nanocrystalline and amorphous Mg20Ni10-xCox(x=0−4) alloys prepared by melt spinning

Nanocrystalline and amorphous Mg₂Ni-type alloys with nominal compositions of Mg₂₀Ni_10-xCo_x (x = 0, 1, 2, 3, 4) were synthesized by melt-spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage characteristics of the as-cast and spun alloys were measured. The obtained results show that the substitution of Co for Ni does not change the major phase of Mg₂Ni, but it leads to the formation of secondary phase MgCo₂ and Mg. No amorphous phase forms in the as-spun alloy (x = 0), whereas the as-spun alloy (x = 4) holds a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni significantly heightens the glass forming ability of the Mg₂Ni-type alloy. The substitution of Co for Ni and melt spinning significantly improve the electrochemical hydrogen storage performances of the alloys. When Co content x increases from 0 to 4, the maximum discharge capacity of the as-cast alloy increases from 30.3 to 113.3 mAh/g, and from 135.5 to 402.5 mAh/g for as-spun (30 m/s) alloy. The capacity retaining rate of the as-cast alloy after 20 cycles rises from 36.71 to 37.04%, and from 27.06 to 83.35% for as-spun (30 m/s) alloy, respectively.     

The roles of cellular and dendritic microstructural morphologies on the corrosion resistance of Pb–Sb alloys for lead acid battery grids

During the past 20 years, lead acid batteries manufacturers have modified grid manufacturing processes and the chemical composition of the used alloys in order to decrease battery grid weight as well as to reduce the production costs, and to increase the battery life-time cycle and the corrosion resistance. The aim of this study was to evaluate the effects of cellular and dendritic microstructures of two different Pb–Sb alloys on the resultant corrosion behavior. A water-cooled unidirectional solidification system was used to obtain cellular and dendritic structures. Macrostructural and microstructural aspects along the casting have been characterized by optical microscopy and SEM techniques. Electrochemical impedance spectroscopy and potentiodynamic polarization curves were used to analyze the corrosion resistance of samples in a 0.5 M H₂SO₄ solution at 25 °C. For cellular microstructures the corrosion rate decreases with increasing cell spacing. In contrast, finer dendritic spacings exhibit better corrosion resistance than coarser ones. The microstructural pre-programming may be used as an alternative way to produce Pb alloy components in conventional casting, rolled-expanded, and continuous drum casting with better corrosion resistance.     

Structures and electrochemical hydrogen storage behaviours of La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.4) alloys prepared by melt spinning

In order to improve the electrochemical performance of the La–Mg–Ni system A₂B₇-type electrode alloys, La in the alloy was partially substituted by Pr and melt spinning technology was used for preparing La_0.75−xPr_xMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures and electrochemical performance of the as-cast and spun alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Pr for La leads to an obvious increase of the (La, Mg)Ni₃ phase and a decrease of the LaNi₅ phase in the alloys. The results of the electrochemical measurement indicate that the discharge capacity of the alloys first increases and then decreases with variation of the Pr content. The cycle stability of the alloy monotonically rises with increasing Pr content. When the Pr content rises from 0 to 0.4, the discharge capacity increases from 389.4 (x = 0) to 392.4 (x = 0.1) and then drops to 383.7 mAh/g (x = 0.4) for the as-cast alloy. Discharge capacity increases from 393.5 (x = 0) to 397.9 (x = 0.1), and then declines to 382.5 mAh/g for the as-spun (5 m/s) alloys. The capacity remaining after 100 cycles increases from 65.32 to 79.36% for the as-cast alloy, and from 73.97 to 93.08% for the as-spun (20 m/s) alloy.     

Microstructure and electrochemical properties of rapidly solidified alloy Ml(NiCoMnTi)5

The microstructure and electrochemical properties of MlNi_3.7Co_0.75Mn_0.5Ti_0.05 alloys prepared by both rapid solidification and conventional cast methods were comparatively investigated. SEM and XRD studies showed that the microstructure of conventional cast alloy cooled slowly from its melt was of dendrite, where obvious segregation of Mn and trace second phase TiNi₃ were found. However, the rapidly solidified alloy (cooling at a rate of about 10⁶ K s⁻¹) was found to be in columnar structure, and contained CaCu₅ type single phase only, Mn segregation was restrained effectively as well. Electrochemical measurements showed that the rapidly solidified alloy had higher discharge capacity, more flat discharge potential plateau and longer cycle life than conventional cast alloy, but its activation process was longer. The improved cyclic stability of rapidly solidified alloy was attributed to its composition homogeneity and the fine columnar structure, which showed a good resistance to pulverization and corrosion during charging/discharging cycles.     

Influence of the substitution of La for Mg on the microstructure and hydrogen storage characteristics of Mg20−xLaxNi10 (x = 0–6) alloys

In order to enhance the glass forming ability of the Mg₂Ni-type hydrogen storage alloy, the Mg in the alloy was partially substituted by La. The alloys Mg_20−xLa_xNi₁₀ (x = 0, 2, 4, 6) were prepared by casting and rapid quenching. The structures and morphologies of the as-cast and the quenched alloys were studied by XRD, SEM and HRTEM. It was found that no amorphous phase was formed in the as-quenched La-free alloy. But the as-quenched alloys containing La held a major amorphous phase, confirming that the substitution of La for Mg significantly enhances the glass forming ability of the alloys. When La content x ≤ 2, the major phase in the as-cast alloys is Mg₂Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La,Mg)Ni₃ + LaMg₃ phase. Thermal stability of the as-quenched alloys was studied by DSC, showing that La content engenders a negligible influence on the crystallization temperature of the amorphous phase. The hydrogen absorption and desorption kinetics of the as-cast and the quenched alloys were measured by an automatically controlled Sieverts apparatus. The results showed that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly rise with increasing La content. For La content x = 2, the as-quenched alloy displays an optimal hydrogen desorption kinetics at 200 °C. The electrochemical measurement showed that the discharge capacities of the as-cast alloys rose with the increase of La content, but those of the as-quenched alloys obtained the maximum values with the variation of La content. The cycle stability of the as-cast and the quenched alloys significantly improved with increasing La content.     

Electrochemical investigation of the anodic corrosion of Pb–Ca–Sn–Li grid alloy in H2SO4 solution

The steady-state and anodic corrosion of Pb–0.17 wt.% Ca–0.88 wt.% Sn, and Pb–0.17 wt.% Ca–0.88 wt.% Sn–0.06 wt.% Li alloys in 4.5 M H₂SO₄ at 25 °C were studied using cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The experimental results show that the lithium added to Pb–Ca–Sn alloy increases corrosion resistance in equilibrium potential and inhibits the growth of the anodic corrosion layer.     

Surface modifications of aluminum alloy 5052 for bipolar plates using an electroless deposition process

This study tries to replace graphite bipolar plates in fuel cells with surface-modified aluminum alloy 5052. To improve the surface characteristics of Al alloy, Ni–Mo–P coatings were deposited on the substrates under various pH values and concentrations of sodium molybdate (Na₂MoO₄) by an electroless deposition process. The effects of the controlling conditions on the microstructure and the corrosion resistance of these deposits were examined. Moreover, the thermal stability and the corrosion resistance of Ni–Mo–P coatings were compared with those of Ni–P deposits in various attacking environments. The experimental results indicate that the electrical conductivity of all deposits produced in this experiment is superior to the U.S. DOE's target. The optimum Ni–Mo–P coating, which is produced in a solution containing 4.13 × 10⁻² M Na₂MoO₄ at pH 7.0 and 70 °C, possesses superior corrosion resistance in a mixed acidic environment. It is also found that Ni–Mo–P coatings exhibit better thermal stability, and superior long-term corrosion resistance than Ni–P deposits. The Ni–Mo–P deposits, therefore, are promising for applications in protecting coatings for bipolar plates.     

A new lead alloy current-collector manufactured by a powder rolling process and its corrosion behavior under lead-acid battery conditions

A new powder rolling process for manufacturing current-collector sheets for lead-acid batteries has been developed. Gas-atomized lead–tin and lead–tin–calcium alloy powders obtained by a rapid solidification process in air were employed as raw materials for the powder rolling process. The corrosion behavior of powder-rolled lead–tin alloys with various compositions of tin has been investigated. A dipping corrosion test of square plain sheets of the alloys was performed in H₂SO₄ at 75 °C. The test was repeated up to 20 cycles with each cycle consisting of a controlled 10 mA cm⁻² oxidation current for 6 h and a rest under open circuit voltage for 6 h. The extent of corrosion–elongation and the appearance of the corroded surface of the tested specimens were the main observations. The corrosion–elongation of the corroded sheet of a powder-rolled lead alloy containing 1.5 wt% tin with ca. 200 μm initial thickness was less than 5%, whereas that of the corroded sheet of the cast-rolled lead alloy containing 1.5 wt% tin with the same initial thickness was 25–30% under the same corrosion test conditions. The corroded powder-rolled sheet of the 1.5 wt% tin lead alloy has uniform corrosion, but the cast-rolled sheet of lead alloy containing 1.5 wt% tin was much distorted and was perforated by the corrosion. Intergranular corrosion of the powder-rolled lead–tin alloys was much suppressed as compared with that of the cast-rolled lead–tin alloys.     

Hydriding and dehydriding characteristics of nanocrystalline and amorphous Mg20Ni10−xCox (x = 0–4) alloys prepared by melt-spinning

In order to improve the hydriding and dehydriding performances of the Mg₂Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg₂₀Ni_10−xCo_x (x = 0–4) hydrogen storage alloys. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. Thermal stability of the as-spun alloys was researched by DSC. The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The results showed that no amorphous phase formed in the as-spun Co-free alloy, but the as-spun alloys containing Co showed certain amount of amorphous phase. The hydrogen absorption capacities of the as-cast alloys first increase and then decrease with the variety of Co content. The hydrogen desorption capacities of as-cast and spun alloys rise with increasing Co content. The rapid quenching significantly improved the hydrogenation and dehydrogenation capacities and the kinetics of the alloys. When the quenching rate increased from 0 (as-cast was defined as spinning rate of 0 m/s) to 30 m/s, the hydrogen absorption capacity of the alloys (x = 0) at 200 °C and 1.5 MPa in 20 min rose from 1.39 to 3.12 wt%, and from 1.91 to 2.96 wt% for the alloy (x = 4). The hydrogen desorption capacity of the alloy (x = 0) in 20 min increased from 0.19 to 0.89 wt%, and from 1.39 to 2.15 wt% for the alloy (x = 4).     

Influence of temperature on corrosion behavior of PbCaSnCe alloy in 4.5 M H2SO4 solution

The temperature effect on corrosion behaviors of PbCaSnCe alloy in 4.5 M H₂SO₄ solution was investigated by using potentiodynamic curve, electrochemical impedance spectra (EIS), Mott-Schottky plot and photocurrent response methods. It was found that PbCaSnCe alloy was in passive state in sulfuric acid solution, a passive film can be formed on alloy surface. The compositions of passive films formed at 0.9 V for 2 h under different temperatures were detected by X-ray photoelectron spectroscopy (XPS). The results showed that the film resistance and the transfer resistance decreased with the increment of the solution temperature. Mott-Schottky analysis and the photocurrent response revealed that the passive film exhibited n-type semi-conductive character, the donor density of the passive film decreased with increasing the solution temperature. Photocurrent response revealed that the photocurrent increased with increasing temperature. XPS results indicated that the PbO₂ content in passive films may increase with increasing the solution temperature.     

The effect of rapid solidification on the microstructure and hydrogen storage properties of V35Ti25Cr40 hydrogen storage alloy

The microstructures and hydrogen storage properties of as-cast and rapidly solidified V₃₅Ti₂₅Cr₄₀ alloys have been investigated in this paper. The results showed that the rapid solidification refined the dendritic microstructure and altered the element distribution of the alloy. And through the positron annihilation measurements of the vacancy trapping rate (K_d1) and vacancy-trapped positron annihilation lifetime (τ₂), it was found that the rapid solidification increased the vacancy concentration and at the same time decreased the vacancy size in the alloy. The XRD results showed that the rapid solidification also significantly enlarged the alloy's lattice parameter. As a result of the microstructure change, the hydrogen absorption capacity and hydrogen absorption rate were increased; and the kinetic mechanism of hydrogen absorption was changed from 3-D diffusion control in the as-cast alloy to chemical reaction control in the rapidly solidified alloy; but the activation property was to some extent weakened after the rapid solidification.     

Effect of conducting composite polypyrrole/polyaniline coatings on the corrosion resistance of type 304 stainless steel for bipolar plates of proton-exchange membrane fuel cells

A bilayer conducting polymer coating composed of an inner layer of polypyrrole (Ppy) with large dodecylsulfate ionic groups obtained by galvanostatic deposition, and an external polyaniline (Pani) layer with small SO₄²⁻ groups obtained by cyclic voltammetric deposition was prepared to protect type 304 stainless steel used for bipolar plates of a proton-exchange membrane fuel cell. The corrosion performance of the bare and coated steel in 0.3 M HCl was examined by electrochemical impedance spectroscopy, polarization and open-circuit potential measurements. The experimental results indicated that both the composite Ppy/Pani coatings and the single Ppy coatings increased the corrosion potential of the bare steel by more than 400 mV (saturated calomel electrode), and increased the pitting corrosion potential by more than 500 mV (saturated calomel electrode). The bilayer coatings could reduce the corrosion of the alloy much more effectively than the single Ppy coatings, serving as a physical barrier and providing passivity protection, with acceptable contact resistance.     

Improved electrochemical properties of amorphous Mg65Ni27La8 electrodes: Surface modification using graphite

Amorphous Mg₆₅Ni₂₇La₈ alloy is prepared by melt-spinning. The alloy surface is modified using different contents of graphite to improve the performances of the Mg₆₅Ni₂₇La₈ electrodes. In detail, the electrochemical properties of (Mg₆₅Ni₂₇La₈) + xC (x = 0–0.4) electrodes are studied systematically, where x is the mass ratio of graphite to alloy. Experimental results reveal that the discharge capacity, cycle life, discharge potential characteristics and electrochemical kinetics of the electrodes are all improved. The surface modification enhances the electrocatalytic activity of the alloy, reduces the contact resistance of the electrodes and obstructs the formation of Mg(OH)₂ on the alloy surface. An optimal content of graphite has been obtained. The (Mg₆₅Ni₂₇La₈) + 0.25 C electrode has the largest discharge capacity of 827 mA h g⁻¹, which is 1.47 times as large as that of the electrode without graphite, and the best electrochemical kinetics. Further increasing of graphite content will lead to the increase of contact resistance and activation energy for charge-transfer reaction of the electrode, resulting in the degradation of electrode performance.     

Effect of minor nickel alloying with zinc on the electrochemical and corrosion behavior of zinc in alkaline solution

The electrochemical and corrosion behavior of pure zinc and Zn-0.5Ni alloy in strong alkaline solution (7 M KOH) was investigated by Tafel plot, potentiodynamic, potentiostatic and electrochemical impedance spectroscopy (EIS) methods, and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Measurements were conducted under different experimental conditions. The results of both Tafel plot extrapolation and the electrochemical impedance spectroscopy (EIS) measurements exhibited the same trend, which the cathodic and anodic processes on the alloy surface are less significant compared with those on the pure zinc. The results revealed that, the shift in steady state of open-circuit potential (E_corr) to more negative potential in the case of the studied alloy compared with that of pure zinc has a positive effect on both charge efficiency and self-discharge.The anodic potentiodynamic measurements demonstrated that the polarization curves exhibited active/passive transition. The active dissolution of both pure zinc and its alloy increases with increasing temperature and scan rate. The activation energy (E_a) value of active region and peak current (I_AI) of the two studied electrodes in the investigated alkaline solution is calculated and compared. In the case of alloy, the results obtained at certain positive potential (+425 mV vs. SCE), exhibited high current density indicating that the most passive layer was destroyed. This indicates that the addition of small amount from Ni to Zn promotes the electrochemical reaction (in the passive region), acting as so-called self catalysis. Accordingly, one can conclude that, the electrochemical behavior of the investigated alloy in strong alkaline solution contributes to suppression of hydrogen gas evolution and increases the corrosion resistance. In addition, reactivation of the alloy surface takes place in the passive region.