Lead-acid Battery Electrodes Research Articles

Mitigating intergranular attack and growth in lead-acid battery electrodes for extended cycle and operating life

Deterioration in the performance of lead acid batteries is primarily governed by weight loss and growth of the positive electrodes, arising from creep and intergranular corrosion/cracking. The present investigation examines the impact of increasing the frequency of grain boundaries having low-Σ misorientations (Σ≤29), described by the Coincident Site Lattice (CSL) model, which are known to be resistant to these intergranular degradation phenomena. Electrode microstructures of various PbCaSn alloys processed to contain frequencies of special boundaries (in excess of 50 pct) exhibited reductions in weight loss of between 26 and 46 pct accompanied by declines in grid growth of between 41 and 72 pct. Moreover, the distribution of intergranular attack/cracking in the microstructure of these alloys can be predicted on the basis of the frequency of low-Σ special boundaries and grain size. In general, improvements in corrosion and creep/cracking occur without compromising tensile properties such as yield strength, ultimate tensile strength (UTS), and ductility. Modifying the crystallographic structure of grain boundaries in Pb alloy battery electrodes, thus, provides an opportunity for minimizing grid thicknesses (weight) and, hence, material costs in battery production, or for maximizing energy densities (Wh/kg) and cycle life performance.

Grain Boundary Engineered Lead Alloys

ABSTRACTThe present work reports oii the effect of grain boundary structure on intergranular corrosion and creep by grain boundary diffusion in polycrystalline lead (Pb). “Special” boundaries characterized by low-Σ misorientations in the Coincident Site Lattice (CSL) model have been shown to exhibit resistance to grain boundary sliding and corrosion. PbCa and PbCaSn alloys having “special” grain boundary frequencies greater than 50% showed a 30 fold reduction in steady-state creep compared with corresponding as-received alloys containing 10% to 28% of low-Σ CSL boundaries in the microstructure of comparable grain size. At the same time, increasing the frequency of “special” boundaries enhanced alloy ductility with no compromize in tensile strength. Results from electrochemical corrosion tests on polarizied Pb alloys immersed in H2SO4 (S.G.=1.28) at 70°C indicate a clear correlation between the frequency of “special” boundaries and the prolifíeration of intergranular corrosion resulting in bulk weight loss from grain-dropping. Collectively, these results advocate adopting a “gram boundary design” approach in developing advanced lead-acid battery electrodes.

A modelling approach to the optimizaton of lead-acid battery electrodes

A resistive grid model was used to study the current and ohmic overpotential distributions along the surface of lead-acid battery electrodes. Analyses were made under two different regimes: the initial behaviour at high current densities and the response with time at low current densities. At high discharge currents the theoretical results show that the geometry of the electrodes and the position of the lug play the most important role in controlling the magnitude of ohmic losses. The best geometry is a square grid with the lug positioned at the upper centre of the electrode. At low discharge currents the model was used to follow the current distribution along the electrode surface as a function of time. In this last study the appearance, for long discharge times, of short-circuited concentration microcells localized in certain regions of the electrode surface was noted. The other regions of the electrode supply the external discharge current and the excess current necessary to charge the internal microcell.

Vibrational spectroscopy on the PbO-PbSO 4 system and some related compounds : Part 1. Fundamentals, infrared and Raman spectroscopy

The following compounds, lead sulphate (PbSO 4), lead oxide (PbO), lead dioxide (PbO 2), monobasic lead sulphate (PbO · PbSO 4), tribasic lead sulphate (3PbO · PbSO 4 · H 2O) and tetrabasic lead sulphate (4PbO · PbSO 4) can occur during the charge and discharge reactions of lead electrodes in lead acid batteries. These substances can also be detected in the active mass of lead acid battery plates throughout the different steps in the production process. The appearance of the basic lead sulphates and of lead oxide is an important indication of the passivation behaviour of the mechanism of the electrodes and points to the chemical and electrochemical oxidation reactions under the passive layer. For the investigation of this sensitive passive layer, it is important to avoid all the disadvantages of the predominantly used ex situ methods (especially x-ray analysis). Therefore, it is necessary to apply an in situ technique for the characterization of the lead electrode surfaces in contact with the commonly used aqueous sulfuric acid solution. For this reason, external reflection absorption FT-IR spectroscopy was applied to investigate lead electrodes under different electrochemical conditions. As a prerequisite for the planned in situ work, the vibrational spectra of the above mentioned compounds in the Pb-PbO-PbSO 4-H 2SO 4 system must be known, in order to allow the identification of these substances on the electrodes in the in situ investigations. This work presents the infrared and Raman spectroscopic characterization of PbO, Pb 3O 4, PbSO 4 PbO · PbSO 4, 3PbO · PbSO 4 · H 2O and 4PbO · PbSO 4.

On the resistance of the grid/active material interphase in lead—acid battery electrodes

The contact resistance between the active PbO 2 mass and a lead grid was measured in situ by a dc method. The influence of the rib resistance was analysed mathematically and the corresponding correction was determined. The slow decrease of the contact resistance of a thermopassivated electrode with the time is discussed in terms of solid-state diffusion of sulphate ions. The lead grid/active mass interface is insensitive against discharge up to 60% of the capacity, whereas at deeper discharges its resistance increases in accord with Winsel's “aggregate of spheres” model. The dependence of the contact resistance on the concentration of H 2SO 4 is essentially in accord with Garche's studies of the passivating layer on lead.

Conducting Polymers as the Additives to the Positive Electrode of Lead-Acid Battery

Conducting Polymers as the Additives to the Positive Electrode of Lead-Acid Battery

On the behaviour of carbon black in positive lead-acid battery electrodes

The addition of carbon black to the positive paste led to an alteration in structure of the PbO2/PbSO4 electrode due to an increase in porosity, in active mass coarsening and in the α/β-PbO2 ratio. These structural effects are explained as being caused by the ability of carbon black to increase the water-accumulating capacity of the paste, to influence the local formation conditions and to participate in the charge transport within the unformed mass. Oxidative removal of carbon black from the active mass was studied.

On thermopassivation of the positive lead—acid battery electrode: Part 3: Thermopassivation of smooth PbO 2 electrodes

Smooth (unpasted) PbO 2 electrodes are passivated after thermal treatment, indicating that such passivation occurs in the region of the grid/corrosion layer phase boundary. Concurrent with the passivation process, however, a synproportionation reaction occurs between the Pb grid and the PbO 2 corrosion layer, which decreases the discharge capacity and accelerates depassivation. The influence of the synproportionation reaction on the discharge behaviour of pasted PbO 2 electrodes is discussed.

The effect of additives on the positive lead—acid battery electrode

The effect of the additives carboxymethylcellulose (CMC), carbon black, silica gel, and fibres on the manufacture of positive active material and on the cycle life was investigated by means of porosimetry, inner surface (BET) determination, X-ray diffractometry, chemical analysis, and by measuring the course of the potential, by testing the low rate and high rate capacities and by overcharge cycling tests. It was shown that the additives can be classified, according to their mode of action, into additives (a) increasing the water accumulating capacity of the paste, (b) influencing the crystallization of the mass, (c) increasing the electronic conductivity of the mass, (d) stabilizing the mass. Types (a), (b), and (c) affect the manufacture of active material and the initial capacities, whereas additive (d) improves the cycle life.

Effect on cathodic reduction of β-PbO 2 in sulfuric acid solution of surface concentration of Pb 2+ ions formed on β-PbO 2

The discharge reaction of positive electrode of lead-acid battery was investigated with the rotating ring-disc electrode. The large supersaturation of Pb 2+ ion on the electrode surface was obtained during discharge of initial period and the PbSO 4 nuclei was formed. The precipitation of PbSO 4 proceeded smoothly in the presence of PbSO 4 nuclei. In the steady state, the colloidal PbSO 4 film on the electrode surface of which stability depended on the concentrations of sulfuric acids was formed from the dissolving Pb 2+ ions. Especially its stability in 1.0 M H 2SO 4 was so low that the concentration of Pb 2+ ions during discharge was the largest of those in any other sulfuric acids, so that the effect of the film on the overpotential during galvanostatic discharge is the smallest, as discussed in a following paper[1]. The particle sizes of PbSO 4 precipitated during discharge were related to the concentration of Pb 2+ ions on the electrode. These sizes increased with increasing concentration of Pb 2+ ions. If the discharge capacity is limited by the passivation with PbSO 4 crystal, the use of 1.0 M H 2SO 4 as the electrolyte of lead-acid battery may be favoured.

Thermopassivation of the positive lead-acid battery electrode Part II. Influence of activating conditions on the thermopassivation of dry-charged positive electrodes of the lead-acid accumulator

On reaction of the PbO n-passivation layer (1 ≦ n < 1.5) causing thermopassivation (η T), with activating sulphuric acid, a decrease of η T to η T O in the thermopassivation of a non-activated PbO 2 electrode occurs. This difference is defined as depassivation (δ T). δ T depends on the activating conditions (activating time Gt A and activating temperature ν A) as well as on the measuring conditions (discharge current, I and measuring temperature ν M). With increase in τ A and ν A an increase of δ T is obtained. At ν A −25 °C the depassivation after τ A = 4 h amounts to only 200 mV. At ν A +35 °C the depassivation after τ A = 1 h amounts to 1400 mV, ie. the electrode is completely depassivated.

Computerized design and evaluation of improved electrodes for lead-acid batteries

A mathematical model of a positive-negative electrode pair in a lead-acid battery has been developed, and can be solved to determine the potential and current density distribution over the electrode surfaces. With the aid of a computer the model was used to improve the grid design of the positive electrode. The results were compared with those obtained by discharging full-size electrode pairs in a laboratory cell. Agreement between projections and experimental data was about 70% with the assumptions made for certain input parameters. Further development is needed before the model can be applied to the design of ‘radial’ grids with curvilinear grid members.

On thermopassivation of positive lead—acid battery electrodes: Part I: The influence of drying positive, dry-charged lead—acid battery electrodes on thermopassivation and its causes

The influence on thermopassivation (η T) of the drying time (τ) and drying temperature (ϑ) of formed positive electrodes for dry-charged lead—acid batteries has been investigated. It has been shown that there is no thermopassivation in the case of τ ⩽ 4 min up to approx. ϑ = 250 °C, while drying temperature has a different influence on thermopassivation at 4 min $ ̌ τ $ ̌ 30 min. Passivation is observed τ > 30 min even where ϑ $ ̌ 100 °C. The effect of thermopassivation increases with falling cell temperature. If drying conditions and cell temperatures are not extreme, thermopassivation has hardly any influence on the immediate ampere-hour capacity, but has a comparatively large influence on the immediate watt-hour energy content. Physico-chemical and electrochemical investigations show that the PbO 2 electrode is thermally damaged during the drying process. This is apparent from changes in the primary structure of the active mass (destruction of preprotonized structure) and — especially at higher temperature — also in the secondary structure (reduction of BET surface) as well as in the composition of passivating layers. However, the contributions of primary and secondary structure variations to the overall amount of thermopassivation are comparatively low. The principal reason for this phenomenon is the generation of poorly conductive and, thus, passivating layers with semi conductor properties.

Study of structural factors of lead-acid battery electrodes

The electrolyte conductivity in the pores, and the true and apparent densities of the active mass, were measured on electrodes of a starter-type lead-acid battery in various stages of discharge, and the porosity of the plates and the tortuosity factor of the pores were evaluated. The results suggest that the charged, cycled positive plates contain a certain fraction of lead dioxide of a lower density, probably amorphous, which is reduced preferentially. Transport restrictions are more important in positive than in negative plates. Volume changes of a negative plate during cycling were found to be reversible, while with a positive plate they were irreversible.