Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 104-105).

published_or_final_version / Civil Engineering / Master / Master of Philosophy

During the course of this work two fundamental aspects of the electrochemistry of the lead acid battery system have been investigated. The first area of study concerns the respective roles of alpha and beta lead dioxide in the positive plate, and more specifically the interconversion behaviour of the two polymorphs. The second research area concerns the occurence of a passivating layer of lead monoxide between substrate lead and the active material of the electrode. A subject of extreme importance to the lead acid battery manufacturer, since passivating layers of this type are acknowledged as being one of the major failure modes. This work has differed from most before it, in that use has been made of electrodeposits of the two modifications to study both the interconversion products, and the conditions necessary for lead monoxide formation. A survey of some of the recommended methods of preparation for the two forms of lead dioxide has been carried out and compared to the data given in the Powder Diffraction File. X-ray diffraction has been the major investigative tool utilised, and electrodes have been subjected to analysis in both the powder and unground state, after both galvanostatic and potentiodynarnic cycling. Cyclic voltarnmetry was used to study the potentiodynarnic conversion products of deposits swept between the hydrogen and oxygen gas evolution regions in sulphuric acid. The galvanostatic cycling showed that a conversion of alpha lead dioxide to the beta does occur, although evidence for conversion of the beta form to the alpha was not found. The potentiodynamic study revealed that in order for lead monoxide to be formed under deposits of beta lead dioxide, the presence of substrate lead is required beneath a lead sulphate film or membrane. Under these conditions it was discovered that the lead monoxide itself is a precursor to alpha lead dioxide formation.

Polypropylene has proven to be the ideal material for the outer shell of the lead acid batteries. Due to its mold-ability and inert properties the material provides a capsule for the functioning components of the lead acid battery and can withstand a variety conditions encountered during its application, such as impact shock resistance, high and low temperatures and acid resistance. Polypropylene has however become of great concern with regards to environmental pollution since it is generally resistant to normal conditions of degradation and can only be properly disposed of by incineration. This factor has encouraged the industry to find ways to regenerate spent polypropylene. A good example of such a process is the recycling of lead acid batteries. This allows not only for the regeneration of lead, but also for the recycling of polypropylene in the manufacturing of battery cases. There are some cost advantages in using recycled polypropylene. However it does have its disadvantages in that the material does start to deteriorate after multiple processes. A common practice amongst battery manufacturers is to add virgin polypropylene to the recycled material in order to ensure performance consistency. The comparative study investigated the use of various ratios of virgin and recycled PP in the manufacturing of lead acid battery cases and their influence on the physical properties and performance of the final material. The degradation of PP was also investigated as the material was subjected to multiple manufacturing processes where the influence of stabilizers was further considered. A common technique of PP analysis such as MFI was shown to be an effective technique to maintain good quality control. The study further showed that it is important that the material grade of PP used in the manufacturing of the battery case and lid is compatible in order to allow for effective heating sealing of the two components. Polypropylene has a waxy surface finish and it is generally difficult to label or write on. Labels tend to fall off in application and make it difficult to maintain a track record of the manufactured batteries with time. This study showed successfully that a laser activated dye can be added to the PP without influencing its color or its performance. This allows for successful labeling of battery cases by various bar coding writers that can trace the battery through its manufacturing process. Lead acid batteries are often operated outside the specified temperature range that is determined by battery manufacturers resulting in premature failure. These failures can occur within the warranty period of the battery and result in illicit claims since the monitoring of the batteries in its application was not possible. A suitable temperature monitoring device was designed that would be incorporated into the vent cap or lid of the battery case. The device contained temperature sensitive indicators that would undergo a permanent color change at specified temperatures thereby giving the battery manufacturer an indication as to the maximum temperature the battery was exposed to.

This thesis describes the effects of phosphoric acid on the positive lead dioxide electrode of a lead-acid cell. The aim of this research was to evolve a mechanism for the action of phosphoric acid on the charge (PbSO4→PbO2) and discharge (PbO2→PbSO4) processes. Industrially, phosphoric acid is added to the battery electrolyte because it has certain beneficial effects of preventing formation of 'hard' sulphate and reduction in shedding of active material resulting in improved cycle life. The main disadvantage of phosphoric acid-containing electrolyte is a reduction in capacity of the cell.

It is well known that a conventional lead acid cell that is exposed to a partial state of charge capacity cycling (PSoCCC) would experience a build-up of irreversible PbSO4 on the negative electrode. This results into a damaged negative electrode due to excessive PbSO4 formation by the typical visual “Venetian Blinds” effect of the active material. This displays the loss of adhesion of the active material with the electrode’s grids thereby making large sections of the material ineffective and reducing the cells useful capacity during high current applications. The addition of certain graphites to the negative paste mix had proven to be successful to reduce this effect. In the first part of the study, the physical and chemical properties of the various additives that are added to the negative electrode paste mix were comparatively studied. This was done to investigate any significant differences between various suppliers that could possibly influence the electrochemical characteristics of the Pb-acid battery performance. This comparative study was done by using the following analytical techniques; BET surface area, laser diffraction particle size, PXRD, TGA-MS and SEM. The study showed that there were no significant differences between the additives supplied from different suppliers except for some anomalies in the usefulness of techniques such as N2 adsorption to study the BET surface area of BaSO4. In order to reduce the sulphation effect from occurring within the Pb-acid battery a number of adjustments are made to the electrode active material. For example, Pb-acid battery manufacturers make use of an inert polymer based material, known as Polymat, to cover the electrode surfaces as part of their continuous electrode pasting process. It is made from a non woven polyester fiber that is applied to the pasted electrodes during the continuous pasting process. In this study the Polymat pasted electrodes has demonstrated a better physical adhesion of the active material to the grid support thereby maintaining the active material’s physical integrity. This however did not reduce the sulphation effect due to the high rate partial state of capacity cycling (HRPSoCCC) test but reduced the physical damage due to the irreversible active material blistering effect. The study investigated what effect the Polymat on the electrodes has on the III battery’s Cold Cranking Ability (CCA) at -18 degree C, the HRPSoCCC cycling and its active material utilization. The study showed that there was little or no differences in the CCA and HRPSoCCC capabilities of cells made with the Polymat when compared to cells without the Polymat, with significant improvement in active material’s adhesion and integrity to the grid wire. This was confirmed by PXRD and SEM analysis. Negative electrodes were made with four types of graphites (natural, flake, expanded and nano fibre) added to the negative paste mixture in order to reduce the effect of sulphation. The study looked at using statistical design of experiment (DoE) principles to investigate the variables (additives) such as different graphites, BaSO4 and Vanisperse to the negative electrode paste mixture where upon measuring the responses (electrochemical tests) a set of controlled experiments were done to study the extent of the variables interaction, dependency and independency on the cells electrochemical properties. This was especially in relation to the improvement of the battery’s ability to work under HRPSoCCC. The statistical analysis showed that there was a notable significant influence of the amounts of vanisperse, BaSO4 and their respective interactions on a number of electrochemical responses, such as the Peukert constant (n), CCA discharge time, material utilization at different discharge rates and the ability to capacity cycle under the simulated HRPSoCCC testing. The study did not suggest an optimized concentration of the additives, but did give an indication that there was a statistical significant trend in certain electrochemical responses with an interaction between the amounts of the additives BaSO4 and Vanisperse. The study also showed that the addition of a small amount of Nano carbon can significantly change the observed crystal morphology of the negative active material and that an improvement in the number of capacity cycles can be achieved during the HRPSoCCC test when compared to the other types of graphite additives.

Thesis (Ph. D.)--University of Idaho, 2005. / Also available online in PDF format. Abstract. "July, 2005." Includes bibliographical references (leaves 94-98).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains x, 165 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 163-165).

Although competitive today, traditional PbA (<1500 cycles) and advanced lead-acid batteries (ALAB) (>4000 cycles) will not be able to compete with lithium and flow batteries by 2020. To compete with novel zinc, lithium and flow batteries, the PbA chemistry needs to achieve significant performance improvements, primarily through sustainable increases to specific energy (Wh/kg), while not negatively impacting cycle life. Inverse charging has been examined for its potential in improving PbA cycle life as a battery maintenance procedure, and as a potential technique for improving electrode specific capacity (mAh/kg) during battery manufacturing and formation. A thorough levelized cost of energy (LCOE) shows that for traditional PbA batteries with cycle lives <2000, inverse charging as a maintenance strategy (to increase cycle life) improves battery economics. Inverse charging to increase cycle life for ALAB systems (>4000 cycle life) was proven to worsen battery economics, as additional costs of capital and maintenance fail to outweigh savings achieved through reductions in replacement cost. On the other hand, inverse charging employed as a manufacturing practice to increase specific energy dramatically reduces the cost of the PbA and ALAB systems, ensuring future cost competitiveness. Inverse charging as a maintenance strategy should be restricted to devices with <2000 cycles and to projects with long project lives (20 years) that require frequent replacement. Inverse charging as a manufacturing strategy (to increase specific energy) is highly preferable in all instances. When successful, inverse charging increases the specific capacity and active material utilization of studied battery electrodes significantly. Successful inverse charging of battery electrodes and pure lead rods show improvements in discharge capacities over a range of discharge rates with negligible impact to coulombic and energy efficiency values. The extent of success, however, depends on several important variables. Thorough examination of inverse charging on Pb rods and porous battery electrodes illustrates the importance of the degree of prior electrode sulfation and obstruction of transport of H₂SO₄. Other important factors include the composition of electrode grid alloys, the peak oxidation voltage applied to the negative electrode during inverse charging, initial particle sizes, and electrolyte additives. Significant challenges to inverse charging exist. For heavily sulfated batteries and lead metals, impeded electrolyte transport results in excessive internal pore pH increases, creating semipermeable membranes through an electrode hydration mechanism, resulting in dramatic inverse charging failure. Additionally, impedance, voltage, x-ray and BET data hint that post-inverse charging, agglomeration of finely divided Pb and PbSO₄ particles occurs, coupled with negative electrode conductive pathway destruction. As such, the influence of expander materials and nucleation additives should be investigated to better prevent sulfation failure, and to better control the nucleation and growth of lead and lead sulfate structures during inverse charging. Cycle life studies on flooded lead antimony batteries subjected to periodic inverse charging illustrate that inverse charging is highly successful on all batteries independent of states-of-health. Batteries with poor states-of-health (discharge capacities <15% of initial values) experienced almost perfect discharge capacity restoration post-inverse charging. Traditional methods of extending cycle life (i.e. prolonged overcharging techniques) were demonstrated to be inadequate at appreciably regenerating battery capacities, providing only marginal increases. The benefits of inverse charging, however, are met with significant challenges to battery redesign. Temporary antimony poisoning effects lead to declines in round-trip-efficiency for batteries with antimony-based positive plates. Tin dissolution results in diminished grid to active material conductivity and reduced capacity for batteries with tin-based positives. For the negative electrode, Brunauer–Emmett–Teller (BET) surface area and x-ray measurements indicate that although large PbSO₄ crystals are oxidized during inverse charging, creating extensive micropore networks during conversion from Pb to PbO₂, surface area and capacity gains are lost during reconversion back to sponge lead due to uncontrolled nucleation and particle fusion. Additionally, active material shedding of the positive and negative electrodes is observed to spike during and after inverse charging. Negative electrode active material suffers excessive degradation and loss of cohesion, particularly for electrodes with small initial particle feature sizes, resulting in a loss of structure upon completion of the technique. Positive electrode composition changes to weakly interconnected b-PbO₂, dramatically increasing electrode capacity while simultaneously accelerating electrode failure through shedding. Loss of particle cohesion in both electrodes promotes excessive shedding and sludging, creating intra-cellular short-circuits. In addition, inverse charging aggravates grid growth, promoting inter-cellular short-circuiting by creating pathways for cell-to-cell electrolyte contact upon seal destruction in current monoblock designs.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references.