Thermo-mechanical treated lead and lead alloys especially for current collectors and connectors in lead-acid batteries

Abstract

Recrystallized lead and lead alloy positive current collectors and connectors such as straps and lugs for use e.g. in lead acid batteries and electrowinning anodes, having an increased percentage of special grain boundaries in at least part of the microstructure, which have been provided by a process comprising of (i) cold or hot rolling or cold or hot extrusion or (ii) steps of deforming the lead or lead alloy, and subsequently annealing the lead or lead alloy. Either a single cycle of working and annealing can be provided, or a plurality of such cycles can be provided. The amount of deformation, the recrystallization time and temperature, and the number of repetitions of such steps are selected to ensure that a substantial increase in the population of special grain boundaries is provided in the microstructure, to improve resistance to creep, intergranular corrosion and intergranular cracking of the current collectors and connectors during battery service, and result in extended battery life and the opportunity to reduce the size and weight of the battery.

Description

[0001] This application is a Continuation-in-Part of pending application Ser. No. 09 / 412,610 filed Oct. 6, 1999, which is a Continuation-in-Part of application Ser. No. 08 / 977,518 filed Nov. 24, 1997, which is a Continuation-in-Part of application Ser. No. 08 / 835,926 filed Apr. 8, 1997 (abandoned), which is a Continuation of application Ser. No. 08 / 609,327 filed Mar. 1, 1996 (abandoned).[0002] This invention relates to wrought and recrystallized lead and lead alloys, with increased resistance to creep and intergranular cracking and corrosion. This invention is more particularly concerned with positive lead and lead alloy current collectors and connectors used in lead-acid batteries which, via recrystallization treatment to generate new grain boundaries in the microstructure, have improved resistance to corrosion and growth, so as to provide enhanced battery reliability, extended service life and greater energy density.[0003] Intergranular degradation (i.e., creep deformation, cracki...

AI Technical Summary

Benefits of technology

[0021] It is a further object of this invention to provide a process which enables the treatment of a finished part without imparting a substantial dimensional change as is normally the case by conventional deformation operations used, including rolling, extruding, forging and the like. This feature enables the treatment of finished parts, e.g. bookmould cast lead-acid battery grids, tubular grids, Pb and Pb-alloy straps and posts as well as "Conroll" grids without substantial deformation of the part.

[0022] It is a further object of the present invention to provide a peening process, optionally followed by a heat-treatment to substantially improve the corrosion resistance of non-consumable electrodes, current collectors and other metallic articles employed in electrochemical cells and, at the same time to increase the surface area and to improve the surface texture resulting in substantially enhanced adhesion of surface coatings, including active material and paste adhesion.

[0023] It is a further object of this invention to provide a method for treating at least part of the outer surface of the current collectors made by any of the commercial processes used including gravity casting of "bookmold" or "tubular" grids and by using the "Con Roll" process (Wirtz Manufacturing Inc., Port Huron, Mich., USA) to increase the surface area and improve paste adhesion.

[0024] It is a further objective of this invention to provide a process capable of improving the corrosion properties of the surface and near-surface layer of metallic parts for use in electrochemical cells and not to necessarily impart uniform physical and chemical properties throughout the part. This will be obvious to anyone skilled in the art as the chemical attack in electrochemical cells mostly occurs on or near the surface of the part, which is exposed to typically corrosive electrolytes.

[0025] It is another object of this invention that the thermo-mechanical treatment employed to treat the lead or lead alloy current collectors or their precursors substantially increases the percentage of special grain boundaries to increase at least one of the resistance of the lead or lead alloy to creep and resistance to intergranular corrosion and intergranular cracking, wherein the lead or lead alloy has been subjected to at least one processing cycle comprising: suitably deforming the lead alloy below the solvus temperature, and subsequently annealing the lead alloy for a time and temperature sufficient to effect recrystallization to substantially increase the concentration of special grain boundaries.

Problems solved by technology

Intergranular degradation (i.e., creep deformation, cracking and corrosion) of lead-based positive current collector grids, tubular spines, foils and connectors (straps, lugs, posts) are the principal cause of premature failure of lead-acid batteries.

Intergranular corrosion limits the life of automotive batteries and affects the life of industrial batteries.

Creep deformation, which arises primarily from grain boundary sliding processes, results in dimensional expansion of the positive current collector.

The so-called "growth" causes a loss of contact between the electrode surface and the PbO.sub.2 paste and leads to shorting between adjacent electrodes.

The growth of the positive current collector also contributes to intergranular "cracking".

Growth of the positive current collector in lead-acid batteries is the predominant failure mode of automotive batteries as under-the-hood temperatures in modern automobiles increase.

Moreover, both precipitation-processed and wrought electrodes have not been shown to display any significant improvements with regard to intergranular corrosion.

However, these studies provide no instruction as to how to achieve a high concentration of special grain boundaries, and as noted, it is only recently that techniques such as Orientation Imaging Microscopy have become available to determine the concentration of special grain boundaries in a polycrystalline material.

However, the process described and claimed in these patents is directed exclusively to certain austenitic stainless steels and nickel-based alloys, and not with any other metals.

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