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

a lead-acid battery and alloy technology, applied in the field of thermally mechanical treatment of lead-acid batteries, can solve the problems of affecting the life of industrial batteries, limiting the life of automotive batteries, and premature failure of lead-acid batteries, so as to improve the cycle life, improve the performance of lead-acid batteries, and improve the cycle life

Inactive Publication Date: 2004-06-17
AUST KARL T +5
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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 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 modem 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.

Method used

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

Examples

Experimental program
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example # 2

EXAMPLE #2

[0081] A series of commercial lead alloys of the Class II type previously described, were obtained in a conventional cast condition in the form of strip. These strips were subsequently processed using the techniques described in the present invention. The specific alloys and processing conditions are summarized as follows.

[0082] A Pb-0.073 wt % Ca-0.07 wt % Sn alloy (Class II) was processed by three cycles each comprised of cold rolling at room temperature to achieve a 40% reduction in thickness, annealing at 270.degree. C. for 10 minutes in air followed by air cooling. The resulting microstructural improvement in terms of special grain boundary content is summarized in FIG. 5 (identified as PbCaSn in FIG. 5). The special grain boundary content was increased from 11% in the as-cast starting material, to 51% in the material processed by the method described.

[0083] A Pb-0.065 wt % Ca-0.07 wt % Sn 0.03 wt % Ag alloy (Class II) was processed by two cycles each comprised of col...

example # 3

EXAMPLE #3

[0087] A Pb-0.03 wt %Ca-0.7 wt. % Sn 0.06 wt %Ag alloy, representative of a Class I alloy was produced using a commercial rotary net shape casting process. The cast strip of 0.86-0.89 mm thickness was subsequently subjected to a single processing cycle comprised of approximately 20% cold tensile strain (room temperature), and heat treatment in an air convection oven at a temperature of 250.degree. C. for 5 minutes followed by cooling to ambient temperature. The strain was introduced at room temperature solely through the grid expansion process and was controlled by the tool die geometry (i.e., diamond height of expanded mesh). For comparison purposes a wrought strip was produced without subsequent recrystallization heat treatment. In this case, cast strip of 1.72 mm thickness was cold rolled by 50% and similarly expanded to mesh. The proportion of special grain boundaries present in the as-cast, wrought, and single step GBE processed materials were found to be 16.0%, 15.4%...

example # 4

EXAMPLE #4

[0089] Various lead alloys were subjected to the deformation and annealing cycle used to make the recrystallized lead-alloy according to this invention. Each of the samples was deformed at room temperature to 25% reduction in thickness and then annealed by heat-treating at 255.degree. C. for five minutes. After the deformation reduction and annealing, each of the aforementioned lead alloys was tested for hardness. A minimum of six hardness measurements at each of two locations of the test alloys were obtained using a Shimadzu model HMV2000 micro hardness tester utilizing a 25 g load. The hardness of each metal was also measured in the same way in the as-cast condition (i.e. without being subjected to deformation and annealing cycle). The f.sub.sp count of the as-cast material samples prior to GBE processing in all cases was between 10 and 15%. The results of the hardness test for each of the lead alloys is shown in Table 2. In all instances, the deformation reduction and h...

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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...

Claims

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Application Information

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IPC IPC(8): C22C11/00C22F1/12H01M4/68H01M4/82
CPCC22C11/00H01M4/82H01M4/685C22F1/12Y02E60/10
Inventor AUST, KARL T.LIMOGES, DAVID L.GONZALEZ, FRANCISCOPALUMBO, GINOTOMANTSCHGER, KLAUSLIN, PETER K.
Owner AUST KARL T
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