WO2000046868A1

WO2000046868A1 - Lead-tin alloy current collectors, batteries made thereof and methods for manufacturing same

Info

Publication number: WO2000046868A1
Application number: PCT/US2000/003049
Authority: WO
Inventors: Ramesh C. Bhardwaj; Tristan E. Jeurgens
Original assignee: Bolder Technologies Corporation
Priority date: 1999-02-04
Filing date: 2000-02-04
Publication date: 2000-08-10
Also published as: AU3223800A

Abstract

The present invention provides a current collector (18, 22) for a battery (16) which comprises lead and at least 0.01 % but less than 0.5 % tin, is less than 0.005 inches thick, and is substantially non-perforated. In another embodiment, the current collector contains at least 0.001 % but less than 0.01 % tin and is less than 0.03 inches thick. The present invention further provides batteries utilizing such current collectors and methods for making same.

Description

LEAD-TIN ALLOY CURRENT COLLECTORS, BATTERIES MADE THEREOF AND METHODS FOR MANUFACTURING SAME

This application is a continuation-in-part of U.S. Application No. 08/784,853, filed 1/15/97, which is a continuation-in-part of U.S. Application No. 08/534,790, filed

9/27/95, now U.S. Patent 5,677,078, both of which are incorporated herein by reference.

FIELD OF INVENTION The present invention relates to the field of current collectors and batteries, especially current collectors for lead-acid batteries. More particularly, the present invention relates to a current collector for a battery which preferably comprises a thin alloy foil containing lead and tin and batteries using such current collectors. Batteries utilizing the current collectors of the present invention are characterized by significantly improved shelf life, cycle life and float life performance relative to prior art batteries. The current invention further relates to methods for manufacturing batteries utilizing the current collectors of the present invention.

BACKGROUND OF INVENTION

Despite considerable research into the development of improved electrochemical storage devices, the lead-acid battery remains a predominant device for delivering electrical current in many electrical operations. A conventional lead-acid battery such as the valve-regulated lead-acid (VRLA) battery is comprised of a plurality of cells. Each cell typically includes a set of interleaved monopolar positive and negative electrodes or plates. The electrodes typically are composed of a lead or lead-alloy current collector or substrate which is sandwiched between layers of an electrochemically active paste. The current collector generally is in the form of a grid. The paste used for the positive electrode contains lead dioxide when charged and is called the positive active material; the negative electrode contains a negative active material, typically sponge lead. Electrodes of opposite polarity are separated one from the other by a porous electrically insulating separator material such as a glass microfiber mat. The cell is completed by adding an acid electrolyte between the positive and negative electrodes and enclosing the entire assembly within a suitable case.

A major goal in the field of lead-acid batteries is to develop batteries having increased cycle life, shelf life and float life. Cycle life is defined as the number of discharging and recharging cycles a battery can sustain while still delivering a certain level of electricity. Cycle life is dependent upon a number of factors including testing conditions and cell construction. With regard to testing parameters, for instance, a cell which achieves 80% of its initial amp-hour rating after 500 cycles but delivers only 50% of its initial amp-hour rating after 1,000 cycles will have two different cycle life values, depending upon whether the cell is rated at 80% or 50% of initial capacity. A related parameter, "total useable capacity," refers to the number of cycles achieved during the life of the cell multiplied by the amp-hours delivered during each cycle. It is equivalent to the area under a curve in which discharge capacity (in amp-hours) is plotted against cycle number and is also a measure of the useful work a cell can provide. Shelf life simply refers to the usable life of a battery when it is not in use. The shelf life of batteries is affected by a process called "self-discharge," i.e., chemical reactions within the cell which cause the consumption of electrolyte and active materials even when the cell is not exposed to an external load. Since the discharge capacity of a cell is proportional to the specific gravity, or concentration, of electrolyte within the cell, self-discharge reduces storage time and discharge capacity, as well as causing voltage decay.

Float life refers to the life of a battery when it is kept on a charger at constant voltage, resulting in a low charging current, typically in the milliamp range. This parameter is of particular importance when batteries are used in applications requiring an uninterrupted power source.

Cycle life, shelf life and float life are dependent in large measure on the chemistry which occurs at the interface between the current collector of the positive electrode and the electrochemically active paste. This interface is referred to as the "corrosion layer" or "passivation layer" depending on the conductivity of the layer. While all of the chemistry that takes place at this interface is not fully understood, battery technologists currently believe that a conductive or semi-conducting corrosion layer is necessary to obtain long cycle life in lead-acid batteries. However, with certain lead and lead-alloy current collectors, in particular pure lead, lead-calcium and lead-low tin compositions, a passivation layer (i.e., a non-conducting layer) can form. Passivation layers are composed primarily of lead oxide (PbO). The lead oxide acts as an electrical insulator and can reduce conductivity such that current cannot pass from the active material through the passivation layer without a significant voltage loss. Thus, whether a conductive or passivation layer exists at the current collector/paste interface can dramatically impact the electrochemical properties of a cell. In particular, the formation of a conductive corrosion layer beneficially results in a cell having a long cycle life. However, the drawback to a corrosion layer is that the cell generally has reduced shelf life due to the ongoing corrosion or oxidation of the lead or lead alloy current collector which consumes needed electrolyte. In contrast, current collectors whose composition tends to create passivation layers have excellent shelf life but relatively poor cycle life and recovery from deep discharge and stand. The extended shelf life is a consequence of the passivation of the corrosion layer which protects the current collector from corrosion and self-discharge and thus voltage decay; yet, as noted above, the passivation process also acts to inhibit current flow during charging, thereby reducing cycle life. Thus, cycle life and shelf life can be inversely related with regard to the effect of the conductive/passivation layer. A conductive corrosion layer enhances cycle life but reduces shelf life; a passivation layer, in contrast, negatively affects cycle life but increases shelf life. Consequently, cell design typically involves choosing materials with the realization that a composition which enhances cycle life generally involves a tradeoff wherein shelf life is sacrificed and vice versa. Thus, there remains a need for current collectors, batteries and methods for making such devices wherein the current collector composition and structure is optimized such that batteries utilizing the current collectors have both high cycle life and shelf life performance, as well as increased float life. SUMMARY OF THE INVENTION

The present invention fulfills the need identified above. In particular, the present invention provides a current collector that has a composition and structure which enhances the shelf life, cycle life and float life of batteries which utilize the current collectors of the present invention as compared to prior art batteries. In addition, the present invention further provides batteries based upon such current collectors and methods for making such batteries.

More specifically, the present invention provides a current collector which preferably is a thin alloy foil that includes lead and tin, the tin concentration being less than 0.5% by weight, although the current collector could be formed into other shapes as well. The current collector preferably has a thickness of less than 0.03 inches and is substantially non-perforated. It has been found that batteries utilizing such current collectors typically have a shelf life, cycle life and float life which is significantly greater than prior art batteries. The current collectors provided in this invention have the further advantage in that they can be prepared according to standard alloying techniques and thus are not difficult to manufacture. Additionally, the current collectors can be used with the standard electrode paste compositions and paste additives know in the art and still exhibit improved shelf life, cycle life and float life. As noted above, the current collectors provided by the present invention preferably have a thickness of less than 0.03 inches. In one embodiment, the current collector may be less than 0.01 inches thick. In yet another embodiment, the current collector may be 0.005 inches or less thick. Preferably, the thickness of the current collector is 0.0005 to 0.005 inches thick, and most preferably the current collector is 0.0015 to 0.005 inches thick. The tin concentration in the current collector is less than

0.5% by weight (all tin concentrations included herein are expressed on a weight percent basis and are expressed relative to the weight of the current collector). In one embodiment, the tin concentration ranges from 0.01% to 0.29%. In another embodiment, the tin concentration is from 0.01% to 0.15%. In yet another embodiment, the tin concentration is at least 0.001% but less than 0.01%. The current collector preferably contains no appreciable amounts of other metals in the alloy. Unlike most other current collector compositions, calcium need not be included in the alloy; in fact, the alloy is preferably, although not necessarily, substantially free of calcium. Also in contrast to conventional current collector design in which the current collector typically has the form of a grid, the current collectors of the present invention are substantially non-perforated.

The present invention further provides batteries or electrochemical cells which include the thin lead-tin alloy current collectors described herein. In general, the battery of the present invention is characterized by positive and negative current collectors which are alternately interleaved with respect to one another. The positive and negative current collectors are kept apart by a separator positioned between them. The combination of a positive and negative current collector and the separator positioned between them define a unit cell. A unit cell, or preferably a collection of unit cells, is encapsulated, together with an electrolyte, in a container to yield a battery which has is characterized by high shelf life, cycle life and float life performance. In this case, active material on the positive and negative current collectors can be formed through a Plante formation process which is known in the art. Although in a preferred embodiment of the battery both the positive and negative current are of the design of the present invention, in another embodiment only the positive electrode of the battery includes such a current collector. In another embodiment, the electrochemical cell includes interleaved positive and negative electrodes. The positive and negative electrodes preferably include a thin lead-tin alloy foil of the present design sandwiched between two layers of electrochemically active paste. A separator is interposed between the positive and negative electrode. Thus, in this case the unit cell includes a positive and negative electrode and the separator positioned therebetween. A unit cell or combination of unit cells can be encapsulated with an electrolyte into a container. Again, at least the positive current collector, and preferably the negative current collector also, are of the design described herein.

If electrochemically active paste is applied to the current collector surface, the paste can be an unsulfated paste or a sulfated paste. The paste can also contain a tin compound or other semiconductor (e.g., antimony, arsenic, germanium, indium or selenium). The tin compound can include, for example, tin sulfate, SnO, metallic tin, tin (II) salts and tin (IV) salts. In one embodiment, the paste is a sulfated paste which includes tin sulfate, the tin sulfate concentration preferably being between approximately 0.1 and 2.0 percent of the sulfated paste by weight. Such tin compounds are useful in increasing the capacity of the cell.

The invention further includes a method for making the batteries of the present invention. In general, the method comprises preparing a positive current collector, such that the positive current collector is a substantially non-perforated alloy foil that contains lead and tin, the tin concentration being less than 0.5% by weight and the thickness of the foil preferably being less than 0.03 inches, and more preferably 0.005 inches or less. A negative current collector is then prepared. Preferably, the negative current collector has the same composition and structure as the positive current collector. A separator is interposed between the positive and negative current collector to create a unit cell. This unit cell, or a combination of unit cells, is then encapsulated with an electrolyte in a container to yield the battery. The method may further include a step wherein at least one of the positive and negative current collectors, and preferably both, are coated with electrochemically active paste. In this instance, the unit cell comprises a positive electrode, a separator and a negative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-sectional view of the alternating positive and negative electrodes that are separated by porous separators according to an embodiment of the present invention. FIG. 2 is a plot of charge acceptance and discharge capacity for cells utilizing 1% tin alloy current collectors (the remainder of the current collector being pure lead).

FIG. 3 is a plot of charge acceptance and discharge capacity for cells utilizing 0.29% tin alloy current collectors (the remainder of the current collector being pure lead). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been found that current collectors having certain structural features and having a particular composition can be used in batteries to simultaneously achieve a high level of cycle life, shelf life and float life performance which significantly exceeds that provided by other prior art batteries. The current collector of the present invention is preferably an alloy foil which includes lead and tin, the tin concentration being less than 0.5% by weight, and wherein the current collector has a thickness of preferably less than 0.03 inches and is substantially non-perforated.

The current collector of the present invention is preferably a thin, substantially non-perforated foil which typically has two major faces. As used herein, "substantially non-perforated" means that the current collector exists as a solid foil rather than as a grid, although the term is not meant to exclude the possibility that the foil might contain a very limited number of small holes. The use of a substantially non-perforated foil is contrary to the use of a grid structure which is conventionally used in the prior art. The current collector in general has a thickness of less than 0.03 inches. In another embodiment, the current collector is less than 0.01 inches thick; in another embodiment, the current collector is 0.005 inches or less thick. Preferably, the current collector thickness is 0.0005 to 0.005 inches thick, and most preferably is 0.0015 to 0.005 inches thick. However, the current collector can also have a thickness of less than 0.0015 inches. With regard to composition, the current collector includes lead and tin, the tin concentration being less than 0.5% by weight (as noted above, all tin concentrations listed herein are on a weight percent basis and are expressed relative to the weight of the current collector). Preferably, the minimum tin concentration is 0.001%, although the minimum tin concentration may be 0.01%. In one embodiment, the tin concentration in the alloy foil is less than 0.29%, such as from 0.01% to 0.29% tin. The tin concentration in another embodiment is less than 0.15%, such as from 0.01% to 0.15% tin. In various low-tin embodiments, the tin concentration may range from at least 0.001% but less than 0.005%, or from at least 0.001% but less than 0.01%.

Other metals in the current collector are preferably present in only the trace amounts which typically exist in lead-tin alloys as part of the manufacturing process. For example, unlike many other current collector compositions, the present current collector need not include calcium or other metals; instead, the current collector is preferably substantially free of other metals besides lead and tin, including being substantially free of calcium. As used herein, the term "substantially free of calcium" means that the alloy contains only the trace calcium which may exist in the alloy as part of the manufacturing of a lead-tin alloy; at such concentrations, the calcium concentration is too low to provide a significant alloying effect, e.g., increase in strength. Similarly, the term "substantially free of other metals except lead and tin" means that the concentration of metals other than lead and tin are at the trace levels which exist in preparing a lead-tin alloy; the concentration of other metals in the alloy is insufficient to provide an alloying effect.

The battery or electrochemical cell provided for in the present invention utilizes the current collectors just described to yield a battery with exceptionally high cycle life, shelf life and float life. A diagrammatic representation of a battery illustrating a preferred embodiment of the present invention is shown in FIG. 1. The drawing of FIG. 1 represents a spirally wound cell, but it should be appreciated that the invention is also applicable to cells having vertical or horizontal stacks of electrodes, as well as other configurations.

As shown in FIG. 1 , an electrochemical unit cell 16 preferably comprises a positive electrode 10, a separator 12 and a negative electrode 14. The positive electrode 10 comprises a positive current collector 18 and a coat of electrochemically active paste

20 on both faces of the current collector. Similarly, the negative electrode 14 comprises a negative current collector 22 that is sandwiched between layers of electrochemically active paste 20. (The terms "positive current collector" and "negative current collector" as used herein refer to the current collector which is electrically connected to the positive and negative terminal of a battery, respectively). At least the positive current collector

18, and preferably the negative current collector 22 as well, has the composition and structure described above, namely the current collector is an alloy which includes lead and tin, the tin concentration being less than 0.5% by weight. The current collector is substantially non-perforated and also has a thickness of preferably less than 0.03 inches, or more preferably 0.005 inches or less. The positive and negative current collectors 18, 22 preferably are foils having two major faces. The positive and negative current collectors 18, 22 are preferably coated on both faces with electrochemically active paste 20, although the paste could be applied to a single face. The space between the elements as depicted in FIG. 1 is only for the sake of clarity; in an actual cell, the positive electrode 10, separator 12 and negative electrode 14 are preferably tightly compressed.

The combination of a positive electrode 10, an adjacent negative electrode 14 and the separator 12 located between them define a unit cell 16. A unit cell 16, or preferably a combination of unit cells, can be encapsulated with an electrolyte (not shown) in an appropriate container (not shown) to yield the battery of the present invention. In the battery, the positive electrodes 10 are electrically connected to a common positive terminal (not shown); likewise, the negative electrodes 14 are similarly connected to a common negative terminal (not shown).

Although the battery shown in FIG. 1 shows electrochemically active paste 20 on both faces of the positive and negative current collectors 18, 22, neither the positive or negative current collectors 18, 22 need to be coated with paste 20, since the active material can be formed through a Plante formation process. In such an instance, the unit cell includes a positive current collector 18, a separator 12, and a negative current collector 22.

In a preferred embodiment, the general construction of the battery is as described in U.S. Patents 5,047,300 and 5,368,961 to Juergens and assigned to the assignee of the present application, these two patents to Juergens being incorporated herein by reference. The difference in the construction being that the lead-tin alloy foils described herein are substituted for those described in the two Juergens' patents.

As described above, the current collector used in a battery of the present invention generally has a thickness of 0.03 inches or less and can have a thickness of less than 0.01 inches or 0.005 inches or less. In a preferred embodiment, the current collector is 0.0005 to 0.005 inches thick, and, in a more preferred embodiment, the thickness is 0.0015 to 0.005 inches thick. Utilizing such thin current collectors, it is possible to greatly increase an important variable in electrochemical cells, namely the ratio of the surface area of the current collector to the amount of electrochemically active paste. This increased ratio provides for significant increases in charging and discharging capabilities and cycle life.

In those cases in which paste is applied to the current collector, each layer of electrochemically active paste 20 is typically less than 0.005 inches thick; preferably, each layer is about 0.002 to 0.003 inches thick or less. However, the paste 20 on the positive current collector 18 can be from 0 to 0.015 inches thick; the thickness of the paste 20 on the negative current collector 22 generally ranges from 0 to 0.01 1 inches. The thickness of the positive or negative electrode 10, 14 (current collector plus paste ~ if any — on both sides of the current collector) generally ranges from 0.0005 to 0.06 inches and preferably are 0.005 to 0.015 inches thick. The preferred spacing between a positive electrode 10 and an adjacent negative electrode 14 is about 0.005 inches or more.

The electrochemically active paste 20 applied to the current collectors can be any of the conventional electrochemically active pastes. The paste may be a sulfated paste or a non-sulfated paste. Thus, for example, the sulfated PbO pastes used on both the positive and negative electrodes provide a satisfactory system, as does the use of PbO and

Pb O₄ on the positive electrode and PbO on the negative electrode. The use of litharge, red lead or leady oxide is also possible. The paste may also include a tin-containing compound or other semi-conductor (e.g., antimony, arsenic, germanium, indium and/or selenium) such as described in U.S. Patent 5,820,639 to Snyder et al. and assigned to the assignee of the present invention, this patent being incorporated herein by reference.

Examples of such compounds include tin sulfate, SnO, metallic tin, a tin (II) salt and/or a tin (IV) salt. If tin sulfate is added to the paste, the tin sulfate concentration in the paste is preferably between 0.1% and 2% by weight . The inclusion of tin can improve the capacity (30 A) of the cell but is not necessary for improving shelf life and cycle life. The separator 12 can be composed of any of the porous separator materials which are known in the art, including those described in U.S. Patent 4,223,379 to Gross et al. and 4,465,748 to Harris, these patents being incorporated herein by reference. Typically, the separator 12 is a glass microfiber material with sufficient porosity to allow oxygen diffusion during recharging. Similarly, the electrolyte can be any of the standard electrolytes used in lead acid batteries. The case also can be any one of the cases typically used in the art, including for example a can composed of polypropylene, metal or other suitable material. A vent means should be provided to vent excess internal pressure which may be generated during recharging. The method of preparing batteries of the present invention involves preparing at least the positive current collector 18 according to the designs described above. A negative current collector 22 is also prepared; preferably, the negative current collector 22 has the same composition and structure as the positive current collector. A porous separator 12 is then inserted between the positive and negative current collectors 18, 22, to define in combination a unit cell 16. Finally, a unit cell 16, or preferably a combination of unit cells, plus an electrolyte are encapsulated within a container to yield the battery. The method may also include applying a coat of electrochemically active paste 20 onto the positive and negative current collectors 18, 22. Preferably, the positive and negative current collectors 18, 22 are sandwiched between two layers of paste 20. In this instance, the unit cell 16 includes a positive and negative electrode 10. 14 (i.e., current collector and layers of paste) and a separator 12 disposed therebetween. The composition and structural characteristics of the electrochemically active paste, the electrolyte and the container are as described above.

As noted above, the current collectors of the present invention can be used to dramatically increase battery performance. Because the current collectors used in the batteries of the present invention are very thin and substantially non-perforated, the ratio of foil surface area to active material is very high. This means that there is very high utilization of the active material which, in turn, enhances the charge and discharge characteristics of the battery. Tin within the current collector at the concentrations described herein further enhances performance by forming the necessary corrosion products to maintain conductivity in the insulating layer at the positive electrode. In particular, the present inventors have found that one of the keys to achieving long shelf life, cycle life and float life for a lead electrochemical cell is to have a semiconducting layer on the surface of the current collector, especially the positive current collector. The present invention achieves this goal by incorporating tin at the levels described above into the current collector. Although not intending to limit the basis for the enhanced performance observed, the tin in the current collectors of the present invention is believed to react with the acid electrolyte present in the battery to form a semi-conducting corrosion layer. This semi- conducting layer permits electrons to flow through the corrosion layer which can develop on the positive current collector. In general, it is believed that the tin reacts with the acid electrolyte to form, for example, soluble tin (II) or insoluble SnO . Without tin in the current collector, a non-conducting passivation layer typically forms. The presence of tin in the concentrations mentioned herein, however, causes tin to be incorporated in the passivation layer, thus lessening the insulative effects of the passivation layer and making the layer semi-conducting. However, the semi-conducting layer does not allow significant ionic or electron transfer when the cell or battery is non-operative, thereby limiting the corrosion of the current collector. The semi-conductor starts behaving as a conductor when the cell is under load and allowed to charge and discharge. The corrosion of the semi-conducting layer is also much less during cycling compared to a conducting layer. Thus, the inclusion of tin in the current collector at the concentration levels listed above increases the shelf life, cycle life and float life of the electrochemical cells of the present invention.

Batteries utilizing the current collectors of the present invention are routinely capable of delivering at least 1200-1500 cycles while maintaining a shelf life of 12-24 months. This contrasts significantly with other batteries using tin alloy current collectors wherein cycle life and shelf life is typically considerably less. The benefits of the batteries according to the present invention, in particular the high shelf life, cycle life and total useable capacity becomes particularly obvious through the examples which follow.

EXAMPLE I

(Cells Having 1% Tin Alloy Current Collectors) Approximately 15 to 20 cells including tin alloy current collectors comprised of a 1% lead-tin alloy were prepared and then tested to determine the typical shelf life, cycle life and useable capacity for such cells. The current collectors used in the cells were foils comprised of 1% tin (the remainder being pure lead). The current collectors were 0.003 inches thick (for both the positive and negative current collectors). The total thickness of the paste applied to both sides of the current collector faces was 0.010 inches for the positive current collector and 0.008 inches for the negative current collector. Thus, the total plate thickness (i.e., current collector plus paste on both faces) was 0.013 inches for the positive plate and 0.01 1 inches for the negative plate. The interplate separation between a positive plate and an adjacent negative plate was approximately 0.005 inches. The positive active material or paste was comprised of lead monoxide with 0.7% tin sulfate, a dispersant and water. Negative active material or paste included lead monoxide and organic and inorganic expanders (0.3% to 1%) and water.

The shelf life of the cells was determined by monitoring the voltage decay of cells kept at room temperature (25 °C ± 3 °C) and determined from 2.18 volts to 1.8 volts. The voltage of the cells was measured every week for two months and extrapolated to 1.8 volts. The number of days required to reach 1.8 volts was divided by 30 days to obtain a value for shelf life in months.

The shelf life values extrapolated (exponential extrapolation) from the measured values for cells utilizing 1 % tin alloy current collectors ranged from 180 to 250 days for different sets of test cells of the construction described above. The variation in the test results for these cells was greater than that for the 0.29% test cells (see below). Cycle life for the cells was tested at 10A discharge and 5% overcharge. The cells were continuously discharged and charged to obtain the total number of cycles. The cells were kept at room temperature during cycling.

The cycle life of cells utilizing 1% tin alloy current collectors is shown in FIG. 2, where plots of average charge acceptance and discharge capacity values for several cells are shown in a graph wherein the number of cycles is plotted against amp hours. As can be seen in FIG. 2, cells having 1% tin alloy current collectors reached 80% of their original capacity after only 500 cycles; useable capacity for the cells was about 500 Ah. EXAMPLE II (Cells Having 0.29% Tin Alloy Current Collectors) Another 15 to 20 cells were prepared using tin alloy current collectors comprised of 0.29% tin, the rest being pure lead. In all other respects, the cells were identical in construction to the cells described in Example I. Likewise, the test conditions for determining shelf life, cycle life and useable capacity were identical to the conditions described in Example I.

The shelf life for cells of this design when extrapolated according to the procedure described in Example I was approximately 570 days, or approximately 19 months.

Hence, the shelf life for cells using current collectors at the lower tin concentration of 0.29% was more than double that for cells having 1% tin alloy current collectors.

FIG. 3 illustrates the cycle life results for cells having 0.29% tin alloy current collectors. As the discharge capacity and charge acceptance plots illustrate (plots reflect the average values for several different cells), cells of this design did not reach 80% capacity even after 1200 cycles. This is more than a two-fold increase in cycle life as compared to cells described in Example I. Furthermore, cells utilizing 0.29% tin alloy current collectors had a useable capacity of 1000 Ah, also a two-fold increase over cells using 1% tin alloy current collectors. Collectively, these results show that significant improvement in cell performance is obtained using current collectors having relatively low tin concentrations, such as the tin concentrations described in the present invention. In particular, cells using low tin alloy current collectors exhibit a marked increase in shelf life, cycle life and useable capacity. Thus, cells using current collectors of the present design are capable of enhancing cycle life performance without sacrificing shelf life performance. In fact, cells utilizing current collectors of the present design achieve a high level of cycle life and shelf life performance which exceeds that of prior art cells or batteries, including those which utilize higher concentrations of tin in the current collector.

The foregoing examples are to be considered in all respects as illustrative of the current invention rather than to be restrictive. It will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described herein may be made without departing from the spirit and broad scope of the current invention.

All references listed herein, including patents and other publications, are incorporated herein by reference in their entirety.

Claims

We claim:

1. A current collector for a battery, comprising: lead and at least 0.01 % but less than

0.5%o tin by weight, having a thickness of 0.005 inches or less and being substantially non-perforated.

2. A current collector according to claim 1, wherein said current collector is 0.0005 to 0.005 inches thick.

3. A current collector according to claim 2, wherein said current collector is 0.0015 to 0.005 inches thick.

4. A current collector according to claim 1 , wherein said current collector contains 0.01% to 0.29% tin by weight.

5. A current collector according to claim 4, wherein said current collector contains 0.01% to 0.15% tin by weight.

6. A current collector according to claim 1 , wherein said current collector is substantially free of calcium.

7. A current collector according to claim 6, wherein said current collector is substantially free of other metals besides lead and tin.

8. A current collector according to claim 2, wherein said current collector is substantially free of calcium.

9. A current collector according to claim 8, wherein said current collector contains 0.01% to 0.29% tin by weight.

10. A current collector for a battery, comprising: lead and at least 0.001% but less than 0.01 ) tin by weight, having a thickness of less than 0.03 inches and being substantially non-perforated.

1 1. A current collector according to claim 10, wherein said current collector is less than 0.01 inches thick.

12. A current collector according to claim 1 1, wherein said current collector is 0.0005 to 0.005 inches thick.

13. A current collector according to claim 10, wherein said current collector is substantially free of calcium.

14. An electrochemical cell, comprising: (a) a positive current collector and a negative current collector, wherein at least said positive current collector includes lead and at least 0.01% but less than 0.5% tin by weight, has a thickness of 0.005 inches or less, and is substantially non-perforated;

(b) a separator interposed between said positive and negative current collector to define, in combination, a unit cell;

(c) an electrolyte; and

(d) a container which encapsulates said unit cell or a collection of unit cells and said electrolyte.

15. An electrochemical cell according to claim 14, wherein said negative current collector includes at least 0.01% but less than 0.5% tin by weight, has a thickness of 0.005 inches or less, and is substantially non-perforated.

16. An electrochemical cell according to claim 14, further comprising an electrochemically active paste coated on said positive and negative current collector.

17. An electrochemical cell according to claim 14, wherein of said positive and negative current collectors at least said positive current collector is 0.0005 to 0.005 inches thick.

18. An electrochemical cell according to claim 17, wherein both of said positive and negative current collector are 0.0005 to 0.005 inches thick.

19. An electrochemical cell according to claim 17, wherein of said positive and negative current collectors at least said positive current collector is 0.0015 to 0.005 inches thick.

20. An electrochemical cell according to claim 19, wherein both of said positive and negative current collector are 0.0015 to 0.005 inches thick.

21. An electrochemical cell according to claim 14, wherein of said positive and negative current collectors at least said positive current collector contains 0.01% to 0.29% tin by weight.

22. An electrochemical cell according to claim 21 , wherein both of said positive and negative current collector contain 0.01% to 0.29% tin by weight.

23. An electrochemical cell according to claim 21 , wherein of said positive and negative current collectors at least said positive current collector contains 0.01% to 0.15% tin by weight.

24. An electrochemical cell according to claim 23, wherein both of said positive and negative current collector contain 0.01% to 0.15% tin by weight.

25. An electrochemical cell according to claim 14, wherein said positive and negative current collector are substantially free of calcium.

26. An electrochemical cell according to claim 25, wherein said positive and negative current collector are substantially free of other metals except lead and tin.

27. An electrochemical cell according to claim 16, wherein said electrochemically active paste is a sulfated paste.

28. An electrochemical cell according to claim 14, wherein said positive current collector, separator and negative current collector are spirally wound.

29. An electrochemical cell according to claim 18, wherein said positive and negative current collector are substantially free of calcium.

30. An electrochemical cell according to claim 29, wherein said positive and negative current collector contain 0.01% to 0.29% tin by weight.

31. An electrochemical cell, comprising:

(a) a positive current collector and a negative current collector, wherein at least said positive current collector includes lead and at least 0.001% but less than 0.01% tin by weight, has a thickness of less than 0.03 inches, and is substantially non-perforated;

(c) an electrolyte; and (d) a container which encapsulates said unit cell or a collection of unit cells and said electrolyte.

32. An electrochemical cell according to claim 31 , wherein said negative current collector includes lead and at least 0.001% but less than 0.01% tin by weight, has a thickness of less than 0.03 inches or less, and is substantially non-perforated.

33. An electrochemical cell according to claim 31 , wherein of said positive and negative current collector at least said positive current collector is less than 0.01 inches thick.

34. An electrochemical cell according to claim 33, wherein of said positive and negative current collector at least said positive current collector is 0.0005 to 0.005 inches thick.

35. An electrochemical cell according to claim 31 , wherein said positive and negative current collector are substantially free of other metals except lead and tin.

36. An electrochemical cell according to claim 32, wherein said positive and negative current collector are substantially free of other metals except lead and tin.

37. A method for manufacturing an electrochemical cell, comprising:

(a) preparing a positive and a negative current collector, wherein at least said positive current collector includes at least 0.01% but less than 0.5% tin by weight, has a thickness of 0.005 inches or less, and is substantially non- perforated;

(b) interposing a separator between said positive and negative current collector to define, in combination, a unit cell;

(c) encapsulating said unit cell, or a collection of unit cells, and an electrolyte within a container.

38. A method according to claim 37, wherein said negative current collector includes lead and at least 0.01% but less than 0.5% tin by weight, has a thickness of 0.005 inches or less, and is substantially non-perforated.

39. A method according to claim 37, further comprising a step of applying a coat of electrochemically active paste to said positive and negative current collector.

40. A method according to claim 37, wherein of said positive and negative current collector at least said positive current collector is 0.0005 to 0.005 inches thick.

41. A method according to claim 40, wherein both of said positive and negative current collector are 0.0005 to 0.005 inches thick.

42. A method according to claim 40, wherein of said positive and negative current collector at least said positive current collector is 0.0015 to 0.005 inches thick.

43. A method according to claim 42, wherein both of said positive and negative current collector are 0.0015 to 0.005 inches thick.

44. A method according to claim 37, wherein of said positive and negative current collector at least said positive current collector contains 0.01% to 0.29% tin by weight.

45. A method according to claim 44, wherein both of said positive and negative current collector contain 0.01% to 0.29% tin by weight.

46. A method according to claim 44, wherein of said positive and negative current collector at least said positive current collector contains 0.01% to 0.15% tin by weight.

47. A method according to claim 46, wherein both of said positive and negative current collector contain 0.01% to 0.15% tin by weight.

48. A method according to claim 37, wherein said positive and negative current collector are substantially free of calcium.

49. A method according to claim 48, wherein said positive and negative current collector are substantially free of other metals except lead and tin.

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50. A method according to claim 39, wherein said electrochemically active paste is a ^" sulfated paste.

51. A method according to claim 37, further comprising spirally winding said positive 5 current collector, said separator and said negative current collector after said interposing step.

52. A method according to claim 41 , wherein said positive and negative current collector are substantially free of calcium. 0

53. A method according to claim 52, wherein said positive and negative current collector contain 0.01% to 0.29% tin by weight.

54. A method for manufacturing an electrochemical cell, comprising: 5 (a) preparing a positive and a negative current collector, wherein at least said positive current collector includes at least 0.001% but less than 0.01% tin by weight, has a thickness of less than 0.03 inches, and is substantially non-perforated; (b) interposing a separator between said positive and negative current 0 collector to define, in combination, a unit cell; (c) encapsulating said unit cell, or a collection of unit cells, and an electrolyte within a container.

55. A method according to claim 54, wherein said negative current collector includes lead and at least 0.001% but less than 0.01% tin by weight, has a thickness of less than 0.03 inches or less, and is substantially non-perforated.

56. A method according to claim 54, wherein of said positive and negative current collector at least said positive current collector is less than 0.01 inches thick.

57. A method according to claim 56, wherein of said positive and negative current collector at least said positive current collector is 0.0005 to 0.005 inches thick.

58. A method according to claim 54, wherein said positive and negative current collector are substantially free of metals except lead and tin.

59. A method according to claim 55, wherein said positive and negative current collector are substantially free of metals except lead and tin.