WO1994029909A1

WO1994029909A1 - Method and apparatus for assembling electrochemical cell

Info

Publication number: WO1994029909A1
Application number: PCT/US1994/006745
Authority: WO
Inventors: Tristan E. Juergens; Leonard F. Hug; Henry L. Zoetewey
Original assignee: Bolder Battery, Inc.
Priority date: 1993-06-14
Filing date: 1994-06-14
Publication date: 1994-12-22
Also published as: AU7108594A

Abstract

An electrochemical cell and a method of manufacturing the same. Plates of opposite polarity are wound spirally and end connectors (310, 314) with protruding hubs (318, 388) are attached to each end. The assembly is placed within a casing (350) having a jacket and an end with a hole through it, whereby one end connector hub (318) extends through the casing end hole. The end connector hub is radially expanded against the casing end by installing a blind rivet (356) in the end connector hub. A casing cover (392) having a hole through it is placed in the other end, and the end connector hub (388) at that end is similarly radially expanded againstthe cover by installing a blind rivet (393) in that end connectorhub. The plates may be of very thin type, and the end connectors may be attached by casting them onto the thin plates.

Description

METHOD AND APPARATUS FOR ASSEMBLING ELECTROCHEMICAL CELL

This is a continuation-in-part of application no. 07/945,805 filed September 16, 1992 which is a continuation-in-part of application no. 07/757,447 filed September 10, 1991, issued as U.S. Patent No. 5,198,313 on March 30, 1993, which is a continuation- in-part of application no. 07/366,867 filed June 14, 1989 and issued as Patent No. 5,047,300 on September 10, 1991.

FIELD OF THE INVENTION

This invention relates to an apparatus and method for manufacture of electrochemical cells having superior recharge and discharge capabilities. Such electrochemical cells are comprised of ultra-thin plates and separators within a container.

BACKGROUND OF THE INVENTION

There have been dramatic improvements in the design and performance characteristics of compact hermetically sealed rechargeable electrochemical cells. These cells are typically configured either as a series of plates or in a spirally wound electrode assembly. The two commonly used chemical systems are the lead acid system and the nickel cadmium system. Although the lead acid battery system has been known and utilized for many decades, solutions to many of the practical difficulties associated with using such cells were not proposed until the mid-1970s. One of the difficulties seen with early lead acid cells was related to the problem of keeping the electrolyte acid contained within the cell. It was necessary to maintain an excess amount of acid (sulfuric acid) in the cell in order to allow for overcharging of the electrodes during the recharge process. Overcharging leads to the production of hydrogen and oxygen within the cell which traditionally was vented from the cell. Electrochemical cells having vent means and free acid generally had to be held upright in order to prevent the acid from leaking from the cell. An additional problem with traditional lead acid cells was in maintaining the physical characteristics of the lead plates within the cell. In order to put some "back bone" in the lead plates, lead containing up to one percent of calcium was often used in cells to give the plates some rigidity.

The breakthrough invention in lead acid cells is described in U.S. Pat. No. 3,862,861 of McClelland et al. The McClelland patent discloses the incorporation of several elements that combine to alleviate each of these problems associated with the traditional lead acid cell. The McClelland invention recognized the potential of utilizing the electrochemical recombination reaction. By capitalizing on the "oxygen cycle", a lead acid cell could be produced such that the electrolyte could be maintained in a "starved" condition. Rather than having an excess of electrolyte, the cell could be operated with a minimal amount of electrolyte present in the system. In order to maintain a starved condition, it is necessary to have sufficient absorbent material or pores within the cell to contain the electrolyte while still having space filled with gas.

By using relatively absorptive separator material, McClelland was able to accomplish two distinct functions. The absorptive separator allowed the flow of gases and electrolyte between the positive and negative plates, thereby allowing the oxygen cycle to function. The absorptive separator also acts as a wick to hold the electrolyte within the cell without the necessity of having free electrolyte in the system. McClelland also discloses a configuration of the plates and separator so that the elements are held tightly together. It was then possible to use considerably purer lead grids that are more corrosion resistent than the calcium-containing lead plates previously used. Venting means are included in the McClelland device as a safety release device to release excess pressure. However, since there is little or no non-absorbed electrolyte in the cell, there is almost no danger of acid leaking from the cell.

Prior to the development of the McClelland device, U.S. Patent Nos. 3,395,043 and 3,494,800 of Shoeld disclosed the use of relatively thin lead plates in an electrochemical cell. The cells described in the Shoeld patents, being prior in time to the McClelland patent, did not use absorptive, gas permeable separators. The cells disclosed did not, therefore, utilize the oxygen cycle, were not maintained in a starved or semi-starved condition, and probably contained free electrolyte in order to function properly. The Shoeld patents do not indicate that the batteries produced would have superior discharge or recharge characteristics. Based on the technigues and materials available at the time of the Shoeld disclosures, it is quite unlikely that the cell disclosed therein would have had any significant advantages over existing cells. An example of an electrochemical cell in which a blind rivet is used to assemble the cell and to act as a conductor is U.S. Patent No. 3,704,173 by McClelland, et al.

Since the McClelland patent, there have been several patents disclosing improvements to the fundamental cell disclosed therein. For example, U.S. Patent Nos. 4,465,748 of Harris, 4,414,259 of Uba, 4,233,379 of Gross, 4,137,377 of McClelland and 4,216,280 of Kono each describe separators to be used in starved lead acid cells. U.S. Patent Nos. 4,725,516 of Okada and 4,648,177 of Uba both identify cell parameters that lead to superior recharge/discharge characteristics in lead acid cells.

U.S. Patent No. 4,769,299 of Nelson to a certain extent incorporates the inventions of Shoeld and McClelland. The Nelson patent describes the use of grid-like plates and absorptive gas permeable separators as described in McClelland with the extremely thin plates disclosed by Shoeld. The result is a lead acid cell with enhanced recharge/discharge properties.

The theoretical advantage of utilizing thin plates in electrochemical cells has been known for decades. The thinner the plates the less distance electrons have to travel within the plate during discharge, and, during recharge, the shorter distance of non-conductive material to be regenerated. To a certain extent, the thickness of plates utilized has been dictated by the available technology for the production and handling of thin lead films.

U.S. Patent No. 5,045,415 by itehira describes a lead-acid battery with extremely thin plates on the order of 5 to 20 micrometers thick (less than .001 inches). However, the plates are not interleafed negative and positive plates, but instead are sandwiched together to form thicker plates which, in turn, are interleafed. U.S. Patent No. 4,173, 066 by Kinsman is for a laminar battery having a zinc coated cellophane substrate. Of course, the function of a cellophane substrate and the manufacturing concerns associated with it are much different from those of a metal foil substrate. U.S. Patent No. 3,377,201 by Wagner is for a liquid electrolyte battery such as a lead-acid cell. One embodiment of the invention is a silver-zinc cell having a positive plate .010 inches thick but the negative plate is .025 inches thick. U.S. Patent No. 3,023,260 by Coler is for a liquid electrolyte battery having an electrode with a thickness of .025 inches. U.S. Patent No. 4,996,128 by Aldecoa is for a lead-acid battery having a foil thickness of "less than .010 inches". The porous paste thickness is not specified, but presumably is greater than the thickness of the foil, to make the total plate thickness in excess of .010 inches. Other references to so-called thin plate designs are U.S. Patent Nos. 4,001,022 by Wheadon (referring to plates in excess of .010 inch thick) and 4,883,728 by Witehira (which describes the use of both thin plates and thick plates in a single battery to provide a variety of discharge characteristics).

The use of thin plates has been seen for some time in alkaline batteries such as nickel-cadmium batteries. For example, U.S. Patent Nos. 4,963,161 by Chi, 4,937,154 by Moses and 4,539,272 by Goebel, describe alkaline batteries having thin plates. However, alkaline batteries normally are formed with plates of materials with higher tensile strengths than lead which are easier than lead to manufacture and handle in thin layers.

For much the same reasons that thin plates produce superior results, thin layers of reactive paste also lead to superior discharge/recharge characteristics. The Nelson patent discloses the use of both thin lead grids and thin layers of reactive paste. A basic shortcoming in the Nelson device, is that the paste residing within the grid openings can have a greatly increased distance to the lead plate material. For example, in the Nelson patent the openings in the lead plate grid are constructed so that the distance from the center of the opening to the grid strands is significantly greater than the thickness of the paste layer on the face of the plate. Since the performance characteristics of electrochemical cells is proportional to the thickness of the lead plates and the thickness of the paste layer, the use of grids or other perforated sheets, greatly decreases the efficiency of the cells. The Nelson patent teaches away from a thin plate design using non-perforated plates, on the grounds that thin plates are prone to corrosion:

"To achieve optimum high rate discharge capability, in theory one would prefer to use thinner plates to reduce the current density on discharge. However, corrosion, particularly at the positive grid as aforementioned, has placed limitations on how thin plates can be made in practice. "

Other patents on thin perforated plates include

U.S. Patent Nos. 4,999,263 by Kabata (which refers to films as thin as 3 micrometers coated with a polymeric material having a thickness of "1,000 micrometers or less"; 3,973,991 by Cestaro (referring to perforated lead foil .019 inches thick before the application of a coating); and 4,874,681 by Rippel (which refers to a woven perforated plate of strands with a .008 inch outside diameter or .005 inch outside diameter before application of any coating) . Other art in the field includes U.S. Patent Nos. 4,064,725 by Hug; 4,099,401 by Hug; 4,112,202 by Hug; 4,158,300 by Hug; 4,212,179 by Juergens; 4,295,029 by Uba; 4,606,982 by Nelson; 4,709,472 by Machida; 4,780,379 by Puester; Japanese Patent Nos. 58-119154 and 59-103282 and U.S.S.R. Patent No. 674124.

Of course, the prior art includes many references to thin plate capacitors. See, for example, U.S. Patent No. 4,720,772 by Yamano. These patents are of marginal relevance, because they are not directed toward battery technology and the plate material is normally aluminum or nickel rather than lead.

SUMMARY OF THE INVENTION

The electrochemical cell of the present invention is characterized by the use of thin non- perforated positive and negative plates having thin active material layers and thin absorptive separator material layers. In the optimum design, the cell is initially produced with an excess volume of electrolyte, but through processing, a volume of electrolyte is achieved in the cell, and the electrolyte volume is maintained, in an almost saturated condition with respect to the absorptive capacity of the separator and the electrode materials.

The cell of the present invention is characterized by an exceptionally high plate surface area to active material ratio. The cells are produced utilizing films of lead or nickel approximately 0.002 inches thick. The active material or paste maintained on the surface of both sides of the sheet are approximately 0.001 to 0.003 inches thick. The inter- plate spacing is 0.005 or more inches. In one preferred embodiment, both the negative plate and the positive plate are of substantially non-perforated sheets having the thickness described above. In another preferred embodiment, one plate is of the thickness described above while the other plate is significantly thicker. In yet another preferred embodiment, one plate (the corroding plate) is a substantially non-perforated sheet while the other plate is perforated. When manufacturing lead acid cells, the active material may be sulfated lead pastes or PbO and Pb₃0₄ or leady oxide for the positive and PbO for the negative plates. When utilizing sulfated pastes, the specific gravity of the electrolyte is about 1.28. The lead films of the plates are preferably greater than 97% pure. If containing tin, the films may be from about .50% to 2.5% tin. If tin is not used, the lead is approximately 99.99% pure. Any number of separator materials known in the art may be utilized with the present invention. One suitable glass microfiber material consists of 90% of fibers of 1 to 4 microns in diameter and 10% of larger fibers existing as a woven or non-oriented mat. Examples of acceptable separator materials are described in U.S. Patent Nos. 4,233,379 of Gross et al. and 4,465,748 of Harris.

The surface of the electrode films may be physically roughened to increase the adhesion of the thin layer of active material to the film surface and to further increase the surface area of the films. Alternatively, the films may be textured in the rolling process by using a textured roller.

The cell in the preferred embodiment utilizes a cast-on end connector to mechanically and electrically connect the thin plates to the cell terminals. The end connectors at each end of the cell extend through an insulating cell case. The end connectors are held in place and the entire assembly is held together by a blind rivet in each end connector, wherein the rivet body is expanded in a hole of the end connector to establish a secure interference fit between the rivet and the end connector and between the end connector and the cell case. The flange of the rivet remains on the cell exterior and functions as the terminal. The cell case may be plastic or may be a metal cylinder with one or both ends crimped radially inward to form a top and bottom.

The cell may be filled using filling systems known in the art. In a preferred embodiment, a novel filling system is employed using a plurality of filling ports spaced on one end of the cell case in a circular depression. After filling is completed, the depression receives an elasto eric O-ring seal. The O-ring seal is biased against the depression and thereby seals the filling ports by a cover washer placed over it and attached to the cell case. The cover washer does not seal the depression, so that excess pressure in the cell can escape to the depression by deforming the O- ring seal and thereby vent to the atmosphere.

The electrochemical cell of the present invention demonstrates dramatic improvements in recharge/discharge capabilities over prior art cells produced as described in the various references cited above. Maximum current capabilities are increased and the current value remains at near its maximum throughout a longer period of its discharge profile. Recharge times are also reduced dramatically. Recharge can be accomplished at currents up to IOC (or ten times the amp hour rating of the cell).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic vertical cross- sectional view of alternating positive and negative plates that are separated by layers of separator according to one embodiment of the present invention.

FIG. 2 is a diagrammatic horizontal cross- sectional view of a spirally wound cell unit according to one embodiment of the present invention. FIG. 3 is a pictorial, partial cross-sectional view of a spirally wound cell unit in accordance with the present invention.

FIG. 4 is a cross-sectional view of a cell in accordance with the present invention, before being fully assembled.

FIG. 5 is a cross-sectional view of a fully assembled cell in accordance with the present invention.

FIG. 6 depicts discharge curves comparing cells of this invention with conventional cells.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, an electrochemical cell having both excellent charge and discharge characteristics is described. Technological breakthroughs in the fields of thin film handling have made it possible to create high rate electrochemical cells that have performance characteristics that are unprecedented in the field. Utilizing ultra-thin films of either lead (for lead acid systems) or nickel (for cadmium nickel systems) in combination with extremely thin layers of active material, it is possible to create cells that have very high utilization of the active material, even at extreme discharge rates. Therefore, even under extreme loads there is little voltage drop within the plates of the cell.

The present invention describes electrochemical cells with quite low plate current densities and low connector current densities, thereby reducing heat creation.

The electrochemical cell of the present invention is composed of ultra-thin films of an electrochemically active metal - generally lead or nickel - that are coated on each side with an electrochemically active paste. Preferably, the positive film (which is the corroding element) is substantially non-perforated while the negative film may be either perforated or non-perforated. The positive and negative plates of the electrochemical cell are maintained apart from each other by separator material. The separator material also acts to absorb the electrolyte that is contained in the enclosed cell system. A diagrammatic view of a cell unit according to the present invention is seen in FIG. 1. Negative plate 14, separator 12 and positive plate 10 constitute an electrochemical unit 16. The negative plate 14, and optionally the positive plate 10, each consist of an ultra-thin film 18 of either lead or nickel partially coated on both major faces with a layer of a suitable electrochemically active paste 20.

According to the present invention, the films 18 utilized in the negative plate of the electrochemical cell are about 0.005 inches thick. In the preferred embodiments, the negative films 18 are about 0.0015 to 0.0030 inches thick. In certain ways, the electrochemical cells of the present invention are constructed along the lines of standard electrolytic capacitors rather than standard batteries, in the sense that they employ extremely thin plates. Handling such thin films and incorporating the same into functional electrochemical cells was previously thought to be impossible. Utilizing such thin films of active material, it is possible to greatly increase an important variable in such electrochemical cells, the ratio of surface area of film to the amount of active paste material. In the present invention, cells having greater than 26.0 square centimeters of surface area per gram of active material are described. In fact, in a preferred embodiment, there are up to 50 square centimeters per gram of active material.

A thin layer of the active material paste 20 is applied to a large portion of both major faces of the negative and positive films 18. Each layer is, at the most, 0.005 inches thick, and in the preferred embodiments of the invention, the layers of active material paste 20 are about 0.002 to 0.003 inches thick or less. The negative plate and, optionally, the positive plate, each have a total thickness of film plus paste of no more than 0.010 inches. In the preferred embodiment the thickness is about 0.005 to 0.008 inches, with an interplate spacing of about 0.005 or more inches. As used herein, the "plate" refers to the film together with the paste that is applied to the film, while the "film" refers to the film not including the applied paste. Thus, a film that is, for example, 0.002 inches thick and coated on both sides with a paste that is .001 inches thick, results in a total plate thickness of .004 inches.

In each unit cell 16, the negative plate 14, the separator 12 and the positive plate 10 are in a specific physical relation as seen in FIG. 1. Both major faces of the films 18 are coated with active material paste 20, except along alternating horizontal edges 26 and 28 where there is left a bare strip about a tenth inch wide. On the negative plate 14, the portions of the major faces 28 adjacent to the lower horizontal edge are not coated with the active material paste 20, and on positive plate 10, the portion of the major faces 26 adjacent to the upper horizontal edge are not coated with the active material paste 20. The separator 12 extends beyond the coated portions of both the negative plate 14 and positive plate 10 in order to separate the plates effectively. However, the separator does not extend as far as the end of the uncoated portions 26 and 28 of the positive plate 10 and negative plate 14, respectively. Thus, those uncoated portions can receive the end connectors in the manner described below. The cell could, of course, be constructed so that the relative position of the positive and negative plates are reversed.

In an embodiment of the invention wherein a "D" size cell is produced, the negative and positive films 18 are each about 1.5 inches high. The uncoated ends extend about one-fourth inch beyond the coated plate of opposite polarity, and the separator 12 extends about one-eighth inch beyond the coating of each plate. The surfaces of the film 18 that are to be coated may be textured by the rolling process prior to application of the active paste 20. The texturing may be accomplished in the rolling of the films by using a textured roller. This allows for a more adequate adhesion between the paste and the film.

In the preferred embodiment of the invention, the electrochemical cell is constructed of a single spirally wound unit cell as shown in FIG. 2. Of course, the invention could also be employed utilizing parallel stacks of any number of unit cells. In the spirally wound configuration 30 of FIG. 2, a single continuous sheet of separator 12 may be employed to separate the negative 14 and positive 10 plates from each other. FIG. 3 is a pictorial, cutaway view of the cell. FIG. 4 shows side sectional views of the two ends of the cell, with the plates omitted for clarity, before complete assembly, and FIG. 5 shows the same views after assembly and after filling of the electrolyte. FIGs. 3-5 show the plates attached to cast-on end connectors in a manner similar but not identical to that described in U.S. Application No. 07/757,447 filed September 10, 1991 for Battery End Connector, now issued as U.S. Patent No. 5,198,313, and the details of the casting process can be found by reference to that patent.

The cast-on positive end connector 310 shown in FIGs. 3-5 has a center hub 318 which extends through a center hole in a non-conductive cell case 350. The center hub 318 of the positive end connector 310 has a hub hole which receives a rivet body 356 of a blind rivet 358 having a flange 360 extending over the hub 318 and partially over the cell case 350. A sealing washer 361 is positioned between the rivet flange 360 and the flush surface of the cell case 350 and center hub 318. The end connector 310 center hub 318 is surrounded by an annular ridge 319, so that the center hub 318 and annular ridge 319 define an annular recess 321 therebetween. The cell case 350 has an annular protrusion 351 which mates with the annular recess 321 of the end connector 310. The annular protrusion 351 is bevelled so that the mating with the annular recess 321 is imperfect, allowing a space for a bead of sealant 377. As best shown in FIG. 5, the inside of the rivet body 356 is expanded against the inside of the hub hole to create an interference fit between the rivet body 356 and the hub 318 and between the hub 318 and the cell case 350, by the expansion action of the blind rivet 358. The bottom of the cell is similar to the top of the cell. A negative end connector 314 has a center hub 388 which extends through a center hole in a cell case cover 392. The hub 388 has a hole which receives the rivet body 393 of a blind rivet 394 having a flange 395 that extends radially over the hub 388 and partially over the cell case cover 392. The rivet body 393 is expanded against the inside of the hub hole to create an interference fit between the rivet body 393 and the hub 388 and between the hub 388 and the cell case cover 392. The cell case cover 392 is ultrasonically welded to the cell case 350 at a circumferential joint 361 to hold the assembly together.

In the preferred embodiment of a filling system used with the cell, the cell case 350 includes a circular depression 370 in its upper surface and a plurality of filling ports 372 spaced around the circular depression as shown in FIG. 3. The filling ports 372 are closed by an O-ring seal 374 positioned in the circular depression 370 as shown in FIGs. 3-5. A cover washer 380 is intermittently attached, as by ultrasonic welding, to the cell case 350 over the 0- ring seal 374 to bias the O-ring seal 374 into place in the circular depression 370 to close the filling ports 372, as shown in FIG. 5. The bottom of the washer 380 may have a depression 381 to receive the O-ring seal 374. The O-ring seal 374 is deformable, and so excess pressure in the cell deforms the O-ring seal to open the filling ports 372 to release the pressure. An alternate means (not shown) for biasing the O-ring seal into the circular depression to seal the filling ports is to include an outer jacket with a flange extending radially inward over the O-ring seal, along the body of the cell, and radially inward over the opposite end of the cell. Either or both of the flanges may be crimped into place.

The cell is preferably assembled as follows. Once the positive and negative end connectors 310 and 314 are cast onto the positive and negative plates, respectively, a bead of sealant 377 is applied to the annular recess 321 of the positive end connector 310, and the plates with cast-on end connectors 310 and 314 is slid into the cell case 350 and seated therein so that the annular protrusion 351 of the cell case 350 mates with the annular recess 321 of the positive end connector and forces the sealant 377 into any spaces to form a sealed connection. The sealing washer 361 is placed over the center hub 318, and the blind rivet 358 is inserted through the sealing washer and into the hole in the center hub 318. The rivet mandrel is withdrawn so that the rivet body 356 expands radially outward against the center hub 318 of the end connector 310 as shown in FIG. 5. This expansion produces a secure electrical and mechanical connection between the rivet 358 and the end connector 310. It also produces a secure mechanical connection between the end connector 310 and the cell case 350 due to the outward radial expansion of the center hub 318 produced by the expanding rivet body 356. The rivet mandrel then breaks, leaving the end 323 of the mandrel within the rivet. It can be appreciated that the rivet thereby permanently holds the cell together. It also establishes a secure electrical and mechanical connection with the end connector center hub 318, and the rivet flange 360 acts as the exterior cell terminal.

The bottom is assembled in essentially the same manner as the top. A bead of sealant is applied to the annular recess of the bottom end connector 314, and the cell case cover 392 is seated onto the bottom end connector 314 and sealed thereon. The cell case cover 392 is then welded (as by, for example, ultrasonic welding) to the cell case 350 at the circumferential joint 361. A blind rivet is placed into the hole of the center hub 388 of the end connector 314, and the rivet mandrel is withdrawn until the mandrel breaks as shown in FIG. 5, thereby producing an interference fit between the rivet body 393 and the end connector center hub 388 and between the end connector center hub 388 and the cell case cover 392.

The cell is filled by injecting electrolyte through the filling ports 372 in the top of the cell. This may be accomplished with a donut-shaped filling spout to mate with the circular depression 370 having the filling ports 372. The positive end connector 310 preferably has electrolyte fill ports 373 arranged in a circular pattern close to the circular pattern of the circular depression 370 of the cell case 350, so that the electrolyte flows freely through the filling ports 372 and through the electrolyte ports 373 and into the cell.

The cell may also be designed for a "flow through" filling process. In that process, the bottom of the cell has drain ports similar to the filling ports in the top of the cell so that electrolyte can be flowed into the cell through the filling ports and out of the cell through the drain ports to achieve high electrolyte uniformity in the cell. Both the filling ports and drain ports are then sealed in an appropriate fashion, such as by the sealing method described above.

For lead acid electrochemical cells, there are a number of widely known combinations of active material pastes that are typically used. Any of these commonly utilized systems would be appropriate for use with this invention. For example, sulfated PbO pastes used on both the positive and negative plates provide a satisfactory system, as does the use of PbO and Pb₃0₄ on the positive plate and PbO on the negative plate. The use of litharge, red lead or leady oxide is also possible. The important factor is that the active material paste be of a nature so that it can be applied to the ultra-thin layer, as described above.

As is commonly seen in the new generation of the lead acid cells as exemplified in the McClelland and Nelson patents, the use of an absorbent, permeable separator, which permits gas transfer, it critical. As described above, there are several separator materials that have been disclosed for use specifically with lead acid system electrochemical cells. For the purposes of the present invention, any of the commonly used absorbent separators will work suitably. In one preferred embodiment, the separator is a glass micro- fiber which is about 95% porous in the uncompressed state and wherein 90% of the fibers are 1-4 microns in diameter.

When utilizing the lead acid system, the lead film 18, at least at the negative plate, may be about 97 to 99.99% pure, with the rest being tin or other metals. As described above, the lead film for each embodiment 18 is about 0.005 inches or less thick, and is preferably about 0.003 to 0.0015 inches thick. When sulfated lead oxides are used as the active material paste, the specific gravity of the sulfuric acid electrolyte solution used is between 1.20 and 1.32. The type of vent used on the electrochemical cell may be similar to those described in the literature and known by those with ordinary skill in the art, and operates to vent excess gases when the internal pressure exceeds a certain level. Some internal pressure (above atmospheric) will be maintained when the cell is in its normal operational state. In its operable state, the cell of the present invention is maintained so that the total void volume of the compressed separator and the active material is not totally filled, so that there is no free electrolyte present.

EXAMPLE As mentioned previously, electrochemical cells produced according to the present invention have distinctly superior discharge and recharge capabilities. FIG. 6 shows the discharge curve for a lead acid electrochemical cell according to the embodiment of the present invention in comparison with discharge curves for the cells described in U.S. Patent Nos. 3,862,861 of McClelland et al. (the lower line of the two prior art lines) and 4,769,299 of Nelson (the upper line of the two prior art lines). As can be seen, the improved performance is more than just an incremental increase.

The electrochemical cell used to create the discharge curve seen in FIG. 6 has the following characteristics: a non-perforated lead film for both the positive plate and negative plate was composed of 99.50% lead and 0.50% tin; the lead films were 0.002 inches thick and were coated with a layer of 0.002 inches thick of sulfated pastes - the total plate thickness being 0.006 inches; the electrolyte was sulfuric acid with a specific gravity of 1.28; the glass micro-fiber separator was 95% porous in its uncompressed state and contained 90% 1-4 micron diameter fibers and 50% larger fibers up to 1 inch in length and had a specific surface area of less than 2m²/g. In a "D" sized electrochemical cell, the lead films would be 45 inches long and 1.5 inches high, and there would be about 26.0 cm² of surface area for each gram of active material paste.

The cells of the present invention can be recharged at extremely high rates relative to cells currently available. As long as significant overcharging is not allowed, the cells can be recharged at up to IOC, or ten times the rated capacity of the cell.

Claims

CLAIMSWhat is claimed is:

1. An electrochemical cell, comprising: interleafed sets of plates of opposite polarity wound into a spiral having two ends; a casing extending around the spiral and having two ends to cover the spiral ends, at least one of the casing ends having a hole therethrough; an end connector attached to one of the sets of plates and extending through the hole of the casing end, the end connector having a hole in the portion extending through the hole of the casing end; the portion of the end connector extending through the hole in the casing end being radially expanded against the hole in the casing end to produce an interference fit between the end connector and the casing end.

2. The cell of claim 1, further comprising an electrical terminal having a tubular portion extending into the hole in the end connector portion extending through the hole in the casing end, the tubular portion being radially expanded against said hole in the end connector portion extending through the hole in the casing end to produce an interference fit between the tubular portion and the end connector.

3. The cell of claim 2, wherein the electrical terminal includes a flange extending radially from the tubular portion and at least partially over the end connector portion extending through the hole of the casing end.

4. The cell of claim 3, wherein the electrical terminal is a portion of a blind rivet.

5. The cell of claim 3, further comprising a sealing washer positioned between the electrical terminal flange and the end connector portion extending through the hole of the casing end to seal the joint between the electrical terminal and the end connector.

6. The cell of claim 5, wherein the sealing washer extends radially over both the end connector portion extending through the hole of the casing end and at least a portion of the casing end to seal the joint between the end connector and casing end.

7. The cell of claim 3, wherein the end connector is substantially disk-shaped and the end connector includes an annular protrusion around the end connector portion extending through the hole of the casing end; and the casing end is substantially disk- shaped and includes an annular recess which receives the end connector annular protrusion.

8. The cell of claim 3, wherein the end connector is cast onto a set of plates wound into said spiral.

9. The cell of claim 1, wherein both casing ends have a hole therethrough; and further comprising a second end connector attached to another of said set of plates and extending through the hole of the other casing end, the second end connector having a hole in the portion extending through the hole of the other casing end, the portion of the end connector extending through the hole in the other casing end being radially expanded against the hole in the other casing end to produce an interference fit between the second end connector and the other casing end.

10. The cell of claim 9, further comprising an electrical terminal having a tubular portion extending into the hole in the second end connector portion extending through the hole in the other casing end, the tubular portion being radially expanded against said hole in the end connector portion extending through the hole in the other casing end to produce an interference fit between the tubular portion and the end connector.

11. The cell of claim 10, wherein the electrical terminal includes a flange extending partially over the second end connector portion extending through the hole of the other casing end.

12. The cell of claim 11, wherein the electrical terminal is a portion of a blind rivet.

13. The cell of claim 11, further comprising a sealing washer positioned between the electrical terminal flange and the second end connector portion extending through the hole of the other casing end to seal the joint between the electrical terminal and the second end connector.

14. The cell of claim 13, wherein the sealing washer extends radially over both the second end connector portion extending through the hole of the other casing end and at least a portion of the other casing end to seal the joint between the second end connector and other casing end.

15. The cell of claim 11, wherein the second end connector is substantially disk-shaped and the second end connector includes an annular protrusion around the second end connector portion extending through the hole of the other casing end, and the other casing end is substantially disk-shaped and includes an annular recess which receives the second end connector annular protrusion.

16. The cell of claim 3, wherein the second end connector is cast onto a set of plates wound into said spiral.

17. A method of manufacturing an electrochemical cell, comprising: winding sets of opposite polarity plates to produce a spiral with two ends; attaching an end connector to one of said sets of plates at one spiral end, the end connector being substantially disk-shaped with a protruding hub; placing the spiral with attached end connector into a casing having a jacket which extends around the spiral and an end with a hole therethrough to receive the end connector hub; and radially expanding the end connector hub against the casing end hole to produce an interference fit between the end connector and the casing.

18. The method of claim 17, wherein the end connector hub has a hole, and wherein said step of expanding the end connector hub against the casing end is by placing a tubular element into the hub hole and radially expanding the tubular element to produce an interference fit between the tubular element and the end connector hub.

19. The method of claim 18, wherein the tubular element is an electrical terminal, and the electrical terminal further includes a flange extending radially over the end connector hub.

20. The method of claim 19, wherein the electrical terminal is part of a blind rivet.

21. The method of claim 19, further comprising placing sealant between the end connector and the casing end before placing the spiral and end connector into the casing.

22. The method of claim 21, further comprising attaching another end connector to another of said sets of plates at the other spiral end and placing a casing cover onto the casing opposite the casing end to close the casing.

23. The method of claim 22, wherein said another end connector is substantially disk-shaped with a protruding hub and the cover is substantially disk- shaped with a hole therethrough to receive the another end connector hub, and further comprising radially expanding the another end connector hub against the cover to produce an interference fit between the another end connector and the cover.

24. The method of claim 23, wherein the another end connector hub has a hole, and wherein the step of expanding the end connector hub against the cover is by placing another tubular element into the another end connector hub hole and radially expanding the another tubular element to produce an interference fit between the another tubular element and the another end connector.

25. The method of claim 24, further comprising attaching the cover to the casing.