Patent Publication Number: US-6670073-B2

Title: Battery constructions having increased internal volume for active components

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/102,951, filed Oct. 2, 1998, U.S. Provisional Application No. 60/097,445, filed Aug. 21, 1998, and U.S. Nonprovisional Application Ser. No. 09/293,376, filed Apr. 16, 1999 now U.S. Pat. No. 6,265,101. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to an electrochemical cell construction. More particularly, the present invention relates to the containers and collector assemblies used for an electrochemical cell, such as an alkaline cell. 
     FIG. 1 shows the construction of a conventional C sized alkaline cell  10 . As shown, cell  10  includes a cylindrically-shaped can  12  having an open end and a closed end. Can  12  is preferably formed of an electrically conductive material, such that an outer cover  11  welded to a bottom surface  14  at the closed end of can  12  serves as an electrical contact terminal for the cell. 
     Cell  10  further typically includes a first electrode material  15 , which may serve as the positive electrode (also known as a cathode). The first electrode material  15  may be preformed and inserted into can  12 , or may be molded in place so as to contact the inner surfaces of the can  12 . For an alkaline cell, first electrode material  15  will typically include MnO 2 . After the first electrode  15  has been provided in can  12 , a separator  17  is inserted into the space defined by first electrode  15 . Separator  17  is preferably a non-woven fabric. Separator  17  is provided to maintain a physical separation of the first electrode material  15  and a mixture of electrolyte and a second electrode material  20  while allowing the transport of ions between the electrode materials. 
     Once separator  17  is in place within the cavity defined by first electrode  15 , an electrolyte is dispensed into the space defined by separator  17 , along with the mixture  20  of electrolyte and a second electrode material, which may be the negative electrode (also known as the anode). The electrolyte/second electrode mixture  20  preferably includes a gelling agent. For a typical alkaline cell, mixture  20  is formed of a mixture of an aqueous KOH electrolyte and zinc, which serves as the second electrode material. Water and additional additives may also be included in mixture  20 . 
     Once the first electrode  15 , separator  17 , the electrolyte, and mixture  20  have been formed inside can  12 , a preassembled collector assembly  25  is inserted into the open end of can  12 . Can  12  is typically slightly tapered at its open end. This taper serves to support the collector assembly in a desired orientation prior to securing it in place. After collector assembly  25  has been inserted, an outer cover  45  is placed over collector assembly  25 . Collector assembly  25  is secured in place by radially squeezing the can against collector assembly  25 . The outer cover  45  is then placed over and in contact with collector assembly  25 . The end edge  13  of can  12  is then crimped over the peripheral lip of collector assembly  25 , thereby securing outer cover  45  and collector assembly  25  within the end of can  12 . As described further below, one function served by collector assembly  25  is to provide for a second external electrical contact for the electrochemical cell. Additionally, collector assembly  25  must seal the open end of can  12  to prevent the electrochemical materials therein from leaking from this cell. Additionally, collector assembly  25  must exhibit sufficient strength to withstand the physical abuse to which batteries are typically exposed. Also, because electrochemical cells may produce hydrogen gas, collector assembly  25  may allow internally-generated hydrogen gas to permeate therethrough to escape to the exterior of the electrochemical cell. Further, collector assembly  25  should include some form of pressure relief mechanism to relieve pressure produced internally within the cell should this pressure become excessive. Such conditions may occur when the electrochemical cell internally generates hydrogen gas at a rate that exceeds that at which the internally-generated hydrogen gas can permeate through the collector assembly to the exterior of the cell. 
     The collector assembly  25  shown in FIG. 1 includes a seal  30 , a collector nail  40 , an inner cover  44 , a washer  50 , and a plurality of spurs  52 . Seal  30  is shown as including a central hub  32  having a hole through which collector nail  40  is inserted. Seal  30  further includes a V-shaped portion  34  that may contact an upper surface  16  of first electrode  15 . 
     Seal  30  also includes a peripheral upstanding wall  36  that extends upward along the periphery of seal  30  in an annular fashion. Peripheral upstanding wall  36  not only serves as a seal between the interface of collector assembly  25  and can  12 , but also serves as an electrical insulator for preventing an electrical short from occurring between the positive can and negative contact terminal of the cell. 
     Inner cover  44 , which is formed of a rigid metal, is provided to increase the rigidity and supports the radial compression of collector assembly  25  thereby improving the sealing effectiveness. As shown in FIG. 1, inner cover  44  is configured to contact central hub portion  32  and peripheral upstanding wall  36 . By configuring collector assembly  25  in this fashion, inner cover  44  serves to enable compression of central hub portion  32  by collector nail  40  while also supporting compression of peripheral upstanding wall  36  by the inner surface of can  12 . 
     Outer cover  45  is typically made of a nickel-plated steel and is configured to extend from a region defined by the annular peripheral upstanding wall  36  of seal  30  and to be in electrical contact with a head portion  42  of collector nail  40 . Outer cover  45  may be welded to head portion  42  of collector nail  40  to prevent any loss of contact. As shown in FIG. 1, when collector assembly  25  is inserted into the open end of can  12 , collector nail  40  penetrates deeply within the electrolyte/second electrode mixture  20  to establish sufficient electrical contact therewith. In the example shown in FIG. 1, outer cover  45  includes a peripheral lip  47  that extends upwardly along the circumference of outer cover  45 . By forming peripheral upstanding wall  36  of seal  30  of a length greater than that of peripheral lip  47 , a portion of peripheral upstanding wall  36  may be folded over peripheral lip  47  during the crimping process so as to prevent any portion of the upper edge  13  of can  12  from coming into contact with outer cover  45 . 
     Seal  30  is preferably formed of nylon. In the configuration shown in FIG. 1, a pressure relief mechanism is provided for enabling the relief of internal pressure when such pressure becomes excessive. Further, inner cover  44  and outer cover  45  are typically provided with apertures  43  that allow the hydrogen gas to escape to the exterior of cell  10 . The mechanism shown includes an annular metal washer  50  and a plurality of spurs  52  that are provided between seal  30  and inner cover  44 . The plurality of spurs  52  each include a pointed end  53  that is pressed against a thin intermediate portion  38  of seal  30 . Spurs  52  are biased against the lower inner surface of inner cover  44  such that when the internal pressure of cell  10  increases and seal  30  consequently becomes deformed by pressing upward toward inner cover  44 , the pointed ends  53  of spurs  52  penetrate through the thin intermediate portion  38  of seal  30  thereby rupturing seal  30  and allowing the escape of the internally-generated gas through apertures  43 . 
     Although the above-described collector assembly  25  performs all the above-noted desirable functions satisfactorily, as apparent from its cross-sectional profile, this particular collector assembly occupies a significant amount of space within the interior of the cell  10 . Because the exterior dimensions of the electrochemical cell are generally fixed by the American National Standards Institute (ANSI), the greater the space occupied by the collector assembly, the less space that there is available within the cell for the electrochemical materials. Consequently, a reduction in the amount of electrochemical materials that may be provided within the cell results in a shorter service life for the cell. It is therefore desirable to maximize the interior volume within an electrochemical cell that is available for the electrochemically active components. 
     It should be noted that the construction shown in FIG. 1 is but one example of a cell construction. Other collector assemblies exist that may have lower profiles and hence occupy less space within the cell. However, such collector assemblies typically achieve this reduction in occupied volume at the expense of the sealing characteristics of the collector assembly or the performance and reliability of the pressure relief mechanism. It is therefore desirable to construct an electrochemical cell where the space occupied by the collector assembly and the space occupied by the container volume are minimized while still maintaining adequate sealing characteristics and a reliable pressure relief mechanism. 
     The measured external and internal volumes for several batteries that were commercially available as of the filing date of this application are listed in the tables shown in FIGS. 2A and 2B. The tables list the volumes (cc) for D, C, AA, and AAA sized batteries. Also provided in FIG. 2A is a percentage of the total cell volume that constitutes the internal volume that is available for containing the electrochemically active materials. The total cell volume includes all of the volume, including any internal void spaces, of the battery. For the battery shown in FIG. 1, the total volume ideally includes all of the cross-hatched area as shown in FIG.  3 A. The “internal volume” of the battery is represented by the cross-hatched area shown in FIG.  3 B. The “internal volume,” as used herein, is that volume inside the cell or battery that contains the electrochemically active materials as well as any voids and chemically inert materials (other than the collector nail) that are confined within the sealed volume of the cell. Such chemically inert materials may include separators, conductors, and any inert additives in the electrodes. As described herein, the term “electrochemically active materials” includes the positive and negative electrodes and the electrolyte. 
     The collector assembly volume includes the collector nail, seal, inner cover, and any void volume between the bottom surface of the negative cover and the seal (indicated by the crosshatched area in FIG.  3 C). It should be appreciated that the sum total of the “internal volume,” “collector assembly volume,” and “container volume” is equal to the total volume. Accordingly, the internal volume available for electrochemically active materials can be confirmed by measuring the collector assembly volume and container volume and subtracting the collector assembly volume and the container volume from the measured total volume of the battery. The “container volume” includes the volume of the can, label, negative cover, void volume between the label and negative cover, positive cover, and void volume between the positive cover and can (shown by the cross-hatched area in FIG.  3 D). If the label extends onto and into contact with the negative cover, the void volume present between the label and negative cover is included in the container volume, and therefore is also considered as part of the total volume. Otherwise, that void volume is not included in either of the container volume or the total volume. The collector assembly volume and the percentage of the total cell volume that constitutes the collector assembly volume is provided in FIG. 2B for those commercially available batteries listed in FIG.  2 A. 
     The total battery volume, collector assembly volume, and internal volume available for electrochemically active material for each battery are determined by viewing a Computer Aided Design (CAD) drawing, a photograph, or an actual cross section of the battery which has been encased in epoxy and longitudinally cross-sectioned. The use of a CAD drawing, photograph, or actual longitudinal cross section to view and measure battery dimensions allows for inclusion of all void volumes that might be present in the battery. To measure the total battery volume, the cross-sectional view of the battery taken through its central longitudinal axis of symmetry is viewed and the entire volume is measured by geometric computation. To measure the internal volume available for electrochemically active materials, the cross-sectional view of the battery taken through its central longitudinal axis of symmetry is viewed, and the components making up the internal volume, which includes the electrochemically active materials, void volumes and chemically inert materials (other than the collector nail) that are confined within the sealed volume of the cell, are measured by geometric computation. Likewise, to determine volume of the collector assembly, the cross-sectional view of the battery taken through its central longitudinal axis of symmetry thereof is viewed, and the components making up the collector assembly volume, which include the collector nail, seal, inner cover, and any void volume defined between the bottom surface of the negative cover and the seal, are measured by geometric computation. The container volume may likewise be measured by viewing the central longitudinal cross section of the battery and computing the volume consumed by the can, label, negative cover, void volume between the label and negative cover, positive cover, and void volume between the positive cover and the can. 
     The volume measurements are made by viewing a cross section of the battery taken through its longitudinal axis of symmetry. This provides for an accurate volume measurement, since the battery and its components are usually axial symmetric. To obtain a geometric view of the cross section of a battery, the battery was first potted in epoxy and, after the epoxy solidified, the potted battery and its components were ground down to the central cross section through the axis of symmetry. More particularly, the battery was first potted in epoxy and then ground short of the central cross section. Next, all internal components such as the anode, cathode, and separator paper were removed in order to better enable measurement of the finished cross section. The potted battery was then cleaned of any remaining debris, was air dried, and the remaining void volumes were filled with epoxy to give the battery some integrity before completing the grinding and polishing to its center. The battery was again ground and polished until finished to its central cross section, was thereafter traced into a drawing, and the volumes measured therefrom. 
     Prior to potting the battery in epoxy, battery measurements were taken with calipers to measure the overall height, the crimp height, and the outside diameter at the top, bottom, and center of the battery. In addition, an identical battery was disassembled and the components thereof were measured. These measurements of components of the disassembled battery include the diameter of the current collector nail, the length of the current collector nail, the length of the current collector nail to the negative cover, and the outside diameter of the top, bottom, and center of the battery without the label present. 
     Once the battery was completely potted in epoxy and ground to center through the longitudinal axis of symmetry, the cross-sectional view of the battery was used to make a drawing. A Mitutoyo optical comparitor with QC-4000 software was used to trace the contour of the battery and its individual components to generate a drawing of the central cross section of the battery. In doing so, the battery was securely fixed in place and the contour of the battery parts were saved in a format that could later be used in solid modeling software to calculate the battery volumes of interest. However, before any volume measurements were taken, the drawing may be adjusted to compensate for any battery components that are not aligned exactly through the center of the battery. This may be accomplished by using the measurements that were taken from the battery before cross sectioning the battery and those measurements taken from the disassembled identical battery. For example, the diameter and length of the current collector nail, and overall outside diameter of the battery can be modified to profile the drawing more accurately by adjusting the drawing to include the corresponding known cross-sectional dimensions to make the drawing more accurate for volume measurements. The detail of the seal, cover, and crimp areas were used as they were drawn on the optical comparitor. 
     To calculate the volume measurements, the drawing was imported into solid modeling software. A solid three-dimensional volume representation was generated by rotating the contour of the cross section on both the left and right sides by one-hundred-eighty degrees (180°) about calculated by the software and, by rotating the left and right sides by one-hundred-eighty degrees (180°) and summing the left and right volumes together an average volume value is determined, which may be advantageous in those situations where the battery has non-symmetrical features. The volumes which include any non-symmetrical features can be adjusted as necessary to obtain more accurate volume measurements. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an aspect of the present invention to solve the above problems by either eliminating the collector assembly from the cell while retaining its functions, or by providing a collector assembly having a significantly lower profile and thereby occupying significantly less space within an electrochemical cell. Another aspect of the present invention is to provide cell constructions exhibiting lower water loss over time than prior assemblies, thereby increasing the cell&#39;s shelf life. An additional aspect of the invention is to provide a battery having a reliable pressure relief mechanism that does not occupy a significant percentage of the available cell volume. Still yet another aspect of the present invention is to provide cell constructions that are simpler to manufacture and that require less materials, thereby possibly having lower manufacturing costs. Another aspect of the invention is to provide cell constructions that require less radial compressive force to be applied by the can to adequately seal the cell, thereby allowing for the use of a can having thinner side walls, and thus resulting in greater internal cell volume. 
     To achieve some of these and other aspects and advantages, a battery of the present invention comprises a can for containing electrochemical materials including positive and negative electrodes and an electrolyte, the can having a first end, an open second end, side walls extending between the first and second ends, and an end wall extending across the first end; a pressure relief mechanism formed in the end wall of the can for releasing internal pressure from within the can when the internal pressure becomes excessive; a first outer cover positioned on the end wall of the can to be in electrical contact therewith and to extend over the pressure relief mechanism; a second outer cover positioned across the open second end of the can; and an insulator disposed between the can and the second outer cover for electrically insulating the can from the second outer cover. 
     Additionally, some of the above aspects and advantages may be achieved by a battery of the present invention that comprises a can for containing electrochemically active materials including at least positive and negative electrodes and an electrolyte, the can having a first end, an open second end, side walls extending between the first and second ends, and an end wall extending across the first end, the can further having a flange that extends outward from the open second end of the can towards the first end; a cover for sealing the open end of the can, the cover having a peripheral edge that extends over and around the flange and is crimped between the flange and an exterior surface of the side walls of the can; and electrical insulation provided between the flange and the peripheral edge of the cover and between the can and the peripheral edge. The electrical insulating material is preferably provided in the form of a coating deposited directly on at least one of the can and the outer cover. 
     Further, some of the above aspects and advantages may also be achieved by an electrochemical cell of the present invention that comprises a can for containing electrochemically active materials including at least positive and negative electrodes and an electrolyte, the can having an open end and a closed end, and side walls extending between the open end and closed end; a first outer cover positioned across the open end of the can; a collector electrically coupled to the first outer cover and extending internally within the can to electrically contact one of the positive and negative electrodes; and an annular seal having an L-shaped cross section disposed between the can and the first outer cover for electrically insulating the can from the first outer cover and creating a seal between the first outer cover and the can. The seal may further include an extended vertical member to form a J-shaped cross section. According to this embodiment, a pressure relief mechanism is preferably formed in a surface of the can for releasing internal pressure from within the can when the internal pressure becomes excessive. 
     Yet, some of the above aspects and advantages may be achieved by an electrochemical cell of the present invention that comprises a can for containing electrochemically active materials including at least positive and negative electrodes and an electrolyte, the can having an open end, a closed end, and side walls extending between the open and closed ends; a cover positioned across the open end of the can and connected to the can, the cover having an aperture extending therethrough; a current collector extending through the aperture in the cover and extending internally within the can to electrically contact one of the positive and negative electrodes; and an insulating material disposed between the collector and the cover for electrically insulating the collector from the cover and creating a seal between the collector and the cover. In addition, the electrochemical cell preferably includes a first contact terminal electrically coupled to the collector and a dielectric material disposed between the first contact terminal and the cover for electrically insulating the cover from the first contact terminal. Also provided is a method of manufacturing an electrochemical cell which includes the steps of dispensing active electrochemical materials in a can having a closed end and an open end; disposing a collector through an aperture formed in a cover; providing a dielectric insulating material between the cover and the collector to provide electrical insulation therebetween; and assembling the cover and collector to the open end of the can. 
     Further, some of the above aspects and advantages may also be achieved by a battery of the present invention that comprises a can for containing electrochemically active materials including positive and negative electrodes and an electrolyte, and a label printed directly on an exterior surface of the can. A method of assembling a battery is also provided including the steps of forming a can having an open end and a closed end, forming an outer cover, dispensing electrochemically active materials in the can, sealing the outer cover across the open end of the can with a layer of electrical insulation provided therebetween, and printing a label directly on the exterior surface of the can. According to this embodiment, the diameter of the can may be correspondingly increased to allow a significant increase in the internal volume of the battery, while maintaining a predetermined total outside diameter. 
     These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a cross section of a conventional C sized alkaline electrochemical cell; 
     FIG. 2A is a table showing the relative total battery volumes and internal cell volumes available for electrochemically active materials, as measured for those batteries that were commercially available at the time this application was filed; 
     FIG. 2B is a table showing the relative total battery volumes and collector assembly volumes as measured for those batteries that were commercially available as provided in FIG. 2A; 
     FIGS. 3A-3D are cross sections of a conventional C sized alkaline electrochemical cell that illustrate the total battery and various component volumes; 
     FIG. 4 is a cross section of a C sized alkaline electrochemical cell having a low profile seal constructed in accordance with a first embodiment of the present invention; 
     FIG. 5 is a partial cross section of an adaption of the first embodiment for use in an AA sized battery shown in comparison with a partial cross section of an adaptation of the conventional construction as currently used in an AA sized battery; 
     FIG. 6 is a cross section of a C sized alkaline electrochemical cell having an ultra low profile seal according to a second embodiment of the present invention; 
     FIG. 7 is a cross section of a C sized alkaline electrochemical cell having an ultra low profile seal and a formed positive cover protrusion according to a third embodiment of the present invention; 
     FIG. 8A is a cross section of a C sized alkaline electrochemical cell constructed in accordance with a fourth embodiment of the present invention having a rollback cover, an annular L-shaped or J-shaped seal, and a pressure relief mechanism formed in the can bottom surface; 
     FIG. 8B is a cross section of the top portion of a C sized alkaline electrochemical cell constructed in accordance with the fourth embodiment of the present invention having a rollback cover and further including an L-shaped annular seal; 
     FIG. 8C is an exploded perspective view of the electrochemical cell shown in FIG. 8A illustrating assembly of the collector seal and cover assembly; 
     FIG. 9 is a bottom view of a battery can having a pressure relief mechanism formed in the closed end of the can; 
     FIG. 10 is a cross-sectional view taken along line X—X of the can vent shown in FIG. 9; 
     FIG. 11 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction according to a fifth embodiment of the present invention; 
     FIG. 12A is a partially exploded perspective view of the battery shown in FIG. 11; 
     FIGS. 12B and 12C are cross-sectional views of a portion of the battery shown in FIG. 11 illustrating the process for forming the beverage can-type construction; 
     FIG. 12D is an enlarged cross-sectional view of a portion of the battery shown in FIG. 11; 
     FIG. 13 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction according to a sixth embodiment of the present invention; 
     FIG. 14A is a table showing the calculated total and internal cell volume for various batteries constructed in accordance with the present invention; 
     FIG. 14B is a table showing the calculated total volume and collector assembly volume for various batteries constructed in accordance with the present invention; 
     FIG. 15 is a cross section of a C sized alkaline electrochemical cell having a collector feed through construction according to a seventh embodiment of the present invention; 
     FIG. 16 is an exploded assembly view of the electrochemical cell shown in FIG. 15; and 
     FIG. 17 is a flow diagram illustrating a method of assembly of the electrochemical cell shown in FIGS.  15  and  16 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As described above, a primary objective of the present invention is to increase the internal volume available in a battery for containing the electrochemically active materials to volumes previously not obtained. To achieve this objective without detrimentally decreasing the reliability of the pressure relief mechanism provided in the battery and without increasing the likelihood that the battery would otherwise leak, various novel modifications are suggested below to the construction of batteries of various sizes. The modifications described below may be implemented separately or in combination in a battery to improve its volume efficiency. 
     As described in further detail below, the various modifications of the present invention that achieve greater internal volume for containing the electrochemically active materials, include a low profile seal (FIG.  4 ), an ultra low profile seal (FIG.  5 ), a positive outer cover protrusion formed directly in the closed end of the can used in combination with the ultra low profile seal (FIG. 6) or the low profile seal, a can vent formed in the closed end of the battery can (FIGS. 7-9) including an L-shaped and J-shaped annular seal (FIGS.  8 A- 8 C), a beverage can-type construction used in combination with a can vent (FIG.  11 ), and a beverage can-type construction with a collector feed through (FIGS.  15 - 17 ). 
     Additionally, through the use of the constructions noted above, the battery can may be made with thinner walls, on the order of 4-8 mils, since the construction techniques outlined below do not require the thicker walls that are required in conventional batteries to ensure a sufficient crimp and seal. Further, in accordance with the present invention, a label may be lithographed directly onto the exterior surface of the battery can. By making the can walls thinner and lithographing the label directly onto the exterior of the can, the internal volume of the cell may be further increased since one does not have to account for the thickness of the label substrate to construct a cell that meets the ANSI exterior size standards. 
     Low Profile Seal 
     FIG. 4 shows a battery constructed using a low profile seal in accordance with a first embodiment of the present invention. Similar to the battery shown in FIG. 1, battery  100  includes an electrically conductive can  112  having a closed end  114  and an open end in which a collector assembly  125  and negative cover  145  are secured in place. Also, battery  100  includes a positive electrode  115  in contact with the interior walls of can  112  and in contact with a separator layer  117  that lies between positive electrode  115  and a negative electrode  120 . Further, battery  100  includes a positive outer cover  111  attached to a bottom surface of the closed end of can  112 . 
     The difference between batteries  10  and  100  lies in the construction of collector assembly  125  and cover  145 . While seal  130  is similar to seal  30  in that it includes an upstanding wall  136  and a central hub  132 , which has an aperture formed therein for receiving the head portion  142  of a collector nail  140 , seal  130  differs from seal  30  in that the V portion  34  of seal  30  is inverted to extend upward toward inner cover  144 , as indicated by reference numeral  134 . By inverting this V portion, collector assembly  125  may rest more squarely upon an upper surface  116  of positive electrode  115 . Further, the volume occupied by the V portion  34  of battery  10  may then be used for the electrochemically active materials. 
     To also reduce the internal volume occupied by collector assembly  125 , inner cover  144  is constructed to more closely conform to the inner surface of outer cover  145  so as to eliminate the void space between outer cover  45  and inner cover  44  in battery  10 . Additionally, by resting collector assembly  125  firmly on top surface  116  of positive electrode  115 , the peripheral edge  147  of outer cover  145  may be flat rather than extend upward, as in the case for battery  10 . By laying peripheral edge  147  flat, collector assembly  125  may be positioned even closer to the end of battery  100 . 
     Collector assembly  125  of battery  100  further differs from collector assembly  25  of battery  10  in that spurs  52  and washer  50  are eliminated. Collector assembly  125 , nevertheless, has a reliable pressure relief mechanism by the provision of a thinned-out section  138  formed in seal  130  immediately adjacent hub  132 . A thickened ring portion  139  of seal  130  is provided adjacent thinned-out portion  138  such that thinned-out portion  138  lies between thickened ring portion  139  and the relatively thick hub  132 . Thus, when the internal pressure of cell  100  becomes excessive, seal  130  rips open in the location of thinned-out portion  138 . As with the construction shown for battery  10 , the internally-generated gas then escapes through apertures  143  formed in inner cover  144  and outer cover  145 . 
     The internal volume available for containing electrochemically active materials in a D sized battery having the conventional construction shown in FIG. 1, is 44.16 cc, which is 87.7 percent of the total volume of 50.38 cc. (See the corresponding entry in the table of FIG. 2A.) If the same cell were constructed using the low profile seal construction shown in FIG. 4, the internal cell volume may be increased to 44.67 cc, which represents 89.2 percent of the total volume, which is 50.07 cc. The internal and external volumes for the cell constructed with the low profile seal of the present invention are for a cell having a 10 mil can thickness. Further, by decreasing the can wall thickness, even greater internal cell volumes may be achieved. 
     The low profile seal described above is disclosed in commonly-assigned U.S. patent application Ser. No. 08/882,572 entitled “A V-SHAPED GASKET FOR GALVANIC CELLS,” filed on Jun. 27, 1997, by Gary R. Tucholski, the disclosure of which is incorporated by reference herein. 
     FIG. 5 shows a modified adaptation of the low profile seal as used in an AA sized battery  100 ′ in comparison with a commercial adaptation of the construction shown in FIG. 1 as used for an AA sized battery  10 ′. Like the collector assembly of battery  100  (FIG.  4 ), the collector assembly of battery  100 ′ includes a seal  130  having an inverted-V portion  134 , a hub portion  132 , and a thinned-out portion  138  provided between hub  132  and a thickened portion  139 . 
     The primary difference between the collector assemblies of batteries  100  and  100 ′ is the elimination of inner cover  144  of battery  100 . To ensure sufficient radial compressive force against upstanding leg  136  of seal  130 , battery  100 ′ uses a rollback cover  145 ′ in place of the flanged cover  145  used in battery  100  and also utilizes a retainer  150 . As will be apparent from a comparison of FIGS. 4 and 5, a rollback cover differs from a flanged cover in that the peripheral edge  147  of a flanged cover  145  is flat whereas the peripheral edge  147 ′ of a rollback cover  145 ′ extends axially downward and is folded to also extend axially upward. Rollback cover  145 ′ provides a sufficient spring force in the radial direction to maintain compression of upstanding leg  136  of seal  130  against the inner wall of can  112  during normal use. 
     Retainer  150  is provided over and around the upper portion of hub  132  of seal  130  to compress hub  132  against collector nail  140 . Also, by configuring retainer  150  to have a J- or L-shaped cross section, the lower radial extension of retainer  150  can ensure that seal  130  will rupture in the vicinity of thinned-out portion  138  when the internal pressure reaches an excessive level. 
     Ultra Low Profile Seal 
     FIG. 6 shows a battery constructed in accordance with a second embodiment of the present invention, which utilizes an ultra low profile seal. Like the conventional cell  10  shown in FIG. 1, cell  200  also includes a cylindrical can  212  made of an electrically conductive material. Also, a first electrode  215  is formed against the inner walls of can  212  preferably by molding. A separator  217  is likewise inserted within the cavity defined by first electrode material  215 , and a mixture  220  of a second electrode and electrolyte are provided within a cavity defined by the separator  217 . 
     As shown in FIG. 6, collector assembly  225  includes an integral seal/inner cover assembly  228  and a collector  240  that passes through a central hole  236  provided in the integral seal/inner cover assembly  228 . Collector  240  is preferably a brass nail including a head  242  and a retainer flange  241  that is provided to cooperate with a speed nut  250  to secure collector nail  240  within central hole  236  of integrated seal/inner cover assembly  228 . 
     Integrated seal/inner cover assembly  228  includes a rigid inner cover  210  and a seal  230  that is formed directly on rigid inner cover  210  by molding or lamination. Seal  230  is preferably made of neoprene, butyl, or ethylene propylene rubber, and rigid inner cover  210  is preferably formed of low-carbon steel  1008  or  1010 . Because rubber is more compressible than the nylon or polypropylene materials often used in such collector assemblies, the radial compressive strength of the rigid inner cover  210  need not be as great. Thus, the inner cover could be made of thinner and/or softer metals. Further, materials other than metal may be used. Also, seal  230  may be formed of other materials provided such materials are chemically inert, water impervious, compressible, and exhibit the ability to bond to the material used to form rigid inner cover  210 . 
     Additionally, by decreasing the radial force required to compress the peripheral upstanding wall of the seal, the thickness of the can walls may be decreased from 0.010 inch (10 mils) to approximately 0.006 (6 mils) or possibly even 0.004 inch (4 mils). 
     By providing a structure that enables rubber materials such as neoprene and butyl rubber to be used as the seal material, the water permeability of the collector assembly is significantly reduced. By reducing the water permeability of the cell, the service maintenance of the battery should be increased. 
     Rigid inner cover  210  is generally disk shaped and has a central aperture  218  formed at its center as well as a plurality of additional apertures  217 . Central aperture  218  and additional apertures  217  extend through rigid inner cover  210  from its upper surface to its bottom surface. If formed of metal, rigid inner cover  210  is preferably produced by stamping it from a sheet of metal. Inner cover  210  may, however, be formed using other known manufacturing techniques. Subsequently, rigid inner cover  210  may be subjected to a surface roughening process, such as sandblasting or chemical etching, to enhance the strength of the bond that is subsequently formed between rigid inner cover  210  and seal  230 . For a C sized cell, rigid inner cover  210  is preferably 0.015 to 0.030 inch thick. 
     After rigid inner cover  210  has been stamped and surface treated, it is preferably inserted into a transfer mold press into which the rubber that forms seal  230  is subsequently supplied. The transfer mold is preferably formed to allow the supplied rubber to form a layer  232  across the bottom surface of rigid inner cover  210 . The thickness of layer  232  is between 0.010 and 0.020 inch thick, and is preferably about 0.016 inch thick. The rubber also flows into apertures  217  to form plugs  238 . Also, the rubber flows within central aperture  218  so as to line the surfaces of central aperture  218  but without completely filling the aperture so as to provide a central hole  236  into which collector nail  240  may subsequently be inserted. The diameter of central hole  236  is preferably sufficiently smaller than the diameter of collector nail  240  such that the rubber lining in central aperture  218  is significantly compressed within aperture  218  when collector nail  240  is driven in place through central hole  236 . By providing a retainer  241  on collector  240  that is pressed against bottom layer  232  of seal  230 , when collector nail  240  has been driven in place, its speed nut  250  and retainer  241  cooperate to also vertically compress the portion of rubber layer  232  lying therebetween. By compressing the rubber seal in the vicinity of collector nail  240  in this manner, the possibility of a leak occurring in the interface between the collector nail  240  and integrated seal/inner cover assembly  228  is significantly reduced. 
     By filling apertures  217  with rubber seal plugs  238  in the manner shown, a pressure relief mechanism is provided that not only works reliably, but which may effectively reseal after internal pressure has been released. When the internal pressure reaches levels considered to be excessive, the excessive pressure ruptures at least one of plugs  238  to allow the expedited release of internally-generated gasses. The pressure at which such rupturing occurs is controllable based upon the materials selected for the seal, the thickness of the seal material, and the diameter of apertures  217 . Further, because of the elasticity of the rubber seal material, the rubber plug  238  substantially assumes its original state once the pressure has been released. Thus, unlike other venting mechanisms used in conventional collector assemblies, the pressure relief mechanism of the present invention does not create a permanent hole within the collector assembly through which electrochemical materials may subsequently leak. Also, such resealing minimizes deterioration of the cell&#39;s internal components, thereby possibly extending the useful cell life. 
     Although only one aperture  217  in plug  238  need be provided to serve as a pressure relief mechanism, added reliability is obtained by providing a plurality of such plugged apertures. Unlike prior art relief mechanism structures, the present invention allows for a plurality of independently-operable pressure relief mechanisms. Even the pressure relief mechanism illustrated in FIG. 1, which includes a plurality of spurs, relies upon the inversion of washer  50  for any one of the spurs to penetrate the seal. Each of the plugged apertures provided in the collector assembly of the present invention, however, is not dependent upon one another, and therefore provide for a more reliable pressure relief mechanism as a whole. 
     As shown in FIG. 6, seal  230  has an upstanding wall  235  formed directly on a peripheral edge of rigid inner cover  210 . By providing this upstanding wall  235 , a sufficient seal may be created when collector assembly  225  is inserted into can  212 . This seal is further enhanced by forming the outer diameter of seal  230  to be greater than the inside diameter of can  212  so that inner cover  210  compresses upstanding wall  235  against the inner surface of can  212 . 
     Seal  230  may additionally be formed to include an extended portion  237  of upstanding wall  235  that extends vertically upward past the upper surface of inner cover  210 . By providing extension  237 , seal  230  may be used as an electrical insulator between the crimped end  224  of can  212  and a peripheral edge of outer cover  245 . 
     Although seal  230  is shown as including a continuous layer  232  across the entire bottom surface of inner cover  210 , it will be appreciated by those skilled in the art that seal  230  need not be formed over the entire bottom surface of inner cover  210 , particularly if inner cover  210  is formed of an inert plastic material. Depending upon the characteristics of the materials used to form seal  230  and inner cover  210 , a bonding agent may be applied to the surfaces of inner cover  210  that will come into contact and be bonded to seal material  230 . 
     Once seal  230  has been molded to inner cover  210  and collector nail  240  is inserted through central hole  236  of integrated seal/inner cover assembly  228  and through retainer  240 , outer cover  245  is placed on the upper surface of collector assembly  225  and is preferably welded to head  242  of collector nail  240 . Subsequently, the collector assembly  225  with the outer cover  245  attached thereto is inserted into the open end of cell can  212 . To hold collector assembly  225  in place prior to crimping, the bottom surface of collector assembly  225  is rested upon an upper surface  216  of first electrode  215 . Thus, collector assembly  225  may be inserted with some degree of force to ensure that the bottom layer  232  of seal  230  rests evenly within the cell can opening on upper surface  216  of electrode  215 . 
     If first electrode  215  is formed by molding it in place within can  212 , first electrode  215  is preferably constructed in the manner disclosed in commonly-assigned U.S. patent application Ser. No. 09/036,115 entitled “ELECTROCHEMICAL CELL STRUCTURE EMPLOYING ELECTRODE SUPPORT FOR THE SEAL,” filed on Mar. 6, 1998, by Gary R. Tucholski et al. to prevent any flashing resulting from the molding of first electrode  215  from interfering with the proper alignment and seal provided by the collector assembly. The disclosure of U.S. patent application Ser. No. 09/036,115 is incorporated by reference herein. 
     By resting collector assembly  225  on electrode  215 , can  212  could be crimped at its open end so as to provide a downward force that is countered by electrode  215 . Thus, the higher profile crimp used in the conventional cell construction shown in FIG. 1 may be replaced with a lower profile crimp, thereby creating about 0.060 inch more space inside the cell. 
     A collector assembly  225  having the construction shown in FIG. 6 has a much lower profile than the conventional collector assembly as illustrated in FIG.  1 . Thus, a cell  200  utilizing collector assembly  225  may include greater amounts of electrochemical materials  215  and  220 , and the service life of the cell is increased accordingly. Despite its lower profile, collector assembly  225  nevertheless exhibits sufficient sealing and electrical insulation. Additionally, the collector assembly of the present invention provides a pressure relief mechanism that is not only reliable, but which provides the advantages of multiple independently-operable pressure relief mechanisms and partial resealing after venting to prevent the subsequent leakage of electrochemical materials from the cell. Further, the collector assembly of the present invention offers improved water permeability characteristics, thereby increasing the service maintenance of the battery. 
     The calculated total volumes (cc) and internal volumes (cc) available for containing electrochemically active materials for batteries of various sizes constructed using the ultra low profile seal shown in FIG. 6, are provided in the table shown in FIG.  14 A. As apparent from the table in FIG. 14A, the internal cell volumes for such cells are generally greater than any of the prior commercially-available cells. For example, a D sized battery employing the ultra low profile seal has an internal volume available for containing electrochemically active materials of 45.53 cc, which is 90.9 percent of the total volume of 50.07 cc. This is greater than the internal volume measured on any of the conventional cells listed in FIG.  2 A. Further, for cells having a can thickness of 8 mils or 6 mils, the internal cell volume may be further significantly increased. The calculated total volumes (cc) are further shown in the table presented in FIG. 14B, in comparison with the collector assembly volumes for batteries of various sizes constructed using the ultra low profile seal shown in FIG.  6 . The collector assembly volume as defined herein includes the collector nail, seal, inner cover, and any void volume between the bottom surface of the negative cover and the seal. The container volume as defined herein includes the volume used by the can, label, negative cover, void volume between the label and the negative cover, positive cover, and the void volume between the positive cover and can. It should be appreciated that the total volume of the battery is equal to the summation of the internal volume available for electrochemically active materials, the collector assembly volume, and the container volume. The total volume of the battery, collector assembly volume and container volume are determined by viewing a CAD drawing of the central longitudinal cross-sectional view of the battery. As is apparent from the table in FIG. 14B, the collector assembly volume is generally less than any of the prior commercially-available cells. It should be appreciated that the collector assembly volume is decreased by using the ultra low profile seal construction. For example, the collector assembly volume consumed in the ultra low profile seal is 1.89 cc, which is 3.8 percent of the total volume of 50.07 cc as shown in FIG.  14 B. In contrast, this is less than any of the collector assembly volumes measured from the conventional batteries as listed in FIG.  2 B. The container volume may also be decreased. Similarly, for cells having a reduced can thickness of 8 mils or 6 mils, the internal cell volume may be further significantly increased, while the container volume is decreased. 
     The ultra low profile seal described above, and several alternative embodiments of the ultra low profile seal, are disclosed in commonly-assigned U.S. patent application Ser. No. 09/036,208 entitled “COLLECTOR ASSEMBLY FOR AN ELECTROCHEMICAL CELL INCLUDING AN INTEGRAL SEAL/INNER COVER,” filed on Mar. 6, 1998, by Gary R. Tucholski, the disclosure of which is incorporated by reference herein. 
     Low Profile Seal and Ultra Low Profile Seal With Formed Positive Protrusion 
     As shown in FIG. 7, the second embodiment shown in FIG. 6 may be modified to have the protrusion  270  for the positive battery terminal formed directly in the closed end  214 ′ of can  212 . In this manner, the void space existing between the closed end  214  of can  212  and positive outer cover  211  (FIG. 6) may be used to contain electrochemically active materials or otherwise provide space for the collection of gasses, which otherwise must be provided within the cell. It will further be appreciated by those skilled in the art that the first embodiment shown in FIG. 4 may similarly be modified, such that the positive outer cover protrusion is formed directly in the bottom of can  112 . Although the increase in cell volume obtained by forming the protrusion directly in the bottom of the can is not provided in the table in FIG. 14A, it will be appreciated by those skilled in the art that the internal volume is typically one percent greater than the volumes listed for the ultra low profile seal or low profile seal listed in the table, which are formed with a separate cover. 
     Pressure Relief Mechanism Formed in Can Bottom with L-Shaped Seal 
     An electrochemical battery  300  constructed in accordance with a fourth embodiment of the present invention is shown in FIGS. 8A through 8C. Battery  300  differs from the prior battery constructions in that a pressure relief mechanism  370  is formed in the closed end  314  of can  312 . As a result, complex collector/seal assemblies may be replaced with collector assemblies that consume less volume and have fewer parts. Thus, a significant improvement in internal cell volume efficiency may be obtained. As shown in FIGS. 8A,  8 B,  9 , and  10 , the pressure relief mechanism  370  is formed by providing a groove  372  in the bottom surface of can  312 . This groove may be formed by coining a bottom surface of can  312 , cutting a groove in the bottom surface, or molding the groove in the bottom surface of the can at the time the positive electrode is molded. For an AA sized battery, the thickness of the metal at the bottom of the coined groove is approximately 2 mils. For a D sized battery, the thickness of the metal at the bottom of the coined groove is approximately 3 mils. The groove may be formed as an arc of approximately 300 degrees. By keeping the shape formed by the groove slightly open, the pressure relief mechanism will have an effective hinge. 
     The size of the area circumscribed by the groove  372  is preferably selected such that upon rupture due to excessive internal pressure, the area within the groove  372  may pivot at the hinge within the positive protrusion of outer cover  311  without interference from outer cover  311 . In general, the size of the area defined by the groove  372 , as well as the selected depth of the groove, depends upon the diameter of the can and the pressure at which the pressure relief mechanism is to rupture and allow internally-generated gasses to escape. 
     Unlike pressure relief mechanisms that have been described in the prior art as being formed in the side or end of the can, the pressure relief mechanism  370  of the present invention is positioned beneath outer cover  311  so as to prevent the electrochemical materials from dangerously spraying directly outward from the battery upon rupture. Also, if the battery were used in series with another battery such that the end of the positive terminal of the battery is pressed against the negative terminal of another battery, the provision of outer cover  311  over pressure relief mechanism  370  allows mechanism  370  to bow outwardly under the positive protrusion and ultimately rupture. If outer cover  311  was not present in such circumstances, the contact between the two batteries may otherwise prevent the pressure relief mechanism from rupturing. Further, if outer cover  311  were not provided over pressure relief mechanism  370 , the pressure relief mechanism at the positive end of the battery would be more susceptible to damage. Outer cover  311  also shields pressure relief mechanism  370  from the corrosive effects of the ambient environment and therefore reduces the possibility of premature venting and/or leaking. Thus, by forming the pressure relief mechanism under the outer cover, the present invention overcomes the problems associated with the prior art constructions, and thus represents a commercially feasible pressure relief mechanism for a battery. 
     Because the formation of a pressure relief mechanism in the bottom surface of a battery can eliminates the need for a complex collector/seal assembly, the open end of the battery can may be sealed using construction techniques that were not previously feasible due to the need to allow gasses to escape through the pressure relief mechanism to the exterior of the battery. For example, as shown in FIGS. 8A and 8B, the open end of can  312  may be sealed by placing either a nylon seal  330  having a J-shaped cross section or a nylon seal  330 ′ having an L-shaped cross section in the open end of can  312 , inserting a negative outer cover  345  having a rolled back peripheral edge  347  within nylon seal  330  or  330 ′, and subsequently crimping the outer edge  313  of can  312  to hold seal  330  or  330 ′ and cover  345  in place. To help hold seal  330  or  330 ′ in place, a bead  316  may be formed around the circumference of the open end of can  312 . Nylon seal  330  or  330 ′ may be coated with asphalt to protect it from the electrochemically active materials and to provide a better seal. 
     Referring particularly to FIGS. 8A and 8C, the annular nylon seal  330  is shown configured with a J-shaped cross section which includes an extended vertical wall  332  at the outermost perimeter thereof, a shorter vertical wall  336  at the radially inward side of the seal and has a horizontal base member  334  formed between the vertical walls  332  and  336 . With the presence of the short vertical section  336 , the annular seal is referred to herein as having either a J-shaped or L-shaped cross section. It should be appreciated that the J-shaped nylon seal  330  could also be configured absent the short vertical section  336  to form a plain L-shaped cross section as shown in FIG.  8 B. 
     With particular reference to FIG. 8C, the assembly of the electrochemical cell shown in FIG. 8A is illustrated therein. The cylindrical can  312  is formed with side walls defining the open end and bead  316  for receiving internally disposed battery materials prior to closure of the can. Disposed within can  312  are the active electrochemical cell materials including the positive and negative electrodes and the electrolyte, as well as the separator, and any additives. Together, the outer cover  345 , with the collector nail  340  welded or otherwise fastened to the bottom surface of cover  345 , and annular nylon seal  330  are assembled and inserted into the open end of can  312  to seal and close can  312 . The collector nail  340  is preferably welded via spot weld  342  to the bottom side of outer cover  345 . Together, collector nail  340  and cover  345  are engaged with seal  330  to form the collector assembly, and the collector assembly is inserted in can  312  such that the rolled back peripheral edge  347  of outer cover  345  is disposed against the inside wall of annular seal  330  above bead  316  which supports seal  330 . The collector assembly is forcibly disposed within the open end of can  312  to snuggly engage and close the can opening. Thereafter, the outer edge  313  of can  12  is crimped inward to axially force and hold seal  330  and outer cover  345  in place. 
     Referring back to FIG. 8B, the inside surface of outer cover  345  and at least a top portion of collector nail  340  are further shown coated with an anti-corrosion coating  344 . Anti-corrosion coating  344  includes materials that are electrochemically compatible with the anode. Examples of such electrochemically compatible materials include epoxy, Teflon®, polyolefins, nylon, elastomeric materials, or any other inert materials, either alone or in combination with other materials. Coating  344  may be sprayed or painted on and preferably covers that portion of the inside surface of outer cover  345  and collector nail  340  which is exposed to the active materials in the void region above the positive and negative electrodes of the cell. It should also be appreciated that the inside surface of cover  345  could be plated with tin, copper, or other similarly electrochemically compatible materials. By providing the anti-corrosion coating  344 , any corrosion of the outer cover  345  and collector nail  340  is reduced and/or prevented, which advantageously reduces the amount of gassing which may otherwise occur within the electrochemical cell. Reduction in gassing within the cell results in reduced internal pressure buildup. 
     As shown in FIG. 14A in the rows referenced “Pressure Relief in Can Bottom” and “Pressure Relief in Can Bottom With Thin Walls,” a D sized battery constructed using the construction shown in FIG. 8A, has an internal volume that is 93.5 volume percent when the can walls are 10 mils thick, and an internal volume that is 94.9 volume percent when the can walls are 8 mils thick. As shown in FIG. 14B, a D sized battery constructed using the construction shown in FIG. 8A, has a collector assembly volume that is 2 percent of the total volume when the can walls are 10 mils thick and 8 mils thick. The C, AA, and AAA sized batteries having similar construction also exhibited significant improvements in internal volume efficiency, as is apparent from the table in FIG.  14 A. 
     Beverage Can-type Construction 
     The use of the pressure relief mechanism illustrated in FIGS. 8A-10, further allows the use of the beverage can-type construction shown in FIG.  11 . The beverage can-type construction shown differs from other forms of battery seal constructions in that it does not require any form of nylon seal to be inserted into the open end of can  412 . Instead, negative outer cover  445  is secured to the open end of can  412  using a sealing technique commonly used to seal the top of a food or beverage can to the cylindrical portion of the can. Such sealing constructions had not previously been considered for use in sealing batteries because they would not readily allow for the negative outer cover to be electrically insulated from the can. 
     The method of making a battery having the construction shown in FIG. 11 is described below with reference to FIGS. 12A-12D. Prior to attaching negative outer cover  445  to the open end of can  412 , a collector nail  440  is welded to the inner surface of cover  445 . Next, as shown in FIG. 12A, the inner surface of cover  445 , as well as the peripheral portion of the upper surface of cover  445 , is coated with a layer  475  of electrical insulation material, such as an epoxy, nylon, Teflon®, or vinyl. The portion of collector nail  440  that extends within the void area between the bottom of cover  445  and the top surface of the negative electrode/electrolyte mixture  120 , is also coated with the electrical insulation. Additionally, the inner and outer surfaces of can  412  are also coated in the region of the open end of can  412 . Such coatings  475  may be applied directly to the can and cover by spraying, dipping, or electrostatic deposition. By providing such a coating, negative outer cover  445  may be electrically insulated from can  412 . 
     By applying the insulation coating to the areas of the can, cover, and collector nail within the battery that are proximate the void area within the battery&#39;s internal volume, those areas may be protected from corrosion. While a coating consisting of a single layer of the epoxy, nylon, Teflon®, or vinyl materials noted above will function to prevent such corrosion, it is conceivable that the coating may be applied using layers of two different materials or made of single layers of different materials applied to different regions of the components. For example, the peripheral region of the cover may be coated with a single layer of material that functions both as an electrical insulator and an anti-corrosion layer, while the central portion on the inner surface of the cover may be coated with a single layer of a material that functions as an anti-corrosion layer but does not also function as an electrical insulator. Such materials may include, for example, asphalt or polyamide. Alternatively, either one of the can or cover may be coated with a material that functions as both an electrical insulator and anti-corrosion layer, while the other of these two components may be coated with a material that functions only as an anti-corrosion layer. In this manner, the electrical insulation would be provided where needed (i.e., between the cover/can interface), while the surfaces partially defining the void area in the internal volume of the cell will still be protected from the corrosive effects of the electrochemical materials within the cell. Further, by utilizing different materials, materials may be selected that are lower in cost or exhibit optimal characteristics for the intended function. 
     To assist in the sealing of outer cover  445  to can  412 , a conventional sealant  473  may be applied to the bottom surface of peripheral edge  470  of cover  445 . Once the sealing procedure is complete, sealant  473  migrates to the positions shown in FIG.  12 D. 
     Once collector nail  440  has been attached to outer cover  445  and the electrical insulation coating has been applied, outer cover  445  is placed over the open end of can  412  as shown in FIG.  12 B. Preferably, can  412  has an outward extending flange  450  formed at its open end. Further, outer cover  445  preferably has a slightly curved peripheral edge  470  that conforms to the shape of flange  450 . Once outer cover  445  has been placed over the open end of can  412 , a seaming chuck  500  is placed on outer cover  445 , such that an annular downward extending portion  502  of seaming chuck  500  is received by an annular recess  472  formed in outer cover  445 . Next, a first seaming roll  510  is moved in a radial direction toward the peripheral edge  470  of outer cover  445 . As first seaming roll  510  is moved toward peripheral edge  470  and flange  450 , its curved surface causes peripheral edge  470  to be folded around flange  450 . Also, as first seaming roll  510  moves radially inward, seaming chuck  500 , can  412 , and outer cover  445  are rotated about a central axis, such that peripheral edge  470  is folded around flange  450  about the entire circumference of can  412 . Further, as first seaming roll  510  continues to move radially inward, flange  450  and peripheral edge  470  are folded downward to the position shown in FIG.  12 C. 
     After peripheral edge  470  and flange  450  have been folded into the position shown in FIG. 12C, first seaming roll  510  is moved away from can  412 , and a second seaming roll  520  is then moved radially inward toward flange  450  and peripheral edge  470 . Second seaming roll  520  has a different profile than first seaming roll  510 . Second seaming roll  520  applies sufficient force against flange  450  and peripheral edge  470  to press and flatten the folded flange and peripheral edge against the exterior surface of can  412 , which is supported by seaming chuck  500 . As a result of this process, the peripheral edge  470  of can  412  is folded around and under flange  450  and is crimped between flange  450  and the exterior surface of the walls of can  412 , as shown in FIGS. 11 and 12D. A hermetic seal is thus formed by this process. 
     To illustrate the hermetic nature of this type of seal, a D sized can constructed in accordance with this embodiment of the present invention was filled with water as was a D sized can constructed with a conventional seal, such as that illustrated in FIG.  1 . The two cans were maintained at 71° C. and weighed over time to determine the amount of water lost from the cans. The conventional construction lost 270 mg per week, and the construction in accordance with the present invention did not lose any weight over the same time period. These results were confirmed using KOH electrolyte, with the conventional construction losing 50 mg per week and the inventive construction again not losing any weight. 
     As will be apparent to those skilled in the art, the beverage can-type construction utilizes minimal space in the battery interior, reduces the number of process steps required to manufacture a battery, and significantly reduces the cost of materials and the cost of the manufacturing process. Further, the thickness of the can walls may be significantly reduced to 6 mils or less. As a result, the internal volume available for containing the electrochemically active materials may be increased. For example, for a D sized battery, the percentage of the total battery volume that may be used to contain the electrochemically active materials may be as high as 97 volume percent, while collector assembly volume may be as low as 1.6 volume percent. The volumes of batteries of other sizes are included in the table shown in FIGS. 14A and 14B. 
     By utilizing the inventive sealing constructions, not only can the can wall thickness be decreased, but also the number of possible materials used to form the can may be increased due to the lessened strength requirements that must be exhibited by the can. For example, the inventive constructions noted above may enable aluminum or plastics to be used for the can rather than the nickel-plated steel currently used. 
     A variation of the beverage can construction is shown in FIG.  13 . In the illustrated embodiment, the battery can is first formed as a tube with two open ends. The tube may be extruded, seam welded, soldered, cemented, etc., using conventional techniques. The tube may be formed of steel, aluminum, or plastic. As shown in FIG. 13, the tube defines the side walls  614  of can  612 . A first open end of the tube is then sealed by securing an inner cover  616  thereto using the beverage can sealing technique outlined above, with the exception that no electrical insulation is required between inner cover  616  and side walls  614 . A positive outer cover  618  may be welded or otherwise secured to the outer surface of inner cover  616 . The battery may then be filled and a negative outer cover  645  may be secured to the second open end of can  612  in the same manner as described above. 
     Printed Label on Can 
     As noted above, the inventive battery constructions may be used in combination with a printed label, rather than the label substrates currently used. Current label substrates have thicknesses on the order of 3 mils. Because such label substrates overlap to form a seam running along the length of the battery, these conventional labels effectively add about 10 mils to the diameter and 13 mils to the crimp height of the battery. As a result, the battery can must have a diameter that is selected to accommodate the thickness of the label seam in order to meet the ANSI size standards. However, by printing a lithographed label directly on the exterior surface of the can in accordance with the present invention, the diameter of the can may be correspondingly increased approximately 10 mils. Such an increase in the diameter of the can significantly increases the internal volume of the battery. All of the batteries listed in the tables of FIGS. 14A and 14B, with the exception of the beverage can constructions, include substrate labels. The internal volume of the batteries with substrate labels can be further increased 2 percent (1.02 cc) for a D sized battery, 2.6 percent (0.65 cc) for a C sized battery, 3.9 percent (0.202 cc) for an AA sized cell, and 5.5 percent (0.195 cc) for an AAA sized battery, if the labels were printed directly on the exterior of the can. Labels may also be printed on the can using transfer printing techniques in which the label image is first printed on a transfer medium and then transferred directly onto the can exterior. Distorted lithography may also be used whereby intentionally distorted graphics are printed on flat material so as to account for subsequent stress distortions of the flat material as it is shaped into the tube or cylinder of the cell can. 
     Prior to printing the lithographed label, the exterior surface of the can is preferably cleaned. To enhance adherence of the print to the can, a base coat of primer may be applied to the exterior surface of the can. The printed label is then applied directly on top of the base coat on the can by known lithography printing techniques. A varnish overcoat is preferably applied over the printed label to cover and protect the printed label, and also to serve as an electrical insulating layer. The printed label may be cured with the use of high temperature heating or ultraviolet radiation techniques. 
     With the use of the printed label, the thickness of a conventional label substrate is significantly reduced to a maximum thickness of approximately 0.5 mil. In particular, the base coat layer has a thickness in the range of about 0.1 to 0.2 mil, the print layer has a thickness of approximately 0.1 mil, and the varnish overcoat layer has a thickness in the range of about 0.1 to 0.2 mil. By reducing the label thickness, the can can be increased in diameter, thereby offering an increase in available volume for active cell materials while maintaining a predetermined outside diameter of the battery. 
     Beverage Can With Feed Through Collector 
     Referring to FIG. 15, an electrochemical cell  700  is shown constructed with a feed through collector according to a seventh embodiment of the present invention. Similar to the electrochemical cell  400  with beverage can-type construction shown in FIG. 11, electrochemical cell  700  includes an electrically conductive can  712  having a closed end  314  and an open end in which a low volume collector assembly  725  and outer negative cover  750  are assembled. Electrochemical cell  700  includes a positive electrode  115  in contact with the interior walls of can  712  and in contact with a separator  117  that lies between a positive electrode  115  and a negative electrode  120 . The positive electrode  115  is also referred to herein as the cathode, while the negative electrode  120  is also referred to herein as the anode. It should be appreciated that the type of materials and their location internal to the electrochemical cell may vary without departing from the teachings of the present invention. 
     Electrochemical cell  700  also includes a pressure relief mechanism  370  formed in the closed end  314  of can  712 . This allows for employment of the low volume collector assembly  725  which consumes less volume than conventional collector assemblies, and therefore achieves enhanced internal cell volume efficiency. The pressure relief mechanism  370  may be formed as a groove as described herein in connection with FIGS. 8A,  8 B,  9 , and  10 . In addition, a positive outer cover  311  is connected to the closed end of can  712  and overlies the pressure relief mechanism  370 . The assembly and location of positive outer cover  311  is provided as shown and described herein in connection with FIG.  8 A. 
     Electrochemical cell  700  includes a collector assembly  725  which closes and seals the open end of can  712 . Collector assembly  725  includes a collector nail  740  disposed in electrical contact with the negative electrode  120 . Also included in the collector assembly  725  is a first or inner cover  745  having a central aperture  751  formed therein. The collector nail  740  is disposed and extends through the aperture  751  in inner cover  745 . A dielectric insulating material  744  is disposed between collector nail  740  and first cover  745  to provide dielectric insulation therebetween. Accordingly, the collector nail  740  is electrically isolated from inner cover  745 . Dielectric insulating material  744  is an organic macromolecular material, such as an organic polymer, and may include an epoxy, rubber, nylon, or other dielectric material that is resistant to attack by KOH and is non-corrosive in the presence of potassium hydroxide in an alkaline cell. The dielectric insulating material is assembled as explained hereinafter. 
     Inner cover  745  in turn is connected and sealed to the open top end of can  712 . Inner cover  745  may be inserted into can  712  and sealed to can  712  by forming a double seam closure at the peripheral edges  450  and  470  as explained herein in connection with FIGS. 11-13. While a double seam can-to-cover closure is shown in connection with the seventh embodiment of the present invention, it should be appreciated that other can-to-cover closures may be employed, without departing from the teachings of the present invention. 
     The electrochemical cell  700 , according to the seventh embodiment allows for a direct connection between can  712  and inner cover  745 , which preferably provides a pressure seal therebetween, but does not require electrical isolation between inner cover  745  and the side walls of can  712 . Instead, the collector nail  740  is dielectically insulated from inner cover  745  such that the negative and positive terminals of the electrochemical cell are electrically isolated from one another. While there is no requirement of maintaining electrical isolation between the can  712  and inner cover  745 , it is preferred that a sealant be applied at the closure joining the can to the cover to adequately seal the can. A suitable sealant may be applied as explained in connection with the battery shown and described herein in connection with FIGS. 11-12D. It should be appreciated that the sealed closure along with the insulating material should be capable of withstanding internal pressure buildup greater than the venting pressure at which pressure release mechanism  370  releases pressure. 
     To provide an acceptable outer battery terminal in accordance with well accepted battery standards, the electrochemical cell  700  further includes an outer cover  750  in electrical contact with collector nail  740 . Outer cover  750  may be welded by spot weld  742  or otherwise electrically connected to collector nail  740 . To insure proper electrical insulation between outer cover  750  and inner cover  745 , a dielectric material such as annular pad  748  is disposed between outer negative cover  750  and inner cover  745 . Suitable dielectric materials may include nylon, other elastomeric materials, rubber, and epoxy applied on the top surface of inner cover  745  or on the bottom surface of outer cover  750 . Accordingly, an acceptable standard battery terminal may be provided at the negative end of electrochemical cell  700 . 
     The assembly of electrochemical cell  700  according to the seventh embodiment of the present invention is illustrated in the assembly view of FIG.  16  and is further illustrated in the flow diagram of FIG.  17 . The method  770  of assembly of electrochemical cell  700  includes providing can  712  formed with a closed bottom end and open top end. Step  774  includes disposing into can  712  the active electrochemical materials including the negative electrode, the positive electrode, and an electrolyte, as well as the separator and other cell additives. Once the active electrochemical cell materials are disposed within can  712 , can  712  is ready for closure and sealing with the collector assembly  725 . Prior to closing the can, the collector assembly is assembled by first disposing the collector nail  740  within aperture  751  formed in inner cover  745  along with a ring of insulating material according to step  776 . Collector nail  740  is disposed in the opening  742  of insulating ring  744  which may include a ring or disk of epoxy which provides dielectric insulation and can be heated to reform and settle between the inner cover  745  and collector nail  740 . Alternately, other organic macromolecular dielectric insulation materials may be used in place of epoxy, such as a rubber grommet, an elastomeric material, or other dielectric materials that may form adequate insulation between collector nail  740  and inner cover  745 . Also shown formed in inner cover  745  is a recess  755  formed in the top surface and centered about aperture  751 . 
     According to the preferred embodiment, ring  744  of insulating material is disposed in recess  755  on top of inner cover  745  and the top head of collector nail  740  is disposed thereabove. In step  778 , the insulating ring  744  is assembled to collector nail  740  and cover  745  and the insulating ring  744  is heated to a temperature sufficiently high enough to melt ring  744  such that ring  744  reforms and flows into the aperture  751  in cover  745  to provide continuous dielectric insulation between collector nail  740  and inner cover  745 . For a ring  744  made of epoxy, a temperature of 20° C. to 200° C. for a time of a few seconds to twenty-four hours may be adequate to reform and cure the insulating material. Once dielectric material  744  forms adequate insulation between collector nail  740  and inner cover  745 , the insulated material is preferably cooled in step  780 . During the heating and cooling steps  778  and  780 , the collector nail  740  is centered in aperture  751  such that nail  740  does not contact cover  745 . Thereafter, in step  782 , an electrical dielectric insulating pad  748  such as an annular dielectric pad is disposed on top of inner cover  745  and extends radially outward from the perimeter of nail  740 . In step  784 , disposed on top of collector nail  740  and pad  748  is a conductive negative cover  750  which is welded or otherwise formed in electrical contact with collector nail  740 . Once the collector assembly is fully assembled, the collector assembly is then connected to the can to sealingly close the open end as provided in step  786 . Can closure may employ a double seam closure or other suitable can closure technique. In addition, the assembly method  770  includes step  788  of connecting a second outer cover to the closed end of the can, preferably overlying the pressure relief mechanism  370 . 
     While the present invention has been described above as having primary applicability to alkaline batteries, it will be appreciated by those skilled in the art that similar benefits may be obtained be employing the inventive constructions in batteries utilizing other electrochemical systems. For example, the inventive constructions may be employed in primary systems such as carbon-zinc and lithium based batteries and in rechargeable batteries, such as NiCd, metal hydride, and Li based batteries. Further, certain constructions of the present invention may be used in raw cells (i.e., cells without a label as used in battery packs or multi-cell batteries). Additionally, although the present invention has been described above in connection with cylindrical batteries, certain constructions of the present invention may be employed in constructing prismatic cells. 
     The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents.