END COVER FOR BATTERY CELLS

Abstract: An electrochemical cell comprises a can having an open and a closed end, a contact terminal being located at the closed end. The terminal only covers a small part of the closed end of the can. The remainder of the end of the can may be covered by a label. By using a smaller contact terminal, the gap (19) (figures 1 and 2) provided between the positive cover (17) and the closed end (14) of can (15), to accommodate cell bulging, is substantially eliminated so that the length of the can may be increased without exceeding the standards established for overall battery length and allowing more active ingredients to be contained in the can, thereby increasing the service life of the electrochemical cell.

Description: END COVER FOR BATTERY CELLS The present invention relates to cells and end covers therefor. Alkaline batteries are typically constructed in the manner shown in Figures 1 and 2. Specifically, alkaline battery 10 includes a steel can 15 having a cylindrical shape with one open end. A metallised, plastic film label (not shown) is formed about the exterior surface of steel can 15, but not covering the ends of can 15. At a closed end 14 of steel can 15 is a positive cover 17, which is preferably formed of plated steel. A cathode 20, preferably formed of a mixture of manganese dioxide, graphite, a solution of potassium hydroxide in deionised water and a TEFLON™ solution, is formed about the interior side surface of steel can 15. A separator 30, which is preferably formed of a non-woven fabric that prevents migration of any solid particles in the battery, is disposed about the interior surface of cathode 20. An electrolyte formed of potassium hydroxide is disposed in the interior of separator 30. An anode 50, preferably formed of zinc powder, a gelling agent, and other additives, is disposed within an electrolyte in contact with a current collector 60, which may be formed of brass. Current collector 60 contacts a brass rivet 70 projecting through a nylon seal 71 formed at the open end of steel can 15 to prevent leakage of the active ingredients contained in steel can 15. Nylon seal 71 contacts a metal washer 72 and an inner cell cover 74, which is preferably formed of steel. A negative cover 75, which is preferably formed of plated steel, is disposed in contact with inner cell cover 74 and brass rivet 70. Rivet 70 contacts current collector 60 through a hole formed in nylon seal 71. Negative cover 75 is electrically insulated from steel can 15 by nylon seal 71. 35 Positive cover 17 includes a protruding nub 18 at its centre which forms the positive contact terminal of the battery. As shown in Figure 1, positive cover 17 has a diameter that is substantially equal to the diameter of cylindrical steel can 15. Positive cover 40 17 contacts the closed end 14 of steel can 15 about its peripheral edge. Because the cell may bulge during storing, discharge, etc. and because positive cover 17 is rigid and inflexible, a gap 19 is provided between the inner surface of positive cover 17 and the exterior surface of closed end 14 of approximately 0.022 inch 45 [0.56 mm] to allow for such bulging. The positive cover 17 can be fastened to the container by welds 42 after the cathode is rammed into place. As shown in Figure 2, positive cover 17 further includes a 50 reinforcing rib 16, which protrudes outward about a peripheral edge of cover 17. In a current design, this reinforcing rib protrudes a little more than 0.042 inch [1.07 mm] from the outer surface of the closed end 14 of can 15. Further, the outer surface of positive contact terminal 18 extends an additional 0.090 inch [2.3 mm] from 55 the outer surface of reinforcing rib 16 in the current design. A primary goal in designing alkaline batteries is to increase the service performance of the cell. The service performance is the length of time for the cell to discharge under a given load to a 60 specific voltage at which the cell is no longer useful for its intended purpose. One approach taken to increase service performance is to increase the interior volume of the cell, in order to increase the amount of active materials within the cell. However, the commercial external size of the cell is fixed, thereby limiting the ability to increase the amount of active materials within the cell. For example, the cell length from the end of positive contact terminal 18 to the exterior surface of negative cover 75 is fixed by standards, as well as the height ' of the protrusion that forms positive contact terminal 18. In order to accommodate more active materials within the cell, while maintaining the external size of the cell, the steel label and insulating paper tube of the original alkaline cell has generally been replaced with one made of thinner metallised plastic film. Thus, the steel can may be enlarged to provide a greater internal volume. By switching to a thinner plastic film label, the service performance of a typical alkaline cell was significantly increased. Another approach taken to increase the service performance of a cell is to provide for better utilisation of the electrode materials. This approach is taken in US-A-5, 501, 924, issued to endi Swierbut et al . , which discloses utilising tin dioxide as an additive to a cathode . Despite past increases in service performance, the need to find new ways to increase service performance remains the primary goal of cell designers. It has now been surprisingly discovered that it is possible to improve the service performance of alkaline cells by providing a reduced diameter end cover for the closed end of the can. This reduces the gap needed between the cover and the can, thereby further increasing the internal volume of the cell. 95 Thus, in a first aspect, the present invention provides an electrochemical cell comprising a can having an open and a closed end, a contact terminal being located at the closed end, characterised in that the terminal only covers a part of the closed end of the can. 100 In an alternative aspect, the present invention provides a composite cover assembly for the closed end of the cylindrical can of an electrochemical cell that includes an electrically conductive contact terminal having a diameter substantially smaller than the 105 diameter of the cylindrical can. It is preferred to provide a flexible disk-shaped label covering the portion of the surface of the closed end of the can that is not covered by the contact terminal . 110 By using a smaller contact terminal, or cover, the gap 19 ( c. f. Figure 1), which is provided between the positive cover 17 and the closed end 14 of can 15 to accommodate cell bulging in the conventional construction, may be substantially eliminated. Accordingly, the length of the can may be increased without 115 exceeding the standards established for overall battery length. In addition, the reinforcing rib on the positive cover may be eliminated, thus permitting the internal cell volume to be further increased, while still maintaining the 0.090 inch [2.3 mm] protrusion distance of the positive contact terminal. 120 In general, cells according to the present invention will comprise a cylindrical can for containing at least an anode and a cathode, the can having one open end and one closed end. Typically, a first contact terminal assembly is mounted within the open end of 125 the cylindrical can in electrical isolation therefrom, and a protruding second contact terminal is mounted in electrical contact with the closed end of the cylindrical can. In the present invention, this second contact terminal covers less than all of an exterior surface of the closed end of the cylindrical can. 130 Some preferred embodiments of the present invention follow. In particular, there is envisaged an electrochemical cell comprising: a cylindrical can for containing at least an anode and a 135 cathode, the cylindrical can having one open end and one closed end; a first contact terminal assembly mounted within the open end of the cylindrical can in electrical isolation therefrom; and a protruding second contact terminal mounted in electrical contact to the closed end of the cylindrical can, the second contact 140 terminal covering substantially less than all of an exterior surface of the closed end of the cylindrical can. It is preferred that the cell is a battery, particularly where the negative terminal assembly is mounted within the open end of the 145 cylindrical can. Preferred batteries are alkaline batteries. We prefer that the first contact terminal assembly is a negative contact terminal assembly electrically coupled to the anode, while the second contact terminal is a positive contact 150 terminal that is electrically coupled to the cathode. In general, we prefer that cells of the invention further include an end cover label mounted to the exterior surface of the closed end of the, preferably cylindrical, can and covering that 155 portion of the exterior surface not covered by the second contact terminal. However, it will be appreciated that it is possible to leave the surface of the can exposed, if desired, or it may be desired to use a label to cover part of the surface, and varnishing the remainder, for example. 160 For convenience, it is generally preferred that the end cover label has an aperture to receive the contact terminal, although this need not necessarily be a snug fit. In addition, it is preferred that the label extend to the perimeter of the can so that an 165 external label, which conventionally overlaps the end of the can, overlaps onto the end label to keep its edges secure. The end cover label is preferably made of a metallised plastic material, although other materials will be readily apparent to those 170 skilled in the art. It is particularly preferred that there is an outer label mounted to an exterior surface of the sides of the cylindrical can so as to overlap a peripheral edge of the positive cover label. 175 The second contact terminal may be of any suitable shape, but it is conventionally preferred that it is round. In addition, although the terminal may be mounted in any desired position, it is preferred that it be mounted concentrically on the closed end of a 180 cylindrical can. It may have any suitable ridges or the like, although it is generally sufficient merely to have a central raised point, if desired, to ensure electrical contact with the apparatus the battery is used in. 185 Although the second contact terminal may be solid, it is generally preferred that it be hollow, such as being formed from a sheet of a metal. This has cost and efficiency advantages, both in saving material, and forming instead of casting. 190 Cells of the invention may have second contact terminals of any diameter less than the diameter of the end of the can, but size advantages are not particularly noticeable if the terminal covers 50% or more of the end of the can. We particularly prefer that the diameter of the terminal is 40% or less, preferably 25 percent or 195 less, of the diameter of the cylindrical can. Various materials are suitable for making the second terminal, but it is generally preferred that the second contact terminal is formed of nickel-plated steel. 200 The second contact terminal is preferably characterised as an electrically conductive substrate having a peripheral zone adapted for mounting the substrate to a closed end of the cylindrical can. It is preferred that the terminal includes a protruding surface, 205 preferably in the form of an annular ridge extending from a bottom surface of the conductive substrate, to provide a positive contact surface with the can. The present invention further provides a composite cover 210 comprising a terminal and end cover label, as defined herein. In a preferred embodiment, there is provided a composite cover for an end of a battery having a cylindrical can for containing an anode and a cathode, the composite cover comprising: a contact terminal mounted on a closed end of the cylindrical 215 can and covering substantially less than all of the surface area of an exterior surface of the closed end; and a disk-shaped cover label mounted to the same closed end of the cylindrical can to cover a portion of the exterior surface of the closed end that is not covered by the contact terminal, the 220 cover label having an opening for exposing the contact terminal, and preferably having a diameter substantially equal to the diameter of the cylindrical can. The present invention further provides a battery comprising: 225 a cylindrical can for containing at least an anode and a cathode, the cylindrical can having one open end and one closed end; a cover terminal assembly mounted within the open end of the cylindrical can in electrical isolation therefrom; and a disk-shaped cover label disposed across at least a 230 substantial portion of either end of the cylindrical can. Such a battery preferably further includes a second cover terminal assembly mounted to the closed end of the cylindrical can, the disk-shaped cover label being mounted over a portion of the second cover terminal assembly. 235 Taking a current construct as an example, it is possible to substantially reduce the diameter of positive contact terminal 102 and eliminate the 0.022 inch [0.56 mm] gap that exists between the conventional positive cover and the exterior surface of the closed 240 end of the steel can. It is also possible to eliminate the 0.020 inch [0.51 mm] reinforcing rib, so that the overall length of the steel can may be increased by at least 0.042 inch [1.07 mm] without increasing the overall external length of the cell, thereby increasing the internal volume of the cell. Thus, more active 245 ingredients may be contained within the cell, thereby improving the service performance of the cell. Further, the use of the smaller diameter positive contact terminal results in a lower cost for the positive cover and a lower 250 overall cost due to the lower cost of the disk-shaped end cover label relative to the larger plated steel positive cover. Also, by providing a label on the positive end of the battery, various labelling indicia may be printed on a portion of the battery that was not previously used for such a purpose. 255 Another advantage of providing a label on the positive end of the battery is that a portion of a battery testing label can be accommodated at the positive terminal, such as an electrochromic or thermochromic testing label. By locating the battery testing label 260 and contact switches at the positive end of the battery, the tester becomes substantially easier to use by consumers and is more visible, both during store merchandising and in use by consumers. This construction also has the potential to be substantially cheaper . 265 As stated above, the preferred diameter of positive cover cap 102 for a D-size cell is approximately 0.563 inch [14.3 mm], thus covering an area of 0.249 square inch [161 mm 2 ]. Given the maximum D-size cell diameter of 1.344 inches [34.14 mm] and an end area of 270 1.419 square inches [915 mm 2 ], then the positive contact terminal 102 of the preferred embodiment covers less than 18 percent of the exterior surface of closed end 114 of can 115, and has a diameter generally less than 25 percent of the diameter of can 115. 275 Although preferred dimensions are stated above for a D-size cell, other dimensions may be employed, provided the resulting cell does not exceed the maximum or minimum external dimension thresholds established by current standards. By making the diameter of positive the contact terminal as small as possible, it is possible 280 to minimise the amount of gap needed between the positive cover and the closed end of the can. Also, although the present invention is generally most suitable for D- and C-size cells, the invention envisages batteries of any size. 285 Although the composite cover assembly of the present invention is generally referred to herein as a positive cover assembly for an alkaline battery, it will be appreciated that it may be used as either a positive or negative cover for different types of cell constructions . 290 The present invention will now be further illustrated with reference to the accompanying drawings, in which: Figure 1 is a cut-away cross-sectional view of an example of an electrochromic cell having a conventional construction; 295 Figure 2 is an enlarged, partial cross-sectional view of the positive cover shown in Figure 1; Figure 3 is a partial cross-sectional view of a cell constructed in accordance with the present invention; and Figure 4 is an exploded perspective view of a cell constructed in 300 accordance with the present invention. Figure 3 shows a partial cut-away cross section of the composite positive cover construction 100 according to the preferred embodiment of the present invention. Composite cover 100 includes a 305 conductive contact terminal 102 having a substantially smaller radial dimension than the conventional positive cover of the prior art, and a disk-shaped label 110 that may overlap the peripheral portion of contact terminal 102. In the preferred construction for a standard D-size cell, contact terminal 102 has a diameter of 0.563 310 ± 0.002 inch [14.3 ± 0.051 mm]. The contact terminal 102 is formed with three weld projections 106 protruding downward from the outer surface and providing a flat of 0.015 ± 0.0015 inch [0.38 ± 0.038 mm] (evenly spaced at 120 ° ) to 315 provide contact through direct welding to the closed end of can 114. By providing these projections 106, welding of contact terminal 102 to the outer closed end surface 114 of steel can 115 may be facilitated while ensuring good electrical contact between contact terminal 102 and end 114 of steel can 115. Preferably, contact 320 terminal 102 is formed of a nickel-plated steel, although other suitable plating materials (i.e., tin, brass, and/or gold) used for positive covers of batteries may likewise be used. A flexible disk-shaped end cover label 110 is provided to 325 improve the appearance of the positive end of the battery and to provide additional insulation on the edges of can surface 114 and under the overlap of label 116. End cover label 110 is preferably formed of either a metallised polyvinyl chloride or polyfilm and polypropylene with a pressure sensitive adhesive applied to the side 330 that is secured to closed end 114 of can 115. By making end cover label 110 flexible, no gap needs to be provided between the cover label and the can to accommodate cell bulging. Further, due to the diminished size of contact terminal 102 no reinforcing rib needs to formed on contact terminal 102. 335 The cell may be formed by conventional methods, except that the smaller diameter contact terminal 102 is centred on closed end 114 and welded thereto, after which a disk-shaped end cover label 110 is applied over closed end 114 before external peripheral label 116 is applied, such that the edges of label 116 will extend over the periphery of disk-shaped end cover label 110.

Claims: CLAIMS 345 1. An electrochemical cell comprising a can having an open and a closed end, a contact terminal being located at the closed end, characterised in that the terminal only covers a part of the closed end of the can. 350 2. A cell according to claim 1 which is cylindrical. 3. A cell according to claim 1 or 2 which is alkaline. 4. A cell according to any preceding claim, wherein the contact 355 terminal covers substantially less than all of an exterior surface of the closed end of the can. 5. A cell according to any preceding claim, contact terminal is a positive contact terminal electrically coupled to the cathode. 360 6. A cell according to any preceding claim, further including an end cover label mounted over the exterior surface of the closed end of the can and covering that portion of the exterior surface not covered by the contact terminal. 365 7. A cell according to claim 6, wherein the cover label is made of a metallised plastic material. 8. A cell according to any preceding claim, wherein the contact 370 terminal is round and the can is cylindrical, the contact terminal being mounted concentrically on the closed end of the can. 9. A cell according to claim 8, wherein the diameter of the contact terminal is generally less than 25 percent of the diameter 375 of the can. 10. A cell according to any preceding claim further including an end label covering at least a part of the closed end of the can not covered by the contact terminal and an outer label mounted to an 380 exterior surface of the sides of the can so as to overlap a peripheral edge of the end label. 11. A cell according to any preceding claim, wherein the contact terminal is formed of nickel-plated steel. 385 12. A cell according to any preceding claim, wherein the contact terminal has a peripheral zone adapted for mounting to a closed end of the can. 390 13. A cell according to claim 12, wherein the contact terminal, wherein an annular ridge extends from a bottom surface of thereof for contacting the exterior surface of the closed end of the can. 14. A cell according to any preceding claim, wherein the contact 395 terminal has a protruding surface for providing a positive contact surface. 15. A battery comprising: a cylindrical can for containing at least an anode and a 400 cathode, the cylindrical can having one open end and one closed end; a cover terminal assembly mounted within the open end of the cylindrical can in electrical isolation therefrom; and a disk-shaped cover label disposed across at least a substantial portion of either end of the cylindrical can. 405 16. A cell according to claim 15, further including a second cover terminal assembly mounted to the closed end of the cylindrical can, wherein the disk-shaped cover label is mounted over a portion of the second cover terminal assembly.

Inventors: LONSBERRY GLENN R, LONSBERRY, GLENN, R.
Applicants: EVEREADY BATTERY INC, EVEREADY BATTERY COMPANY, INC.
Application year: 1998
Main classification: H01M2
IPC codes: H01M2, H01M6, H01M10