BATTERY CONSTRUCTION HAVING DOUBLE SEAM COVER CLOSURE

Abstract: An electrochemical cell (400) is provided comprising: a can (412) for containing elecrochemically active materials (120), the can (412) having a first end and an open end; a cover (445) positioned across the open end of the can (412); and a coating of an insulating material deposited directly on at least one of the can (412) and the cover (445) for electrically insulating the can (412) from the cover (445). A pressure relief mechanism is preferably formed in the closed end of the can (412). Also provided is a method of preparing an electrochemical cell (400) comprising the steps of: forming a can (412) having an open end and a closed end; forming a cover (445) for the open end of the can (412); dispensing electrochemically active materials (120) in the can (412); depositing a coating of an insulating material directly on at least one of the can (412) and the cover (445) for electrically insulating the can (412) from the cover (445); and sealing the cover (445) across the open end of the can (412) with the insulating material provided therebetween. The cell construction allows a large internal volume to be available for containing electrochemically active materials.

Description: BATTERY CONSTRUCTION HAVING DOUBLE SEAM COVER CLOSURE 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. Figure 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 moulded 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 end edge 13 of can 12 is 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 Figure 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 πgid metal, is provided to increase the rigidity and support the radial compression of collector assembly 25 thereby improving the sealing effectiveness. As shown in Figure 1, inner cover 44 is configured to contact central hub portion 32 and peπpheral upstanding wall 36. By configuπng 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 peπpheral 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 peπpheral upstanding wall 36 of seal 30 and to be in electπcal 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 Figure 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 electπcal contact therewith. In the example shown in Figure 1, outer cover 45 includes a peπpheral lip 47 that extends upwardly along the circumference of outer cover 45. By forming peπpheral upstanding wall 36 of seal 30 of a length greater than that of peπpheral lip 47, a portion of peπpheral upstanding wall 36 may be folded over peπpheral lip 47 duπng the cπmpmg 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 Figure 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 hydrogen gas to escape to the exteπor 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. Each spur 52 includes 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 ruptuπng seal 30 and allowing the escape of the internally-generated gas through apertures 43 Although the above-descπbed collector assembly 25 performs all the above- noted desirable functions satisfactory, as apparent from its cross-sectional profile this particular collector assembly occupies a significant amount of space within the mteπor of the cell 10 It should be noted that the construction shown in Figure 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 characteπstics of the collector assembly or the performance and reliability of the pressure relief mechanism The measured external and internal volumes for several batteπes that were commercially available at the pπoπty date of this application are listed m the tables shown in Figures 2A and 2B. The tables list the volumes (cc) for D, C, AA, and AAA sized batteπes. The collector assembly volume and the percentage of the total cell volume that constitutes the collector assembly volume is provided in Figure 2B for those commercially available batteπes listed in Figure 2A. Also provided in Figure 2A is a percentage of the total cell volume that constitutes the internal volume that is available for containing the electrochemically active mateπals. The "total cell volume" includes all of the volume, including any internal void spaces, of the battery. For the battery shown m Figure 1, the total volume ideally includes all of the cross-hatched area as shown in Figure 3A. The "internal volume" of the battery is represented by the cross-hatched area shown m Figure 3B The "internal volume", as used herein, is that volume inside the cell or battery that contains the electrochemically active mateπals as well as any voids and chemically inert mateπals (other than the collector nail) that are confined within the sealed volume of the cell. Such chemically inert mateπals 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, washer, spurs and any void volume between the bottom surface of the negative cover and the seal (indicated by the cross-hatched area in Figure 3C). The "container volume" includes the volume of the can, label, negative cover (outer cover 45), 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 Figure 3D). 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. 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. Because the exterior dimensions of the electrochemical cell are generally fixed by the American National Standards Institute (ANSI) or other standards organisations, 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 maximise the interior volume within an electrochemical cell that is available for the electrochemically active components. We have now found that this may be achieved by constructing an electrochemical cell where the space occupied by the collector assembly and the space occupied by the container volume are minimised while still maintaining adequate sealing characteπstics and allowing a reliable pressure relief mechanism. Accordingly, in a first aspect, the present invention provides an electrochemical cell compπsing: a can for containing electrochemically active mateπals 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 cover positioned across the open second end of the can; and a coating of an insulating matenal deposited directly on at least one of the can and the cover for electπcally insulating the can from the cover. In a second aspect, the present invention provides a method of prepaπng an electrochemical cell compπsing the steps of: forming a can having an open end and a closed end; forming a cover for the open end of the can; dispensing electrochemically active mateπals in the can; depositing a coating of an insulating matenal directly on at least one of the can and the cover for electπcally insulating the can from the cover; and sealing the cover across the open end of the can with the insulating matenal provided therebetween. Preferably, a pressure relief mechanism is formed m a surface of the can, more preferably in a surface at the closed end of the can. Preferably, the cover is sealed to the can by a beverage can-type seal to form a double seam closure Advantageously, by depositing insulating matenal directly on the can or the cover, or both, a collector assembly may be employed that has a significantly lower profile and thereby occupies significantly less space within an electrochemical cell. Furthermore, this arrangement may enable cell constructions exhibiting lower water loss over time than pπor assemblies, thereby increasing the cell's shelf life. An additional advantage of the invention is that a reliable pressure relief mechanism can be provided that does not occupy a significant percentage of the available cell volume Yet another advantage is that the cell constructions may be simpler to manufacture and require less mateπals, thereby possibly having lower manufactuπng costs Moreover, cell constructions are enabled 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 The present invention will be further understood by reference to the drawings, in which- Figure 1 is a cross section of a conventional C sized alkaline electrochemical cell, Figure 2A is a table showing the relative total battery volumes and internal cell volumes available for electrochemically active mateπals, as measured for those batteπes that were commercially available at the pπoπty date of this application; Figure 2B is a table showing the relative total battery volumes and collector assembly volumes as measured for those batteπes that were commercially available as provided in Figure 2A; Figures 3A-3D are cross sections of a conventional C sized alkaline electrochemical cell that illustrate the total battery and vaπous component volumes, Figure 4 is a bottom view of a battery can having a pressure relief mechanism formed the closed end of the can; Figure 5 is a cross-sectional view taken along line X-X of the can vent shown in Figure 4; Figure 6 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction according to an embodiment of the present invention; Figure 7A is a partially exploded perspective view of the battery shown Figure 6; Figures 7B and 7C are cross-sectional views of a portion of the battery shown m Figure 6 illustrating the process for forming the beverage can-type construction; Fig 7D is an enlarged cross-sectional view of a portion of the battery shown in Figure 6, Figure 8 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction according to an embodiment of the present invention; Figure 9A is a table showing the calculated total and internal cell volume for various batteries; and Figure 9B is a table showing the calculated total volume and collector assembly volume for various batteries. 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, 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. The electrochemical cell includes a collector assembly which closes and seals the open end of a can. The collector assembly includes a collector, such as a nail, disposed in electrical contact with an electrode, for example the negative electrode. An insulating material is deposited directly on the cover or the can, or both, so as to electrically insulate the can from the cover when the cover is assembled to the can. The cover is sealed across the open end of the can to form a double seam closure. A pressure relief mechanism is preferably formed in a surface of the can, more preferably in the closed end of the can, for releasing internal pressure from within the can when the internal pressure becomes excessive. As a result, the known complex collector/seal assemblies may be replaced with a collector assembly in accordance with the present invention that consumes less volume and has fewer parts. Thus, a significant improvement in internal cell volume efficiency may be obtained. The pressure relief mechanism is preferably formed by providing a groove in the surface of can. This groove may be formed, for example, by coining a bottom surface of the can, cutting a groove in the bottom surface, or moulding the groove in the bottom surface of the can at the time the positive electrode is moulded. For an AA sized battery, a suitable thickness of the metal at the bottom of the coined groove is approximately 50 μm (2 mils) For a D sized battery, a suitable thickness is approximately 75 μm (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 hmge The pressure relief mechanism is preferably positioned beneath an outer cover so as to prevent the electrochemical matenals from dangerously spraying directly outward from the battery upon rupture Also, if the battery were used in seπes 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 an outer cover over pressure relief mechanism allows the mechanism to bow outwardly under the positive protrusion and ultimately rupture If no outer cover is present in such circumstances, the contact between the two batteπes may otherwise prevent the pressure relief mechanism from ruptuπng Furthermore, if an outer cover is not provided over the pressure relief mechanism, the pressure relief mechanism at the positive end of the battery may be more susceptible to damage. The outer cover also shields the pressure relief mechanism from the corrosive effects of the ambient environment and therefore reduces the possibility of premature venting and/or leaking. Thus, preferably the pressure relief mechanism is formed under an outer cover at the closed end of the battery can. The outer cover preferably serves as the positive external battery terminal. The size of the area circumscnbed by the groove is preferably selected such that upon rupture due to excessive internal pressure, the area within the groove may pivot at the hmge within the positive protrusion of the outer cover without interference from the outer cover. In general, the size of the area defined by the groove, 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 gases to escape. The cover of the collector assembly is in turn connected and sealed to the open top end of the can to form a double seam closure in which the can is electncally insulated from the cover Preferably, a beverage can-type sealing technique is used to form the closure. The beverage can-type construction 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 the can. Instead, the cover is secured to the open end of the can 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 cover to be electrically insulated from the can. However, prior to attaching the cover to the open end of the can, a collector such as a nail is electrically connected, preferably by welding, to the inner surface of the cover. Next, a coating of electrically insulating material, such as an epoxy, nylon, Teflon®, or vinyl, is deposited on the cover or the can, or both. Preferably the inner surface of the cover, as well as the peripheral portion of the upper surface of the cover, is coated with a layer of the electrical insulation material. The portion of the collector that extends within the void area between the bottom of the cover and the top surface of the electrode/electrolyte mixture, is preferably also coated with the electrical insulation. Preferably, the inner and outer surfaces of the can are also coated in the region of the open end of the can. Such coatings may be applied directly to the can and cover, for example by spraying, dipping, or electrostatic deposition. It will be appreciated that the coating of electrically insulating material may be applied either to the cover or to the can, or to both the cover and the can, by any suitable means provided that it forms an electrically insulating seal between the cover and the can. By providing such a coating, the cover may be electrically insulated from the can. 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'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. Furthermore, by utilising 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 the cover to the can, a conventional sealant may be applied to the bottom surface of the peripheral edge of the cover. Once the collector has been attached to the cover and the electrical insulation coating has been applied, the cover is placed over the open end of the can. Preferably, the can has an outward extending flange formed at its open end. Furthermore, the cover preferably has a slightly curved peripheral edge that conforms to the shape of the flange. Once the cover has been placed over the open end of can, a seaming chuck may be used to form a double seam closure. For example, in one embodiment a seaming chuck is placed on the cover, such that an annular downward extending portion of the seaming chuck is received by an annular recess formed in the cover. Next, a first seaming roll is moved in a radial direction toward the peripheral edge of the cover. As the first seaming roll is moved toward the peripheral edge and flange, its curved surface causes the peripheral edge to be folded around the flange. Also, as the first seaming roll moves radially inward, the seaming chuck, can, and cover are rotated about a central axis, such that the peripheral edge is folded around the flange about the entire circumference of the can. Furthermore, as the first seaming roll continues to move radially inward, the flange and peripheral edge are folded downward After the peπpheral edge and the flange have been folded into this position, the first seaming roll is moved away from the can. and a second seaming roll is then moved radially inward toward the flange and peπpheral edge The second seaming roll has a different profile than the first seaming roll The second seaming roll applies sufficient force against the flange and peπpheral edge to press and flatten the folded flange and penpheral edge against the exteπor surface of the can, which is supported by the seaming chuck As a result of this process, the peπpheral edge of the can is folded around and under the flange and is cπmped between the flange and the exteπor surface of the walls of the can 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 Figure 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 peπod. 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 utilises minimal space in the battery intenor, reduces the number of process steps required to manufacture a battery, and significantly reduces the cost of matenals and the cost of the manufactuπng process Furthermore, the thickness of the can walls may be significantly reduced, for example to 150 μm (6 mils) or less. As a result, the internal volume available for containing the electrochemically active mateπals may be increased For example, for a D sized battery according to the present invention, the percentage of the total battery volume that may be used to contain the electrochemically active mateπals may be as high as 97 volume percent, while collector assembly volume may be as low as 1.6 volume percent. The volumes of batteπes of other sizes are included in the table shown in Figures 9A and 9B By utilising the beverage can-type construction, 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 beverage can construction noted above may enable aluminium or plastics to be used for the can rather than the nickel-plated steel currently used. In a variation of the beverage can-type construction, the battery can is first formed as a tube with two open ends. The tube may for example be extruded, seam welded, soldered or cemented, using conventional techniques. The tube may be formed for example of steel, aluminium, or plastic. The tube defines the side walls of the can. A first open end of the tube is then sealed by securing a cover thereto using the beverage can sealing technique outlined above. A positive contact terminal may be welded or otherwise secured to the outer surface of the cover. The battery may then be filled and the cover of a collector assembly may be secured to the second open end of the can in the same manner as described above. Alternatively, the cover of the collector assembly may be sealed to the tube before the tube is filled and sealed to the other cover. In a preferred embodiment, a battery is provided 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. In a further embodiment, a hermetically sealed electrochemical cell is provided comprising: a can for containing electrochemically active mateπals 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 second end of the can, the cover having a peπpheral edge that extends over and around the flange and is cπmped between the flange and an exteπor surface of the can, and a sealant provided between the flange and the peπpheral edge of the cover In a further embodiment, the can may be formed to have the protrusion for the positive battery terminal formed directly in the closed end of the can In this manner, the void space existing between the closed end of the can and the positive outer cover may be used to contain electrochemically active matenals or otherwise provide space for the collection of gases, which otherwise must be provided withm the cell Although the increase in cell volume obtained by forming the protrusion directly the bottom of the can is not provided m the table in Figure 9A, 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 cells listed in the table which are formed with a separate cover. In a further embodiment, a pnnt layer may be applied directly onto the exteπor surface of the battery can to provide a label. By applying the label directly onto the exteπor of the can as a pnnt layer, rather than with a label substrate, the internal volume of the cell may be further increased since one does not have to account for the thickness of a label substrate to construct a cell that meets the ANSI or other exteπor size standards. By "directly" is meant that no label substrate is present between the pnnt layer and the external surface of the battery can. Current label substrates have thicknesses on the order of 75 μm (3 mils). Because such label substrates overlap to form a seam running along the length of the battery, these conventional labels effectively add about 250 μm (10 mils) to the diameter and of 330 μm (13 mils) to the cπmp 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 or other size standards However, by pnnting a lithographed label directly on the exteπor surface of the can, the diameter of the can may be correspondingly increased approximately 250 μm (10 mils) Such an increase in the diameter of the can significantly increases the internal volume of the battery Thus, the internal volume of the batteπes with substrate labels could be further increased, for example by 2 percent (1.02 cc) for a D sized batte . 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 pnnted directly on the exteπor of the can Labels may also be pπnted on the can using transfer pnnting techniques in which the label image is first pπnted on a transfer medium and then transferred directly onto the can exteπor Distorted lithography may also be used whereby intentionally distorted graphics are pπnted on flat matenal so as to account for subsequent stress distortions of the flat matenal as it is shaped into the tube or cylinder of the cell can. Pπor to pπntmg the lithographed label, the exteπor surface of the can is preferably cleaned. To enhance adherence of the pnnt to the can, a base coat of pnmer may be applied to the extenor surface of the can The pnnt layer is then applied directly on top of the base coat on the can by known lithographic pnnting techniques. The label may further compnse an electncally insulating overcoat. A varnish overcoat is preferably applied over the pnnt layer to cover and protect the pnnt layer, and also to serve as an electncally insulating layer The pπnted label may be cured with the use of high temperature heating or ultraviolet radiation techniques. With the use of the pnnted label, the thickness of the label may be significantly reduced compared with a conventional label on a substrate, to a maximum thickness of approximately 13 μm (0.5 mils). In a particular embodiment, the pπnted label has a base coat layer of a thickness in the range of about 2.5 to 5 μm (0.1 to 0.2 mil), a pnnt layer of a thickness of approximately 2.5 μm (0.1 mil), and a varnish overcoat layer of a thickness in the range of about 2.5 to 5 μm (0.1 to 0.2 mil) By reducing the label thickness, the can is able to be increased in diameter, thereby offering a further increase in available volume for active cell materials while maintaining a predetermined outside diameter of the battery. As will be appreciated, through the use of the constructions noted above, a battery can may be made with thinner walls, on the order of 100-200 μm (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. Furthermore, 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. 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 utilising 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. Furthermore, 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 present invention will now be further described by reference to the embodiments shown in Figures 4 to 9B: Figure 6 shows an embodiment of a battery constructed in accordance with the beverage can-type sealing technique, as described below with reference to Figures 7A- 7D. 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 Figure 7A, 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. 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. The coating thus provides electrical insulation between the cover and the can and, 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's internal volume, those areas may be protected from corrosion. A sealant 473 is 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 Figure 7D. 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 Figure 7B. Can 412 has an outward extending flange 450 formed at its open end. Further, outer cover 445 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 Figure 7C. After peπpheral edge 470 and flange 450 have been folded into the position shown in Figure 7C, 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 peπpheral 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 penpheral edge 470 to press and flatten the folded flange and peπpheral edge against the extenor surface of can 412, which is supported by seaming chuck 500 As a result of this process, the penpheral edge 470 of can 412 is folded around and under flange 450 and is cnmped between flange 450 and the exteπor surface of the walls of can 412, as shown in Figures 6 and 7D A hermetic seal is thus formed by this process Figure 8 shows a further embodiment of the present invention, m which the battery can is first formed as a tube with two open ends. The tube defines the side walls 614 of can 612 A first open end of the tube is then sealed by secuπng an inner cover 616 thereto using the beverage can sealing technique outlined above, with the exception that no electncal insulation is present 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 descπbed above. It will be understood that the embodiments shown in the drawings and descnbed above are merely for illustrative purposes and not intended to limit the scope of the invention EXAMPLE The total battery volume, collector assembly volume, and internal volume available for electrochemically active matenal 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 batten 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 geometπc computation To measure the internal volume available for electrochemically active mateπals, 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 matenals, void volumes and chemically inert mateπals (other than the collector nail) that are confined within the sealed volume of the cell, are measured by geometnc 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 geometπc 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 symmetnc To obtain a geometπc 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 debns, was air dned, and the remaining void volumes were filled with epoxy to give the battery some mtegnty before completing the grinding and polishing to its centre. 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 Pnor to pott g the battery in epoxy, battery measurements were taken with callipers to measure the overall height, the cnmp height, and the outside diameter at the top, bottom, and centre 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 centre of the battery without the label present Once the battery was completely potted in epoxy and ground to centre through the longitudinal axis of symmetry, the cross-sectional view of the battery was used to make a drawing. A Mitutoyo optical comparator 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 place and the contour of the battery parts were saved in a format that could later be used in solid modelling 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 centre 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 cπmp areas were used as they were drawn on the optical comparator. To calculate the volume measurements, the drawing was imported into solid modelling software. A solid three-dimensional volume representation was generated by rotating the contour of the cross section on both the left and nght sides by one-hundred- eighty degrees (180°) about the longitudinal axis of symmetry Accordingly, the volume of each region of interest is 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. Figures 9A and 9B show volumes of various different types of battery constructions that are more fully disclosed in US 60/102,951 filed 2 October 1998 and US 60/097,445 filed 21 August 1998. As shown in Figure 9A in the row referenced "Beverage Can-Type Construction", a D sized battery constructed using the construction shown in Figure 6, had an internal volume that was 97.0 volume percent when the can walls were 200 μm (8 mils) thick. As shown in Figure 9B, a D sized battery constructed using the construction shown in Figure 6 had a collector assembly volume that was 1.6 percent of the total volume when the can walls were 200 μm (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 Figure 9A.

Claims: CLAIMS: 1. An electrochemical cell comprising: a can for containing electrochemically active 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 cover positioned across the open second end of the can; and a coating of an insulating material deposited directly on at least one of the can and the cover for electrically insulating the can from the cover. 2. An electrochemical cell according to claim 1, wherein the insulating material is selected from epoxy, nylon, Teflon®, vinyl, and combinations thereof. 3. An electrochemical cell according to claim 1 or claim 2, wherein a coating of the insulating material is deposited directly on both of the cover and the can. 4. An electrochemical cell according to any preceding claim, comprising a sealant deposited between the cover and the can. 5. An electrochemical cell according to claim 4, wherein the insulating material and sealant comprise separate layers of sealant and insulating material. 6. An electrochemical cell according to claim 4 or claim 5, wherein the sealant material is asphalt. 7. An electrochemical cell according to claim 4, wherein the insulating material and sealant comprise an annular seal having an L-shaped cross section. 8. An electrochemical cell according to claim 7, wherein the annular seal is made of nylon and is coated with asphalt. 9. An electrochemical cell according to any preceding claim, wherein the can has a flange that extends outward from the open second end of the can towards the first end, the cover has 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 insulating material is provided between the flange and the peripheral edge of the cover and between the can and the peripheral edge. 10. An electrochemical cell according to claim 9, wherein insulating material is coated on both interior and exterior surfaces of the peripheral edge of the cover. 11. An electrochemical cell according to claim 9 or claim 10, wherein insulating material is coated on both interior and exterior surfaces of the flange. 12. An electrochemical cell according to any of claims 9 to 11, wherein insulating material is coated on the exterior surface of the can in an area that otherwise would contact the peripheral edge of the cover. 13. An electrochemical cell according to any preceding claim, wherein insulating material is coated on the entire interior surface of the cover. 14. An electrochemical cell according to any preceding claim, comprising a collector attached to an interior surface of the cover. 15. An electrochemical cell according to claim 13, wherein the collector is a nail and insulating material is coated on a portion of the collector nail adjacent the cover. 16. An electrochemical cell according to any preceding claim, comprising a pressure relief mechanism formed in the end wall of the can. 17. An electrochemical cell according to claim 16, wherein the pressure relief mechanism includes a groove formed in the end wall of the can. 18. An electrochemical cell according to claim 16 or claim 17, compπsing an outer cover attached to an exterior surface of the end wall of the can in electrical contact therewith and extending over the pressure relief mechanism. 19. An electrochemical cell according to claim 18, wherein the outer cover is electrically coupled to the positive electrode to serve as a positive external battery terminal and the cover over the second end is electrically coupled to the negative electrode to serve as a negative external battery terminal. 20. An electrochemical cell according to any of claims 1 to 19, wherein the first end of the can has an end wall integrally formed with the side walls of the can. 21. An electrochemical cell according to any of claims 1 to 19, wherein the can is formed as a tube with the end wall being a cover secured across the first end. 22. An electrochemical cell according to claim 21, wherein the can has a second flange that extends outward from the first end of the can towards the second end, and the cover over the first end has 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. 23. An electrochemical cell according to any preceding claim, wherein the can has a label printed directly on an exterior surface thereof. 24. An electrochemical cell according to any preceding claim, wherein the can has a wall thickness of 200 μm (8 mils) or less, preferably a wall thickness of 150 μm (6 mils) or less. 25. An electrochemical cell according to any preceding claim, wherein the can is cylindrical. 26. A method of preparing an electrochemical cell comprising the steps of: forming a can having an open end and a closed end; forming a cover for the open end of the can; dispensing electrochemically active materials in the can; depositing a coating of an insulating material directly on at least one of the can and the cover for electrically insulating the can from the cover; and sealing the cover across the open end of the can with the insulating material provided therebetween. 27. A method according to claim 26, wherein insulating material is deposited directly on both the can and the cover. 28. A method according to claim 26 or claim 27, wherein insulating material is deposited directly on interior and exterior surfaces of the can in a region surrounding the open end. 29. A method according to any of claims 26 to 28, wherein insulating material is deposited directly on a peripheral edge and an interior surface of the cover. 30. A method according to any of claims 26 to 29, further including the step of applying a sealant between the cover and the can. 31. A method according to claim 26, comprising the steps of: forming a can having an open end and a closed end with an outward extending flange formed at the open end; forming a cover having a peripheral edge that extends outward beyond the flange when placed across the open end of the can; coating at least one of the flange or the peripheral edge with an electrical insulation material; dispensing electrochemically active materials in the can; placing the cover across the open end of the can; bending the peripheral edge of the cover over and around the flange; and flattening the folded peripheral edge and flange against an exterior surface of the can such that the flange is bent back away from the open end and the peripheral edge is crimped between the flange and the exterior surface of the can. 32. A method according to claim 31, wherein the coating step includes coating both the flange and the peripheral edge of the cover with insulating material. 33. A method according to any of claims 26 to 32, further including the step of forming a pressure relief mechanism in the closed end of the can. 34. A method according to any of claims 26 to 33, further including the step of attaching a collector to the cover. 35. A method according to any of claims 26 to 34, wherein the step of forming a can includes the substeps of forming a tube to define side walls of the can, and securing an end wall to an open end of the tube to form the closed end of the can.

Inventors: SONDECKER GEORGE R, TUCHOLSKI GARY R, SONDECKER, GEORGE, R., TUCHOLSKI, GARY, R.
Applicants: EVEREADY BATTERY INC, EVEREADY BATTERY COMPANY, INC.
Application year: 1999
Main classification: H01M2
IPC codes: H01M2, H01M4, H01M6