ELECTROCHEMICAL CELL HAVING COLLECTOR ELECTRICALLY INSULATED FROM COVER

Abstract: An electrochemical cell (700) is provided comprising: a can (712) for containing electrochemically active materials including at least positive (115) and negative (120) electrodes and an electrolyte, the can (712) having an open end and a closed end; a cover (745) positioned across the open end of the can (712) and connected to the can (712), the cover (745) having an aperture (751) extending therethrough; a current collector (740) extending through the aperture (751) of the cover (745) and extending internally within the can (712) to electrically contact one of the positive (115) and negative (120) electrodes; and a first insulating material (744) disposed between the collector (740) and the cover (745) for electrically insulating the collector (740) from the cover (745) and providing a seal between the collector (740) and the cover (745). A pressure relief mechanism (370) is preferably formed in the closed end of the can (712). Also provided is a method of assembling an electrochemical cell (700) comprising the steps of: dispensing electrochemically active materials in a can (712) having a closed end and an open end; disposing a current collector (740) through an aperture (751) formed in a cover (745); providing an nsulating material (744) between the cover (745) and the collector (740), preferably by melting the insulating material (744) such that the melted insulating material (744) reforms between the collector (740) and the cover (745); and assembling the cover (745) and the collector (740) to the open end of the can (712). The cell construction allows a large internal volume to be available for containing electrochemically active materials.

Description: ELECTROCHEMICAL CELL HAVING COLLECTOR ELECTRICALLY INSULATED FROM COVER 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 mside 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 oπentation pπor to secuπng 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 cπmped over the peπpheral lip of collector assembly 25, thereby secuπng outer cover 45 and collector assembly 25 within the end of can 12. As descπbed further below, one function served by collector assembly 25 is to provide for a second external electπcal contact for the electrochemical cell Additionally, collector assembly 25 must seal the open end of can 12 to prevent the electrochemical mateπals therein from leaking from this cell. Additionally, collector assembly 25 must exhibit sufficient strength to withstand the physical abuse to which batteπes 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 exteπor 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 exteπor 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 peπpheral upstanding wall 36 that extends upward along the peπphery of seal 30 in an annular fashion. Peπpheral upstanding wall 36 not only serves as a seal between the interface of collector assembly 25 and can 12, but also serves as an electπcal insulator for preventing an electrical short from occurπng 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 πgidity 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 thm 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. 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 characteristics of the collector assembly or the performance and reliability of the pressure relief mechanism. The measured external and internal volumes for several batteries that were commercially available at the priority date of this application are listed in the tables shown in Figures 2A and 2B. The tables list the volumes (cc) for D, C, AA, and AAA sized batteries. 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 batteries 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 materials. The "total cell volume" includes all of the volume, including any internal void spaces, of the battery. For the battery shown in 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 in Figure 3B. 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, 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, 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 (outer cover 45), 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 at least positive and negative electrodes and an electrolyte, the can having an open end and a closed end; a cover positioned across the open end of the can and connected to the can, the cover having an aperture extending therethrough, a cuπent collector extending through the aperture of the cover and extending internally within the can to electπcally contact one of the positive and negative electrodes; and a first insulating mateπal disposed between the collector and the cover for electπcally insulating the collector from the cover and providing a seal between the collector and the cover. In a second aspect, the present invention provides a method of assembling an electrochemical cell compπsing the steps of: dispensing electrochemically active mateπals in a can having a closed end and an open end, disposing a current collector through an aperture formed in a cover; providing an insulating mateπal between the cover and the collector to provide electπcal insulation therebetween; and assembling the cover and collector to the open end of the can. Preferably, a pressure relief mechanism is formed in a surface of the can, more preferably in a surface at the closed end of the can. In addition, the electrochemical cell preferably compπses a contact terminal electπcally coupled to the collector and a dielectπc mateπal disposed between the contact terminal and the cover for electπcally insulating the cover from the contact terminal. Advantageously, by providing a collector assembled through an aperture in the cover, the collector assembly 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, m 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 in the closed end of the can; Figure 5 is a cross-sectional view taken along line X-X of the can vent shown m Figure 4; Figure 6 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction; Figure 7A is a partially exploded perspective view of the battery shown in Figure 6, Figures 7B and 7C are cross-sectional views of a portion of the battery shown in Figure 6 illustrating the process for forming the beverage can-type construction; Figure 7D is an enlarged cross-sectional view of a portion of the battery shown m Figure 6; Figure 8 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction; Figure 9A is a table showing the calculated total and internal cell volumes for vaπous batteπes; Figure 9B is a table showing the calculated total volume and collector assembly volume for vaπous batteπes; Figure 10 is a cross section of a C sized alkaline electrochemical cell having a collector feed through construction according to an embodiment of the present invention; Figure 11 is an exploded assembly view of the electrochemical cell shown in Figure 10; and Figure 12 is a flow diagram illustrating a method of assembly of the electrochemical cell shown m Figures 10 and 11. As descπbed above, a pπmary objective of the present invention is to increase the internal volume available in a battery for containing the electrochemically active mateπals, without detπmentally 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 electπcal contact with an electrode, for example the negative electrode. Also included in the collector assembly is a first or inner cover having an aperture preferably formed centrally in the cover. The collector is disposed m and extends through the aperture in the cover. A dielectric insulating material is disposed between the collector and the cover to provide dielectric insulation therebetween. Accordingly, the collector nail is electrically isolated from the cover. The dielectric insulating material may be an organic macromolecular material, such as an organic polymer. Suitable materials include epoxy, rubber, and nylon. Other dielectric materials may be used that are resistant to the electrolyte used. For alkaline cells, preferably the dielectric material is resistant to attack by potassium hydroxide (KOH) and is non-corrosive in the presence of potassium hydroxide. The dielectric insulating material may be assembled to the collector assembly as explained further below. A pressure relief mechanism is preferably formed in a surface of the can, more preferably in the closed end of the can. 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 hinge. The pressure relief mechanism is preferably positioned beneath an outer cover 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 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 batteries may otherwise prevent the pressure relief mechanism from rupturing. 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 circumscribed by the groove is preferably selected such that upon rupture due to excessive internal pressure, the area within the groove may pivot at the hinge 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. The use of a pressure relief mechanism in a surface of the can allows the use of a beverage can-type construction to form a double seam 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. Therefore, in a preferred embodiment, the cover of the collector assembly is sealed to the can by forming a double seam closure by a beverage can-type sealing technique. Accordingly, the can preferably 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 peπpheral edge of the cover. As the first seaming roll is moved toward the peπpheral edge and flange, its curved surface causes the peπpheral 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 peπpheral 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 peπpheral 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 mward 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 peπpheral 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 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. 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 materials 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 materials may be as high as 96 volume percent, while collector assembly volume may be as low as 2.6 volume percent. The volumes of batteries of other sizes are included in the table shown in Figures 9A and 19B. 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. While a double seam can-to-cover closure is prefeπed, it should be appreciated that other can-to-cover closures may be employed in accordance with the present invention The electrochemical cell according to the present invention allows for a direct connection between the can and the cover, which preferably provides a pressure seal therebetween, but does not require electπcal isolation between the cover and the side walls of the can Instead, the collector, preferably a nail, is dielectπcally insulated from the cover such that the negative and positive terminals of the electrochemical cell are electrically isolated from one another While there is no requirement of maintaining electπcal isolation between the can and the cover, it is prefeπed that a sealant be applied at the closure joining the can to the cover to assist in the sealing of the cover to the can A conventional sealant may be applied to the bottom surface of the penpheral edge of the cover. In a beverage can construction, once the sealing procedure is complete, the sealant migrates to the positions shown in Figure 7D. It should be appreciated that the sealed closure along with the insulating mateπal should be capable of withstanding internal pressure build-up greater than the venting pressure at which the pressure release mechanism releases pressure. To provide an acceptable outer battery terminal m accordance with well accepted battery standards, the electrochemical cell preferably further includes an outer cover in electπcal contact with the collector. The outer cover may be welded by spot weld or otherwise electπcally connected to the collector. To ensure proper electπcal insulation between the outer cover and the inner cover, preferably a dielectπc mateπal such as annular pad is disposed between the outer cover and the inner cover. Suitable dielectπc mateπals include nylon, other elastomeπc mateπals, rubber, and epoxy, which may be applied on the top surface of the inner cover or on the bottom surface of the outer cover. Accordingly, an acceptable standard battery terminal may be provided, preferably as the negative terminal, at the collector end of the electrochemical cell. The assembly of an electrochemical cell according to a preferred embodiment of the present invention is illustrated in the assembly view of Figure 11 and is further illustrated in the flow diagram of Figure 12. The preferred method of assembly includes providing a can formed with a closed bottom end and open top end, and disposing into the can 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 the can, the can is ready for closure and sealing with the collector assembly. Prior to closing the can, the collector assembly is assembled by first disposing the collector, preferably a nail, within an aperture formed in the cover, preferably along with a ring or disc of insulating material, so that the collector is disposed in the opening of the insulating ring. The insulating ring is preferably formed of a material which provides dielectric insulation and can be heated to reform and settle between the cover and the collector, for example epoxy. Alternatively, 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 the collector and the cover. Preferably, a recess is formed in the top surface of the cover, centred about the aperture. Accordingly, the ring of insulating material may be disposed in the recess on top of the cover and the top head of a collector nail may be disposed thereabove. Thus, the insulating ring may assembled to the collector nail and cover, and the insulating ring heated to a temperature sufficiently high enough to melt the ring such that the ring reforms and flows into the aperture in the cover to provide continuous dielectric insulation between the collector nail and the cover. For a ring 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 the dielectric material forms adequate insulation between the collector nail and the cover, the insulated material is preferably cooled. During the heating and cooling steps, the collector nail is centred in the aperture such that the nail does not contact the cover. Thereafter, preferably an electrical dielectric insulating pad such as an annular dielectric pad is disposed on top of the cover so as to extend radially outward from the perimeter of the nail. A conductive negative cover is then preferably disposed on top of the collector nail and pad, and is welded or otherwise formed in electrical contact with the collector nail. Once the collector assembly is fully assembled, the collector assembly is then connected to the can to sealingly close the open end. Can closure preferably employs a double seam closure, although other suitable can closure techniques may be used. In addition, preferably a second cover is connected to the closed end of the can, preferably overlying a pressure relief mechanism. In a preferred embodiment, a method is provided comprising the steps of: forming a can having an open end and a closed end; forming a cover having an aperture; dispensing electrochemically active materials in the can; assembling a current collector extending through the aperture in the cover; disposing an insulating material continuously between the collector and the cover; and placing the cover across the open end of the can to cover and seal the open end of the can. 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 materials or otherwise provide space for the collection of gases, which otherwise must be provided within the cell. 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 Figure 9 A, 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 beverage can with feed through collector cells listed in the table, which are formed with a separate cover. In a further embodiment, a pπnt 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 pπnt 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 pπnt 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 pπntmg 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 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 pπnted directly on the exteπor of the can Labels may also be pπnted on the can using transfer pπntmg techniques m which the label image is first pπnted on a transfer medium and then transfeπed directly onto the can exteπor Distorted lithography may also be used whereby intentionally distorted graphics are pπnted on flat mateπal so as to account for subsequent stress distortions of the flat mateπal 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 pπnt to the can, a base coat of pπmer may be applied to the exteπor surface of the can. The pπnt layer is then applied directly on top of the base coat on the can by known lithographic pπntmg techniques The label may further compπse an electπcally insulating overcoat A varnish overcoat is preferably applied over the pπnt layer to cover and protect the pπnt layer, and also to serve as an electπcally insulating layer The pπnted label may be cured with the use of high temperature heating or ultraviolet radiation techniques With the use of the pπnted 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 pπnt 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 offeπng a further increase in available volume for active cell mateπals 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 batteπes to ensure a sufficient cπmp and seal Furthermore, a label may be lithographed directly onto the exteπor surface of the battery can By making the can walls thinner and lithographing the label directly onto the exteπor 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 exteπor size standards While the present invention has been descπbed above as having pπmary applicability to alkaline batteπes, it will be appreciated by those skilled in the art that similar benefits may be obtained be employing the inventive constructions m batteπes utilising other electrochemical systems For example, the inventive constructions may be employed m pπmary systems such as carbon-zinc and lithium based batteπes and in rechargeable batteπes, such as NiCd, metal hydπde, and Li based batteπes 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 12: Referring to Figure 10, an electrochemical cell 700 is shown constructed with a feed through collector according to an embodiment of the present invention. Similar to the electrochemical cell 400 with beverage can-type construction shown in Figure 6, 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. A positive electrode (cathode) 115 is in contact with the interior walls of can 712 and in contact with a separator 117 that lies between positive electrode 115 and a negative electrode (anode) 120. A pressure relief mechanism 370 is formed in the closed end 314 of can 712. The pressure relief mechanism 370 is formed as a groove 372 as described herein in connection with Figures 4 and 5. In addition, a positive outer cover 311 is connected to the closed end of can 712 and overlies the pressure relief mechanism 370. Collector assembly 725 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. Inner cover 745 is connected and sealed to the open top end of can 712 by a double seam closure at the peripheral edges 450 and 470. An outer cover 750 is in electrical contact with collector nail 740. A dielectric annular pad 748 is disposed between outer negative cover 750 and inner cover 745. Accordingly, a negative battery terminal is provided by cover 750. As shown by 015 with reference to Figures 7A-D, batteπes in accordance with a preferred embodiment of the present invention may be prepared having beverage can- type seals. Cover 745 (coπesponding to cover 445 in Figures 7A-D) is placed over the open end of can 712 (corresponding to can 412 in Figures 7A-D) as shown in Figure 7B. Can 712 has an outward extending flange 450 formed at its open end. Further, cover 745 has a slightly curved peπpheral edge 470 that conforms to the shape of flange 450. Once cover 745 has been placed over the open end of can 712, a seaming chuck 500 is placed on cover 745, such that an annular downward extending portion 502 of seaming chuck 500 is received by an annular recess 472 formed in cover 745. Next, a first seaming roll 510 is moved m a radial direction toward the peπpheral edge 470 of cover 745. As first seaming roll 510 is moved toward peπpheral edge 470 and flange 450, its curved surface causes peπpheral edge 470 to be folded around flange 450. Also, as first seaming roll 510 moves radially mward, seaming chuck 500, can 712, and cover 745 are rotated about a central axis, such that peπpheral edge 470 is folded around flange 450 about the entire circumference of can 712. Further, as first seaming roll 510 continues to move radially mward, flange 450 and peπpheral 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 712, and a second seaming roll 520 is then moved radially mward toward flange 450 and penpheral 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 peπpheral edge against the exteπor surface of can 712, which is supported by seaming chuck 500. As a result of this process, the peπpheral edge 470 of can 712 is folded around and under flange 450 and is cπmped between flange 450 and the exteπor surface of the walls of can 712, as shown in Figures 7D and 10. To assist in the sealing of outer cover 745 to can 712, a conventional sealant 473 may be applied to the bottom surface of peπpheral edge 470 of cover 745. Once the sealing procedure is complete, sealant 473 migrates to the positions shown in Figure 7D. A hermetic seal is thus formed by this process. Figure 8 shows a vaπation of a beverage can construction, in 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 securing an inner cover 616 thereto using the beverage can sealing technique outlined above, with no electrical insulation 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 collector assembly 725 (not shown) secured to the second open end of can 612 in the same manner as described above. The assembly of electrochemical cell 700 according to an embodiment of the present invention is illustrated in the assembly view of Figure 11 and is further illustrated in the flow diagram of Figure 12. The method 770 of assembly of electrochemical cell 700 includes providing can 712 formed with a closed bottom end and open top end in step 772. 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 provides dielectric insulation and can be heated to reform and settle between the inner cover 745 and collector nail 740. A recess 755 is formed in the top surface and centred about aperture 751. 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 centred in aperture 751 such that nail 740 does not contact cover 745 Thereafter, in step 782, an electncal dielectπc insulating pad 748 such as an annular dielectπc pad is disposed on top of inner cover 745 and extends radially outward from the peπmeter 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 electπcal 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 It will be understood that the embodiments shown in the drawings and descπbed 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 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 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 mateπals, void volumes and chemically inert mateπals (other than the collector nail) that are confined within the sealed volume of the cell, are measured by geometπc 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 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. Prior to potting the battery in epoxy, battery measurements were taken with callipers to measure the overall height, the crimp 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 in 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 cuπent 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 coπesponding 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 πght 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 πght sides by one-hundred-eighty degrees (180°) and summing the left and πght volumes together an average volume value is determined, which may be advantageous in those situations where the battery has non-symmetπcal features The volumes which include any non-symmetπcal features can be adjusted as necessary to obtain more accurate volume measurements Figures 9A and 9B show volumes of vaπous 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 With Feed Through Collector", a D sized battery constructed using the construction shown in Figure 10, had an internal volume that was 96.0 volume percent when the can walls were 200 μm (8 mils) thick. As shown m Figure 9B, a D sized battery constructed using the construction shown in Figure 10 had a collector assembly volume that was 2.6 percent of the total volume when the can walls were 200 μm (8 mils) thick. The C, AA, and AAA sized battenes having similar construction also exhibited significant improvements in internal volume efficiency, as is apparent from the table in Figure 9 A.

Claims: CLAIMS: 1 An electrochemical cell compπsing a can for containing electrochemically active mateπals including at least positive and negative electrodes and an electrolyte, the can having an open end and a closed end; 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 of the cover and extending internally within the can to electπcally contact one of the positive and negative electrodes, and a first insulating mateπal disposed between the collector and the cover for electπcally insulating the collector from the cover and providing a seal between the collector and the cover. 2 An electrochemical cell according to claim 1, further compπsing a pressure relief mechanism formed in a surface of the can 3. An electrochemical cell according to claim 2, wherein the pressure relief mechanism is formed in a surface at the closed end of the can. 4. The electrochemical cell according to claim 3, wherein the pressure relief mechanism compπses a groove formed m the closed end of the can. 5. An electrochemical cell according to claim 3 or claim 4, further compπsing a first contact terminal positioned on the closed end of the can in electπcal contact therewith, wherein the first contact terminal overlies the pressure relief mechanism. 6 An electrochemical cell according to any preceding claim, further compπsmg. a second contact terminal electπcally coupled to the collector; and a second insulating mateπal disposed between the second contact terminal and the cover for insulating the second contact terminal from the cover. 7 An electrochemical cell according to claim 6, wherein the first contact terminal is electπcally coupled to the positive electrode to serve as a positive external battery terminal and the second contact terminal is electπcally coupled to the negative electrode to serve as a negative external battery terminal. 8. An electrochemical cell according to any preceding claim, wherein the electrolyte compπses KOH and the first insulating mateπal compπses an organic macromolecular mateπal that is resistant to chemical attack by the KOH. 9. An electrochemical cell according to any preceding claim, wherein the cover is formed separately from the can. 10. An electrochemical cell according to any preceding claim, wherein the collector compπses a nail. 11. An electrochemical cell according to claim 6 or claim 7, wherein the collector compπses a nail and the nail is welded to the second contact terminal. 12. An electrochemical cell according to any preceding claim, wherein the can has a flange that extends outward from the open end of the can toward the closed end, and the cover has a peπpheral edge that extends over and around the flange and is cπmped between the flange and an extenor surface of the can. 13. An electrochemical cell according to claim 12 further compπsing a sealant provided between the flange and the outer peπpheral edge of the cover. 14 An electrochemical cell according to any of claims 1 to 13, wherein the first insulating mateπal compπses a mateπal selected from epoxy, rubber and nylon 15 An electrochemical cell according to any preceding claim, wherein the cell is a cylmdπcal cell 16 A method of assembling an electrochemical cell compπsing the steps of: dispensing electrochemically active mateπals in a can having a closed end and an open end, disposing a current collector through an aperture formed in a cover; providing an insulating mateπal between the cover and the collector to provide electπcal insulation therebetween; and assembling the cover and collector to the open end of the can. 17. A method according to claim 16, further compπsing the step of forming a pressure relief mechanism in a surface of the can. 18. A method according to claim 17, wherein the pressure relief mechanism is formed in the closed end of the can. 19. A method according to claim 18, further compπsing the step of connecting a first contact terminal in electπcal contact with the closed end of the can and overlying the pressure relief mechanism. 20. A method according to any of claims 16 to 19, wherein the step of disposing the insulating mateπal includes at least partially melting the insulating mateπal such that the melted insulating mateπal reforms between the current collector and the cover. 21 A method according to any of claims 16 to 20, further compπsing the steps of. disposing an outer insulating mateπal on top of the cover; and connecting a second contact terminal on top of the outer insulating mateπal and in electπcal contact with the cuπent collector. 22 A method according to any of claims 16 to 21, wherein the cover is formed separate from the can 23. A method according to any of claims 16 to 22, further compπsing the step of forming a double seam closure between the cover and the can. 24. A method according to claim 23, wherein the step of forming a double seam closure compπses the steps of placing a peπpheral edge of the cover to extend over and around a flange of the open end of the can, and cπmping the peπpheral edge of the cover between the flange and an exteπor surface of the can. 25. A method according to any of claims 16 to 24, wherein the insulating mateπal compπses a mateπal selected from epoxy, rubber and nylon.

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