Title of Invention

AN ELECTROCHEMICAL CELL

Abstract An electrochemical cell, preferably a cylindrical cell, is provided comprising: a can 312 for containing electrochemically active materials including positive and negative electrodes and an electrolyte, the can 312 having an open end, a closed end with an end wall 314 extending across the closed end, and side walls extending between the open and closed ends; a first cover 345 positioned across the open end; and a pressure relief mechanism 370 formed in a surface of the can 312, preferably an arc-shaped groove 372 formed in the end wall 314 of the can 312. A second cover 311 is preferably positioned on the end wall of the can 312 to be in electrical contact therewith and to extend over the pressure relief mechanism 370. Also provided is a method of preparing an electrochemical cell comprising the steps of; forming a can 312 having an open end and a closed end; forming a pressure relief mechanism 370 in a surface of the can 312; dispensing electrochemically active materials in the can 312; and sealing a first cover 345 across the open end of the can 312. The cell construction allows a large internal volume to be available for containing electrochemically active materials. [Figure 4A]
Full Text 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 ceil.
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 MnO2. 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 rigid 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 peripheral upstanding wall 36. By configuring collector assembly 25 in this fashion, inner cover 44 serves to enable compression of central hub portion 32 by collector nail 40 while also supporting compression of peripheral upstanding wall 36 by the inner surface of can 12.
Outer cover 45 is typically made of a nickel-plated steel and is configured to extend from a region defined by the annular peripheral upstanding wall 36 of seal 30 and to be in electrical contact with a head portion 42 of collector nail 40. Outer cover 45 may be welded to head portion 42 of collector nail 40 to prevent any loss of contact. As shown in 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 electrical contact therewith. In the example shown in Figure 1, outer cover 45 includes a peripheral lip 47 that extends upwardly along the circumference of outer cover 45. By forming peripheral upstanding wall 36 of seal 30 of a length greater than that of peripheral lip 47, a portion of peripheral upstanding wall 36 may be folded over peripheral lip 47 during the crimping process so as to prevent any portion of the upper edge 13 of can 12 from coming into contact with outer cover 45.
Seal 30 is preferably formed of nylon. In the configuration shown in 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 the hydrogen gas to escape to the exterior of cell 10. The mechanism shown includes an annular metal washer 50 and a plurality of spurs 52 that are provided between seal 30 and inner cover 44. 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 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 3 A. 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 stiil maintaining adequate sealing characteristics and a reliable pressure relief mechanism.
Accordingly, in a first aspect, the present invention provides an electrochemical cell comprising:
a can for containing electrochemically active materials including positive and negative electrodes and an electrolyte, the can having an open end, a closed end with an end wall extending across the closed end, and side walls extending between the open and closed ends;
a first cover positioned across the open end;
a pressure relief mechanism formed in the end wall of the can; and
a second cover is positioned on the end wall of the can to be in electrical contact therewith and to extend over the pressure relief mechanism.
In a second aspect, the present invention provides a method of preparing an electrochemical cell comprising the steps of:
forming a can having an open end and a closed end;
forming a pressure relief mechanism in the closed end of the can;
attaching a second cover to the closed end of the can such that the second cover extends over the pressure relief mechanism;
dispensing electrochemically active materials in the can; and
sealing a first cover across the open end of the can.
The pressure relief mechanism is formed in the end wall of the can, and preferably includes an arc-shaped groove formed in a surface of the end wall of the can. A second cover is positioned on the end wall of the can to be in electrical contact therewith and to extend over the pressure relief mechanism. The cell is preferably a cylindrical cell.
Advantageously, by providing a pressure relief mechanism in the end wall of the can, 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 prior 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
is that the cell constructions may be simpler to manufacture and require less materials, thereby possibly having lower manufacturing 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 therefore provides an electrochemical cell comprising:
- a can for containing electrochemically active materials including positive and negative electrodes and an electrolyte, the can having an open end, a closed end with an end wall extending across the closed end, and side walls extending between the open and closed ends;
- a first cover positioned across the open end;
- a pressure relief mechanism formed in the end wall of the can; and
- a second cover is positioned on the end wall of the can to be in electrical contact therewith and to extend over the pressure relief mechanism.
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 materials, as measured for those batteries that were commercially available at the priority date of this application;
Figure 2B is a table showing the relative total battery volumes and collector assembly volumes as measured for those batteries that were commercially available as provided in Figure 2A;
Figures 3 A-3D are cross sections of a conventional C sized alkaline electrochemical cell that illustrate the total battery and various component volumes;
Figure 4A is a cross section of a C sized alkaline electrochemical cell constructed in accordance with a first preferred embodiment of the present invention having a rollback cover, an annular L-shaped (J-shaped) seal, and a pressure relief mechanism formed in the can bottom surface;
Figure 4B is a cross section of the top portion of a C sized alkaline electrochemical cell constructed in accordance with a first preferred embodiment of the present invention having a rollback cover and including an L-shaped annular seal;
Figure 4C is an exploded perspective view of the electrochemical cell shown in Figure 4A illustrating assembly of the collector seal and cover assembly;
Figure 5 is a bottom view of a battery can having a pressure relief mechanism formed in the closed end of the can, in accordance with an embodiment of the present invention;
Figure 6 is a cross-sectional view taken along line X-X of the can vent shown in Figure 5;
Figure 7 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction according to a second preferred embodiment of the present invention;
Figure 8A is a partially exploded perspective view of the battery shown in Figure 7;
Figures 8B and 8C are cross-sectional views of a portion of the battery shown in Figure 7 illustrating the process for forming the beverage can-type construction;
Figure 8D is an enlarged cross-sectional view of a portion of the battery shown in Figure 7;
Figure 9 is a cross section of a C sized alkaline electrochemical cell having a beverage can-type construction according to a second preferred embodiment of the present invention;
Figure 10A is a table showing the calculated total and internal cell volume for various batteries constructed in accordance with the present invention;
Figure 1 OB is a table showing the calculated total volume and collector assembly volume for various batteries constructed in accordance with the present invention;
Figure 11 is a cross section of a C sized alkaline electrochemical cell having a collector feed through construction according to a third preferred embodiment of the present invention;
Figure 12 is an exploded assembly view of the electrochemical cell shown in Figure 11; and
Figure 13 is a flow diagram illustrating a method of assembly of the electrochemical cell shown in Figures 11 and 12.
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.
This may be achieved by forming a pressure relief mechanism 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 that consumes less volume and has fewer pans. 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 lime 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 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, 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.
Accordingly, in a preferred embodiment, a battery is provided that comprises a can for containing electrochemical materials including positive and negative electrodes and an electrolyte, the can having a first end, an open second end, side walls extending between the first and second ends, and an end wall extending across the first end; a pressure relief mechanism formed in the end wall of the can for releasing internal pressure from within the can when the internal pressure becomes excessive; a first outer cover positioned on the end wall of the can to be in electrical contact therewith and to extend over the pressure relief mechanism; a second outer cover positioned across the open second end of the can; and an insulator disposed between the can and the second outer cover for electrically insulating the can from the second outer cover.
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.
In a first preferred embodiment, an electrochemical cell is provided that 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. Also included in the collector assembly is a cover. An annular seal having an L-shaped cross section is disposed between the can and the cover for electrically insulating the can from the cover and creating a seal between the cover and the can. The seal may further include an extended vertical member to form a J-shaped cross section. The pressure relief mechanism is present in a surface of the can.
The open end of the can is sealed by placing an annular seal, having either a J-shaped or an L-shaped cross section, in the open end of the can. Preferably, the seal is of nylon, although other suitable materials could be used. An outer cover, preferably
serving as the negative terminal, which preferably has a rolled back peripheral edge, is inserted within the seal. Subsequently the outer edge of the can may be crimped to hold the seal and cover in place. To help hold the seal in place, a bead is preferably formed around the circumference of the open end of the can. The seal is preferably coated with a material such as asphalt to protect it from the electrochemically active materials and to provide a better seal.
The annular seal may be configured with a J-shaped cross section which includes an extended vertical wall at the outermost perimeter thereof, a shorter vertical wall at the radially inward side of the seal and has a horizontal base member formed between the vertical walls. With the presence of the short vertical section, the annular seal is referred to herein as having either a J-shaped or L-shaped cross section. It should be appreciated that the J-shaped seal could also be configured absent the short vertical section to form a plain L-shaped cross section.
The electrochemical cell may be assembled as follows. The can, preferably a cylindrical can, is formed with side walls defining the open end and preferably a bead for receiving internally disposed battery materials prior to closure of the can. Disposed within the can are the active electrochemical cell materials including the positive and negative electrodes and the electrolyte, as well as the separator, and any additives. Together, the outer cover, with a collector fastened to the bottom surface of the cover, and the annular seal, are assembled and inserted into the open end of the can to seal and close the can. The collector, preferably a nail, is preferably fastened to the bottom side of the outer cover by welding, such as via a spot weld. Together, the collector and cover are engaged with the seal to form a collector assembly, and the collector assembly is inserted in the can such that the preferably rolled back peripheral edge of the outer cover is disposed against the inside wall of the annular seal above the bead, which supports the seal. The collector assembly is forcibly disposed within the open end of the can to snugly engage and close the can opening. Thereafter, the outer edge of the can is preferably crimped inward to axially force and hold the seal and outer cover in place.
Preferably, the inside surface of the outer cover and at least a top portion of the collector arc coated with an anti-corrosion coating. The anti-corrosion coating includes materials that are elcctrochcmically compatible with the anode. Examples of such electrochemically compatible materials include epoxy, Teflon®, polyolefins, nylon, elastomenc materials, or any other inert materials, either alone or in combination with other materials. The coating may be sprayed or painted on and preferably covers that portion of the inside surface of the outer cover and collector which is exposed to the active materials in the void region above the positive and negative electrodes of the cell. It should also be appreciated that the inside surface of the cover could be plated with tin, copper, or other similarly electrochemically compatible materials. By providing an anti-corrosion coating, any corrosion of the outer cover and collector may be reduced and/or prevented, which advantageously reduces the amount of gassing which may otherwise occur within the electrochemical cell. Reduction in gassing within the cell results in reduced internal pressure build-up.
Accordingly, in an example of the first embodiment, an electrochemical cell is provided that comprises a can for containing electrochemically active materials including at least positive and negative electrodes and an electrolyte, the can having an open end and a closed end, and side walls extending between the open end and closed end; a first outer cover positioned across the open end of the can; a collector electrically coupled to the first outer cover and extending internally within the can to electrically contact one of the positive and negative electrodes; and an annular seal having an L-shaped cross section disposed between the can and the first outer cover for electrically insulating the can from the first outer cover and creating a seal between the first outer cover and the can. The seal may further include an extended vertical member to form a J-shaped cross section. A pressure relief mechanism is formed in a surface of the can for releasing internal pressure from within the can when the internal pressure becomes excessive.
In a second preferred embodiment, an electrochemical cell is provided that 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 electncal contact with
an electrode, for example the negative electrode. Also included in the collector assembly is a cover. 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. The pressure relief mechanism is present in a sutface of the can.
The cover of the collector assembly is connected and sealed to the open top end of the can to form a double seam closure in which the can is electrically insulated from the cover. Preferably, a beverage can-type sealing technique is used to form the closure.
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 peripheral 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 peripheral 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 peripheral edge to press and flatten the folded flange and peripheral edge against the exterior surface of the can, which is supported by the seaming chuck. As a result of this process, the peripheral edge of the can is folded around and under the flange and is crimped between the flange and the exterior 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 period. These results were confirmed using KOH electrolyte, with the conventional construction losing 50 mg per week and the inventive construction again not losing any weight.
As will be apparent to those skilled in the art, the beverage can-type construction 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 second preferred embodiment, the percentage of the total battery volume that may be used to contain the electrochemically active materials may be as high as 97 volume percent, while collector assembly volume
may be as low as 1.6 volume percent. The volumes of batteries of other sizes are included in the table shown in Figures 10A and 1013.
In a variation of the second preferred embodiment, 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, with the exception that no electrical insulation is required between this cover and the side walls. 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.
Accordingly, in an example of the second 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. A pressure relief mechanism is formed in a surface of the can for releasing internal pressure from within the can when the internal pressure becomes excessive.
in a third preferred embodiment, an electrochemical cell is provided that 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. Also included in the collector assembly is a cover having an aperture preferably formed centrally in the cover. The collector is disposed in 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 pressure relief mechanism is present in a surface of the can.
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.
The cover of the collector assembly is connected and sealed to the open top end of the can, preferably 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, as described above for the second preferred embodiment. While a double seam can-to-cover closure is preferred, it should be appreciated that other can-to-cover closures may be employed in accordance with the third preferred embodiment.
In a variation of the third preferred embodiment, 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.
The electrochemical cell according to the third preferred embodiment allows for a direct connection between the can and the cover, which preferably provides a pressure seal therebetween, but does not require electrical isolation between the cover and the side walls of the can. Instead, the collector, preferably a nail, is dielectrically 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 electrical isolation between the can and the cover, it is preferred 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 peripheral edge of the cover. In a beverage can construction, once the sealing procedure is complete, the sealant migrates to the positions shown in Figure 8D. It should be appreciated that the sealed closure along with the insulating material 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 in accordance with well accepted battery standards, the electrochemical cell preferably further includes an outer cover in electrical contact with the collector. The outer cover may be welded by spot weld or otherwise electrically connected to the collector. To ensure proper electrical insulation between the outer cover and the inner cover, preferably a dielectric material such as annular pad is disposed between the outer cover and the inner cover. Suitable dielectric materials include nylon, other elastomeric materials, 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 the third preferred embodiment is illustrated in the assembly view of Figure 12 and is further illustrated in the flow diagram of Figure 13. 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, a second cover is connected to the closed end of the can,
overlying a pressure relief mechanism.
For a D sized battery according to the third preferred embodiment, 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 10A and 10B.
Accordingly, in an example of the third embodiment, an electrochemical cell is provided that comprises a can for containing electrochemically active materials including at least positive and negative electrodes and an electrolyte, the can having an open end, a closed end, and side walls extending between the open and closed ends; a cover positioned across the open end of the can and connected to the can, the cover having an aperture extending therethrough; a current collector extending through the aperture in the cover and extending internally within the can to electrically contact one of the positive and negative electrodes; and an insulating material disposed between the collector and the cover for electrically insulating the collector from the cover and creating a seal between the collector and the cover. A pressure relief mechanism is formed in a surface of the can for releasing internal pressure from within the can when the internal pressure becomes excessive. In addition, the electrochemical cell preferably includes a first contact terminal electrically coupled to the collector and a dielectric
material disposed between the first contact terminal and the cover for electrically insulating the cover from the first contact terminal.
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 eiectrochemically 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 10A, 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 print layer may be applied directly onto the exterior surface of the battery can to provide a label. By applying the label directly onto the exterior of the can as a print 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 exterior size standards. By "directly" is meant that no label substrate is present between the print 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 Igngth of the battery, these conventional labels effectively add about 250 urn (10 mils) to the diameter and of 330 µm (13 mils) to the crimp height of the battery. As a result, the battery can must have a diameter that is selected to accommodate the thickness of the label seam in order to meet the ANSI or other size standards. However, by printing a lithographed label directly on the exterior 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 batteries 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 A A sized cell, and 5.5 percent (0.195 cc) for an AAA sized battery, if the labels were printed directly on the exterior of the can.
Labels may also be printed on the can using transfer printing techniques in which the label image is first printed on a transfer medium and then transferred directly onto the can exterior. Distorted lithography may also be used whereby intentionally distorted graphics are printed on flat material so as to account for subsequent stress distortions of the flat material as it is shaped into the tube or cylinder of the cell can.
Prior to printing the lithographed label, the exterior surface of the can is preferably cleaned. To enhance adherence of the print to the can, a base coat of primer may be applied to the exterior surface of the can. The print layer is then applied directly on top of the base coat on the can by known lithographic printing techniques. The label may further comprise an electrically insulating overcoat. A varnish overcoat is preferably applied over the print layer to cover and protect the print layer, and also to serve as an electrically insulating layer. The printed label may be cured with the use of high temperature heating or ultraviolet radiation techniques.
With the use of the printed label, the thickness of 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 printed 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 print layer of a thickness of approximately 2.5 urn (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 urn (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 battenes, 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 4A to 13:
An electrochemical battery 300 constructed in accordance with a first preferred embodiment of the present invention is shown in Figures 4A through 4C. A pressure relief mechanism 370 is formed in the closed end 314 of can 312. The pressure relief mechanism 370 is formed by providing a groove 372 in the bottom surface of can 312, as shown in Figures 5 and 6. The groove is formed as an arc of approximately 300 degrees. The shape formed by the groove is slightly open so that the pressure relief mechanism has an effective hinge. The size of the area circumscribed by the groove 372 is selected such that upon rupture due to excessive internal pressure, the area within the groove 372 may pivot at the hinge within the positive protrusion of outer cover 311 without interference from outer cover 311.
The pressure relief mechanism 370 is positioned beneath outer cover 311 so as to prevent the electrochemical materials from dangerously spraying directly outward from the battery upon rupture.
The open end of can 312 is sealed by placing either a nylon seal 330 having a J-shaped cross section or a nylon seal 330' having an L-shaped cross section in the open end of can 312, inserting a negative outer cover 345 having a rolled back peripheral edge 347 within nylon seal 330 or 330', and subsequently crimping the outer edge 313 of can 312 to hold seal 330 or 330' and cover 345 in place. To help hold seal 330 or 330' in place, a bead 316 is formed around the circumference of the open end of can 312. Nylon seal 330 or 330' is coated with asphalt to protect it from the electrochemically active materials and to provide a better seal.
Referring particularly to Figures 4A and 4C, the annular nylon seal 330 is shown configured with a J-shaped cross section which includes an extended vertical wall 332 at the outermost perimeter thereof, a shorter vertical wall 336 at the radially inward side of the seal and has a horizontal base member 334 formed between the vertical walls 332 and 336. As shown in Figure 4B, the J-shaped nylon seal 330 is configured absent the short vertical section 336 to form a plain L-shaped cross section.
With particular reference to Figure 4C, the assembly of the electrochemical cell shown in Figure 4A is illustrated therein. The cylindrical can 312 is formed with side walls defining the open end and bead 316 for receiving internally disposed battery materials prior to closure of the can. Disposed within can 312 are the active electrochemical cell materials including the positive and negative electrodes and the electrolyte, as well as the separator, and any additives. Together, the outer cover 345, with the collector nail 340 welded or otherwise fastened to the bottom surface of cover 345, and annular nylon seal 330 are assembled and inserted into the open end of can 312 to seal and close can 312. The collector nail 340 is preferably welded via spot weld 342 to the bottom side of outer cover 345. Together, collector nail 340 and cover 345 are engaged with seal 330 to form the collector assembly, and the collector assembly is
inserted in can 312 such that the rolled back peripheral edge 347 of outer cover 345 is disposed against the inside wall of annular seal 330 above bead 316 which supports seal 330. The collector assembly is forcibly disposed within the open end of can 312 to snugly engage and close the can opening. Thereafter, the outer edge 313 of can 12 is crimped inward to axially force and hold seal 330 and outer cover 345 in place. Referring back to Figure 4B, the inside surface of outer cover 345 and at least a top portion of collector nail 340 are further shown coated with an anti-corrosion coating 344.
An electrochemical battery 400 constructed in accordance with a second preferred embodiment of the present invention is shown in Figures 7 through 9. A negative outer cover 445 is secured to the open end of can 412 using a beverage can-type sealing technique. The method of making a battery having the construction shown in Figure 7 is described below with reference to Figures 8A-8D. 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 8A, 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. Thus, negative outer cover 445 is electrically insulated from can 412.
To assist in the sealing of outer cover 445 to can 412, 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 8D.
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 8B. 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 41 2, 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 8C.
After peripheral edge 470 and flange 450 have been folded into the position shown in Figure 8C, first seaming roll 510 is moved away from can 412, and a second seaming roll 520 is then moved radially inward toward flange 450 and peripheral edge 470. Second seaming roll 520 has a different profile than first seaming roll 510. Second seaming roll 520 applies sufficient force against flange 450 and peripheral edge 470 to press and flatten the folded flange and peripheral edge against the exterior surface of can 412, which is supported by seaming chuck 500. As a result of this process, the peripheral edge 470 of can 412 is folded around and under flange 450 and is crimped between flange 450 and the exterior surface of the walls of can 412, as shown in Figures 7 and 8D. A hermetic seal is thus formed by this process.
A variation of the beverage can construction is shown in Figure 9. In the illustrated embodiment, 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 the exception that no electrical insulation is required between inner cover 616 and side walls 614. A positive outer cover 618 is welded to the outer surface of inner cover 616. The battery is then filled and a negative outer cover 645 secured to the second open end of can 612 in the same manner as described above.
An electrochemical battery 700 constructed with a feed through collector in accordance with a third preferred embodiment of the present invention is shown in Figures 1 1 through 13. Similar to the electrochemical cell 400 with beverage can-type construction shown in Figure 7, electrochemical cell 700 includes an electrically conductive can 712 having a closed end 314 and an open end in which a low volume collector assembly 725 and outer negative cover 750 are assembled. Electrochemical cell 700 includes a positive electrode 115 in contact with the interior walls of can 712 and in contact with a separator 117 that lies between a positive electrode 115 and a negative electrode 120.
Electrochemical cell 700 includes a pressure relief mechanism 370 formed in the closed end 314 of can 712, which allows for employment of low volume collector assembly 725. The pressure relief mechanism 370 is formed as a groove as described herein in connection with Figures 4A, 4B, 5, and 6. In addition, a positive outer cover 311 is connected to the closed end of can 712 and overlies the pressure relief mechanism 370. The assembly and location of positive outer cover 311 is provided as shown and described herein in connection with Figure 4A.
Electrochemical cell 700 includes a collector assembly 725 which closes and seals the open end of can 712. Collector assembly 725 includes a collector nail 740 disposed in electrical contact with the negative electrode 120. Also included in the collector assembly 725 is a first or inner cover 745 having a central aperture 751 formed therein. The collector nail 740 is disposed and extends through the aperture 751 in inner cover 745. A dielectric insulating material 744 is disposed between collector nail 740 and first cover 745 to provide dielectric insulation therebetween. Accordingly, the collector nail 740 is electrically isolated from inner cover 745.
Inner cover 745 in turn is connected and sealed to the open top end of can 712. Inner cover 745 is sealed to can 712 by forming a double seam closure at the peripheral edges 450 and 470 as explained herein in connection with Figures 7-9. The collector nail 740 is dielectrically insulated from inner cover 745 such that the negative and
positive terminals of the electrochemical cell arc electrically isolated from one another. A sealant is applied at the closure joining the can to the cover to adequately seal the can. as explained in connection with the battery shown and described herein in connection with Figures 7-8D.
Electrochemical cell 700 further includes an outer cover 750 in electrical contact with collector nail 740. Outer cover 750 is welded by spot weld 742 to collector nail 740. A dielectric material as annular pad 748 is disposed between outer negative cover 750 and inner cover 745. Accordingly, an acceptable standard battery terminal is provided at the negative end of electrochemical cell 700.
The assembly of electrochemical cell 700 is illustrated in the assembly view of Figure 12 and is further illustrated in the flow diagram of Figure 13. The method 770 of assembly of electrochemical cell 700 includes providing can 712 formed with a closed bottom end and open top end. Step 774 includes disposing into can 712 the active electrochemical materials including the negative electrode, the positive electrode, and an electrolyte, as well as the separator and other cell additives. Once the active electrochemical cell materials are disposed within can 712, can 712 is ready for closure and sealing with the collector assembly 725. Prior to closing the can, the collector assembly is assembled by first disposing the collector nail 740 within aperture 751 formed in inner cover 745 along with a ring of insulating material according to step 776. Collector nail 740 is disposed in the opening 742 of insulating ring 744 which may include a ring or disk of epoxy which provides dielectric insulation and can be heated to reform and settle between the inner cover 745 and collector nail 740. Also shown formed in inner cover 745 is a recess 755 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. 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 electrical dielectric insulating pad 748 such as an annular dielectric pad is disposed on top of inner cover 745 and extends radially outward from the perimeter of nail 740. In step 784, disposed on top of collector nail 740 and pad 748 is a conductive negative cover 750 which is welded in electrical contact with collector nail 740. Once the collector assembly is fully assembled, the collector assembly is then connected to the can to sealingly close the open end as provided in step 786. The can closure employs a double seam closure. In addition, the assembly method 770 includes step 788 of connecting a second outer cover to the closed end of the can overlying the pressure relief mechanism 370.
EXAMPLE
The total battery volume, collector assembly volume, and internal volume available for electrochemically active material for each battery are determined by viewing a Computer Aided Design (CAD) drawing, a photograph, or an actual cross section of the battery which has been encased in epoxy and longitudinally cross-sectioned. The use of a CAD drawing, photograph, or actual longitudinal cross section to view and measure battery dimensions allows for inclusion of all void volumes that might be present in the battery. To measure the total battery volume, the cross-sectional view of the battery taken through its central longitudinal axis of symmetry is viewed and the entire volume is measured by geometric computation. To measure the internal volume available for electrochemically active materials, the cross-sectional view of the battery taken through its central longitudinal axis of symmetry is viewed, and the components making up the internal volume, which includes the electrochemically active materials, void volumes and chemically inert materials (other than the collector nail) that are confined within the sealed volume of the cell, are measured by geometric computation. Likewise, to determine volume of the collector assembly, the cross-sectional view of the battery taken through its central longitudinal axis of symmetry thereof is viewed, and the components making up the collector assembly volume, which include the collector nail, seal, inner cover, and any void volume defined between the
bottom surface of the negative cover and the seal, are measured by geometric computation. The container volume may likewise be measured by viewing the central longitudinal cross section of the battery and computing the volume consumed by the can, label, negative cover, void volume between the label and negative cover, positive cover, and void volume between the positive cover and the can.
The volume measurements are made by viewing a cross section of the battery taken through its longitudinal axis of symmetry. This provides for an accurate volume measurement, since the battery and its components are usually axial symmetric. To obtain a geometric view of the cross section of a battery, the battery was first potted in epoxy and, after the epoxy solidified, the potted battery and its components were ground down to the central cross section through the axis" of symmetry. More particularly, the battery was first potted in epoxy and then ground short of the central cross section. Next, all internal components such as the anode, cathode, and separator paper were removed in order to better enable measurement of the finished cross section. The potted battery was then cleaned of any remaining debris, was air dried, and the remaining void volumes were filled with epoxy to give the battery some integrity before completing the grinding and polishing to its 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 current collector nail, and overall outside diameter of the battery can be modified to profile the drawing more accurately by adjusting the drawing to include the corresponding known cross-sectional dimensions to make the drawing more'accurate for volume measurements. The detail of the seal, cover, and crimp areas were used as they were drawn on the optical comparitor.
To calculate the volume measurements, the drawing was imported into solid modelling software. A solid three-dimensional volume representation was generated by rotating the contour of the cross section on both the left and right sides by one-hundred-eighty degrees (180°) about 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 10A and 10B 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 I0A in the rows referenced "Pressure Relief in Can Bottom" and "Pressure Relief in Can Bottom With Thin Walls," a D sized battery constructed using the construction shown in Figure 4A, has an internal volume that is 93.5 volume percent when the can walls are 250 µm (10 mils) thick, and an internal volume that is 94.9 volume percent when the can walls arc 200 urn (8 mils) thick. As shown in Figure 10B, a D sized battery constructed using the construction shown in Figure 4A, has a collector assembly volume that is 2 percent of the total volume when the can walls are 250 µm (10 mils) thick and 200 urn (8 mils) thick. As shown in Figure 10A in the row referenced "Beverage Can-Type Construction", a D sized battery constructed using the construction shown in Figure 11, had an internal volume that was 97.0 volume percent when the can walls were 200 urn (8 mils) thick. As shown in Figure 10B, a D sized battery constructed using the construction shown in Figure 7 had a collector assembly volume that was 1.6 percent of the total volume when the can walls were 200 urn (8 mils) thick. As shown in Figure 10A in the row referenced "Beverage Can With Feed Through Collector", a D sized battery constructed using the construction shown in Figure 11, had an internal volume that was 96.0 volume percent when the can walls were 200 µm (8 mils) thick. As shown in Figure 10B, a D sized battery constructed using the construction shown in Figure 11 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 batteries having similar construction also exhibited significant improvements in internal volume efficiency, as is apparent from the table in Figure 10A.
Furthermore, using these techniques to measure and calculate battery volumes, it was found that the internal volume of the batteries with substrate labels could be further increased 2 percent (1.02 cc) for a D sized battery, 2.6 percent (0.65 cc) for a C sized battery, 3.9 percent (0.202 cc) for an AA sized cell, and 5.5 percent (0.195 cc) for an AAA sized battery, if the labels were printed directly on the exterior of the can.



We claim:
1. An electrochemical cell comprising:
- a can for containing electrochemically active materials
including positive and negative electrodes and an electrolyte,
the can having an open end, a closed end with an end wall
extending across the closed end, and side walls extending
between the open and closed ends;
a first cover positioned across the open end; characterized by a pressure relief mechanism formed in the end wall of the can; and
- a second cover is positioned on the end wall of the can to be
in electrical contact therewith and to extend over the pressure
relief mechanism.
2. An electrochemical cell as claimed in claim 1, wherein the end wall is integrally formed with the side walls of the can.
3. An electrochemical cell as claimed in claim 1, wherein the can is formed as a tube with the end wall being a cover secured across the closed end.
4. An electrochemical cell as claimed in any preceding claim, wherein the pressure relief mechanism is formed by coining a surface of the end wall of the can.
5. An electrochemical cell as claimed in any preceding claim, wherein the pressure relief mechanism includes a hinged portion that pivots out from the end wall of the can upon rupture.
6. An electrochemical cell as claimed in any preceding claim, wherein the pressure relief mechanism includes an arc-shaped groove formed in a surface of the end wall of the can.
7. An electrochemical cell as claimed in claim 6, wherein the arc-shaped groove is formed as a 300 degree partial circle.
8. An electrochemical cell as claimed in any preceding claim, wherein the second cover includes a centrally disposed contact terminal protrusion, and wherein the pressure relief mechanism is formed in the end wall of the can in a region underlying the protrusion.
9. An electrochemical cell as claimed in any preceding claim, wherein the second cover is electrically coupled to the positive electrode to serve as a positive external battery terminal and the first cover is
electrically coupled to the negative electrode to serve as a negative external battery terminal.

10. An electrochemical cell as claimed in any preceding claim, wherein an insulator is disposed between the can and the first cover for electrically insulating the can from the first cover.
11. An electrochemical cell as claimed in claim 10, wherein the insulator is a coating of insulating material deposited on at least one of the can and the first cover.
12. An electrochemical cell as claimed in any preceding claim, wherein the cell is a cylindrical cell.
13. A method of preparing an electrochemical cell comprising the steps of:

• forming a can having an open end and a closed end;
• forming a pressure relief mechanism in the closed end of the can;
• attaching a second cover to the closed end of the can such that the second cover extends over the pressure relief mechanism;
• dispensing electrochemically active materials in the can; and
• sealing a first cover across the open end of the can.

14. A method as claimed in claim 13, wherein the step of sealing including providing a layer of electrical insulation between the can and the first cover.
15. A method as claimed in claim 13 or claim 14, wherein the step of forming the can includes the substeps of forming a tube to define side walls of the can, and securing a cover across an open end of the tube to define an end wall across the closed end of the can.
16. A method as claimed in any of claims 13 to 15, wherein the step of forming a pressure relief mechanism comprises forming a groove. 17. 17.A method as claimed in claim 16, wherein the groove is formed by moulding.


Documents:


Patent Number 249472
Indian Patent Application Number IN/PCT/2001/00131/DEL
PG Journal Number 43/2011
Publication Date 28-Oct-2011
Grant Date 21-Oct-2011
Date of Filing 13-Feb-2001
Name of Patentee EVEREADY BATTERY COMPANY INC.
Applicant Address P.O.BOX 450777, 25225 DETROIT ROAD, WESTLAKE, OHIO 44145, U.S.A
Inventors:
# Inventor's Name Inventor's Address
1 SONDECKER GEORGE R 2202 BERKLEY LANE, ASHEBORO, NORTH CAROLINA 27203, U.S.A
2 LAISY GARY A 27142 COOK ROAD, OLMSTED TOWNSHIP, OHIO 44138-1034, U.S.A
PCT International Classification Number H01M 2/12
PCT International Application Number PCT/US1999/18667
PCT International Filing date 1999-08-16
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/102,951 1998-10-02 U.S.A.
2 09/293,225 1999-04-16 U.S.A.
3 60/097,445 1998-08-21 U.S.A.