ELECTROCHEMICAL CELL FORMED WITH BIG MOUTH OPEN END CAN

Abstract: A cell with considerably less wasted space may be prepared by starting with a non-cylindrical can (10) where the open end has an over-sized mouth (18) which, after at least partial filling of the can, can be crimped and, ultimately, sealed.

Description: ELECTROCHEMICAL CELL FORMED WITH BIG MOUTH OPEN END CAN The present invention generally relates to electrochemical cells and, more particularly, to a method of assembling an electrochemical cell having a non-cylindrical container. Conventional alkaline cells commonly employ a cylindrical shaped steel can provided with a positive cover at one end and a negative cover at the opposite end. The cylindrical steel can houses a positive electrode, referred to as the cathode, which is preferably formed of a mixture of manganese dioxide, graphite, potassium hydroxide solution, deionised water, and other additives, and is commonly formed about the interior side surface of the cylindrical steel can. A cup-shaped separator is commonly disposed about the interior surface of the cathode. A negative electrode, referred to as the anode, which is typically formed of zinc powder, a gelling agent, and other additives, is dispensed within the separator along with electrolyte solution. Conventional cylindrical cells are widely available in sizes AAAA, AAA (R03), AA (R6), C (R14), and D (R20) for use as the power source for various electrically operated devices. Despite the popularity of the conventional cylindrical cells, it has been discovered that there is a potential need to provide for non-cylindrical cell configurations. One such potential need exists for use in a multiple-cell battery, such as the 9-volt battery, which commonly houses six 1.5 volt cells electrically connected in series. In the past, multiple cylindrical cells have been assembled together in a rectangular container, thereby resulting in unused space between adjacent cells as well as between each cell and the inside walls of the battery container. In addition, it has also been discovered that many battery operated electrical devices are capable of using non-cylindrical cells which may allow for increased service performance. An example of a non-cylindrical cell is disclosed in co-pending U.S. application Serial No. 09/110119, entitled "Electrochemical Cell and Battery" filed on April 2, 1998, to Lewis Urry. A primary goal in designing alkaline batteries is to increase the service performance of the cell Another goal is to achieve high quality cell assembly techniques The service performance is the length of time for the cell to discharge under a given load to a specific voltage at which the cell is no longer useful for its intended purpose Commercially available alkaline cells and batteries have an external size that is commonly defined by industry standards, thereby limiting the ability to increase the amount of active mateπals within a given cell and to confine the volume that is available Accordingly, the need to find new ways to increase service performance and provide suitable assembly techniques remains a primary goal of the cell designer It has now been found that it is possible to provide a cell with considerably less wasted space by starting with a non-cy ndπcal can where the open end has an over-sized mouth which, after at least partial filling of the can, can be cπmped and, ultimately, sealed The present invention improves the assembly of a cell having a non-cy ndπcal pπsmatic can, such as a rectangularly configured can, by providing the can with an enlarged open end to accommodate assembly of active mateπals into the cell, and reducing the enlarged open end to a reduced size round open end that may advantageously be fit with a compact round cover Accordingly, in a first aspect, the present invention provides a technique, or method, of assembling an electrochemical cell, compπsing using an open-ended, non-cyhndπcal can, preferably having a substantially fixed cross-section along its length, the mouth of the open end being generally circular, the mouth having no dimension smaller than any dimension of the radial cross-section of the can, and wherein the mouth of the can is reduced m size duπng or after the loading of the other elements, before being sealed In such a way, there is no impedance of loading of the constituents of the cell, and the end cover may, conveniently, be circular In general, it is preferred that the mouth be coaxial with the remainder of the body of the can This provides for ease of manufacture, and minimal wasted mateπal in the construction of the mouth of the can The body of the can may be of any general shape, such as square, rectangular, or oval, or may have an irregular shape, but it is generally preferred that the cross-section is consistent along the length of the cell, for filling purposes The mouth of the can will then have no dimension smaller than the largest cross-sectional dimension of the can, and is preferably substantially circular The transition from the open end of the can to the mouth is not crucial to the invention The transition may be abrupt, or gradated However, a gradated transition is generally preferred, in order to minimise wastage of mateπal, both from the point of view of construction, and the amount of mateπal that needs to be compressed or cπmped to reduce the mouth size The mouth need not necessaπly be circular after reduction, but other shapes often tend to be more difficult to produce, reliably, leading to problems with assembling covers onto them Thus, a substantially circular reduced mouth is preferred It will be appreciated that, while the starting size of the mouth is generally bigger than the can, the final size is preferably as small as, or smaller than, the overall radial area of the can, preferably with no dimensions exceeding any of those of the radial cross-section of the can In general, the cell may be constructed by means known in the art, and such as are descπbed below Generally, the present invention provides a method of assembling an electrochemical cell compπsing the steps of providing a can having a pπsmatic section with a closed bottom end and a big mouth round open top end The big mouth round open top end has a diameter that is at least as wide as the maximum inside cross-sectional width of the pπsmatic section The method includes the step of disposing a cathode into the pπsmatic section through the big mouth open top end The cathode is configured with a cavity formed therein and is disposed in the can such that the cathode consumes a substantial volume of the pπsmatic section between the cavity and inner walls of the can The method further includes the steps of disposing a separator withm the cavity and further disposing an anode withm the separator in the cavity. According to the method, the size of the big mouth open top end is reduced in size to provide a reduced diameter open top end upon which a round cover is assembled. In another aspect, the present invention provides a method of assembling an electrochemical cell comprising the steps of: providing a can having a prismatic section with a closed bottom end and a big mouth open top end that is substantially round with a diameter equal to or greater than the maximum inside cross-sectional width of the prismatic section; disposing a cathode through the big mouth open top end and into the prismatic section, the cathode having a cavity centrally, formed therein and disposed so that the cathode consumes a substantial volume of the prismatic section between the cavity and inner walls of the can; disposing a separator within the cavity; disposing an anode within the separator in the cavity; reducing the size of the big mouth open top end of the can to provide a reduced size round open top end; and assembling a cover to the reduced size round open top end. More generally, there is provided a method of assembling an electrochemical cell comprising the steps of: providing a can having a non-cylindrical section with a closed bottom end and a big mouth open top end that is substantially round with a diameter equal to or greater than the maximum inside cross-sectional width of the non-cylindrical section; disposing a first electrode through the big mouth open top end and into the non- cylindrical section, the first electrode having a cavity centrally formed therein and disposed so that the first electrode consumes a substantial volume of the non-cylindrical section between the cavity and inner walls of the can; disposing a separator within the cavity; disposing a second electrode within the separator in the cavity; reducing the size of the big mouth open top end of the can to provide a reduced size round open top end; and assembling a cover to the reduced size round open top end. In a preferred embodiment, there is provided a ring moulding method of assembling an electrochemical cell comprising the steps of: providing a can having a prismatic section with a closed bottom end and a big mouth open top end that is substantially round with a diameter equal to or greater than the maximum inside cross-sectional width of the prismatic section; forming one or more moulded cathode rings, each of the cathode rings configured to fit inside the prismatic section of the can and further having a cavity formed therein; disposing the one or more cathode rings through the big mouth open top end and into the prismatic section such that the one or more cathode rings consumes a substantial volume of the prismatic section between the cavity and inner walls of the can; disposing a separator within the cavity; disposing an anode within the separator in the cavity; reducing the size of the big mouth open top end of the can to provide a reduced size round open top end; and assembling a cover to the reduced size round open top end. In an alternative embodiment, there is provided a method of assembling an electrochemical cell comprising the steps of: providing a can having a prismatic section with a closed bottom end in a big mouth open top end that is substantially round with a diameter equal to or greater than the maximum inside cross-sectional width of the prismatic section; disposing a cathode into the prismatic section; disposing an anode into the prismatic section; disposing a separator between the anode and cathode; reducing the size of the big mouth open top end of the can to provide a reduced size round open top end; and assembling a cover to the reduced size round open top end. It is preferred to form the can to include a cylindrical section that provides the big mouth open top end. It is also preferred to form a tapered transition between the prismatic section and the cylindrical section. In general, it is prefeπed to reduce the big mouth open top end such that the diameter of the reduced open top end is less than or equal to the minimum cross-sectional width of the pπsmatic section A prefeπed technique for doing this is rotary swaging. In a preferred embodiment, the pπsmatic section has a substantially rectangular section It is preferred that the step of disposing the cathode into the can compπses a cathode πng moulding process, especially where the cathode πng moulding process includes the step of inserting multiple cathode πngs stacked one on top of another. In general, it is preferred to dispense a current collector m contact with the anode The can is preferably a steel can The non-cyhndπcal section is preferably a pπsmatic section. It is preferred that the anode and cathode are disposed within the pπsmatic section such that the pπsmatic section is substantially consumed by the anode and cathode The step of disposing the cathode into the pπsmatic section preferably includes forming a cavity centrally therein and disposing the cathode such that the cathode consumes a substantial volume of the pπsmatic section between the cavity and inner walls of the can, wherein the anode and separator are disposed within the cavity. The present invention also provides an electrochemical cell compπsing: a container having a pπsmatic section with a closed bottom end and a round open top end, the container initially having a big mouth open top end with a diameter greater than or equal to the maximum inside cross-sectional width of the pπsmatic section; a first electrode disposed substantially within the pπsmatic section; a second electrode disposed substantially with the pπsmatic section; a separator disposed between the first and second electrodes; and a round cover, wherein the big mouth open top end of the can is reduced in size to a reduced size round open end subsequent to the insertion of the first electrode so that the reduced round open end has a diameter that is less than or equal to the minimum cross- sectional width of the pπsmatic section, and the cover is assembled to the reduced round open end of the can Generally preferred features of such a cell are as detailed above, with respect to the method of the invention The big mouth open top end of the can advantageously allows for assembly of the cathode, particularly for πng moulding assembly, and reduction of the big mouth open top end subsequent to insertion of the cathode allows for a reduced size round top cover to be assembled thereto The present invention will be further illustrated with reference to the accompanying drawings, in which Figure 1 is a perspective view of a pπsmatic steel can having a cylindπcal section with a big mouth open end for use in the cell assembly of the present invention, Figure 2 is a top end view of the pπsmatic can of Figure 1 , Figure 3 is a perspective view of a pπsmatic steel can with the big mouth open end and further including a tapered transition according to another embodiment, Figure 4 is a flow diagram illustrating the method of assembly of an electrochemical cell according to the present mvention, Figure 5 is an exploded view of a partially assembled cell illustrating πng moulded cathode assembly, Figure 6 is a perspective view of a partially assembled cell illustrating the pnsmatic can having a reduced size round open end according to the assembly method of the present invention, Figure 7 is a top end view of the partially assembled cell of Figure 6 further illustrating the reduced size round open end of the can, Figure 8 is a cross-sectional view of the fully assembled cell taken through its longitudinal axis; and Figure 9 is a radial cross-sectional view of the fully assembled cell taken through lines DC-DC of Figure 8. Referπng to Figures 1 and 2, a pπsmatic steel can 10 is shown having an enlarged open end, which is referred to herein as the big mouth open end 18, for use in the assembly of an electrochemical cell according to the present invention Steel can 10 includes a non- cy ndπcal pπsmatic section 12, shown configured as a rectangular section, having a closed bottom end 16 Opposite the bottom end 16, steel can 10 has a cylindπcal section 14 that transitions from the pπsmatic section 12 to the big mouth open top end 18 The pπsmatic section 12 of cell 10 is provided with four substantially planar and rectangularly-shaped side walls that may be configured with rounded adjoining edges to provide a substantially rectangular radial cross section with rounded corners With particular reference to Figure 2, the cylindπcal section 14 of can 10 provides for an enlarged opening that leads into the inteπor of pπsmatic section 12 Cylindπcal section 14 provides the big mouth round opening 18 having a diameter D) that is greater than the cross-sectional width Wi between opposite walls of the pπsmatic section 12 Moreover, it is prefeπed that the big mouth diameter D] of cylindπcal section 14 be equal to or greater than the largest cross-sectional width W 2 of the inteπor of pπsmatic section 12 so that cell mateπals can be easily assembled into steel can 10 and will not be impeded by the configuration of cyhndπcal section 14. The steel can 10 may be configured according to another embodiment as shown in Figure 3 According to this other embodiment, steel can 10 further includes the addition of flat tapered transitions 20 that transition at a sloped angle θ from each of the planar side walls of pπsmatic section 12 to the cylindπcal section 14 Each of the tapered transitions 20 is provided at a sloped angle θ greater than zero degrees and up to ninety degrees The tapered transition 20 provides a lead in for closing to aide in a smooth reduction m size of the cylindπcal section 14. In addition, tapered transition 20 allows for enhanced handling and use in roller feeders and other assembly equipment present in the cell production assembly The pπsmatic steel can 10 with enlarged big mouth opening 18 is employed m accordance with a method of assembling an electrochemical cell according to the present invention. Referπng to Figure 4, the cell assembly method 24 is illustrated therein. The cell assembly method 24 begins with the step 26 of forming a pπsmatic steel can 10 having a big mouth open end 18 as descπbed above m connection with Figures 1-3. Steel can 10 can be formed with the pπsmatic section 12 and the cylindπcal section 14 by deep drawing can formation techniques, stamping, hydroforming, or other vaπous steel can manufactuπng techniques The method of assembly of the present invention generally requires that the steel can 10 have a pπsmatic section 12 that is non-cyhndπcal and an enlarged big mouth round opening 18 having a diameter Di that is equal to or greater than the maximum inside cross- sectional width W 2 of the pπsmatic section 12 to allow for easy assembly of the cell's internal mateπals This is particularly useful for allowing πng moulded cathode insertion techniques, in which the positive electrode, referred to as the cathode, is dispensed in the can in a preformed πng configuration. For a πng moulded cathode cell assembly, cell assembly method 24 provides the step 28 of forming one or more πng moulded cathodes. The process of forming πng moulded cathodes generally includes adding a measured charge of cathode mix to a πng shaped die set and, with the use of a die press, moulding the cathode mix into the shape of a πng The process of forming πng moulded cathodes is widely known in the art However, the moulded cathode πngs of the present invention are preferably configured to substantially conform to the shape and size of the inside of the pπsmatic section 12, and have a cylindπcal cavity extending centrally therethrough. Next, step 30 provides for the insertion of one or more πng moulded cathodes into the steel can 10. This may be accomplished by loading a fixed number of one or more cathode πngs onto a mandrel, which is then lowered into the can 10 and the cathode πngs are pressed into the can by way of an upper punch. The number of cathode πngs inserted into a particular cell may vary depending on the size of the cell. For cells having a length and width comparable to AAA and AAAA size alkaline cells, three or four cathode moulded πngs may be adequate to form the cathode for each cell. Referπng bπefly to Figure 5, the step 30 of inserting πng moulded cathodes into the can 10 is illustrated therein. Each of the moulded cathode πngs 40 has a rectangular configuration that substantially conforms to the size and shape as defined by the inteπor walls of the pπsmatic section 12. The cathode πngs 40 are inserted and stacked one on top of the other within the pπsmatic section 12, preferably in a snug-fit relationship such that each of the cathode πngs abuts each of the surrounding walls on the inside of can 10. The outer walls defining the peπmeter of each of the cathode πngs may further be impregnated with carbon. In addition, each of the cathode πngs includes a cylindπcal opening 42 extending therethrough When assembled in the can 10, the cylindπcal openings 42 align to define the anode cavity into which the separator and anode are disposed Returning to the assembly method 24 of Figure 4, subsequent to insertion of the πng moulded cathode into the pπsmatic section of can 10, an inner cylmdπcal cavity extends through the central longitudinal axis of can 10 and the cathode substantially consumes the remaining volume of the pnsmatic section 12 According to step 34, a cup-shaped separator is disposed withm the inner cylindπcal cavity Disposed inside the cup-shaped separator is the negative electrode, refeπed to as the anode, which may include a gelled anode An electrolyte solution is further disposed within can 10 Once the above-identified cell mateπals have been disposed within can 10, cell assembly method 24 provides the step 36 of reducing the size of the big mouth open end 18 by reducing the size of cylindπcal section 14 The partially assembled can 10 with reduced size round open end is shown in Figures 6 and 7 following assembly step 36, but pπor to full assembly The big mouth open end 18 is preferably reduced in size to a round open end 55 having a diameter D 2 that is less than or equal to the minimum cross-sectional width W] of the pπsmatic section 12 of can 10 The reduced size open end 55 is achieved by squeezing the cylindπcal section 14 radially inward This preferably forms a bottleneck 54 that transitions from the pπsmatic section 12 to the reduced size round open end 55 It is preferred that the big mouth open end reduction not exceed a maximum diameter reduction of thirty percent (30%) by diameter (linear) reduction or seventy percent (70%) by cross-sectional area In addition, the reduced round top end may include a substantially cylindπcal section leading to a round open end The cylindπcal section is preferably short in length and the round cover seahngly engages to the open round end The reduction of big mouth opening 18 of diameter Dj to reduced size open end 55 of diameter D 2 may be achieved by any one of a number of can closure techniques which include but are not limited to impact closing, beaded closing, rotary swaging, and roller closing One such technique for closing the opening on an electrochemical cell is disclosed in US-A-3,069,489, entitled "Container Closure" Referπng again to Figure 4, assembly method 24 further includes step 38 in which a collector is assembled in contact with the anode, and a seal and cover assembly is assembled to the reduced size round open top end 55 This step 38 closes and seals the can 10. Accordingly, the use of a can containing a big mouth open end 18 allows for easy insertion of cell mateπals, and by reducing the open end m size to a reduced size round open end allows for a round cover and seal assembly of the conventional type to close and seal the can Reduction of the open end advantageously enables a plurality of cells to interface with each other without interference According to another embodiment, the assembly method 24 of the electrochemical cell may further include the step 32 of partially reducing the round big mouth open end, following the step 30 of inserting the πng moulded cathodes into the can. This intermediate reduction step 32 provides a partially reduced round open end, through which the separator, anode, and electrolyte are subsequently inserted pursuant to step 34. According to this approach, step 36 completes the reduction in the size of the round open end to its fully reduced dimension, and the seal and cover assembly is then assembled thereto. Referπng to Figures 8 and 9, a fully assembled electrochemical cell 50 assembled according to assembly method 24 of the present invention is shown therein. The active cell mateπals are shown disposed substantially within the pπsmatic section 12 of can 10. A round cover and seal assembly 56 is assembled to the reduced size open end of can 10. With adequate reduction m size of the open end, the round cover and seal assembly 56 is equal to or less than the cross-sectional width W t of the pπsmatic section 12. Accordingly, the round cover and seal assembly 56 preferably does not extend radially beyond any of the side walls defining the pπsmatic section 12. The round cover and seal assembly 56 can be easily welded, attached by adhesive or otherwise assembled to the reduced size round top end The cover and seal assembly 56 with outer negative cover 62 is shown assembled to the top end of the cell 50. A thin layer of shπnk tube insulation 72 covers the sides of steel can 10 to electπcally insulate the metal casing of the cell. The cathode 40, preferably formed of a mixture of manganese dioxide, graphite, potassium hydroxide solution, deionised water, and other additives, is disposed between the separator 44 and inner walls of can 10 substantially throughout the pπsmatic section 12. The cup-shaped separator 44 is preferably formed of a non-woven fabπc that prevents migration of any solid particles in the cell As shown, the active mateπals of cell 50, including the anode 46 and cathode 40, are substantially disposed within the pπsmatic section 12 Cover and seal assembly 56 provides the closure to the assembly of cell 50 and includes a seal body 76 and compression member 74 The seal body 76 is generally shaped like a disk and made from electπcally non-conductive mateπal The compression member 74 is a tubular-shaped metallic component that compresses the seal body 76 around the cuπent collector 70 The seal assembly 56 also includes an outer negative cover 62 welded to the exposed end of the current collector 70 to form the cell's negative terminal The nm of steel can 10 is cπmped inwardly toward the cell body to form a seal The seal assembly 56 with cover 62 may include a conventional round assembly, such as that disclosed in US-A- 5,422,201 The bottom end 16 of cell 50 serves as a positive cover to provide a positive cell terminal The cover and seal assembly 56 includes a negative cell cover terminal 62 When using a pπsmatic can 10, cell 50 realises an increased volume in the pπsmatic section 12 in contrast to the conventional cylindπcal cell of a diameter equal to cell wall width Wi, while having a round top end 55 that easily accommodates a standard round negative cover and seal assembly 56 This allows for an increase in active cell mateπals over that of the conventional cyhndπcal cell of a size having a diameter equal to the width of the side walls of the pπsmatic section 12. It should be appreciated that the negative electrode, referred to as the anode 46, is preferably disposed in the inner cylindπcal volume of the pπsmatic section 12 of can 10, while the positive electrode, referred to as the cathode 40, fills the volume between the separator 44 and the inteπor walls of the steel can 10, including all the corners of the can 10 By providing a rectangular configuration, the volume within the pπsmatic section 12 of cell 50 is larger than that of a conventional cylindπcal cell having dimensions that would fit within the rectangular walls of cell 50. This allows for an increase in the volume of the cathode 40 as well as the anode 46. In addition, the cup-shaped separator 44 may be further disposed radially outwardly from the longitudinal axis of cell 50 so as to provide a greater anode-to-cathode interface surface areas separating the anode 46 and cathode 40 from each other It should be appreciated that the additional active mateπals, including those disposed in the comers of the cathode 40, discharge to increase the capacity of the cell 50 Cell 50 of the present invention advantageously employs a can 10 having a non- cylindπcal pπsmatic section 12 with a large big mouth opening 18 at one end for receiving active mateπals of the cell, and is particularly well suited for a πng moulded cathode assembly However, it should be appreciated that the assembly method of the present invention is likewise applicable to other cathode assembly techniques such as impact moulding In addition, the teachings of the present invention are not limited to bobbin type cells, as such teachings may be applicable to other cell assemblies such as the jelly roll configuration or stacked plate cell assemblies, among other possible cell assemblies.

Claims: Claims 1 A method of assembling an electrochemical cell, compπsing using an open-ended, non-cy ndπcal can, the mouth of the open end being generally circular, the mouth having no dimension smaller than any dimension of the radial cross-section of the can, and wherein the mouth of the can is reduced in size duπng or after the loading of the other elements, before being sealed with an end cover 2. A method of assembling an electrochemical cell compπsing the steps of providing a can having a pπsmatic section with a closed bottom end and a big mouth open top end that is substantially round with a diameter equal to or greater than the maximum mside cross-sectional width of the pπsmatic section; disposing a cathode through the big mouth open top end and into the pπsmatic section, the cathode having a cavity centrally formed therein and disposed so that the cathode consumes a substantial volume of the pπsmatic section between the cavity and inner walls of the can; disposing a separator within the cavity; disposing an anode within the separator in the cavity; reducing the size of the big mouth open top end of the can to provide a reduced size round open top end; and assembling a cover to the reduced size round open top end. 3. A cell according to claim 1 or 2, wherein the body of the can has a substantially fixed cross-section along its length. 4. A cell according to any preceding claim, wherein the mouth is coaxial with the remainder of the body of the can. 5. A cell according to any preceding claim, wherein the mouth of the can, immediately pπor to sealing, has no dimension exceeding the greatest of any of those of the radial cross- section of the can. 6 A cell according to any preceding claim, wherein the reduced mouth is substantially circular 7 A method according to any preceding claim, further compπsing the step of forming the can to include a cylindncal section that provides the mouth 8 A method according to any preceding claim, further compπsing the step of forming a tapered transition from the body of the can to the mouth 9 A method according to any preceding claim, wherein the step of reducing the mouth includes the step of rotary swaging 10 A method according to any preceding claim, wherein the can has a substantially rectangular section 11 A method according to any preceding claim, wherein a cathode is disposed into the can by a cathode πng moulding process 12 A method according to claim 11, wherein the cathode πng moulding process compπses inserting multiple cathode πngs stacked one on top of another 13. A method according to any preceding claim, further compπsing the step of dispensing a current collector m contact with the anode 14 A method according to any preceding claim, wherein the can is a steel can 15. A cell prepared by a method according to any preceding claim 16. An electrochemical cell compπsing a can which has had an oversize mouth, of dimensions greater than those of the remainder of the radial cross-section of the can, reduced to a size less than any maximum radial dimension of the can

Inventors: KELEMEN MARC P, SVEC SUSAN L, KELEMEN, MARC, P., SVEC, SUSAN, L.
Applicants: EVEREADY BATTERY INC, EVEREADY BATTERY COMPANY, INC.
Application year: 1999
Main classification: H01M2
IPC codes: H01M2