CN100466336C - Alkaline batteries with flat case - Google Patents

Abstract

An alkaline battery with a flat casing, preferably a cubic shape. The battery may have an anode comprising zinc and a cathode comprising _MnO₂ . The casing may have a relatively small overall thickness, typically about 5-10 mm. The battery contents can be supplied through an open end in the casing and an end cap assembly inserted therein to seal the battery. A gap may also exist between the separator and the cathode for inserting additional electrolyte. The end cap assembly includes a venting mechanism, preferably a grooved vent, which is activated when the gas pressure in the battery reaches a threshold level typically about 250-800 psig (1724 × ^10⁻³ - 5515 × ^10⁻³ Pa gauge pressure). The battery may have supplemental venting mechanisms, such as laser-welded areas on the casing surface, which can be activated at higher pressure levels.

Description

Alkaline batteries with flat case

The present invention relates to alkaline cells having a substantially flat outer housing. The present invention relates to alkaline cells having an anode comprising zinc, a cathode comprising manganese dioxide, and an electrolyte comprising aqueous potassium hydroxide.

Conventional alkaline electrochemical cells have an anode comprising zinc and a cathode comprising manganese dioxide. Batteries are typically formed by a cylindrical outer casing. The open circuit voltage (EMF) of a new battery in medium drain service (100-300 mA) is about 1.5 volts and the typical average operating voltage is about 1.0-1.2 volts. A cylindrical housing is initially formed by an enlarged open end and an opposite closed end. After the battery contents are provided, the end cap assembly with the insulating grommet and the negative end cap is inserted into the open end of the case. The open end is closed by crimping the edge of the housing over the edge of the insulating plug and compressing the housing radially around the insulating plug to provide a tight seal. An insulating grommet electrically insulates the negative terminal cap from the battery case. A portion of the cell casing at the opposite closed end forms the positive terminal.

A problem associated with the design of various electrochemical cells, especially alkaline cells, is the tendency of the cell to gas as the cell continues to discharge above a certain point, normally near the point at which the cell's useful capacity is completely exhausted. Electrochemical cells, particularly alkaline cells, typically have a rupturable separator or membrane in the end cap assembly. A rupturable diaphragm or membrane may be formed in a plastic insulating member, such as described in U.S. Patent 3,617,386.

The prior art discloses a rupturable vent membrane integrally formed as a thinned region in an insulating disc included in an end cap assembly. Such venting films can be oriented so that they lie in a plane perpendicular to the longitudinal axis of the cell, as shown in U.S. Patent 5,589,293, or they can be oriented so that they are inclined relative to the longitudinal axis of the cell, as shown in U.S. Patent 4,227,701. U.S. Patent 6,127,062 discloses an insulating sealing disc and an integrally formed rupturable membrane oriented vertically, ie, parallel to the central longitudinal axis of the cell. When the gas pressure in the cell rises to a predetermined level, the membrane ruptures, releasing the gas pressure to the outside environment through a small hole in the end cap.

Other types of vents are disclosed in the art for relieving gas pressure in electrochemical cells. One such vent is the resettable rubber plug, which has been used effectively for small flat rectangular nickel metal hydride rechargeable batteries. One such rechargeable battery with a resettable rubber plug is a 7/5-F6 size nickel metal hydride rechargeable battery, commercially available as battery model GP14M145 manufactured by Gold Peak Batteries, Hong Kong. Physically compress the rubber plugs to seat securely in the angled holes in the cavity or in the cell's end cap assembly. When the cell's internal gas pressure reaches a predetermined level, the pin disengages from its seat thus allowing gas to escape through the small hole below. The plug resets itself when the gas pressure in the battery returns to normal.

Alkaline electrochemical primary cells typically include zinc anode active material, alkaline electrolyte, manganese dioxide cathode active material, and an electrolyte permeable separator, typically cellulose or cellulose-based and polyvinyl alcohol fibers. The anode active material may include, for example, zinc particles mixed with a conventional gelling agent, such as sodium carboxymethylcellulose or a sodium salt of an acrylic acid polymer, and an electrolyte. The gelling agent is used to suspend the zinc particles and keep them in contact with each other. Typically, a conductive metal spike inserted into the anode active material acts as the anode current collector, which is electrically connected to the negative terminal cap. The electrolyte may be an aqueous solution of an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide or lithium hydroxide. The cathode typically includes particulate manganese dioxide as the electrochemically active material mixed with a conductive additive, typically a graphite material, to enhance electrical conductivity. Optionally, small amounts of polymeric binders such as polyethylene binders and other additives such as titanium-containing compounds can be added to the cathode.

The manganese dioxide used for the cathode is preferably electrolytic manganese dioxide (EMD), which is produced by direct electrolysis of a bath of manganese sulfate and sulfuric acid. Due to its high density and high purity, EMD is desired. The conductivity (resistivity) of EMD is relatively low. A conductive material is added to the cathode mixture to improve electrical conductivity between individual manganese dioxide particles. Such conductive additives also improve the electrical conductivity between the manganese dioxide particles and the cell casing, which is also used as the cathode current collector in conventional cylindrical alkaline cells. Suitable conductive additives may include, for example, graphite, graphite-like materials, conductive carbon powders, such as carbon black, including acetylene black. Preferred conductive materials include flaky crystalline natural graphite, or flaky crystalline synthetic graphite, including expanded or exfoliated graphite or graphitic carbon nanofibers, and mixtures thereof.

Small rectangular rechargeable batteries are now available, which are used to provide power to small electronic devices such as MP3 audio players and mini disk (MD) players. These cells are typically small cubes (rectangular parallelepipeds) in shape, somewhat the size of a chewing gum wrapper. The term "cube" as used herein shall denote its normal geometric definition, ie, "rectangular parallelepiped". Such batteries may, for example, be in the form of replaceable rechargeable nickel metal hydride (NiMH) size F6 or 7/5F6 size cubes according to the standard dimensions of such batteries specified by the International Electrotechnical Commission (IEC). The F6 size has a thickness of 6.0mm, a width of 17.0mm and a length of 35.7mm (without the label). There are variations of the F6 size, where the length can be as large as about 48.0mm. The 7/5-F6 size has a thickness of 6.0mm, a width of 17.0mm, and a length of 67.3mm. According to the IEC standard, the allowable deviations for the 7/5-F6 size are +0mm, -0.7mm in thickness, +0mm, -1mm in width, and +0, -1.5mm in length. The average operating voltage of a F6 or 7/5F6 NiMH rechargeable battery is about 1.1-1.4 volts, typically about 1.12 volts when used to power a miniature digital audio player such as an MP3 audio player or a mini disk (MD) player .

When used to power a Mini Disk (MD) player, the battery drains at a rate of about 200-250 milliamps. When used to power a digital audio MP3 player, the battery typically drains at a rate of about 100 milliamps.

There is a need for a small flat alkaline battery having the same size and shape as a small size cube-shaped (rectangular parallelepiped) nickel metal hydride battery, so that the small size alkaline battery can be used interchangeably with the nickel metal hydride battery to support small electronic devices Such as minidisk or MP3 player to provide power.

There is a need to use primary (non-rechargeable) alkaline cells, preferably zinc/ _MnO2 alkaline cells, as an alternative to small rectangular rechargeable cells, especially small size nickel metal hydride rechargeable cells.

However, a particular problem associated with the design of rectangular (cubic) primary Zn/ _MnO2 alkaline cells is the tendency of the electrodes to swell during discharge of the cell. Both the anode and cathode swell during discharge.

For a given enclosure wall thickness, it is recognized that a rectangular cell enclosure is less able to withstand a given increase in cell internal pressure (due to gassing and cathode expansion) than a cylindrical enclosure of comparable size and volume. This is due to the significantly higher circumferential stress (hoop stress) exerted on a rectangular (cubic) enclosure than on a similarly sized cylindrical enclosure for a given pressure and enclosure wall thickness. The swelling or swelling problem associated with rectangular cells can be overcome by significantly increasing the wall thickness of the enclosure. However, for rectangular cells with small overall thicknesses, such as below about 10 mm, a significant increase in the thickness of the casing walls can result in a significant reduction in the volume of available anode and cathode material. The increased wall thickness increases the manufacturing cost of the cell. In this regard it is desirable to keep the housing wall thickness to less than about 0.50 mm, preferably less than about 0.47 mm.

There is therefore a need to design small flat (non-rechargeable) alkaline cells, such as F6 or 7/5-F6 size cells, with a rectangular (cubic) casing, but still with a small casing wall thickness, where the casing does not expand significantly during normal battery use or swelling.

There is a need for such a rectangular battery as a replacement for small size flat nickel metal hydride rechargeable batteries.

The main aspect of the invention relates to primary (non-rechargeable) alkaline cells which produce hydrogen gas when discharged, wherein the cell has an outer casing (casing), end cap assembly including a venting mechanism, and when the gas pressure reaches a predetermined level The vent mechanism allows hydrogen gas to escape from the cell. The casing has at least one pair of opposing flat walls running the length of the cell.

The end cap assembly is inserted into the open end of the housing and sealed by crimping or welding to close the housing. The edge of the case at the open end can be crimped over an insulating sealing member, typically nylon or polypropylene, inserted into the open end, but preferably a metal cap is laser welded to the case to seal its open end. Alkaline batteries can be parallelepiped in shape, but desirably have a cubic (rectangular parallelepiped) shape. The housing, therefore, preferably has a cuboid shape, which does not have any overall cylindrical sections. Alkaline cells desirably have an anode comprising zinc, and an aqueous alkaline electrolyte, preferably an aqueous solution of potassium hydroxide.

The end cap assembly includes a vent mechanism and a preferably rectangular metal shroud. The cap is used to seal off the open end of the case after the battery contents have been inserted into the case. If an insulating layer is interposed between the edge of the cover and the edge of the case or the insulating sealing member and the edge of the case are crimped over the insulating layer, the metal cover can form the negative terminal of the battery. Alternatively, the cover can be welded directly to the edge of the housing. If the cover is welded to the edge of the case, a separate end cap separate from the cover can be in electrical communication with the anode for functioning as the negative terminal of the cell. The case is positive sexing and forms the positive terminal of the battery.

On the one hand the metal cap is welded directly to the case edge to close the case open end, and the plastic packing sealant is stacked on top of the metal cap and the negative end plate in turn stacked onto the plastic packing. On the other hand paper gaskets are used instead of plastic packing.

A cathode comprising _MnO2 is inserted, preferably in the form of multiple densified blocks or discs. The cathode blocks or disks are preferably rectangular, each having a central hollow core running through the thickness of the block. Insert blocks so they are stacked on top of each other. The blocks are aligned along the length of the cell so that their outer surfaces are in contact with the inner surface of the case. The stacked cathode blocks form a central hollow core running along the longitudinal axis of the cell. The central hollow core in the stacked cathode blocks forms the anode cavity. The inner surface of each cathode block, which defines the central hollow core (anode cavity) in the block, is preferably a curved surface. Such a curved inner surface improves the mechanical strength of the block during transfer and handling and also provides a more uniform contact between the electrolyte permeable separator and the cathode. The separator is inserted into the central hollow core (anode cavity) of the cell such that the outer surface of the separator abuts and intimately contacts the inner surface of the cathode. An anode slurry including zinc particles is inserted into the anode cavity and a separator membrane provides the interface between the anode and cathode. The end cap assembly has an elongated anode current collector inserted into the anode slurry and in electrical communication with the negative terminal of the cell. The end cap assembly has an insulating sealing member that insulates such anode current collector from the outer casing of the cell.

The anode cavity preferably has an elongated or rectangular configuration when viewed in plan view through a cross-section of the cathode block taken along a plane perpendicular to the longitudinal axis of the cell. The outer housing (casing) is desirably steel, preferably nickel-plated steel. The housing wall thickness is desirably about 0.30-0.50 mm, typically about 0.30-0.45 mm, preferably about 0.30-0.40 mm, more desirably about 0.35-0.40.

In one aspect a reusable or reactivatable vent, preferably a resettable cock vent mechanism can be used as the primary vent mechanism. The resettable plug is preferably designed to allow for when the internal gas pressure of the cell reaches about 100-300 psig (689.5×10 ³ -2069×10 ³ Pascal gauge), desirably about 100-200 psig (689.5×10 ³ -1379×10 ³ Pascal Gauge pressure) is activated at the threshold level pressure P1.

In another aspect, another spaced groove vent, preferably a single continuous groove vent (embossed vent) with at least one stamped or scored area on the housing surface may Used as the main exhaust mechanism. The grooved vent may be stamped, cut or scored into the shell surface so the underlying thinned region ruptures at a pressure P1 of about 250-800 psig (1724 x 103 ^- 5515 x ¹⁰³ Pascal gauge). The resettable pins can be eliminated in such a design. Preferably, the air outlet of the groove is arranged close to the closed end of the housing and close to the positive end. Groove boundaries can be closed or open. The groove may be straight or substantially straight, preferably parallel to the housing edge. The groove width is typically small, for example under about 1 mm. However, the term "groove" or "groove vent" as used herein is not intended to be limited to any particular width or shape, but rather includes any depression in the cell casing that results in when the gas pressure in the cell reaches The underlying material region that is thinned at the target threshold level is expected to fracture or rupture. By way of non-limiting example, in a 7/5-F6 size rectangular cell, the recessed vent may be located on the wide face of the case and parallel to the wide edge, preferably near the closed end of the case. There may be multiple such groove vents, but desirably only a single groove vent is on the broad side of the housing and is about 8mm in length and about 5-10mm from the closed end of the housing.

In such an aspect of the invention, the thinned material under the groove vent is designed to burst when the gas pressure in the cell reaches about 250-800 psig (1724 x ^{103 -} 5515 x ¹⁰³ Pascal gauge) Burst at pressure P1. To achieve a burst pressure in the range of about 250-800 psig (1724 x 10 ³ -5515 x 10 ³ Pascal gauge), the thickness of the thinned material under the groove may be about 0.04-0.15 mm. Alternatively, the thinned material below the grooved vent can be designed so that when the gas pressure in the cell reaches about 400-800 psig (2758×10 ³ -5515×10 ³ Pascal gauge), desirably about 400-600 psig ( 2758×10 ³ -4136×10 ³ Pascal gauge pressure) when the design burst pressure ruptures. To achieve a burst pressure of 400-800 psig (2758 x 10 ³ -5515 x 10 ³ Pascal gauge), the thickness of the thinned material under the groove may be about 0.07-0.15 mm.

Groove vents may be prepared by imprinting the housing surface with a die, preferably a die with a knife edge. The arbor is held against the inner surface of the housing as the stamping die stamps into the outer surface of the housing. The grooves may conveniently be cut in a V shape with sides of equal length or in a V shape with sides of unequal length. In the former case the sides forming the V-shaped groove desirably form an acute angle of about 40 degrees and in the latter case they form an angle of preferably about 10-30 degrees.

In conjunction with the recessed exhaust there may be a supplemental exhaust system comprising one or more laser welds securing the metal cover to the housing. Such welds may comprise one or both of a weak laser weld and a strong laser weld which may be designed to rupture at a pressure higher than the rupture pressure P1 of the thinned region below the groove vent. Such laser welds are preferably produced using a Nd:Yag laser.

In aspects of the invention there may be only one laser weld, ie a strong weld that secures the peripheral edge of the entire metal cover to the housing. Strong welds can be used as supplemental venting systems designed to rupture under catastrophic conditions, such as if the battery is inadvertently subjected to recharging at particularly high currents or under particularly abusive conditions, causing gas production in the battery to suddenly rise to about 800psig-2500psig (5515×10 ³ -17235×10 ³ Pascal gauge pressure) level.

Therefore, in a preferred aspect there is at least a single groove vent stamped or cut into the battery case. A single groove vent can be used as the main venting mechanism for the cell, where the thinned material under the groove is designed to rupture if the gas in the cell rises to about 250-800 psig (1724×10 ³ -5515×10 ³ Pascals gauge), more typically 400-800 psig (2758×10 ³ -5515×10 ³ Pascals gauge). And in conjunction there is a supplemental exhaust system that includes strong laser welds that secure the edge of the metal cover to the casing. Such intense laser welds are designed to break or rupture in catastrophic conditions, where the gas in the cell suddenly rises to levels of about 800 psig-2500 psig (5515×10 ³ -17235×10 ³ Pascal gauge). In such a case the gas in the cell quickly escapes by rupture and the internal pressure of the cell immediately returns to the nominal level.

In one aspect of the invention, the cell is balanced so that the cathode is in excess. The cell is desirably balanced so that the ratio of the theoretical capacity of _MnO2 (based on a theoretical ratio of 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on a theoretical ratio of 820 mAmp-hr/g zinc) is about 1.15-2.0, Desirably about 1.2-2.0, preferably about 1.4-1.8. It has been determined that the design of flat alkaline cells here reduces the amount of overall swelling at higher ratios of _MnO2 theoretical capacity to zinc theoretical capacity. The above ratio of _MnO theoretical capacity to zinc theoretical capacity can feasibly be as high as about 2.5 or even up to about 3.0 to reduce overall swelling, but cell designs at such higher ratios greater than about 2.0 more significantly reduce cell capacity and thus From that point of view less is desired. Not sure why this happens. It may be due in part to the fact that nearly all of the zinc is excreted. In such cases less, if any, zinc hydroxide intermediate is left in the anode, which can cause swelling.

The ratio of anode thickness to casing exterior thickness is desirably about 0.30-0.40. (Such thicknesses are measured through the outer thickness of the battery in a plane perpendicular to the longitudinal axis of the battery.) Thus controlling the swelling of the battery during discharge allows flat or rectangular alkaline batteries to be used as primary batteries for electronic devices such as portable digital audio players, etc. power supply.

In a specific aspect, the alkaline cell has an overall shape of a cuboid (rectangular parallelepiped), typically with an external thickness of about 5-10 mm, especially about 5-7 mm in thickness. The outer thickness is measured by the distance between the outer surfaces on opposite sides of the casing, which defines the short dimension of the cell. In such an embodiment the primary (non-rechargeable) alkaline cells of the present invention can be used, for example, as a replacement for small size flat rechargeable cells. In particular such alkaline primary cells can be used as replacements for the same rechargeable nickel metal hydride cells, eg 7/5-F6 size rectangular rechargeable nickel metal hydride cells.

In one aspect of the invention, the separator can be fabricated in the shape of a pouch having an open end and an opposite closed end. Such a separator can easily be formed by winding a single sheet of separator material and closing one end with an adhesive or by heat sealing. After the cathode disk is inserted into the battery case, the wound separator is then inserted so that the separator surface faces the exposed cathode surface. Preferably, the width of the separator is somewhat smaller than the width of the total anode cavity. This results in a gap between one short side of the separator and the cathode disc. The gap is about 2-4 mm, preferably about 2-3 mm. Anode material can then be filled into the anode cavity through the separator membrane open end. This results in a case filled with anode material, cathode material, and a separator in between, with a gap (void space) between one short side of the separator and the cathode.

Additional alkaline electrolyte solution can now be added to the interior of the battery by pouring it into the gap. It may be necessary to add a small amount of additional alkaline electrolyte solution to the cell after the anode and cathode are in place in the cell. Additional electrolyte can be added in small increments to this gap between the separator and cathode, desirably with short time intervals between incremental electrolyte dispenses. In an alternative embodiment a portion of additional electrolyte may be added to the gap after the cathode is in place but before the anode material is inserted into the anode cavity. The anode material is then inserted into the anode cavity of the cell and thereafter additional electrolyte can be added to the gap. After the final amount of alkaline electrolyte is added to this gap between the separator and cathode, the anode swells to push the separator surface flush against the cathode, thus causing the gap to disappear.

Additional alkaline electrolyte solutions can help improve anode utilization and overall battery performance. It can also be a factor that tends to hinder battery swelling. If additional electrolyte is added to the gap, it is preferably added in dispense increments with a sufficient time delay between dispenses, eg, about 1-4 minutes, to allow for electrolyte absorption. Such a process allows absorption of added electrolyte to the anode and cathode without causing electrolyte to enter the end cap assembly cavity, ie, flood the space above the anode. Such flooding can cause wetting of the metal cover surfaces and edges sufficiently to interfere with uniform laser welding of the metal cover to the housing.

Figure 1 is a perspective view of a flat alkaline cell of the present invention showing the negative terminal of the cell.

Figure 1A is a perspective view of the flat alkaline battery of Figure 1 showing the positive terminal of the battery.

FIG. 2 is a cross-sectional view of the battery shown in FIG. 1A taken along viewing line 2-2.

Figure 2A is a cross-sectional view of the battery shown in Figure 1 taken along viewing line 2-2 and showing the modified plug design.

FIG. 3 is a cross-sectional view of the battery shown in FIG. 1A taken along viewing line 3-3.

FIG. 3A is a cross-sectional view of the battery shown in FIG. 1A taken along viewing line 3-3 and showing the modified plug design.

Figure 4 is an exploded view of the components making up the end cap assembly for a flat alkaline cell.

Figure 4A is a perspective view of the improved plug shown in Figures 2A and 3A before it is compressed into its housing cavity.

Figure 4B is a plan view of a cell cross-section taken along line 4B-4B of Figure 1A in a plane perpendicular to the longitudinal axis of the cell to show the elongated anode cavity.

Figure 4C is a plan view of a cross-section of a cell showing another embodiment of an elongated anode cavity.

Figure 4D is a plan view showing a cross-section of a third embodiment of an elongated anode cavity.

Figure 5 is an exploded view showing the installation of the battery contents and end cap assembly into the battery case (casing).

Figure 6 is a plan view of a metal cover plate laser welded along its edges with strong and weak welds to the inside surface of the battery case shown.

6A is a plan view of a metal cover plate shown laser welded along its edge with strong and weak welds to the battery case curled edge.

Fig. 7 is a view of a battery case showing an embodiment of strong and weak welds therein.

Figure 7A is a view of a battery case showing an embodiment in which strong and weak welds are bent.

Fig. 8 is a side view of the cell showing the recess in the casing showing the underlying region of the thinned material.

Figure 8A is a side view of a cell showing multiple grooves in the housing, where each groove forms an underlying region of thinned material.

Figure 9 is a cross-sectional view of the representative groove shown in Figures 8 and 8A.

10 is a top plan view of a metal cover laser welded to the battery case shown in FIG. 10A.

Figure 10A is a side view of an embodiment of a flat alkaline cell showing a single grooved vent on the broad side of the case.

Fig. 11 is a cross-sectional view along the broad side of the battery shown in Fig. 10A.

Figure 12 is a cross-sectional view along the short side of the cell shown in Figure 10A.

Figure 13 is an exploded view of the components making up the end cap assembly for the flat cell shown in Figure 10A.

Figure 14 shows the fabrication of the battery separator used in Figure 10A from a single sheet of separator material.

Figure 14A shows a method of forming a wound separator sheet.

Figure 14B shows the completed wound separator having an open end and an opposite closed end.

Figure 15 shows another type of V-shaped groove cut for a grooved vent.

Figure 16 shows an embodiment where there is a gap between the short side of the separator and the cathode.

Figure 17 shows an alternative embodiment of a cell similar to Figure 11, except that paper gaskets are stacked on welded metal covers instead of plastic fillers.

A specific embodiment of the flat alkaline cell 10 of the present invention is shown in FIGS. 1-5. Battery 10 has at least two flat opposing sides that are parallel to the longitudinal axis of the battery. The cell 10 is preferably rectangular, ie cuboid, as shown in Figures 1 and 1A. The term "cube" as used herein shall mean geometrically defined, which is a rectangular parallelepiped. However, the cell 10 can also be a parallelepiped. The outer housing 100 shown in the figures is preferably cuboid in shape and therefore does not have any overall cylindrical cross-section. The thickness of the cell 10 is typically less than its width and the width less than its length. When the battery thickness, width and length are of different dimensions, the thickness is normally considered to be the smallest of these three dimensions.

The battery 10 preferably includes a cuboid-shaped casing (casing) 100, preferably of nickel-plated steel. The interior surface of housing 100 is preferably coated with a layer of a solvent-based carbon paint, such as that available under the trade designation TIMREX E-LB. In the embodiment shown in the figures, housing (housing) 100 is bounded by a pair of opposing large flat walls 106a and 106b; a pair of opposing small flat walls 107a and 107b; a closed end 104; The thickness of the cell is defined by the distance between the outer surfaces of walls 106a and 106b. The width of the cell is defined by the distance between the outer surfaces of walls 107a and 107b. The housing 100 is desirably coated on its inner surface with a layer of carbon or indium to improve electrical conductivity. The contents of the cell, including anode 150, cathode 110 and separator 140 therebetween, are provided through open end 102. In a preferred embodiment the anode 150 comprises granular zinc and the cathode 110 comprises _MnO2 . An aqueous solution of potassium hydroxide forms part of the anode and cathode.

Cathode 110 may be in the form of a plurality of blocks 110a having a hollow central core 110b through its thickness, as best shown in FIG. 5 . Cathode block 110a preferably has an overall rectangular shape. Cathode slabs 110a are inserted into casing 100 and stacked vertically one on top of the other along the length of the cell as shown in FIGS. 2 , 3 and 5 . Each cathode block 110a may be compacted after it is inserted into the casing 100 . Such recompression ensures that the outer surface of each cathode block 110 a is in intimate contact with the inner surface of the casing 100 . Preferably, the hollow central core 110b in the cathode block 110a is arranged to form one continuous central core along the longitudinal axis 190 of the cell for receiving the anode slurry 150 . Optionally, the cathode block 110a closest to the closed end 104 of the casing 100 may have a bottom surface that adjoins and covers the inner surface of the closed end 104 .

Cathode block 110a may be mold cast or compression molded. Alternatively, cathode 110 may be formed from a cathode material that is extruded through a nozzle to form a single continuous cathode 110 with a hollow core. Cathode 110 may also be formed from a plurality of blocks 110 a and hollow core 110 b , where each block is extruded into casing 100 .

After insertion of the cathode 110, an electrolyte permeable separator 140 is then disposed in the central core 110b of each block 110a such that the outer surface of the separator 140 abuts the inner surface of the cathode, as shown in FIGS. 2 , 3 and 5 . The inner surface of each cathode block 110a, which defines the hollow central core 110b, is preferably a curved surface. Such a curved inner surface improves the mechanical strength of the block during transfer and handling and also provides a more uniform contact between the separator 140 and the cathode 110 .

The central core 110b of the block 110a is arranged as described above to form one continuous core. After insertion of the separator 240 , the successive cores form the anode cavity 155 containing the anode material 150 . The anode cavity is in the central core of the cathode block 110a, which is devoid of cathode material. The anode cavity 155 has an elongated or rectangular shape when viewed in plan view (FIG. 4B) in cross-section of the cathode block 110a taken along a plane perpendicular to the longitudinal axis 190 of the cell. The cross-section of the anode cavity 155 defined by the bounding perimeter 156 may be elliptical or substantially elliptical. The long dimension D1 of cavity 155 is greater than its short dimension D2. Cavity 155 may thus have a diameter (or width) D1 that is greater in its diameter (or width) along a planar path parallel to the cell's broad side (106a or 106b) than in a planar direction parallel to the cell's narrow side (107a or 107b). ) D2 is large. Thus, by way of non-limiting example, the anode cavity 155 may take the shape of an ellipse or appear to be substantially elliptical when viewed in cross-section along a plane perpendicular to the central longitudinal axis 190 . The relatively long boundary edges 158a and 158b of the anode cavity may be flat or substantially flat when viewed in cross-section (FIG. 4B), so the overall configuration is not a perfect ellipse, but nevertheless has an elongated or rectangular shape as shown.

The cavity 155 has an elongated or rectangular shape when viewed in a cross-section ( FIGS. 4B , 4C and 4D ) obtained by cutting the cathode block 110a in a plane perpendicular to the cell's central longitudinal axis 190 . Such an elongated shape may be an elongated polygon or a rectangle, as shown in Figure 4C. The axes defining the long dimension D1 and short dimension D2 of cavity 155 defined by boundary perimeter 156 may be inclined, as shown in FIG. 4D . Preferably, cavity 155 has at least a portion of its bordering perimeter 156 that is curved when viewed in a cross-section ( FIG. 4B ) obtained by cutting cathode block 110 a in a plane perpendicular to cell central longitudinal axis 190 ( FIG. 1A ). Cavity 155 desirably has a rectangular configuration. In a preferred embodiment substantially all of the boundary perimeter 156 defining cavity 155 is curved. It is particularly desirable that at least the opposing surfaces 157a and 157b of the cavity 155 closest to the opposing narrow sides 107a and 107b of the cell be curved, as best shown in Figure 4B. Preferably, substantially all of the perimeter 156 of the cavity 155 is curved when viewed in cross-section as described above. The relatively long edges 158a and 158b are preferably outwardly curved (convex) when viewed from the outer housing 100, as shown in FIG. 4B. However, long edges 158a and 158b may be flat or substantially flat. Alternatively, the long edges 158a and 158b may be slightly curved inward (concave) or slightly outward (convex) or may have a curved curvature, eg, with alternating convex and concave surfaces. Similarly short edges 157a and 157b may be slightly inwardly curved (concave) or slightly outwardly curved (convex) or may have a curly curvature, for example with alternating convex and concave surfaces. In any cross-section of cathode block 110a taken along a plane perpendicular to the longitudinal axis of the cell, there is a long dimension D1 of cavity 155 representing its greatest length in that plane and a short dimension D2 representing its greatest width in that plane. The major diameter (D1) is normally in a direction along a plane parallel to the cell's broad side (106a or 106b) and the minor diameter (D2) is in a direction along a plane parallel to the cell's narrow side (107a or 107b), as shown in Figure 4B Show. Cavity 155 has at least some curvature when viewed in cross-section as described above and is characterized by a ratio D1/D2 greater than 1.0, reflecting its elongated or rectangular configuration. The shape of cavity 155 desirably has a symmetrical rectangular configuration with a D1/D2 ratio greater than 1.0 when viewed in cross-section along a plane perpendicular to longitudinal axis 190 . In such a case dimensions D1 and D2 are perpendicular to each other, as shown in Figure 4B. By way of specific, non-limiting example, the shape of cavity 155 is oblong in shape when viewed in such cross-section and may be elliptical or substantially elliptical.

Anode 150 is preferably in the form of a gelled zinc slurry comprising zinc particles and an aqueous alkaline electrolyte. The anode slurry 150 is poured into the central core 155 of the cell along the longitudinal axis 190 of the cell. The anode 150 is thus separated from direct contact with the cathode 110 by the separator 140 in between.

After the battery contents are provided, the battery assembly 12 ( FIG. 4 ) is then inserted into the open end 102 to seal the battery and provide the negative terminal 290 . The closed end 104 of the case can serve as the positive terminal of the battery. The closed end 104 may be stretched or stamped to provide a protruding positive pad (pip) or an end plate 184 with a protruding pip 180 may be welded to the closed end 104 of the housing, as shown in FIG. 1A .

The components that make up a particular embodiment of the end cap assembly 12 are best shown in FIG. 4 . The end cap assembly 12 includes an elongated anode current collector 160; an insulating sealing member 220; a metal cover 230 positioned above the sealing member 220; a metal rivet 240 partially passing through the insulating sealing member 220; a plastic spacer 250 which separates the rivet 240 and metal shroud 230 ; rubber vent plug 260 in cavity 248 of rivet 240 ; vent standoff cap 270 on rubber plug 260 ; plastic packing seal 280 ; and negative end plate 290 on plastic packing 280 .

It is recognized herein that the rubber vent plug 260 is located in the cavity 248 in the rivet 240, and that the vent bracket cap 270 on the rubber plug 260 is disclosed and compared to a commercial 7/5-F6 manufactured by Gold Peak Batteries, Hong Kong. Size Rectangular Rechargeable Nickel Metal Hydride Battery Model No.GP14M145 for use in combination. However, the applicants of the present patent application herein determined that the end cap assembly as a whole in this Nickel Metal Hydride Rechargeable Cell Model No. GP14M145 caused corrosion and promoted outgassing if applied to a primary zinc/ _MnO2 alkaline cell. Since the widest portion of the current collector is very close (less than about 0.5mm) to the inner surface of the battery case, such corrosion was found to occur between the elongated current collector and the inner surface of the battery case. It is recognized that the wide portion of the collector 160, ie the flange 161, is used in conjunction with the resettable vent plug design. Such a wide portion of the collector (flange 161 ) is required due to the fact that the collector is rivet-connected to the underside of the insulating sealing member 220 . Therefore, the flange 161 must be wide enough to secure the base 246 of the rivet 240 thereto. The edge of the flange 161 thus terminates access to the inner surface of the housing 100 if the battery 10 is a flat battery of small size, for example a cube-shaped battery with an overall thickness of about 5-10 mm.

Applicants improved the subassembly comprising current collector 160 and insulating sealing member 220 by redesigning insulating sealing member 220 - providing it with surrounding skirt 226. An insulating sealing skirt 226 surrounds the widest part of the anode current collector 160 , ie the flange 161 . The insulating skirt 161 thus provides shielding between the edge of the collector flange 161 and the inner surface of the housing 100 . Determining the insulating skirt 161 reduces the generation of corrosive chemicals, typically metal-containing complexes or compounds, in the space between the flange 161 and the inner surface of the housing 100 during battery discharge. Such corrosive chemicals, if produced in certain quantities, can interfere with battery performance and promote battery gassing. Likewise, the widest portion of the anode current collector 160, ie, the flange 161, is about 0.5-2 mm, preferably about 0.5-1.5 mm from the inner surface of the housing in the modified design described herein. It was determined that this combined with the use of an insulating sealing skirt 226 around the collector flange 161 prevents the generation of any significant amount of corrosive chemicals between the collector wide portion (flange 161 ) and the housing 100 inner surface. This improved design of the present invention in turn makes the resettable rubber vent plug assembly suitable as a useful venting mechanism for the flat alkaline primary cells described herein.

The components of the end cap assembly 12 best shown in FIGS. 4 and 5 can be assembled in the following manner: the anode current collector 160 comprises a monolithic process at its bottom end terminating in a tip 163 and at its top end extending outwardly. An elongated shaft or wire 162 terminating in flange 161, which is preferably at a suitable angle to shaft 162. Thus when the current collector 160 is inserted into the anode 150 , the edge of the outwardly extending flange 161 may be closer to the inner surface of the casing 100 than the shaft 162 . The insulating sealing member 220 has a top plate 227 and an opposite open bottom 228 . The insulating seal member 220 is preferably nylon 66 or nylon 612, which is durable, alkali resistant, and hydrogen permeable. Alternatively, insulating sealing member 220 may be composed of polypropylene, talc filled polypropylene, sulfonated polyethylene, or other polyamide (nylon) grades, which are durable and hydrogen permeable. The insulating member 220 is preferably rectangular so it can fit snugly in the open end 102 of the housing 100 . Opposing side walls 226 a and opposing end walls 226 b extending from a top end 227 of insulating member 220 form a downwardly extending skirt 226 around top plate 227 . The skirt 226 delimits an open bottom 228 of the insulating sealing member 220 . There is an aperture 224 through the top plate 227 . There is a metal shield 230, which may be a metal plate with an aperture 234 therethrough. There is a metal rivet 240 having a head 247 and a base 245 . Rivet 240 may be nickel plated steel or stainless steel. Rivet 240 has a cavity 248 in head 247 . Cavity 248 passes completely through rivet head 247 and rivet shaft 245 . The flange 161 of the current collector 160 is inserted into the open bottom 228 of the insulating sealing member 220 so the flange 161 of the current collector 160 is surrounded and protected by the insulating skirt 226 of the sealing member 220 . As shown in FIG. 4, the flange portion 161 of the current collector 160 has an aperture 164 therethrough. The base 246 of the rivet 240 can be connected to the flange 161 through the aperture 164 and the rivet to keep the current collector 160 electrically connected to the rivet.

In such an embodiment the insulating skirt 226 provides shielding between the flange 161 of the current collector and the inner surface of the battery case 100 . It has been determined that a narrow gap, such as less than about 0.5 mm, between any surface of the anode current collector 160 and the inner surface of the battery housing 100 can provide an area where corrosive by-products can be produced during alkaline battery discharge. This in turn can passivate adjacent regions of the anode current collector 160 and promote gassing. The downwardly extending skirt 226 of the insulating sealing member 220 desirably surrounds an extended portion of the current collector 160 such as the integral flange 161 outwardly, thus providing shielding between the widest portion of the current collector 160 and the housing 100 . Make sure this dissipates corrosion problems and reduces outgassing. Applicants improved the design by redesigning the preferred widest part of the current collector by providing a shield, ie insulating skirt 226, around the widest part, ie the flange 161 of the anode current collector 160. The placement and effect of the skirt 226 is described in more detail in the following paragraphs herein. In applicant's improved design described herein, the widest portion of the anode current collector 160, ie, the flange 161, is about 0.5-2 mm, preferably about 0.5-1.5 mm, from the inner surface of the housing. Likewise, surrounding insulating skirt 226 provides shielding between collector flange 161 and housing 100 . These design features were determined to dissipate the corrosion problem and make the resettable rubber vent plug assembly suitable as a useful venting mechanism for the flat alkaline primary cells of the present invention.

In forming the end cap assembly 12 , the flange portion 161 of the current collector 160 is arranged so that the aperture 164 therebetween is aligned with the aperture 224 through the top plate 227 of the insulating sealing member 220 . The metal cap 230 is disposed on the top plate 227 of the insulating sealing member 220 so that the aperture 234 through the metal cap 230 is aligned with the aperture 224 . The plastic shim disc 250 is inserted over the metal cover 230 so that the aperture 252 through the shim disc 250 is aligned with the aperture 234 of the metal cover 230 . In a preferred embodiment ( FIG. 4 ), the base 246 of the rivet 240 is passed through the small hole 252 of the plastic spacer 250 and also through the small hole 234 of the metal cover 230 . The base 246 of the rivet 240 is also passed through the aperture 224 of the insulating sealing member 220 and the aperture 164 of the collector flange 161 . The plastic spacer 250 separates the rivet 240 from the metal cover 230 . The base 246 of the rivet shaft 245 extends through the aperture 224 of the insulating sealing member 220 and the underlying aperture 164 in the top flange portion 161 of the anode current collector 160 . The base 246 of the rivet shaft may be hammered into place against the bottom surface of the collector flange 161 using an orbital riveter or the like. This locks the rivet shaft in position in the aperture 224 of the insulating sealing member 220 and also secures the current collector 160 - rivet shaft 245 . This maintains permanent electrical contact of the current collector 160 with the rivet 240 and prevents dislodgement or dislocation of the rivet shaft 245 from the aperture 224 of the insulating sealing member 220 . The rivet head 247 is seated snugly on the plastic spacer 250 . This forms a subassembly comprising rivets 240 , plastic spacer 250 , metal cap 230 , insulating sealing member 220 and anode current collector 160 . Subassemblies can be stored until ready for further assembly.

The assembly process is completed by inserting the rubber vent plug 260 into the cavity 248 in the rivet head 247 . The peg 260 is preferably truncated tapered and designed to fit snugly within the cavity 248 of the rivet head 247 . The plug 260 is preferably a compressible, resilient material that is resistant to alkaline electrolytes. A preferred material for the plug 260 is rubber, preferably neoprene or EPDM (ethylene-propylene-diene terpolymer) rubber or other alkali resistant compressible rubber. The surface of the plug 240 is preferably coated with a non-wetting agent such as Teflon (polytetrafluoroethylene), asphalt or polyamide. Metal vent standoff cap 270 is then inserted over plug 260 . Squeeze the vent standoff cap 270 onto the plug 260 with sufficient force to compress the plug by approximately 0.55mm. It was determined that this provided a seal that could withstand internal gas pressure buildup of approximately 200 psig (13.79 x ¹⁰⁵ Pascals). The pin can be adjusted to 260 compression so the seal can withstand typically about 100-300 psig (6.895× ¹⁰ 5 -20.69×10 ⁵ Pascal gauge), desirably about 100-200 psig (6.895×10 ⁵ -13.79×10 ⁵ Pascal gauge ) internal pressure. Higher degrees of compression of the plug 260 are also possible to subject the seal to higher pressures, ie, greater than 300 psig (20.69 x ¹⁰⁵ Pascal gauge), if desired. An opposite reduced compression of the plug 260 is possible, if desired, so that the seal is maintained up to a pressure threshold at any desired value below 100 psig. The base 273 of the vent standoff cap 270 may have several downwardly extending sections that fit into indentations in the top surface of the plastic spacer 250 when the vent cap 270 is pressed onto the plug 260 or Crack 253. This is best shown in Figure 5. The vent cap 270 is welded to the rivet head 247 after the vent standoff cap 270 has been inserted over the pin 260 , thus compressing the pin in the rivet head cavity 248 . The plug 260 is thus held compressed in the rivet head cavity 248 . A plastic packing member 280 is placed on the vent cap head 271 . Vent cap head 271 protrudes through a small hole 282 in plastic packing 280 . The terminal end plate 290 (negative end) is then soldered to the vent cap head 271 . Vent cap 270 is thus welded to both end plate 290 and rivet 240 . Terminal end plate 290 is constructed of conductive metal with good mechanical strength and corrosion resistance, such as nickel-plated cold-rolled steel or stainless steel, preferably nickel-plated mild steel. Thus, the completed end cap assembly 12 is formed with the terminal end plate 290 in permanent electrical contact with the current collector 163 .

The completed end cap assembly 12 is then inserted into the open end 102 of the housing 100 . The current collector shaft 162 penetrates the anode slurry 150 . The edge of the metal cover 230 is welded, preferably by laser welding, to the top peripheral edge 104 of the housing. This securely holds the end cap assembly 12 in place and seals the open end 102 of the housing, as shown in FIGS. 1 and 1A. End plate 290 is in electrical contact with current collector 160 and anode 150, and thus forms the negative cell terminal for the zinc/ _MnO2 alkaline cell embodiments described herein. It is recognized that the negative end plate 290 is electrically insulated from the housing 100 by the plastic filler 280 . Rivet 240 and anode current collector 160 are electrically insulated from casing 100 by plastic gasket 250 and insulating sealing member 220 . As shown in Figures 1A, 2 and 3, a standoff 180 at the opposite closed end of the housing 100 forms the positive terminal of the battery. Standoff 180 may be integrally formed from closed end 104 of the housing or may be formed from a separate plate 184 that is individually welded to the closed end, as shown in FIG. 1A . The completed cell is shown in perspective in FIGS. 1 and 1A and in cross-section in FIGS. 2 and 3 .

In operation during battery discharge or storage, the plug 260 disengages in the rivet head cavity 248 if the gas pressure in the battery builds up above a design threshold level. This would allow gas to escape from the interior of the battery through the rivet head cavity 248 , then through the vent aperture 272 of the vent cap 270 and to the outside environment. The plug 260 resets in the rivet head cavity 248 when the pressure in the battery is reduced.

As an added safety feature, the battery may have a second vent that acts as a supplemental resettable plug vent 260 . The supplemental vent can be designed to activate in a catastrophic situation, for example if the user inadvertently attempts to recharge the primary battery 10 with a battery charger for flat rechargeable batteries for an extended period of time. The battery 10 of the present invention is designed to be a primary (non-rechargeable) battery. Despite the extensive written notice on the battery label that the battery should not be recharged, it is always possible that a user with a conventional flat battery charger, such as a charger designed to recharge flat nickel metal hydride batteries, inadvertently attempts to recharge Battery. If the battery is abused in this way by attempting to recharge for an extended period of time, there is a danger that the internal pressure level may rise dramatically.

If the battery 10 is inadvertently subjected to recharging (despite wishing it were the original (non-rechargeable) battery), when the internal gas pressure reaches the design threshold, approximately 100-300 psig (6.895×10 ⁵ -20.69×10 ⁵ Pa When the pressure is high, the plug vent 260 is disengaged, thereby releasing the pressure. If the pressure builds up again when charging is continued for an extended period of time, the plug 260 is disengaged again. This process of unsealing and resetting the pins can be repeated many times, resulting in a pulsed release of gas pressure from inside the cell. Under such abuse conditions there is a possibility that the KOH electrolyte will gradually enter and crystallize in the free space between the plug 260 and the inner surface of the rivet head cavity 248 that houses the plug 260 . (Plug 260 is held compressed in rivet head cavity 248 by vent cap 270 welded to the rivet head). This accumulation of crystalline KOH reduces the amount of free space between the plug 260 and the inner surface of the vent cap 270 . This makes the plug 260 progressively more difficult to dislodge as the recharging process continues, since there is less free space available for the plug 260 to expand when the threshold gas pressure is reached. Accumulation of crystalline KOH in the small amount of free space in rivet head 248 may also prevent proper venting of gases through vent apertures 272 in vent cap 270 .

Several improvements in the design are proposed here to reduce the detrimental effect of such KOH crystallization buildup between the plug 260 and the inner surface of the vent cap 270 .

The exhaust system of the present invention may include primary and supplemental exhaust mechanisms. The main exhaust mechanism is activated when the gas pressure in the battery accumulates to the design pressure threshold level P1. It is desirable to have a supplemental venting mechanism. The supplemental venting mechanism is activated at a higher pressure level P2 if the main venting mechanism fails to operate properly or if the battery experiences an abuse condition, resulting in a rapid build-up of gas pressure. One such abuse condition can occur, for example, if a battery is inadvertently subjected to charging for an extended period of time. In one embodiment of the present invention a resettable plug 240 is used as the primary venting mechanism, which is activated at a design threshold pressure P1 of about 100-300 psig. The supplemental vent mechanism may be a weak laser weld anywhere in the housing 100 or end cap assembly 12 cutout. The weak laser weld is designed to rupture when the gas pressure in the cell reaches a higher pressure P2, desirably about 400-800 psig. There may be strong welds, preferably adjacent to weaker welds. Strong welds are designed to rupture at still higher pressures P3, desirably about 800-2500 psig.

An embodiment supplemental exhaust system may be provided by forming a weak laser weld along a portion of the laser weld interface between the metal cover 230 and the inner surface of the housing 100. (The metal cap 230 is used to seal the open end 102 of the housing 100.) Preferably, a weak laser weld 310a may be applied between a major portion of one of the metal cap long edges 230a and the housing edge 108a, as shown in FIG. A weak laser weld 310a may be applied so that the weld thickness is such that it fractures or bursts as desired when the gas in the cell builds up to a pressure of about 400-800 psig ( ^{2748x103-5515x103 Pascal} ). The penetration depth of weak welds can be adjusted to achieve the desired bursting pressure. Burst pressures of about 400-800 psig (2748 x ^103-5515 x ¹⁰³ pascal gauge) can be achieved with laser weld penetration depths of about 2-4 mils (0.0508-0.102 mm). The weak weld may desirably run along a substantial portion of at least one long edge 230 a of the metal cover 230 . Preferably, the weak weld begins at point 312a, which is at least about 1 mm from the corner of housing 100 where short edge 108c and long edge 108a meet. Thus, the length of the weak weld for a flat 7/5-F6 cell may be at least about 10 mm, typically about 13 mm.

The remaining peripheral interface between the edge of the metal cover 230 and the edge of the shell (shell edges 107c, 107d, and 106d) (FIG. 6) may have an intense laser weld 310b designed to operate at a higher pressure level. , such as about 800-2500 psig (5515×10 ³ -17235×10 ³ Pascal gauge), typically about 800-1600 psig (5515×10 ³ -11030×10 ³ Pascal gauge) gas pressure. The depth of penetration at the strong weld can be adjusted to achieve the desired bursting pressure. Burst pressures of about 800-2500 psig (5515 x ¹⁰³ - 17235 x ¹⁰³ pascal gauge) can be achieved with laser weld penetration depths of about 5-7 mils (0.127-0.178 mm). The depth of penetration of strong welds can be finely tuned, allowing the weld to rupture at desired pressure levels, eg, about 1300-1600 psig (8962 x ¹⁰³ - 11030 x ¹⁰³ Pascal gauge).

Although the edge of the metal plate 230 is shown welded to the inner surface of the metal housing 100, as shown in FIG. of the inner surface. One such alternative embodiment is shown in Figure 6A. In such an embodiment ( FIG. 6A ) the housing edge 108 defined by relatively long edges 108a and 108b and relatively short edges 108c and 108d is crimped so that such edges lie in the same plane as metal plate 230 . Thus, edges 230 a and 230 b of sheet metal 230 may be directly laser welded to crimped housing edge 180 . A strong laser weld 310b can be applied between the plate edge 230b and the shell edges 108b, 108c, and 108d; a weak laser weld 310a can be applied between the plate edge 230a and the shell edge 108a.

There may be cut-outs in the body of the housing 100 in still other embodiments. The cut out parts can have varying shapes. For example, the cut-out portion may be polygonal (FIG. 7) or at least a part of its boundary may be curved (FIG. 7A). A metal plate, such as plate 400 (FIG. 7) or plate 500 (FIG. 7A), may be inserted into such a cut-out. The edge of metal plate 400 (FIG. 7) or metal plate 500 (FIG. 7A) may be laser welded to the housing to seal the cutout. The welds may desirably be in the form of a strong laser weld 410b and an adjacent weak laser weld 410a, as shown in the embodiment of FIG. 7 . The weld may be in the form of a strong laser weld 510b and preferably an adjacent weak laser weld 510a, as shown in the embodiment of Figure 7A.

Strong and weak welds can be achieved using different types of lasers operating in the peak power output range. The following are non-limiting examples of weak and strong welds produced using a Nd:Yag laser. When the gas pressure in the cell reaches a threshold pressure of about 400-800 psig (2758 x ^103-5515 x ¹⁰³ Pascal gauge), the weak welds described above break or crack as described above. When the gas pressure in the cell reaches a threshold pressure of about 800-2500 psig (5515×10 ³ -17235×10 ³ Pascal gauge), typically about 800-1600 psig (5515×10 ³ -11030×10 ³ Pascal gauge) , strong welds will break. The weak welds specifically provide a supplemental venting system, allowing gases to escape from the battery if the battery is abused as described above.

Alternatively, the supplemental vent mechanism may be in the form of a grooved vent, ie, one or more grooves in the surface of the housing 100 that result in an underlying thinned material region. The groove depth and thickness of the underlying thinned material region can be adjusted so that the thinned region ruptures when the gas pressure in the cell rises to a pressure P2 greater than P1. In another embodiment the resettable pin can be eliminated and the laser weld can be used as the main venting mechanism activated at pressure P1. In such an embodiment the supplemental vent mechanism may be a thinned material on the surface of the housing below the groove. The thinned material can be engineered to rupture at higher pressure levels P2.

In yet another embodiment there may be a plurality of grooves on the housing surface. One groove may have an underlying thinned region of small thickness, allowing it to rupture when gas builds up in the cell to the design pressure level P1. A second groove on the surface of the case, which may be adjacent to or spaced from the first groove, may have an underlying thinned region designed to rupture if gas pressure in the cell builds up to a higher P2.

When the casing 100 is steel, such as nickel-plated cold-rolled steel or stainless steel, grooves such as groove 600a (FIG. 8) can be formed on the surface of the casing so that when the gas pressure in the battery reaches about 10 ³ -5515×10 ³ Pascal gauge), the thinned material under the groove will rupture. The average wall thickness of the non-grooved portion of the housing may typically be about 0.3-0.50 mm, desirably about 0.3-0.45 mm. To achieve a burst pressure of about 400-800 psig (2758 x ^103-5515 x ¹⁰³ pascal gauge), the grooves are formed so that the thickness of the underlying thinned material is typically about 0.07-0.08 mm. In a specific non-limiting example, if the grooves are formed so that the underlying thinned material has a thickness of about 0.074 mm, when the gas pressure in the cell reaches a level of about 435 psig (2999 x ¹⁰³ Pascal gauge) then The underlying material cracked.

The groove 600, which may for example be in the form of a groove 600a or 600b (Figs. 8-8A) on the housing surface, is prepared by imprinting the housing surface with a die, preferably a die having a cutter edge. The arbor is held against the inner surface of the housing as the stamping die stamps into the outer surface of the housing. For grooves formed using such an embossing or cutting die, the thickness of the underlying thinned region 610 (FIG. 9) primarily determines the pressure at which the thinned region ruptures. The groove cut can desirably be V-shaped (Figure 9), which is preferably obtained using an embossing die with a knife edge. The V-shaped groove desirably has an acute angle, α, of about 40 degrees. The groove 600 can be made by other methods, for example by chemical etching.

The thinned material under the groove 600 is preferably the same as the housing material, typically nickel plated cold rolled steel. Grooves 600 may have straight or curved boundaries or may have a combination of straight and curved portions. The groove 600 may have rectangular, polygonal or rectangular boundaries. The grooves are curved, ie partly convex and partly concave, at least part of their boundaries. Groove boundaries can be closed or open. The grooves may be straight or substantially straight in preferred embodiments herein, preferably parallel to the wide edge 108a of the housing (Figs. 8-8A). For example, in a 7/5-F6 size rectangular cell, the groove 600a (Figs. 8 and 8A) may desirably be positioned parallel to and about 10 mm from the case wide edge 108a and may be about 8 mm in length.

There may be a second groove 600b spaced apart from the first groove 600a, as shown in FIG. 8A. In a specific non-limiting embodiment, the second groove 600b may be parallel to the groove 600a and about 10 mm from the positive end 180 (closed end). The length of the groove 600b may be about 8 mm. In such a case the underlying material thickness of each groove 600a and 600b may be different so that the underlying material in each breaks when the gas pressure in the cell reaches different pressure levels. For example, the thinned material under groove 600a can be designed to rupture when the gas pressure in the cell reaches a design burst pressure of about 250-800 psig. To achieve such a burst pressure range of about 250-800 psig (1724×10 ³ -5515×10 ³ Pascals gauge), the thickness of the thinned material under groove 600 a is about 0.04-0.15 mm. Alternatively, the thinned material under groove 600a can be designed to rupture when the gas pressure in the cell reaches a ^design burst pressure of about 400-800 psig ( ^{2758x103-5515x103} Pascal gauge). To achieve such a burst pressure of 400-800 psig, the thickness of the thinned material under groove 600a is about 0.07-0.15 mm. The thinned material under the second groove 600b can be designed to rupture when, in a catastrophic situation, the gas pressure in the battery ruptures when the battery is misused and the gas pressure in the battery rises rapidly to about 800-1600 psig (5515×10 ³ -11030×10 ³ Pascal gauge pressure) level. To achieve rupture at pressure levels of about 800-1600 psig, the thickness of the thinned material 610 below the groove 600b is typically about 0.15-0.35 mm.

Example 1 (weak weld using Nd:Yag laser)

Weak welds (FIG. 6 or 6A) for welding the metal cap 230-casing 100 along the housing edge 106c can be produced using a Nd:Yag laser. The laser operates at a frequency of about 100 Hz. The peak power output per pulse is about 35 watts. The average power output is 0.5 kW. The pulse width (cycle time between peak powers) was about 0.7 milliseconds. The laser feed rate (speed of movement of the laser along the weld path) was about 3 inches per minute. A uniform weld is created along the long edge 106c of the housing and thus the adjoining long edge 230a of the metal cover 230 to which it is welded. The weld has a uniform penetration depth of about 2-4 mils (0.0508-0.102 mm), typically about 3 mils (0.0762 mm). When the pressure in the cell reaches a level of about 400-800 psig (2757 x ¹⁰³ - 5515 x ¹⁰³ pascal gauge) the weld breaks and if compromises the operation of the main vent (plug 260) thus serves as a supplementary vent .

Example 2 (Strong Weld Using Nd:Yag Laser

Strong welds for welding the metal cover 230-housing 100 along the casing edges 106d, 107c and 107d (Fig. 6 or 6A) can be produced by using a Nd:Yag laser. Strong welds for welding the metal cap 230-casing 100 along the casing edges 106d, 107c and 107d can be produced by using a Nd:Yag laser. The laser operates at a frequency of about 12 Hertz. The peak power output per pulse is about 46 watts. The average power output is 0.65 kW. The pulse width (cycle time between peak powers) was about 5.9 milliseconds. The laser feed rate (the rate of movement of the laser along the weld path) was about 2 inches per minute. Uniform welds are produced along the long edges 106d, 107c and 107d of the housing, and thus the adjoining edges of the metal cover 230 are welded thereto, as shown in FIG. 6 . The uniform penetration depth of the weld is about 5-7 mils (0.127-0.178 mm), typically about 6 mils (0.152 mm). The weld breaks when the pressure in ^the cell reaches a level of about 800-2500 psig ( ^{5515x103-17235x103} Pascal gauge), typically about 800-1600 psig ( ^{5515x103-11030x103 Pascal} ).

In commercial production the Nd:Yag laser described above can be operated at a higher peak power of about 125 watts to produce weak welds and at a peak power of about 150 watts to produce strong welds. Such operation at higher peak power allows the laser to move at a higher speed (feed rate) along the weld path.

Additionally to reduce the detrimental effect of any KOH crystallization buildup between the plug 260 and the inner surface of the vent cap 270, which can occur if the battery is inadvertently subjected to charging, the plug 260 can be modified so that it is within the rivet head 247 housing the plug 260. takes up less space in the cavity. A specific embodiment of such an improved design is shown as pin 260 in Figures 2A, 3A and 4A. In the improved design of the key 260 shown in FIG. 4 , the key takes up less space in the rivet head cavity 248 than the frusto-conical design of the key shown in FIGS. 2 , 3 and 4 . After the key 260 has been compressed into the rivet head cavity 248, the amount of free space in the cavity 248 housing the key is greater than about 10%, desirably about 10-40%. In contrast, the amount of free space in the rivet cavity of the peg 260 shown in the frusto-conical embodiments shown in Figures 2, 3, and 4 is typically less than about 10%.

It has been determined that a greater amount of free space, typically about 10-40% in the rivet head cavity 248, which is achieved by the improved bolt design (FIG. 4A), ensures more efficient operation of the bolt under abuse conditions, for example if the The battery undergoes charging unintentionally. Such a modified plug 260 (FIG. 4A) desirably disengages when the gas pressure in the cell reaches a design threshold level, such as about 100-300 psig. The greater amount of free space in the rivet head cavity 248 accommodates therein any gradual KOH crystallization buildup that might occur if the battery is abused by inadvertent charging. Yet enough free space remains in the rivet head cavity 248 to allow the plug 260 to operate effectively in resetting itself to allow gas pressure to release when the pressure in the cell builds up to a design threshold level.

The shape of the peg 260 can be varied as shown in FIG. 4A to achieve a greater amount of free space in the rivet head cavity 248 . In a modified design (FIG. 4A), the peg 260 has a cylindrical base 262 and a smaller, integrally formed cylindrical body 261 extending therefrom. After the improved plug 260 ( FIG. 4A ) is compressed in the cavity, the ratio of the diameter of the body 261 to the diameter of the base 262 can be adjusted as required to achieve a larger amount of free space in the rivet head cavity 248, typically about 10- 40%. The cylindrical shape of the body 261 better withstands the pressure of the compression plug 260 in the rivet head cavity 248 . The modified plug 260 (FIG. 4A) is compressed in the rivet head cavity 248 by applying force to the top surface 263 of the plug and then welding the vent cap 270-rivet head 247. This keeps the pin 260 tightly in compression within the rivet head cavity 248 . In the compressed state the body 261 of the plug 260 assumes a spherical configuration, as shown in Figures 1A and 2A. When the gas pressure in the cell builds up to a threshold level, desirably about 100-300 psig, the plug disengages itself, thus allowing the gas in the cell to escape through the vent orifice 272 in the vent cap 270 . There are preferably at least two vent caps 272 in the vent cap 270 - provided there is a clear path through which gas can escape from the vent cap 270 when the plug 270 is out of position. The plug 260 is desirably of an elastomeric, preferably rubbery material that is sufficiently compressible and resilient when in contact with an alkaline electrolyte, yet resistant to chemical attack or physical degradation. A preferred rubber material for plug 260 is vulcanized EPDM rubber, desirably about 80-85 durometer durometer.

While the modified configuration of the plug 260 shown in FIG. 4A is preferred, it is recognized that other shapes for the plug may help achieve the desired increase in free space in the rivet head cavity 248 that houses the plug. For example, the main body 261 of the plug could be slightly sloped rather than cylindrical as shown in FIG. 4A. Also the width of the rivet head cavity can vary across the broadside of the cell (FIG. 2A). In this case the rivet head cavity 248 is elongated along one axis, ie in the direction of the broad side of the battery (FIG. 2A). However, a symmetrical (circular) rivet head cavity 248 is preferred, as presently shown in the figures.

It is not intended to limit the invention to any particular size of rectangular battery. However, by way of specific example, the alkaline battery 100 may be rectangular (cubic) of small size, typically about 5-10 mm thick, especially about 5-7 mm thick, as indicated by the exterior of the housing in the direction of battery thickness. ^* Surface measurements. The cell width may typically be about 12-30 mm and the cell length may typically be about 40-80 mm. In particular, the alkaline battery 10 of the present invention can be used as a replacement for a rechargeable nickel metal hydride battery of the same size, eg, a standard 7/5-F6 size rectangular battery. The 7/5-F6 size battery has a thickness of 6.1 mm, a width of 17.3 mm, and a length of about 67.3 mm.

Chemical composition of a representative battery

The following description of the battery composition regarding the chemical composition of the anode 150, the cathode 110, and the separator 140 is applicable to the flat battery disclosed in the above-mentioned embodiment.

ne Poulenc购得的有机磷酸酯类表面活性剂)。这样的混合物仅作为说明性例子给出和不希望限制本发明。锌阳极的其它代表性胶凝剂公开于U.S.专利No.4,563,404。In the battery 10 described above, the cathode 110 includes manganese dioxide, and the anode 150 includes zinc and an electrolyte. Aqueous electrolytes include KOH, zinc oxide, and conventional mixtures of gelling agents. The anode material 150 may be in the form of a gelled mixture comprising mercury-free (zero added mercury) zinc alloy powder. That is, the battery has a total mercury content of less than about 100 parts by weight per million (ppm) zinc, preferably less than 50 parts by weight mercury per million parts zinc. The cell also preferably does not contain lead in any added amount and is therefore substantially lead-free, ie less than 30 ppm total lead and desirably less than 15 ppm total zinc in the anode. Such a mixture may typically comprise an aqueous KOH alkaline electrolyte solution, a gelling agent (e.g., an acrylic copolymer commercially available under the tradename CARBOPOL C940 from BF Goodrich), and a surfactant (e.g., under the tradename GAFAC RA600 from Rh

ne Poulenc commercially available organophosphate surfactants). Such mixtures are given as illustrative examples only and are not intended to limit the invention. Other representative gelling agents for zinc anodes are disclosed in US Patent No. 4,563,404.

Cathode 110 desirably has the following composition: 87-93 wt% electrolytic manganese dioxide (e.g., Trona D from Kerr-McGee), 2-6 wt% (total) graphite, 5-7 wt% KOH at a concentration of about 30-40 wt % of a 7-10 equivalent (Normal) KOH aqueous solution; and 0.1-0.5 wt % of an optional polyethylene binder. The average particle size of the electrolytic manganese dioxide is typically about 1-100 microns, desirably about 20-60 microns. The form of graphite is typically natural, or expanded graphite or mixtures thereof. Graphite may also include graphitic carbon nanofibers alone or in admixture with natural or expanded graphite. Such cathode mixtures are intended to be illustrative and not limiting of the invention.

ne-Poulenc购得的二壬基苯酚磷酸酯表面活性剂(100-1000ppm)。在此使用的术语锌应当理解为包括锌合金粉末，该粉末包括非常高浓度的锌，例如至少99.9wt％锌。这样的锌合金材料基本与纯锌那样电化学起作用。Anode material 150 includes: zinc alloy powder 62-69wt% (99.9wt% zinc containing indium including 200-500ppm indium as alloy and plating material), KOH aqueous solution including 38wt% KOH and about 2wt% ZnO; C940" is a cross-linked acrylic polymer gellant (e.g., 0.5-2 wt%) commercially available from BF Goodrich and grafted onto the starch backbone commercially available from Grain Processing Co. under the trade designation "Waterlock A-221". Hydrolyzed polyacrylonitrile (0.01-0.5 wt%); organophosphate ester surfactant RA-600 or trade name RM-510 from Rh

Dinonylphenol phosphate surfactant (100-1000 ppm) available from ne-Poulenc. The term zinc as used herein should be understood to include zinc alloy powders comprising very high concentrations of zinc, for example at least 99.9 wt% zinc. Such zinc alloy materials essentially behave electrochemically like pure zinc.

With respect to the anode 150 of the flat alkaline cell 10 of the present invention, the average particle size of the zinc powder is desirably about 1-350 microns, desirably about 1-250 microns, preferably about 20-250 microns. Typically, the zinc powder may have an average particle size of about 150 microns. The zinc particles in the anode 150 may be needle-shaped or spherical in shape. The preferably spherical zinc particles are used for filling the relatively small anode cavity of the cell with the zinc slurry due to their better distribution from the dispensing nozzle. The bulk density of zinc in the anode is about 1.75-2.2 grams of zinc per cubic centimeter of anode. The volume percent of the aqueous alkaline electrolyte in the anode is preferably about 69.2-75.5 volume percent of the anode.

Cell 10 can be balanced in a conventional manner so that the mAmp-hr capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc) is about 1. However, it is preferable to balance the cell so there is a significant excess of cathode. Cell 10 is preferably balanced such that the total theoretical capacity of _MnO2 divided by the total theoretical capacity of zinc is about 1.15-2.0, desirably about 1.2-2.0, preferably about 1.4-1.8, more preferably about 1.5-1.7. Due to the smaller conversion percentage of _MnO2 to MnOOH upon discharge based on total cell weight, cell balancing with such a cathode excess was determined to reduce the amount of cathode expansion. This in turn reduces the amount of swelling of the battery case. The above ratio of theoretical capacity of _MnO2 to theoretical capacity of zinc can feasibly be as high as about 2.5 or even up to about 3.0 to reduce overall swelling, but cell designs at such higher ratios greater than about 2.0 reduce cell capacity more significantly And thus less desirable from that point of view.

It is determined that the housing 100 wall thickness is about 0.30-0.50 mm, typically about 0.30-0.45 mm, preferably about 0.30-0.40 mm, more desirably about 0.35-0.40. The battery 10 is preferably in the shape of a cube with an overall thickness desirably about 5-10 mm (Figs. 1 and 2). In conjunction with this balance the battery so that the cathode is in excess. The cell is desirably balanced such that the ratio of the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc) is about 1.15-2.0, desirably about 1.2-2.0, preferably about 1.4-1.8. The ratio of anode thickness to casing exterior thickness is desirably about 0.30-0.40. (Such thicknesses are measured in a plane perpendicular to the longitudinal axis 190 through the thickness (minor dimension) of the cell.)

Separator 140 may be a conventional ionically porous separator consisting of an inner layer of nonwoven material of cellulose and polyvinyl alcohol fibers and an outer layer of cellophane. Such materials are illustrative only and are not intended to limit the invention.

Housing 100 is preferably nickel-plated steel. Housing 100 is desirably coated on its inner surface with a carbon paint, preferably a graphitic carbon paint. Such graphite coatings may be in the form, for example, of an aqueous based graphite dispersion which may be applied to the housing interior surface and subsequently dried under ambient conditions. Graphitic carbon improves electrical conductivity and can indirectly reduce cell outgassing by reducing the likelihood of surface corrosion occurring on the inner surface of the casing. Metal shield 230, negative end plate 290 and positive end plate 180 are also preferably nickel-plated steel. Current collector 160 may be selected from various known conductive materials found as current collector materials, such as brass, tin-plated brass, bronze, copper, or indium-plated flavonoids. The insulating sealing member 220 is preferably nylon 66 or nylon 612.

The following are specific examples showing comparative performance using the same size rectangular cells versus different cell balances. The new cells were in each case 5.6mm thick, 17mm wide, and 67mm long. (Unless otherwise specified, all dimensions are external dimensions without labels around the case.) Case 100 wall thickness was the same 0.38 mm for each cell tested. The casing 100 of each cell is nickel-plated steel coated with graphitic carbon on its inner surface. The cell configuration was the same in each case, as shown in the accompanying drawings (Figs. 1-5). The edge of the wide portion (flange 161 ) of the anode current collector 160 is about 0.5 mm from the inner surface of the case 100 . The surrounding skirt 226 of the insulating sealing member 220 surrounds this wide portion (flange 161 ) of the current collector 160 , thus providing shielding between it and the inner wall surface of the housing 100 .

All cell components were the same as above and each cell tested had the vent cap assembly 12 shown in the drawings. The only differences are in cell balance and anode composition. The comparative cell (Comparative Example) was balanced such that the equilibrium ratio, the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc), was 1.1. Balance Test The test cell of Example 1 was such that the balance ratio, ie, the theoretical capacity of _MnO2 divided by the theoretical capacity of zinc, was 1.25. The test cells of Examples 2 and 3 were balanced so that the theoretical capacity of _MnO2 divided by the theoretical capacity of zinc was 1.6 and 2.0, respectively.

The comparative and test cells in the following examples were intermittently discharged under a cycle of 90 milliwatts of power on followed by three hours of power off until a cutoff voltage of 0.9 volts was reached. (Such intermittent discharges simulate typical use of portable solid state digital audio players, which are typically capable of MP3 audio format.) The total actual service hours are then recorded and the amount of swelling of the battery case is evaluated and recorded.

Comparative example (comparative battery)

A comparative test cell 10 and end cap assembly was prepared in the rectangular (cubic) configuration shown in the figures. The battery, defined by the outer dimensions of the housing 100, has a length of about 67 mm, a width of about 17 mm and a thickness (before discharge) of about 5.6 mm. Anode 150 and cathode 110 have the following composition:

Anode Composition:

wt%

Zinc ¹ 70.0

Surfactant ² 0.088

(RA 600)

Electrolyte ³

(9 equivalents of KOH) 29.91

                                                                   

Remark:

1. The zinc particles have an average particle size of about 150 microns and are alloyed and plated with indium to give a total indium content of about 200 ppm.

ne Poulenc的有机磷酸酯类表面活性剂溶液RA600。2. From Rh

ne Poulenc's organophosphate surfactant solution RA600.

3. The alkaline electrolyte solution comprises the gelling agents Waterlock A221 and Carbopol C940 which together make up about 1.5% by weight of the alkaline electrolyte solution.

Cathode composition:

wt%

MnO ₂ (EMD)

(Trona D from Kerr McGee) 87.5

Graphite ¹

(NdG15 natural graphite) 7.4

electrolyte

(9 equivalents of KOH) 5.1

100.0

Remark:

1. Graphite NdG15 is a natural graphite from Nacional De Grafite.

The wall thickness of the battery case 100 is 0.38 mm. The new battery 10 has a length of 67mm, a thickness of 5.6mm and a width of 17mm. The anode 150 and cathode 110 of the cell were balanced such that the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc) was 1.1. The anode has 2.8 grams of zinc. (The cathode has 6.89 grams of _MnO2 .) Anode 150, cathode 110 and separator 140 make up approximately 66% of the external volume of housing 100 in the configuration shown in Figures 1 and 1A. The ratio of anode thickness to casing exterior thickness is about 0.35. Thickness is measured along a plane perpendicular to the longitudinal axis 190 through the outer thickness (small dimension) of the cell.

The cells were intermittently discharged under cycles of 90 milliwatts "power on" followed by three hours "power off" until a cutoff voltage of 0.9 volts was reached. Actual service life is 24.5 hours. The shell swells from a thickness of 5.6mm to a thickness of 6.13mm. (Thickness is measured between the outer surfaces of sidewalls 106a and 106b shown in FIG. 1A.)

Test cell example 1

A test cell 10 was prepared in a rectangular configuration and the same dimensions as in the comparative example. The anode 150 and the cathode 110 have the following compositions.

Anode Composition:

wt%

Zinc ¹ 66.0

Surfactant ² 0.083

(RA 600)

Electrolyte ³

(9 equivalents of KOH) 34.0

100.08

Remark:

1. The zinc particles have an average particle size of about 150 microns and are alloyed and plated with indium to give a total indium content of about 200 ppm.

ne Poulenc的有机磷酸酯类表面活性剂溶液RA600。2. From Rh

ne Poulenc's organophosphate surfactant solution RA600.

3. The alkaline electrolyte solution comprises the gelling agents Water lock A221 and Carbopol C940 which together constitute about 1.5% by weight of the alkaline electrolyte solution.

Cathode composition:

wt%

MnO ₂ (EMD)

(Trona D from Kerr McGee) 87.5

Graphite ¹

(NdG15 natural graphite) 7.4

electrolyte

(9 equivalents of KOH) 5.1

100.0

Remark:

1. Graphite NdG15 is a natural graphite from Nacional De Grafite.

The casing 100 wall thickness of the test cell was 0.38 mm. The new battery 10 has a length of 67mm, a thickness of 5.6mm and a width of 17mm. The anode 150 and cathode 110 of the cell were balanced such that the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc) was 1.25. The anode has 2.56 grams of zinc. (The cathode has 7.11 grams of MnO ₂ .) The anode, cathode, electrolyte and separator make up about 66% of the external volume of the casing 100 , ie measured between its closed end 104 and open end 102 . The ratio of anode thickness to casing exterior thickness is about 0.35. Thickness is measured along a plane perpendicular to the longitudinal axis 190 through the outer thickness (small dimension) of the cell.

The cells were intermittently discharged under cycles of 90 milliwatts "power on" followed by three hours "power off" until a cutoff voltage of 0.9 volts was reached. Actual service life is 24.3 hours. The shell swells from a thickness of 5.6mm to a thickness of 6.03mm. (Thickness is measured between the outer surfaces of sidewalls 106a and 106b shown in FIG. 1A.) Service hours were about the same as in the comparative example, however, the case swelled less.

Test cell example 2

A test cell 10 was prepared in a rectangular configuration and the same dimensions as in the comparative example. The anode 150 and the cathode 110 have the following compositions.

Anode Composition:

wt%

Zinc ¹ 60.0

Surfactant ² 0.083

(RA600)

Electrolyte ³

(9 equivalents of KOH) 39.92

100.00

Remark:

1. The zinc particles have an average particle size of about 150 microns and are alloyed and plated with indium to give a total indium content of about 200 ppm.

ne Poulenc的有机磷酸酯类表面活性剂溶液RA600。2. From Rh

ne Poulenc's organophosphate surfactant solution RA600.

3. The alkaline electrolyte solution comprises the gelling agents Waterlock A221 and Carbopol C940 which together make up about 1.5% by weight of the alkaline electrolyte solution.

Cathode composition:

wt%

MnO ₂ (EMD)

(Trona D from Kerr McGee) 87.5

Graphite ¹

(NdG15 natural graphite) 7.4

electrolyte

(9 equivalents of KOH) 5.1

100.0

Remark:

1. Graphite NdG15 is a natural graphite from Nacional De Grafite.

The casing 100 wall thickness of the test cell was 0.38 mm. The new battery 10 has a length of 67mm, a thickness of 5.6mm and a width of 17mm. The anode 150 and cathode 110 of the cell were balanced such that the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc) was 1.6. The anode has 2.01 grams of zinc. (The cathode has 7.13 grams of MnO ₂ .) The anode, cathode and separator make up about 66% of the outer volume of the casing 100 . The ratio of anode thickness to casing exterior thickness is about 0.35.

Thickness is measured along a plane perpendicular to the longitudinal axis 190 through the outer thickness (small dimension) of the cell.

The cells were intermittently discharged under cycles of 90 milliwatts "power on" followed by three hours "power off" until a cutoff voltage of 0.9 volts was reached. The actual service life is 20.9 hours. The shell swells from a thickness of 5.6mm to a thickness of 5.95mm. (Thickness is measured between the outer surfaces of sidewalls 106a and 106b shown in FIG. 1A.)

Test Cell Example 3

A test cell 10 was prepared in a rectangular configuration and the same dimensions as in the comparative example. The anode 150 and the cathode 110 have the following compositions.

Anode Composition:

wt%

Zinc ¹ 52.0

Surfactant ² 0.083

(RA600)

Electrolyte ³

(9 equivalents of KOH) 47.92

                                                                         

Remark:

1. The zinc particles have an average particle size of about 150 microns and are alloyed and plated with indium to give a total indium content of about 200 ppm.

ne Poulenc的有机磷酸酯类表面活性剂溶液RA600。2. From Rh

ne Poulenc's organophosphate surfactant solution RA600.

3. The alkaline electrolyte solution comprises the gelling agents Water lock A221 and Carbopol C940 which together constitute about 1.5% by weight of the alkaline electrolyte solution.

Cathode composition:

wt%

MnO ₂ (EMD)

(Trona D from Kerr McGee) 87.5

Graphite ¹

(NdG15 natural graphite) 7.4

electrolyte

(9 equivalents of KOH) 5.1

100.0

Remark:

1. Graphite NdG15 is a natural graphite from Nacional De Grafite.

The casing 100 wall thickness of the test cell was 0.38 mm. The new battery 10 has a length of 68mm, a thickness of 5.6mm and a width of 17mm. The anode 150 and cathode 110 of the cell were balanced such that the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc) was 2.0. The anode had 1.61 grams of zinc. (The cathode has 7.13 grams of MnO ₂ .) The anode, cathode and separator make up about 66% of the outer volume of the casing 100 . The ratio of anode thickness to casing exterior thickness is about 0.35. Thickness is measured along a plane perpendicular to the longitudinal axis 190 through the outer thickness (small dimension) of the cell.

The cells were intermittently discharged under cycles of 90 milliwatts "power on" followed by three hours "power off" until a cutoff voltage of 0.9 volts was reached. Actual service life is 18.5 hours. The shell swells from a thickness of 5.6mm to a thickness of 5.87mm. (Thickness is measured between the outer surfaces of sidewalls 106a and 106b shown in FIG. 1A.)

In the above tests, flat cells of the same size were balanced at progressively higher balance ratios. The edge of the wide portion (flange 161 ) of the anode current collector 160 is about 0.5 mm from the inner surface of the case 100 and is surrounded by an insulating shield 226 . The equilibrium ratio is defined as the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc). When the cell balance ratio (theoretical capacity of _MnO2 to that of zinc) was about 1.1 in the above comparative test, the swelling of the flat test cell increased significantly from the total thickness of 5.6 mm to 6.13 mm. In Test Example 1 (Balance Ratio 1.25) the battery swelled less, ie from 5.6mm to 6.03mm. The cell swelled from 5.6 mm to 5.95 mm in Test Example 2 (balance ratio 1.6). In test example 3 (balance ratio 2.0) the cell swelled even less from 5.6mm to 5.87mm. Battery service life is modestly smaller (from 24.5 hours to 20.9 hours) when the balance ratio is increased between 1.1 and 1.6 and significantly smaller (18.5 hours) at the highest balance ratio of 2.0.

Another preferred embodiment of the present invention is shown in Figures 10-17. Although a reusable or reactivatable vent mechanism such as resettable plug 260 is required, it can be eliminated as in the embodiment shown in FIGS. 10-17. It has been indicated above that the resettable pin 260 can be eliminated and a weak laser weld can be used as the main venting mechanism, which is at the activation pressure of the resettable pin, which is preferably about 100-300 psig (689 x 10 ³ -2068 x 10 ³ Pascals). Fracture or rupture under pressure P1. In such a case (elimination of the resettable pin) the above description that the supplemental venting mechanism could be a thinned material area on the housing surface below the groove (groove 600a or 600b). The thinned material can be engineered to rupture at higher pressure levels P2.

As now shown in the embodiment of FIGS. 10-17 it has been determined that one or more groove vents, preferably a single groove vent 600a or 600b, can be used as the primary venting mechanism. In such cases a single groove vent such as 600a or 600b could be cut or scored into the housing surface so the underlying thinned area ruptures under pressure P1. Preferably, the single-groove exhaust port 600b is arranged near the closed end of the housing near the positive end 180, as shown in FIG. 10A. Groove boundaries can be closed or open. The grooves may be straight or substantially straight in preferred embodiments herein, preferably parallel to the wide edge 108a of the housing (Figs. 8-8A). For example, in a 7/5-F6 size rectangular battery, the recessed vent 600b may be located on the wide face 106a of the case (FIG. 10a). In a preferred embodiment the groove vent 600b comprises the only groove vent on the surface of the housing. By way of non-limiting example, groove 600b may be a straight groove parallel to the closed end of the battery (FIG. 10A). The ends of the preferred straight groove 600b may be equidistant from the narrow side of the housing. In such a preferred embodiment the groove 600b may be about 8 mm in length and about 5-10 mm from the closed end 104 of the housing, as shown in Figure 10A. Although straight grooves 600b are desired, it is not desirable to limit such grooves to this configuration. It is recognized that the groove vent 600b may have other configurations, such as a curvilinear shape or the sum of parts straight and parts curved may form an open or closed border pattern.

The thinned material under groove 600b (FIG ^. 10A) can be designed to rupture when the gas pressure in the cell reaches a design burst pressure of about 250-800 psig ( ^{1724x103-5515x103} Pascal gauge). To achieve such a burst pressure range of about 250-800 psig (1724×10 ³ -5515×10 ³ Pascals gauge), the thickness of the thinned material under groove 600b is about 0.04-0.15 mm. Alternatively, the thinned material under groove 600b can be designed to rupture when the gas pressure in the cell reaches a design burst pressure of about 400-800 psig (2758×10 ³ -5515×10 ³ Pascal gauge). To achieve such a burst pressure range of about 400-800 psig (2758×10 ³ -5515×10 ³ Pascals gauge), the thickness of the thinned material under groove 600b is about 0.07-0.15 mm. The width of groove 600b (FIG. 10A) at its base (adjacent thinned region 610) may typically be about 0.1-1 mm, more typically about 0.1-0.5 mm. In this range the burst pressure is mainly controlled by the thickness of the underlying thinned region. However, it is recognized that wider grooved or cut regions on the housing 100 with an underlying thinned region are also possible.

The groove 600b may be prepared by embossing the surface of the housing 100 with a die, preferably a die having a cutter edge. The arbor is held against the inner surface of the housing as the stamping die stamps into the outer surface of the housing. The groove 600b may be cut in a V shape with sides of equal length as shown in FIG. 9 or in a V shape with sides of unequal length as shown in FIG. 15 . In the former case ( FIG. 9 ) the sides forming the V-groove desirably form an acute angle of about 40 degrees, α and in the latter case ( FIG. 15 ) it has an angle of preferably about 10-30 degrees. In conjunction with the groove 600b there may be one or more laser welds securing the metal cover 230 - housing 100 . Such welds may include one or both of a weak laser weld and a strong laser weld, which may be designed to rupture at a pressure higher than the rupture pressure of the thinned region below the groove 600b. Such laser welds can be produced using a Nd:Yag laser as previously described. The arrangement of adjacent weak and strong laser welds, such as welds 310a and 310b, for securing metal cover 230 to housing 100 has been shown and described with reference to FIGS. 6 and 6A. In a preferred embodiment there may be only one laser weld, a strong weld 310b securing the entire circular strike edge of the metal cover 230 to the housing 100 as shown in FIG. 10 . The weld 310 can be strong to rupture under catastrophic conditions, for example, if the battery is inadvertently subjected to recharging at a particularly high current or under particularly abusive conditions, causing gas generation in the battery to suddenly rise to about 800 psig-2500 psig (5515 ×10 ³ -17235×10 ³ Pascal gauge) level.

Thus, in the modified preferred cell embodiment shown in Figures 10 and 13, a single groove 600b serves as the main venting mechanism for the cell, wherein the thinned material 610 (Figures 9 and 15) beneath the groove 600b is designed. If the gas in the cell rises to a level of about 250-800 psig (1724×10 ³ -5515×10 ³ Pascal gauge), more typically about 400-800 psig (2758×10 ³ -5515×10 ³ Pascal gauge) And burst. And a strong laser weld 310b (FIG. 10) designed to secure the edge of the metal cover 230 to the case 100 serves as a supplemental exhaust system for the battery. Such intense laser welds 310b are designed to break or rupture in catastrophic conditions when the gas pressure in the cell suddenly rises to levels of about 800 psig-2500 psig. The rupture of the laser weld 310b under such catastrophic conditions allows gas to escape rapidly therethrough, reducing the gas pressure in the cell to nominal levels.

Figures 10 and 1OA show the cell in the cross-sectional view of Figure 11 taken through a plane parallel to the large side 106a and in the cross-sectional view of Figure 12 taken through a plane parallel to the narrow side 107a. The resettable pin 260 ( FIGS. 2 and 4 ) introduced in the previous embodiment is eliminated as shown in FIGS. 11 and 12 . It is also possible to eliminate associated components forming the end cap assembly 12 of the cell, ie, the vent standoff cap 270 and the plastic spacer disc 250 shown in the earlier embodiments (FIGS. 2 and 4). The reduced number of the many components that form the end cap assembly 12 is also reflected in Figure 13, which is an exploded view of the internal components of the cell. Thus, in a modified embodiment (Figs. 10-13) the rivet 240 may be welded directly to the negative end plate 290, as best shown in Figs. 11 and 12 .

The welding of the rivet 240 to the negative end plate 290 can effectively be performed by resistance welding. Rivet 240 is preferably brass, typically about 1-3 microns thick brass plated with a tin layer as desired. The negative end plate 290 is preferably nickel plated cold rolled steel. It has been determined that welding can be performed most efficiently and that a uniform weld is easily achieved when the thickness of the end plate 290 at the welded portion is about 4 mils (0.102 mm). The remainder of the end plate 290 needs to be thicker, preferably about 8 mils (0.204 mm) for overall strength. Since 8 mil thick cold rolled steel is commercially available, defining the central portion 290a (FIG. 13) of the end plate 290, i.e. the weld area can easily be stamped using mandrels to reduce its plate thickness at the weld to about 4 mils. Mil (0.102mm). Embossing is preferably performed from the top side of the end plate 290 (FIG. 13) to form an embossed region 290a. Such a process would leave the remaining portion 290b (FIG. 13) of the end plate 290 at its original 8 mil (0.204 mm) thickness.

The central portion 290a (FIG. 13) of the end plate 290 can take various configurations, such as rectangular, circular or oval indentations. In case of a rectangular or elliptical embossed area 290a, the long dimension of the embossed area 290a (in the direction of the wide side of the housing) should be somewhat larger than the diameter of the rivet head 247 to allow for placement of welding electrodes (not shown). For example, with a 3mm diameter rivet head 247, the long dimension of embossed region 209a may be about 4mm and the short dimension of embossed region 290a may be about 3-4mm. If the embossed area is circular, it may be about 3-4mm in diameter, if the rivet head 247 is about 3mm in diameter.

In assembling the modified embodiment flat alkaline cell 10 ( FIGS. 10-13 ), an anode material 150 comprising zinc and a cathode material comprising MnO ₂ with a separator 140 therebetween are inserted into the battery case 100 through the open end 102 . The end cap assembly 12 ( FIG. 13 ) is formed by inserting the metal cover 230 over the insulating sealing member 220 so that the protruding head 221 of the sealing member is inserted into the small hole 234 of the metal cover 230 . The rivet shaft 240 is then inserted through the aperture 234 in the metal cover plate 230 (FIG. 13). The rivet shaft 240 is separated from the metal cover 230 by the protruding head 221 of the insulating sealing member 220 . The top flange portion 161 of the anode current collector 160, preferably brass, is pushed upward against the bottom surface of the sealing member 220 and secured to the lower portion of the rivet 240, preferably brass or tin-plated brass, by conventional rivet joining techniques, thus electrically connecting the set Appliance 160 to rivet 240. There is a small hole 164 in the collector flange 161 and also an opening 249a in the lower part of the rivet 240 to make it easier to fix the anode current collector 160 to the rivet 240 . (The upper portion 249b of the rivet 240 is desirably solid, as shown in FIGS. 11 and 12.) When securing the current collector 160 to the rivet 240, the sealing member 220 is between the current collector flange 161 and the bottom surface of the metal cover 230. wedged.

As shown in Figures 10 and 11, metal cover 230 is welded to the inner surface of housing 100 by a strong laser weld (burst pressure preferably 800-2500 psig). Scoring or recessing a central portion of metal cap 230 forms well region 235 (FIG. 11). A sealing material 236, preferably an asphalt sealant commercially available under the trade designation KORITE Asphalt Sealant (Customer Products) is applied to the recessed well area 235 on the surface of the metal cover 230 (FIGS. 11 and 13). KORITE Bitumen Sealer is a non-hardening bitumen comprising a mixture of about 55-70 wt% bitumen and 30-45% bitumen. The viscosity of the sealer can be adjusted by adjusting the bitumen/solvent ratio and the temperature at which the sealer is applied. Preferably, the mantle 230 and the well area 235 in the rivet head 247 are heated prior to pouring the asphalt sealant into the well area 235 . Desirably, the asphalt sealant has a viscosity of about 1000 centipoise when it is poured into the well area 235 . Asphalt fills recessed area 235 and provides additional sealing protection between rivet 240 and sealing member 220 . The subassembly comprising the metal cover 230 rivet 240 and insulating sealing member 220 is then inserted into the open end 102 of the case so the current collector shaft 162 penetrates the anode material 150 (Figs. 11 and 12). After laser welding the circumferential edge of the metal cover 230 to the housing 100 , a plastic packing seal 280 ( FIG. 13 ) may be inserted over the rivets 240 . This is done by inserting the rivet head 247 through the aperture 282 of the plastic filler 280. The flat negative metal plate 290 is then placed onto the top surface of the plastic filler 280 so it contacts the protruding rivet head 247 . The negative plate 290 is then welded to the rivet head 247 to complete the construction of the end cap assembly 12 . The completed end cap assembly 12 in cell 10 is shown in FIGS. 11 and 12 .

A thermally conductive medium, desirably a liquid or metal, is preferably applied to the metal cover 230 at the edge of the laser welded metal cover 230 into the housing 100 . The heat transfer medium is preferably a liquid, which can be conveniently placed in wells or grooved areas 235 on the surface of the metal shield 230 . Such a heat transfer medium can absorb a substantial part of the heat generated during laser welding. When using a Nd:Yag (or equivalent) laser, enough heat can be absorbed in this manner to prevent the metal shield 230 from reaching temperatures greater than about 100° C. during welding. Alternatively, the metal enclosure can be precooled to a temperature less than ambient room temperature (21°C), preferably to a temperature close to the freezing point of water and even lower. Such pre-cooling also helps to prevent the metal shield 230 from exceeding 100°C during the welding operation. In addition, the metal cover 230 may be pre-cooled and a heat transfer medium may also be applied to the metal cover 230 .

A plastic packing seal 280 is press fit into the housing 100 above the metal cover 230 . If metal shield 230 is not kept sufficiently cool during laser welding, seal 280 may overheat to the point of adversely affecting its physical properties. This can lead to a loss of radial compression, i.e. a loosening of the tight fit between seal 280 and housing 100, which in turn provides a path to the outside of the housing for electrolyte which can leak into the gap between metal cover 230 and metal cover 280. area. Therefore, it is recommended to keep the metal cover 230 sufficiently cool, or to apply a heat transfer medium to the metal cover to ensure sufficient heat absorption during the laser welding operation. A convenient way to accomplish this is to simply add a small amount of cooled deionized water, eg at about 5-10° C., to the trench region 235 of the metal shield 230 . This keeps the temperature of the metal cover 230 below about 100°C, which in turn allows the seal 280 (Figs. 11 and 12) to stay at a favorable operating temperature. (A sealant, such as a bitumen sealant, may be added to the well region 235 after the laser welding operation in the manner previously described.) Alternatively, a metal plate (optionally pre-cooled) may be applied in contact with the metal cover 230 . The metal plates, typically steel, can absorb sufficient heat during the welding operation to ensure that the metal shield 230 does not reach a temperature greater than about 100°C.

Although water may be added to well region 235 to keep metal shield 230 cool during laser operation, it is recognized that other suitable coolants may be used. For example, instead of pure water, a cooled aqueous solution of polyvinyl alcohol and potassium hydroxide may be used. Polyvinyl alcohol is coated on the top surface of the metal cover 230 , thus providing additional sealing protection between the metal cover 230 and the seal 280 . Such a solution may also be applied directly to the underside of plastic seal 280 ( FIGS. 11 and 12 ), thus providing additional seal protection to the lower surface of seal 280 .

Alternatively, a gelling agent may be added to the aqueous cooling solution applied to well 235 . The term gelling agent is intended to include conventional gelling agents as well as superabsorbents. Such gelling agents include polyacrylic acid, polyacrylate esters, sodium salts of acrylic acid copolymers, carboxymethylcellulose, sodium carboxymethylcellulose, starch graft copolymers, and the like. The gelling agent coats the surface of the metal cover 230 to provide additional sealing protection between the metal cover 230 and the seal 280 . The gelling agent may be applied as a powder to the underside of the plastic seal 280 ( FIGS. 11 and 12 ) using a compression roller or the like to thereby coat the seal 280 with the gelling agent and provide additional seal protection.

In the embodiment shown in FIG. 17 where paper gasket 295 is used instead of plastic seal 280, the paper gasket can be presaturated with an aqueous solution including a gelling agent or with an aqueous solution of polyvinyl alcohol and potassium hydroxide. Such rewetting of the paper gasket 295 provides additional seal protection if electrolyte leaks into the area between the metal cover 230 and the end plate 290 (FIG. 17). Alternatively, a separate layer comprising the gellant powder may be extruded onto the outside of the gasket 295 or dispersed within the fibrous network comprising the gasket 295 using compression rollers or the like, as described in U.S. Patent 4,999,264.

A separate protruding metal member 180 may be welded to the opposite closed end 104 of the cell. In the completed battery 10 (Figs. 10-13) the metal member 180 is in electrical contact with the battery casing and thus forms the positive terminal of the battery. End plate 290 is in electrical contact with rivet 240, which in turn is in electrical contact with anode current collector 160 and thus forms the negative terminal of the cell.

While the invention has been described in detail in terms of specific embodiments, it is recognized that variations in specific component designs are possible and contemplated within the concept of the invention. For example, current collector 160 (FIGS. 4 and 13) is shown as an elongated member in the shape of a nail terminating at its top, terminating in a horizontally extending flange 161 having an aperture 164 therethrough. This design is attractive because it makes it easy to secure the top flange 161 of the current collector 160 to the bottom surface 249 of the rivet 240 (FIG. 11). This can be accomplished by conventional riveting techniques where the bottom surface 249 of the rivet is inserted into the flange aperture 164 and then crimped to secure the collector flange 161 to the rivet 240 . In such a design the current collector axis is offset, it is not arranged along the central longitudinal axis of the cell. Such offsets do not appear to significantly interfere with the effective discharge of the anode or with the overall performance of the cell. The collector shaft 162 is shown as a straight nail in the embodiment shown in FIG. 4 and as a straight nail with a curved surface in the embodiment shown in FIG. 13 . In either case the nail is offset from the central longitudinal axis 190 of the battery, as shown, for example, in FIG. 11 .

It is recognized that other current collector designs are possible. For example, rivet 240 may be a solid member having a head portion 247 ( FIG. 11 ) and an integrally formed elongated shaft portion (not shown) in the shape of a nail extending downwardly from head 247 and penetrating at least partially into anode 150 . In such cases the current collector axis may be oriented so that it is centered along the central longitudinal axis 190 of the cell. Thus the head portion 247 of the rivet can still be welded to the terminal end plate 290 in the manner described above.

Another embodiment of the flat cell of the present invention is shown in FIG. 17 . In this embodiment, a paper gasket 295 such as kraft paper may be used between the metal cover 290 and the negative end plate 290 in place of the plastic filler 280 . The kraft paper gasket is durable and provides the necessary electrical insulation between the metal shield 230 and the end plate 290 . Such a design reduces the height of the rivet head 247 , thereby compressing the overall height of the end cap assembly 12 . It also has the advantage of eliminating the need to mold plastic filler 280 . This in turn results in more available volume for anode/cathode active materials in the interior of the battery. (The other components of the battery shown in Figure 17 are substantially the same as those shown and described with respect to the battery shown in Figures 10-12). It is recognized that the rivet 240 shown in FIG. 17 with the current collector 160 secured thereto may be replaced by a single rivet with an integrally elongated current collector shaped like a nail extending therefrom and penetrating at least a portion of the anode 150. . Such an integral current collector may be centrally located along the central longitudinal axis 190 of the cell.

It is recognized that each battery embodiment desirably has a conventional membrane label wrapped around the battery case. Suitable plastic films for such labels are known in the art and typically include polyvinyl chloride. Labels can be in desired design or stamped. Such labels may be adhesive coated, typically applied at the edges and by wrapping around the housing surface. Alternatively, the label can be applied in the form of a sleeve and heat shrunk onto the housing surface. A typical label 12 is shown in FIG. 17 .

Separator manufacturing

In the battery embodiment shown in FIGS. 10-13, the separator 140 may conveniently be formed from separator materials commonly used in alkaline batteries. For example, typically cellulose or cellulose-based and polyvinyl alcohol fibers. Cell 10 (Figs. 10-13) may conveniently be in a cuboid configuration with an overall thickness of about 6 mm, a width of about 17 mm and a length of about 35-67 mm. The desired separator may consist of two layers, an outer layer (facing the cathode 110) comprising cellulosic and polyvinyl alcohol fibers and an inner layer facing the anode 150 comprising a cellulosic material such as rayon. The separator 140 is inserted after the cathode disc 110 is inserted into the housing through the open end 102 (FIG. 11) so the separator faces the exposed cathode surface.

The separator 140 (Figs. 10-13) for the flat cells described above is conveniently prepared by rolling the flat separator sheet shown in Figs. 14-14B. First the near edge 140a is folded inwardly in direction F1 along the bend line 140b, which is about 3-5 mm from the edge 140a. A mandrel (not shown) may be placed against the separator surface 140d. The separator distal edge 140c can then be wrapped around the mandrel so that the edge 140c passes around the edge 140a, resulting in the partially wrapped configuration shown in Figure 14A. The distal edge 140c is wound continuously on the surface of the separator in direction F2 (FIG. 14A). Edge 140c may be secured to the surface of the release film by an adhesive. The bottom separator edge 142 may then be folded inwardly about 3 mm over the rear surface of the separator, as shown in FIG. 14B and secured thereto by adhesive. The use of adhesive to secure edge 140c and/or bottom separator edge 142 can be eliminated by simply folding bottom separator edge 140c in direction F3 and then squeezing it to form the bag configuration. The cathode shape also helps to maintain the separator in the pouch configuration shown in Figure 14B when the folded separator is inserted into the housing. Remove the arbor (not shown). The resulting wound separator 140 ( FIG. 14B ) has the shape of a bag with a closed boundary surface 148 and an open end 144 and an opposite closed end 143 . The separator boundary surface 148 defines a cavity 155 into which the anode material 150 is inserted.

After the cathode disc 110a is inserted into the battery case 100, a wound separator 140 configured as shown in FIG. 14B is inserted so that the separator surface faces the exposed cathode surface. The separator boundary surface 148 forms an anode cavity 155 . Anode cavity 155 preferably has a rectangular configuration as shown in Figure 14B. The short dimension of the rectangular configuration of cavity 155 may typically be about 2-3 mm for a cubic configuration of battery 10 and an overall thickness of about 6 mm. Preferably, the long dimension of the rectangular configuration is somewhat smaller than the width of the space available in the cell for the overall anode cavity 155 . This results in a gap 145 between one short side of the separator and the cathode disc 110a, as shown in FIG. 16 . The gap 145 is about 2-4 mm, preferably about 2-3 mm. Anode material 150 may then be filled into anode cavity 155 through separator open end 143, resulting in housing 100 filled with anode material 150, cathode material 110, and separator 140 therebetween, wherein on one short side of the separator and the cathode There is a gap 145 (void space) in between, as shown in FIG. 16 .

Having determined that additional alkaline electrolyte solution can now be added to the interior of the cell by dispensing it directly into gap 145 if desired. Additional electrolyte can be dispensed into gap 145 by inserting a dispensing nozzle directly into the gap. In a preferred embodiment, a small amount of additional alkaline electrolyte solution may be added to gap 145 after anode 150 and cathode 110 are in place in the cell. In an alternative embodiment a portion of additional electrolyte may be added to gap 145 after the cathode is in place but before the anode material is inserted into the anode cavity. Anode material can then be inserted into the anode cavity of the cell and thereafter a final quantity of electrolyte can be added to gap 145 . In either case the additional electrolyte helps to improve anode utilization (percent anode active expelled) and overall cell performance. It can also be a factor that tends to hinder battery swelling.

The addition of the alkaline electrolyte solution into the gap 145 between the separator 140 and the cathode 110 as described above avoids flooding problems which can occur if the electrolyte is added directly to the anode. For example, if there is initially no gap between separator 140 and cathode 110 and additional electrolyte is added to the interior of the cell, there may be electrolyte flooding into void space 146 above anode 150 (FIG. 11). Such flooding is not desired since it may cause wetting along the underside or edge of the metal cover 230 after it is placed in place covering the cell open end 102 . Such wetting in turn adversely affects proper laser welding of metal cover 230 to housing 100 .

If additional electrolyte is added to gap 145, it is recommended that it be done in incremental steps. For example, if additional electrolyte is added to gap 145 after insertion of anode 150, cathode 110, and separator 140 into the housing, it is recommended that such additional electrolyte be incrementally added in multiple dispensing steps that take into account the passage of time, typically Leave for about 1-4 minutes between dispensing. This allows time for each incremental amount of electrolyte to be absorbed into the anode, separating the membrane and cathode, reducing the likelihood of any flooding occurring which could interfere with proper laser welding of the metal cover 230 . If the cell is a rectangular 7/5-F6 size cell, typically the amount of additional alkaline electrolyte solution to be added to gap 145 is less than about 1 gram. Preferably, in such cases the electrolyte can be added in about four incremental equal apportionments, with a time interval of about 1-4 minutes between apportionments to allow proper absorption of incremental amounts of electrolyte into the anode, cathode and isolation film of sufficient time. Surprisingly, it has been found that when this total amount of additional electrolyte is dispensed into the gap 145 , the anode 150 swells sufficiently to expand the anode cavity 155 bounded by the separator surface 148 . As the anode 150 swells the separator surface 148 is pushed flush against both the anode and cathode, thus completely sealing the gap 145.

Performance testing of cells 10 prepared according to the embodiments shown and described with reference to Figures 10-16 was performed and reported in Test Cell Example 4 below.

Test Cell Example 4

A test cell 10 in a rectangular configuration of the same dimensions as in the comparative example was prepared in the embodiment shown in FIGS. 10-13. The amount of zinc in the anode is 2.01g and the amount of _MnO2 is 6.69. The anode 150 and the cathode 110 have the following compositions.

Anode Composition:

wt%

Zinc ¹ 60.0

Surfactant ² 0.075

(RM510)

Electrolyte ³

(9 equivalents of KOH) 39.9

100.00

Remark:

1. The zinc particles have an average particle size of about 150 microns and are alloyed and plated with indium to give a total indium content of about 200 ppm.

ne Poul enc的有机磷酸酯类表面活性剂溶液RM510。2. From Rh

ne Poul enc organic phosphate surfactant solution RM510.

3. The alkaline electrolyte solution comprises the gelling agents Waterlock A221 and Carbopol C940 which together make up about 1.5% by weight of the alkaline electrolyte solution.

Cathode composition:

wt%

MnO ₂ (EMD)

(Trona D from Kerr McGee) 84.0

Graphite ¹

(NdG15 natural graphite) 10.0

electrolyte

(9 equivalents of KOH) 6.0

100.0

Remark:

1. Graphite NdG15 is a natural graphite from Nacional De Grafite.

An additional total of 0.82 g of 9N KOH electrolyte was added in four dispensing increments (0.205 g per increment) into the gap 145 between the separator 140 and the cathode after placing the anode and cathode in the battery case ( Figure 16). The time interval between dispense increments was about 1-4 minutes. The addition of a total of 0.82 g of electrolyte did not significantly change the above anode and cathode compositions. A portion of the total added electrolyte is absorbed into the anode, another portion into the cathode and a portion into the separator. Electrolyte added to gap 145 causes the anode to swell and thus closes gap 145 . This technique allows for additional electrolyte to be added to the anode without causing flooding of electrolyte into the void space 146 above the anode. Such flooding of the electrolyte is undesirable since it can cause wetting of the edges of the metal cover 230 which in turn can interfere with proper welding of the cover 230 to the battery case.

The casing 100 wall thickness of the test cell was 0.38 mm. The new battery 10 has a length of 67mm, a thickness of 5.6mm and a width of 17mm. The anode 150 and cathode 110 of the cell were balanced such that the theoretical capacity of _MnO2 (based on 370 mAmp-hr/g _MnO2 ) divided by the mAmp-hr capacity of zinc (based on 820 mAmp-hr/g zinc) was 1.5. The anode has 2.01 grams of zinc. (The cathode has 6.69 grams of MnO ₂ .) The anode, cathode and separator make up about 66% of the outer volume of the casing 100 . The ratio of anode thickness to casing exterior thickness is about 0.35.

Thickness is measured along a plane perpendicular to the longitudinal axis 190 through the outer thickness (small dimension) of the cell.

The cells were intermittently discharged under cycles of 90 milliwatts "power on" followed by three hours "power off" until a cutoff voltage of 0.9 volts was reached. Actual service life is 20.1 hours. The shell swells from a thickness of 5.6mm to a thickness of 5.99mm. (Thickness is measured between the outer surfaces of sidewalls 106a and 106b shown in FIG. 1A or FIG. 12).

When the equilibrium ratio of the cell (theoretical capacity of _MnO2 to that of zinc) was about 1.1 in the comparative test, the swelling of the flat test cell increased significantly from a total thickness of 5.6 mm to 6.13 mm. In the above test example 4 (balance ratio 1.5) the battery swelled less, ie from 5.6 mm to 6.03 mm. In this test example 4 (equilibrium ratio 1.5) the cell swelled from 5.6 mm to 5.99 mm.

Although the preferred embodiment of the invention has been described with reference to a flat alkaline cell having a cubic (rectangular parallelepiped) overall shape, it is recognized that variations of such overall shape are possible and intended to be within the concept of the invention. In the case of flat cells, for example in the shape of a cube (rectangular parallelepiped), the ends of the casings may taper slightly outwards or inwards, still maintaining their rectangular configuration. The general appearance of such varying shapes is still essentially that of a cube and the meaning that aspires to belong to a cube or its legal equivalent. Other variations of the general shape such as slightly changing the angles so that the ends of the cells create either side of the casing, so that the parallelepiped deviates slightly from the strict rectangle, are also intended to fall within the meaning of cube (rectangular parallelepiped) as used here and in the claims.

The invention desirably extends to an overall battery shape which is flat in that the outer case sides along the length of the case are substantially flat. Accordingly, it should also be understood that the term "flat" is intended to extend to and include surfaces that are substantially flat to the extent that such surfaces may be slightly curved. In particular the concept of the present invention is intended to be extended to flat batteries in which the battery case surface sides along the length of the case have flat polygonal surfaces. The cell may thus have the general shape of a polyhedron, with all sides of the outer casing being polygonal. The invention is also intended to extend to batteries in which the sides of the battery case along its length have surfaces which are parallelograms and in which the overall shape of the battery is prismatic.

Claims (28)

1. An alkaline primary cell comprising a negative terminal and a positive terminal, and a cubic-shaped outer casing having a closed end and a relatively open end, the battery further comprising an anode comprising zinc and a cathode comprising _MnO in the casing , a separator between the anode and cathode, and an end cap assembly sealing the open end of the housing, thereby forming a boundary surface around the cell interior; wherein the cathode comprises a plurality of rectangular cathode blocks; wherein each block has a central opening devoid of cathode material; wherein the cathode blocks are stacked in an enclosure such that the opening devoid of cathode material forms a nucleus and the outer surface of the cathode contacts the enclosure The inner surface; Wherein the cell includes a venting mechanism on the boundary surface, wherein the venting mechanism activates when gas pressure rises to release the gas pressure from inside the cell, the venting mechanism includes a first rupture zone comprising a groove on the boundary surface, the groove defining an underlying material region thinner than the average thickness of the boundary; and a second rupture zone on the boundary surface, wherein when the gas pressure in the cell rises to the first pressure level and the second zone ruptures when the gas pressure in the cell rises to a second pressure level higher than the first pressure level, so that gas from the cell escapes from the interior of the cell through the rupture, Where the cell is balanced so that the cathode is in excess such that the ratio of the theoretical capacity of _MnO2 based on a theoretical ratio of 370mAh/g _MnO2 divided by the mAh capacity of zinc based on a theoretical ratio of 820mAh/g Zinc is 1.2-2.0. 2. The alkaline cell of claim 1, wherein the first and second rupture regions are spaced apart on the boundary surface. 3. The alkaline battery of claim 1, wherein the first rupture zone ruptures when the gas pressure in the container rises to a pressure of 1724×10 ³ -5515×10 ³ Pascal gauge. 4. The alkaline battery of claim 1, wherein the first rupture zone ruptures when the gas pressure in the container rises to a pressure of 2758×10 ³ -5515×10 ³ Pascal gauge. 5. The alkaline battery of claim 1, wherein the second rupture zone ruptures when the gas pressure in the container reaches a pressure of 5515×10 ³ -17235×10 ³ Pascal gauge. 6. The alkaline cell of claim 1, wherein the second rupture zone includes a laser weld in a portion of the boundary surface. 7. The alkaline battery of claim 1, wherein the groove is formed by embossing the boundary surface. 8. The alkaline cell of claim 6, wherein the end cap assembly includes a metal cover and the laser weld is formed between the casing and the metal cover fitted in the open end of the casing, thereby sealing the open end. 9. The alkaline cell of claim 6, wherein the end cap assembly includes a metal cover and the laser weld is formed between the inner surface of the casing and the edge of the metal cover fitted in the open end of the casing, thereby sealing the open end . 10. The alkaline battery of claim 6, wherein the laser weld is formed by a Nd:Yag laser and the laser weld ruptures when the gas pressure in the battery rises to a level of 5515×10 ³ -17235×10 ³ Pascal gauge . 11. The alkaline battery of claim 8, wherein the metal cover is a rectangular metal plate. 12. The alkaline cell of claim 8, wherein the metal cover is a rectangular plate with an aperture therethrough. 13. The alkaline cell of claim 12, wherein the end cap assembly comprises the metal cover, a terminal end plate, an insulating sealing member, and an elongated conductive member a portion of which passes through both the insulating sealing member and the metal cover, wherein The conductive member is electrically connected to the terminal end plate. 14. The alkaline battery of claim 13, wherein the conductive member is electrically connected to the anode. 15. The alkaline cell of claim 14, wherein a portion of the elongated conductive member penetrates the anode and acts as an anode current collector. 16. The alkaline cell of claim 14, wherein the end cap assembly further comprises an electrically insulating member between the terminal end plate and the metal cover to insulate the terminal end plate from the metal cover. 17. The alkaline cell of claim 16, wherein the electrically insulating member between the terminal end plate and the metal cover comprises a plastic material. 18. The alkaline cell of claim 16, wherein the electrically insulating member between the terminal end plate and the metal cover comprises a paper material. 19. The alkaline cell of claim 16, wherein the terminal end plate has a central region having a thickness less than an average thickness of the terminal end plate, wherein the elongate conductive member is welded at the central region by resistance welding to the terminal end plate. 20. The alkaline cell of claim 13, wherein a sealant material comprising pitch is applied between at least a portion of the surface of the elongated conductive member and the metal cover to prevent leakage of alkaline electrolyte therethrough. 21. The alkaline cell of claim 1, wherein at least a portion of the central opening in the cathode block forms a cavity that houses the anode. 22. The alkaline cell of claim 21, wherein the cavity has a rectangular configuration. 23. The alkaline battery of claim 1, wherein the battery includes an alkaline electrolyte comprising an aqueous solution of potassium hydroxide. 24. The alkaline cell of claim 23, wherein the cell is balanced so that the cathode is in excess such that the ratio of the theoretical capacity of MnO based on a theoretical ratio of 370 mAh/g _MnO divided by the mAh _capacity of zinc based on a theoretical ratio of 820 mAh/g zinc is 1.4 -1.8. 25. The alkaline cell of claim 1, wherein the cell has an overall thickness of 5-10 mm, wherein the overall thickness is defined as the distance between the outer surfaces of opposite sides of the casing that defines the short dimension of the casing. 26. The alkaline cell of claim 1, wherein the housing comprises metal having a wall thickness of 0.30 mm to 0.50 mm. 27. The alkaline cell of claim 1, wherein the housing comprises metal having a wall thickness of 0.30 mm to 0.40 mm. 28. The alkaline cell of claim 1, wherein the housing comprises steel.

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