Patent Application
20070054168
The invention relates to a metal/air cell preferably having an anode comprising zinc and an air cathode. The invention relates to a metal/air cell having an anode comprising zinc and an air cathode with spacer member of varying shape and structure within the air inlet space between cathode can and cathode assembly to facilitate air diffusion.
Zinc/air depolarized cells are typically in the form of miniature button cells which have particular utility as batteries for electronic hearing aids including programmable type hearing aids. Such miniature cells typically have a disk-like cylindrical shape of diameter between about 4 and 20 mm, typically between about 4 and 16 mm and a height between about 2 and 9 mm, preferably between about 2 and 6 mm. Zinc air cells can also be produced in somewhat larger sizes having a cylindrical casing of size comparable to conventional AAAA, AAA, AA, C and D size Zn/MnO2 alkaline cells and even larger sizes.
The miniature zinc/air button cell typically comprises an anode casing (anode can), and a cathode casing (cathode can). The anode casing and cathode casing each have a closed end an open end and integral side walls extending from the closed end to the open end. The anode casing is fitted with an insulating seal ring which tightly surrounds the anode casing side wall. Anode material is inserted into the anode casing and air diffuser, electrolyte barrier material, and cathode assembly are inserted into the cathode casing. After the necessary materials are inserted into the anode and cathode casings, the open end of the cathode casing is typically pushed over the open end of the anode casing during assembly so that a portion of the cathode casing side walls covers a portion of the anode casing side wall with insulating seal therebetween. The anode and cathode casing are then interlocked in a second step by crimping the edge of the cathode casing over the insulator seal and anode casing. During the crimping procedure (or in a separate step) radial forces are also applied to the cathode casing walls to assure tight seal between the anode and cathode casings.
The anode casing of zinc/air button cells may be filled with a mixture comprising particulate zinc. Typically, the zinc mixture contains mercury and a gelling agent and becomes gelled when electrolyte is added to the mixture. The electrolyte is usually an aqueous solution of potassium hydroxide, however, other aqueous alkaline electrolytes can be used. The closed end of the cathode casing (when the casing is held in vertical position with the closed end on top) may have a flat raised portion near its center. This raised portion forms the positive terminal and typically contains a plurality of air holes therethrough. In this design, the cathode casing closed end also typically has an annular recessed step which surrounds the raised positive terminal. Alternatively, the closed end of the cathode casing may be completely flat across its diameter, that is, without any raised portion at its center. In such design the central portion of such flat area at the closed end of the cathode casing typically forms the cell's positive terminal. In either case, the closed end of the cathode casing of button zinc/air cells is punctured with one or more small air holes to allow air to enter the cell. Such air then traverses an air diffusion layer (or air diffuser) in order to reach the cathode disk.
Catalytic material typically comprising a mixture of particulate manganese dioxide, carbon, and hydrophobic binder can be compacted into a disk shape forming a cathode disk within a cathode assembly. The cathode assembly with cathode disk therein can then be inserted into the cathode casing over the air diffuser on the side of the air diffuser that faces away from the air holes. Typically a cathode assembly is formed by laminating a layer of electrolyte barrier material (hydrophobic air permeable film), preferably Teflon (polytetrafluoroethylene), to one side of the catalytic cathode disk and an electrolyte permeable (ion permeable) separator material to the opposite side of the catalytic cathode disk. The cathode assembly with cathode disk therein is then typically inserted into the cathode casing so that its central portion covers the air diffuser and a portion of the electrolyte barrier layer rests against the inside surface of the step. The cathode disk in the final cell contacts the cathode casing walls around its perimeter.
If the cell is not adequately sealed, electrolyte can migrate around the catalytic cathode assembly and leak from the cathode casing through the air holes. Also electrolyte leakage can occur between the crimped edge of the cathode can and insulator if this area is not tightly sealed. The wall thickness of commercial zinc/air button cells are typically greater than about 6 mil (0.152 mm), for example, between about 6 and 15 mil (0.152 and 0.381 mm). The potential for leakage is greater when the anode casing and cathode casing is of very thin wall thickness, for example, between about 2 and 5 mil (0.0508 and 0.127 mm). Such low wall thickness is desirable, since it results in greater internal cell volume.
After the cell is assembled a removable tab is placed over the air holes on the surface of the cathode casing. Before use, the tab is removed to expose the air holes allowing air to ingress and activate the cell.
The cathode casing typically contains an air diffuser material which covers the inside surface of the cathode casing closed end. That is, the air diffuser material is placed in the air inlet space (plenum space) between the cathode casing closed end and the cathode assembly. If the closed end of the cathode casing has a raised central portion forming the positive terminal contact area, then the air diffuser material underlies such raised central portion. That is, the air inlet space in such design is normally between the raised central portion of the closed end of the cathode casing and the cathode assembly.
The conventional air diffuser serves several purposes. The air diffuser material serves to provide uniform air dispersion within the air inlet space. It can also be composed of electrolyte absorbent material which acts as a blotter to absorb alkaline electrolyte which may leak into the air inlet space. The air diffuser material may provide support for the underlying cathode assembly thus preventing the cathode assembly, which is normally flexible, from bending into the air inlet space (plenum space) or into the air diffusion layer during cell assembly and discharge. Gas pressure buildup during cell usage tends to cause cathode assemblies to bend into the air inlet space unless there is air diffusion material present within such space. Bending of the cathode assembly toward the cathode casing is undesirable since it would block air holes and interfere with proper air diffusion within the air inlet space.
The air diffuser material is normally composed of one or more sheets of air permeable paper or porous cellulosic material. Such permeable paper or porous cellulosic material can also serve as a blotter to absorb trace amounts of electrolyte which may leak into the air inlet space. The air diffuser is normally placed uniformly within the air inlet space (plenum space) between the closed end of the cathode casing and cathode assembly. The air diffuser material fills most or all of such air inlet space and covers the air holes in the closed end of the cathode casing. Commercial button size zinc/air cells which are commonly used in hearing aid devices may have only one air hole or may have a plurality of small air holes, for example, between 2 and 6 air holes and even more depending on cell size.
In some prior art button type zinc/air cells the cathode assembly has a dome shape. That is, they have a convex shape if viewed from the closed end of the cathode casing down into the cathode casing interior, or in other words, away from the air holes. U.S. Pat. Nos. 3,897,265 and 6,087,030 show button zinc/air cells with domed cathode assemblies. Both these references have a porous air diffusion material which fills the air inlet space between the cathode can closed end (adjacent the air holes) and cathode assembly. Such prior art designs may eliminate use of porous diffuser material within the air inlet space, since the domed cathode assembly tends to resist bending and flexing into the air inlet space during cell assembly and cell usage. However, if there is no air diffuser material filling the air inlet space, the domed cathode assemblies are still subject to at least some bending into the air inlet space as gas pressure within the cell builds. Such build up of gas pressure may ultimately cause the domed cathode assembly to bend or push against the air holes and thereby block air flow from these holes. Also domed cathode assemblies are more difficult to fabricate, because of the bending or shaping required during fabrication to form the dome. The domed cathode assembly is also more subject to fracture or cracking during fabrication, particularly if the cathode assembly is intended to be thin.
It is thus desirable to employ flat cathode assemblies which are more economically and reliably fabricated than domed cathode assemblies. However, flat cathode assemblies of desired composition and thickness for use in button size zinc/air cells can gradually bend into the cell's air inlet space thereby obstructing the air holes unless the air inlet space is filled with air diffuser material. U.S. Pat. No. 5,279,905; U.S. Pat. No. 6,602,629 B1; and U.S. Pat. No. 6,830,847 B2 show zinc/air button cells with cathode assemblies having a flat surface abutting the air inlet space of the cathode can and an air diffuser material filling said air inlet space.
Although air diffusers of the prior art that are comprised of paper or cellulosic materials may serve to enhance the dispersion of incoming air, they also tend to slow the rate of air transport directly to the cathode disk, particularly in the regions removed from the holes. This can limit the performance of zinc-air cells in some applications.
Accordingly, it is desirable to provide a configured support material within the air inlet space (plenum space) adjacent air holes in the cathode can of a zinc/air cell, wherein said configured material provides both structural support for the cathode assembly preventing the cathode assembly from bending or penetrating into the air inlet space and also allows for efficient air dispersion into the cathode assembly.
It is desirable to provide a zinc/air cell having a cathode assembly adjacent the air inlet space (plenum space) of the cathode can, wherein there is a configured material within the air inlet space to support the cathode assembly and prevent said cathode assembly from bending into the air inlet space. It is desirable that the cathode assembly have a flat or substantially flat surface facing said air inlet space. It is desirable that the support material be configured to provide channels of unoccupied (free) spaces underlying the air holes so that air may enter the air inlet space and pass freely into the cathode assembly.
It is desirable to position materials of proper configuration within the air inlet space between the cathode assembly and air holes in the cathode can in order to provide enhanced dispersion of incoming air to the cathode assembly.
It is desirable to eliminate any need for using blotter paper within the air inlet space of the cathode can of a zinc/air cell, since the blotter paper retards the rate of transport of incoming air to the cathode assembly.
The invention is directed to zinc/air cells, particularly miniature zinc/air cell in the form of button cells. Such miniature button cells typically have a cathode can and an anode can. There is at least one air hole, typically a plurality of air holes running through the closed end of the cathode can. After the anode and cathode components are inserted into the respective cans, the cathode can side walls are crimped over the cathode can side walls with insulator material therebetween. The invention is directed to inserting an air spacer member of varying shape and structure within the air inlet space (plenum region) adjacent the air holes at the closed end of the cathode can.
The miniature zinc/air button cell of the invention typically has a disk-like cylindrical shape of diameter between about 4 and 20 mm, typically between about 4 and 16 mm, and a height between about 2 and 9 mm, preferably between about 2 and 6 mm. The zinc/air cells may have anode can and cathode can wall thickness, typically covering a range between about 2 mil and 15 mil (0.0508 and 0.381 mm). Desirably, the zinc/air cells may have thin anode can and cathode can walls of thicknesses between about 2.0 and 5 mils (0.0508 and 0.127 mm). These wall thicknesses may apply to the thickness of a single layer (unfolded) anode and cathode can side wall and also the thickness of the closed end of the anode and cathode can. When the anode can wall thicknesses are very thin, that is, approaching the lower limit of the above wall thickness ranges, it is preferred to have the anode can side wall once folded in effect forming a double side wall. In such embodiment it will be appreciated that the above wall thickness ranges apply to each one of the double side walls.
In a principal aspect the spacer member of the invention is inserted into the air inlet space (plenum region) located between the inside surface of the closed end of the cathode can and the cathode assembly. There is at least one air hole running through the closed end of the cathode can and typically there are a plurality of air holes. The air spacer member of the invention may be of a disk-like shape and is characterized in that it has one or more apertures or cut out sections therethrough forming individual channels of unoccupied (free) space running through the body of said spacer member. The air spacer member is inserted into the cathode can within the air inlet space (plenum region) so that it abuts the air holes. When the spacer member is inserted into the cathode can, the channels of unoccupied space underlie air holes in the cathode can and provide unobstructed (continuous) channels of unoccupied space between the air holes and cathode assembly (the cathode assembly includes cathode material and one or more electrolyte barrier sheets). The peripheral edge of the spacer member may be circular, noncircular, irregular or jagged depending on the shape and placement of the cut out sections. The thickness of the spacer member, however, is preferably uniform and about equal to the depth of the air inlet space (air inlet plenum region) of the cathode can.
There may also be one or more channels of unoccupied (free) space created around the air spacer member of the invention when it is inserted into the air inlet region of the cathode can and some or all of those unoccupied (free) spaces around the spacer member may be aligned so they underlie at least some of the air holes. The spacer member is positioned so that at least one of the unoccupied channels of free space running through or around said spacer member underlies at least one of the air holes. Typically, there may be a plurality of apertures or cut out sections through the spacer member creating a plurality of channels of unoccupied (free) spaces underlying individual air holes in the cathode can. Preferably there are sufficient numbers of unoccupied channels of free space through or around said spacer member aligned so that said channels of unoccupied free space underlie the majority of the air holes. Preferably the unoccupied channels of free space underlie all of the air holes. Desirably there are individual channels of free space running through or around the spacer member which are aligned with individual air holes so that said channels of free space run uninterrupted (continuous) and preferably perpendicularly between individual air holes and the cathode assembly.
The individual channels of free space running through or around the spacer member of the invention and which underlie the individual air holes in the cathode can are characterized in that they have a diameter which is at least 2 times and desirably between about 2 and 18 times, typically between 2 and 16 times the diameter of the individual air holes in the cathode can. The term “diameter” as used herein shall be interpreted to include the equivalent diameter for non-circular holes or apertures. The equivalent diameter is the diameter which gives the same actual cross sectional area of the hole or aperture as if the cross sectional area is that of a circle. The total channels of free space running through or around the air spacer member of the invention comprises between about 10 and 90 percent, typically between about 50 and 90 percent of the available space in the air inlet region (plenum region) located between the cathode can closed end and cathode assembly before the spacer member is inserted therein. The spacer members of the invention having wide channels of unoccupied (free) space underlying the air holes in the cathode can improves air flow to the cathode assembly thereby improving cell performance and efficiency.
In one aspect the air spacer member of the invention is formed of solid plastic or metal material. The member may be rigid or flexible. The spacer member may also be of durable, compression resistant rubber, for example, styrene-butadiene (SBR) rubber, silicone rubber or equivalent. Preferably the air spacer member is formed of a durable plastic which is durable but resists compression. For example, it may be formed of common plastic materials which resist cold flow (i.e., resist compression when squeezed) such as, but not limited to nylon, high density polyethylene or polypropylene. Since the seal around the cathode assembly is tight, as described the specific embodiments, it is not expected that the spacer member will be exposed to electrolyte leakage. Therefore the spacer member does not specifically have to resist attack by alkaline electrolyte.
The air spacer members of the invention preferably have wide channels of unoccupied (free) space underlying the air holes in the cathode can. Such unoccupied space form continuous channels between individual air holes and the cathode assembly, thereby improving air flow to the cathode assembly. This in turn results in improved cell performance. Simultaneously the spacer member provides sufficient support for the underlying cathode assembly so that the cathode assembly cannot bend or protrude into the air inlet space.
The spacer member of the invention may be of varying shape. The spacer member may be of a disk shape having a plurality of cut out portions therethrough. Spacer member may be in the form of a disk having a plurality of polyhedron or partial polyhedron cut out sections therethrough. The cut out sections may be within the bounds of the circumferential peripheral edge of the disk. The walls of the cut out sections may thus have curvature or they may be straight or substantially straight. In a preferred arrangement the cut out portions are triangular or pyramidal in shape. The spacer disk is placed within the air inlet (plenum region) of the cathode can and registered (positioned) so that the individual cut out sections running through the spacer disk also underlie at least the majority of the individual air holes in the cathode can. Thus, the cut out portions running through the spacer disk form channels of unoccupied (free) space underlying the individual air holes and running uninterrupted (continuous) between the individual air holes and the cathode assembly.
The spacer member of the invention may be a disk shaped member with fingers or leafs jutting out from the center of the disk. Each finger or leaf has an aperture running therethrough. The spacer disk is inserted against the inside surface of the closed end of the cathode can within the air inlet space (plenum region) of the cathode can. The air spacer disk is registered so that the individual apertures running through the fingers in the spacer disk underlie individual air holes in the cathode can. Channels of unoccupied (free) space are thus formed directly under the air holes in the cathode can so that air entering the cathode can passes directly to the cathode assembly. Additionally there are wide channels of unoccupied (free) space between the individual fingers of the spacer disk. The resulting wide channels of unoccupied free space run uninterrupted between the air holes and cathode assembly and improve the flow of air to the cathode assembly. The spacer disk simultaneously provides sufficient support to the cathode assembly preventing it from bending into the air inlet space (plenum region) of the cathode can.
The air spacer member may be in the form of a disk having a star-like configuration. The disk may be shaped so that there are pointed star-like sections jutting out from the center of the disk. Each section may be formed of a pair of straight or curved side walls which terminate in a pointed apex. There may be, for example, two, three, or more pronged sections. There can be wide unoccupied channels of space between adjacent pronged sections of the disk. The spacer disk is placed within the air inlet (plenum region) of the cathode can and registered so that the unoccupied channels of free space between the individual pronged sections of the disk are aligned to underlie individual air holes in the closed end of the cathode can. The resulting individual wide channels of unoccupied free space run in continuous paths, preferably perpendicular paths, between the air holes and cathode assembly and improve the flow of air to the cathode assembly. The spacer disk simultaneously provides sufficient support to the cathode assembly preventing it from bending into the air inlet space (plenum region) of the cathode can.
The air spacer member may in the form of a disk having one or more apertures running therethrough, for example, in the center of the disk. Each aperture running through the disk has a diameter or is wider than the air holes in the cathode can. Typically there is one aperture in the center of the disk. The diameter of the disk is smaller than the distance between pairs of opposing air holes in the cathode can. Thus, when the spacer disk is inserted into the air inlet space (plenum region) of the cathode can, there are wide channels of unoccupied free space underlying preferably each of the air holes in the cathode can including air holes that lie outside of the disk peripheral edge. Thus, some of the wide channels of unoccupied free space underlying the air holes in the cathode can are formed by free space residing outside of the spacer disk peripheral edge and other channels of unoccupied free space are formed by wide apertures running through the spacer disk. Such wide channels of unoccupied free space run uninterrupted and preferably perpendicularly between the air holes and cathode assembly and thus improve the flow of air to the cathode assembly. The spacer disk simultaneously provides sufficient support to the cathode assembly preventing it from bending into the air inlet space (plenum region) of the cathode can.
The air spacer member of the invention may be in the form of a mesh or grid of woven or non woven polymer or metal fiber. Preferably air spacer member is formed of a mesh of woven polymer fiber, for example, woven fibers of nylon, polyolefin, or polyester or other common durable polymer fiber. Alternatively, it may be formed of a mesh of woven metallic fiber, for example, woven stainless steel fiber. Preferably, the mesh is woven so that there are relatively wide openings creating channels of unoccupied free space between the fibers. The mesh may be woven so that there are formed unoccupied channels of “free space” which have diameter generally larger than the diameter of each of the air holes in the cathode can. The mesh is inserted into the air inlet space (plenum region) of the cathode can. The mesh thus abuts the air holes on one side and the cathode assembly on the opposite side. Preferably, the channels of “free space” underlying the air holes run perpendicularly between each respective air hole to the cathode assembly. However, the channels of “free space” formed by spaces between the fibers may take other pathways (non perpendicular) pathways between each air holes and cathode assembly. The individual channels of free space running through or around the mesh member of the invention which underlie the individual air holes in the cathode can are characterized in that they have a diameter at least 2 times and desirably between about 2 and 18 times, typically between about 2 and 16 times, for example, between about 3 and 16 times the diameter of the individual air holes in the cathode can. The total channels of free space running through or around the mesh member of the invention comprises between about 10 and 90 percent, typically between about 50 and 90 percent of the available space in the air inlet region (plenum region) located between the cathode can closed end and cathode assembly before the mesh member is inserted therein. The wide channels of unoccupied free space running through the mesh and underlying the individual air holes in the cathode can improve the distribution and flow of air to the cathode assembly. The mesh simultaneously provides sufficient support to the cathode assembly preventing it from bending into the air inlet space (plenum region) of the cathode can.
The air spacer member of the invention may be formed from a plurality of grooves or indentations, formed integrally on the outside surface of the closed end of the cathode casing or from projections from the inside surface of the cathode can reaching the cathode assembly. These features may be formed during or after fabrication of the cathode can, for example, by applying a punch or die to the top surface at the closed end of the cathode can. They may also be formed as the cathode can is stamped, such that the exterior surface at the closed end or terminal end of the cathode can remains flat. Projections can further be formed by depositing material in selected locations on the inside surface of the cathode can closed end. Such material could consist of nodules of epoxy, nylon, polyethylene or other plastic that is deposited from the melt or semi-liquid state, or prehardened materials that are fastened in place using adhesives. The grooves, indentations or projections are positioned in regions on the cathode can closed end preferably between rows of air holes penetrating the closed end. The placement of the grooves, indentations, or projections in this manner forms a plurality of channels of unoccupied (free) space underlying the air holes when the cathode assembly is inserted into the cathode can. The channels of unoccupied space created by the grooves, projections or indentations are of width which is desirably greater than the diameter of each of the air holes. The apex of each feature is positioned at level so that it may contact the flat surface of cathode assembly, thereby providing support to the cathode assembly. The channels of unoccupied (free) space resulting from such features in the cathode can which protrude into the air inlet space (plenum region) provide wide channels for air to pass from the air holes to the cathode assembly.
The invention will be better understood with reference to the drawings in which:
The invention is directed to air depolarized electrochemical cells. Such cells have a metal anode, typically comprising zinc within an anode casing, and there is an air inlet to the cathode material within the cathode casing. The cell is commonly referred to as a metal/air or air-depolarized cell, and more typically a zinc/air cell.
The zinc/air cell of the invention is desirably in the form of a miniature button cell. It has particular application as a power source for small electronic devices such as hearing aids. But such cells may also be used to power other electronic devices. The miniature zinc/air button cell of the invention typically has a disk-like cylindrical shape of diameter between about 4 and 20 mm, for example, between about 4 and 16 mm, preferably between about 4 and 12 mm. The miniature zinc/air button cell has a height between about 2 and 9 mm, preferably between about 2 and 6 mm. The miniature zinc/air cell typically has an operating load voltage between about 1.2 Volts to 0.2 Volts. The cell typically has a substantially flat discharge voltage profile between about 1.1 and about 0.9 Volts whereupon the voltage can then fall fairly abruptly to zero. The miniature zinc/air cell can be discharged at a rate usually between about 0.2 and 25 milliAmperes. The term “miniature cells” or “miniature button cells” as used herein is intended to include such small size button cells, but is not intended to be restricted thereto, since other shapes and sizes for small zinc/air cells are possible. For example, zinc air cells could also be produced in somewhat larger sizes having a cylindrical casing of size comparable to conventional AAAA, AAA, AA, C and D size Zn/MnO2 alkaline cells and even larger.
The cell of the invention may contain added mercury, for example, about 3 percent by weight of the zinc in the anode or can be essentially mercury free (zero added mercury cell). In such zero added mercury cells there is no added mercury and the only mercury present is in trace amounts naturally occurring with the zinc. Accordingly, the cell of the invention can have a total mercury content less than about 100 parts per million parts by weight of zinc, preferably less than 40 parts per million parts (ppm) by weight of zinc, more preferably less than about 20 parts per million parts by weight of zinc. (The term “essentially mercury free” as used herein shall mean the cell has a mercury content less than about 100 parts per million parts by weight of zinc.) The cell of the invention can have a very small amount of lead additive in the anode. If lead is added to the anode, the lead content in the cell can typically be between about 100 and 800 ppm of zinc in the anode. However, the cell desirably does not contain added amounts of lead and thus can be essentially lead free, that is, the total lead content is less than 30 ppm, desirably less than 15 ppm of zinc in the anode.
The zinc/air cell 210 of the invention (
The anode casing 260 (anode can) contains an anode mixture 250 comprising particulate zinc and alkaline electrolyte. The particulate zinc is desirably alloyed with between about 100 and 1000 ppm indium. The zinc particles may also be plated with additional indium, preferably between about 100 and 1500 ppm indium. The cathode casing 240 has a plurality of air holes 243 in the raised portion 244 of its surface at the closed end thereof. A cathode catalytic assembly 230 containing a catalytic composite material 234 (
A representative cathode casing 240 (cathode can) is shown in
In the embodiment shown in
A cathode catalytic assembly 230 (
In a preferred embodiment a separate electrolyte barrier sheet 232, preferably of Teflon, can be applied to adhesive ring 143 on the inside surface 245a of step 245, thereby bonding electrolyte barrier sheet 232 to the inside surface of step 245. The catalytic assembly 230 can then be applied over electrolyte barrier sheet 232, preferably with the surface of second electrolyte barrier sheet 235, preferably of Teflon, contacting the barrier sheet 232 (
Conventional blotter air diffuser material is of air permeable paper or porous cellulosic material which is inserted against the closed end 249 of the cathode casing 240 so that it covers air holes 243 and completely fills air inlet space 288. Although such air diffuser material acts as a cushion preventing the cathode assembly 230 from bending into the air inlet space 288, it can impede the free flow of incoming air to the cathode assembly 230.
It has been determined in the present invention that conventional air diffuser material filling available air inlet space 288 can be replaced with solid plastic or metal structures of varying configurations. Such structures are herein referred to as air spacer members of the invention. Specific embodiments of such spacer members which are intended to be representative of the invention are presented herein as spacer members 300 (
The above air spacer members 300, 400, 500, and 600, which are representative of the invention, have apertures or cut out sections therethrough which form “channels of unoccupied (free) space” when they are inserted within the air inlet region 288 (plenum region) of the cathode can 240. The spacer members 300, 400, 500, and 600 may be of a disk-like shape. The peripheral edge of the spacer member may be circular, noncircular, irregular or jagged depending on the shape and placement of the apertures or cut out sections therethrough. The thickness of the spacer member, however, is preferably uniform and about equal to the depth of the air inlet region 288 within cathode can 240. When inserted and registered properly within air inlet region 288 said air spacer members of the invention form “channels of unoccupied free space” 284 underlying at least a majority of air holes 243, and such unoccupied channels 284 extend between at least the majority of the air holes 243 and the cathode assembly 230. The channels of unoccupied free space 284 run continuously between individual air holes 243 and the cathode assembly 230. The “unoccupied channels” are preferably channels of “free space” extending perpendicularly from an individual air hole 243 to the cathode assembly 230. The “channels of unoccupied space” underlying the air holes 243 have a diameter or are wide enough that they cover the cross section of individual air holes. Preferably the channels of unoccupied space have diameter which are greater than the diameter of the air holes. Desirably there are enough individual “unoccupied channels” underlying at least the majority of the air holes. Since such individual “unoccupied channels” are continuous, that is, with no obstructions between at least the majority of the individual air holes 243 and the cathode assembly 230, air will flow through the individual air holes 243 directly to the cathode assembly 230. This provides a more effective and more efficient air flow distribution within air inlet space 288 (plenum region) of cathode can 240 than if conventional air diffuser material (air permeable paper or porous cellulosic material) were used. The conventional air diffuser material would fill available air inlet space 288 and cover the air holes 243. By contrast the spacer members of the invention have pockets of “unoccupied space” forming individual continuous channels of free space 284 underlying the air holes 243.
The individual channels of free space 284 running through or around the spacer member, for example, spacer members 300, 400, 500, and 600 of the invention are characterized in that they have a diameter which is at least 2 times and desirably between about 2 and 18 times, typically between about 2 and 16 times, for example, between about 3 and 16 times the diameter of individual air holes in the cathode can which they underlie. (The term “diameter” as used herein shall be interpreted to include the equivalent diameter for non-circular holes or apertures. The equivalent diameter is the diameter which gives the same actual cross sectional area of the hole or aperture as if the cross sectional area is that of a circle. The cross sectional area of the hole or aperture is the area taken through a plane perpendicular to the longitudinal axis of the hole or aperture.) The total channels of free space 284 running through or around the air spacer member of the invention comprises between about 10 and 90 percent, typically between about 50 and 90 percent of the available space in the air inlet region 288 (plenum region) located between the cathode can closed end 249 and cathode assembly 230 before the spacer member of the invention is inserted therein.
Representative embodiments of the spacer members of the invention, for example, space members 300, 400, 500, and 600 are illustrated in the cross sectional drawings of
In a first embodiment of the invention a spacer member 300 having the configuration shown best in
Spacer disk 300 is inserted into the available air inlet space 288 (plenum region) underlying air holes 243. The spacer disk 300 is preferably registered so that cut out sections 310a and 310b underlie air 243a and 243b, respectively. Cut out sections 310d and 310e underlie air holes 243d and 243e, respectively. Thus, there will be channels of unoccupied (open) space 284 for at least the regions within air inlet space 288 underlying air holes 243a, 243b, 243d, and 243e. Only air hole 243c (which may be eliminated) will have material from spacer disk 300 underlying and blocking this air hole. (Thus, in the configuration of spacer disk 300 shown in
In the cross sectional drawing shown in
A second embodiment of the air spacer of the invention is shown as air spacer member 400 (
Air spacer disk 400 is inserted within air inlet space between the cathode can closed end 249 and cathode assembly 230. Spacer disk 400 is registered so that aperture 410a underlies air hole 243a, aperture 410b underlies air hole 243b, aperture 410d underlies air hole 243d, and aperture 410e underlies air hole 243e. The apertures 410a, 410b, 410d, and 410e have a larger diameter than the diameter of the respective air holes 243a, 243b, 243d, and 243e. Channels of unoccupied (free) space are thus formed directly under the air holes 243a, 243b, 243d, and 243e so that air entering these air holes passes directly to cathode assembly 230. Only air hole 243c is blocked by underlying material from air spacer 400, and in the embodiment shown, hole 243c may be eliminated. Additionally, there are channels of unoccupied (free) space between fingers 405a, 405b, 405d, and 405e. Thus when air spacer 400 is inserted into the air inlet region 288 of cathode can 240 there are individual channels of unoccupied space 284 underlying each of the air holes 243a, 243b, 243d, and 243e and additional channels of free space created from the space between fingers 405a, 405b, 405d, and 405e. Desirably, the total unoccupied space created by air spacer 400 may be between about 10 and 90 percent, typically between about 50 and 90 percent of the total available space of the air inlet (plenum) region 288 of cathode casing 240 before air spacer 400 is inserted therein.
As in the previous embodiment the solid material in air spacer disk 400 provides support for the underlying cathode assembly 230, and prevents the cathode assembly 230 from bending into the air inlet space 288 during cell assembly or usage. Simultaneously, the channels of unoccupied (free) space 284 underlying air holes 243a, 243b, 243d, and 243e provides unobstructed air distribution from air entering these air holes to cathode assembly 230. Thus incoming air from these air holes passes directly to the cathode assembly 230. Such unobstructed distribution of incoming air improves overall cell performance compared to conventional embodiments wherein all of the available air inlet space 288 (plenum region) underlying the air holes 243 is completely filled with air diffuser material such as paper or porous cellulosic material.
A third embodiment of the air spacer member of the invention is shown as air spacer 500 (
In cross sectional
As in the previous embodiments the solid material in air spacer disk 400 provides support for the underlying cathode assembly 230, and prevents the cathode assembly 230 from bending into the air inlet space 288 during cell assembly or usage. Simultaneously, the unoccupied (free) space 284 underlying air holes 243a, 243b, 243d, and 243e provides unobstructed air distribution of air entering these air holes. Thus incoming air from these air holes passes directly to the cathode assembly 230. Such unobstructed distribution of incoming air improves overall cell performance compared to conventional embodiments wherein all of the available space in the air inlet space 288 (plenum region) underlying the air holes 243 is completely filled with air diffuser material such as paper or porous cellulosic material.
A fourth embodiment of the air spacer member of the invention is shown as air spacer 600 (
The solid material in air spacer disk 600 provides support for the underlying cathode assembly 230 and prevents the cathode assembly 230 from bending into the air inlet space 288 (plenum region) during cell assembly or usage. Simultaneously, the unoccupied (free) space 284 underlying air holes 243a, 243b, 243d, and 243e provides unobstructed air distribution of air entering these air holes. Thus incoming air from these air holes passes directly to the cathode assembly 230. Such unobstructed distribution of incoming air improves overall cell performance compared to conventional embodiments wherein all of the available air inlet space 288 (plenum region) underlying the air holes 243 is completely filled with air diffuser material such as paper or porous cellulosic material.
A fifth embodiment of the air spacer member of the invention is shown as air spacer 700 (
The mesh 700 may be woven so that there are formed unoccupied channels of “free space” 705a which have diameter generally larger than the diameter of each of the air holes 243a-243e. Preferably, the channels of “free space” 705a which underlie the air holes 243a-243e run perpendicularly and continuously between each respective air hole to the cathode assembly 230. However, the channels of “free space” formed by spaces 705a between the fibers may take other pathways (non perpendicular) pathways between each air holes 243a-243e and cathode assembly 230. The diameter or width of at least the majority of such channels of “free” space have diameter or width which is greater than the diameter of the individual air holes 243a-243e. Such large channels of free space 705a assure that there will be high rate of air diffusion from the air holes 243a-243e to the cathode assembly 230. The diameter of at least the majority of such channels of “free” space running through the mesh are at least 2 times and desirably between about 2 and 18 times, typically between about 2 and 16 times the diameter of the individual air holes. Desirably, the channels of free space 705a within spacer mesh 700 comprises between about 10 and 90 percent, typically between about 50 and 90 percent of the total available space within the air inlet (plenum) region 288. The mesh 700 simultaneously provides sufficient support to the cathode assembly 230 to prevent the cathode assembly 230 from bending into the air inlet region 288 between the cathode casing closed end 249 and cathode assembly 230.
A sixth embodiment of the air spacer member of the invention is shown in
A typical groove 280 having side walls 282 terminating in apex 285 is formed as shown in
Thus incoming air from these air holes passes directly to cathode assembly 230 (
It will be appreciated that grooves or indentations 280 may be of configuration other than as shown in
A preferred embodiment of a complete zinc/air cell of the invention is shown in
The anode casing 260 and cathode casing 240 are initially separate pieces. The anode casing 260 and cathode casing 240 are separately filled with active materials, whereupon the open end 267 of the anode casing 260 can be inserted into the open end 247 of cathode casing 240. The anode casing 260 can have a folded side wall formed of a first outer straight body portion 263e which extends vertically upwards (
The body 242 of cathode casing 240 has a straight portion 242a of maximum diameter extending vertically downwardly from closed end 249. The body 242 terminates in peripheral edge 242b. The peripheral edge 242b of cathode casing 240 and underlying peripheral edge 273b of insulator ring 270 are initially vertically straight as shown in
Anode casing 260 can be separately filled with anode active material by first preparing a mixture of particulate zinc and powdered gellant material. The zinc average particle size is desirably between about 30 and 350 micron. The zinc can be pure zinc but is preferably in the form of particulate zinc alloyed with indium (100 to 1000 ppm). The zinc can also be in the form of particulate zinc alloyed with indium (100 to 1000 ppm) and lead (100 to 1000 ppm). Other alloys of zinc, for example, particulate zinc alloyed with indium (100 to 1000 ppm) and bismuth (100 to 1000 ppm) can also be used. These particulate zinc alloys are essentially comprised of pure zinc and have the electrochemical capacity essentially of pure zinc. Thus, the term “zinc” shall be understood to include such materials.
The gellant material can be selected from a variety of known gellants which are substantially insoluble in alkaline electrolyte. Such gellants can, for example, be cross linked carboxymethyl cellulose (CMC); starch graft copolymers, for example in the form of hydrolyzed polyacrylonitrile grafted unto a starch backbone available under the designation Waterlock A221 (Grain Processing Corp.); cross linked polyacrylic acid polymer available under the trade designation Carbopol C940 (B.F. Goodrich); alkali saponified polyacrylonitrile available under the designation Waterlock A 400 (Grain Processing Corp.); and sodium salts of polyacrylic acids termed sodium polyacrylate superabsorbent polymer available under the designation Waterlock J-500 or J-550. A dry mixture of the particulate zinc and gellant powder can be formed with the gellant forming typically between about 0.1 and 1 percent by weight of the dry mixture. A solution of aqueous KOH electrolyte solution comprising between about 30 and 40 wt % KOH and about 2 wt % ZnO is added to the dry mixture and the formed wet anode mixture 250 can be inserted into the anode casing 260. Alternatively, the dry powder mix of particulate zinc and gellant can be first placed into the anode casing 260 and the electrolyte solution added to form the wet anode mixture 250.
A catalytic cathode assembly 230 (
Catalytic cathode composite 234 desirably comprises a catalytic cathode mixture 233 of particulate manganese dioxide, carbon, and hydrophobic binder which is applied by conventional coating methods to a surface of an electrically conductive screen 237. Screen 237 may be of woven metallic fibers, for example, nickel or nickel plated steel fibers. The cathode mixture 233 is formed in the shape of a disk, which may be termed herein as the cathode disk. Other catalytic materials may be included or employed such as metals like silver, platinum, palladium, and ruthenium or other oxides of metals or manganese (MnOx) and other components known to catalyze the oxygen reduction reaction. During application the catalytic mixture 233 is substantially absorbed into the porous mesh of screen 237. The manganese dioxide used in the catalytic mixture 233 can be conventional battery grade manganese dioxide, for example, electrolytic manganese dioxide (EMD). The manganese dioxide in catalytic mixture 233 can also be manganese dioxide formed from the thermal decomposition of manganous nitrate Mn(NO3)2 or potassium permanganate KMnO4. The carbon used in preparation of mixture 233 can be in various forms including graphite, carbon black and acetylene black. A preferred carbon is carbon black because of its high surface area. A suitable hydrophobic binder can be polytetrafluroethylene (Teflon). The catalytic mixture 233 may typically comprise between about 3 and 10 percent by weight MnO2, 10 and 20 percent by weight carbon, and remainder binder. During cell discharge the catalytic mixture 233 acts primarily as a catalyst to facilitate the electrochemical reaction involving the incoming air. However, additional manganese dioxide can be added to the catalyst and the cell can be converted to an air assisted zinc/air or air assisted alkaline cell. In such cell, which can be in the form of a button cell, at least a portion of manganese dioxide becomes discharged, that is, some manganese is reduced during electrochemical discharge along with incoming oxygen. The adhesive ring 143 is intended to be applicable for use as well in such air assisted cells to prevent leakage of electrolyte therefrom.
In the preferred embodiment (
By way of a specific non-limiting example, the cell size could be a standard size 312 zinc/air cell having an outside diameter of between about 0.3025 and 0.3045 inches (7.68 and 7.73 mm) and a height of between about 0.1300 and 0.1384 inches (3.30 and 3.52 mm). The anode 250 can contain zero added mercury (mercury content can be less than 20 ppm of cell weight) and can have the following composition: zinc 78.1 wt % (the zinc can be alloyed with 200 to 800 ppm each of indium and lead), electrolyte (40 wt % KOH and 2 wt % ZnO) 21.9 wt %, gelling agent (Waterlock J-550) 0.3 wt %. Sufficient anode material 250 is supplied to fill the internal volume of anode casing 260. The cathode catalyst composite 237 can have the following composition: MnO2 4.6 wt. %, carbon black 15.3 wt %, Teflon binder 18.8 wt. %, and nickel mesh screen, 61.2 wt. %. The total cathode catalyst composite 237 can be 0.140 g.
The adhesive sealant 143 can be applied as a continuous ring to the inside surface of the cathode casing recessed step 245. The adhesive 143 to be applied to the inside surface 245a of step 245 may be a solvent based mixture comprising a polyamide based adhesive component as described in U.S. Pat. No. 6,436,156 B1 and incorporated herein by reference. The adhesive component is thus desirably a low molecular weight thermoplastic polyamide resin. A preferred polyamide resin is available under the trade designation REAMID-100 or VERSAMID-100 (from Henkel Corp. or Cognis Corp.). REAMID-100 or Versamid-100 is a low molecular weight polyamide which is a gel at room temperature. It is as a dimerized fatty acid which is the reaction product of a dimerized fatty acid and diamine. The adhesive mixture may be formed by dissolving the REAMID-100 polyamide in a solvent of isopropanol 50 parts by weight and toluene 50 parts by weight. The polyamide adhesive layer 143 applied to the inside surface 245a of cathode casing step 245 provides a very strong bond between Teflon sheet 232 and the nickel plated cathode casing step 245. The adhesive 143 also has the advantage that it is resistant to chemical attack from the potassium hydroxide electrolyte.
Cell 210 can be assembled by first inserting the cathode components above described into the precrimped cathode casing 240. The air spacer 300, 400, 500, 600, or 700 of the invention is inserted against air holes 42 within air inlet space 284. Alternatively, the air spacer 280 may be formed of a plurality of integral grooves 285 on closed end 249 of cathode casing 240. An electrolyte barrier layer 232, preferably of Teflon, is placed over the air spacer 300, 400, 500, 600, 700, or 280 of the invention. Preferably the inside surface 245a of the cathode casing step 245 is coated with the above described adhesive 143 so that the edge of electrolyte barrier layer 232 adheres to the inside surface 245a of step 245. Preferably, the bottom surface (facing the cell interior) of the enlarged portion 273a of the insulating sealing disk 270 is also coated with a ring of an adhesive 144 as shown in
The anode casing 260 may be drawn to the shape shown in
The cathode casing body 242 is then pushed over the outside surface insulator 270. Crimping forces are applied to crimp edge 242b of cathode casing 240 over slanted surface 263b of the anode casing 260 with insulator edge 273b therebetween. Radial forces may be applied during crimping to assure a tight seal between the anode and cathode casings.
Although the invention has been described with reference to specific embodiments, it should be appreciated that other embodiments are possible without departing from the concept of the invention. Thus, the invention is not intended to be limited to the specific embodiments but rather its scope is reflected by the claims and equivalents thereof.
