Abstract:
A battery includes a cylindrical housing, a first electrode, a second electrode, and a separator. The second electrode includes a plurality of cavities within the first electrode.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to batteries. 
     Batteries, such as alkaline batteries, are commonly used as energy sources. Generally, alkaline batteries include a cathode, an anode, a separator, and an electrolytic solution. The cathode is typically formed of an active material (e.g., manganese dioxide), carbon particles, and a binder. The anode can be a gel including an active material (e.g., zinc particles). The separator is usually disposed between the cathode and the anode. The electrolytic solution, which is dispersed throughout the battery, can be a hydroxide solution. 
     Alkaline batteries include the conventional AA, AAA, AAAA, C, and D batteries commonly sold in stores. These conventional alkaline batteries include a cylindrical container containing a central, cylindrical zinc gel anode surrounded by a ring-shaped manganese dioxide cathode. 
     It generally is desirable for a battery to have a long life. One measure of the life of a battery is the length of time the battery can discharge under a given load before the voltage drops to an unacceptable level. 
     Mick et al., U.S. Pat. No. 5,869,205 (“the Mick patent”) describes a battery which has an enhanced “service performance” (i.e., a longer life). According to Mick, the service performance in conventional alkaline batteries is limited by the restricted “anode-to-cathode interface area” in the alkaline batteries. The Mick patent gets around this restriction by replacing the center cylindrical cavity that, for example, is the zinc anode in conventional alkaline batteries with a plurality of cylindrical cavities that together make up the anode. By replacing, for example, a central zinc anode with a zinc anode including multiple cavities, the interface area between the zinc anode and the cathode is increased, providing the enhanced service performance. 
     SUMMARY OF THE INVENTION 
     The life, or service performance, of a battery also depends on the efficiency with which the battery uses the active materials of the anode and the cathode during discharge. This invention relates to a battery including multiple cavities which efficiently use the active materials in the anode and cathode. 
     More particularly, in one aspect the invention features a battery including a housing, a first electrode within the housing, a second electrode within the housing, and a separator between the first and second electrodes. The second electrode includes a plurality of cavities within the first electrode. The battery has a length and, at some position along the length of the battery, each of the cavities is a minimum distance (d 1 ) from the housing and a minimum distance (d 2 ) from each of the other cavities, with each ratio d 2 :d 1  for each cavity being between 1.5:1 and 2.5:1, preferably between 1.7:1 and 2.3:1, more preferably between 1.8:1 and 2.2:1, and most preferably between 1.9:1 and 2.1:1. Each ratio d 2 :d 1  can be the average ratio d 2 :d 1  along the length of the battery. The ratio can be determined, for example, at the mid-point along the length of the battery, or a third of the distance along the length of the battery, or two-thirds of the distance along the length of the battery. Preferably, at least 50 percent of, more preferably at least 75 percent of, and most preferably substantially the entire outer circumference of each cavity at that position fulfills this relationship. The housing preferably is cylindrical. 
     The minimum distance (d 1 ) between a cavity and the housing can be measured by determining the minimum distance between a surface of the first electrode adjacent the cavity and a surface of the first electrode adjacent the housing. The minimum distance (d 2 ) between two cavities is measured at the same position along the length of the battery by determining the minimum distance between a surface of the first electrode adjacent one cavity and a surface of the first electrode adjacent the second cavity. 
     Preferably, the ratio d 2 :d 1 , for each cavity is an average of between 1.5:1 and 2.5:1, more preferably between 1.7:1 and 2.3:1, and most preferably between 1.8:1 and 2.2:1 or even between 1.9:1 and 2.1:1. 
     In another aspect, the invention also features a battery including a housing, a first electrode within the housing, and a separator between the first and second electrodes. But this aspect of the invention, the second electrode includes two generally D-shaped cavities within the first electrode. Preferably, the flat side of the D-shaped cavities face each other, and the cavities have the ratio d 2 :d 1  discussed above. 
     In a third aspect, the invention again features a battery having a housing, a first electrode within the housing, and a separator between the first electrode and the second electrode. But this aspect of the invention, the second electrode includes three or more generally triangular-shaped cavities within the first electrode. Preferably, the housing is cylindrical and a corner of each cavity is directed towards the center of the battery, and when this is the case the side of the triangle generally aligned with the cylindrical housing is curved to match the curvature of the housing. Preferably, the cavities have the ratio d 2 :d 1 , discussed above. 
     In preferred embodiments, the first electrode is a cathode including manganese dioxide and the second electrode is an anode including zinc. The battery may be, for example, an AA, AAA, AAAA, C, or D battery. 
     The invention also relates to a battery in which the ratio d 2 :d 1 , described above is present at least once for at least one of the cavities. 
     Generally, the invention also relates to the current collector/seal arrangement that can be used with the multi-cavity batteries described above. The battery includes a top cap on an end of the battery, a seal between the top cap and the anode and cathode, and a multi-prong current collector. As end of each prong is electrically connected with the top cap, and each prong passes through the seal and into one of the anode cavities. 
     Other features and advantages of the invention will be apparent from the description of the preferred embodiments thereof, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a battery, including an anode consisting of two general D-shaped cavities; 
     FIG. 2 is a side-sectional view of the battery in FIG. 1, taken through the center of the battery; 
     FIG. 3 is a cross-sectional view of the battery in FIG. 1, taken at III—III in FIG. 2; 
     FIG. 4 is a top view of a battery including an anode consisting of three generally triangle-shaped cavities, without top cap, seal, and current collector; and 
     FIG. 5 is a top view of a battery including an anode consisting of four generally triangle-shaped cavities, without top coat, seal, and current collector. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-3, battery  10  includes a cathode  12 , an anode consisting of two generally D-shaped cavities  14  and  16 , separators  18 , and cylindrical housing  20 . Battery  10  also includes a current collector that has two prongs  22  and  24  passing through seal  26  into anode cavities  14  and  16 , respectively. The end of each prong is connected to negative metal top cap  28 , which serves as the negative terminal for the battery. The cathode is in contact with the housing, and the positive terminal of the battery is at the opposite end of the battery from the negative terminal. An electrolytic solution is dispersed throughout battery  10 . 
     Cathode  12  includes manganese dioxide, carbon particles, and a binder. 
     Any of the conventional forms of manganese dioxide used for cathodes can be used. The preferred manganese dioxide is EMD, although CMD can also be used. Distributors of such manganese dioxides include Kerr McGee, Co. (Trona D), Chem Metals, Co., Tosoh, Delta Manganese, Mitsui Chemicals and JMC. Generally, the cathode will include between 80% and 88% of manganese dioxide by weight. 
     The carbon particles also can be any of the conventional carbon particles used in cathodes. They can be synthetic or nonsynthetic, and they can be expanded or nonexpanded. In certain embodiments, the carbon particles are nonsynthetic, nonexpanded graphite particles. In these embodiments, the graphite particles preferably have an average particle size of less than about 20 microns, more preferably from about 2 microns to about 12 microns, and most preferably from about 5 microns to about 9 microns as measured using a Sympatec HELIOS analyzer. Nonsynthetic, nonexpanded graphite particles can be obtained from, for example, Brazilian Nacional de Grafite (Itapecirica, MG Brazil (MP-0702X). Generally, the cathode will include between 5% and 8% of carbon particles by weight. 
     Examples of binders include polyethylene powders, polyacrylamides, Portland cement and fluorocarbon resins, such as PVDF and PTFE. An example of a polyethylene binder is sold under the tradename COATHYLENE HA-1681 (Hoescht). Generally, the cathode includes between 0.1 percent to about 1 percent of binder by weight. 
     Cathode  12  can include other additives. Examples of these additives are disclosed in U.S. Pat. No. 5,342,712, which is hereby incorporated by reference. Cathode  12  may include, for example, from about 0.2 weight percent to about 2 percent TiO 2  weight. 
     The electrolyte solution also is dispersed through cathode  12 , and the weight percentages provided above are determined after the electrolyte solution has been dispersed. 
     The anode can be formed of any of the standard zinc materials used in battery anodes. For example, anode  14  can be a zinc gel that includes zinc metal particles, a gelling agent and minor amounts of additives, such as gassing inhibitor. In addition, a portion of the electrolyte solution is dispersed throughout the anode. 
     The zinc particles can be any of the zinc particles conventionally used in gel anodes. Other examples of zinc particles used in the anode include these described in U.S. Ser. No. 08/905,254. U.S. Ser. No. 09/115,867, and U.S. Ser. No. 09/156,915, which are assigned to the assignee in the present application and are hereby incorporated by reference. Generally, the anode includes between 67% and 71% of zinc particles by weight. 
     Gelling agents that can be used in anode  14  include polyacrylic acids, grafted starch materials, salts of polyacrylic acids, polyacrylates, carboxymethylcellulose or combinations thereof. Examples of such polyacrylic acids are CARBOPOL 940 and 934 (B.F. Goodrich) and POLYGEL 4P (3V), and an example of a grafted starch material is WATERLOCK A221 (Grain Processing Corporation, Muscatine, IA). An example of a salt of a polyacrylic acid is ALCOSORB G1, (Ciba Specialties). The anode generally includes from 0.1 percent to about 1 percent gelling agent by weight. These weight percentages correspond to when the electrolytic solution is dispersed throughout the anode. 
     Gassing inhibitors can be inorganic materials, such as bismuth, tin, lead and indium. Alternatively, gassing inhibitors can be organic compounds, such as phosphate esters, ionic surfactants or nonionic surfactants. Examples of ionic surfactants are disclosed in, for example, U.S. Pat. No. 4,777,100, which is hereby incorporated by reference. 
     Separators  18  can have any of the conventional designs for battery separators. In some embodiments, separators  18  can be formed of two layers of nonwoven, non-membrane material with one layer being disposed along a surface of the other. To minimize the volume of separators  18  while providing an efficient battery, each layer of nonwoven, non-membrane material can have a basis weight of about 54 grams per square meter, a thickness of about 5.4 mils when dry and a thickness of about 10 mils when wet. In these embodiments, the separator preferably does not include a layer of membrane material or a layer of adhesive between the nonwoven, non-membrane layers. Generally, the layers can be substantially devoid of fillers, such as inorganic particles. 
     In other embodiments, separators  18  include an outer layer of cellophane with a layer of nonwoven material. The separator also includes an additional layer of nonwoven material. The cellophane layer can be adjacent cathode  12  or the anode. Preferably, the nonwoven material contains from about 78 weight percent to about 82 weight percent PVA and from about 18 weight percent to about 22 weight percent rayon with a trace of surfactant. Such nonwoven materials are available from PDM under the tradename PA36. 
     The electrolytic solution dispersed throughout battery  10  can be any of the conventional electrolytic solutions used in batteries. Typically, the electrolytic solution is an aqueous hydroxide solution. Such aqueous hydroxide solutions include potassium hydroxide solutions including, for example, between 33% and 38% by weight percent potassium hydroxide, and sodium hydroxide solutions. 
     Housing  20  can be any conventional housing commonly used in primary alkaline batteries. The housing typically includes an inner metal wall and an outer electrically nonconductive material such as heat shrinkable plastic. optionally, a layer of conductive material can be disposed between the inner wall and the cathode  12 . This layer may be disposed along the inner surface of wall, along the outer circumference of cathode  12  or both. This conductive layer can be formed, for example, of a carbonaceous material. Such materials include LB1000 (Timcal), ECCOCOAT 257 (W.R. Grace &amp; Co.), EIECTRODAG 109 (Acheson Industries, Inc.), ELECTRODAG 112 (Acheson) and EB0005 (Acheson). Methods of applying the conductive layer are disclosed in, for example, Canadian Patent No. 1,263,697, which is hereby incorporated by reference. 
     The current collector is made from a suitable metal, such as brass. Seal  26  can be made, for example, of nylon. 
     An example of battery  10  can be prepared as follows. A cathode mixture is prepared by combining 85.5% EMD (from Kerr McGee), 7.3% graphite (COATHYLENE HA1681 from Hoechst), 0.3% polyethylene binder (MP-0702X from Nacional de Graphite), and 6.9% electrolyte solution. The mixture then is compressed under pressure in a die slotted into a two “D” cavity. The formed pellet was attracted out of the die by a counter punch. Four pellets (for a AA battery) or three pellets (for a AAA battery) were aligned vertically by half-moon mandrels and slipped into the housing and then recompacted inside the housing to make contact with the housing. The separator (P.G.I. NONWOVEN 7638) is placed within each cavity. An anode mixture was prepared by combining (in weight percentages) 70% zinc powder (Zinc Corp. of America 1216), a gelling agent (CARBOPOL 940 from BF Goodrich), and 30% electrolyte (composed of 98.6% liquid electrolyte and 1.4% of the dissolved gelling agent). The anode mixture then was dispersed into the cavities. The top assembly including top cap  28 , the current collector, and seal  26 , was placed over the housing and mechanically crimped over to seal the battery. A sealant (SPEC SEAL) was applied to the side of the housing prior to the assembly. 
     In battery  10 , anode cavities  14  and  16  are positioned equal distances (d 1 ,) from housing  20  and equal distances (d 2 ) from each other. The ratio of d 2 :d 1 , is approximately 2:1 around the entire circumference of each cavity. During use of battery  10 , the cathode material closest to the anode cavities will be consumed first, and over time areas of consumed cathode material form around each cavity. Because d 2  is approximately twice d 1 , as the area of consumed cathode material expands it will tend to reach housing  20  and the area of consumed cathode material expanding from the other cavity after approximately the same time. As a result, the efficiency of consumption of the cathode material is maximized, thus increasing the life of the battery. 
     In contrast, referring to FIG. 3, in the battery described in the Mick patent that includes four anode cavities, for the anode cavities across from each other d 2  is much greater than two and a half times d 1 . Thus, as the battery is used, the area of consumed cathode material around each cavity generally will reach the housing before the areas of consumed cathode material around cavities across from each other meet. 
     Other embodiments are within the claims. For example, referring to FIG. 4, a battery includes a cathode  32  and an anode comprising three triangle-shaped cavities ( 34 ,  36 ,  38 ) that also have a d 2 :d 1 , ratio of approximately 2:1. Similarly referring to FIG. 5, a battery  40  includes a cathode  42  and an anode comprising four triangle-shaped cavities  44 ,  46 ,  48 , and  50  that also have a d 2 :d 1  ratio of approximately 2:1. 
     In addition, the positions of the cathode and the anode may be reversed. 
     The battery also may be provided with a switch that allows a user to select which cavity or cavities will be in operation at a given time. A switch on the battery in FIGS. 1-3, for example, may have three positions. One position connects prong  22  to top cap  28 , but disconnects prong  24  from top cap  28 ; another position connects prong  24  to top cap  28 , but disconnects prong  22  from top cap  28 ; the third position connects both prongs  22  and  24  to top cap  28 . Analogous switches may be used with the batteries in FIGS. 4 and 5.