BATTERY SEPARATOR

Abstract: A separator (16) for batteries that does not include a layer of membrane material is provided. The separator (16) includes two layers (16a, 16b) of materials that are disposed adjacent each other. The layers can be formed of the same or different materials. The materials can be woven or nonwoven. In certain embodiments, the layers are formed of the same nonwoven, non-membrane material which is a matrix of polyvinyl alcohol fibers, cellulose fibers and a polyvinyl alcohol binder.

Description: BATTERY SEPARATOR The invention relates to batteries. Batteries, such as alkaline batteries, are commonly used as energy sources. Generally, alkaline batteries have a cathode, an anode, a separator and an electrolytic solution. The cathode is typically formed of manganese dioxide, carbon particles and a binder. The anode can be formed of a gel including 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. The invention relates to batteries, such as alkaline batteries, having separators that do not include a layer of a membrane material. These batteries have good performance characteristics. For example, the batteries can exhibit high energy output at a high discharge rate, such as a discharge rate equal to at least the battery's capacity (in units of Ampere-hours) discharged in one hour. The batteries can have a variety of industry standard sizes, such as A A, AAA, AAAA, C or D. "Membrane materials" have an average pore size of at most about 0.5 microns, whereas "non-membrane materials" have an average pore size of at least about 5 microns. In one aspect, the invention features a battery separator that includes first and second nonwoven, non-membrane materials. The first material is devoid of any filler, and the second material is disposed along a surface of the first material. The battery separator is devoid of a membrane material. In another aspect, the invention features an electrochemical cell that has a long axis and at least short axis which is perpendicular to the short axis. The electrochemical cell includes an anode, a cathode and a separator disposed between the anode .and the cathode. The separator includes first and second nonwoven, non-membrane materials. The second material is disposed along a surface of the first material. At least about 60% of the fiberlength direction of the first material is within about 10 degrees of parallel to the long axis of the electrochemical cell. The fiber- length direction of a nonwoven material refers to the axis along which the fibers of the nonwoven material are generally oriented. It is to be noted, however, that the individual fibers of these nonwoven materials can be oriented in any direction. The first and second materials can absorb a similar amount of an electrolytic solution. For example, the first material can absorb from about 1.1 to about 0.9 times the amount of electrolytic solution that the second material can absorb. The cathode can include manganese dioxide and nonsynthetic, nonexpanded graphite particles having an average particle size of less than about 20 microns as measured by a Sympatec HELIOS analyzer. For a given sample of graphite particles, the average particle size is the particle size for which half the volume of the sample has a smaller particle size. "Nonsynthetic graphite particles" refer to graphite particles that are prepared by a process that does not include industrial or laboratory graphitization. "Nonexpanded graphite particles" refer to graphite particles that have undergone no industrial or laboratory expansion process. The battery can have a relatively small amount of manganese dioxide and/or zinc particles compared to the amount of electrolytic solution. For example, the weight ratio of manganese dioxide to electrolytic solution can be from about 2.2 to about 2.9, and the weight ratio of zinc particles to electrolytic solution can be from about 0.9 to about 1.25. This is calculated based on the amount of electrolytic solution dispersed throughout the battery. The cathode can have a porosity of from about 21% to about 28%. The cathode porosity corresponds to the amount of the cathode that is not taken up by solid material, such as, for example, manganese dioxide, carbon particles and binder. The anode can have a porosity of from about 2 grams of zinc to about 2.45 grams of zinc per cubic centimeter of anode volume that is taken up by liquid or solid material. The batteries can be AA or AAA batteries that demonstrate good results when tested according to the cc photo test, the 1 Watt continuous test, the half Watt continuous test, the pulsed test, the half Watt rm test and/or the quarter Watt rm test. These tests are described below. Other features and advantages of the invention will be apparent from the description of the preferred embodiments thereof and the claims. Fig. 1 is a cross-sectional view of a battery; Fig. 2 is a cross-sectional view of a separator; and Fig. 3 is an elevational view of a nonwoven material. The preferred batteries are alkaline batteries that have a separator that does not include a layer of membrane material. Fig. 1 shows such a battery 10 that has a cathode 12, an anode 14, a separator 16, an outer wall 18 that contacts the outer diameter of cathode 12 and an insulating layer 26. Battery 10 further includes an anode collector 20 that passes through a seal member 22 and into anode 14. The upper end of anode collector 20 is connected to a negative end cap 24 which serves as the negative external terminal of battery 10. Layer 26 can be formed of an electrically nonconducting material, such as a heat shrinkable plastic. In addition, an electrolytic solution is dispersed throughout cathode 12, anode 14 and separator 16. As shown in Fig. 2, separator 16 includes a layer of non-membrane material 16a and a layer of non-membrane material 16b which is disposed along a surface of layer 16a. Layers 16a and 16b can be a single sheet of material which is folded over on itself or wound around itself. Alternatively, layers 16a and 16b can be formed of separate sheets of material. In either embodiment, layer 16a can be formed of the same or different material as layer 16b. In certain embodiments, layer 16a can absorb a similar amount of electrolyte as layer 16b. In these embodiments, layer 16a should be able to absorb from about 1.1 to about 0.9 times the amount of electrolytic solution that layer 16b can absorb. Typically, layer 16a can absorb from about 1.05 to about 0.95 times the amount of electrolytic solution that layer 16b can absorb. Materials appropriate for use in forming layers 16a and 16b can include any of the conventional non-membrane materials used in separators. Generally, these materials do not include fillers such as, for example, inorganic particles. In some embodiments, layer 16a and/or layer 16b can be formed of a woven material. Such materials can be formed from, for example, cellulose, polyvinyl alcohol (PVA), polyamides, polysulfones and mixtures thereof. In certain embodiments, layer 16a and/or 16b can be formed of a nonwoven material. Examples of nonwoven materials include cellulose, PVA, polyamides, polysulfones and mixtures thereof. For example, layer 16a and 16b can each be nonwoven layers formed of a matrix of PVA fibers, PVA binder and cellulose fibers, such as Tencel fibers (Courtaulds), Lyocel fibers (Courtaulds) or rayon fibers. The cellulose fibers can be about 1.5 denier at 6 millimeters long, and the PVA fiber can be about 0.5 denier at 6 millimeters long. In some embodiments, layers 16a and 16b can each be nonwoven layers formed of from about 20 weight percent to about 40 weight percent rayon fibers, from about 55 weight percent to about 65 weight percent PVA fibers and from about 5 weight percent to about 15 weight percent PVA binder. In one embodiment, layer 16a and 16b are each nonwoven layers formed of about 57 weight percent PVA fibers, about 30 weight percent cellulose fibers and 13 about weight percent PVA binder. If separator 16 is too thin, there can be shorting between cathode 12 and anode 14. Separator 16 should not be too thick, however, because this can decrease the volume of battery 10 that is available for cathode 12, anode 14 and the electrolytic solution which reduces the energy capacity of battery 10. Therefore, when dry, layers 16a and 16b are each preferably at least about 4 mils thick, more preferably from about 4 mils to about 6 mils thick, and most preferably about 5.4 mils thick. When wet, layers 16a and 16b are each preferably at least about 8 mils thick, more preferably from about 8 mils to about 12 mils thick, and most preferably about 10 mils thick. The basis weight of separator 16 should not be too low since this can result in shorting between cathode 12 and anode 14, but, if the basis weight of separator 16 is too high, the discharge capability of battery 10 can be decreased. Thus, layers 16a and 16b are each preferably formed of a material having a basis weight of at least about 20 grams per square meter, more preferably from about 40 grams per square meter to about 60 grams per square meter and most preferably about 54 grams per square meter. Separator 16 can be placed within battery 10 using any of the conventional processes. Preferably, separator 16 is placed within battery 10 using a cross-placing technique. In this method, cathode 12 is formed within battery 10, and, prior to forming anode 14, layer 16b is placed on a surface of layer 16a such that the fiber-length direction of layer 16b is approximately perpendicular to the fiber-length direction of layer 16a. Layers 16a and 16b are then pressed into battery 10 such that a portion of the surface of layer 16a is disposed along the inner circumference of cathode 12. In nonwoven materials, the individual fibers can usually be oriented in any direction. However, as shown in Fig. 3, during the manufacturing process, some nonwoven materials can develop a general orientation along one axis, referred to herein as the fiber-length direction. When layers 16a and 16b are formed of nonwoven materials and the cross-placing technique is used, preferably at least about 60%) of layers 16a and 16b have their fiber-length direction within about 10 degrees of parallel to the longest axis of battery 10, more preferably at least about 85%o of layers 16a and 16b are within about 10 degrees of parallel to the longest axis of battery 10, and most preferably about 90%> of layers 16a and 16b have their fiber-length direction within about 10 degrees of parallel with the longest axis of battery 10. Cathode 12 can be formed of any of the standard materials used in battery cathodes. Typically, cathode 12 is formed of a mixture of manganese dioxide, carbon particles and optionally a binder. Cathode 12 can include other additives. Examples of these additives are disclosed in U.S. Patent No. 5,342,712, which is hereby incorporated by reference. In some embodiments, cathode 12 preferably includes from about 0.2 weight percent to about 2 weight percent Ti0 2 , more preferably about 0.8 weight percent Ti0 2 . In some embodiments, cathode 12 can be a single pellet of material. Alternatively, cathode 12 can be formed of a number of pellets that are stacked on top of each other. In either case, the cathode pellets can be made by first mixing the manganese dioxide, carbon particles and optionally a binder. For embodiments in which more than one pellet is used, the mixture can be pressed to form the pellets. The pellet(s) are fit within battery 10 using standard processes. For example, in one process, a core rod is placed in the central cavity of battery 10, and a punch is then used to pressurize the top most pellet. When using this process, the interior of wall 18 can have one or more vertical ridges that are spaced circumferentially around wall 18. These ridges can assist in holding cathode 12 in place within battery 10. In embodiments in which cathode 12 is formed of a single pellet, the powder can be placed directly within battery 10. A retaining ring can be set in place, and an extrusion rod can pass through the ring, densifying the powder and forming cathode 12. In some embodiments, a layer of a conductive material can be disposed between wall 18 and the outer circumference of cathode 12. This layer can be disposed along the inner surface of wall 18, along the outer circumference of cathode 12 or both. Typically, this conductive layer is formed of a carbonaceous material. Such materials include LB 1000 (Timcal), Eccocoat 257 (W.R. Grace & Co.), Electrodag 109 (Acheson Industries, Inc.), Electrodag 112 (Acheson) and EB005 (Acheson). Methods of applying the electrolytic material are disclosed in Canadian Patent No. 1,263,697, which is hereby incorporated by reference. Including such a layer of conductive material, especially EB005, can reduce the pressure used when forming cathode 12 within battery 10. Thus, the porosity of cathode 12 can be made relatively high without the pellet(s) being crushed or cracked when forming cathode 12 within battery 10. However, if the porosity of cathode 12 is too low, an insufficient amount of electrolytic solution can be dispersed within cathode 12, reducing the efficiency of battery 10. Thus, in certain embodiments, cathode 12 preferably has a porosity of from about 21%> to about 28%o, more preferably from about 25%) to about 27%>, and most preferably about 26%o. Any of the conventional forms of manganese dioxide used in battery cathodes may be used in cathode 12. Suppliers of such manganese dioxide include Kerr McGee, Co., Broken Hill Proprietary, Chem Metals, Co., Tosoh, Delta Manganese, Mitsui Chemicals and JMC. In certain embodiments, cathode 12 can have from about 8.9 grams of manganese dioxide to about 9.8 grams of manganese dioxide. In these embodiments, cathode 12 preferably has from about 9.3 grams to about 9.75 grams of manganese dioxide, more preferably from about 9.4 grams to about 9.65 grams of manganese dioxide, and most preferably from about 9.45 grams to about 9.6 grams of manganese dioxide. In other embodiments, cathode 12 preferably has from about 4 grams to about 4.3 grams of manganese dioxide, more preferably from about 4.05 grams to about 4.25 grams of manganese dioxide, and most preferably from about 4.1 grams to about 4.2 grams of manganese dioxide. In embodiments in which cathode 12 includes carbon particles, the average particle size of the carbon particles is limited only by the dimensions of cathode 12. In addition, the carbon particles can be nonsynthetic or synthetic and expanded or nonexpanded. In certain embodiments, the carbon particles are formed of nonsynthetic, nonexpanded graphite particles which 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 are available from, for example, Brazilian Nacional de Grafite, located in Itapecirica, MG Brazil. The amount of carbon particles disposed within cathode 12 should be high enough to improve the conductivity of cathode 12 while having minimal impact on the energy capacity of battery 10. Preferably, cathode 12 is from about 4 weight percent to about 10 weight percent carbon particles, more preferably from about 5 weight percent to about 9 weight percent carbon particles, and most preferably from about 6 weight percent to about 8 weight percent carbon particles. These weight percentages correspond to when the electrolytic solution is not dispersed within cathode 12. In certain embodiments, cathode 12 may further include a binder. Such binders include polyethylene powders, polyacrylamides, Portland cement and fluorocarbon resins, such as PVDF and PTFE. In some embodiments, cathode 12 includes a binder sold under the tradename coathylene HA- 1861 (Hoescht). When cathode 12 includes a binder, the binder preferably makes up at most about 1 weight percent of cathode 12, more preferably from about 0.1 weight percent to about 0.5 weight percent of cathode 12, and most preferably about 0.3 weight percent of cathode 12. These weight percentages correspond to when cathode 12 does not include the electrolytic solution. Anode 14 can be formed of any of the standard zinc materials used in anodes. Often, anode 14 is formed of a zinc gel that includes zinc metal particles, a gelling agent and minor amounts of additives, such as gassing inhibitors. In addition, a portion of the electrolytic solution is dispersed within anode 14. If the porosity of anode 14 is too high, the amount of zinc within battery 10 is reduced which decreases the energy capacity of battery 10. However, if the porosity of anode 14 is too low, an insufficient amount of electrolytic solution can be dispersed within anode 14. Therefore, in some embodiments, anode 14 has a porosity of from about 2 grams of zinc particles to about 2.45 grams of zinc particles per cubic centimeter of anode volume, more preferably from about 2.1 grams of zinc particles to about 2.35 grams of zinc particles per cubic centimeter of anode volume, and most preferably from about 2.15 grams of zinc particles to about 2.3 grams of zinc particles per cubic centimeter of anode volume. In certain embodiments, anode 14 preferably has from about 3.7 grams to about 4.25 grams of zinc particles, more preferably from about 3.8 grams to about 4.15 grams of zinc particles, and most preferably from about 3.9 grams to about 4.05 grams of zinc particles. In other embodiments, anode 14 preferably has from about 1.5 grams to about 1.9 grams of zinc particles, more preferably from about 1.55 grams to about 1.85 grams of zinc particles, and most preferably from about 1.65 grams to about 1J5 grams of zinc particles. In some embodiments, anode 14 preferably includes from about 64 weight percent to about 76 weight percent zinc particles, more preferably from about 66 weight percent to about 74 weight percent zinc particles, and most preferably from about 68 weight percent to about 72 weight percent zinc particles. These weight percentages correspond to when the electrolytic solution is dispersed within anode 14. Gelling agents that can be used in anode 14 include polyacrylic acids, grafted starch materials, polyacrylates, salts of polyacrylic acids, carboxymethylcellulose and mixtures thereof. Examples of polyacrylic acids are Carbopol 940 (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 CL15 (Allied Collords). In some embodiments, anode 14 preferably includes from about 0.2 weight percent to about 1 weight percent total gelling agent, more preferably from about 0.4 weight percent to about 0.7 weight percent total gelling agent, and most preferably from about 0.5 weight percent to about 0.6 weight percent gelling agent. These weight percentages correspond to when the electrolytic solution is dispersed within anode 14. 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 examples, U.S. Patent No. 4,777,100, which is hereby incorporated by reference. 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, for example, potassium hydroxide solutions and sodium hydroxide solutions. In some embodiments, the electrolytic solution is an aqueous potassium hydroxide solution including from about 33 weight percent to about 38 weight percent potassium hydroxide. In certain embodiments, battery 10 preferably includes from about 3.4 grams to about 3.9 grams of electrolytic solution, more preferably from about 3.45 grams to about 3.65 grams of electrolytic solution, and most preferably from about 3.5 grams to about 3.6 grams of electrolytic solution. In other embodiments, battery 10 preferably includes from about 1.6 grams to about 1.9 grams of electrolytic solution, more preferably from about 1.65 grams to about 1.85 grams of electrolytic solution, and most preferably from about 1J grams to about 1.8 grams of electrolytic solution. The weight ratio of manganese dioxide to electrolytic solution can be from about 2.2 to about 2.9, and the weight ratio of zinc particles to electrolytic solution can be from about 0.9 to about 1.25. In some embodiments, the weight ratio of manganese dioxide to electrolytic solution is preferably from about 2.5 to about 2.9, and the weight ratio of zinc particles to electrolytic solution is preferably from about 1.1 to about 1.25. In other embodiments, the weight ratio of manganese dioxide to electrolytic solution is preferably from about 2.5 to about 2.65, and the weight ratio of zinc particles to electrolytic solution is preferably from about 0.9 to about 1.2. The batteries can be AA or AAA batteries that demonstrate good results when tested according to the cc photo test, the 1 Watt continuous test, the half Watt continuous test, the pulsed test, the half Watt rm test and/or the quarter Watt rm test. These tests are described below. Battery 10 can be a AA battery that exhibits excellent performance when tested according to the 1 Watt continuous test (described below). For example, when discharged to 1 Volt according to the 1 Watt continuous test, the AA battery can give at least about 0.6 hours, at least about 0.65 hours, at least about 0.7 hours or at least about 0.75 hours. When discharged to 0.9 Volts according to the 1 Watt continuous test, the AA battery can give at least about 0.95 hours, at least about 1 hour, at least about 1.05 hours or at least about 1.1 hours. Battery 10 can be a AA battery that exhibits excellent performance when tested according to the pulsed test (described below). For example, when discharged to 1 Volt according to the pulsed test, the AA battery can give at least about 1.6 hours, at least about 1J5 hours, at least about 2 hours or at least about 2.15 hours. When discharged to 0.9 Volts according to the pulsed test, the AA battery can give at least about 2.75 hours, at least about 3 hours, at least about 3.25 hours or at least about 3.3 hours. Battery 10 can be a AA battery that exhibits excellent performance when tested according to the half Watt rm test (described below). For example, when discharged to 1 Volt according to the half Watt rm test, the AA battery can give at least about 1.5 hours, at least about 2 hours, at least about 2.5 hours or at least about 2.65 hours. When discharged to 0.8 Volts according to the half Watt rm test, the AA battery can give at least about 2.9 hours, at least about 3 hours, at least about 3.25 hours or at least about 3.4 hours. Battery 10 can be a AA battery that offers excellent performance according to the half Watt rm test (described below). For example, when discharged to 1.1 Volts according to the half Watt rm test, the AA battery can give at least about 1.5 hours, at least about 2 hours, at least about 2.5 hours or at least about 2.65 hours. When discharged to 0.8 Volts according to the half Watt rm test, the AA battery can give at least 2.9 hours, at least about 3 hours, at least about 3.25 hours or at least about 3.4 hours. Battery 10 can be a AAA battery that offers excellent performance according to the half Watt continuous test (described below). For example, when discharged to 1 Volt according to the half Watt continuous test, the AAA battery can give at least about 0.65 hours, at least about 0.7 hours, at least about 0.75 hours or at least about 0.8 hours. When discharged to 0.9 Volts according to the half Watt continuous test, the AAA battery can give at least 0.9 hours, at least about 0.95 hours, at least about 1.0 hour or at least about 1.05 hours. Battery 10 can be a AAA battery that offers excellent performance according to the pulsed test (described below). For example, when discharged to 1 Volt according to the pulsed test, the AAA battery can give at least about 0.35 hours, at least about 0.4 hours, at least about 0.45 hours or at least about 0.5 hours. When discharged to 0.9 Volts according to the pulsed test, the AAA battery can give at least 0.65 hours, at least about 0.7 hours, at least about 0.75 hours or at least about 0.8 hours. Battery 10 can be a AAA battery that offers excellent performance according to the half Watt rm test (described below). For example, when discharged to 1.1 Volts according to the half Watt rm test, the AAA battery can give at least about 0.4 hours, at least about 0.45 hours, at least about 0.5 hours or at least about 0.55 hours. When discharged to 0.9 Volts according to the half Watt rm test, the AAA battery can give at least 0.9 hours, at least about 0.95 hours, at least about 1 hour or at least about 1.05 hours. Battery 10 can be a AAA battery that offers excellent performance according to the quarter Watt rm test (described below). For example, when discharged to 1.1 Volts according to the quarter Watt rm test, the AAA battery can give at least about 2 hours, at least about 2.1 hours, at least about 2.2 hours or at least about 2.3 hours. When discharged to 0.9 Volts according to the quarter Watt rm test, the AAA battery can give at least 3.1 hours, at least about 3.25 hours, at least about 3.4 hours or at least about 3.5 hours. Example I A A batteries were prepared with the following components. The cathode included about 9.487 grams of manganese dioxide (Kerr-McGee, Co.), about 0.806 grams of nonsynthetic, nonexpanded graphite having an average particle size of about 7 microns (Brazilian Nacional de Grafite) and about 0.3 weight percent of coathylene HA- 1681. The anode included about 3.976 grams of zinc particles, about 50 ppm surfactant (RM 510, Rhone Poulenc) relative to zinc, and about 0.5 weight percent total gelling agent (Carbopol 940 and A221). The porosity of the cathode was about 26%>, .and the porosity of the anode was about 2.173 grams of zinc per cubic centimeter of anode. The separator was a two-layer structure with each layer formed of a nonwoven material including about 57 weight percent PVA fibers (about 0.5 denier at 6 millimeters), about 30 weight percent rayon fibers (about 1.5 denier at 6 millimeters) and about 13 weight percent PVA binder. Each layer was about 5.4 mils thick when dry and about 10 mils thick when wet. Each layer had a basis weight of about 54 grams per square meter. The separator did not include an adhesive, and the layers were substantially devoid of any filler. The battery also included about 3.598 grams of an aqueous potassium hydroxide (about 35.5 weight percent potassium hydroxide) solution. A thin coating of EB005 (Acheson) was disposed between the outer wall of the battery and the outer periphery of the cathode. The AA batteries were stored at a temperature of from about 20.1°C to about 22.1°C for five days. The AA batteries were then stored according to the following procedure. Each battery is visually examined for leakage or material damage and identified such that battery identification can be maintained throughout the test program. The batteries are oriented on their sides in holding trays such that the batteries are not in physical contact with each other. The holding trays are made to be resistant to heat and electrolytes. The trays are stored for 1 day at ambient conditions, after which the trays are placed in a preheated chamber. The trays are spaced so that there is at least about 5 cm (2 inches) of space between the chamber wall, and the tray above, below, or adjacent to each tray. The following 24 hour test sequence, shown in Table I, is repeated for 14 days. Table I The trays are removed from the chamber and each battery is visually examined for leakage and material damage. The following tests were subsequently performed on individual AA batteries. Each test was conducted at a temperature of from about 20.1°C to about 22.1°C. A AA battery was discharged from an open circuit voltage of about 1.6 Volts under constant current conditions of ten seconds per minute for one hour per day ("the cc photo test"). The AA battery reached 1 Volt after 203 pulses, and the AA battery reached 0.8 Volts after 443 pulses. A AA battery was continuously discharged from an open circuit voltage of about 1.6 Volts at 1 Watt ("the 1 Watt continuous test"). The AA battery reached 1 Volt after about 0.75 hours, and the AA battery reached 0.8 Volts after about 1.00 hours. A AA battery was continuously discharged from an open circuit voltage of about 1.6 Volts at a rate that alternated between 1 Watt (3 second pulses) .and 0.1 Watt (7 second pulses) ("the pulsed test"). The AA battery reached 1 Volt after about 2.16 hours, and the AA battery reached 0.8 Volts after about 3.72 hours. A AA battery was discharged from an open circuit voltage of about 1.6 Volts at 0.5 Watts for 15 minutes per hour ("the half Watt rm test"). The AA battery reached 1.1 Volts after about 1.87 hours, and the AA battery reached 0.9 Volts after about 3.34 hours. Example II A AAA battery was prepared. The cathode 12 included about 4.155 grams of manganese dioxide (Kerr McGee, Co.), about 0.353 grams of non- synthetic, nonexpanded graphite having an average particle size of about 7 microns (Brazilian Nacional de Grafite) and about 0.3 weight percent of coathylene HA- 1681. The anode 14 included about 1.668 grams of zinc particles, about 50 ppm surfactant (RM 510, Rhone Poulenc), and about 0.5 weight percent total gelling agent (Carbopol 940 and A221). The porosity of the cathode was about 26%), and the porosity of the anode was about 2.266 grams of zinc per cubic centimeter of anode 14. The separator included two layers of nonwoven material. The separator was a two layer structure with each layer formed of a non woven material including about 57 weight present PVA fibers (about 0.5 denier at (millimeters), about 30 weight percent cellulose fibers (about 1.5 denier at 6 millimeters) and about 13 weight percent PVA binder. Each layer was about 5.4 mils thick when dry and about 10 mils thick when wet. Each layer had a boxes weight of about 54 grams per square meter. The separator did not include an adhesive, and the layer were substantially devoid of any filler. The battery also included about 1.72 grams of an aqueous potassium hydroxide (about 35.5 weight percent) solution. A thin coating of EB005 (Acheson) was disposed between the outer wall of the battery and the outer periphery of the cathode. The AAA batteries were stored as described in Example I. Each AAA battery was discharged from an open circuit voltage of about 1.6 Volts, and the tests were conducted within the temperature range described in Example I. A AAA battery was continuously discharged from an open circuit voltage of about 1.6 Volts at one half Watt ("the half Watt continuous test"). The AAA battery reached 1 Volt after about 0.76 hours, and the AAA battery reached 0.8 Volts after about 0.96 hours. With the pulsed test, a AAA battery took about 0.55 hours to reach 1 Volt, and about 0.84 hours to reach 0.8 Volts. With the half Watt rm test, a AAA battery took about 0.57 hours to reach 1 Volt, and about 1.08 hours to reach 0.8 Volts. A AAA battery was discharged from an open circuit voltage of about 1.6 Volts at 0.25 Watts for 15 minutes per hour ("the quarter Watt rm test"). The AAA battery reached 1.1 Volts after about 2.4 hours, and the AAA battery reached 0.9 Volts after about 3.65 hours. Other embodiments are within the claims.

Claims: C L A I M S 1. An electrochemical cell having a long axis and at least one short axis perpendicular to the long axis, the electrochemical cell comprising: an anode; a cathode; and a separator disposed between the anode and the cathode, wherein the separator comprises: a first nonwoven, non-membrane material having a fiber-length direction, at least about 60%> of the fiber-length direction of the first material being within about 10 degrees of parallel to the long axis of the electrochemical cell; and a second nonwoven, non-membrane material disposed along a surface of the first material. 2. The electrochemical cell according to claim 1, wherein the separator is devoid of a membrane material. 3. The electrochemical cell according to claim 1, wherein the separator is devoid of an adhesive material between the first and second materials. 4. The electrochemical cell according to claim 1, wherein the first and second materials are cross-placed. 5. The electrochemical cell according to claim 1, wherein the first material is devoid of any filler. 6. The electrochemical cell according to claim 5, wherein the second material is devoid of any filler. 7. The electrochemical cell according to claim 1 , wherein the first and second materials each have a basis weight of at least about 20. 8. The electrochemical cell according to claim 1, wherein the first and second materials each have a thickness of at least about 4 mils. 9. The electrochemical cell according to claim 1, wherein the first and second materials are formed of different sheets of material. 10. The electrochemical cell according to claim 1, wherein the first material comprises a matrix of poly vinyl alcohol fibers, cellulose fibers and a polyvinyl alcohol binder. 11. The electrochemical cell according to claim 1 , wherein the first and second materials are capable of absorbing a similar amount of an electrolytic solution. 12. The electrochemical cell according to claim 1, wherein the electrochemical cell is an alkaline battery. 13. The electrochemical cell according to claim 1, wherein the electrochemical cell is selected from the group consisting of AA batteries, AAA batteries, AAAA batteries, C batteries and D batteries. 14. The electrochemical cell according to claim 1, wherein the cathode comprises manganese dioxide and nonsynthetic, nonexpanded graphite particles having an average particle size of at most about 20 microns. 15. The electrochemical cell according to claim 1, wherein the cathode comprises manganese dioxide and carbon particles, and wherein the cathode has a porosity of from about 21%> to about 28%>. 16. The electrochemical cell according to claim 1, wherein the anode comprises zinc particles, and wherein the anode has a porosity of from about 2 grams of zinc particles to about 2.45 grams of zinc particles per cubic centimeter of anode volume. 17. The electrochemical cell according to claim 1, further comprising an electrolytic solution, wherein the cathode comprises manganese dioxide, and wherein a weight ratio of manganese dioxide to electrolytic solution is from about 2.2 to about 2.9. 18. The electrochemical cell according to claim 1, further comprising an electrolytic solution, wherein the anode comprises zinc particles, and wherein a weight ratio of zinc particles to electrolytic solution is from about 0.9 to about 1.25. 19. A battery separator, comprising: a first nonwoven, non-membrane material being devoid of any filler; and a second nonwoven, non-membrane material disposed along a surface of the first material, wherein the battery separator is devoid of a membrane material. 20. The battery separator according to claim 19, wherein the second material is devoid of any filler. 21. The battery separator according to claim 19, wherein the separator is devoid of an adhesive material between the first and second materials. 22. The battery separator according to claim 19, wherein the first and second materials each have a basis weight of at least about 20. 23. The battery separator according to claim 19, wherein the first and second materials each have a thickness of at least about 4 mils. 24. The battery separator according to claim 19, wherein the first and second materials are formed of different sheets of material. 25. The battery separator according to claim 19, wherein the first material comprises a matrix of polyvinyl alcohol fibers, cellulose fibers and polyvinyl alcohol binder. 26. The battery separator according to claim 19, wherein the battery separator is in contact with an electrolytic solution. 27. The battery separator according to claim 19, wherein the first and second materials are capable of absorbing a similar amount of an electrolytic solution.

Inventors: BRYS BARBARA, CERVERA JAMES, FARISS GREGORY A, HAMILTON TERRY L, HARRIS PETER B, HOWARD MARTIN W, TAY GEORGE I, WOODNORTH DOUGLAS J, BRYS, BARBARA, CERVERA, JAMES, FARISS, GREGORY, A., HAMILTON, TERRY, L., HARRIS, PETER, B., HOWARD, MARTIN, W., TAY, GEORGE, I., WOODNORTH, DOUGLAS, J.
Applicants: DURACELL INC, DURACELL INC.
Application year: 1998
Main classification: H01M2
IPC codes: H01M2, H01M4, H01M6