Button type alkaline battery

Abstract

The purpose of the present invention is to provide a button type alkaline battery excellent in battery characteristics such as storage characteristics and discharge characteristics.　This button type alkaline battery according to the present invention has a positive electrode, a negative electrode, and a separator enclosed in a battery container that has an outer can and a sealing can. The positive electrode has a mixture layer A containing a silver oxide as a positive electrode active material and a mixture layer B containing a manganese oxide as a positive electrode active material, where the inner bottom surface of the outer can faces the mixture layer A and is electrically connected thereto, and the separator faces the mixture layer B. The mixture layer A contains 98 mass % or more of the silver oxide and 0.1 mass % or more of a carbon material. The mixture layer B contains 94 mass % or more of the manganese oxide and 0.5 mass % or more of the carbon material, where the mass ratio of the silver oxide and the manganese oxide in the entire positive electrode is 55:45-95:5.

Description

Button-type alkaline batteries

[0001] This invention relates to a button-type alkaline battery having silver oxide as the positive electrode active material and exhibiting excellent battery characteristics such as storage characteristics and discharge characteristics.

[0002] In button-type alkaline batteries that use silver compounds such as silver oxide or silver-nickel oxide as the positive electrode, an alkaline aqueous solution is used as the electrolyte, and the separator is a film made by integrating a graft membrane, which is a polyolefin resin film graft polymerized with hydrophilic vinyl monomer, with cellophane. Of these, the graft membrane suppresses the movement of silver ions eluted from the positive electrode to the negative electrode, and the cellophane has the function of reducing silver ions passing through the graft membrane and suppressing their movement.

[0003] Button-type alkaline batteries have a problem in that the separator, which is in direct contact with the positive electrode, is easily oxidized due to the strong oxidizing power of the silver oxide used in the positive electrode. Furthermore, during storage at high temperatures or for long periods, some silver ions may pass through the separator and move to the negative electrode, where they are reduced, potentially causing self-discharge or internal short circuits. Therefore, it is necessary to suppress the movement of silver ions to the negative electrode.

[0004] In contrast, Patent Document 1 proposes a laminated structure for the positive electrode consisting of a silver oxide pellet layer and a manganese dioxide pellet layer, with the manganese dioxide pellet layer placed on the side in contact with the separator. This configuration prevents the reaction between the separator and silver oxide. Furthermore, since an appropriate amount of conductive additive can be distributed to each active material, a highly efficient battery can be constructed.

[0005] Japanese Patent Publication No. 2019-160672

[0006] On the other hand, in order to further improve battery characteristics, there is still room for further investigation even in the technology described in Patent Document 1.

[0007] This invention has been made in view of the above circumstances, and its purpose is to provide a button-type alkaline battery with excellent battery characteristics such as storage characteristics and discharge characteristics.

[0008] The button-type alkaline battery of the present invention comprises a positive electrode, a negative electrode, and a separator, which are sealed within a battery container having an outer casing and a sealed casing. The positive electrode comprises a composite layer A containing silver oxide as a positive electrode active material and a composite layer B containing manganese oxide as a positive electrode active material. The inner bottom surface of the outer casing is electrically connected to the composite layer A, and the separator faces the composite layer B. The composite layer A contains silver oxide in a proportion of 98% by mass or more and carbon material in a proportion of 0.1% by mass or more, and the composite layer B contains manganese oxide in a proportion of 94% by mass or more and carbon material in a proportion of 0.5% by mass or more. The mass ratio of silver oxide to manganese oxide in the entire positive electrode is in the range of 55:45 to 95:5.

[0009] In the battery industry, flat-shaped batteries with a diameter greater than their height are sometimes called button batteries or coin batteries. However, there is no clear distinction between button batteries and coin batteries, and the button-shaped alkaline battery of the present invention does not exclude what are called coin batteries. Such batteries called coin batteries are also included within the scope of the button-shaped alkaline battery of the present invention.

[0010] According to the present invention, it is possible to provide a button-type alkaline battery with excellent battery characteristics such as storage characteristics and discharge characteristics.

[0011] This is a schematic cross-sectional view showing an example of the button-type alkaline battery of the present invention. These are the discharge curves obtained during the discharge capacity measurement of Example 3 and Comparative Examples 1 to 5. This figure shows the discharge capacity of the button-type alkaline batteries of Examples 1, 2 and Comparative Example 1 after storage at 60°C. This figure shows the discharge voltage at each discharge depth of the button-type alkaline batteries of Examples 1, 2 and Comparative Example 1.

[0012] Figure 1 shows a schematic cross-sectional view illustrating an example of the button-type alkaline battery of the present invention. In the button-type alkaline battery 1 shown in Figure 1, a sealing can 3 containing a negative electrode 5 is fitted into the opening of an outer can 2 containing a positive electrode 4 and a separator 6 via an L-shaped, annular gasket 7. The open end of the outer can 2 is tightened inward, causing the gasket 7 to contact the sealing can 3, thereby sealing the opening of the outer can 2 and creating a sealed structure inside the battery. In other words, in the button-type alkaline battery 1 shown in Figure 1, the power generation elements including the positive electrode 4 and negative electrode 5 are loaded into the space (sealed space) inside the battery container consisting of the outer can 2, the sealing can 3, and the gasket 7, and an alkaline electrolyte (not shown) is also contained within. Furthermore, in the button-type alkaline battery 1 shown in Figure 1, the peripheral edge of the positive electrode 4 is positioned between the inner bottom surface of the outer can 2 and the bottom surface of the gasket 7 (hereinafter, this structure will be referred to as the "bottom structure"). In the battery shown in Figure 1, the outer casing 2 also serves as the positive terminal, and the sealing casing 3 also serves as the negative terminal.

[0013] Furthermore, the positive electrode 4 of the button-type alkaline battery 1 has a composite layer A41 containing silver oxide as the positive electrode active material and a composite layer B42 containing manganese oxide as the positive electrode active material. The inner bottom surface of the outer casing 2 is electrically connected to the composite layer A41, and the separator 6 is connected to the composite layer B42.

[0014] The button-type alkaline battery of the present invention (hereinafter sometimes simply referred to as "battery"), as shown in Figure 1, comprises a positive electrode, a negative electrode, and a separator enclosed in a battery container having an outer casing and a sealed casing. The positive electrode has a composite layer A containing silver oxide as the positive electrode active material and a composite layer B containing manganese oxide as the positive electrode active material. The inner bottom surface of the outer casing is electrically connected to composite layer A, and the separator is connected to composite layer B.

[0015] The positive electrode is composed of a composite layer A containing silver oxide and a composite layer B containing manganese oxide as the positive electrode active material. By placing composite layer B on the separator side, i.e., the negative electrode side, silver ions can move to the negative electrode side and be reduced, suppressing the growth of silver on the negative electrode. This prevents problems such as self-discharge and internal short circuits from occurring in the battery when it is stored.

[0016] Furthermore, by using the above-described configuration for the positive electrode, the initial internal resistance of the battery can be significantly reduced. This is thought to be because, when the battery is not discharged, the internal resistance of the composite layer A, which contains silver oxide (which has lower conductivity than manganese oxide), is high. By bringing the composite layer A into contact with the outer casing, which functions as a current collector, it becomes easier to collect current, thereby ensuring conductivity between the silver oxide and the outer casing.

[0017] Furthermore, in the positive electrode, composite layer A contains 98% or more by mass of silver oxide and 0.1% or more by mass of carbon material, and composite layer B contains 94% or more by mass of manganese oxide and 0.5% or more by mass of carbon material, so that the mass ratio of silver oxide to manganese oxide in the entire positive electrode is in the range of 55:45 to 95:5. Having a positive electrode with this configuration allows the battery voltage to be maintained at a high level from the initial stage of discharge.

[0018] In batteries using silver oxide as the positive electrode active material, the resistance of the composite layer is usually high and the discharge voltage is relatively low in the initial stages of discharge. However, by making the composite layer A containing silver oxide conductive with the outer casing to facilitate current collection, the resistance of the composite layer quickly decreases, the discharge voltage rises, and discharge can proceed at a relatively high discharge voltage. On the other hand, in batteries using manganese oxide as the positive electrode active material, the discharge voltage decreases gradually as discharge progresses. Once the positive electrode discharge has progressed to a certain extent, the characteristics of composite layer B become apparent, and the discharge voltage gradually decreases.

[0019] Therefore, the button-type alkaline battery of the present invention, with the positive electrode configured as described above, can be made into a battery with excellent discharge characteristics, where the discharge voltage is high from the start of discharge and the high voltage can be maintained until a certain depth of discharge is reached.

[0020] The button-type alkaline battery of the present invention is a primary battery. Details of the battery of the present invention are described below.

[0021] (Positive electrode) The positive electrode has a composite layer A with silver oxide as the active material and a composite layer B with manganese oxide as the active material. Composite layers A and B can be formed from a molded body made by molding a composite material (positive electrode composite) containing the active material.

[0022] Examples of silver oxides contained in compound layer A include silver oxide, silicic oxide, silver-nickel composite oxide, and other silver-containing composite oxides, and one or more of these can be used.

[0023] While there are no particular limitations on the particle size of the silver oxide, it is preferable that the average particle diameter be 10 μm or less, and more preferably 2 μm or less.

[0024] However, since silver oxide with very small particle sizes is difficult to manufacture and handle afterward, the average particle size of the silver oxide is preferably 0.01 μm or larger, and more preferably 0.03 μm or larger.

[0025] In this specification, the particle size of silver oxides and other particles (graphite particles, carbon black particles, insulating inorganic particles, and zinc particles related to the negative electrode) is measured using a laser scattering particle size analyzer (for example, Horiba LA-920) by dispersing these particles in a non-dissolving medium.

[0026] The composite layer A contains a carbon material as a conductive additive. Examples of carbon materials to be included in composite layer A include carbon black and graphite, with graphite being preferred. In addition, carbon black and graphite may be used in combination in composite layer A.

[0027] By using carbon black, a good conductive network can be easily formed in the composite layer A. Compared to using only graphite, for example, the number of contact points with the silver oxide (and its particles), which is the positive electrode active material, is increased, and the electrical resistance within the composite layer A can be effectively reduced.

[0028] On the other hand, when using only carbon black, depending on the thickness of the composite layer A, it may be necessary to use a binder to improve its moldability. However, when graphite is also used, the moldability of the composite layer A is improved. For example, even when the composite layer A is thin, such as 0.4 mm or less, more preferably 0.3 mm or less, its moldability is good, making it easier to prevent manufacturing defects without using a binder.

[0029] The graphite in the composite layer A may be either natural graphite (such as flaky graphite) or artificial graphite, and one or more of these can be used.

[0030] As described above, graphite has the function of improving the moldability of the composite layer A. From the viewpoint of better exhibiting this function, the average particle size of the graphite is preferably 1 μm or more, more preferably 2 μm or more, and from the viewpoint of improving conductivity, it is preferably 7 μm or less, and more preferably 5 μm or less.

[0031] Examples of carbon blacks used in the composite layer A include furnace black, channel black, acetylene black, and thermal black, and one or more of these can be used. Among these carbon blacks, acetylene black, which has high conductivity and low impurity content, is preferably used.

[0032] Regarding the composition of composite layer A, from the viewpoint of ensuring the battery capacity and maintaining a high voltage from the initial to the final stages of battery discharge, it is preferable that the proportion of silver oxide in composite layer A is 98% by mass or more, and preferably 98.5% by mass or more, and that the proportion of carbon material in composite layer A is 0.1% by mass or more, and preferably 0.2% by mass or more. The upper limit of the proportion of silver oxide in composite layer A is determined, for example, within the range in which the proportion of carbon material satisfies the lower limit. The upper limit of the proportion of carbon material in composite layer A is determined, for example, within the range in which the proportion of silver oxide satisfies the lower limit.

[0033] The composite layer A can be composed of silver oxide and a carbon material, but other components (active materials other than silver oxide, binders, etc.) can also be contained in the composite layer A. When components other than silver oxide and the carbon material are contained in the composite layer A, the ratios of these components are set within the range where the ratios of the silver oxide and the carbon material respectively satisfy the above lower limit values.

[0034] Examples of the active materials other than silver oxide that can be contained in the composite layer A include manganese oxide (the same as those that can be contained in the composite layer B), nickel oxyhydroxide, hydrogen storage alloys (such as LaNi ５ etc.). Examples of the binders that can be contained in the composite layer A include fluororesins such as polytetrafluoroethylene (PTFE), and olefin resins such as polyethylene (PE).

[0035] Examples of the manganese oxide to be contained in the composite layer B include Mn ２ O ３ 、Mn ３ O ４ 、MnOOH、MnO ２ (manganese dioxide), ZnMn ２ O ４ 、LiMn ２ O ４ etc., oxides or complex oxides containing Mn, and one or more of these can be used.

[0036] Examples of the carbon material to be contained in the composite layer B include the same various carbon materials as those exemplified above that can be contained in the composite layer A, and one or more of these can be used.

[0037] As the composition of the composite agent layer B, from the viewpoint of ensuring the capacity of the battery and ensuring the effect of maintaining a high voltage from the initial stage of battery discharge to a certain depth of discharge, the proportion of manganese oxide in the composite agent layer B is 94% by mass or more, preferably 95% by mass or more, and the proportion of the carbon material in the composite agent layer B is 0.5% by mass or more, preferably 1% by mass or more. The upper limit value of the proportion of manganese oxide in the composite agent layer B is determined, for example, within the range where the proportion of the carbon material satisfies the above lower limit value. Also, the upper limit value of the proportion of the carbon material in the composite agent layer B is determined, for example, within the range where the proportion of the manganese compound satisfies the above lower limit value.

[0038] The composite agent layer B can contain a binder. Examples of the binder that can be contained in the composite agent layer B include fluororesins such as polytetrafluoroethylene (PTFE) and olefin resins such as polyethylene (PE).

[0039] The composite agent layer B may contain an active material other than manganese oxide. Examples of the active material other than manganese oxide that can be contained in the composite agent layer B include silver oxide (the same as those that can be contained in the composite agent layer A), nickel oxyhydroxide, hydrogen storage alloys (such as LaNi ５ etc.).

[0040] When the composite agent layer B contains components other than manganese oxide and carbon material (such as a binder and an active material other than manganese oxide), the proportions of these components are set within the range where the proportions of manganese oxide and carbon material satisfy the respective lower limit values.

[0041] The total amount of silver oxide and manganese oxide in the positive electrode can be adjusted so that, from the viewpoint of increasing the discharge capacity of the battery and extending the time that the voltage can be maintained at a high level from the initial stage of discharge, the amount of silver oxide and manganese oxide contained in composite layer A and composite layer B is in the range of X ≤ 45, where the mass ratio of silver oxide:manganese oxide = 100 - X:X, and it is preferable that X ≤ 40, more preferably X ≤ 30, and particularly preferable X ≤ 25. In other words, the proportion of silver oxide in the positive electrode active material should be 55% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferable 75% by mass or more.

[0042] On the other hand, from the viewpoint of suppressing a decrease in the battery's storage characteristics due to the movement of silver ions to the negative electrode, the amounts of silver oxide and manganese oxide contained in composite layer A and composite layer B should be adjusted so that X ≥ 5, preferably X ≥ 10, and more preferably X ≥ 15. In other words, the proportion of manganese oxide in the positive electrode active material should be 5% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more, so that the proportion of composite layer B in the entire positive electrode is above a certain level.

[0043] The total amount of silver oxide in the positive electrode includes the amount of silver oxide contained in composite layer B, if any, and the total amount of manganese oxide in the positive electrode includes the amount of manganese oxide contained in composite layer A, if any.

[0044] In the positive electrode, the compound layer A and compound layer B may be integrated, or they may be separate molded bodies stacked within the battery, but it is preferable that they be integrated.

[0045] The composite layer A and composite layer B can be manufactured, for example, by mixing an active material and a carbon material, and optionally an alkaline electrolyte (the same alkaline electrolyte injected into the battery can be used), and then press-molding the prepared positive electrode composite (positive electrode composite for composite layer A and positive electrode composite for composite layer B) into a predetermined shape.

[0046] Alternatively, a positive electrode can be manufactured by dispersing the positive electrode mixture for mixture layer A and the positive electrode mixture for mixture layer B in water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture-containing composition (slurry, paste, etc.), applying this to a substrate, drying it, and, if necessary, performing a press treatment such as calendering before peeling it off the substrate.

[0047] However, the positive electrode is not limited to those manufactured by the methods described above, but may be manufactured by other methods.

[0048] Furthermore, in order to integrate the composite layer A and composite layer B to form a positive electrode, the composite layer A and composite layer B, which are formed individually, may be bonded together. For example, one of the composite layer A and composite layer B may be molded first, and then the other layer may be molded on top of it to integrate them.

[0049] When compound layer A and compound layer B are formed by pressure molding, the total thickness of compound layer A and compound layer B is preferably 0.15 to 4 mm. On the other hand, when compound layer A and compound layer B are formed by a step of applying a positive electrode compound-containing composition containing a solvent, the total thickness of compound layer A and compound layer B is preferably 30 to 300 μm. The ratio of the thicknesses of compound layer A and compound layer B should be adjusted so that the ratio of silver oxide to manganese oxide in the entire positive electrode satisfies the above range.

[0050] A current collector can be used for the positive electrode. When a current collector is used to connect the composite layer A to the outer casing which also serves as the positive electrode terminal, the current collector may be placed on the outer casing side of the composite layer A, and the composite layer A and the outer casing may be connected via the current collector. Examples of current collectors include those made from stainless steel such as SUS316, SUS430, and SUS444; aluminum or aluminum alloys; and examples of their form include plain weave wire mesh, expanded metal, lath mesh, perforated metal, metal foam, and foil (plate). The thickness of the current collector is preferably, for example, 0.05 to 0.2 mm. It is also desirable to apply a paste-like conductive material such as carbon paste or silver paste to the surface of such a current collector.

[0051] (Negative Electrode) The negative electrode of the battery contains zinc particles (including zinc alloy particles; unless otherwise specified, "zinc particles" below refers to both zinc particles and zinc alloy particles), and the zinc in the particles acts as the active material. To suppress the generation of hydrogen gas from the negative electrode in the battery, it is desirable that the zinc particles contain one or more elements such as indium, bismuth, aluminum, and magnesium.

[0052] The preferred content of the aforementioned elements in the zinc particles is 0.03% by mass or more for indium, 0.02% by mass or more for bismuth, 0.0005% by mass or more for aluminum, and 0.0002% by mass or more for magnesium.

[0053] On the other hand, if the content of the aforementioned elements in the zinc particles is too high, problems such as a decrease in the discharge characteristics of the battery and an increase in the amount of hydrogen gas generated are likely to occur. Therefore, it is preferable that the content of each element be 0.07 mass% or less for indium, 0.06 mass% or less for bismuth, 0.01 mass% or less for aluminum, and 0.003 mass% or less for magnesium.

[0054] Furthermore, from the perspective of environmental impact, the zinc particles used are usually those that do not contain harmful elements such as mercury or lead.

[0055] The particle size of the zinc particles is preferably such that, for example, the proportion of particles with a particle size of 75 μm or less in the total powder is 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less. Furthermore, the proportion of particles with a particle size greater than 75 μm and 150 μm or less is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more.

[0056] The particle size of zinc particles can be determined based on the percentage of particles that pass through a sieve with a mesh size of 75 μm (200 mesh), the percentage of particles that pass through a sieve with a mesh size of 150 μm (100 mesh) but not through a sieve with a mesh size of 75 μm, and the percentage of particles that do not pass through a sieve with a mesh size of 150 μm (provided that the sum of these percentages equals 100% by mass).

[0057] The negative electrode is constructed, for example, using a mixture of zinc particles and an alkaline electrolyte. The mixture of the negative electrode may also contain, if necessary, a gelling agent such as sodium polyacrylate or carboxymethylcellulose.

[0058] (Separator) There are no particular restrictions on the separator for the battery. For example, nonwoven fabrics mainly composed of vinylon and rayon, vinylon-rayon nonwoven fabrics (vinylon-rayon blended paper), polyamide nonwoven fabrics, polyolefin-rayon nonwoven fabrics, vinylon paper, vinylon-linter pulp paper, vinylon-mercerized pulp paper, and graft films composed of graft polymers having a polyolefin main chain and side chains derived from (meth)acrylic acid or its derivatives that are bound to the main chain can be used. Alternatively, a separator may be made by stacking a hydrophilic treated microporous polyolefin film (such as a microporous polyethylene film or a microporous polypropylene film), a cellophane film, and an absorbent layer such as vinylon-rayon blended paper.

[0059] Furthermore, the separator can be a laminate of a cellophane film and a graft film, which consists of a graft polymer having a main chain of polyolefin (polyethylene, polypropylene, etc.) and side chains derived from (meth)acrylic acid or its derivatives that are bound to the main chain. The graft polymer constituting the graft film in the laminate only needs to have the above-described form and does not have to be produced by a method of graft polymerization of polyolefin with (meth)acrylic acid or its derivatives.

[0060] The (meth)acrylic acid or its derivatives that constitute the graft polymer are represented by the following general formula (1). Note that of the following general formula (1), R １ is H or CH ３ And R ２ is H or NH ４ This refers to hydrophilic substituents such as Na, K, Rb, and Cs.

[0061]

[0062] The aforementioned graft films and cellophane films are characterized by the fact that the polymers constituting these films themselves have the function of absorbing electrolytes and allowing ions to pass through.

[0063] The graft polymer constituting the graft film preferably has a graft rate of 160% or more, as defined by the following formula (2). Since there is a correlation between the graft rate of the graft polymer and the electrical resistance of the graft film, using a graft polymer with a graft rate of the above value allows the electrical resistance of the graft film to be 20 to 120 mΩ·in ２ The value can be controlled to a suitable level. The electrical resistance of the graft film is obtained by the AC voltage drop method (1 kHz). The ambient temperature is 20 to 25°C, the film is immersed in a 40% KOH (specific gravity: 1,400 ± 0.005) aqueous solution at 25 ± 1°C, and after 5 to 15 hours, it is removed and the electrical resistance is measured.

[0064] Graft rate (%) = 100 × (A - B) / B (2)

[0065] In formula (2) above, A: mass of the graft polymer (g), and B: mass of the polyolefin that forms the main chain in the graft polymer (g). Note that in formula (2), "B (mass of the polyolefin that forms the main chain in the graft polymer)" can be determined by, for example, measuring the mass of the polyolefin that forms the main chain used in the graft polymerization when the graft polymer is formed by graft polymerization of (meth)acrylic acid or its derivatives onto the polyolefin that forms the main chain. Furthermore, the grafting rate in the graft polymer may exceed 100% because the monomers used in the graft polymerization [(meth)acrylic acid or its derivatives] polymerize with each other, resulting in long-chain graft molecules (side chains). The upper limit of the grafting rate of the graft polymer defined in formula (2) is preferably 400%. Note that "(meth)acrylic acid" refers collectively to acrylic acid and methacrylic acid.

[0066] In the case of a separator composed of a laminate of a graft film and a cellophane film, the total thickness of the graft film and the cellophane film is preferably 30 μm or more, more preferably 40 μm or more, and preferably 70 μm or less, and more preferably 60 μm or less.

[0067] Furthermore, in the case of a separator composed of a laminate of graft film and cellophane film, the thickness of the graft film is preferably 15 μm or more, more preferably 25 μm or more, and preferably 30 μm or less.

[0068] Examples of laminates of graft film and cellophane film used to constitute a separator include those commercially available from GS Yuasa Membrane Corporation under the names "YG9132," "YG9122," "YG2122," and "YG2152."

[0069] (Alkaline Electrolyte) An alkaline aqueous solution is used as the alkaline electrolyte for the battery. Suitable electrolyte salts to be included in the alkaline electrolyte include alkali metal hydroxides (such as sodium hydroxide, potassium hydroxide, and lithium hydroxide), with potassium hydroxide being particularly preferred. The concentration of the alkaline electrolyte is, for example, in the case of an aqueous solution of potassium hydroxide, preferably 20% by mass or more, and more preferably 28% by mass or more. On the other hand, to increase ionic conductivity, the concentration of potassium hydroxide is preferably 40% by mass or less, and more preferably 35% by mass or less. By adjusting the concentration of the aqueous solution of potassium hydroxide to these values, a battery with superior load characteristics can be constructed.

[0070] In addition to the components described above, various known additives may be added to the alkaline electrolyte as needed, provided that they do not impair the effects of the present invention. For example, zinc oxide may be added to prevent corrosion (oxidation) of zinc particles used in the negative electrode of the battery. Zinc oxide can also be added to the negative electrode.

[0071] (Battery container) As shown in Figure 1, the battery container used for a battery consists of an outer casing, a sealing casing, and a gasket.

[0072] For the outer casing, materials such as nickel-plated iron or stainless steel can be used.

[0073] Furthermore, as the battery sealing casing, for example, nickel-plated iron or stainless steel can be used. When zinc particles, which are the negative electrode active material, are in direct contact with the inner surface of the sealing casing, it is preferable to form a metal layer made of copper or a copper alloy such as brass on the surface of the sealing casing that is in contact with the negative electrode, and it is even more preferable to form a layer of tin on the surface of the metal layer. The reason for forming a metal layer made of copper or a copper alloy on the surface of the sealing casing that is in contact with the negative electrode is to suppress the formation of local galvanic cells with zinc and prevent zinc corrosion, but the corrosion prevention effect can be further enhanced by forming a layer of tin on the surface of the metal layer.

[0074] Examples of battery gaskets include those made from materials such as nylon and polypropylene.

[0075] The shape of the battery in plan view may be circular, or it may be a polygon such as a square or rectangle. In the case of a polygon, its corners may be curved.

[0076] The present invention will be described in detail below based on examples. However, the following examples are not intended to limit the present invention.

[0077] (Example 1) As an alkaline electrolyte, an aqueous solution with a potassium hydroxide concentration of 36% by mass was prepared by dissolving 4% by mass of zinc oxide and 1000 ppm of indium hydroxide.

[0078] Next, a mixture (compound 1) containing 98.7% by mass of granular silus oxide with an average particle size of 150 μm, 1.2% by mass of graphite, and 0.1% by mass of low molecular weight polytetrafluoroethylene (Daikin Industries, Ltd.'s "Lubron (product name)" L-5) was filled into a mold and pressure-molded to form a disc-shaped compound layer A with a diameter of 9.1 mm and a height of 0.58 mm. Then, a mixture (compound 2) containing 98.8% by mass of manganese dioxide and 1.2% by mass of graphite was filled onto compound layer A in the mold and pressure-molded to form a disc-shaped compound layer B on top of compound layer A, thereby obtaining a positive electrode with a diameter of 9.1 mm and a height of 0.91 mm in which compound layers A and B were integrated. The ratio of silus oxide to manganese dioxide in the obtained positive electrode was 79.05:20.95 by mass. A portion of the electrolyte was impregnated into the obtained positive electrode.

[0079] Furthermore, a zinc alloy powder (silver-free zinc alloy) containing 10 ppm Al, 100 ppm Bi, 500 ppm In, and 5 ppm Mg was used for the negative electrode. This zinc alloy powder had a particle size of 75 μm or less, determined by the method described above, with a proportion of 25% by mass and an average particle size of 120 μm.

[0080] The separator used was a laminate (YG2152, manufactured by GS Yuasa Membrane Co., Ltd.) consisting of a graft film (thickness: 30 μm) made of a graft copolymer having a structure in which acrylic acid is graft copolymerized onto a polyethylene main chain, and a cellophane film (thickness: 20 μm). In addition, a vinylon-rayon blended paper with a thickness of 200 μm was used as the electrolyte retention layer. The separator and electrolyte retention layer were punched out into circles with a diameter of 9.29 mm.

[0081] The outer can was made using SUS430 stainless steel. Furthermore, the sealing can was made using copper-stainless steel (SUS304)-nickel clad sheet.

[0082] Using the aforementioned positive electrode, negative electrode, alkaline electrolyte, outer casing, sealing casing, separator, and electrolyte retention layer, and further using an annular gasket made of nylon 66, a button-type alkaline battery with a diameter of 9.5 mm and a thickness of 2.7 mm was manufactured with the bottom structure shown in Figure 1. Although the electrolyte retention layer is not shown in Figure 1, in the battery of Example 1, the electrolyte retention layer was placed on the upper side of the separator 6 (negative electrode 5 side).

[0083] (Example 2) A button-type alkaline battery was manufactured in the same manner as in Example 1, except that the composition of mixture 1 was changed to 99.6% by mass of silius oxide, 0.3% by mass of graphite, and 0.1% by mass of low molecular weight polytetrafluoroethylene, and the composition of mixture 2 was changed to 95.6% by mass of manganese dioxide and 4.4% by mass of graphite, and a positive electrode in which mixture layer A and mixture layer B were integrated was manufactured.

[0084] The ratio of silver oxide to manganese dioxide in the resulting positive electrode was 78.35:21.65 by mass.

[0085] (Example 3) A button-type alkaline battery was manufactured in the same manner as in Example 1, except that the composition of mixture 1 was changed to 99.1% by mass of silius oxide, 0.8% by mass of graphite, and 0.1% by mass of low molecular weight polytetrafluoroethylene, and the composition of mixture 2 was changed to 97.1% by mass of manganese dioxide and 2.9% by mass of graphite, and a positive electrode with a height of 0.9 mm was made by integrating mixture layers A and B with a height of 0.6 mm.

[0086] The ratio of silver oxide to manganese dioxide in the resulting positive electrode was 79.03:20.97 by mass.

[0087] (Comparative Example 1) A mixture (compound 3) containing 78% by mass of granular silius oxide with an average particle size of 150 μm, 20.7% by mass of manganese dioxide, 1.2% by mass of graphite, and 0.1% by mass of low molecular weight polytetrafluoroethylene (Daikin Industries, Ltd.'s "Lubron (product name)" L-5) was filled into a mold and pressure-molded to form a positive electrode consisting of a disc-shaped compound layer with a diameter of 9.1 mm and a height of 0.9 mm. Furthermore, a button-type alkaline battery similar to that in Example 1 was manufactured using this positive electrode.

[0088] The ratio of silver oxide to manganese dioxide in the resulting positive electrode was 79.03:20.97 by mass.

[0089] (Comparative Example 2) A button-type alkaline battery was manufactured in the same manner as in Example 1, except that the composition of compound 1 was changed to 98.6% by mass of silius oxide, 1.2% by mass of graphite, and 0.2% by mass of low molecular weight polytetrafluoroethylene, and a positive electrode with a height of 0.88 mm was made by integrating compound layer A and compound layer B with a height of 0.3 mm.

[0090] The ratio of silver oxide to manganese dioxide in the resulting positive electrode was 50.0:50.0 by mass.

[0091] (Comparative Example 3) A button-type alkaline battery was manufactured in the same manner as in Example 1, except that the composition of mixture 1 was changed to 98.3% by mass of silius oxide, 1.5% by mass of graphite, and 0.2% by mass of low molecular weight polytetrafluoroethylene, and the composition of mixture 2 was changed to 99.0% by mass of manganese dioxide and 1.0% by mass of graphite, and a positive electrode with a height of 0.89 mm was made by integrating mixture layers A and B with a height of 0.24 mm.

[0092] The ratio of silver oxide to manganese dioxide in the resulting positive electrode was 41.22:58.78 by mass.

[0093] (Comparative Example 4) A button-type alkaline battery was manufactured in the same manner as in Comparative Example 1, except that the composition of mixture 3 was changed to 49.35% by mass of silius oxide, 49.35% by mass of manganese dioxide, 1.2% by mass of graphite, and 0.1% by mass of low molecular weight polytetrafluoroethylene, and a positive electrode consisting of a mixture layer with a height of 0.89 mm was prepared.

[0094] The ratio of silver oxide to manganese dioxide in the resulting positive electrode was 50.0:50.0 by mass.

[0095] (Comparative Example 5) A button-type alkaline battery was manufactured in the same manner as in Comparative Example 1, except that the composition of mixture 3 was changed to 40.7% by mass of silius oxide, 58% by mass of manganese dioxide, 1.2% by mass of graphite, and 0.1% by mass of low molecular weight polytetrafluoroethylene, and a positive electrode consisting of a mixture layer with a height of 0.89 mm was prepared.

[0096] The ratio of silver oxide to manganese dioxide in the resulting positive electrode was 41.24:58.76 by mass.

[0097] Table 1 shows the configuration of the positive electrode in the button-type alkaline batteries of the examples and comparative examples. Note that the positive electrode of the batteries in Comparative Examples 1, 4, and 5 is a single-layer structure that is not divided into composite layer A and composite layer B, but its configuration is described in the column for composite layer A. Also, in Table 1, guarrous oxide is written as "silver oxide".

[0098]

[0099] For each battery in the examples and comparative examples, the discharge capacity was measured at a temperature of 20°C with a 15kΩ discharge resistor connected until the battery voltage dropped to 1.2V. Measurements were performed on three batteries of each example, and the average value was calculated. The results are shown in Table 2. In addition, for the batteries of Example 3 and Comparative Examples 1 to 5, the change in battery voltage during discharge was also measured. The discharge curves for each battery obtained are shown in Figure 2.

[0100]

[0101] As shown in Table 2, the batteries of Examples 1 to 3, in which the positive electrode was composed of a composite layer A containing silver oxide and a composite layer B containing manganese oxide as the positive electrode active material, and the proportion of silver oxide in the total amount of silver oxide and manganese oxide in the positive electrode was 55% by mass or more, had almost the same discharge capacity as Comparative Example 1, in which the positive electrode was composed of a composite layer with the same proportion of silver oxide and uniformity, and the total volume of the positive electrode composite was approximately 64 mm ３ The ratio of the battery's discharge capacity (approximately 60 mAh) to the number of units discharged is 0.94 (mAh / mm³). ３ This resulted in a high-capacity battery. Furthermore, as shown in Figure 2, the flat portion of the voltage in the discharge curve is wide, resulting in a battery with excellent discharge characteristics.

[0102] On the other hand, even when the positive electrode was constructed using a composite layer A containing silver oxide and a composite layer B containing manganese oxide, the batteries of Comparative Examples 2 and 3, in which the proportion of silver oxide in the entire positive electrode was less than 60% by mass, showed a narrower width of the flat portion of the voltage in the discharge curve. Furthermore, their discharge capacity was lower than that of the batteries of Comparative Examples 4 and 5, in which the positive electrode was constructed using composite layers with the same uniform proportion of silver oxide as the aforementioned batteries, resulting in inferior discharge characteristics.

[0103] For each battery in Examples 1 and 2 and Comparative Example 1, the batteries were placed in a 60°C constant temperature bath and stored for a predetermined period of 20 to 100 days. After storage, they were removed, cooled to room temperature, and then a 15kΩ discharge resistor was connected to measure the discharge capacity until the battery voltage dropped to 1.2V. Measurements were performed on three batteries of each type, and the average value was calculated. The measurement results, along with the measurement results of the batteries before storage, are shown in Figure 3.

[0104] As shown in Figure 3, in the batteries of Examples 1 and 2, in which the composite layer B, configured to have a manganese oxide content of 94% by mass or more, is positioned opposite the separator, i.e., on the negative electrode side, the movement of silver ions from the composite layer A to the negative electrode is suppressed. Compared to Comparative Example 1, in which the positive electrode is constructed with a uniform composite layer, these batteries exhibit superior storage characteristics that allow them to maintain the high capacity for a long period of time.

[0105] Next, for each battery in Example 3 and Comparative Examples 1 to 5, a 200Ω discharge resistor was connected at a temperature of 20°C, and the battery voltage (discharge voltage) was measured 0.3 seconds after the start of discharge. Measurements were taken for 15 batteries in each example, and the average value was calculated. The results are shown in Table 3.

[0106]

[0107] Furthermore, for each battery in Examples 1 and 2 and Comparative Example 1, a 15kΩ discharge resistor was connected at a temperature of 20°C to perform a certain amount of discharge. When the discharge capacity of the battery before storage obtained in the above measurement was set to 100%, batteries with a depth of discharge of 40% and 80% were prepared. Next, a 200Ω discharge resistor was connected to the battery that had not been discharged and to the batteries with a depth of discharge of 40% and 80%, respectively, and the voltage of the battery (discharge voltage) 5 seconds after the start of discharge was measured. Measurements were performed on three batteries of each type, and the average value was calculated. The measurement results for the battery with a depth of discharge of 0% (the battery that was not discharged), and the batteries with a depth of discharge of 40% and 80% are shown in Figure 4.

[0108] As shown in Table 3, the batteries of Example 3, Comparative Example 2, and Comparative Example 3, in which a composite layer A containing silver oxide at a ratio of 98% by mass or more was made electrically conductive with the outer casing to facilitate current collection, were able to achieve a higher discharge voltage compared to the batteries of Comparative Example 1, Comparative Example 4, and Comparative Example 5, in which silver oxide and manganese oxide were uniformly mixed to form the positive electrode. Furthermore, as shown in Figure 4, the batteries of Examples 1 and 2 and Comparative Example 1 were able to maintain a high discharge voltage from the start of discharge (depth of discharge: 0%) until the depth of discharge reached 80%, demonstrating that the battery configuration of the embodiments of this application resulted in batteries with excellent discharge characteristics.

[0109] Furthermore, a button-type alkaline battery of Comparative Example 6 was manufactured in the same manner as in Example 1, except that the composite layer A and composite layer B prepared in Example 1 were used, with composite layer B placed on the inner bottom surface side of the outer casing and composite layer A on the separator side. A 2kΩ discharge resistor was connected to this battery (depth of discharge: 0%) in the same manner as described above, and the voltage of the battery (discharge voltage) was measured 0.3 seconds after the start of discharge. The results are shown in Table 4, along with the measurement results of the batteries of Example 1 and Comparative Example 1. Table 4 shows the average values ​​of the measurement results obtained from three batteries each.

[0110]

[0111] As shown in Table 4, similar to the results in Figure 4, the battery of Example 1, which facilitated the collection of current from the silver oxide, was able to achieve a higher discharge voltage at the start of discharge compared to the battery of Comparative Example 1. On the other hand, in the battery of Comparative Example 6, in which the stacking order of composite layer A and composite layer B was reversed compared to the battery of Example 1, it became even more difficult to collect current from the silver oxide than in the battery of Comparative Example 1, resulting in a lower discharge voltage than the battery of Comparative Example 1.

[0112] The present invention can also be implemented in forms other than those described herein, without departing from its spirit. The embodiments disclosed herein are examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the claims attached, which take precedence over the description herein, and all modifications within the scope equivalent to the claims are included in the claims.

[0113] The button-type alkaline battery of the present invention can be applied to the same uses as known alkaline primary batteries.

[0114] 1. Button-type alkaline battery 2. Outer casing 3. Sealed casing 4. Positive electrode 41. Compound layer A 42. Compound layer B 5. Negative electrode 6. Separator 7. Gasket

Claims

1. A button-type alkaline battery comprising a positive electrode, a negative electrode, and a separator enclosed in a battery container having an outer casing and a sealed casing, wherein the positive electrode comprises a composite layer A containing silver oxide as a positive electrode active material and a composite layer B containing manganese oxide as a positive electrode active material, the inner bottom surface of the outer casing is electrically connected to the composite layer A, the separator faces the composite layer B, the composite layer A contains silver oxide in a proportion of 98% by mass or more and carbon material in a proportion of 0.1% by mass or more, the composite layer B contains manganese oxide in a proportion of 94% by mass or more and carbon material in a proportion of 0.5% by mass or more, and the mass ratio of silver oxide to manganese oxide in the entire positive electrode is in the range of 55:45 to 95:

5.

2. The button-type alkaline battery according to claim 1, wherein the mass ratio of silver oxide to manganese oxide in the entire positive electrode is in the range of 70:30 to 95:

5.

3. The button-type alkaline battery according to claim 1, wherein the composite layer A contains a binder.

4. The button-type alkaline battery according to claim 1, wherein the composite layer B contains a binder.

5. The button-type alkaline battery according to claim 1, wherein the composite layer A and the composite layer B are integrated.

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