Button-type alkaline batteries

Abstract

To provide a button-type alkaline battery with excellent battery characteristics such as discharge characteristics and storage characteristics. [Solution] The button-type alkaline battery of the present invention has a positive electrode containing silver oxide as a positive electrode active material, a negative electrode, and a separator that separates the positive electrode and the negative electrode, and is characterized in that the separator and an annular separator are arranged on top of each other at the periphery of the positive electrode.

Description

Technical Field

[0001] The present invention relates to a button-shaped alkaline battery having silver oxide as a positive electrode active material and excellent battery characteristics such as discharge characteristics and storage characteristics.

Background Art

[0002] In button-shaped alkaline batteries using silver compounds such as silver oxide and silver nickel oxide as the positive electrode, an alkaline aqueous solution is used as the electrolyte, and the separator is a film in which a graft film obtained by graft-polymerizing a hydrophilic vinyl monomer on a polyolefin resin film and cellophane are integrated. Among these, the graft film suppresses the movement of silver ions eluted from the positive electrode to the negative electrode, and cellophane has a function of reducing silver ions passing through the graft film and suppressing the movement.

[0003] In button-shaped alkaline batteries, the peripheral portion of the separator is sandwiched between the positive electrode and the annular gasket to assemble the battery. Since the graft film in this portion is pressed and compressed by the gasket, silver ions are likely to permeate. Since the amount of silver ions that can be reduced by cellophane and restricted in movement is limited, during storage at high temperatures or long-term storage, at the peripheral portion of the separator, some silver ions pass through the separator and move to the negative electrode, and are reduced at the negative electrode, which may cause self-discharge and internal short circuit, etc., and there is a risk of deteriorating the storage characteristics. Therefore, in button-shaped batteries containing silver oxide in the positive electrode, it is particularly required to suppress the movement of silver ions at the peripheral portion of the separator. [[ID=I8]]

[0004] In Patent Document 1, in order to prevent a decrease in the ability to block the permeation of silver ions due to the rolling of the peripheral portion of the separator by the pressure during sealing, heat treatment is performed on the peripheral portion of the graft film of the separator to increase the electrical resistance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, the technology described in Patent Document 1 had the problem that it was difficult to adjust the location and degree of heat treatment and perform the process without variation, making process control complicated.

[0007] Another possibility is to increase the number of separators separating the positive and negative electrodes to suppress the movement of silver ions. However, this would also hinder ion movement during discharge, leading to increased internal resistance and a decrease in discharge characteristics.

[0008] For these reasons, there is a need to develop batteries that have excellent storage characteristics while minimizing the deterioration of their discharge characteristics.

[0009] 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 discharge characteristics and storage characteristics. [Means for solving the problem]

[0010] The button-type alkaline battery of the present invention has a positive electrode containing silver oxide as a positive electrode active material, a negative electrode, and a separator that separates the positive electrode and the negative electrode, and is characterized in that the separator and an annular separator are arranged on top of each other at the periphery of the positive electrode.

[0011] 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. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a button-type alkaline battery with excellent battery characteristics such as discharge characteristics and storage characteristics. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing an example of the button-type alkaline battery of the present invention. [Figure 2] This is a schematic plan view showing an example of an annular separator in the button-type alkaline battery of the present invention. [Figure 3] This graph shows the relationship between the number of days of storage at 60°C and the discharge capacity of button-type alkaline batteries in the examples and comparative examples. [Modes for carrying out the invention]

[0014] The button-type alkaline battery of the present invention (hereinafter sometimes simply referred to as "battery") has a positive electrode containing silver oxide as a positive electrode active material, a negative electrode, and a separator that separates the positive electrode and the negative electrode, wherein the separator and an annular separator are arranged in a stacked manner at the periphery of the positive electrode.

[0015] When a battery is constructed by stacking multiple separators that separate the positive and negative electrodes, as mentioned above, it is expected that self-discharge and internal short circuits that may be caused by the movement of silver ions from the positive to the negative electrode can be effectively suppressed. However, when OH occurs on the surfaces where the positive and negative electrodes face each other during discharge, - Since ion movement is also inhibited, the battery's discharge characteristics deteriorate.

[0016] Therefore, in this invention, a separator for separating the positive electrode and the negative electrode (hereinafter referred to as "separator (A)") and an annular separator located on the periphery of the positive electrode (hereinafter referred to as "separator (B)") are arranged in a stacked configuration.

[0017] That is, in the battery of the present invention, at the location corresponding to the peripheral portion of the positive electrode, since the separator (A) and the annular separator (B) exist, the movement of silver ions can be well suppressed. On the other hand, inside the peripheral portion of the positive electrode, that is, at the location where the positive electrode and the negative electrode face each other, since substantially only the separator (A) exists, the OH - ion movement during discharge can proceed smoothly. Therefore, in the battery of the present invention, while suppressing the decrease in discharge characteristics as much as possible, it is possible to well suppress the decrease in storage characteristics that may occur due to the movement of silver ions from the positive electrode to the negative electrode.

[0018] FIG. 1 shows a cross-sectional view schematically representing an example of the button-shaped alkaline battery of the present invention. In the button-shaped alkaline battery 1 shown in FIG. 1, a sealing can 3 filled with a negative electrode 5 is fitted through an annular gasket 8 having an L-shaped cross section to the opening of an exterior can 2 filled with a positive electrode 4 and a separator 6. The opening end of the exterior can 2 is tightened inward, and thereby the gasket 8 abuts against the sealing can 3, so that the opening of the exterior can 2 is sealed and the inside of the battery has a sealed structure. That is, in the button-shaped alkaline battery 1 shown in FIG. 1, a power generation element including a positive electrode 4 and a negative electrode 5 is loaded into the space (sealed space) inside the battery container composed of the exterior can 2, the sealing can 3, and the gasket 8, and further an alkaline electrolyte (not shown) is accommodated. Also, in the button-shaped alkaline battery 1 shown in FIG. 1, the peripheral portion of the positive electrode 4 is disposed between the inner bottom surface of the exterior can 2 and the bottom surface of the gasket 8 (hereinafter, this structure is referred to as a "bottom-laying structure"). In the battery shown in FIG. 1, the exterior can 2 also serves as a positive electrode terminal, and the sealing can 3 also serves as a negative electrode terminal. However, in the battery of the present invention, the exterior can may also serve as a negative electrode terminal, and the sealing can may also serve as a positive electrode terminal.

[0019] Between the positive electrode 4 and the negative electrode 5, a separator (A) 6 that separates the positive electrode 4 and the negative electrode 5 and an annular separator (B) 7 located at the peripheral portion of the positive electrode 4 are overlapped and arranged.

[0020] The button-shaped alkaline battery of the present invention includes a primary battery and a secondary battery. Hereinafter, the details of the battery of the present invention will be described.

[0021] (Positive electrode) For the positive electrode of the battery, a molded body obtained by molding a positive electrode mixture containing a positive electrode active material or the like, or a structure having a layer made of a positive electrode mixture (positive electrode mixture layer) on one or both sides of a current collector can be used.

[0022] As the positive electrode active material, silver oxides such as composite oxides containing silver such as silver monoxide, silver dioxide, and silver nickel composite oxide are used.

[0023] The silver oxide is not particularly limited in terms of its particle size, but the average particle diameter is preferably 10 μm or less, more preferably 2 μm or less. In particular, when the battery is a secondary battery, when silver oxide of such a size is used, the utilization rate during charging is improved, and a large charge capacity can be obtained even when the charge termination voltage is relatively low. Therefore, the charge-discharge cycle characteristics of the battery can be further enhanced, and for example, it is possible to suppress the swelling of the battery that may occur by increasing the charge termination voltage.

[0024] However, since silver oxide with too small a particle size is difficult to manufacture and handle thereafter, the average particle diameter of the silver oxide is preferably 0.01 μm or more, more preferably 0.03 μm or more.

[0025] The particle size of the silver oxide and other particles (graphite particles, carbon black particles, insulating inorganic particles, and zinc particles related to the negative electrode) referred to in this specification is a value measured by dispersing these particles in a medium that does not dissolve the particles using a laser scattering particle size distribution meter (for example, "LA-920" manufactured by Horiba, Ltd.). The average particle diameter is the value of the 50% diameter (D 50 ) in the volume-based integrated fraction when obtaining the integrated volume from particles with a small particle size.

[0026] Examples of conductive additives for the positive electrode mixture include carbonaceous material particles such as carbon black particles and graphite particles. It is preferable to use at least graphite particles as the conductive additive, and carbon black particles and graphite particles can be used in combination.

[0027] By using carbon black particles, a good conductive network can be easily formed within the molded positive electrode mixture. Compared to using only graphite particles, for example, the number of contact points with the silver oxide particles, which are the positive electrode active material, is increased, and the electrical resistance within the molded positive electrode mixture can be effectively reduced. For example, when the battery is a rechargeable battery, this makes it possible to improve the reaction efficiency of the positive electrode active material during charging.

[0028] On the other hand, when using only carbon black particles, depending on the thickness of the molded body of the positive electrode mixture, it may be necessary to use a binder to improve its moldability. However, when graphite particles are also used, the moldability of the molded body of the positive electrode mixture is improved. For example, even when the molded body of the positive electrode mixture 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 particles in the positive electrode mixture may be either natural graphite particles (such as flaky graphite) or artificial graphite particles, and one or more of these may be used.

[0030] As described above, graphite particles have the function of improving the moldability of the positive electrode mixture molded body. From the viewpoint of better exhibiting this function, the average particle diameter of the graphite particles 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 black particles used in the positive electrode mixture include furnace black, channel black, acetylene black, and thermal black, and one or more of these can be used. Among these carbon black particles, acetylene black, which has high conductivity and low impurity content, is preferably used.

[0032] Furthermore, when the battery is a secondary battery and silver oxide is used as the positive electrode active material, it is preferable to further include insulating inorganic particles in the positive electrode mixture, thereby further improving the battery's charge-discharge cycle characteristics. In addition, when insulating inorganic particles are used, further including carbon black particles and graphite particles in the positive electrode mixture can further improve the battery's charge-discharge cycle characteristics.

[0033] Examples of insulating inorganic particles for the positive electrode mixture include oxides of at least one element selected from Si, Zr, Ti, Al, Mg, and Ca. Specific examples of the oxides include Al2O3, TiO2, SiO2, ZrO2, MgO, CaO, AlOOH, and Al(OH)3. Particles that are insoluble or sparingly soluble in alkaline electrolytes are preferably used. These insulating inorganic particles may be used individually or in combination of two or more.

[0034] If the particle size of insulating inorganic particles is too large, there is a risk that the effect of improving the charge-discharge cycle characteristics of the battery will be reduced. Therefore, from the viewpoint of further improving the charge-discharge cycle characteristics of the battery, the average particle size of the insulating inorganic particles is preferably 0.5 μm or less, and more preferably 0.3 μm or less.

[0035] Furthermore, if the particle size of the insulating inorganic particles is too small, there is a risk that the effect of improving the battery's charging efficiency (initial capacity) will be reduced. Therefore, from the viewpoint of further improving the battery's charging efficiency, the average particle size of the insulating inorganic particles is preferably 0.01 μm or larger, and more preferably 0.05 μm or larger.

[0036] Regarding the composition of the positive electrode mixture, in order to ensure sufficient volume, when silver oxide is used as the positive electrode active material, its content is preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on 100% by mass of the total solid content constituting the positive electrode mixture.

[0037] Other materials besides silver oxides, such as manganese oxide (e.g., manganese dioxide) and nickel oxide (e.g., nickel hydroxide), can also be used as the positive electrode active material. In that case, the total content of the positive electrode active material should be adjusted to fall within the aforementioned range, with the total solid content constituting the positive electrode mixture being 100% by mass.

[0038] Furthermore, the content of the conductive additive in the positive electrode mixture is preferably 0.2% by mass or more, preferably 0.5% by mass or more, and particularly preferably 1% by mass or more, from the viewpoint of conductivity. On the other hand, to prevent capacity reduction and gas generation during charging, it is preferably 8% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, and particularly preferably 3% by mass or less.

[0039] Furthermore, when the positive electrode mixture contains carbon black particles and graphite particles, the content of graphite particles is preferably 1% by mass or more, and more preferably 2% by mass or more, from the viewpoint of ensuring a good improvement in the battery's charging efficiency and charge-discharge cycle characteristics by using them in combination with carbon black particles. In addition, when the positive electrode mixture contains carbon black particles and graphite particles, the content of graphite particles is preferably 7% by mass or less, and more preferably 4% by mass or less, from the viewpoint of preventing a decrease in battery capacity due to, for example, too little positive electrode active material in the positive electrode mixture.

[0040] Furthermore, when the positive electrode mixture contains both carbon black particles and graphite particles, the carbon black particle content is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more, from the viewpoint of ensuring a good improvement in the battery's charging efficiency and charge-discharge cycle characteristics through the combined use of carbon black particles and graphite particles. However, if the amount of carbon black particles in the positive electrode mixture is too high, there is a risk that the positive electrode will swell significantly, for example, when the battery is stored at high temperatures. Therefore, from the viewpoint of suppressing the swelling of the positive electrode during battery storage (especially storage at high temperatures of around 60°C) and improving the battery's storage characteristics, the carbon black particle content when the positive electrode mixture contains both carbon black particles and graphite particles is preferably 1.5% by mass or less, and more preferably 1% by mass or less.

[0041] Furthermore, when insulating inorganic particles are included in the positive electrode mixture, their content is preferably 0.1% by mass or more, and more preferably 3% by mass or more, from the viewpoint of ensuring a good effect from their use (particularly the effect of improving the battery's charge-discharge cycle characteristics). However, if the amount of insulating inorganic particles in the positive electrode mixture is too high, the amount of positive electrode active material filled will decrease, leading to a decrease in battery capacity. In addition, depending on the type of insulating inorganic particles, the discharge capacity may suddenly decrease as the charge-discharge cycle progresses. Therefore, the content of insulating inorganic particles in the positive electrode mixture is preferably 7% by mass or less, and more preferably 5% by mass or less.

[0042] As described above, the positive electrode mixture can be formed without using a binder, but a binder may be used when it is necessary to increase strength (for example, when graphite is not used as a conductive additive). Examples of binders for the positive electrode mixture include fluororesins such as polytetrafluoroethylene (PTFE) and olefin resins such as polyethylene (PE). When a binder is used, the binder content in the positive electrode mixture is preferably 0.1% by mass or more, and more preferably 1% by mass or more. On the other hand, in order not to inhibit the reaction of the positive electrode active material, it is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0043] In the case of a positive electrode consisting only of a molded positive electrode mixture, it can be manufactured by, for example, mixing a positive electrode active material, a conductive additive, and, if necessary, an alkaline electrolyte (the same alkaline electrolyte used in batteries can be used), and then press-molding the prepared positive electrode mixture into a predetermined shape.

[0044] Furthermore, in the case of a positive electrode having a molded positive electrode mixture (positive electrode mixture layer) and a current collector, for example, it can be manufactured by dispersing a positive electrode active material and a conductive additive 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 current collector and drying it, and then performing a press treatment such as calendering as necessary.

[0045] However, the positive electrode is not limited to those manufactured by the methods described above, but may be manufactured by other methods.

[0046] When only a molded body of the positive electrode mixture is used as the positive electrode, its thickness is preferably 0.15 to 4 mm. On the other hand, in the case of a positive electrode having a positive electrode mixture layer and a current collector, the thickness of the positive electrode mixture layer (thickness per side of the current collector) is preferably 30 to 300 μm.

[0047] When a current collector is used for the positive electrode, examples of materials for the current collector include stainless steel such as SUS316, SUS430, and SUS444; aluminum; and aluminum alloys. Examples of its 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.

[0048] (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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The particle size of 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. Also, the average particle diameter (D 50 Preferably, the particle size is 75 μm or more and 150 μm or less, and 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.

[0053] 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 sieve), the percentage of particles that pass through a sieve with a mesh size of 150 μm (100 mesh sieve), which does not use the 75 μm sieve, and the percentage of particles that do not pass through the 150 μm sieve (however, the sum of these percentages must equal 100 mass%).

[0054] 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.

[0055] (Separator) There are no particular restrictions on the battery separators [separator (A) and cyclic separator (B)], and 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 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.

[0056] Furthermore, the separator can be a laminate of a graft film composed 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, and a cellophane film. 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.

[0057] 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 CH3, and R 2 This refers to hydrophilic substituents such as H or NH4, Na, K, Rb, and Cs.

[0058] [ka]

[0059] 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.

[0060] 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, by using a graft polymer with a graft rate of the above value, the electrical resistance of the graft film can be controlled to a suitable value of 20 to 120 mΩ·in². The electrical resistance of the graft film is obtained by the AC voltage drop method (1 kHz). The film can be immersed in a 40% KOH (specific gravity: 1,400 ± 0.005) aqueous solution at an ambient temperature of 20 to 25°C and 25 ± 1°C, and the electrical resistance can be measured after 5 to 15 hours.

[0061] Graft rate (%) = 100 × (AB) / B (2)

[0062] In formula (2) above, A is the mass of the graft polymer (g), and B is the 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 beforehand, 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.

[0063] 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.

[0064] 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.

[0065] 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."

[0066] The separator (A) and the annular separator (B) that separate the positive electrode and the negative electrode may be of the same type or different types, but it is preferable to use a laminate of the graft film and cellophane film for both separator (A) and separator (B).

[0067] The width of the annular separator (B) is preferably longer than the width of the gasket (length in the horizontal direction in Figure 1) when the battery has a bottom-fill structure in which the peripheral edge of the positive electrode 4 is positioned between the inner bottom surface of the outer casing 2 and the bottom surface of the gasket 8, for example, as shown in Figure 1 of the battery 1. That is, in a plan view, it is preferable that the inner circumferential end of the annular separator (B) is located inside the inner circumferential end of the bottom surface of the gasket, and that the annular separator (B) overlaps with the outer circumferential end of the bottom surface on the separator side of the negative electrode 5. More specifically, in a plan view, the width (length) of the portion of the inner circumferential end of the annular separator (B) that protrudes beyond the inner circumferential end of the gasket is preferably 0.2 mm or more, and more preferably 0.5 mm or more. This makes it possible to more efficiently suppress the movement of silver ions from the positive electrode to the negative electrode, which can cause internal short circuits.

[0068] Furthermore, it is preferable to adjust the size of the annular separator (B) so that, in a flat state, its outer peripheral edge protrudes further outward than the outer peripheral edge of the positive electrode.

[0069] Figure 2 shows a schematic plan view illustrating an example of an annular separator (B). The width of the annular separator (B) 7 is the length in the horizontal direction in Figure 1. More specifically, as shown in Figure 2, when the outer and inner circumferences of the annular separator (B) are composed of two concentric circles, the width means 1 / 2 of the difference between the diameter of the outer circle and the diameter of the inner circle that form the annular separator (B) 7 (length a in the figure). The dotted lines in the figure are lines drawn radially from the centers O of the outer and inner circles that form the annular separator (B) 7.

[0070] Figure 2 shows an example of an annular separator (B) with a circular outer and inner circumference, but the outer and inner circumferences may be other shapes such as ellipses.

[0071] (Anionic conductive film) In the case of a rechargeable battery, it is preferable to place an anion-conducting film between the positive and negative electrodes, together with the separator, the film having a polymer matrix in which particles of at least one metal compound selected from the group consisting of metal oxides, hydroxides, carbonates, sulfates, phosphates, borates, and silicates are dispersed.

[0072] (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, preferably 20% by mass or more, and more preferably 28% by mass or more, in the case of an aqueous solution of potassium hydroxide. 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.

[0073] 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.

[0074] Furthermore, if the battery is a rechargeable battery, one or more compounds selected from the group consisting of manganese compounds, tin compounds, and indium compounds may be dissolved in the alkaline electrolyte.

[0075] In alkaline secondary batteries having a positive electrode containing silver oxide as the positive electrode active material, silver is generated from the silver oxide in the positive electrode during discharge. However, when the battery is charged, silver oxide crystals form around the silver, effectively reducing the reaction area of ​​the positive electrode active material and inhibiting subsequent battery reactions. However, when these compounds are dissolved in the alkaline electrolyte, ions derived from these compounds (manganese ions, tin ions, indium ions) adsorb onto the positive electrode, suppressing the growth of silver oxide crystals and refining the resulting silver oxide crystals. Therefore, the problem of silver oxide crystals forming during battery charging inhibiting battery reactions is suppressed, making it possible to improve the charge-discharge cycle characteristics of the secondary battery, for example.

[0076] Examples of manganese compounds that can be dissolved in an alkaline electrolyte include manganese chloride, manganese acetate, manganese sulfide, manganese sulfate, and manganese hydroxide. Examples of tin compounds that can be dissolved in an alkaline electrolyte include tin chloride, tin acetate, tin sulfide, tin bromide, tin oxide, tin hydroxide, and tin sulfate. Examples of indium compounds that can be dissolved in an alkaline electrolyte include indium hydroxide, indium oxide, indium sulfate, indium sulfide, indium nitrate, indium bromide, and indium chloride.

[0077] The concentrations of indium compounds, manganese compounds, and tin compounds in the alkaline electrolyte (the concentration of only one of these compounds if only one is dissolved, and the total concentration if two or more are dissolved) are preferably 50 ppm or more, more preferably 500 ppm or more, and more preferably 10,000 ppm or less, and more preferably 5,000 ppm or less, on a mass basis, from the viewpoint of ensuring the above-mentioned effects more effectively.

[0078] In the case of a secondary battery, it is preferable to include polyalkylene glycols or calcium compounds in at least one of the negative electrode, alkaline electrolyte, and separator. In this case, the growth of zinc dendrites on the negative electrode can be suppressed by the action of the polyalkylene glycols or calcium compounds, thereby improving the charge-discharge cycle characteristics and storage characteristics of the battery.

[0079] Furthermore, if the battery is a rechargeable battery, it is preferable to include tellurium or a compound thereof (such as tellurium dioxide) in at least one of the components within the battery, for example, the positive electrode, the negative electrode, and the separator, or in the alkaline electrolyte. This can improve the battery's charge-discharge cycle characteristics and load characteristics.

[0080] (Exterior) As shown in Figure 1, the battery enclosure uses a battery container consisting of an outer casing, a sealing casing, and a gasket.

[0081] For the outer casing, materials such as nickel-plated iron or stainless steel can be used.

[0082] 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.

[0083] Examples of battery gaskets include those made from materials such as nylon and polypropylene.

[0084] 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.

[0085] Furthermore, the shape of the annular separator (B) can be set to match the shape of the battery in a plan view.

[0086] The button-type alkaline battery of the present invention can be applied to the same uses as conventionally known alkaline primary batteries and alkaline secondary batteries. [Examples]

[0087] The present invention will be described in detail below based on examples. However, the following examples are not intended to limit the present invention.

[0088] (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.

[0089] Next, a positive electrode consisting of a disc-shaped mixture with a diameter of 9.1 mm and a height of 0.91 mm was produced by filling a mold with a mixture 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) and pressurizing it. The obtained positive electrode was then impregnated with a portion of the electrolyte.

[0090] For the negative electrode, mercury-free zinc alloy particles commonly used in alkaline primary batteries were used, containing In: 500 ppm, Bi: 100 ppm, and Al: 10 ppm as additive elements. The particle size of the zinc alloy particles, determined by the method described above, was the average particle diameter (D 50 The particle size was 120 μm, and the proportion of particles with a particle size of 75 μm or less was 25% by mass.

[0091] A laminate (YG2122, 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), was used as separator (A) and annular separator (B). For separator (A), the laminate was cut into a circle with a diameter of 9.29 mm and used, and for annular separator (B), the laminate was cut into an annular shape (width: approximately 1.72 mm) with an outer diameter (twice the length of b in Figure 2) of 9.29 mm and an inner diameter (diameter of the opening, twice the length of c in Figure 2) of 5.86 mm. In addition, a vinylon-rayon blended paper with a thickness of 200 μm, cut into a circle with a diameter of 9.29 mm, was used as the electrolyte holding layer.

[0092] The outer can was made using SUS430 stainless steel. Furthermore, the sealing can was made using copper-stainless steel (SUS304)-nickel clad sheet.

[0093] 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 the structure shown in Figure 1, having a diameter of 9.5 mm and a thickness of 2.7 mm, was assembled. 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 (negative electrode 5 side) of separator (A) 6. Also, in plan view, the width (length) of the portion of the annular separator (B) that protrudes beyond the inner edge of the gasket was 0.55 mm.

[0094] (Comparative Example 1) A button-type alkaline battery was assembled in the same manner as in Example 1, except that two separators (A) were stacked instead of using a ring-shaped separator (B) as the separator. (Comparative Example 2)

[0095] A button-type alkaline battery was assembled in the same manner as in Example 1, except that only separator (A) was used as the separator, and not the annular separator (B).

[0096] For each battery in the examples and comparative examples, the batteries were placed in a constant temperature bath at 60°C and stored for a predetermined period of 20 to 100 days. After removal, they were cooled to room temperature, and the discharge capacity was measured until the battery voltage dropped to 1.2V by connecting a 15kΩ discharge resistor. 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.

[0097] As shown in Figure 3, the battery of Example 1, which used a separator (A) that separates the positive and negative electrodes and an annular separator (B) located on the periphery of the positive electrode, and the battery of Comparative Example 1, which used two separators (A) stacked together, suppressed the movement of silver ions from the positive electrode to the negative electrode compared to the battery of Comparative Example 2, which used only one separator (A), resulting in batteries with superior storage characteristics that can maintain the battery capacity for a long period of time.

[0098] Furthermore, for each battery in the examples and comparative examples, the AC impedance at 1kHz with an applied voltage of 10mV was measured to determine the internal resistance of the battery. In addition, a 200Ω discharge resistor was connected, and the battery voltage (discharge voltage) 5 seconds after the start of discharge was measured. Measurements were performed on three batteries for each example, and the average value was calculated. The measurement results are shown in Table 1.

[0099] [Table 1]

[0100] As shown in Table 1, although the battery of Example 1, by using an annular separator (B), has a higher internal resistance than the battery of Comparative Example 2, which uses only one separator (A), the rate of increase in internal resistance is smaller than that of the battery of Comparative Example 1, which uses an additional separator (A). This allows for a higher discharge voltage than the battery of Comparative Example 1, resulting in a battery with superior discharge characteristics. [Explanation of Symbols]

[0101] 1 Button-type alkaline battery 2 outer cans 3 Sealed cans 4 Positive electrode 5 Negative electrode 6 Separator (A) 7. Ring-shaped separator (B) 8 Gaskets

Claims

1. A button-type alkaline battery having a positive electrode containing silver oxide as a positive electrode active material, a negative electrode, and a separator that separates the positive electrode and the negative electrode, A button-type alkaline battery characterized in that the separator and an annular separator are arranged in a stacked manner at the periphery of the positive electrode.

2. The button-type alkaline battery according to claim 1, wherein the separator is a laminate of a graft film composed of a graft polymer having a polyolefin main chain and side chains derived from (meth)acrylic acid or a derivative thereof bound to the main chain, and a cellophane film.

3. The button-type alkaline battery according to claim 1, wherein, in a plan view, the inner circumferential end of the annular separator is located inside the inner circumferential end of the bottom surface of the gasket.

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