Alkaline secondary battery and manufacturing method therefor

Abstract

The present invention provides an alkaline secondary battery that contains zinc metal, a zinc alloy, or a zinc compound as a negative electrode active material and exhibits excellent charging and discharging cycle characteristics, and a method for manufacturing the alkaline secondary battery.　The alkaline secondary battery according to the present invention is characterized by containing: a negative electrode that is provided with a negative electrode active material layer containing zinc metal, a zinc alloy, or a zinc compound as a negative electrode active material; a positive electrode; and a separator. The alkaline secondary battery is also characterized by having a zinc oxide-containing layer between the negative electrode active material layer and the separator. The alkaline secondary battery is further characterized in that the mass ratio of the mass of zinc oxide in the zinc oxide-containing layer to the total mass of Zn in the negative electrode active material is 1-10 mass%. The method for manufacturing an alkaline secondary battery according to the present invention is characterized by comprising a step for laminating a negative electrode active material layer, a zinc oxide-containing layer containing zinc oxide, and a separator, and by the mass ratio of the mass of zinc oxide contained in the zinc oxide-containing layer to the total amount of Zn in the negative electrode active material being 1-10 mass%.

Description

Alkaline secondary battery and method for manufacturing the same

[0001] This invention relates to an alkaline secondary battery containing zinc metal, zinc alloy, or zinc compound as a negative electrode active material, which has excellent charge-discharge cycle characteristics, and to a method for manufacturing the same.

[0002] Alkaline batteries, which have a negative electrode containing zinc metal, zinc alloy, or zinc compound as the negative electrode active material, and an alkaline electrolyte, are widely used as primary batteries, but their application to secondary batteries is also being considered.

[0003] In alkaline secondary batteries as described above, there is a need to improve the charge-discharge cycle characteristics, just as with other secondary batteries. For example, Patent Document 1 proposes providing a zincate ion supply that contains zinc oxide or zinc hydroxide and is not electrically connected to either the negative or positive electrode in a secondary battery having a negative electrode, a positive electrode, and an alkaline electrolyte containing zinc oxide.

[0004] Zinc oxide (zinc), used as the negative electrode active material in secondary batteries, undergoes repeated reactions during the charge-discharge cycle: one in which zinc oxide dissolves from the negative electrode into the electrolyte to generate zincate ions, and the other in which zinc precipitates at the negative electrode to generate zinc. However, if zinc precipitation does not occur uniformly throughout the negative electrode, the uniformity of the zinc distribution within the negative electrode is disrupted, causing a change in the morphology of the negative electrode. This leads to a partial passivation of the negative electrode, an increase in internal resistance, and a deterioration in charge-discharge cycle characteristics. In the secondary battery described in Patent Document 1, zincate ions are continuously supplied to the alkaline electrolyte from a zincate ion supplier. This ensures uniform zinc precipitation at the negative electrode, suppresses changes in the negative electrode's morphology, and prevents passivation of the negative electrode and an increase in internal resistance. Furthermore, the zincate ion supplier suppresses the growth of dendrites toward the positive electrode. In the secondary battery described in Patent Document 1, these effects ensure excellent charge-discharge cycle characteristics.

[0005] Furthermore, Patent Document 1 states that, in order to enhance the effect of suppressing problems caused by dendrites in secondary batteries, it is preferable that the total amount of zinc oxide and zinc hydroxide per unit area in the zincate ion supplier (total content obtained by converting metallic zinc to zinc oxide) be 10% by mass or more of the amount of zinc oxide per unit area in the negative electrode.

[0006] Japanese Patent Publication No. 2021-114458 (Claims, paragraphs

[0017] to

[0019] ,

[0050] ,

[0051] )

[0007] However, using a zinc ion supplier may cause an increase in the internal resistance of the battery, and even the technology described in Patent Document 1 still has room for improvement.

[0008] The present invention has been made in view of the above circumstances, and its object is to provide an alkaline secondary battery containing zinc metal, zinc alloy, or zinc compound as a negative electrode active material, having excellent charge-discharge cycle characteristics, and a method for manufacturing the same.

[0009] The alkaline secondary battery of the present invention comprises a negative electrode, a positive electrode, and a separator, each having a negative electrode active material layer containing zinc metal, a zinc alloy, or a zinc compound as the negative electrode active material, and having a zinc oxide-containing layer between the negative electrode active material layer and the separator, wherein the mass of zinc oxide contained in the zinc oxide-containing layer is 1 to 10% by mass in terms of mass ratio to the total amount of Zn in the negative electrode active material.

[0010] Furthermore, the present invention relates to a method for manufacturing an alkaline secondary battery comprising a negative electrode, a positive electrode, and a separator, the negative electrode having a negative electrode active material layer containing zinc metal, a zinc alloy, or a zinc compound as the negative electrode active material, and comprising the step of laminating the negative electrode active material layer, a zinc oxide-containing layer containing zinc oxide, and a separator, characterized in that the mass of zinc oxide contained in the zinc oxide-containing layer is 1 to 10% by mass in terms of mass ratio to the total amount of Zn in the negative electrode active material.

[0011] According to the present invention, it is possible to provide an alkaline secondary battery containing zinc metal, a zinc alloy, or a zinc compound as the negative electrode active material, which has excellent charge-discharge cycle characteristics, and a method for manufacturing the same.

[0012] This is a schematic cross-sectional view showing an example of the alkaline secondary battery of the present invention. This is a diagram showing the change in discharge capacity during the evaluation of the charge-discharge cycle characteristics of the alkaline secondary batteries of the examples and comparative examples.

[0013] The alkaline secondary battery of the present invention (hereinafter sometimes simply referred to as "battery") includes a negative electrode, a positive electrode, and a separator, each comprising a negative electrode active material layer containing zinc metal, zinc alloy, or zinc compound (hereinafter, zinc metal, zinc alloy, and zinc compound may be collectively referred to as "zinc, etc.") as the negative electrode active material, and further comprising a zinc oxide-containing layer between the negative electrode active material layer and the separator.

[0014] By placing a zinc oxide-containing layer between the negative electrode active material layer and the separator, zinc oxide ions ([Zn(OH)) are released from the zinc oxide-containing layer. ４ ] ２－ Because ) is supplied to the alkaline electrolyte, the concentration of zincate ions in the alkaline electrolyte is increased near the negative electrode active material layer. This can promote the deposition of zinc oxide during the discharge of the alkaline secondary battery and allow for uniform deposition of zinc on the negative electrode during the charging of the alkaline secondary battery, thereby improving the reversibility of charge and discharge and thus improving the charge-discharge cycle characteristics of the alkaline secondary battery.

[0015] Generally, an increase in the amount of intervening material between the positive and negative electrodes tends to increase the internal resistance of the battery and degrade its discharge characteristics. However, in the alkaline secondary battery of the present invention, by adjusting the mass of zinc oxide contained in the zinc oxide-containing layer to 1 to 10% by mass as a mass ratio to the total amount of Zn in the negative electrode active material, it is possible to improve the charge-discharge cycle characteristics while suppressing as much as possible the degradation of the battery's discharge characteristics caused by the presence of the zinc oxide-containing layer.

[0016] Figure 1 shows a schematic cross-sectional view illustrating an example of the alkaline secondary battery of the present invention. In the alkaline secondary battery 1 shown in Figure 1, a sealing can 3 containing a negative electrode 5 is fitted to the opening of an outer can 2, which contains a positive electrode 4, a separator 6 (graft film / cellophane film laminate 6a and anion conductive film 6b), and a zinc oxide-containing layer 7, via an L-shaped, annular gasket 8. The opening end of the outer can 2 is tightened inward, causing the gasket 8 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 alkaline secondary 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 8, and an alkaline electrolyte (not shown) is also contained within. Furthermore, in the alkaline secondary battery 1 shown in Figure 1, 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 (hereinafter, this structure will be referred to as the "bottom casing structure"). In the battery shown in Figure 1, the outer casing 2 also serves as the positive electrode terminal and the sealing casing 3 also serves as the negative electrode terminal. However, in the battery of the present invention, the outer casing can also serve as the negative electrode terminal and the sealing casing can also serve as the positive electrode terminal.

[0017] In the alkaline secondary battery 1 shown in Figure 1, a zinc oxide-containing layer 7 is placed between the separator 6 and the negative electrode (negative electrode active material layer) 5. Although Figure 1 shows a separator 6 made of a graft film / cellophane film laminate 6a and an anion-conducting film 6b, an alkaline secondary battery can also use just one single-layer separator.

[0018] The details of the alkaline secondary battery of the present invention will be described below.

[0019] (Zinc Oxide-Containing Layer) The zinc oxide-containing layer contains zinc oxide. The zinc oxide-containing layer supplies zincate ions to the alkaline electrolyte. Therefore, over time, zinc oxide gradually dissipates from the zinc oxide-containing layer.

[0020] From the viewpoint of ensuring a good effect of improving charge-discharge cycle characteristics by placing the zinc oxide-containing layer inside the battery, the mass of zinc oxide contained in the zinc oxide-containing layer is preferably 1% by mass or more, more preferably 2% by mass or more, and more preferably 5% by mass or more, as a mass ratio to the total amount of Zn (zinc atoms) in the negative electrode active material contained in the battery (i.e., when the mass of Zn is set to 100% by mass). However, if the mass of zinc oxide contained in the zinc oxide-containing layer is too high, the internal resistance of the battery will increase and the discharge characteristics will deteriorate. Therefore, from the viewpoint of improving the discharge characteristics of the battery, the mass of zinc oxide contained in the zinc oxide-containing layer is preferably 10% by mass or less, and more preferably 8% by mass or less, as a mass ratio to the total amount of Zn in the negative electrode active material contained in the battery.

[0021] The zinc oxide-containing layer can be composed of, for example, a sheet containing zinc oxide (zinc oxide-containing sheet). An example of a zinc oxide-containing sheet is a sheet containing an insulating porous substrate and zinc oxide powder, in which the zinc oxide powder is held within the voids of the insulating porous substrate. Examples of insulating porous substrates include nonwoven fabrics and woven fabrics, but nonwoven fabrics are preferred.

[0022] As materials for insulating porous substrates, resins with high alkali resistance are preferred. Specifically, examples include polyolefins (polyethylene, polypropylene, etc.), polyesters (polyethylene terephthalate, etc.), polyimides, polyamides (nylon 66, etc.), and polyurethanes.

[0023] The porosity of the insulating porous substrate is preferably, for example, 50 to 90%. Furthermore, the thickness of the insulating porous substrate is preferably, for example, 100 to 300 μm.

[0024] The zinc oxide powder to be held within the voids of the insulating porous substrate preferably has an average particle size of 0.1 to 10 μm.

[0025] In this specification, the particle size of zinc oxide powder and other particles (silver oxide particles, graphite particles, carbon black particles, insulating inorganic particles contained in the positive electrode, and zinc particles related to the negative electrode) is measured using a laser scattering particle size analyzer (e.g., Horiba LA-920) by dispersing these particles in a non-dissolving medium, and the average particle diameter is the 50% diameter value in the volume-based integrated fraction when determining the integrated volume from the smallest particle size (D ５０ This means...

[0026] In a sheet in which zinc oxide powder is held within the voids of an insulating porous substrate, the zinc oxide powder can be bound to the insulating porous substrate using a binder.

[0027] The binder is not particularly limited, but it is preferable to use a resin with high alkali resistance. Preferably, it is an ethylene-acrylic acid copolymer such as ethylene-vinyl acetate copolymer (EVA, containing 20 to 35 mol% of structural units derived from vinyl acetate), ethylene-ethyl acrylate copolymer, fluororesin, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), acrylic resin, polyurethane, epoxy resin, etc., and one or more of these can be used.

[0028] In a sheet in which zinc oxide powder is held within the voids of an insulating porous substrate, when a binder is used, it is preferable that the ratio of binder to 100 parts by mass of zinc oxide powder be 0.5 parts by mass or more, and more preferably 1 part by mass or more, in order to properly bind the zinc oxide powder to the insulating porous substrate. However, since the binder is a factor that increases the internal resistance of the battery, from the viewpoint of ensuring a better effect of lowering the internal resistance of the battery, it is preferable that the ratio of binder to 100 parts by mass of zinc oxide powder in a sheet in which zinc oxide powder is held within the voids of an insulating porous substrate be 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less.

[0029] In the sheet in which zinc oxide powder is held in the voids of the insulating porous substrate, the amount of the zinc oxide powder may be such that the mass ratio of the mass of zinc oxide introduced into the battery by such a sheet to the total amount of Zn in the negative electrode active material satisfies the above value. For example, it may be adjusted in consideration of the thickness and porosity of the insulating porous substrate to be used, etc.

[0030] Among the zinc oxide-containing sheets, the sheet in which zinc oxide powder is held in the voids of the insulating porous substrate can be produced, for example, by preparing a zinc oxide-containing composition containing zinc oxide powder, a binder, and a solvent (such as water), applying this to the insulating porous substrate, filling the voids therein, drying to remove the solvent, and, if necessary, performing a pressing treatment.

[0031] The thickness of the zinc oxide-containing sheet thus obtained is preferably, for example, 50 to 300 μm.

[0032] (Negative electrode) For the negative electrode of the battery, a negative electrode active material layer containing a negative electrode active material or the like can be used as it is, or the negative electrode active material layer can be formed integrally with a current collector and used.

[0033] The negative electrode active material layer contains one or more of zinc metal (zinc simple substance), zinc alloy, and zinc compound (such as zinc oxide) as the negative electrode active material, and the negative electrode active material layer may be composed of only the negative electrode active material, or may be formulated together with other constituent materials to form the negative electrode active material layer. For example, the negative electrode may or may not contain an insulating porous substrate (non-woven fabric, woven fabric, etc.) as a support. Also, a negative electrode obtained by pressure-molding a negative electrode active material or the like into a molded body may be used.

[0034] Examples of the alloy components in the zinc alloy include indium, bismuth, aluminum, etc., and one or more of the above elements can be contained. As the content of each alloy component in the zinc alloy, for example, indium: 0.005 to 0.1% by mass, bismuth: 0.002 to 0.5% by mass, aluminum: 0.0001 to 0.15% by mass are preferable.

[0035] As for the particle size of the negative electrode active material particles, for example, it is preferable that the proportion of particles with a particle size of 75 μm or less in the total powder is 30% by mass or less, and that the average particle diameter is preferably in the range of 100 to 200 μm.

[0036] The negative electrode may contain, for example, a gelling agent (such as sodium polyacrylate or carboxymethylcellulose) in addition to the zinc particles as needed, and a negative electrode composition (gel-like negative electrode) may be used, which is formed by adding an alkaline electrolyte to this. The amount of gelling agent in the negative electrode is preferably, for example, 0.5 to 1.5% by mass.

[0037] In the negative electrode mixture, the zinc content included as the negative electrode active material is preferably 85 to 99% by mass, in the form of elemental zinc, zinc alloy, or zinc compound.

[0038] The negative electrode mixture may contain a conductive additive. Examples of conductive additives include carbon materials such as carbon black (furnace black, channel black, acetylene black, thermal black, etc.) and graphite (natural graphite (flaky graphite, etc.), artificial graphite), and one or more of these may be used. The content of the conductive additive in the negative electrode mixture is preferably 0.01 to 5% by mass.

[0039] The negative electrode mixture may contain a binder. Examples of binders include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); styrene-butadiene rubber (SBR); fluororesins are preferred, and PTFE is more preferred. The binder content in the negative electrode mixture is preferably 0.1 to 2% by mass.

[0040] In the case of a negative electrode consisting only of a negative electrode mixture, for example, the mixture can be prepared by mixing it with a negative electrode active material and, if necessary, a conductive additive, a binder, and an alkaline electrolyte (the same alkaline electrolyte used in batteries can be used). If necessary, the negative electrode mixture may be pressure-molded into a predetermined shape before use.

[0041] Also, in the case of a negative electrode having a molded body of a negative electrode binder (negative electrode binder layer) and a current collector, for example, a negative electrode active material, a conductive auxiliary agent, etc. are dispersed in water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a negative electrode binder-containing composition (slurry, paste, etc.), which is applied onto the current collector and dried, and can be manufactured through a process of performing a pressing process such as calendar processing as necessary.

[0042] However, the negative electrode is not limited to those manufactured by the above methods, and those manufactured by other methods may also be used.

[0043] The thickness of the negative electrode active material layer is preferably 0.15 to 4 mm. On the other hand, when forming and integrating the negative electrode active material layer on one or both sides of a current collector made of a metal foil, the thickness of the negative electrode active material layer (thickness per side of the current collector) is preferably 30 to 300 μm.

[0044] When using a current collector for the negative electrode, examples of the current collector include those made of nickel; stainless steels such as SUS316, SUS430, SUS444; copper and copper alloys; and examples of its form include plain woven wire mesh, expanded metal, lath, punching metal, metal foam, foil (sheet), etc. The thickness of the current collector is preferably, for example, 0.05 mm or more, preferably 4 mm or less in the case of a metal foam, and preferably 0.2 mm or less in the case of other forms. It is also desirable to apply a paste-like conductive material such as carbon paste or silver paste on the surface of such a current collector.

[0045] (Positive electrode) For the positive electrode of the battery, a molded body obtained by molding a positive electrode binder containing a positive electrode active material, etc., or a structure having a layer made of a positive electrode binder (positive electrode binder layer) on one or both sides of a current collector can be used.

[0046] As the positive electrode active material, silver oxide (cuprous oxide, silver oxide, silver nickel composite oxide, etc.); manganese oxide (Mn ２ O ３ 、Mn ３ O ４ 、MnOOH、MnO ２ 、ZnMn ２ O４ LiMn ２ O ４ Examples include Mn-containing oxides or complex oxides; nickel oxides (nickel hydroxide, nickel oxyhydroxide, etc.); and one or more of these can be used. Among these, silver oxide is preferred because it can secure a relatively stable and high discharge voltage from the initial stage to the final stage of discharge.

[0047] 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. In particular, when using silver oxide of this size when the battery is a secondary battery, the utilization rate during charging is improved, and a large charging capacity can be obtained even with a relatively low charging termination voltage, thereby further improving the charge-discharge cycle characteristics of the battery. Furthermore, it is possible to suppress battery swelling that may occur by increasing the charging termination voltage, for example.

[0048] 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.

[0049] Examples of conductive additives for positive electrode mixtures include carbon materials such as carbon black and graphite. Furthermore, carbon black and graphite can be used in combination as conductive additives.

[0050] By using carbon black, a good conductive network can be easily formed in the molded body of the positive electrode mixture. Compared to using graphite alone, for example, there are more contact points with the silver oxide particles, which are the positive electrode active material. This effectively reduces the electrical resistance within the molded body of the positive electrode mixture, thereby improving the reaction efficiency of the positive electrode active material during charging.

[0051] On the other hand, when using only carbon black, 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 is 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.

[0052] For the graphite in the positive electrode mixture, one or more of the types previously exemplified as possible in the negative electrode mixture may be used.

[0053] As mentioned above, graphite has the function of improving the moldability of the positive electrode mixture molded body. From the viewpoint of exhibiting this function more effectively, the graphite preferably has an average particle diameter of 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.

[0054] For the carbon black in the positive electrode mixture, one or more of the types previously exemplified as potentially being included in the negative electrode mixture may be used.

[0055] Furthermore, when using silver oxide as the positive electrode active material, it is preferable to further include insulating inorganic particles in the positive electrode mixture, thereby further improving the charge-discharge cycle characteristics of the battery. In addition, when using insulating inorganic particles, further including carbon black particles and graphite particles in the positive electrode mixture can further improve the charge-discharge cycle characteristics of the battery.

[0056] Examples of insulating inorganic particles related to the positive electrode mixture include particles such as oxides of at least one element selected from Si, Zr, Ti, Al, Mg, and Ca. Specific examples of the oxides include Al ２ O ３ , TiO ２ SiO ２ , ZrO ２ , MgO, CaO, AlOOH, Al(OH) ３Examples include particles that do not dissolve in alkaline electrolytes or are sparingly soluble, which are preferably used. These insulating inorganic particles may be used individually or in combination of two or more types.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Furthermore, when carbon black and graphite are included in the positive electrode mixture, the graphite content 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 through the combined use of carbon black and graphite. In addition, when carbon black and graphite are included in the positive electrode mixture, the graphite content 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.

[0062] Furthermore, when carbon black and graphite are included in the positive electrode mixture, the carbon black 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 and graphite. 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 content when carbon black and graphite are included in the positive electrode mixture is preferably 1.5% by mass or less, and more preferably 1% by mass or less.

[0063] Furthermore, when insulating inorganic particles are included in the positive electrode mixture, the 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 charge-discharge cycle characteristics of the battery). However, if the amount of insulating inorganic particles in the positive electrode mixture is too large, 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.

[0064] 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). For the binder in the positive electrode mixture, one or more of the binders previously exemplified for inclusion in the negative electrode mixture can be used. When a binder is used, the binder content in the positive electrode mixture is preferably 0.1 to 20% by mass.

[0065] 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.

[0066] 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 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.

[0067] However, the positive electrode is not limited to those manufactured by the methods described above, but may be manufactured by other methods.

[0068] 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.

[0069] When a current collector is used for the positive electrode, examples of materials for the current collector include nickel; stainless steel such as SUS316, SUS430, and SUS444; and 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.

[0070] (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.

[0071] 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.

[0072] 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.

[0073]

[0074] 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.

[0075] 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.

[0076] Graft rate (%) = 100 × (A - B) / B (2)

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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."

[0081] (Anion-conducting film) For the separator used in the battery, it is preferable to use an anion-conducting film in which a polymer is used as the matrix and particles of at least one metal compound selected from the group consisting of metal oxides, hydroxides, carbonates, sulfates, phosphates, borates, and silicates are dispersed in the matrix, together with the separator as described above. The anion-conducting film can be placed, for example, between the zinc oxide-containing layer and the separator as described above.

[0082] (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.

[0083] 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, when using pure zinc or a zinc alloy for the negative electrode of a battery, zinc oxide may be added to prevent corrosion (oxidation) of these materials. Zinc oxide can also be added to the negative electrode (when the negative electrode active material is something other than zinc oxide).

[0084] Furthermore, one or more compounds selected from the group consisting of manganese compounds, tin compounds, and indium compounds may be dissolved in the alkaline electrolyte.

[0085] 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 battery's charge-discharge cycle characteristics, for example.

[0086] 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.

[0087] 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.

[0088] Furthermore, 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.

[0089] Furthermore, it is preferable to include tellurium or a compound thereof (such as tellurium dioxide) in at least one of the components within the battery, such as the positive electrode, negative electrode, and separator, or in the alkaline electrolyte, thereby improving the battery's charge-discharge cycle characteristics and load characteristics.

[0090] (Outer casing) For the battery outer casing, for example, a battery container consisting of an outer can, a sealing can, and a gasket as shown in Figure 1; a sheet-like outer casing made of resin film or metal-resin laminate film; a battery container having a metal outer can with a bottomed cylindrical shape (cylindrical or rectangular) and a sealing structure that seals its opening; etc. can be used.

[0091] In the case of a battery container consisting of an outer casing, a sealing casing, and a gasket, the outer casing can be made of materials such as nickel-plated iron or stainless steel.

[0092] In the case of a battery container consisting of an outer can, a sealing can, and a gasket, the sealing can can be made of, for example, iron with nickel plating or stainless steel. When the negative electrode active material, such as pure zinc or a zinc alloy, is in direct contact with the inner surface of the sealing can, it is preferable to form a metal layer made of copper or a copper alloy such as brass on the surface of the sealing can 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 can that is in contact with the negative electrode is to suppress the formation of local galvanic cells with pure zinc or a zinc alloy and prevent corrosion of these cells, but the corrosion prevention effect can be further enhanced by forming a layer of tin on the surface of the metal layer.

[0093] In the case of a battery container consisting of an outer casing, a sealing casing, and a gasket, the gasket can be made of materials such as nylon or polypropylene.

[0094] Furthermore, in the case of batteries having a battery container composed of an outer casing, a sealing casing, and a gasket, or batteries having a sheet-like outer casing, the plan view shape 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.

[0095] The present invention will be described in detail below based on examples. However, the following examples are not intended to limit the present invention.

[0096] Example 1 (Preparation of positive electrode) Silver(I) oxide (Ag) with an average particle size of 1.4 μm and containing 3.7% (by mass) of Bi relative to the total amount of silver. ２ O) and carbon black (BET specific surface area of ​​68 m²) ２ A mixture was prepared by mixing acetylene black (with an average primary particle size of 35 nm) at a mass ratio of 98:2 with the aforementioned mixture. Furthermore, the mixture and graphite particles (BET specific surface area: 20 m²) were mixed. ２ ( / g, average particle size: 3.7 μm) and TiO ２ A cathode mixture was prepared by mixing particles (average particle size: 250 nm) in a mass ratio of 95.2:3.8:1.

[0097] This positive electrode mixture: 76 mg was filled into the mold, with a filling density of 5.7 g / cm³. ３ The positive electrode mixture molded body was then fabricated by pressure molding it into a disc shape with a diameter of 5.2 mm and a height of 0.62 mm.

[0098] (Fabrication of the negative electrode) For the negative electrode active material, mercury-free zinc alloy particles commonly used in alkaline primary batteries were used, containing In: 500 ppm, Bi: 400 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 or less.

[0099] The zinc alloy particles (18 mg) and ZnO (0.56 mg) were mixed (mass ratio = 97:3), and the resulting composition (composition for negative electrode) was used to produce a negative electrode (a negative electrode consisting of a negative electrode active material layer).

[0100] (Alkaline Electrolyte) For the alkaline electrolyte, a mixed solution was used, which was prepared by dissolving potassium hydroxide at a concentration of 35% by mass, dissolving zinc oxide at a concentration of 3% by mass in an aqueous solution, and further dissolving lithium hydroxide at a concentration of 1% by mass, polyethylene glycol at 1% by mass, and tellurium dioxide at a concentration of 9.2% by mass. The tellurium content in the electrolyte was 7.4% by mass.

[0101] (Preparation of anion-conducting film) 5 g of an aqueous dispersion of polytetrafluoroethylene (solids content: 60% by mass), 2.5 g of an aqueous solution of sodium polyacrylate (concentration: 2% by mass), and 2.5 g of hydrotalcite particles (average particle size: 0.4 μm) were kneaded and rolled to produce an anion-conducting film with a thickness of 100 μm. Furthermore, this was punched out into circles with a diameter of 5.7 mm and used in the assembly of a battery.

[0102] (Preparation of Zinc Oxide-Containing Sheet) A zinc oxide-containing composition was prepared by mixing 99.8 parts by mass of zinc oxide powder with an average particle size of 0.6 μm, 0.2 parts by mass of carboxymethylcellulose, and water, and then adding 0.9 parts by mass of PTFE per 100 parts by mass of zinc oxide and mixing. This zinc oxide-containing composition was then filled into a polypropylene nonwoven fabric, dried at 80°C, and then pressed to produce a zinc oxide-containing sheet with a thickness of 150 μm, which would become the zinc oxide-containing layer. This sheet was then cut into circles with a diameter of 3 mm and used in the assembly of the battery.

[0103] (Battery Assembly) The battery separator used the aforementioned anion-conducting film and a graft film / cellophane film laminate. For the graft film / cellophane film laminate, 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 cut into a circle with a diameter of 5.7 mm and used.

[0104] An electrolyte absorbent made of vinylon-rayon nonwoven fabric, with a diameter of 5.5 mm and made of steel plate with a gold-plated interior, was placed on the inner bottom surface of the outer can. The positive electrode (positive electrode mixture molded body) was then placed on top of the absorbent, and 9 μL of alkaline electrolyte was dropped onto it. A button-type alkaline secondary battery with a diameter of 5.8 mm and a thickness of 2.7 mm was assembled, having the structure shown in Figure 1, except for the use of an electrolyte absorber. This battery was constructed by placing the negative electrode (negative electrode composition) inside a sealing can made of a copper-stainless steel (SUS304)-nickel clad plate fitted with a nylon 66 annular gasket, dropping 10 μL of alkaline electrolyte onto it, and then sequentially stacking a zinc oxide-containing sheet, an anion-conducting film, a graft film / cellophane film laminate, and an outer can containing the positive electrode on top of the negative electrode of the sealing can.

[0105] Furthermore, the mass of zinc oxide contained in the zinc oxide-containing layer (zinc oxide-containing sheet) was 6.3% by mass relative to the total mass of Zn in all zinc alloy particles that constitute the negative electrode active material.

[0106] Comparative Example 1 A button-type alkaline secondary battery was assembled in the same manner as in Example 1, except that the battery was assembled without using a zinc oxide-containing sheet.

[0107] For the button-type alkaline secondary batteries of Example 1 and Comparative Example 1, a charge-discharge cycle was repeated, consisting of constant current discharge at a current of 1 mA (discharge termination: 1 V), constant current charging at a current of 2 mA up to 1.8 V, and constant voltage charging at 1.8 V (charging terminated when the current value dropped to 0.2 mA), followed by constant current discharge at a current of 1 mA (discharge termination: 1 V). The changes in discharge capacity during this process are shown in Figure 2.

[0108] In addition to the above tests, the AC impedance of the button-type alkaline rechargeable batteries of Example 1 and Comparative Example 1 was measured at an applied voltage of 10 mV and 1 kHz to determine the internal resistance of the batteries. Furthermore, a 200 Ω discharge resistor was connected, and the battery voltage (discharge voltage) was measured 0.3 seconds after the start of discharge. Measurements were performed on five batteries of each type, and the average value was calculated. The measurement results are shown in Table 1.

[0109]

[0110] As shown in Figure 2, the battery of Example 1, in which a zinc oxide-containing layer was placed between the negative electrode active material layer and the separator, was able to improve the charge-discharge cycle characteristics compared to the battery of Comparative Example 1, which did not have a zinc oxide-containing layer.

[0111] On the other hand, as shown in Table 1, the zinc oxide-containing layer increases the internal resistance of the battery and lowers the discharge voltage of the battery. Therefore, from the viewpoint of suppressing a decrease in discharge characteristics, the amount of zinc oxide contained in the zinc oxide-containing layer must be 10% by mass or less in terms of mass ratio to Zn in the negative electrode active material.

[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 alkaline secondary battery of the present invention can be applied to the same uses as known alkaline secondary batteries.

[0114] 1. Alkaline rechargeable battery 2. Outer casing 3. Sealing casing 4. Positive electrode 5. Negative electrode 6. Separator 7. Zinc oxide-containing layer 8. Gasket

Claims

1. An alkaline secondary battery having a negative electrode, a positive electrode, and a separator, the negative electrode having a negative electrode active material layer containing zinc metal, a zinc alloy, or a zinc compound as the negative electrode active material, wherein a zinc oxide-containing layer is provided between the negative electrode active material layer and the separator, and the mass of zinc oxide contained in the zinc oxide-containing layer is 1 to 10% by mass in terms of mass ratio to the total amount of Zn in the negative electrode active material.

2. The alkaline secondary battery according to claim 1, wherein the zinc oxide-containing layer contains zinc oxide powder and an insulating porous substrate, and the zinc oxide powder is held within the voids of the insulating porous substrate.

3. The alkaline secondary battery according to claim 1, wherein the negative electrode active material layer contains a zinc alloy.

4. The alkaline secondary battery according to claim 1, wherein the positive electrode contains silver oxide as a positive electrode active material.

5. A method for manufacturing an alkaline secondary battery having a negative electrode, a positive electrode, and a separator, the negative electrode having a negative electrode active material layer containing zinc metal, a zinc alloy, or a zinc compound as the negative electrode active material, the method comprising the step of laminating a negative electrode active material layer, a zinc oxide-containing layer containing zinc oxide, and a separator, characterized in that the mass of zinc oxide contained in the zinc oxide-containing layer is 1 to 10% by mass in terms of mass ratio to the total amount of Zn in the negative electrode active material.

6. The method for manufacturing an alkaline secondary battery according to claim 5, wherein the zinc oxide-containing layer contains zinc oxide powder and an insulating porous substrate, and the zinc oxide powder is held in the voids of the insulating porous substrate.

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