Negative electrode for secondary battery and secondary battery

Abstract

To provide a secondary battery that has a negative electrode containing a zinc-based material and is excellent in charge-discharge cycle characteristics.SOLUTION: A negative electrode for a secondary battery disclosed in the present application includes a zinc-based material and aluminum oxide that is partially dissolved in an alkaline electrolyte. The elution ratio of the aluminum oxide to a 8 mol / L of potassium hydroxide aqueous solution is 5-30% in mass ratio. The aluminum oxide preferably includes χ-alumina or γ-alumina. A secondary battery disclosed in the present application comprises the negative electrode for a secondary battery, a positive electrode, a separator, and an alkaline electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to a negative electrode containing a zinc-based material and a secondary battery using the negative electrode and having excellent charge-discharge cycle characteristics. [Background technology]

[0002] In recent years, the use of anodes made of metals, alloys, intermetallic compounds, or metal oxides has been investigated to construct high-capacity, high-energy-density secondary batteries. Among these, zinc and zinc alloys, which are widely used in alkaline primary batteries that use alkaline aqueous electrolytes, are being considered for use in the anodes of secondary batteries, and development of secondary batteries combining these materials with cathode materials such as silver oxide and nickel hydroxide is progressing.

[0003] However, secondary batteries that use zinc, zinc alloys, or zinc compounds such as zinc oxide as the negative electrode material have problems such as the generation of zinc dendrites in the negative electrode, shape changes due to aggregation of the negative electrode material, gas generation, and passivation of the negative electrode material, which result in issues with the charge-discharge cycle life.

[0004] In order to improve the charge-discharge cycle characteristics of the secondary battery, various methods have been investigated, including forming an anti-dendrite layer containing at least one of carbon and alkaline earth metal hydroxide and alumina fiber on the surface of the negative electrode (Patent Document 1), constructing a zinc electrode from a mixture of zinc oxide and inorganic fibers containing silica and alumina (Patent Document 2), and constructing an electrode containing zinc powder, an electrically active component made of a metal oxide such as Al2O3, an organic gelling agent, an organic binder, and calcium zincate (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 167264 / 1983 [Patent Document 2] Special Publication No. 2004-522256 [Patent Document 3] Special Publication No. 2008-537302 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the effect of improving the charge-discharge cycle characteristics by the above method is not sufficient. For example, when the amount of active material in the negative electrode is increased to increase capacity, problems such as the generation of zinc dendrites and changes in shape due to aggregation of the negative electrode material have not been solved.

[0007] The present application has been made in view of the above circumstances, and aims to provide a negative electrode that uses zinc as an active material and can constitute a secondary battery that has excellent charge-discharge cycle characteristics, and a secondary battery that uses the negative electrode. [Means for solving the problem]

[0008] A first aspect of the negative electrode for a secondary battery disclosed in the present application includes a zinc-based material and an aluminum oxide that is partially soluble in an alkaline electrolyte, and the aluminum oxide has a leaching rate of 5 to 30% by mass in an 8 mol / L aqueous potassium hydroxide solution.

[0009] A second aspect of the negative electrode for a secondary battery disclosed in the present application is characterized in that it contains a zinc-based material and an aluminum oxide that is partially soluble in an alkaline electrolyte, and the aluminum oxide contains χ-alumina.

[0010] A third aspect of the negative electrode for a secondary battery disclosed in the present application is characterized in that it contains a zinc-based material and an aluminum oxide that is partially soluble in an alkaline electrolyte, and the aluminum oxide contains γ-alumina.

[0011] Furthermore, the secondary battery disclosed in the present application includes a positive electrode, a negative electrode, a separator, and an alkaline electrolyte, and is characterized in that the negative electrode is the negative electrode for a secondary battery of the present application. [Effects of the Invention]

[0012] According to the present application, it is possible to provide a secondary battery having a negative electrode containing a zinc-based material and having excellent charge-discharge cycle characteristics. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graph showing the results of evaluation of the charge-discharge cycle characteristics of the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 at 40° C. and a current value of 128 mA. [Figure 2] 1 is a graph showing the results of evaluation of the charge-discharge cycle characteristics of the secondary batteries of Example 1, Examples 3 and 4, and Comparative Example 1 at a current value of 64 mA at 40° C.; DETAILED DESCRIPTION OF THE INVENTION

[0014] (Negative electrode for secondary batteries) An embodiment of a negative electrode for a secondary battery disclosed in the present application will be described. The negative electrode for a secondary battery of this embodiment includes a zinc-based material and an aluminum oxide that is partially soluble in an alkaline electrolyte, and the aluminum oxide has a dissolution rate of 5 to 30% by mass in an 8 mol / L aqueous potassium hydroxide solution.

[0015] This makes it possible to suppress the aggregation of the negative electrode active material (metallic zinc) that occurs during charge and discharge in a negative electrode containing a zinc-based material, thereby suppressing the decrease in capacity of the secondary battery during repeated charge and discharge, and improving the charge and discharge cycle characteristics. Here, the zinc-based material includes at least one material selected from zinc, a zinc alloy, and zinc oxide.

[0016] In the present application, the reason why aggregation of the negative electrode active material (metallic zinc) that accompanies charge and discharge can be suppressed is not clear, but it is speculated that the following mechanism may be involved.

[0017] In anodes containing zinc-based materials, metallic zinc, the anode active material, aggregates and expands with charge-discharge cycles, increasing the amount of zinc that cannot be discharged, reducing the utilization rate of the active material and accelerating anode degradation. This anode degradation is one of the major factors that cause secondary batteries with anodes containing zinc-based materials to reach the end of their cycle life.

[0018] In contrast, in the present application, by incorporating aluminum oxide, which dissolves at a certain rate into the negative electrode of an "8 mol / L potassium hydroxide aqueous solution," which is a common composition for the electrolyte of alkaline secondary batteries, the aluminum oxide that remains in the negative electrode without dissolving acts as a physical barrier against the aggregation of metallic zinc, and is thought to suppress the enlargement of metallic zinc.

[0019] On the other hand, even if metallic zinc grows in the negative electrode and covers the surface of the aluminum oxide, part of the aluminum oxide dissolves in the electrolyte, ensuring a flow path for the electrolyte. This is thought to prevent the charge / discharge reaction of zinc from being inhibited, suppress a decrease in the utilization rate of the negative electrode active material, and maintain excellent cycle characteristics.

[0020] Furthermore, the above-mentioned function of aluminum oxide is also effective when the amount of active material in the negative electrode is increased, and is thought to be useful in increasing the capacity of the secondary battery.

[0021] In the present application, the elution rate of aluminum oxide, which is partially dissolved in alkaline electrolyte (8 mol / L aqueous potassium hydroxide solution), is a value determined by the following elution test.

[0022] <Dissolution test> 1 g of aluminum oxide is immersed in 20 mL of an 8 mol / L potassium hydroxide aqueous solution held at 40°C, and after leaving it to stand at 40°C for 300 hours, the remaining aluminum oxide is washed with water and dried, and its weight x (g) is measured. The percentage of the weight loss (1-x) relative to the original weight is taken as the elution rate. Here, if 20 mL of 8 mol / L potassium hydroxide aqueous solution is used for 1 g of aluminum oxide, this will be a sufficient amount to elute all of the components in the aluminum oxide that are elutable in an alkaline electrolyte at 40°C.

[0023] The elution ratio of the aluminum oxide in the alkaline electrolyte is preferably 5% or more by mass, and more preferably 8% or more, in order to ensure sufficient electrolyte flow paths and prevent a decrease in the utilization rate of the negative electrode active material.

[0024] On the other hand, in order to function as a skeleton that prevents metallic zinc from agglomerating and enlarging, a small elution rate is desirable, and the elution rate of aluminum oxide in the alkaline electrolyte is preferably 30% or less, and more preferably 20% or less, by mass ratio.

[0025] An example of an aluminum oxide that dissolves partially in an alkaline electrolyte and can prevent metallic zinc from aggregating and enlarging is aluminum oxide (χ-alumina) whose crystal structure, as determined by X-ray diffraction, is "χ-type." χ-alumina has moderate solubility in alkaline electrolytes, and most of it remains undissolved in the electrolyte. This allows the electrolyte to flow through a sufficient amount, preventing a decrease in the utilization rate of the negative electrode active material, and also allows the aluminum oxide to function as a skeleton that prevents metallic zinc from aggregating and enlarging.

[0026] In addition, chi-alumina contains detachable water molecules (crystal water) within the crystals, and the water gradually emerges from the crystals, causing zinc to dissolve. This is also thought to prevent metallic zinc from agglomerating and becoming enlarged.

[0027] Furthermore, γ-alumina can also be used as the aluminum oxide. γ-alumina has a coarse crystal structure and is soluble in alkaline electrolytes similar to χ-alumina, and is thought to have the same effects as χ-alumina.

[0028] The proportion of the aluminum oxide is preferably 5 to 30 mass % of the total amount of the zinc-based material and the aluminum oxide, because if the proportion of aluminum oxide is too high, the negative electrode capacity decreases, and if it is too low, it tends to be difficult for the aluminum oxide to function as a skeleton that prevents the metal zinc from agglomerating and enlarging.

[0029] The number average particle size of the aluminum oxide is preferably 10 to 300 μm. If the particle size of the aluminum oxide is too small, the zinc metal can grow by incorporating the aluminum oxide, and the effect of inhibiting coarse growth is not easily achieved. Therefore, the number average particle size is preferably 10 μm or more, and more preferably 50 μm or more.

[0030] On the other hand, if the particle size of the aluminum oxide is too large, the gaps between the aluminum oxide particles become large, making it easier for metallic zinc to grow, so the number average particle size is preferably 300 μm or less, and more preferably 200 μm or less.

[0031] In the present specification, the number average particle size of aluminum oxide particles and other particles (such as zinc oxide particles) can be measured, for example, by using a laser scattering particle size distribution analyzer (for example, HORIBA's "LA-920") to disperse the particles in a medium that does not dissolve or swell the particles.

[0032] The specific surface area of ​​the aluminum oxide as determined by nitrogen gas adsorption (hereinafter referred to as "specific surface area") is 1 m² from the viewpoint of improving the liquid retention, cycle life, and shape stability. 2 / g or more, and 2On the other hand, if the specific surface area of ​​the aluminum oxide is too large, it may be difficult to prepare the mixture. 2 / g or less, and 2 It is more preferable that the saturation coefficient is 1 / g or less.

[0033] In the present specification, the specific surface area of ​​aluminum oxide particles and other particles (such as zinc oxide particles) can be measured, for example, using a specific surface area / pore size analyzer (for example, "QUADRASORB evo" manufactured by Quantachrome) using the BET multipoint method based on nitrogen gas adsorption.

[0034] Regarding the acidity of the aluminum oxide, any of acidic, neutral, and basic oxides can be suitably used, but the preferred pH of the aluminum oxide is less than 9.0, and it is more preferred that the aluminum oxide be acidic or neutral.

[0035] The negative electrode of this embodiment may have a structure in which a negative electrode mixture layer containing a zinc-based material such as zinc oxide and the above-mentioned aluminum oxide is formed on a current collector.

[0036] When zinc oxide is used as the zinc-based material, the number average particle size of the zinc oxide is preferably 0.01 μm or more, more preferably 0.05 μm or more, and is preferably 10 μm or less, more preferably 1 μm or less.

[0037] The content of zinc oxide in the negative electrode mixture layer is preferably 60 to 95 mass %.

[0038] Zinc can be used instead of the zinc oxide, or a mixture of the two can be used. When using zinc, the proportion of zinc used can be determined in accordance with that of zinc oxide. Furthermore, zinc may be used as a zinc alloy containing additional elements such as In, Bi, Al, Mg, and Ca to prevent reaction with the electrolyte.

[0039] The negative electrode mixture layer usually contains a binder. Examples of the binder for the negative electrode mixture layer include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); and styrene butadiene rubber (SBR); with fluororesins being preferred and PTFE being more preferred.

[0040] The content of the binder in the negative electrode mixture layer is preferably 0.1 to 2 mass %. In particular, when a fluororesin is used as the binder, if the content is too high, the water repellency of the negative electrode mixture layer and the composition for forming the negative electrode mixture layer (the negative electrode mixture composition described below) becomes strong, which may result in reduced productivity and non-uniform battery reactions.

[0041] The negative electrode mixture layer may contain a conductive additive, such as carbon blacks (e.g., acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black), carbon fibers, graphite, and other carbon materials, as well as powders and fibers of metals (e.g., tin, bismuth, silver, and copper).

[0042] The content of the conductive auxiliary agent in the negative electrode mixture layer is preferably 0.01 to 5% by mass.

[0043] The negative electrode mixture layer can be formed, for example, by dispersing zinc oxide, the aforementioned aluminum oxide, and optionally added binders and conductive additives, in a solvent to prepare a negative electrode mixture composition (e.g., a paste), and then rolling the resulting mixture into a sheet (negative electrode mixture sheet). This allows for the easy formation of a negative electrode mixture layer with a thickness of, for example, 1 mm or more. Using a negative electrode with a thick negative electrode mixture layer makes it possible to obtain a secondary battery with higher capacity and higher energy density.

[0044] To obtain a negative electrode using the negative electrode mixture layer (negative electrode mixture sheet), the negative electrode mixture layer may be attached to, for example, a negative electrode current collector.

[0045] Furthermore, in the case of a negative electrode having a thinner negative electrode mixture layer than the above, for example, a negative electrode mixture composition (such as a slurry) having a lower solid content concentration can be prepared, applied to a current collector, dried, and then, if necessary, subjected to a pressing process to produce the negative electrode mixture.

[0046] Although water is usually used as the solvent for the negative electrode mixture composition, a solvent other than water, such as alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.), may be added as appropriate for the purposes of uniformly dispersing the zinc-based material, uniformly dissolving or dispersing the binder, controlling interfacial tension, etc. Furthermore, an aqueous solution containing an electrolyte salt used as an electrolyte solution for a battery may also be used as the solvent for the negative electrode mixture composition.

[0047] The solid content concentration of the negative electrode mixture composition (total content of all components other than the solvent) is preferably 70 to 95 mass %.

[0048] It is also preferable to add a water-soluble polymer material to the negative electrode mixture composition in order to provide stability over time.

[0049] Examples of water-soluble polymer materials that can be used in the negative electrode mixture composition include CMC (carboxymethyl cellulose), PVA (polyvinyl alcohol), PVP (polyvinylpyrrolidone), PAA (polyacrylic acid), ammonium polycarboxylates, lecithin, sugars exemplified by glycosides such as saponin and polysaccharides such as xanthan gum, and polyether polyols such as PEO (polyethylene oxide), sucrose polyether polyol, polyoxypropylene sorbitol ether, trimethylolpropane polyether polyol, and pentaerythritol polyether polyol. The negative electrode mixture composition may contain two or more water-soluble polymer materials.

[0050] Among the above water-soluble polymer materials, it is preferable to use at least one of carboxymethyl cellulose and polyether polyol, and it is more preferable to use both carboxymethyl cellulose and polyether polyol.

[0051] The content of the water-soluble polymer material in the negative electrode mixture composition is preferably 0.02% by mass or more, and more preferably 0.05% by mass or more, of all components excluding the solvent (hereinafter referred to as "solid content"), from the viewpoint of favorably thickening the negative electrode mixture composition and making it easier to form a thick negative electrode mixture layer. However, since the water-soluble polymer material acts as a resistance component in the formed negative electrode mixture layer, if the amount of water-soluble polymer material in the negative electrode mixture composition is too high, there is a risk of impairing the characteristics (such as capacity) of the secondary battery. Therefore, the content of the water-soluble polymer material in the negative electrode mixture composition is preferably 0.2% by mass or less, and more preferably 0.15% by mass or less, of the solid content.

[0052] The method for preparing the negative electrode mixture composition is not particularly limited. For example, any method may be employed that can uniformly disperse the zinc-based material, the aluminum oxide, the binder, and the conductive additive in the mixture composition, and, when a water-soluble polymer material is used, can uniformly distribute the water-soluble polymer material in the mixture composition.

[0053] The thickness of the negative electrode mixture layer can be 0.1 mm or more, but from the viewpoint of increasing the energy density of the secondary battery, it is preferably 1 mm or more, more preferably 1.5 mm or more, and the upper limit of the thickness of the negative electrode mixture layer is preferably, for example, 10 mm.

[0054] Examples of the negative electrode current collector include mesh, foil, expanded metal, punched metal, and foam metal made of metal such as nickel, copper, and stainless steel; and carbon sheet and mesh. These current collectors are preferably coated, for example, with a material having a high hydrogen overvoltage, such as tin, lead, or indium. The thickness of the negative electrode current collector is preferably 5 to 300 μm.

[0055] Furthermore, in the secondary battery of the present application, which will be described later, a sheet-like outer casing can be applied, and the surface of this sheet-like outer casing that is intended to become the inner surface (the surface that comes into contact with the sheet that will become the negative electrode mixture layer) can be coated with carbon paste to form a current collector, or a metal layer (described later) that constitutes the sheet-like outer casing can be used as a current collector.

[0056] The negative electrode can be provided with an external terminal in accordance with a conventional method for electrically connecting the secondary battery to a device to which it is applied.

[0057] The negative electrode has a capacity per area of ​​the negative electrode mixture layer of 150 mAh / cm 2 It is preferable that the capacity is 300mAh / cm or more. 2 By using a negative electrode with such a capacity, a secondary battery with a high energy density can be obtained.

[0058] In the case of a secondary battery using a negative electrode having a thick negative electrode mixture layer, for example, 1 mm or more, or a negative electrode having a high capacity per area as described above, the charge-discharge reaction in the mixture layer is more likely to be non-uniform, and shape changes due to the generation of zinc dendrites and zinc aggregation are more likely to occur, resulting in a greater deterioration of the charge-discharge cycle characteristics, compared to a secondary battery using a negative electrode having a thin negative electrode mixture layer or a negative electrode having a low capacity per area. However, in the present application, by incorporating the above-mentioned aluminum oxide into the negative electrode, it is possible to prevent a deterioration in the charge-discharge cycle characteristics and achieve a high battery capacity, even in a secondary battery having such a negative electrode.

[0059] The capacity per unit area of ​​the negative electrode mixture layer can be controlled to the above value by adjusting the thickness and packing density of the negative electrode mixture layer (and therefore adjusting the amount of negative electrode active material per unit area of ​​the negative electrode mixture layer). Each type of negative electrode active material is known to have a specific capacity, and these values ​​are published, so these values ​​are used to calculate the capacity per unit area of ​​the negative electrode mixture layer.

[0060] The packing density of the negative electrode mixture layer is 1.8 to 2.8 g / cm 3 is good, 2.1 to 2.4 g / cm 3 If the packing density is too high, the porosity of the negative electrode mixture layer becomes too low, making it difficult for the electrolyte to penetrate into the negative electrode mixture layer, which may result in a deterioration in the battery characteristics.

[0061] The zinc oxide in the negative electrode changes to metallic zinc upon charging, and the content of zinc oxide per unit area in the negative electrode can be determined by converting the metallic zinc into zinc oxide.

[0062] (Secondary battery) Next, an embodiment of the secondary battery disclosed in the present application will be described. The secondary battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an alkaline electrolyte, and uses the above-mentioned negative electrode for secondary batteries of the present application as the negative electrode.

[0063] The secondary battery of the present embodiment is only required to include the above-described negative electrode, and the configurations of the positive electrode, separator, alkaline electrolyte, etc. are not particularly limited, and general-purpose positive electrodes, separators, alkaline electrolytes, etc. used in alkaline secondary batteries, air secondary batteries, etc. can be used.

[0064] Hereinafter, the components other than the negative electrode of the secondary battery of this embodiment and related matters will be described.

[0065] <Positive electrode> When the secondary battery of the present embodiment is an alkaline secondary battery, the positive electrode may have a structure in which a positive electrode mixture layer containing a positive electrode active material, a conductive additive, and a binder is provided on one or both sides of a current collector.

[0066] When the secondary battery is an alkaline secondary battery, usable positive electrode active materials include silver oxide (silver(I) oxide, silver(II) oxide, etc.); manganese oxides such as manganese dioxide; nickel oxyhydroxide; and composite oxides of silver and cobalt, nickel, or bismuth.

[0067] Examples of the conductive additive for the positive electrode mixture layer that can be used include carbon materials such as carbon blacks, such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; carbon fibers; conductive fibers, such as metal fibers; carbon fluoride; metal particles, such as copper and nickel; and organic conductive materials, such as polyphenylene derivatives.

[0068] Examples of binders for the positive electrode mixture layer include fluororesins (PVDF, PTFE, etc.), SBR, CMC, and polyvinylpyrrolidone (PVP).

[0069] The positive electrode mixture layer preferably contains 80 to 98% by mass of positive electrode active material, 1.5 to 10% by mass of conductive additive, and 0.5 to 10% by mass of binder. The thickness of the positive electrode mixture layer (thickness per surface of the current collector) is preferably 1 to 20 mm.

[0070] A positive electrode having a positive electrode mixture layer can be produced, for example, by dispersing a positive electrode active material, a conductive additive, a binder, and the like in water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture-containing composition (slurry, paste, etc.) (the binder may be dissolved in the solvent), applying this onto a current collector, drying it, and, if necessary, performing a pressing process such as calendaring.

[0071] When the secondary battery of this embodiment is an air secondary battery, the positive electrode may have a catalyst layer, for example, a structure in which a catalyst layer and a current collector are laminated.

[0072] The catalyst layer may contain a catalyst, a binder, and the like.

[0073] Examples of the catalyst for the catalyst layer include silver, platinum group metals or alloys thereof; transition metals; platinum / metal oxides such as Pt / IrO2; La 1-x Ca xExamples of known materials include perovskite oxides such as CoO3; brownmillerite transition metal oxides such as Ca2Fe2O5 and Ca2FeCoO5; carbides such as WC; nitrides such as Mn4N; manganese oxides such as manganese dioxide; and carbon (graphite, carbon black (acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc.), charcoal, activated carbon, etc.), and one or more of these may be used.

[0074] The catalyst layer preferably contains 1% by mass or less of heavy metals, excluding components of the electrolyte solution. In the case of a positive electrode having a catalyst layer with such a low heavy metal content, the battery can be disposed of without any special treatment, resulting in a low environmental impact.

[0075] The content of heavy metals in the catalyst layer referred to in this specification can be measured by X-ray fluorescence analysis. For example, it can be measured using a Rigaku X-ray fluorescence analyzer "ZSX100e" under the conditions of an excitation source of Rh 50 kV and an analysis area of ​​φ10 mm.

[0076] Therefore, it is recommended that the catalyst for the catalyst layer does not contain heavy metals, and it is more preferable to use the various carbons mentioned above.

[0077] Examples of binders for the catalyst layer include fluororesin binders such as PVDF, PTFE, vinylidene fluoride copolymers, and tetrafluoroethylene copolymers (e.g., vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), vinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE), vinylidene fluoride-tetrafluoroethylene copolymer (PVDF-TFE), and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (PVDF-HFP-TFE)). Among these, tetrafluoroethylene polymers (PTFE) or copolymers are preferred, with PTFE being more preferred. The binder content in the catalyst layer is preferably 3 to 50% by mass.

[0078] A positive electrode having a catalyst layer can be produced, for example, by mixing the catalyst, binder, etc. with water, rolling the mixture with a roll, and then adhering it to a current collector. Alternatively, the positive electrode can be produced by dispersing the catalyst and a binder, etc., used as needed, in water or an organic solvent to prepare a catalyst layer-forming composition (slurry, paste, etc.), applying the composition to the surface of the current collector, drying the composition, and then subjecting the resulting mixture to a pressing process such as calendering, as needed.

[0079] For the current collector for a positive electrode having a positive electrode mixture layer or a positive electrode having a catalyst layer, for example, a mesh, foil, expanded metal, or punched metal made of a metal such as titanium, nickel, stainless steel, or copper; a carbon mesh or sheet; or the like can be used.

[0080] In addition, as described below, a sheet-like outer casing can be applied to the positive electrode current collector, but it is also possible to apply carbon paste to the surface of this sheet-like outer casing that is intended to be the inner surface, or to use a metal layer (described below) that constitutes the sheet-like outer casing.

[0081] The positive electrode can be provided with an external terminal in accordance with a conventional method for electrically connecting the secondary battery to a device to which it is applied.

[0082] <separator> Examples of the separator for the secondary battery of this embodiment include separators commonly used in various batteries, such as porous resin membranes (microporous membranes, nonwoven fabrics, etc.) and semipermeable membranes such as cellophane films. In particular, when the secondary battery is an air secondary battery, it is preferable to use an anion conductive membrane or a semipermeable membrane as the separator, from the viewpoint of preventing short circuits and improving load characteristics.

[0083] Examples of resins that can be used to form separators made of porous resin films include polyolefins such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers.

[0084] In the case of a resin separator, the porosity is preferably 30 to 80% and the thickness is preferably 10 to 100 μm, but multiple sheets may be stacked.

[0085] Furthermore, when a semipermeable membrane such as a cellophane film is used as the separator, the separator may be constructed solely from the semipermeable membrane. However, because the semipermeable membrane has low strength, problems such as breakage during battery assembly are likely to occur. Therefore, it is also recommended to construct the separator from a laminate in which a semipermeable membrane and a graft film composed of a polymer in which (meth)acrylic acid or its derivatives are graft-polymerized onto a polyolefin (PE, PP, etc.) backbone polymer are laminated. Note that the term "(meth)acrylic acid" used above refers collectively to acrylic acid and methacrylic acid.

[0086] In the case of a separator made of only a cellophane film, the thickness is, for example, preferably 15 μm or more, and preferably 40 μm or less, and more preferably 30 μm or less.

[0087] Furthermore, 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, for example, preferably 30 μm or more, more preferably 40 μm or more, and preferably 70 μm or less, more preferably 60 μm or less.

[0088] Furthermore, in the case of a separator formed of a laminate of a graft film and a cellophane film, the thickness of the graft film is, for example, preferably 15 μm or more, more preferably 25 μm or more, and preferably 30 μm or less.

[0089] Examples of laminates of a graft film and a cellophane film for forming a separator include those commercially available from Yuasa Membrane Systems Co., Ltd. under the names "YG9132," "YG9122," and "YG2152."

[0090] The separator may also be constructed by combining a cellophane film with a liquid-absorbent layer (electrolyte solution retention layer) such as vinylon-rayon mixed paper. Alternatively, the separator may also be constructed by combining a laminate of a graft film and a cellophane film with the above-mentioned liquid-absorbent layer. The thickness of such a liquid-absorbent layer is preferably 20 to 500 μm.

[0091] <Alkaline electrolyte> The alkaline electrolyte for the secondary battery of this embodiment can be an alkaline aqueous solution containing an aqueous solution of an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, or lithium hydroxide, or one to which zinc oxide has been added. The concentration of the alkali metal hydroxide in the alkaline electrolyte is preferably 6 to 50 mass %, more preferably 10 to 45 mass %, in the case of potassium hydroxide, for example. When zinc oxide is used, its concentration is, for example, 1.0 to 4.0 mass %, but can be changed as appropriate depending on the purpose. Considering that zinc oxide contributes to an increase in battery capacity, a saturated concentration is preferred.

[0092] It is preferable that an indium compound is dissolved in the alkaline electrolyte, since when an indium compound is dissolved in the alkaline electrolyte, generation of hydrogen gas in the battery can be effectively suppressed.

[0093] Examples of the indium compound to be dissolved in the alkaline electrolyte include indium hydroxide, indium oxide, indium sulfate, indium sulfide, indium nitrate, indium bromide, and indium chloride.

[0094] The concentration of the indium compound in the alkaline electrolyte is, by mass, preferably 0.005% or more, more preferably 0.01% or more, and particularly preferably 0.05% or more, and is preferably 1% or less, more preferably 0.5% or less, and particularly preferably 0.1% or less.

[0095] The alkaline electrolyte may contain various known additives as needed.

[0096] <Battery type> The shape of the secondary battery of this embodiment is not particularly limited, and the battery may be any of the following: a flat type (including a coin type and a button type) having a battery case in which the outer can and the sealing plate are crimped and sealed via a gasket, or the outer can and the sealing plate are sealed by welding; a sheet type having a sheet-like outer body made of a resin film; or a cylindrical type (cylindrical, square (rectangular cylindrical)) having a battery case in which the outer can and the sealing plate are crimped and sealed via a gasket, or the outer can and the sealing plate are sealed by welding.

[0097] Examples of resin films constituting the sheet-like outer packaging body include nylon films (such as nylon 66 films), polyester films (such as polyethylene terephthalate (PET) films), etc. The thickness of the resin film is preferably 20 to 100 μm.

[0098] The sheet-like outer packaging body is generally sealed by heat sealing the edges of the upper and lower resin films of the sheet-like outer packaging body, but to facilitate this heat sealing, a heat-sealing resin layer may be laminated on the resin film exemplified above and used for the sheet-like outer packaging body. Examples of heat-sealing resins that constitute the heat-sealing resin layer include modified polyolefins (such as modified polyolefin ionomers), polypropylene, and copolymers thereof. The thickness of the heat-sealing resin layer is preferably 20 to 100 μm.

[0099] A metal layer may be laminated on the resin film. The metal layer may be made of an aluminum film (aluminum foil, aluminum alloy foil, etc.), a stainless steel film (stainless steel foil), etc. The thickness of the metal layer is preferably 10 to 150 μm.

[0100] The resin film constituting the sheet-like outer packaging body may be a film having a configuration in which the heat-sealable resin layer and the metal layer are laminated together.

[0101] The shape of the sheet-like outer casing may be polygonal in plan view (triangle, quadrangle, pentagon, hexagon, heptagon, octagon), or may be circular or elliptical in plan view. In the case of a sheet-like outer casing that is polygonal in plan view, the positive electrode external terminal and the negative electrode external terminal may be led out from the same side or from different sides.

[0102] Furthermore, when using an exterior body that is crimp-sealed, the material of the gasket placed between the exterior can and the sealing plate can be polypropylene, nylon, etc., or fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene ether (PPE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), etc. A glass hermetic seal can also be used for sealing.

[0103] When the secondary battery of this embodiment is an air secondary battery, air holes are formed in the exterior body to allow air to enter the positive electrode (air electrode). There is no particular limitation on the number of air holes, and it is sufficient to select a number that allows air to enter to the extent that the air battery can discharge properly. There is also no particular limitation on the shape of the air holes, and they may be circular in plan view, or may be elliptical or polygonal (triangle, square, etc.).

[0104] Furthermore, when the secondary battery is an air secondary battery, it is preferable to place a water-repellent film between the positive electrode (air electrode) and the exterior body to prevent moisture from entering the battery through the air holes. The water-repellent film is a film that is water-repellent but air-permeable, and specifically, a film made of a resin such as fluororesin such as PTFE; or polyolefin such as PP or PE; The thickness of the water-repellent film is preferably 50 to 250 μm.

[0105] Furthermore, when the secondary battery is an air secondary battery, an air diffusion membrane may be disposed between the exterior body and the water-repellent film to supply air taken into the exterior body to the positive electrode. The air diffusion membrane may be a nonwoven fabric made of a resin such as cellulose, polyvinyl alcohol, PP, or nylon. The thickness of the air diffusion membrane is preferably 100 to 250 μm. [Example]

[0106] The secondary battery disclosed in the present application will be described in detail below based on examples, but the following examples do not limit the scope of the secondary battery disclosed in the present application.

[0107] Example 1 <Preparation of negative electrode> First, zinc oxide (number average particle diameter: 0.6 μm): 70 parts by mass, χ-alumina (number average particle diameter: 38 μm, specific surface area: 124 m 2 A negative electrode mixture composition having a solids concentration of 73.9% by mass was prepared by mixing 21.5 parts by mass of lead oxide, 2.0 parts by mass of lead oxide, 1.5 parts by mass of PTFE, and 5 parts by mass of acetylene black with water. This negative electrode mixture composition was mixed in a planetary mixer at 2000 rpm for 5 minutes to obtain a bulk mixture, which was then stretched multiple times in a roll press through a gap of 0.650 mm in thickness to form a block. The gap of the roll press was then adjusted to form a 2 mm thick sheet, which was then cut into a 20 mm x 20 mm rectangular negative electrode mixture sheet.

[0108] Next, the negative electrode mixture sheet was attached to a copper wire mesh with 100 mesh openings cut to 20 mm x 23 mm, which served as a current collector, and the sheet was molded using a roll press with the roll distance adjusted to 2.1 mm. A copper lead with a thickness of 100 μm and a width of 3 mm was welded to the exposed part of the current collector to form a current extraction part, thereby obtaining a negative electrode with a thickness of 2 mm.

[0109] <Preparation of positive electrode> A positive electrode mixture composition with a solids concentration of 75% by mass was prepared by mixing 89.8 parts by mass of nickel hydroxide, 0.2 parts by mass of CMC, 5 parts by mass of cobalt monoxide, and 5 parts by mass of tricobalt tetroxide with water. This positive electrode mixture composition was mixed in a planetary mixer at 2000 rpm for 5 minutes, and then 0.9 parts by mass of PTFE was added to 100 parts by mass of nickel hydroxide and mixed at 2000 rpm for 30 seconds. The resulting mixture was filled into a 2 mm thick nickel foam, leaving a partially uncoated area. The mixture was then dried at 80°C for 1 hour and then rolled to a thickness of 1 mm using a roll press. This was then cut into an electrode with a 25 mm x 25 mm rectangular positive electrode mixture layer forming portion and a 3 mm wide exposed current collector (nickel foam) portion. Two of these electrodes were stacked and integrated using a roll press, and a 100 μm thick, 3 mm wide nickel lead was welded to the exposed current collector to form a current extraction section, producing a 2 mm thick positive electrode. The fabricated positive electrode was wrapped in a 120 μm thick nonwoven fabric bag except for the current extraction section.

[0110] <Preparation of alkaline electrolyte> An excess amount of commercially available zinc oxide was dissolved in a commercially available 8M aqueous potassium hydroxide solution, and the solution was stirred at room temperature for 12 hours or more. The remaining zinc oxide was then filtered off to prepare an alkaline electrolyte solution containing zinc oxide dissolved at a saturated concentration.

[0111] <Assembling alkaline secondary batteries> An alkaline secondary battery (model cell) was assembled using the fabricated negative electrode, positive electrode, and the prepared alkaline electrolyte.

[0112] First, a laminated film (graft film / graft film / PP nonwoven fabric) consisting of two 30 μm-thick graft films and a 120 μm-thick polypropylene nonwoven fabric was used as the separator. The negative and positive electrodes were sandwiched between the separator to form an electrode assembly. Next, two polypropylene sheets shaped to 35 mm x 60 mm were stacked to fit the electrode assembly, and three sides were welded together to form a bag-like outer casing. The electrode assembly was then inserted into this, and the assembly was sandwiched between 50 mm x 50 mm x 8 mm acrylic plates and screwed at the four corners. After that, 3.5 mL of the alkaline electrolyte was injected into the outer casing and vacuum-impregnated, and the remaining side of the outer casing was sealed to complete the model cell.

[0113] Example 2 An alkaline secondary battery (model cell) was assembled in the same manner as in Example 1, except that the mixed amounts of the negative electrode mixture composition were changed to 81 parts by mass of zinc oxide and 10.5 parts by mass of χ-alumina.

[0114] Example 3 Instead of χ-alumina, acidic γ-alumina (number average particle diameter: 95 μm, specific surface area: 154 m) was used. 2 An alkaline secondary battery (model cell) was assembled in the same manner as in Example 1, except that a negative electrode mixture composition was prepared using PEG-40 ...

[0115] Example 4 Instead of χ-alumina, neutral γ-alumina (number average particle diameter: 96 μm, specific surface area: 132 m) was used. 2 An alkaline secondary battery (model cell) was assembled in the same manner as in Example 1, except that a negative electrode mixture composition was prepared using PEG-40 ...

[0116] (Comparative Example 1) An alkaline secondary battery (model cell) was assembled in the same manner as in Example 1, except that χ-alumina was not added to the negative electrode mixture composition, the amount of zinc oxide mixed in the negative electrode mixture composition was changed to 91.5 parts by mass, and the thickness of the negative electrode mixture sheet was changed to 1.2 mm.

[0117] (Comparative Example 2) Aluminum hydroxide (number average particle diameter: 90 μm, specific surface area: 104 m) was used in place of χ-alumina in the negative electrode mixture composition. 2 An alkaline secondary battery (model cell) was assembled in the same manner as in Example 1, except that 17.5 parts by mass of zinc oxide ( / g) was added and the amount of zinc oxide mixed in the negative electrode mixture composition was changed to 74 parts by mass.

[0118] (Comparative Example 3) In place of χ-alumina, α-alumina (number average particle diameter: 29 μm, specific surface area: 0.68 m) was used in the negative electrode mixture composition. 2 An alkaline secondary battery (model cell) was assembled in the same manner as in Example 1, except that 21.5 parts by mass of PEG-40 / g) was added.

[0119] <Aluminum compound elution test> The aluminum compounds used in Examples 1 to 4 and Comparative Examples 2 and 3 were subjected to an elution test in which they were immersed in 20 mL of an 8 M potassium hydroxide aqueous solution per 1 g for 300 hours at 40° C. The elution rates as a result are shown in Table 1.

[0120] [Table 1]

[0121] <Charge / discharge cycle characteristics> The charge-discharge cycle characteristics of the secondary battery thus prepared were evaluated in an atmosphere of 40° C. by the following method.

[0122] First, for each of the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3, at a current value of 128 mA, (1) The charging capacity reaches 320mAh. (2) The battery voltage reaches 2.2V during charging. (3) The battery voltage during charging drops by 50 mV from the maximum value (-ΔV = 50 mV). Charge until either of the following occurs, then charge at a current of 128mA. (4) The battery voltage reaches 1.0 V during discharge. (5) The discharge capacity reaches 320mAh. The charge-discharge cycle was repeated until one of the following conditions was met, and the discharge capacity was measured at the first cycle (initial) and every 10 cycles thereafter to evaluate the charge-discharge cycle characteristics.

[0123] The measured discharge capacity of each battery is shown in Figure 1, expressed as a relative value with the initial discharge capacity of each battery set at 100.

[0124] As shown in Fig. 1, the secondary batteries of Examples 1 and 2 were able to maintain a large capacity even after 70 charge / discharge cycles. In contrast, the batteries of Comparative Examples 1 to 3 showed a decrease in capacity after about 30 to 40 charge / discharge cycles, as shown in Fig. 1.

[0125] Next, for each secondary battery of Example 1, Examples 3 to 4, and Comparative Example 1, a different battery was used in Example 1 and Comparative Example 1, and the current value was 64 mA. (6) The charging capacity reaches 480mAh. (7) The battery voltage reaches 2.2V during charging. (8) The battery voltage during charging drops by 50 mV from the maximum value (-ΔV = 50 mV). Charge until either of the following occurs, then charge at a current of 64mA. (9) The battery voltage reaches 1.0V during discharge. (10) The discharge capacity reaches 480mAh. The charge-discharge cycle was repeated until one of the following conditions was met, and the discharge capacity was measured at the first cycle (initial) and every 10 cycles thereafter to evaluate the charge-discharge cycle characteristics.

[0126] The measured discharge capacity of each battery is shown in Figure 2, expressed as a relative value with the initial discharge capacity of each battery set at 100.

[0127] As shown in Fig. 2, the secondary batteries of Examples 1 and 3 to 4 were able to maintain a large capacity even after 20 to 30 charge-discharge cycles. In contrast, the battery of Comparative Example 1 began to lose capacity immediately after the start of charge-discharge cycles, as shown in Fig. 2, and was no longer able to maintain a sufficient capacity. [Industrial Applicability]

[0128] The secondary battery disclosed in the present application has excellent charge / discharge cycle characteristics and can be preferably used as a power source for various electronic devices (particularly portable electronic devices such as mobile phones and notebook personal computers).

Claims

1. A negative electrode for a secondary battery including a negative electrode mixture layer containing a zinc-based material and an aluminum oxide that is partially dissolved in an alkaline electrolyte, The aluminum oxide has a dissolution rate of 5 to 30% by mass in an 8 mol / L aqueous potassium hydroxide solution.

2. A negative electrode for a secondary battery comprising a zinc-based material and an aluminum oxide that is partially dissolved in an alkaline electrolyte, The negative electrode for a secondary battery is characterized in that the aluminum oxide contains χ-alumina.

3. A negative electrode for a secondary battery including a negative electrode mixture layer containing a zinc-based material and an aluminum oxide that is partially dissolved in an alkaline electrolyte, The negative electrode for a secondary battery is characterized in that the aluminum oxide contains γ-alumina.

4. 4. The negative electrode for a secondary battery according to claim 1, wherein the zinc-based material is at least one selected from the group consisting of zinc, a zinc alloy, and zinc oxide.

5. 5. The negative electrode for secondary batteries according to claim 1, wherein the proportion of the aluminum oxide is 5 to 30 mass% in the total amount of the zinc-based material and the aluminum oxide.

6. 6. The negative electrode for a secondary battery according to claim 1, wherein the number average particle size of the aluminum oxide is 10 to 300 μm.

7. The specific surface area of ​​the aluminum oxide is 1 to 500 m 2 7. The negative electrode for a secondary battery according to claim 1, wherein the molecular weight of the negative electrode is 1 / g.

8. A secondary battery including a positive electrode, a negative electrode, a separator, and an alkaline electrolyte, A secondary battery, wherein the negative electrode is the negative electrode for secondary batteries according to any one of claims 1 to 7.

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