Alkaline zinc secondary battery and separator for alkaline zinc secondary battery

Abstract

Provided are a separator for an alkaline zinc secondary battery, and the alkaline zinc secondary battery, the separator including a porous substrate and a porous layer provided on one or both surfaces of the porous substrate, wherein: the porous substrate is a microporous membrane containing polyolefin; the porous layer includes a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond, and has a three-dimensional network structure; and the resin is additionally contained within the pores of the porous substrate.

Description

Alkaline zinc secondary battery and separator for alkaline zinc secondary battery

[0001] The present disclosure relates to an alkaline zinc secondary battery and a separator for an alkaline zinc secondary battery.

[0002] Alkaline zinc secondary batteries are said to be highly safe and low-cost because they use an aqueous electrolyte instead of a flammable organic solvent, and are therefore being considered for use as emergency power sources in factories and in vehicles.

[0003] However, alkaline zinc secondary batteries use zinc as the negative electrode in an alkaline aqueous solution and generate electromotive force through the oxidation of zinc. This means that zinc deposits and grows easily from the negative electrode during charging. These deposits are called dendrites. In alkaline zinc secondary batteries, the growth of dendrites can sometimes cause short circuits.

[0004] Alkaline-zinc secondary batteries use separators made of nonwoven fabrics commonly used in batteries, and it is known that the separator is a polyethylene microporous film having a specific pore size and is hydrophilized with a surfactant or the like to provide short-circuit resistance (Patent Document 1).

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-102352

[0006] In alkaline zinc secondary batteries, in order to suppress short circuits caused by dendrites and improve battery performance, for example, when a separator made of nonwoven fabric is used, the nonwoven fabric has been used in a thicker state. However, this is insufficient to suppress short circuits, and the thicker the separator, the lower the energy density, which may lead to a deterioration in battery performance. In the alkaline zinc secondary battery described in Patent Document 1, there is no mention of the stability of the surfactant, such as surfactant elution, and the effect on battery performance is unclear.

[0007] An object of the present disclosure is to provide an alkaline zinc secondary battery and a separator for an alkaline zinc secondary battery that have excellent battery characteristics.

[0008] Specific means for solving the problems include the following aspects. <1> An alkaline zinc secondary battery comprising a positive electrode, a negative electrode containing zinc, a separator disposed between the positive electrode and the negative electrode, and an alkaline electrolyte, wherein the separator comprises a porous substrate and a porous layer disposed on one or both sides of the porous substrate, the porous substrate being a microporous membrane containing polyolefin, the porous layer comprising a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule and having a three-dimensional network structure, the resin also being contained within the pores of the porous substrate. <2> The alkaline zinc secondary battery according to <1>, wherein the positive electrode comprises at least one selected from the group consisting of manganese dioxide, cobalt hydroxide, nickel hydroxide, and activated carbon. <3> The alkaline zinc secondary battery according to <1> or <2>, wherein the alkaline electrolyte comprises sodium hydroxide and / or potassium hydroxide. <4> The alkaline zinc secondary battery according to any one of <1> to <3>, wherein the porous layer has a thickness of 5.0 μm to 20 μm. <5> The alkaline zinc secondary battery according to any one of <1> to <4>, wherein the porous layer further contains a filler. <6> The alkaline zinc secondary battery according to <5>, wherein the filler has a volume-average particle size of primary particles of 0.5 μm to 3.0 μm. <7> The alkaline zinc secondary battery according to <5> or <6>, wherein the porous layer contains the filler in an amount of 60 vol% to 95 vol% based on the total solid volume of the porous layer. <8> The alkaline zinc secondary battery according to any one of <5> to <7>, wherein the filler is at least one of a metal hydroxide and a metal sulfate. <9> A separator for an alkali-zinc secondary battery, comprising a porous substrate and a porous layer provided on one or both sides of the porous substrate, wherein the porous substrate is a microporous membrane containing polyolefin, the porous layer contains a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond, and has a three-dimensional network structure, and the resin is also contained within the pores of the porous substrate. <10> The separator for an alkali-zinc secondary battery according to <9>, wherein the porous layer has a thickness of 5.0 μm to 20 μm. <11> The separator for an alkali-zinc secondary battery according to <9> or <10>, wherein the porous layer further contains a filler.<12> The separator for an alkali-zinc secondary battery according to <11>, wherein the porous layer contains a filler in a range of 60% by volume to 95% by volume based on the total solid volume of the porous layer. <13> The separator for an alkali-zinc secondary battery according to <11> or <12>, wherein the filler has a volume-average particle size of primary particles of 0.5 μm to 3.0 μm. <14> The separator for an alkali-zinc secondary battery according to any one of <11> to <13>, wherein the filler is at least one of a metal hydroxide and a metal sulfate. <15> The separator for an alkali-zinc secondary battery according to any one of <9> to <14>, wherein the porous layer includes an inner layer formed on a porous substrate and a porous coating film forming an outer surface of the inner layer, and the inner layer has a three-dimensional mesh structure with a mesh size larger than the pore size of the porous coating film.

[0009] According to the present disclosure, an alkaline zinc secondary battery and a separator for an alkaline zinc secondary battery having excellent battery characteristics are provided.

[0010] 1 is an image showing the results of TEM-EDS analysis of a separator according to the present disclosure, illustrating that a resin with a three-dimensional network structure is contained within the pores of a polyolefin microporous film.

[0011]

[0023] The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

[0012] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in an example.

[0013] In the present disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" means that it may be only A, only B, or a combination of A and B.

[0014] In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0015] In the present disclosure, when referring to the amount of each component in a composition, if the composition contains multiple substances corresponding to each component, the total amount of the multiple substances present in the composition is referred to unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be included. If the composition contains multiple types of particles corresponding to each component, the particle size of each component refers to the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0016] In this disclosure, MD (Machine Direction) refers to the longitudinal direction of a separator manufactured in a long shape, and TD (Transverse Direction) refers to the direction perpendicular to the MD in the plane direction of the separator. In this disclosure, TD is also referred to as the "width direction."

[0017] In the present disclosure, when the stacking relationship of each layer constituting a separator is expressed as "upper" and "lower," the layer closer to the porous substrate is referred to as "lower," and the layer farther from the porous substrate is referred to as "upper."

[0018] In the present disclosure, the volume of the porous layer excluding pores is referred to as the "solid content volume."

[0019] <Alkaline zinc secondary battery> The alkaline zinc secondary battery of the present disclosure is an aqueous secondary battery that includes a positive electrode, a negative electrode containing zinc, a separator disposed between the positive electrode and the negative electrode, and an alkaline electrolyte, and generates electromotive force by oxidizing zinc. In the present disclosure, the term "alkaline zinc secondary battery" refers to a battery that uses an alkaline aqueous solution as the electrolyte and zinc in the negative electrode.

[0020] In the alkaline zinc secondary battery of the present disclosure, the separator includes a porous substrate and a porous layer provided on one or both sides of the porous substrate, the porous substrate is a microporous membrane containing polyolefin, the porous layer includes a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule, and has a three-dimensional network structure, and the resin is further contained within the pores of the porous substrate.

[0021] The background to the present disclosure will be explained. Conventionally, nonwoven fabric separators have been used in aqueous electrolyte secondary batteries, such as zinc secondary batteries. However, nonwoven fabrics are prone to short circuits, and although nonwoven fabrics have been used in thicker forms, such as by laminating, this has not been sufficient to prevent short circuits. Furthermore, zinc secondary batteries using thicker nonwoven fabrics have been disadvantageous in terms of energy density. When a microporous membrane containing polyethylene is used as a separator, problems arise with impregnation of an electrolyte solution consisting of an alkaline aqueous solution due to the hydrophobicity of polyethylene. Therefore, it has been necessary to subject the polyethylene-containing microporous membrane to a hydrophilic treatment. When a surfactant is used as the hydrophilic treatment, the surfactant may be eluted, potentially affecting the battery characteristics.

[0022] In the alkaline zinc secondary battery or separator for alkaline zinc secondary batteries of the present disclosure, the separator comprises a microporous membrane containing a polyolefin as a porous substrate, a porous layer of a specific structure containing a specific resin, and the resin is further contained within the pores of the porous substrate. This eliminates the need for hydrophilization treatment and provides excellent electrolyte impregnation, resulting in better battery characteristics than when conventional separators are used. The reason for the excellent battery characteristics of the alkaline zinc secondary battery of the present disclosure is unclear, but it is believed that the separator of the present disclosure has excellent electrolyte impregnation, which does not impede the necessary flow of electrolyte, various ions, etc., in the alkaline zinc secondary battery, while effectively suppressing the flow of components for forming dendrites and grown dendrites to the positive electrode, thereby exhibiting favorable characteristics as a separator for zinc secondary batteries. Furthermore, the separator for alkaline zinc secondary batteries of the present disclosure exhibits the above-mentioned favorable effects as a separator and provides excellent battery characteristics, even when used in a thinner state than conventional nonwoven fabric separators. Therefore, the alkaline zinc secondary battery of the present disclosure has improved energy density. Furthermore, since the separator for an alkaline zinc secondary battery of the present disclosure does not require hydrophilization treatment, it is possible to improve the productivity of the separator, material costs, etc.

[0023] [Positive Electrode] In the alkaline zinc secondary battery of the present disclosure, the positive electrode can be a known positive electrode used in alkaline zinc secondary batteries. The positive electrode includes, for example, a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector. The positive electrode current collector can be, for example, a flat metal plate. Examples of metals used for the positive electrode current collector include copper, copper alloys such as brass, various nickels such as corrosion-resistant nickel, various zincs such as metallic zinc, copper, and silver. Specific examples of metals used for the positive electrode current collector include foils such as copper foil, mesh-like metals such as copper mesh, foamed metals such as foamed copper, porous bodies such as nickel cermet, punched metals such as punched copper, and plate-like metals such as steel plates.

[0024] The positive electrode current collector may contain various elements or may be plated with various elements, such as nickel (Ni), zinc (Zn), tin (Sn), lead (Pb), mercury (Hg), bismuth (Bi), indium (In), and thallium (Tl).

[0025] The positive electrode material contains a positive electrode active material. The positive electrode active material preferably contains at least one selected from the group consisting of manganese dioxide, cobalt hydroxide, nickel hydroxide, and activated carbon, and may be a mixture of these. For example, nickel hydroxide is oxidized to nickel oxyhydroxide (NiOOH) during charging, and the nickel oxyhydroxide accepts water and electrons during discharging, generating nickel hydroxide and hydroxide ions.

[0026] The positive electrode active material may be in the form of particles, layers, or the like. For example, a positive electrode material layer may be formed in the form of a layer on a positive electrode current collector. When the positive electrode current collector has a porous body or a three-dimensional mesh structure, the positive electrode material layer may be formed by filling the pores or spaces between the meshes of the positive electrode current collector with the positive electrode material.

[0027] The positive electrode material may contain various elements in the form of a solid solution in the positive electrode active material or may be coated on the positive electrode active material. Examples of elements to be dissolved or coated include cobalt, zinc, cadmium, and compounds thereof.

[0028] The positive electrode material may contain additives in addition to the positive electrode active material. Examples of additives include conductive additives and binders. The conductive additives are used to increase the conductivity within the electrode, and the binders are used to bind the positive electrode active material, conductive additives, and the like to the positive electrode current collector. Examples of conductive additives include carbon-based materials such as acetylene black, ketjen black, carbon nanotubes, and carbon nanofibers, and rare earth metal compounds. Examples of binders include various polymers, specifically carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), sodium polyacrylate (SPA), polyvinyl alcohol (PVA), and the like. CMC is also used as a thickener to adjust the viscosity of the slurry for forming the positive electrode material to a level suitable for coating. In addition to the above, zinc compounds, calcium compounds, rare earth metal compounds, and the like may also be used as additives.

[0029] The content of these additives is, for example, preferably 3 to 40 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of the positive electrode material.

[0030] The positive electrode material is preferably porous. The porosity is preferably 10 to 55% by volume, more preferably 15 to 50% by volume, even more preferably 15 to 45% by volume, and particularly preferably 18 to 40% by volume. The porosity refers to the ratio of the volume of voids to the entire positive electrode material, calculated from the volume and density of the positive electrode material.

[0031] [Negative Electrode] In the alkaline zinc secondary battery of the present disclosure, the negative electrode can be a known negative electrode used in alkaline zinc secondary batteries. The negative electrode can be, for example, a metal zinc plate, or can include a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector. As with the above-mentioned positive electrode current collector, the negative electrode current collector can be a flat metal plate. The metal used for the negative electrode current collector is the same as that for the above-mentioned positive electrode current collector, and various metals can also be added.

[0032] The negative electrode material contains a negative electrode active material. The negative electrode active material contains zinc. Examples of zinc include metallic zinc, zinc oxide, and zinc alloys. In the alkaline zinc secondary battery of the present disclosure, the negative electrode active material is zinc, and electromotive force is generated by the oxidation of zinc. The negative electrode contains zinc during charging and zinc oxide during discharging.

[0033] The shape of the negative electrode active material may be the same as that of the positive electrode active material, such as granular, layered, etc. When the negative electrode current collector has a porous body, a three-dimensional mesh structure, or the like, similar to the positive electrode current collector, the negative electrode material may be filled into the pores or between the meshes of the negative electrode current collector to form a negative electrode material layer.

[0034] The negative electrode material may contain additives in addition to the negative electrode active material. Examples of the additives include binders. Examples of binders that can be used include polytetrafluoroethylene, hydroxyethyl cellulose, and polyethylene oxide.

[0035] As additives other than the binder, metal oxides such as indium oxide and thallium oxide can be used to maintain the porosity of the zinc electrode used in the negative electrode, increase overvoltage, etc. Furthermore, calcium compounds, fluorine compounds, etc. may be used to improve battery characteristics.

[0036] The content of these additives is, for example, preferably 0.5 to 20 parts by mass, and more preferably 1 to 10 parts by mass, per 100 parts by mass of the negative electrode material.

[0037] <Separator> The separator of the present disclosure includes a porous substrate and a porous layer provided on one or both sides of the porous substrate, wherein the porous substrate is a microporous membrane containing a polyolefin, the porous layer includes a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond, and has a three-dimensional network structure, and the resin is further contained within the pores of the porous substrate.

[0038] [Porous Substrate] In the separator of the present disclosure, the porous substrate is a microporous membrane containing a polyolefin. In the present disclosure, a microporous membrane refers to a membrane having a large number of micropores therein, which are interconnected, and which allows gas or liquid to pass through from one surface to the other.

[0039] Examples of microporous membranes containing polyolefin (hereinafter also referred to as "polyolefin microporous membranes") include polyolefin microporous membranes used in conventional lithium ion battery separators, and it is preferable to select from these membranes one that has sufficient mechanical properties, ion permeability, etc.

[0040] The polyolefin microporous film is preferably a microporous film containing polyethylene or polypropylene, from the viewpoint of heat resistance that prevents film rupture when exposed to high temperatures.

[0041] The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight (Mw) of 100,000 to 5,000,000. When the Mw of the polyolefin is 100,000 or more, the microporous membrane can be imparted with sufficient mechanical properties. On the other hand, when the Mw of the polyolefin is 5,000,000 or less, the microporous membrane has good shutdown properties and is easy to mold. The Mw of the polyolefin is the molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC). The polyolefin extracted from the microporous membrane or the polyolefin used to form the microporous membrane is used as a sample for measurement.

[0042] The average pore size of the polyolefin microporous membrane is preferably 15 to 100 nm from the viewpoint of achieving both ion permeability and suppression of short circuits in the battery. The average pore size of the polyolefin microporous membrane is measured using a perm porometer (CFP-1500-A, PMI) in accordance with ASTM E1294-89.

[0043] Examples of methods for producing a polyolefin microporous membrane include a method in which a molten polyolefin resin is extruded through a T-die to form a sheet, which is crystallized, stretched, and then heat-treated to form a microporous membrane; and a method in which a molten polyolefin resin together with a plasticizer such as liquid paraffin is extruded through a T-die, cooled to form a sheet, stretched, the plasticizer is extracted, and then heat-treated to form a microporous membrane.

[0044] The surface of the porous substrate may be subjected to various surface treatments to improve wettability with the coating liquid for forming the porous layer, as long as the properties of the porous substrate are not impaired. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0045] (Characteristics of porous substrate) From the viewpoint of increasing the energy density of the battery, the thickness of the porous substrate is preferably 10.0 μm or less, more preferably 8.0 μm or less, and from the viewpoint of the separator production yield and the battery production yield, the thickness is preferably 3.0 μm or more, more preferably 5.0 μm or more.

[0046] The Gurley value (JIS P8117:2009) of the porous substrate is preferably 50 seconds / 100 mL to 400 seconds / 100 mL, and more preferably 50 seconds / 100 mL to 200 seconds / 100 mL, from the viewpoint of suppressing short circuits in the battery or obtaining sufficient ion permeability. In the present disclosure, the Gurley value is measured using a Gurley densometer in accordance with JIS P8117:2009.

[0047] The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining appropriate membrane resistance and shutdown function. The porosity ε (%) of the porous substrate is calculated by the following formula: ε = {1 - Ws / (ds·t)} × 100, where Ws is the basis weight (g / m ２ ), ds is the true density of the porous substrate (g / cm ３ ), t is the thickness (μm) of the porous substrate. Basis weight is the mass per unit area.

[0048] From the viewpoint of the separator production yield and the battery production yield, the puncture strength of the porous substrate is preferably 200 g or more. The puncture strength of the porous substrate refers to the maximum puncture load (g) measured by a puncture test using a Kato Tech KES-G5 handy compression tester under the conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / sec.

[0049] A preferred embodiment of the porous substrate is one in which the walls of the pores of the porous substrate are partially or entirely covered with a resin, which allows the electrolyte to easily permeate the porous substrate.

[0050] [Porous Layer] In the separator of the present disclosure, the porous layer contains a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule, and has a three-dimensional network structure. The porous layer has numerous micropores that allow gas or liquid to pass from one surface to the other.

[0051] (Resin) The resin contained in the porous layer has at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule. The resin is fibril-like and forms a three-dimensional network structure. In this disclosure, the network structure refers to a structure in which the resin is continuously connected in a network-like manner and has a large number of pores, and such a structure continuously connected three-dimensionally in the plane direction and thickness direction of the separator is referred to as a "three-dimensional network structure." In some cases, the resin also forms a porous coating. The porous coating will be described later. The porous layer preferably contains a resin and a filler. When the porous layer contains a filler, the resin may be included as a binder resin that connects the fillers together.

[0052] Examples of resins having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in the molecule include wholly aromatic polyamides, polyamide-imides, polyimides, polyetherimides, etc. These resins may be used alone or in combination of two or more.

[0053] The weight average molecular weight (Mw) of the resin is 1×10 ３~1 x 10 ７ is preferred, and 5 × 10 ３ ~5 x 10 ６ is more preferable, and 1×10 ４ ~1 x 10 ６ The Mw of the resin is a molecular weight measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0054] Among resins, fully aromatic polyamides are preferred from the viewpoint of durability. Fully aromatic polyamides refer to polyamides whose main chains are composed only of benzene rings and amide bonds. However, a small amount of aliphatic monomers may be copolymerized into the fully aromatic polyamides. Fully aromatic polyamides are also called aramids. Fully aromatic polyamides may be polyamides copolymerized with aliphatic monomers, polyamides not copolymerized with aliphatic monomers, or mixtures of these. Fully aromatic polyamides may be meta- or para-type. Among fully aromatic polyamides, meta-type fully aromatic polyamides are preferred from the viewpoints of ease of forming a porous layer and excellent oxidation-reduction resistance in electrode reactions. Specifically, polymetaphenylene isophthalamide or polyparaphenylene terephthalamide is preferred as the fully aromatic polyamide, with polymetaphenylene isophthalamide being more preferred. The weight-average molecular weight (Mw) of the fully aromatic polyamide contained in the porous layer is 1×10 ３ ~1 x 10 ７ is preferred, and 5 × 10 ３ ~5 x 10 ６ is more preferable, and 1×10 ４ ~1 x 10 ６ The Mw of the wholly aromatic polyamide is a molecular weight measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0055] The resin contained in the porous layer may contain a resin other than a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in the molecule (hereinafter also referred to as "other resin"). Examples of other resins include polyamideimide, poly-N-vinylacetamide, polyacrylamide, copolymerized polyether polyamide, polyimide, polyetherimide, acrylic resin, fluorine-containing rubber, polyvinylidene fluoride resin, styrene-butadiene copolymer, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), celluloses such as carboxymethyl cellulose and hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), polysulfone, polyketone, polyether ketone, polyether sulfone, and mixtures thereof. One type of other resin may be used alone, or two or more types may be used in combination. The content of the other resin is preferably 0% by mass to 50% by mass, more preferably 0% by mass to 40% by mass, and even more preferably 0% by mass to 30% by mass, relative to the total amount of all resins contained in the porous layer, in order to maintain the effect of the resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in the molecule.

[0056] The total amount of resins having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in the molecule is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on the total amount of all resins contained in the porous layer.

[0057] (Filler) From the viewpoint of impregnation with an electrolytic solution and heat resistance, the porous layer preferably further contains a filler. The filler may be used alone or in combination of two or more.

[0058] The shape of the filler is not limited, and may be any of spherical, elliptical, plate-like, needle-like, and amorphous. From the viewpoint of suppressing short circuits in the battery, the filler contained in the porous layer is preferably plate-like particles or non-aggregated primary particles.

[0059] The volume average particle size of the primary particles of the filler is preferably 0.01 μm to 10 μm. The lower limit is more preferably 0.1 μm or more, and the upper limit is more preferably 5 μm or less. It is even more preferably 0.5 μm to 3.0 μm. A value within the above range is preferable because good discharge capacity can be obtained. The volume average particle size of the primary particles is a value measured in accordance with JIS Z 8819-2:2019.

[0060] The particle size distribution of the filler is preferably 0.1 μm<d90-d10<3 μm. Here, d10 represents the particle size (μm) at 10% of the cumulative volume in the particle size distribution calculated from the small particle side, and d90 represents the particle size (μm) at 90% of the cumulative volume in the particle size distribution calculated from the small particle side. The particle size distribution is measured, for example, using a laser diffraction particle size analyzer (e.g., Mastersizer 2000, Sysmex Corporation) with water as the dispersion medium and a trace amount of the nonionic surfactant Triton X-100 as the dispersant.

[0061] When the porous layer contains a filler, the volume ratio of the filler to the solid volume of the porous layer is preferably 60% by volume or more, more preferably 65% ​​by volume or more, from the viewpoints of high discharge capacity expression, impregnation with an electrolyte solution, and heat resistance. The mass ratio of the inorganic particles in the porous layer is preferably 95% by volume or less, more preferably 90% by volume or less, and even more preferably 85% by volume or less, from the viewpoint of preventing the porous layer from peeling off from the porous substrate.

[0062] The volume ratio V (vol %) of the filler to the solid volume of the porous layer is calculated by the following formula: V = {(Xa / Da) / (Xa / Da + Xb / Db + Xc / Dc + ... + Xn / Dn)} x 100, where a represents the filler, b represents the other constituent materials, and n represents the masses of the constituent materials contained in a predetermined area of ​​the porous layer (Xa, Xb, Xc, ..., Xn (g)), and Da, Db, Dc, ..., Dn (g / cm) represent the true densities of the constituent materials. ３ ) Xa and the like substituted in the above formula are the mass (g) of the constituent material used to form a porous layer of a predetermined area, or the mass (g) of the constituent material removed from a porous layer of a predetermined area. Da and the like substituted in the above formula are the true density (g / cm) of the constituent material used to form the porous layer. ３ ), or the true density (g / cm 3 ) of the constituent material extracted from the porous layer ３ )

[0063] The filler is preferably an inorganic particle. The inorganic particles are contained in the porous layer, for example, bound and covered by the porous layer or porous coating. The filler is preferably at least one of a metal hydroxide and a metal sulfate. Examples of inorganic particles include metal hydroxide particles such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide; metal oxide particles such as silica, alumina, zirconia, and magnesium oxide; carbonate particles such as calcium carbonate and magnesium carbonate; and sulfate particles such as barium sulfate and calcium sulfate. From the viewpoints of stability in the electrolyte and electrochemical stability, metal hydroxide particles, metal oxide particles, or metal sulfate particles are preferred as inorganic particles. Specifically, from the viewpoint of discharge capacity, magnesium hydroxide is more preferred as the inorganic particles. The inorganic particles may be surface-modified with a silane coupling agent or the like.

[0064] (Characteristics of the Porous Layer) In the separator of the present disclosure, the thickness of the porous layer is preferably 2.5 μm or more on one side, more preferably 3.0 μm or more on one side, from the viewpoints of battery characteristics, discharge capacity, separator electrolyte impregnation, heat resistance, or handleability. From the viewpoint of separator handleability, it is preferably 10 μm or less on one side, more preferably 8.0 μm or less on one side. Whether the porous layer is present on only one side or both sides of the porous substrate, the thickness of the porous layer is preferably 5.0 μm or more, more preferably 6.0 μm or more, and preferably 20 μm or less, more preferably 16 μm or less, as the total thickness of both sides. In particular, the thickness of the porous layer is preferably 5.0 μm to 20 μm. The thickness of the porous layer (total thickness of both sides of the porous substrate, μm) is the value obtained by subtracting the thickness of the porous substrate (μm) from the thickness of the separator (mA) (μm).

[0065] In the separator of the present disclosure, the mass per unit area of ​​the porous layer is, in terms of battery characteristics, discharge capacity, impregnation of the separator with an electrolyte, heat resistance, or handling, 1.0 g / m in total on both sides. ２ More than 2.0 g / m is preferable. ２ More preferably, from the viewpoint of the handling property of the separator or the energy density of the battery, 10.0 g / m ２ Preferably, 8.0 g / m or less ２ The following is more preferred:

[0066] In the separator of the present disclosure, the porosity of the porous layer is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more from the viewpoint of the ion permeability of the separator, and is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less from the viewpoint of the thermal dimensional stability of the separator. The porosity ε (%) of the porous layer is calculated by the following formula.

[0067]

[0068] Here, for constituent material 1, constituent material 2, constituent material 3, ..., constituent material n of the porous layer, the mass per unit area of ​​each constituent material is W1, W2, W3, ..., Wn (g / cm ２ ), and the true densities of the constituent materials are d1, d2, d3, ..., dn (g / cm３ ) and the thickness of the porous layer is t (cm).

[0069] In the separator of the present disclosure, the peel strength between the porous substrate and the porous layer is preferably 5 N / m or more, more preferably 10 N / m or more, even more preferably 15 N / m or more, and even more preferably 20 N / m or more, from the viewpoint of adhesive strength of the separator to the electrode. From the viewpoint of ion permeability, the peel strength is preferably 75 N / m or less, more preferably 60 N / m or less, and even more preferably 50 N / m or less. When the separator of the present disclosure has porous layers on both sides of the porous substrate, the peel strength between the porous substrate and the porous layer is preferably in the above range on both sides of the porous substrate.

[0070] The resin constituting the porous layer is also contained within the pores of the porous substrate, which allows the separator to be entirely impregnated with the electrolyte.

[0071] "Containing a resin inside the pores of a porous substrate" refers to a state in which the resin has permeated part or all of the interior of the pores of the porous substrate. The resin may be present on the surface opposite to the side having the porous layer of the porous substrate. "Having a resin on the surface opposite to the side having the porous layer of the porous substrate" refers to a state in which, when a coating liquid for forming a porous layer is applied to one side of the porous substrate, the resin in the coating liquid permeates from one side of the porous substrate and passes through the inside of the pores in the porous substrate, and the resin reaches the other side, thereby confirming the presence of the resin. The resin in the porous substrate may spread along the inner walls of the pores of the porous substrate, or may be present in the form of a fiber or a three-dimensional network within the pores of the porous substrate. The presence of the resin can be confirmed by determining whether the contact angle after application of the coating liquid for forming the porous layer is lower than the contact angle on the surface of the porous substrate before application of the coating liquid for forming the porous layer.

[0072] The presence of the resin in the porous substrate can also be confirmed by elemental imaging using a combination of a transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). ４) is easily stained by Ru, and the resin is detected by Ru imaging. ４ The method for preparing the stained sample is as follows.

[0073] (1) Cut the separator into a triangle (base approximately 0.5 mm x height approximately 1 mm, MD is the base). (2) Affix the triangular sample to a slide glass and place it in a sealed container with a capacity of approximately 50 ml. ４ Approximately 0.5 ml of the aqueous solution was introduced into a sealed container and subjected to steam staining at room temperature for 15 minutes. These staining conditions do not stain polyolefins. (3) The stained sample was impregnated with embedding resin. A stepwise substitution process was performed to ensure that the embedding resin penetrated the porous interior of the sample. Specifically, the sample was placed in n-butyl glycidyl ether, n-butyl glycidyl ether:embedding resin = 1:1, and n-butyl glycidyl ether:embedding resin = 1:3, successively for 30 minutes each, and then left in the embedding resin overnight. (4) The sample was placed on an embedding plate, and the embedding resin was injected and allowed to fully harden. (5) Ultrathin sections approximately 80 nm thick were prepared using an ultramicrotome at room temperature. The sample was cut so that the separator's MD was visible on the cross section. A carbon support film was attached to the ultrathin section and mounted on a Cu grid.

[0074] FIG. 1 shows an example of the results of TEM-EDS analysis. This example shows the results of analysis of a separator comprising a polyethylene microporous membrane as the polyolefin microporous membrane. The three images shown in FIG. 1 are a TEM image on the left, a STEM-HAADF image of a portion of the left in the center, and a Ru imaging image of the same field of view as the center in the right. In the TEM image, the cells are pores in the polyolefin microporous membrane, and the partition walls between the cells are pore walls of the polyolefin microporous membrane. The TEM image and STEM-HAADF image show that there are fine fibers inside the pores. The STEM-HAADF image and Ru imaging image show that the fine fibers inside the pores are wholly aromatic polyamide.

[0075] When the coating liquid for forming the porous layer is applied to both sides of the porous substrate, the resin in the coating liquid penetrates into one side of the porous substrate, passes through the pores in the porous substrate, and reaches the other side, where there are portions that come into contact with the resin that has penetrated into the pores in the porous substrate from the other side. The presence of the resin in the porous layer improves the affinity of the separator with the electrolyte solution and enhances the impregnation of the electrolyte solution. Therefore, battery characteristics such as discharge capacity are improved.

[0076] The porous layer may have a uniform structure as a whole. Examples of the form of a porous layer having a uniform structure include the following forms (a) and (b). The following forms (a) and (b) are also referred to as sponge structures. Form (a): The porous layer is a layer having a three-dimensional network structure made of a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond. Form (b): The porous layer further contains inorganic particles, and is a layer having a three-dimensional network structure in which the inorganic particles are bound and covered by a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond.

[0077] The porous layer preferably includes an inner layer formed on a porous substrate and a porous coating that forms the outer surface of the inner layer, and the inner layer preferably has a three-dimensional mesh structure with a mesh size larger than the pore size of the porous coating. When the porous layer includes a porous coating and an inner layer, examples of the porous layer include the following forms (c) and (d). Note that the finger skin structure described below is also referred to as a skin-core structure.

[0078] Form (c): The porous layer comprises an inner layer formed on a porous substrate, the inner layer containing a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule, and a porous coating formed to cover the outer surface of the inner layer, the porous coating containing a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule. The inner layer has a three-dimensional network structure with meshes larger than the pore size of the porous coating. The porous layer as a whole exhibits a so-called finger-skin structure.

[0079] Form (d): The porous layer comprises an inner layer formed on a porous substrate, the inner layer containing a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule, and a porous coating formed to cover the outer surface of the inner layer, the porous coating containing a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule. The inner layer has a three-dimensional network structure in which inorganic particles are bonded by a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule, and the network is larger than the pore size of the porous coating. The porous layer as a whole exhibits a so-called finger-skin structure.

[0080] The porous coating has many micropores, allowing gas or liquid to pass through from one surface to the other. The porous coating can be confirmed using a scanning electron microscope. By observing the cross section of the separator or the outer surface of the porous layer from a direction perpendicular to the surface, a resin portion extending in a film-like shape on the outer surface of the porous layer can be observed, and it can be seen that many pores are formed in the resin portion. A dense porous coating having micropores can be formed on a porous substrate by adjusting the composition of the coating liquid or coagulation liquid in the wet coating method described below. When the porous layer has a porous coating, the porous layer has excellent toughness and is less likely to undergo cohesive failure.

[0081] The porous coating is a dense coating having micropores that forms the outer surface of the porous layer. The average pore size of the micropores in the porous coating is preferably 1,000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less. From the viewpoint of ion permeability, the average pore size is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more.

[0082] The coverage of the porous coating on the outer surface of the porous layer is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more, of the area of ​​the porous layer in a plan view.

[0083] In addition, the resin contained in the pores of the porous substrate may also have a finger skin structure in the pores of the porous substrate, in which case the porous layer containing the resin may have a finger skin structure in the pores of the porous substrate.

[0084] [Separator Characteristics] The thickness of the separator of the present disclosure is preferably 8.0 μm or more, more preferably 9.0 μm or more, from the viewpoint of the mechanical strength of the separator, and is preferably 20.0 μm or less, more preferably 15.0 μm or less, from the viewpoint of the energy density of the battery.

[0085] The puncture strength of the separator of the present disclosure is preferably 150 g to 1000 g, and more preferably 200 g to 600 g, from the viewpoint of the mechanical strength of the separator or the short-circuit resistance of the battery. The method for measuring the puncture strength of the separator is the same as the method for measuring the puncture strength of the porous substrate.

[0086] The porosity of the separator of the present disclosure is preferably 30% to 60% from the viewpoints of adhesiveness to electrodes, ease of handling of the separator, ion permeability, or mechanical strength.

[0087] The Gurley value (JIS P8117:2009) of the separator of the present disclosure is preferably 50 seconds / 100 mL to 800 seconds / 100 mL, more preferably 80 seconds / 100 mL to 500 seconds / 100 mL, and even more preferably 100 seconds / 100 mL to 400 seconds / 100 mL, from the viewpoint of the balance between mechanical strength and ion permeability.

[0088] In the separator of the present disclosure, from the viewpoint of ion permeability, the Gurley value of the separator (in a state in which a porous layer is formed on a porous substrate) minus the Gurley value of the porous substrate is preferably 300 seconds / 100 mL or less, more preferably 200 seconds / 100 mL or less, and even more preferably 150 seconds / 100 mL or less. From the viewpoint of adhesion to an electrode, the lower limit of the value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the separator is preferably 20 seconds / 100 mL or more.

[0089] The separator of the present disclosure has a tensile strength in the MD direction of 500 kgf / cm from the viewpoint of the mechanical strength or handleability of the separator. ２ More than 600 kgf / cm is preferable. ２ More preferably, 700 kgf / cm or more ２ From the above viewpoint, the higher the tensile strength in the MD direction, the more preferable. ２ The following is the result.

[0090] The separator of the present disclosure has a tensile strength in the TD direction of 500 kgf / cm from the viewpoint of the mechanical strength or handleability of the separator. ２ More than 600 kgf / cm is preferable. ２ More preferably, 700 kgf / cm or more ２ From the above viewpoint, the higher the tensile strength in the TD direction, the more preferable. ２ The following is the result.

[0091] The tensile strength of the separator of the present disclosure can be controlled by, for example, the content of inorganic particles in the porous layer, the thickness of the porous layer, the porosity of the porous layer, the thickness of the adhesive layer, etc.

[0092] [Alkaline Electrolyte] In the alkaline zinc secondary battery of the present disclosure, an alkaline aqueous solution is used as the alkaline electrolyte. Examples of the alkaline aqueous solution include aqueous solutions containing sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. The alkaline electrolyte preferably contains sodium hydroxide and / or potassium hydroxide. The alkaline electrolyte may contain an additive. Specific examples of the additive include zinc hydroxide, etc., since zinc oxide is produced during charging and discharging.

[0093] <Method for manufacturing separator> The separator of the present disclosure is manufactured, for example, by the following manufacturing method A or manufacturing method B. In manufacturing methods A and B, the porous layer is formed on the porous substrate by a wet coating method or a dry coating method. In manufacturing method B, the porous layer is formed by the wet coating method. In the present disclosure, the wet coating method is a method in which a coating layer is solidified in a coagulation liquid, and the dry coating method is a method in which a coating layer is solidified by drying.

[0094] Production method A (discontinuous production method): A porous layer is formed on a porous substrate unwound from a roll to obtain a separator, and the completed separator is wound up on another roll.

[0095] Manufacturing method B (continuous manufacturing method): Porous layers are formed continuously or simultaneously on a porous substrate unwound from a roll, and the completed separator is wound up on another roll.

[0096] One embodiment of production method B: A porous layer-forming coating liquid is applied to a porous substrate, and the substrate is immersed in a coagulating liquid to solidify the coating layer, and then the substrate is pulled out of the coagulating liquid, washed with water, and dried.

[0097] The steps included in the manufacturing method will be described in detail below, taking manufacturing method B as an example.

[0098] In one embodiment of the manufacturing method B, a porous layer is formed on at least one surface of a porous substrate by a wet coating method to obtain a laminate of the porous substrate and the porous layer. The manufacturing method B includes the following steps (1) to (4), which are carried out in order.

[0099] Step (1): Preparation of Porous Layer-Forming Coating Liquid When producing a separator, a porous layer-forming coating liquid (hereinafter referred to as "coating liquid" in the description of the production method) is prepared by dissolving a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in the molecule in a solvent. Inorganic particles or other components may be dispersed or dissolved in the coating liquid as necessary.

[0100] When producing a separator, the solvent used in preparing the coating solution contains a solvent (hereinafter also referred to as a "good solvent") that dissolves a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in the molecule. Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide.

[0101] From the viewpoint of forming a porous layer having a good pore structure, the solvent used in preparing the coating liquid preferably contains a phase separation agent that induces phase separation. Therefore, the solvent used in preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with the good solvent in an amount that ensures a viscosity appropriate for coating. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0102] From the viewpoint of forming a good porous structure, the solvent used for preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent, the mixed solvent containing 60 mass% or more of the good solvent and 40 mass% or less of the phase separation agent. The good porous structure refers to, for example, a porous layer including an inner layer formed on a porous substrate and a porous coating that forms the outer surface of the inner layer, and the inner layer has a three-dimensional mesh structure with a mesh size larger than the pore size of the porous coating.

[0103] The resin concentration of the coating liquid is preferably 1% by mass to 20% by mass from the viewpoint of forming a good porous structure.

[0104] Step (2): Coating of coating liquid The coating liquid is applied to at least one surface of the porous substrate to form a coating layer on the porous substrate. Methods for applying the coating liquid to the porous substrate include knife coating, Mayer bar coating, die coating, reverse roll coating, roll coating, gravure coating, screen printing, inkjet printing, and spraying. When forming a porous layer on both sides of the porous substrate, it is preferable from the viewpoint of productivity to simultaneously apply the coating liquid to both sides of the porous substrate.

[0105] Step (3): Solidification of the coating layer The porous substrate on which the coating layer has been formed is immersed in a coagulation liquid, and while inducing phase separation in the coating layer, the resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule is solidified to form a porous layer containing a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule. This results in a laminate consisting of the porous substrate and the porous layer.

[0106] The coagulation liquid generally contains the good solvent and phase separation agent used in preparing the coating liquid, as well as water. From a productivity perspective, it is preferable that the mixing ratio of the good solvent and the phase separation agent be the same as the mixing ratio of the mixed solvent used in preparing the coating liquid. From the viewpoints of forming a porous structure and productivity, the water content in the coagulation liquid is preferably 40% by mass to 90% by mass. The temperature of the coagulation liquid is, for example, 20°C to 50°C.

[0107] Step (4): Washing and drying of coating layer The laminate is lifted out of the coagulating solution and washed with water. By washing with water, the coagulating solution is removed from the laminate. Furthermore, by drying, water is removed from the laminate. Washing with water is carried out, for example, by transporting the laminate in a water washing bath. Drying is carried out, for example, by transporting the laminate in a high-temperature environment, by blowing air on the laminate, or by bringing the laminate into contact with a heat roll. The drying temperature is preferably 40°C to 80°C.

[0108] The manufacturing method A or manufacturing method B for manufacturing a separator can be carried out by partially omitting or modifying the above steps (1) to (4).

[0109] <Method for manufacturing alkaline zinc secondary battery> The alkaline zinc secondary battery of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is enclosed in an exterior material together with an electrolyte. The positive electrode, negative electrode, separator, and electrolyte are as described above.

[0110] Examples of the exterior packaging include metal cans, packs made of aluminum laminated film, etc. The shape of the battery may be rectangular, cylindrical, coin-shaped, etc., and the separator of the present disclosure is suitable for any shape.

[0111] The alkaline zinc secondary battery of the present disclosure can be manufactured using known manufacturing methods, for example, by disposing the separator of the present disclosure between a positive electrode and a negative electrode, winding them in the lengthwise direction to manufacture a wound body, inserting the wound body into an exterior material, injecting an electrolyte solution, and sealing it. The same applies when an element manufactured by a method in which at least one layer of a positive electrode, separator, and negative electrode is stacked in this order (so-called stack method) is used instead of the wound body.

[0112] The alkaline zinc secondary battery and separator for alkaline zinc secondary battery of the present disclosure will be described in more detail below with reference to examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the alkaline zinc secondary battery and separator for alkaline zinc secondary battery of the present disclosure should not be interpreted as being limited by the specific examples shown below.

[0113] In the following description, syntheses, treatments, manufacturing, etc. were carried out at room temperature (25° C.±3° C.) unless otherwise specified.

[0114] Examples 1 to 13 Manganese-zinc secondary batteries were fabricated as alkaline-zinc secondary batteries.

[0115] (Preparation of Positive Electrode) A manganese electrode was prepared as the positive electrode as follows. A nickel foam substrate (Ni porous body, manufactured by Nilaco Corporation) with a porosity of 98% was filled with a paste-like active material. The paste-like active material was prepared by stirring a mixture of 95 parts by mass of manganese dioxide powder with an average diameter of 20 μm and 5 parts by mass of acetylene black as an additive in a 2 wt % aqueous solution of carboxymethyl cellulose. The composite electrode filled with the paste-like active material was dried at 80° C. for 60 minutes and then rolled to form a manganese electrode positive electrode.

[0116] (Preparation of Negative Electrode) A metal zinc plate (manufactured by Nilaco Corporation, Zn plate, purity 99.2%) was used as the zinc negative electrode.

[0117] (Preparation of Separator) In Examples 1 to 13, separators were prepared by the above-described manufacturing method B. A polyethylene microporous membrane (thickness 9 μm, TND9 manufactured by Shanghai Energy Co., Ltd.) was used as the porous substrate. 20 parts by mass of meta-aramid resin (Teijin Limited, Conex (registered trademark)) was dissolved in a solvent as the coating liquid for forming the porous layer, and magnesium hydroxide (Mg(OH) ２ , manufactured by Kyowa Chemical Industry Co., Ltd., primary particle volume average particle size 0.8 μm), barium sulfate (BaSO ４、 Sakai Chemical Industry Co., Ltd., primary particle volume average particle size 0.05 μm), barium sulfate (BaSO ４、 Sakai Chemical Industry Co., Ltd., primary particle volume average particle size 0.1 μm), barium sulfate (BaSO ４、 Sakai Chemical Industry Co., Ltd., primary particle volume average particle size 0.3 μm), or barium sulfate (BaSO ４、 The dispersion was prepared by dispersing 80 parts by mass of a primary particle having a volume average particle size of 0.7 μm (manufactured by Sakai Chemical Industry Co., Ltd.) in the dispersion. 424 parts by mass of N,N-dimethylacetamide was used as the solvent.

[0118] After preparing a coating solution for forming a porous layer, it was coated on both sides of a polyethylene microporous membrane using a gravure coater. The porous substrate with the coating layer formed thereon was immersed in a coagulation solution containing N,N-dimethylacetamide and water, then removed and washed with water. After washing with water, the laminate was dried at a drying temperature of 60°C by blowing air on it to obtain a separator consisting of a polyethylene microporous membrane as a porous substrate and a porous layer. The inorganic particles of magnesium hydroxide or barium sulfate were contained in the amounts shown in Table 1, based on the total volume of the solid content of the porous layer. The thickness was measured using a micrometer (PMU150-25MX, manufactured by Mitutoyo Corporation).

[0119] (Preparation of Secondary Battery) A single-layer laminate type manganese-zinc secondary battery was prepared using the positive and negative electrodes obtained above and the separators prepared in each of Examples 1 to 13. An aqueous solution containing 34 mass% potassium hydroxide and 5 mass% zinc oxide was used as the electrolyte. The positive and negative electrodes were placed in a battery case to prepare an unformed manganese-zinc secondary battery, which was then filled with the electrolyte and left for 10 hours. Thereafter, the battery was charged at 15 mA for 15 hours in an environment of 25°C to prepare a manganese-zinc secondary battery with a design capacity of 150 mAh.

[0120] <Measurement method and measurement results> (Porous layer structure) The structure of the porous layer of each of the separators produced in Examples 1 to 13 was observed using a scanning electron microscope. When the porous layer structure was observed, it was found that the porous layer had a three-dimensional network structure in each of the separators produced in Examples 1 to 13. Furthermore, in each of Examples 1 to 7, the porous layer had a finger skin structure, and in each of Examples 8 to 13, the porous layer had a sponge structure. Furthermore, in each of Examples 1 to 13, it was confirmed using a transmission electron microscope that there were also portions in which the resin was contained within the pores of the porous substrate.

[0121] (Thickness of Porous Layer) For the separators produced in each of Examples 1 to 13, the thickness [μm] of the porous layer was measured by subtracting the thickness of the substrate from the thickness of the separator. The measurement results are shown in Table 1. The thickness of the porous layer can be the thickness of the coating layer.

[0122] (Measurement of Discharge Capacity) In order to confirm the discharge capacity of the manganese-zinc secondary batteries prepared using the separators prepared in each of Examples 1 to 13, batteries were prepared and the discharge capacity [unit: mAh / g (MnO ２ The measurement results are shown in Table 1.

[0123] Comparative Example 1: A polyethylene microporous membrane (thickness: 20 μm) was used as the separator. A manganese-zinc secondary battery was produced in the same manner as in Example 1, but the discharge capacity could not be measured because the separator was not impregnated with the electrolyte. In Table 1, for Comparative Example 1, the discharge capacity could not be measured, so "-" is entered in the discharge capacity column.

[0124] Comparative Example 2: A polypropylene nonwoven fabric (50 μm thick) was used as the separator. A manganese-zinc secondary battery was fabricated in the same manner as in Example 1, and the discharge capacity was measured. However, a short circuit occurred, making the discharge capacity unmeasurable. In Table 1, for Comparative Example 2, the discharge capacity was unmeasurable, so "-" is entered in the discharge capacity column.

[0125] Comparative Example 3 A separator and a manganese-zinc secondary battery were fabricated in the same manner as in Example 1, except that a polyethylene microporous membrane was pre-impregnated with N,N-dimethylacetamide, and a pore-forming coating liquid was applied to both sides of the polyethylene microporous membrane using a gravure coater. As in Example 1, the structure of the porous layer was observed, the thickness of the porous layer was measured, and the discharge capacity was measured. Observation of the porous layer structure confirmed by a transmission electron microscope that the porous layer had a three-dimensional network structure and a finger-skin structure, and that no resin was contained within the pores of the porous substrate. The discharge capacity of the battery of Comparative Example 3 could not be measured because the separator was not impregnated with the electrolyte. In Table 1, the discharge capacity column for Comparative Example 3 is marked "-" because the discharge capacity could not be measured.

[0126]

[0127] It was found that in each of Examples 1 to 13, in which the separator included a porous substrate that was a microporous membrane containing polyolefin and a porous layer provided on both sides of the porous substrate, the porous layer having a three-dimensional network structure containing resin, and the resin also being contained within the pores of the porous substrate, the battery characteristics as an alkaline zinc secondary battery were excellent. Each of Comparative Examples 1 to 3 did not have a porous layer, or the porous layer had a three-dimensional network structure and did not have a configuration in which the resin was contained within the pores of the porous substrate, and therefore could not be used as an alkaline zinc secondary battery.

[0128] The disclosure of Japanese Patent Application No. 2024-055057, filed on March 28, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An alkaline-zinc secondary battery comprising: a positive electrode, a negative electrode containing zinc, a separator disposed between the positive electrode and the negative electrode, and an alkaline electrolyte; the separator comprising a porous substrate and a porous layer disposed on one or both sides of the porous substrate; the porous substrate being a microporous film containing polyolefin; the porous layer comprising a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond in its molecule, and having a three-dimensional network structure; and the resin being further contained within the pores of the porous substrate.

2. The alkaline zinc secondary battery according to claim 1, wherein the positive electrode contains at least one material selected from the group consisting of manganese dioxide, cobalt hydroxide, nickel hydroxide, and activated carbon.

3. The alkaline zinc secondary battery according to claim 1, wherein the alkaline electrolyte contains sodium hydroxide and / or potassium hydroxide.

4. The alkaline zinc secondary battery according to claim 1, wherein the porous layer has a thickness of 5.0 μm to 20 μm.

5. The alkaline zinc secondary battery according to claim 1, wherein the porous layer further contains a filler.

6. The alkaline zinc secondary battery according to claim 5, wherein the filler has a volume average particle size of primary particles of 0.5 μm to 3.0 μm.

7. The alkaline-zinc secondary battery according to claim 5, wherein the porous layer contains the filler in an amount ranging from 60% to 95% by volume based on the total solid volume of the porous layer.

8. The alkaline zinc secondary battery according to claim 5, wherein the filler is at least one of a metal hydroxide and a metal sulfate.

9. A separator for an alkaline zinc secondary battery, comprising: a porous substrate; and a porous layer provided on one or both sides of the porous substrate, wherein the porous substrate is a microporous membrane containing polyolefin; the porous layer contains a resin having at least one bonding group selected from the group consisting of an amide bond, an amide-imide bond, and an imide bond, and has a three-dimensional network structure; and the resin is further contained within the pores of the porous substrate.

10. The separator for an alkaline zinc secondary battery according to claim 9, wherein the porous layer has a thickness of 5.0 μm to 20 μm.

11. The separator for an alkaline zinc secondary battery according to claim 9, wherein the porous layer further contains a filler.

12. The separator for an alkaline-zinc secondary battery according to claim 11, wherein the porous layer contains the filler in an amount ranging from 60% to 95% by volume based on the total solid volume of the porous layer.

13. The separator for an alkaline zinc secondary battery according to claim 11, wherein the filler has a volume average particle size of primary particles of 0.5 μm to 3.0 μm.

14. The separator for an alkali-zinc secondary battery according to claim 11, wherein the filler is at least one of a metal hydroxide and a metal sulfate.

15. A separator for an alkaline-zinc secondary battery as described in claim 9, wherein the porous layer includes an inner layer formed on the porous substrate and a porous coating that forms the outer surface of the inner layer, and the inner layer has a three-dimensional mesh structure with a mesh size larger than the pore size of the porous coating.

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