Metal-air secondary battery

Abstract

The purpose of the present invention is to provide a metal-air secondary battery capable of suppressing a decrease in discharge potential and an increase in overvoltage while including a discharge air electrode catalyst that is a carbon-based catalyst. This metal-air secondary battery is provided with: a comb-shaped charging air electrode layer that contains a charging air electrode catalyst, a conductive material, and a binder; a comb-shaped discharging air electrode layer that contains a binder and is provided so as to be separated from each other and mesh with each other in the same plane as the comb-shaped charging air electrode layer; a metal negative electrode layer that is provided so as to face a composite air electrode layer composed of the charging air electrode layer and the discharging air electrode layer in the same plane; an electrolyte solution that is impregnated into the metal negative electrode layer; and a separator that is interposed between the composite air electrode layer and the metal negative electrode layer so as to be in contact with the composite air electrode layer, and that isolates the composite air electrode layer so as to be capable of hydroxide ion conduction with the metal negative electrode layer.

Description

Metal-air secondary battery

[0001] The present disclosure relates to metal-air secondary batteries.

[0002] Metal-air secondary batteries are one of the candidates for innovative batteries. In metal-air secondary batteries, oxygen, which is the positive electrode active material, is supplied from the air, so the space inside the battery container can be used to the fullest extent for filling the negative electrode active material, which in principle makes it possible to achieve a high energy density. For example, in zinc-air secondary batteries that use zinc as the negative electrode active material, an alkaline aqueous solution such as potassium hydroxide is used as the electrolyte, and a separator (partition) is used to prevent short circuits between the positive and negative electrodes. During discharge, O is produced on the air electrode (positive electrode) side, as shown in the following reaction formula: ２ is reduced to OH － is produced, while zinc is oxidized at the negative electrode to produce ZnO. ２ +2H ２ O+4e － →4OH － Negative electrode: 2Zn+4OH － → 2ZnO + 2H ２ O+4e －

[0003] It is known that in zinc secondary batteries, such as zinc-air secondary batteries and nickel-zinc secondary batteries, metallic zinc precipitates in the form of dendrites from the negative electrode during charging, penetrates the pores of separators such as nonwoven fabrics, and reaches the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the battery's life after repeated charge and discharge. Furthermore, zinc-air secondary batteries also suffer from the problem that carbon dioxide in the air passes through the air electrode and dissolves in the electrolyte, precipitating alkaline carbonates and reducing battery performance. Similar problems can also occur in lithium-air secondary batteries.

[0004] To address the above problems, batteries have been proposed that include a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to pass through while preventing penetration by zinc dendrites. For example, Patent Document 1 (WO 2013 / 073292) discloses that an LDH separator is provided between the air electrode and the negative electrode in a zinc-air secondary battery to prevent both short circuits between the positive and negative electrodes caused by zinc dendrites and the inclusion of carbon dioxide. Furthermore, Patent Document 2 (WO 2016 / 076047) discloses a separator structure that includes an LDH separator fitted or bonded to a resin outer frame, and that the LDH separator has such high density that it is gas-impermeable and / or water-impermeable. This document also discloses that the LDH separator can be composited with a porous substrate. Furthermore, Patent Document 3 (WO 2016 / 067884) discloses various methods for forming a dense LDH membrane on the surface of a porous substrate to obtain a composite material (LDH separator). This method includes a step of uniformly attaching an initiator substance capable of providing a starting point for LDH crystal growth to the porous substrate, and subjecting the porous substrate to hydrothermal treatment in a raw material aqueous solution to form a dense LDH membrane on the surface of the porous substrate. Patent Document 4 (WO 2019 / 124270) discloses an LDH separator that includes a porous substrate made of a polymer material and a layered double hydroxide (LDH) that blocks the pores of the porous substrate, and has an in-line transmittance of 1% or more at a wavelength of 1000 nm.

[0005] In the field of metal-air secondary batteries such as zinc-air secondary batteries, an air electrode / separator assembly has been proposed in which an air electrode layer is provided on an LDH separator. Patent Document 5 (WO 2015 / 146671) discloses an air electrode / separator assembly having an air electrode layer on an LDH separator, the air electrode layer including an air electrode catalyst, an electron conductive material, and a hydroxide ion conductive material. Patent Document 6 (WO 2020 / 246177) also discloses an air electrode / separator assembly including a hydroxide ion conductive separator, an interfacial layer covering one side of the separator and including a hydroxide ion conductive material and an electrically conductive material, and an air electrode layer provided on the interfacial layer and including an outermost catalyst layer composed of a porous current collector and a layered double hydroxide (LDH) covering the surface of the porous current collector. Patent Documents 5 and 6 also disclose the use of LDH as the hydroxide ion conductive material.

[0006] Furthermore, although they cannot be called LDHs, LDH-like compounds are known as hydroxides and / or oxides with a layered crystal structure similar to LDHs, and they exhibit hydroxide ion conductive properties similar enough to be collectively referred to as hydroxide ion conductive layered compounds together with LDHs. For example, Patent Document 7 (WO 2020 / 255856) discloses a hydroxide ion conductive separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that plugs the pores of the porous substrate, wherein the LDH-like compound is a hydroxide and / or oxide with a layered crystal structure containing Mg and one or more elements, including at least Ti, selected from the group consisting of Ti, Y, and Al. Patent Document 8 (WO2021 / 229916) discloses an LDH separator using an LDH-like compound containing (i) Ti, Y, and optionally Al and / or Mg, and (ii) an additional element M which is at least one selected from the group consisting of In, Bi, Ca, Sr, and Ba. Furthermore, Patent Document 9 (WO2021 / 229917) discloses an LDH separator using an LDH-like compound and In(OH) ３With regard to an LDH separator containing a mixture of the above, one has been disclosed in which the LDH-like compound is a hydroxide and / or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In. The separators disclosed in Patent Documents 7 to 9 are said to have superior alkali resistance compared to conventional LDH separators and to be able to more effectively suppress short circuits caused by zinc dendrites.

[0007] Various metal-air secondary batteries employing hydroxide ion-conductive separators such as LDH separators have been proposed. For example, Patent Document 10 (WO2022 / 209009) discloses a metal-air secondary battery including a hydroxide ion-conductive separator such as an LDH separator, a catalyst layer covering one side of the hydroxide ion-conductive separator, a gas diffusion electrode provided on the catalyst layer opposite the hydroxide ion-conductive separator, a metal negative electrode, and an electrolyte, and the catalyst layer is said to include an air electrode catalyst, a hydroxide ion-conductive material, a conductive material, a binder, and a humidity conditioner.

[0008] WO2013 / 073292WO2016 / 076047WO2016 / 067884WO2019 / 124270WO2015 / 146671 WO2020 / 246177WO2020 / 255856WO2021 / 229916WO2021 / 229917WO2022 / 209009

[0009] In conventional metal-air secondary batteries, the same air electrode is generally used for both charging and discharging. However, when a carbon-based discharge catalyst is used for the air electrode, exposure to an oxidation potential (charging potential) causes the carbon-based catalyst to oxidize and deteriorate, resulting in a decrease in discharge potential and an increase in overvoltage.

[0010] The present inventors have now discovered that by employing a metal-air secondary battery in which the charge air electrode layer and the discharge air electrode layer are spaced apart from each other and arranged in a comb-like pattern so that they interdigitate with each other within the same plane, it is possible to prevent the discharge air electrode catalyst (carbon-based catalyst) from being exposed to the charge potential, thereby suppressing a decrease in discharge potential and an increase in overvoltage.

[0011] Therefore, an object of the present invention is to provide a metal-air secondary battery that can suppress a decrease in discharge potential and an increase in overvoltage even while containing a discharge air electrode catalyst that is a carbon-based catalyst.

[0012] The present disclosure provides the following aspects: [Aspect 1] A metal-air secondary battery comprising: a comb-teeth-shaped charge air electrode layer including a charge air electrode catalyst, a conductive material, and a binder, a comb-teeth-shaped discharge air electrode layer including a discharge air electrode catalyst that is a carbon-based catalyst and a binder, and disposed in the same plane as the comb-teeth-shaped charge air electrode layer so as to be spaced apart and interdigitated with each other, a metal anode layer disposed opposite a composite air electrode layer composed of the charge air electrode layer and the discharge air electrode layer in the same plane, an electrolyte impregnated in the metal anode layer, and a separator interposed between the composite air electrode layer and the metal anode layer so as to be in contact with the composite air electrode layer, and isolating the composite air electrode layer from the metal anode layer in a manner capable of conducting hydroxide ions. [Aspect 2] The metal-air secondary battery according to Aspect 1, wherein the metal-air secondary battery includes a pair of the composite air electrode layers facing each other at a distance from each other, the separator is interposed between each of the pair of composite air electrode layers and the metal negative electrode layer, and the metal negative electrode layer is sandwiched between the pair of composite air electrode layers with the separator interposed therebetween. [Aspect 3] The metal-air secondary battery according to Aspect 1 or 2, wherein the charging air electrode catalyst is a layered double hydroxide (LDH). [Aspect 4] The metal-air secondary battery according to Aspect 3, wherein the LDH serving as the charging air electrode catalyst contains at least Ni and Fe as constituent elements. [Aspect 5] The metal-air secondary battery according to Aspect 3, wherein the LDH serving as the charging air electrode catalyst contains at least Ni, Fe, V, and Co as constituent elements. [Aspect 6] The metal-air secondary battery according to any one of Aspects 1 to 5, wherein the separator is a hydroxide ion-conductive separator that separates the composite air cathode layer from the metal anode layer in a manner that allows hydroxide ions to be conducted, the charge air cathode layer further comprising a hydroxide ion-conductive material, and the discharge air cathode layer further comprising a hydroxide ion-conductive material. [Aspect 7] The metal-air secondary battery according to Aspect 6, wherein the hydroxide ion-conductive separator is a layered double hydroxide (LDH) separator. [Aspect 8] The metal-air secondary battery according to Aspect 7, wherein the LDH separator is composited with a porous substrate.[Aspect 9] The metal-air secondary battery of any one of Aspects 6 to 8, wherein the hydroxide ion-conductive separator prevents the electrolyte from entering the composite air electrode layer, thereby preventing the electrolyte from being present within the air electrode layer. [Aspect 10] The metal-air secondary battery of any one of Aspects 1 to 9, further comprising: a charge air electrode current collector provided on the outside of the charge air electrode layer and extending from an end of the charge air electrode layer; a discharge air electrode current collector provided on the outside of the discharge air electrode layer and extending from an end of the discharge air electrode layer; and a negative electrode current collector supporting the metal negative electrode layer and extending from the end of the metal negative electrode layer. [Aspect 11] The metal-air secondary battery of Aspect 10, further comprising: a charge gas diffusion electrode provided between the charge air electrode layer and the charge air electrode current collector; and a discharge gas diffusion electrode provided between the discharge air electrode layer and the discharge air electrode current collector.

[0013] 6 is a schematic front view conceptually showing an example of a metal-air secondary battery of the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 of the metal-air secondary battery shown in FIG. 1. FIG. 3 is a cross-sectional view taken along line 3-3 of the metal-air secondary battery shown in FIG. 1. FIG. 4 is a cross-sectional view taken along line 4-4 of the metal-air secondary battery shown in FIG. 1. FIG. 5 is a schematic front view showing an example of a holding member used in the metal-air secondary battery shown in FIG. 1. FIG. 6 is a schematic front view showing the metal-air secondary batteries produced in Examples 1 and 2. FIG. 7 is a cross-sectional view taken along line 7-7 of the metal-air secondary battery shown in FIG. 6. FIG. 8 is a cross-sectional view taken along line 8-8 of the metal-air secondary battery shown in FIG. 6. FIG. 9 is a cross-sectional view taken along line 9-9 of the metal-air secondary battery shown in FIG. 6. FIG. 6 is a schematic cross-sectional view showing the metal-air secondary battery produced in Example 3 (Comparative Example). FIG. 7 is a graph showing the change in discharge potential measured in charge-discharge tests performed on the metal-air secondary batteries produced in Examples 1 to 3.

[0014] FIG. 1 shows an example of a metal-air secondary battery of the present invention. The metal-air secondary battery 10 shown in FIG. 1 includes a charge air cathode layer 12, a discharge air cathode layer 14, a metal anode layer 18, an electrolyte (not shown), and a separator 20. The charge air cathode layer 12 and the discharge air cathode layer 14 are both comb-shaped and spaced apart from each other in the same plane. This combination of the charge air cathode layer 12 and the discharge air cathode layer 14 in the same plane is referred to herein as a composite air cathode layer 16. The charge air cathode layer 12 includes a charge air cathode catalyst, a conductive material, a binder, and optionally, a hydroxide ion conductive material. The discharge air cathode layer 14 includes a discharge air cathode catalyst that is a carbon-based catalyst, a binder, and optionally, a hydroxide ion conductive material. The metal anode layer 18 is disposed opposite the composite air cathode layer 16. The metal anode layer 18 is impregnated with an electrolyte. The separator 20 is interposed between the composite air electrode layer 16 and the metal negative electrode layer 18 so as to be in contact with the composite air electrode layer 16, and isolates the composite air electrode layer 16 from the metal negative electrode layer 18 in a manner that allows hydroxide ion conduction. By employing a metal-air secondary battery 10 in which the charge air electrode layer 12 and the discharge air electrode layer 14 are spaced apart from each other in the same plane and arranged in a comb-like pattern that interdigitates with each other, it is possible to prevent the discharge air electrode catalyst (carbon-based catalyst) from being exposed to the charge potential, and to suppress a decrease in discharge potential and an increase in overvoltage.

[0015] As mentioned above, conventional metal-air secondary batteries typically use the same air electrode for both charging and discharging. However, when a carbon-based discharge catalyst is used in the air electrode, exposure to an oxidation potential (charging potential) can cause the carbon-based catalyst to oxidize and deteriorate, resulting in a decrease in discharge potential and an increase in overvoltage. According to the inventors' findings, when a single air electrode contains a mixture of a conductive material (e.g., carbon), a charging catalyst, a hydroxide ion conductive material (e.g., LDH), and a discharge catalyst (e.g., a carbon-based catalyst), the charging potential overlaps with the oxidation potential of the carbon, making the carbon-based catalyst more susceptible to oxidation and deterioration. This oxidation and deterioration of the carbon-based catalyst is thought to result in a decrease in discharge potential and an increase in overvoltage. In this regard, according to the present invention, by providing the charging air electrode layer 12 and the discharge air electrode layer 14 in a comb-like configuration spaced apart from each other and interdigitated with each other in the same plane, the discharge air electrode catalyst (carbon-based catalyst) can be prevented from being exposed to the charging potential, thereby suppressing oxidation and deterioration of the carbon-based catalyst. In other words, because the region of the charge air electrode layer 12 and the region of the discharge air electrode layer 14 are separated from each other despite being in the same plane, the region of the discharge air electrode layer 14 is not exposed to the charge potential even while the charge reaction is occurring in the region of the charge air electrode layer 12, making it difficult for oxidation and deterioration of the carbon-based catalyst to progress. As a result of this suppression of a decrease in electrode activity, it is thought that a decrease in discharge potential and an increase in overvoltage are suppressed.

[0016] The charging air electrode layer 12 contains a charging air electrode catalyst, a conductive material, a binder, and, optionally, a hydroxide ion conductive material. The charging air electrode catalyst has a spherical, plate-like, or fibrous form and is dispersed in the charging air electrode layer 12. The charging air electrode catalyst may also serve as a conductive material or a hydroxide ion conductive composite material. The charging air electrode catalyst is not particularly limited as long as it has catalytic activity for the charging reaction. It may be a hydroxide catalyst, an oxide catalyst, or a carbon-based catalyst, but is preferably a layered double hydroxide (LDH). The LDH used as the charging air electrode catalyst is preferably an LDH containing at least Ni and Fe as constituent elements (Ni-Fe-LDH), and more preferably an LDH containing at least Ni, Fe, V, and Co as constituent elements (Ni-Fe-V-Co-LDH). In this specification, the phrase "contained as a constituent element" excludes elements contained as impurities and refers to the metal elements or metal ions that constitute the hydroxide base layer that constitutes the LDH. The charging air electrode catalyst is preferably in the form of fine particles to increase the reaction field. Specifically, the particle size of the charging air electrode catalyst is preferably 5 μm or less, more preferably 0.5 nm to 3 μm, and even more preferably 1 nm to 3 μm.

[0017] The discharge air electrode layer 14 contains a discharge air electrode catalyst, which is a carbon-based catalyst, a binder, and, if desired, a hydroxide ion conductive material. The discharge air electrode catalyst has a spherical, plate-like, or fibrous form and is dispersed in the discharge air electrode layer 14. The discharge air electrode catalyst may also serve as a conductive material or a hydroxide ion conductive composite material. The discharge air electrode catalyst is not particularly limited as long as it is a carbon-based catalyst that has catalytic activity for a discharge reaction. In this specification, the term "carbon-based catalyst" refers to a catalyst containing carbon, and may be carbon that itself has catalytic activity, or carbon that supports a catalytically active metal or oxide. A preferred example of a carbon-based catalyst is carbon powder that supports a catalyst. Examples of catalysts supported on carbon powder include (i) transition metal elements such as cobalt and nickel, (ii) platinum group elements such as palladium and platinum, (iii) perovskite oxides containing transition metals such as cobalt, manganese, and iron, (iv) noble metal oxides such as ruthenium and palladium, (v) manganese oxide, and (vi) any combination thereof. Platinum group elements such as palladium and platinum are particularly preferred, and platinum is most preferred. Another preferred example of a carbon-based catalyst is a carbon powder catalyst in which the carbon itself exhibits discharge activity. Examples of such carbon include (i) nitrogen-doped carbon, (ii) nitrogen-phosphorus-doped carbon, (iii) nitrogen-boron-doped carbon, (iv) nitrogen-sulfur-doped carbon, and (v) any combination thereof. Nitrogen-doped carbon and nitrogen-boron-doped carbon are particularly preferred, and nitrogen-doped carbon is most preferred. It is desirable for the discharge air electrode catalyst to be in the form of fine particles to increase the reaction field. Specifically, the particle size of the discharge air electrode catalyst is preferably 5 μm or less, more preferably 0.5 nm to 3 μm, and even more preferably 1 nm to 1 μm.

[0018] The conductive material contained in the chargeable air cathode layer 12 is not particularly limited as long as it is a material that can impart conductivity to the chargeable air cathode layer 12, but is preferably a carbon-based material, a conductive oxide, or a metal. Examples of carbon-based materials include carbon black, graphite, carbon nanotubes, graphene, reduced graphene oxide, ketjen black, and any combination thereof. The conductive oxide is preferably a conductive ceramic, and a preferred example of the conductive ceramic is LaNiO. ３ , LaSr ３ Fe ３ O １０ and the like. Preferred examples of metals include nickel and titanium. In the discharge air electrode layer 14, a conductive material is not essential because the carbon-based catalyst itself exhibits conductivity, but it may be added separately from the carbon-based catalyst. In this case, the conductive material is preferably a carbon-based material. Examples of carbon-based materials include carbon black, graphite, carbon nanotubes, graphene, reduced graphene oxide, ketjen black, and any combination thereof.

[0019] Known binder resins can be used as the binder contained in the charge air electrode layer 12 and the discharge air electrode layer 14. Examples of binder resins include acrylate resins, butyral resins, vinyl alcohol resins, celluloses, vinyl acetal resins, polytetrafluoroethylene, polyvinylidene fluoride, and any combination thereof, with acrylate resins, butyral resins, polytetrafluoroethylene, polyvinylidene fluoride, and any combination thereof being preferred. The binder is preferably present to bind the air electrode catalyst, the conductive material, and the optional hydroxide ion conductive composite material together and to adequately expose these components so that they can come into contact with air.

[0020] The charge air electrode layer 12 and / or the discharge air electrode layer 14 may contain a hydroxide ion conductive material, if desired. In this case, the hydroxide ion conductive material has a spherical, plate-like, or strip-like shape, and forms a conductive path throughout the catalyst layer. The hydroxide ion conductive material is not particularly limited as long as it has hydroxide ion conductivity, but is preferably LDH. The composition of LDH is not particularly limited, but is preferably a hydroxide ion conductive material having the general formula: M ２＋ １－ｘ M ３＋ ｘ (OH) ２ A ｎ－ ｘ／ｎ ・mH ２ O (in the formula, M ２＋ is at least one divalent cation, and M ３＋ is at least one trivalent cation, and A ｎ－ is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is any real number. ２＋ can be any divalent cation, but preferred examples include Ni ２＋ , Mg ２＋ , Ca ２＋ , Mn ２＋ , Fe ２＋ , Co ２＋ , Cu ２＋ , Zn ２＋ Examples include: ３＋ can be any trivalent cation, but preferred examples include Fe ３＋ , Al ３＋ , Co ３＋ , Cr ３＋ , In ３＋ In particular, in order for LDH to have both catalytic activity and hydroxide ion conductivity, M ２＋ and M ３＋ are each preferably a transition metal ion. ２＋ is Ni ２＋ , Mn ２＋ , Fe ２＋ , Co ２＋ , Cu ２＋ and the like, and particularly preferably Ni ２＋ On the other hand, the more preferred M３＋ is Fe ３＋ , Co ３＋ , Cr ３＋ and the like, and particularly preferably Fe ３＋ In this case, M ２＋ Part of it is Mg ２＋ , Ca ２＋ , Zn ２＋ may be substituted with metal ions other than transition metals, such as M ３＋ Part of it is Al ３＋ , In ３＋ The metal ions may be substituted with metal ions other than transition metals, such as A. ｎ－ can be any anion, but a preferred example is NO ３－ , CO ３ ２－ , S.O. ４ ２－ , O.H. － , Cl － , I － ,Br － , F － and more preferably NO ３ － and / or CO ３ ２－ Therefore, the above general formula is M ２＋ Ni ２＋ Including M ３＋ is Fe ３＋ Including A ｎ－ But NO ３ － and / or CO ３ ２－ It is preferable that the compound contains the compound represented by the formula (1). n is an integer of 1 or more, preferably 1 to 3. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is any real number. More specifically, m is a real number or integer of 0 or more, typically greater than 0 or 1 or more.

[0021] The hydroxide ion conductive material may be a hydroxide ion conductive composite material including hydrophilic fibers and a plurality of hydroxide ion conductive particles supported on the surface of the hydrophilic fibers in a connected state. The "a plurality of hydroxide ion conductive particles supported on the surface of the hydrophilic fibers" may be specified as hydroxide ion conductive particles supported on the surface of the hydrophilic fibers that are in contact with adjacent hydroxide ion conductive particles at at least one location. The hydrophilic fibers are not particularly limited as long as hydroxyl groups (OH groups) are coordinated or can be coordinated on the surface of the hydrophilic fibers. Hydroxide ion conductive particles (e.g., LDH platelet particles) can be synthesized and supported on the surface of such hydrophilic fibers by a coprecipitation method or the like so that they are connected to each other (e.g., so that the planes of the LDH platelet particles are parallel to each other). In other words, the use of hydrophilic fibers allows the hydroxide ion conductive particles (e.g., LDH platelet particles) to form a continuum (i.e., an aggregate of particles continuously connected to each other in the planar direction). This is presumably because, during coprecipitation or other methods, the hydroxyl groups (OH groups) coordinated on the surface of the hydrophilic fibers are converted to O-groups, with the hydrogen ions removed, by the action of a strong base such as NaOH. These groups then electrostatically attract metal ions in the raw material aqueous solution containing the constituent elements of LDH, resulting in the precipitation of LDH plate-like particles on the surface. Preferred examples of hydrophilic fibers include cellulose nanofibers, chitin nanofibers, chitosan nanofibers (CNF), and combinations thereof, with cellulose nanofibers (CNF) being more preferred. The length of the hydrophilic fibers is not particularly limited, but is preferably 0.1 to 100 μm, more preferably 0.1 to 50 μm, even more preferably 0.2 to 50 μm, particularly preferably 5 to 50 μm, and most preferably 10 to 50 μm. Depending on the size of the raw material used, hydrophilic fibers ranging from short (e.g., several hundred nanometers) to long (e.g., several tens of μm) fiber lengths are available, with longer fiber lengths being preferred. This is because a longer fiber length results in a longer hydroxide ion conduction distance, and the hydroxide ion conduction path required for the charge / discharge reaction in the charging air electrode layer 12 is not interrupted, allowing hydroxide ions to be sufficiently distributed throughout the charging air electrode layer 12.The hydroxide ion conductive particles are not particularly limited as long as they have hydroxide ion conductivity. However, as described above, they are preferably composed of layered double hydroxides (LDHs). In this case, the hydroxide ion conductive particles may be LDH plate-like particles. The LDH constituting the hydroxide ion conductive particles preferably contains at least two elements selected from the group consisting of Ni, Fe, Mg, Al, and Ti as constituent elements, and more preferably, these at least two elements include Mg and Al. By containing at least the two elements Mg and Al, better anion conductivity (e.g., hydroxide ion conductivity) can be achieved. In this case, the Al / Mg atomic ratio of the Mg-Al-LDH determined by energy dispersive X-ray spectroscopy (EDX) is preferably 0.30 to 0.55, more preferably 0.40 to 0.55. When Mg-Al-LDH having an atomic ratio within this range is used as a hydroxide ion conductive material for the air electrode of a metal-air battery, hydroxide ion conductivity can be particularly effectively improved, resulting in a further increase in the reaction rate of the charge / discharge reaction and a further decrease in the charge / discharge overvoltage. The anion between the layers of the LDH is preferably a hydroxide ion. That is, the LDH has an atomic ratio of [M. ２＋ １－ｘ M ３＋ ｘ (OH) ２ ][An －ｘ／ｎ ・zH ２ O] (M ２＋ is Mg ２＋ Including M ３＋ is Al ３＋ An －ｘ／ｎ OH － Preferably, the LDH is represented by the general formula: (x≦x≦0.4, z is any real number greater than 0). LDH can be synthesized by coprecipitation. For example, a raw material aqueous solution containing the constituent elements of LDH may be dropped into an aqueous solution containing carbonate ions and a fibrous material such as cellulose nanofibers (CNF) at a pH of 9.5 to 12, followed by hydrothermal treatment. For example, an aqueous NaOH solution may be used to adjust the pH. The crystal size, crystallinity, and / or orientation of the resulting reaction product can be controlled by subjecting it to aging treatment such as stirring, heating, or pressurization, as necessary.

[0022] When the charge air electrode layer 12 and / or the discharge air electrode layer 14 contain a hydroxide ion conductive material, the content thereof is preferably an amount that allows an ion conduction path to be formed in the charge air electrode layer 12 .

[0023] The charge air electrode layer 12 or the discharge air electrode layer 14 can be manufactured by preparing a paste containing an air electrode catalyst, a binder, and optionally, a conductive material and / or a hydroxide ion conductive material, and applying the paste to the surface of a hydroxide ion conductive separator such as an LDH separator. The paste can be prepared by adding an organic polymer (binder resin) and an organic solvent to a mixture containing the air electrode catalyst and optionally, a conductive material and / or a hydroxide ion conductive material, as appropriate, using a known kneader such as a three-roll mill or a jet mill. Preferred examples of the organic solvent include alcohols such as butyl carbitol and terpineol, and acetate ester solvents such as butyl acetate. The paste can be applied to the hydroxide ion conductive separator in a comb-like pattern by printing. While this printing can be performed using various known printing methods, screen printing is preferred. Alternatively, a clay-like mixture containing an air electrode catalyst, a binder, and optionally an electrically conductive material and / or a hydroxide ion conductive material may be prepared, rolled using a roll press or the like, and the resulting rolled sheet may be dried and then processed into a comb-like shape using a laser processing machine or the like.

[0024] Both the charge air electrode layer 12 and the discharge air electrode layer 14 are arranged in a comb-like shape. Specifically, the charge air electrode layer 12 and the discharge air electrode layer 14 each have a bus bar air electrode 12a, 14a and a plurality of air electrode fingers 12b, 14b extending from the bus bar air electrode 12a, 14a in a comb-like shape. The plurality of air electrode fingers 12b, 14b are arranged so as to be spaced apart from each other and interdigitate with each other in the same plane. Therefore, the plurality of air electrode fingers 12b, 14b are arranged so that the air electrode fingers 12b of the charge air electrode layer 12 and the air electrode fingers 14b of the discharge air electrode layer 14 alternate in the direction perpendicular to the extension direction of the air electrode fingers 12b, 14b.

[0025] The width W of each of the air electrode fingers 12b, 14b of the charge air electrode layer 12 or the discharge air electrode layer 14 is not particularly limited as long as charge and discharge are possible, but it is desirable that there be little comb-tooth-shaped segregation of zinc produced during charge and zinc oxide produced during discharge in the metal anode layer 18 provided opposite the composite air electrode layer 16 (i.e., the charge air electrode layer 12 and the discharge air electrode layer 14). From this perspective, the width W of each of the air electrode fingers 12b, 14b is preferably 8 mm or less, more preferably 0.05 to 5 mm, and even more preferably 0.1 to 4 mm. Typically, a charge reaction occurs in the anode portion of the metal anode layer 18 facing the charge air electrode layer 12, and a discharge reaction occurs in the anode portion facing the discharge air electrode layer 14. However, by setting the width W of the air electrode fingers 12b, 14b to a suitable width as described above, the charge / discharge reaction can be continued using the negative electrode active material in the negative electrode portion away from the negative electrode portion facing each of the air electrode fingers 12b, 14b.

[0026] The distance D between the air electrode fingers 12b, 14b of the charge air electrode layer 12 or the discharge air electrode layer 14 is not particularly limited as long as they are spaced apart and interdigitated with each other, but it is desirable to minimize comb-like segregation of zinc produced during charge and zinc oxide produced during discharge in the metal negative electrode layer 18. From this perspective, the distance D between adjacent air electrode fingers 12b, 14b (i.e., the distance from the side edge of the charge air electrode finger 12b to the side edge of the discharge air electrode finger 14b) is preferably 4 mm or less, more preferably 0.05 to 3 mm, and even more preferably 0.1 mm to 2 mm. By arranging the air electrode fingers 12b, 14b at such a suitable distance D, the charge and discharge reactions can be continued using the negative electrode active material in the negative electrode portion away from the negative electrode portion facing each air electrode finger 12b, 14b.

[0027] The composite air electrode layer 16 refers to a combination of a charge air electrode layer 12 and a discharge air electrode layer 14 in the same plane. The charge air electrode layer 12 and the discharge air electrode layer 14 are both comb-shaped and spaced apart from each other but interdigitated with each other in the same plane, so they are not in contact with each other. Therefore, the composite air electrode layer 16 is not a single continuous layer, but rather a combination of a pair of charge air electrode layers 12 and discharge air electrode layers 14 that are spaced apart from each other.

[0028] The metal anode layer 18 is disposed opposite the composite air cathode layer 16. The metal anode layer 18 may be selected from metal anodes of known compositions depending on the type of metal-air secondary battery. For example, in the case of a zinc-air secondary battery, the metal anode layer 18 contains at least one material selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds. That is, zinc may be contained in any form, such as zinc metal, zinc compound, or zinc alloy, as long as it has electrochemical activity suitable for the anode. Preferred examples of anode materials include zinc oxide, zinc metal, and calcium zincate, with a mixture of zinc metal and zinc oxide being more preferred. The metal anode layer 18 may be formed in a clay-like or gel-like form, or may be mixed with an electrolyte to form an anode composite. For example, a gelled anode can be easily obtained by adding an electrolyte and a thickener to the anode active material.

[0029] The metal negative electrode layer 18 is impregnated with an electrolyte (not shown). Furthermore, if the separator 20 is a liquid-permeable separator (i.e., not a liquid-impermeable hydroxide ion-conducting separator), the separator 20 and the composite air cathode layer 16 are also impregnated with the electrolyte. The electrolyte may be any of various aqueous electrolytes, particularly alkaline electrolytes, commonly used in metal-air secondary batteries such as zinc-air secondary batteries. Examples of such electrolytes include aqueous alkali metal hydroxide solutions, such as potassium hydroxide and sodium hydroxide solutions, and aqueous solutions containing zinc chloride or zinc perchlorate. Among these, aqueous alkali metal hydroxide solutions, particularly potassium hydroxide solutions, are preferred, with potassium hydroxide solutions having a concentration of 6 to 9 mol / L being more preferred. To suppress the self-dissolution of zinc alloys, a zinc compound, such as zinc oxide or zinc hydroxide, may be dissolved in the electrolyte. For example, zinc oxide may be dissolved in the electrolyte until it reaches saturation.

[0030] The separator 20 is interposed between the composite air electrode layer 16 and the metal negative electrode layer 18 so as to be in contact with the composite air electrode layer 16, and isolates the composite air electrode layer 16 from the metal negative electrode layer 18 in a manner that allows hydroxide ions to be conducted between them. The separator 20 is not particularly limited as long as it can prevent electrical contact between the composite air electrode layer 16 and the metal negative electrode layer 18 and allows hydroxide ions to move between the composite air electrode layer 16 and the metal negative electrode layer 18, and various separators can be used, such as a microporous membrane separator, a nonwoven fabric separator, a cellulose separator, or a hydroxide ion conductive separator, which will be described later.

[0031] A preferred separator 20 is a hydroxide ion-conductive separator. A hydroxide ion-conductive separator is defined as a separator that includes a hydroxide ion-conductive solid electrolyte and selectively transmits hydroxide ions solely by utilizing hydroxide ion conductivity. A preferred hydroxide ion-conductive solid electrolyte is a layered double hydroxide (LDH) and / or an LDH-like compound. Therefore, the hydroxide ion-conductive separator is preferably an LDH separator. As used herein, an "LDH separator" is defined as a separator that includes LDH and / or an LDH-like compound and selectively transmits hydroxide ions solely by utilizing the hydroxide ion conductivity of the LDH and / or LDH-like compound. As used herein, an "LDH-like compound" is a hydroxide and / or oxide with a layered crystalline structure that has hydroxide ion conductivity, even if it may not be called an LDH, and can be considered an equivalent of an LDH. However, in a broader sense, "LDH" can be interpreted to include not only LDH but also LDH-like compounds. The LDH separator is preferably composited with a porous substrate. Therefore, the LDH separator preferably further comprises a porous substrate, and is composited with the porous substrate in a form in which the pores of the porous substrate are filled with LDH and / or LDH-like compounds. That is, in a preferred LDH separator, the pores of the porous substrate are filled with LDH and / or LDH-like compounds so as to exhibit hydroxide ion conductivity and gas impermeability (and therefore function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymeric material, and it is particularly preferred that the LDH and / or LDH-like compounds are incorporated throughout the entire thickness of the porous substrate made of a polymeric material. For example, known LDH separators such as those disclosed in Patent Documents 1 to 10 can be used. The thickness of the LDH separator is preferably 5 to 100 μm, more preferably 5 to 80 μm, even more preferably 5 to 60 μm, and particularly preferably 5 to 40 μm.

[0032] When the separator 20 is a hydroxide ion conductive separator (e.g., an LDH separator), it is preferable that the charge air electrode layer 12 contains a hydroxide ion conductive material and the discharge air electrode layer 14 contains a hydroxide ion conductive material. Hydroxide ion conductive materials that can be used for the air electrode layers 12, 14 are as described above. That is, a hydroxide ion conductive separator (e.g., an LDH separator) has a dense structure that is impermeable to electrolyte, so the hydroxide ion conductive separator prevents the electrolyte from penetrating into the composite air electrode layer 16, resulting in no electrolyte present within the composite air electrode layer 16. In other words, the electrolyte cannot be used as a hydroxide ion conductive medium within the composite air electrode layer 16. Therefore, by incorporating a hydroxide ion conductive material into the charge air electrode layer 12 and the discharge air electrode layer 14, hydroxide ion conduction paths can be secured.

[0033] Furthermore, when the separator 20 is a hydroxide ion conductive separator (e.g., an LDH separator), the separator 20 is preferably provided so as to cover not only both surfaces but also the end surfaces (excluding the upper end surface) of the metal negative electrode layer 18, as shown in Figures 2 to 4. In other words, covering or enveloping the entire metal negative electrode layer 18 with a hydroxide ion conductive separator (e.g., an LDH separator) is preferable in that short circuits caused by zinc dendrites can be more effectively suppressed.

[0034] 1 to 4, a configuration in which a metal negative electrode layer 18 is sandwiched between a pair of composite air cathode layers 16 is preferred because it allows composite air cathode layers 16 to be disposed on both sides of the metal-air secondary battery 10, thereby making effective use of space. That is, according to a preferred embodiment of the present invention, the metal-air secondary battery 10 includes a pair of composite air cathode layers 16 that face each other at a distance, a separator 20 is interposed between each of the pair of composite air cathode layers 16 and the metal negative electrode layer 18, and the metal negative electrode layer 18 is sandwiched between the pair of composite air cathode layers 16 via the separator 20. However, the metal-air secondary battery 10 of the present invention is not limited to this embodiment, and may also have a configuration in which a composite air cathode layer 16 is provided on only one side of the metal negative electrode layer 18, as shown in FIGS. 6 to 9 described below.

[0035] Preferably, a charge air electrode current collector 22 is provided on the outside of the charge air electrode layer 12 so as to extend (e.g., upward or laterally) from the end of the charge air electrode layer 12, while a discharge air electrode current collector 24 is provided on the outside of the discharge air electrode layer 14 so as to extend (e.g., upward or laterally) from the end of the discharge air electrode layer 14. The air electrode current collectors 22, 24 are preferably also arranged in a comb-like shape on the comb-like portions of the air electrode layers 12, 14. The air electrode current collectors 22, 24 can be made of a general conductive porous material, preferably metal. Preferred examples of metals constituting the air electrode current collectors 22, 24 include stainless steel, titanium, nickel, brass, and copper. When made of metal, the shape of the air electrode current collectors 22, 24 is not particularly limited as long as they ensure conductivity and breathability; preferred examples include porous metal, metal mesh, and textured metal plate. Examples of porous metals include metal products with open pores, such as foam metals and sintered porous metals. Examples of metal meshes include laminated metal meshes and laminated metal meshes. As the metal plate with a concave-convex shape, a corrugated porous metal plate such as a punched metal may also be used.

[0036] Preferably, a negative electrode current collector 26 is provided, supporting the metal negative electrode layer 18 and extending (e.g., upward or sideways) from an end of the metal negative electrode layer 18. Preferred examples of the negative electrode current collector include a metal plate or mesh made of stainless steel, copper (e.g., copper punched metal), nickel, or the like, carbon paper, and oxide conductors. For example, a negative electrode plate consisting of the metal negative electrode layer 18 / negative electrode current collector 26 can be preferably produced by applying a mixture containing zinc oxide powder and / or zinc powder, and optionally a binder (e.g., polytetrafluoroethylene particles), to a copper punched metal. In this case, it is also preferable to press the dried negative electrode plate (i.e., the metal negative electrode layer 18 / negative electrode current collector 26) to prevent the electrode active material from falling off and improve electrode density.

[0037] Optionally, a charge gas diffusion electrode 28 may be provided between the charge air cathode layer 12 and the charge air cathode current collector 22, while a discharge gas diffusion electrode 30 may be provided between the discharge air cathode layer 14 and the discharge air cathode current collector 24. The gas diffusion electrodes 28, 30 are preferably arranged in a comb-like shape on the comb-like portions of the air cathode layers 12, 14. The gas diffusion electrodes 28, 30 preferably include a microporous layer (MPL) and a gas diffusion substrate, and are preferably formed on one side of the air cathode layers 12, 14 so that the microporous layer (MPL) is in contact with the air cathode layers 12, 14. The gas diffusion substrate is not particularly limited as long as it is a porous material that has electronic conductivity and can diffuse oxygen throughout the electrode, but carbon paper or a porous metal body is preferred. The thickness of the gas diffusion substrate is preferably 0.4 μm or less, more preferably 0.1 to 0.3 μm, from the viewpoint of ensuring gas diffusibility while reducing energy density. Furthermore, from the viewpoint of gas permeation rate, the porosity of the gas diffusion substrate is preferably 70% or more, more preferably 70 to 90%, and particularly preferably 75 to 85%. With this porosity, excellent gas diffusivity can be ensured and a wide reaction region can be secured. Furthermore, the large amount of pore space makes clogging with generated water less likely to occur. Porosity can be measured by mercury intrusion porosimetry. The microporous layer is not particularly limited as long as it has electronic conductivity and water repellency sufficient to prevent water generated in the air electrode reaction from penetrating the gas diffusion substrate, but preferably contains a carbon material and polytetrafluoroethylene (PTFE).

[0038] As described above, the air cathode layers 12, 14 preferably include comb-like portions, and the gas diffusion electrodes 28, 30 and / or air cathode current collectors 22, 24 are preferably arranged in the comb-like portions in a similar comb-like configuration. To easily realize such a complex structure, the metal-air secondary battery 10 preferably includes a holding member 32 having comb-like openings 32a that can accommodate the comb-like air cathode layers 12, 14, the comb-like gas diffusion electrodes 28, 30, and / or the comb-like air cathode current collectors 22, 24. That is, by using such a holding member 32, the metal-air secondary battery 10 can be easily assembled by fitting the comb-like air cathode layers 12, 14, the comb-like gas diffusion electrodes 28, 30, and / or the comb-like air cathode current collectors 22, 24 into the comb-like openings 32a. Furthermore, the holding member 32 can reliably secure each component of the assembled metal-air secondary battery 10. The material of the holding member 32 is not particularly limited as long as it is an insulating material, but is preferably an insulating elastic material such as a rubber sheet. When a holding member 32 made of an elastic material such as a rubber sheet is used, pressure can be applied to each component of the metal-air secondary battery 10 so as to tightly adhere the composite air cathode layer 16, the separator 20, and the metal anode layer 18 to one another, which has the advantage of reducing battery resistance and easily improving the performance of the metal-air secondary battery 10. In addition, the elasticity of a material such as a rubber sheet has the advantage that the comb-shaped air cathode layers 12, 14, comb-shaped gas diffusion electrodes 28, 30, and / or comb-shaped air cathode current collectors 22, 24 fitted into the holding member 32 can maintain a shape that allows gas diffusion (without excessive deformation) while maintaining suitable electronic conductive contact.

[0039] The metal-air secondary battery according to the present invention is not particularly limited to a particular type as long as it is an air secondary battery using a metal negative electrode, but a zinc-air secondary battery using a zinc electrode as the metal negative electrode is particularly preferred, and may also be a lithium-air secondary battery using a lithium electrode as the metal negative electrode.

[0040] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0041] Example 1: Example using nonwoven fabric separator A metal-air secondary battery 10 having the configuration shown in FIGS. 6 to 9 and using a nonwoven fabric separator as the separator 20 was fabricated as follows and evaluated.

[0042] (1) Preparation of a charging comb-like laminate. 50% by volume of carbon powder (Tokai Carbon Co., Ltd., Toka Black #3855) and 50% by volume of LDH powder (Ni—Fe-LDH powder prepared by coprecipitation) were mixed in a mortar to obtain a blended powder. 100 parts by weight of the blended powder were mixed with 7 parts by weight of a polytetrafluoroethylene (PTFE) aqueous dispersion (Daikin Industries, Ltd., solids content 60%) and 58 parts by weight of propylene glycol, and then kneaded. The mixture was then rolled using a roll press to obtain a 0.15 mm-thick charging air cathode layer 12. The resulting charging air cathode layer 12 and a charging gas diffusion electrode 28 (SIGRACET29BC) were stacked and pressed using a uniaxial press. The mixture was then dried at 80°C for 14 hours in a vacuum dryer. After drying, the cathode fingers 12b were processed using a laser processing machine into a comb-like shape with a width of 8 mm and a spacing of 16 mm between the cathode fingers 12b, thereby obtaining a charging comb-like laminate consisting of a charging cathode layer 12 and a charging gas diffusion electrode 28.

[0043] (2) Preparation of Discharge Comb Laminate: 100 parts by weight of platinum-supported carbon powder (manufactured by Toyo Corporation, EC-20-PTC), 7 parts by weight of a polytetrafluoroethylene (PTFE) aqueous dispersion (manufactured by Daikin Industries, Ltd., solids content 60%), and 58 parts by weight of propylene glycol were added and kneaded, and then rolled with a roll press to obtain a discharge air electrode layer 14 with a thickness of 0.15 mm. The obtained discharge air electrode layer 14 and discharge gas diffusion electrode 30 (SIGRACET29BC) were stacked, pressed with a uniaxial press, and then dried at 80 ° C. for 14 hours in a vacuum dryer. After drying, the air electrode fingers 14b were processed with a laser processing machine into comb-like shapes with a width of 8 mm and a spacing of 16 mm between the air electrode fingers 14b, to obtain a discharge comb-like laminate composed of the discharge air electrode layer 14 and the discharge gas diffusion electrode 30.

[0044] (3) Preparation of Negative Electrode Structure 100 parts by weight of ZnO powder (manufactured by Seido Chemical Industry Co., Ltd., JIS Class 1 grade, average particle size D50: 0.2 μm) was added to 50 parts by weight of metal Zn powder (manufactured by Mitsui Mining & Smelting Co., Ltd., doped with Bi and In, Bi: 1000 ppm by weight, In: 1000 ppm by weight, average particle size D50: 100 μm), and 1.7 parts by weight of a polytetrafluoroethylene (PTFE) aqueous dispersion (manufactured by Daikin Industries, Ltd., solids content 60%) was added in solids equivalent, and kneaded with propylene glycol. The resulting kneaded mixture was rolled using a roll press to obtain a negative electrode active material sheet with a thickness of 0.2 mm. This negative electrode active material sheet was placed on both sides of a tin-plated copper expand metal, pressure-bonded, and then dried in a vacuum dryer at 80 ° C. for 14 hours. The dried negative electrode sheet was cut into a 2 cm square at the portion coated with the active material, and copper foil was welded to the end of the copper expand metal to obtain a negative electrode structure composed of a zinc oxide negative electrode as the metal negative electrode layer 18 and copper expand metal and copper foil as the negative electrode current collector 26.

[0045] (4) Assembly of Evaluation Cell As shown in Fig. 5, a rubber sheet having two comb-shaped openings 32a capable of accommodating a charge comb-shaped laminate and a discharge comb-shaped laminate so that they are spaced apart and interlock with each other was prepared as the holding member 32. A charge air electrode current collector 22 (nickel mesh) having a charge comb-shaped laminate and a corresponding comb-shaped portion was fitted into the opening 32a of this rubber sheet, and a discharge air electrode current collector 24 (nickel mesh) having a discharge comb-shaped laminate and a corresponding comb-shaped portion was fitted into the other opening 32a. In the composite air electrode layer 16 thus obtained, the width W of each of the air electrode fingers 12b, 14b was 8 mm, and the separation distance D between adjacent air electrode fingers 12b, 14b was 4 mm. A nonwoven fabric (FT-7040P, manufactured by Nippon Vilene Co., Ltd.) was placed as a separator 20 on one side of the metal negative electrode layer 18, and a rubber sheet with a charging comb-like laminate and a discharging comb-like laminate embedded therein was placed on the side of the nonwoven fabric that did not contact the negative electrode structure. The resulting laminate was sandwiched between a holding jig with a sealing member tightly interlocked with the outer periphery of the nonwoven fabric, and firmly fixed with screws. This holding jig had an oxygen inlet on the comb-like laminate side and a liquid injection port on the negative electrode structure side through which an electrolyte solution could be introduced. A 5.4 M KOH aqueous solution saturated with zinc oxide was added through the liquid injection port of the resulting assembly to prepare an evaluation cell.

[0046] (5) Evaluation The charge / discharge characteristics of the evaluation cell were measured under the following conditions using an electrochemical measurement device (VMP3, manufactured by Bio-Logic Science Instruments). The results are shown in FIG. 11. Air electrode gas: water vapor saturated (25°C) oxygen (flow rate 200 cc / min) Charge / discharge current density: 4 mA / cm ２ (For the electrode area of ​​the zinc oxide negative electrode) Charge / discharge time: 60 minutes charge / 60 minutes discharge Number of cycles: 20 cycles

[0047] Example 2: Example using hydroxide ion conductive separator A metal-air secondary battery 10 having the configuration shown in FIGS. 6 to 9 and using an LDH separator as the separator 20 was fabricated as follows and evaluated.

[0048] (1) Preparation of Composite Air Electrode Layer / Separator Assembly 50% by volume of carbon powder (Tokai Carbon Co., Ltd., Toka Black #3855) and 50% by volume of LDH powder (Ni—Fe-LDH powder prepared by coprecipitation) were mixed in a mortar to obtain a blended powder. To 100 parts by weight of the blended powder, 7 parts by weight of butyral resin and 80 parts by weight of butyl carbitol were added, and the mixture was kneaded using a three-roll and centrifugal mixer (Thinky Corporation, ARE-310) to form a paste. This paste was applied by screen printing to the surface of an LDH separator (20) (a polyethylene microporous membrane in which an Mg—Al—Ti—Y-LDH-like compound was precipitated by hydrothermal synthesis within the pores and on the surface and roll-pressed, thickness: 20 μm) to form a comb-like electrode with an electrode width of 10 mm and an interelectrode distance of 20 mm, forming a charging air electrode layer 12. Thereafter, before the paste dried, a charging gas diffusion electrode 28 (SIGRACET29BC) having the same comb-like shape was placed on the charging air cathode layer 12. In this way, a charging comb-like laminate composed of the charging air cathode layer 12 and the charging gas diffusion electrode 28 was obtained.

[0049] Next, 7 parts by weight of butyral resin and 80 parts by weight of butyl carbitol were added to 100 parts by weight of platinum-supported carbon powder (EC-20-PTC, manufactured by Toyo Corporation), and the mixture was kneaded using a three-roll mill and a centrifugal mixer (ARE-310, manufactured by Thinky Corporation) to form a paste. This paste was applied by screen printing to the surface of the LDH separator 20 on which the charge air electrode layer 12 had previously been formed, with an electrode width of 10 mm and an interelectrode distance of 20 mm, so as to form a comb-like shape that was spaced apart from and interdigitated with the charge air electrode layer 12, to form the discharge air electrode layer 14. Thereafter, a discharge gas diffusion electrode 30 (SIGRACET29BC) with the same comb-like shape was placed on the discharge air electrode layer 14 before the paste dried. A weight was placed on the resulting laminate, which was then dried in a vacuum dryer at 80°C for 30 minutes to form a discharge comb-shaped laminate comprising the discharge air electrode layer 14 and the discharge gas diffusion electrode 30. In this way, a composite air electrode layer / separator assembly was obtained comprising the comb-shaped composite air electrode layer 16 and gas diffusion electrodes 28, 30 on the separator 20.

[0050] (2) Preparation of Negative Electrode Structure In the same manner as in Example 1, a negative electrode structure was prepared which was composed of a zinc oxide negative electrode as the metal negative electrode layer 18 and a copper expand metal and Cu foil as the negative electrode current collector 26 .

[0051] (3) Assembly of Evaluation Cell As shown in FIG. 5 , a rubber sheet (fluororesin) with two comb-shaped openings 32 a was prepared as the holding member 32, capable of accommodating the charge comb-shaped laminate and the discharge comb-shaped laminate in a spaced-apart, interlocking relationship, as shown in FIG. 5 . A charge air electrode current collector 22 and a discharge air electrode current collector 24 (both made of nickel mesh) with corresponding comb-shaped portions were fitted into the two openings 32 a of this rubber sheet, and the comb-shaped portions were aligned with the printed surface of the composite air electrode layer / separator assembly. The assembly was then pressed together using a uniaxial press. A negative electrode structure was then laminated on the LDH separator side of the composite air electrode layer / separator assembly. The resulting laminate was clamped between a clamping jig with a sealing member tightly interlocked with the outer periphery of the LDH separator, and firmly secured with screws. The clamping jig had an oxygen inlet on the comb-shaped laminate side and a liquid inlet on the negative electrode side for introducing electrolyte. A 5.4 M KOH aqueous solution saturated with zinc oxide was added through the liquid inlet of the assembly thus obtained to prepare an evaluation cell.

[0052] (4) Evaluation The charge-discharge characteristics of the evaluation cell were measured in the same manner as in Example 1. The results are shown in FIG.

[0053] Example 3 (Comparison) A metal-air secondary battery 10 having the configuration shown in FIG. 10 was fabricated as follows, using an LDH separator as the separator 20 and a flat, non-comb-shaped charge-discharge air electrode layer 17, and was evaluated.

[0054] (1) Preparation of Air Electrode Layer / Separator Assembly 50% by volume of platinum-supported carbon powder (manufactured by Toyo Corporation, EC-20-PTC) and 50% by volume of LDH powder (Ni-Fe-LDH powder prepared by coprecipitation) were mixed in a mortar to obtain a blended powder. 7 parts by weight of butyral resin and 80 parts by weight of butyl carbitol were added to 100 parts by weight of the blended powder, and the mixture was kneaded using a three-roll and rotation / revolution mixer (manufactured by Thinky Corporation, ARE-310) to form a paste. This paste was applied by screen printing to the surface of an LDH separator (a polyethylene microporous membrane in which an Mg-Al-Ti-Y-LDH-like compound was precipitated by hydrothermal synthesis and roll-pressed, thickness: 20 μm) to form a dual-use air electrode layer 17. Thereafter, before the paste dried, a gas diffusion electrode 31 (SIGRACET29BC) was placed on the air cathode layer 17. A weight was placed on the resulting laminate, and it was dried in a vacuum dryer at 80°C for 30 minutes to obtain an air cathode layer / separator assembly comprising a non-comb-shaped air cathode layer 17 and a gas diffusion electrode 31 on the separator 20.

[0055] (2) Preparation of Negative Electrode Structure In the same manner as in Example 1, a negative electrode structure was prepared which was composed of a zinc oxide negative electrode as the metal negative electrode layer 18 and a copper expand metal and Cu foil as the negative electrode current collector 26 .

[0056] (3) Assembly of Evaluation Cell As shown in FIG. 10 , an evaluation cell was assembled in the same manner as in Example 1, except that an air cathode layer / separator assembly was laminated on one side of the negative electrode structure and an air cathode current collector 25 that was not comb-shaped was used.

[0057] (4) Evaluation The charge / discharge characteristics of the evaluation cells were measured in the same manner as in Example 1. The results are shown in FIG. 11. As can be seen from the results shown in FIG. 11, the evaluation cells according to the present invention prepared in Examples 1 and 2 were able to suppress initial deterioration associated with catalyst oxidation and exhibited a high discharge potential compared to the evaluation cell prepared in Example 3 (Comparative Example). Furthermore, the fact that they exhibited a high discharge potential means that an increase in overvoltage was suppressed.

Claims

1. A metal-air secondary battery comprising: a comb-shaped charge air electrode layer including a charge air electrode catalyst, a conductive material, and a binder; a comb-shaped discharge air electrode layer including a discharge air electrode catalyst which is a carbon-based catalyst, and a binder, and disposed in the same plane as the comb-shaped charge air electrode layer so as to be spaced apart from and interdigitate with each other; a metal negative electrode layer disposed opposite a composite air electrode layer composed of the charge air electrode layer and the discharge air electrode layer in the same plane; an electrolyte impregnated in the metal negative electrode layer; and a separator interposed between the composite air electrode layer and the metal negative electrode layer so as to be in contact with the composite air electrode layer, and isolating the composite air electrode layer from the metal negative electrode layer in a manner capable of conducting hydroxide ions.

2. The metal-air secondary battery according to claim 1, wherein the metal-air secondary battery comprises a pair of the composite air electrode layers spaced apart and facing each other, the separator is interposed between each of the pair of composite air electrode layers and the metal negative electrode layer, and the metal negative electrode layer is sandwiched between the pair of composite air electrode layers via the separator.

3. The metal-air secondary battery according to claim 1 or 2, wherein the charging air electrode catalyst is a layered double hydroxide (LDH).

4. The metal-air secondary battery according to claim 3, wherein the LDH serving as the charging air electrode catalyst contains at least Ni and Fe as constituent elements.

5. The metal-air secondary battery according to claim 3, wherein the LDH serving as the charging air electrode catalyst contains at least Ni, Fe, V and Co as constituent elements.

6. The metal-air secondary battery according to claim 1 or 2, wherein the separator is a hydroxide ion conductive separator that isolates the composite air electrode layer from the metal negative electrode layer in a manner that allows hydroxide ion conductivity, the charging air electrode layer further contains a hydroxide ion conductive material, and the discharging air electrode layer further contains a hydroxide ion conductive material.

7. The metal-air secondary battery according to claim 6, wherein the hydroxide ion conducting separator is a layered double hydroxide (LDH) separator.

8. The metal-air secondary battery according to claim 7, wherein the LDH separator is composited with a porous substrate.

9. The metal-air secondary battery of claim 6, wherein said hydroxide ion conducting separator prevents said electrolyte from entering said composite air cathode layer, such that no electrolyte is present within said air cathode layer.

10. The metal-air secondary battery as described in claim 1 or 2, further comprising: a charge air electrode current collector provided on the outside of the charge air electrode layer and extending from an end of the charge air electrode layer; a discharge air electrode current collector provided on the outside of the discharge air electrode layer and extending from an end of the discharge air electrode layer; and a negative electrode current collector supporting the metal negative electrode layer and extending from the end of the metal negative electrode layer.

11. The metal-air secondary battery according to claim 10, further comprising: a charge gas diffusion electrode provided between the charge air electrode layer and the charge air electrode current collector; and a discharge gas diffusion electrode provided between the discharge air electrode layer and the discharge air electrode current collector.

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