Positive electrode for zinc-air secondary battery, zinc-air secondary battery, and method for manufacturing the same.

Abstract

To provide a positive electrode for zinc-air secondary batteries that has low geopolitical supply risks, is highly safe, is made of inexpensive materials, and exhibits excellent activity in oxygen reduction and oxygen evolution reactions. [Solution] A positive electrode for a zinc-air secondary battery comprising a porous support film, an oxygen evolution reaction catalyst, a precursor of an oxygen evolution reaction catalyst, or a combination thereof, and an oxygen reduction reaction catalyst, wherein the oxygen evolution reaction catalyst, the precursor of an oxygen evolution reaction catalyst, or a combination thereof comprises first carbon particles and NiFe Prussian blue analog, NiFe layered double hydroxide, or a combination thereof supported on the first carbon particles, and the oxygen reduction reaction catalyst comprises second carbon particles and iron azaphthalocyanine supported on the second carbon particles.

Description

Technical Field

[0001] The present invention relates to a positive electrode for a zinc-air secondary battery, a zinc-air secondary battery, and methods for manufacturing them.

Background Art

[0002] Towards the construction of a sustainable energy society, for example, in Japan too, the installation area of natural energy power generation such as megasolar panels is increasing.

[0003] However, in power distribution via transmission lines, in order to prevent mismatches between the power generation amount and the consumption amount, the maintenance of existing thermal power generation and nuclear power generation is prioritized, and the power supply from megasolar panels may be cut off. As a result, there is a current situation where a huge amount of electric power is being discarded unused.

[0004] To address this problem, diversity in batteries is being demanded. In particular, battery designs based on an element strategy with less geopolitical supply risk are being demanded. For example, in lithium-ion secondary batteries, the geopolitical risk of lithium itself is increasing. Regarding artificial graphite used in the negative electrode, most of it depends on some countries. Also, in the face of increasingly severe natural disasters, lithium-ion secondary batteries have issues remaining in terms of safety because they can catch fire when moisture comes into contact when the battery is damaged.

[0005] From these backgrounds, zinc-air batteries using zinc as the negative electrode, which have less geopolitical supply risk, high safety, and inexpensive materials, have attracted attention and research is being conducted. Metallic zinc not only has a small geopolitical risk, but is also inexpensive and has relatively high safety. Furthermore, it has a much larger volume capacity than lithium or sodium and its weight capacity is not small.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007] [Non-Patent Document 1] APL Energy 2023, 1, 016106 [Non-Patent Document 2] ACS Appl. Energy Mater. 2020, 3, 9040-9050 [Non-Patent Document 3] A Review of Rechargeable Zinc-Air Batteries: Recent Progress and Future Perspective, G, Nazir et al., Nano-Micro Lett. 2024, 16, 138 [Overview of the project] [Problems that the invention aims to solve]

[0008] As shown in Figure 1, a zinc-air battery uses oxygen from the air as the positive electrode and metallic zinc as the negative electrode to generate electromotive force. For example, a high-power zinc-air primary battery capable of high voltage and fast discharge has been proposed using iron azaphthalocyanine as an oxygen reduction reaction (ORR) catalyst (Patent Document 1, Non-Patent Document 1). The ORR catalyst can be made by supporting iron azaphthalocyanine on carbon conductive additive (carbon) particles such as Ketjenblack, and functions on a porous electrode (GDE) that diffuses air (gas), such as carbon paper (CP) made of carbon material, thus having low geopolitical supply risks, high safety, and low cost.

[0009] On the other hand, realizing a zinc-air secondary battery requires a cathode that combines an ORR catalyst with an Oxygen Evolution Reaction (OER) catalyst that oxidizes water molecules to generate oxygen. However, a cathode for zinc-air secondary batteries that has low geopolitical supply risks, is highly safe, is made of inexpensive materials, and exhibits excellent activity in both oxygen reduction and oxygen evolution reactions has yet to be proposed.

[0010] Therefore, there is a need for a positive electrode for zinc-air secondary batteries that has low geopolitical supply risks, is highly safe, is made of inexpensive materials, and exhibits excellent activity in both oxygen reduction and oxygen evolution reactions. [Means for solving the problem]

[0011] The gist of this invention is as follows: (1) A porous support film, an oxygen evolution reaction catalyst, a precursor of an oxygen evolution reaction catalyst, or a combination thereof, and an oxygen reduction reaction catalyst, The oxygen evolution catalyst, the precursor of the oxygen evolution catalyst, or a combination thereof comprises first carbon particles, and a NiFe Prussian blue analog, a NiFe layered double hydroxide, or a combination thereof supported on the first carbon particles. The oxygen reduction reaction catalyst comprises second carbon particles and iron azaphthalocyanine supported on the second carbon particles. Positive electrode for zinc-air rechargeable batteries. (2) The positive electrode according to (1) above, wherein the oxygen evolution catalyst, the precursor of the oxygen evolution catalyst, or a combination thereof and the oxygen reduction catalyst are each arranged in layers, and a laminate of the layered oxygen evolution catalyst, the precursor of the oxygen evolution catalyst, or a combination thereof and the layered oxygen reduction catalyst is located on the porous support film. (3) The positive electrode according to (1) above, wherein the oxygen evolution reaction catalyst, the precursor of the oxygen evolution reaction catalyst, or a combination thereof, and the oxygen reduction reaction catalyst are a mixture, and the mixture is located on the porous support film. (4) The amount of NiFe Prussian blue analog, NiFe layered double hydroxide, or combination thereof supported on the first carbon particles per unit area of ​​the positive electrode is 0.001 μmol / cm² 2 More than 1000μmol / cm 2 The positive electrode is one of the following, as described in (1) to (3) above. (5) The amount of iron azaphthalocyanine supported on the second carbon particles per unit area of ​​the positive electrode is 10 μg / cm³2 The above 5.0 × 10 3 μg / cm 2 The positive electrode is one of the following, as described in (1) to (4) above. (6) A zinc-air secondary battery including the positive electrode described in any of (1) to (5) above. (7) Charge / discharge voltage at a constant current density (vs. Zn / Zn 2+ A zinc-air secondary battery as described in (6) above, wherein the difference between the voltages is 1.0V or less. (8) Charging voltage at a constant current density (vs. Zn / Zn 2+ A zinc-air secondary battery as described in (6) or (7) above, wherein the voltage is 2.2V or less. (9) Prepare a first dispersion by dispersing a NiFe Prussian blue analog in a first solvent. Prepare a solution by dissolving iron azaphthalocyanine in a second solvent. Mixing the first dispersion, the solution, and the carbon particles, To obtain a precursor liquid containing the NiFe Prussian blue analog as a precursor of an oxygen evolution reaction catalyst supported on carbon particles, and the iron azaphthalocyanine as an oxygen reduction reaction catalyst supported on carbon particles, and The precursor solution is applied to the porous support film, and the first and second solvents are removed to form a mixture of the oxygen evolution catalyst precursor and the oxygen reduction catalyst on the porous support film. A method for manufacturing a positive electrode for a zinc-air secondary battery, including the method described above. (10) A method for producing a positive electrode for a zinc-air secondary battery according to (9) above, wherein forming the mixture comprises hydrolyzing a precursor of the oxygen evolution reaction catalyst to form an oxygen evolution reaction catalyst, thereby forming a mixed catalyst of the oxygen evolution reaction catalyst and the oxygen reduction reaction catalyst. (11) Prepare a first dispersion by dispersing a NiFe Prussian blue analog in a first solvent. Mixing the first carbon particles into the first dispersion, The objective is to obtain a precursor liquid for an oxygen evolution reaction catalyst in which the NiFe Prussian blue analog is supported on the first carbon particles, and The first solvent is removed from the precursor liquid to form a precursor for an oxygen evolution reaction catalyst in which the NiFe Prussian blue analog is supported on the first carbon particles. Prepare a solution by dissolving iron azaphthalocyanine in a second solvent. To prepare a second dispersion by dispersing second carbon particles in the aforementioned solution, and The second solvent is removed from the second dispersion to form an oxygen reduction reaction catalyst on which the iron azaphthalocyanine is supported on the second carbon particles. Combining a porous support film, a precursor of the oxygen evolution reaction catalyst, and an oxygen reduction reaction catalyst. A method for manufacturing a positive electrode for a zinc-air secondary battery, including the method described above. (12) Forming the precursor of the oxygen evolution reaction catalyst, The precursor solution is applied onto the porous support film, and the first solvent is removed to form a layer of the oxygen evolution reaction catalyst precursor on the porous support film. Includes, Forming the oxygen reduction reaction catalyst is The second dispersion is applied onto the precursor layer, and the second solvent is removed to form an oxygen reduction reaction catalyst layer on the precursor layer. including, A method for manufacturing a positive electrode for a zinc-air secondary battery as described in (11) above. (13) Forming the oxygen reduction reaction catalyst The second dispersion is applied onto the porous support film, and the second solvent is removed to form an oxygen reduction reaction catalyst layer on the porous support film. Includes, Forming a precursor for the oxygen evolution reaction catalyst The precursor solution is applied onto the oxygen reduction reaction catalyst layer, and the first solvent is removed to form a layer of the oxygen evolution reaction catalyst precursor on the oxygen reduction reaction catalyst layer. including, A method for manufacturing a positive electrode for a zinc-air secondary battery as described in (11) above. (14) A method for producing a positive electrode for a zinc-air secondary battery according to any one of (11) to (13) above, comprising hydrolyzing a precursor of the oxygen evolution reaction catalyst to form the oxygen evolution reaction catalyst. (15) A method for manufacturing a zinc-air secondary battery, comprising a positive electrode, an electrolyte, and a negative electrode manufactured by any of the manufacturing methods described in (9) to (14) above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a positive electrode for a zinc-air secondary battery that has low geopolitical supply risks, is highly safe, is composed of inexpensive materials, and exhibits excellent activity in oxygen evolution catalytic reactions and oxygen reduction catalytic reactions. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic diagram showing the configuration of one embodiment of the zinc-air secondary battery according to the present invention. [Figure 2] Figure 2 is a schematic diagram showing the stacking order of the Ni mesh, carbon paper (CP), ORR (oxygen reduction reaction catalyst), and OER (oxygen evolution reaction catalyst, precursor of oxygen evolution reaction catalyst, or combination thereof) of the positive electrode prepared in the example, as well as the stacking order of the Ni mesh, carbon paper (CP), and ORR&OER mixed layer (catalyst mixed layer) of the positive electrode prepared in the example. [Figure 3] Figure 3 shows graphs of the charge-discharge characteristics of zinc-air secondary batteries with varying stacking orders of the positive electrode Ni mesh, carbon paper (CP), ORR catalyst, and OER catalyst, OER catalyst precursor, or combinations thereof, as well as zinc-air secondary batteries containing the positive electrode Ni mesh, carbon paper (CP), and ORR&OER mixed layer (catalyst mixed layer) as prepared in the examples. [Figure 4] Figure 4 shows a graph of the charge and discharge characteristics of a zinc-air secondary battery when the auxiliary electrolytes prepared in the example were zinc chloride and zinc acetate. [Figure 5] Figure 5 is a graph showing the charge-discharge characteristics of zinc-air secondary batteries depending on the type of auxiliary electrolyte used in the examples. [Figure 6] Figure 6 is a graph showing the charge-discharge characteristics of the zinc-air secondary battery at different concentrations of the auxiliary electrolyte prepared in the example. [Figure 7] Figure 7 shows graphs of the charge-discharge characteristics of the zinc-air secondary battery prepared in the example, measured at constant current densities of 10 mA / cm² and 20 mA / cm². [Figure 8] Figure 8 is a schematic diagram illustrating the method for forming the catalyst layer. [Modes for carrying out the invention]

[0014] This disclosure relates to a positive electrode for a zinc-air secondary battery (hereinafter also referred to as "this positive electrode") comprising a porous support film, an OER catalyst, a precursor of the OER catalyst, or a combination thereof, and an oxygen reduction reaction catalyst, wherein the OER catalyst, the precursor of the OER catalyst, or a combination thereof comprises first carbon particles and a NiFe Prussian blue analog, NiFe layered double hydroxide, or a combination thereof supported on the first carbon particles, and the oxygen reduction reaction catalyst comprises second carbon particles and iron azaphthalocyanine supported on the second carbon particles.

[0015] In this cathode, catalysts having separate functions, such as an OER catalyst, an OER catalyst precursor, or a combination thereof (hereinafter also referred to as OER catalyst etc.), and an ORR catalyst, are combined and contained within a single cathode, functioning as a bifunctional electrode. The combined OER catalyst etc. and the ORR catalyst exist independently within the cathode. In this application, OER means oxygen evolution reaction or oxygen evolution reaction catalyst, and ORR means oxygen reduction reaction or oxygen reduction reaction catalyst.

[0016] This cathode contains a composite of an OER catalyst and an ORR catalyst, each possessing superior performance. This cathode exhibits higher performance than an OER / ORR bifunctional catalyst, which is a single catalyst possessing both OER and ORR catalytic activity. Furthermore, in the manufacturing of this cathode, the OER catalyst and the ORR catalyst can be manufactured separately and then composited to create a catalyst with the desired characteristics, resulting in excellent manufacturing efficiency. Manufacturing the OER catalyst and the ORR catalyst separately means manufacturing separate catalysts that exhibit OER catalytic function and ORR catalytic function, respectively, although they may be manufactured simultaneously.

[0017] ORR requires porous electrodes that function at the air / electrolyte solution interface to take in oxygen from the air. Although ORR competes with hydrogen generation, using metal electrodes such as stainless steel mesh as porous electrodes would result in water repellency and electrolyte leakage. Therefore, water-repellent carbon-based porous electrodes are used.

[0018] On the other hand, conventional OER catalysts have the problem of carbon corrosion due to charging voltage, so catalyst particles are grown and attached directly to the surface of metal electrodes such as stainless steel mesh.

[0019] Therefore, conventionally, it has been difficult to develop electrodes equipped with catalysts that exhibit excellent activity in both ORR and OER, and currently, ORR catalysts and OER catalysts are developed independently.

[0020] This cathode has a composite layer of an OER catalyst and an ORR catalyst on the same porous support film (porous electrode film), and can have electrode characteristics that maintain the respective functions of both the OER catalyst and the ORR catalyst.

[0021] This cathode is composed of materials that are less prone to geopolitical risks, are highly safe, and inexpensive. Furthermore, because this cathode combines highly active OER catalysts and ORR catalysts, it exhibits excellent OER and ORR catalytic activity. This cathode also has a low OER overpotential, which helps suppress carbon corrosion.

[0022] The porous support membrane included in this positive electrode is a membrane that functions as an electrode for diffusing the interfacial gas of the air / electrolyte solution. The porous support membrane is not particularly limited as long as it possesses electron conductivity, high gas diffusivity, and high corrosion resistance. Examples of porous support membranes include carbon-based porous materials such as carbon paper, carbon cloth, and carbon nanotube membranes, as well as nickel foam, and lightweight, corrosion-resistant carbon materials are preferably used. The porous support membrane may also be made by compounding carbon fibers with carbon paper.

[0023] An OER catalyst, an OER catalyst precursor, or a combination thereof (OER catalyst, etc.) comprises first carbon particles and a NiFe Prussian blue analog, a NiFe layered double hydroxide, or a combination thereof supported on the first carbon particles. The OER catalyst comprises a NiFe layered double hydroxide supported on the first carbon particles. The OER catalyst precursor comprises a NiFe Prussian blue analog supported on the first carbon particles.

[0024] NiFe layered double hydroxides are obtained by hydrolyzing NiFe Prussian blue analogs (hereinafter also referred to as NiFePBA). NiFe layered double hydroxides supported on first carbon particles can be obtained by mixing the first carbon particles into a dispersion of NiFePBA in a first solvent, and then removing the first solvent to hydrolyze the NiFePBA.

[0025] During the fabrication of this positive electrode, NiFePBA may be supported on the first carbon particles, or NiFe layered double hydroxide obtained by hydrolysis of NiFePBA may be supported on the first carbon particles, or a combination thereof may be supported on the first carbon particles. When this positive electrode contains NiFePBA supported on the first carbon particles, during the fabrication of the zinc-air secondary battery, the NiFePBA is hydrolyzed by contact with the alkaline electrolyte solution such as KOH in the zinc-air secondary battery to become NiFe layered double hydroxide.

[0026] The NiFe layered double hydroxide is also called NiFe-LDH (NiFe-layered double hydroxide). NiFe-LDH has a structure in which octahedral basic layers of hydroxide and intermediate layers composed of interlayer water and anions are alternately stacked. For example, Ni x Fe 1-x (OH) y (where x is greater than 0 and less than 1, and y is not particularly limited, for example, in the range of 2 to 3) is represented by the chemical formula.

[0027] NiFePBA can be in the form of particles. The NiFePBA particles can be nanoparticles having an average diameter of, for example, 1 nm or more and 1000 nm or less, preferably 1 nm or more and 200 nm or less. The average diameter of the NiFePBA particles can be measured by a transmission electron microscope (TEM).

[0028] NiFePBA enables uniform arrangement and composition ratio control at the elemental levels of nickel and iron. The composition of NiFePBA can be Ni x Fe 1-x [Fe(CN)6] 0.67 (where x is greater than 0 and less than 1). x is preferably 0.4 or more and 0.8 or less, more preferably 0.5 or more and 0.7 or less. When x is within the above preferred range, the layered double hydroxide can be obtained more favorably.

[0029] The NiFePBA particles are chemically surface-modified. Thereby, they can be dispersed in a first solvent such as water. By binding a protective molecule or ion to the elements exposed on the surface of the NiFePBA particles, the surface of the NiFePBA particles is charged within a predetermined range, and the NiFePBA particles can be substantially independently dispersed without aggregating due to electrostatic repulsion.

[0030] NiFePBA particles are supported on carbon particles using a dispersion that exists in a state close to primary particles, where aggregation is suppressed in a first solvent through prior surface modification. The NiFePBA particles do not need to be completely primary particles; it is sufficient if each particle is distinguishable in an electron microscope image. A general method can be used to obtain a dispersion in which NiFePBA particles are dispersed in a state close to primary particles, and there are no particular limitations. For example, if ferrocyanate ions or ferricyanate ions are bonded to the water (OH2) coordinated to the metal on the surface of the NiFePBA particles via a cyanide ligand, the surface charge of the NiFePBA particles becomes negative (they acquire a negative zeta potential), and they can be well independently dispersed in water, alcohol, or a combination thereof due to electrostatic repulsion between the particles.

[0031] The first carbon particles are conductive carbon materials, and may consist of one type of carbon material or contain two or more types of carbon materials. Examples of the first carbon particles include carbon black, carbon nanotubes, graphene, fullerene, carbon fiber, graphite, amorphous carbon, activated carbon, mesocarbon microbeads, microcapsule carbon, carbon nanoforms, and carbon nanohorns. Among these, carbon black, carbon nanotubes, graphene, fullerene, and carbon fiber are preferred, carbon black and carbon nanotubes are more preferred, and carbon black is even more preferred. Carbon black is relatively inexpensive and can produce a positive electrode that exhibits a low OER overpotential, so the positive electrode structure can be stably maintained even if vigorous oxygen evolution occurs due to the OER catalyst.

[0032] Examples of carbon black include Ketjenblack, Furnaceblack, Channelblack, Acetyleneblack, and Thermalblack.

[0033] From the viewpoints of cost, granulation and compounding with binder resin (particle size control, etc.), and environmental and safety considerations, it is preferable to use carbon black that is uniformly dispersed in water. Dispersants may be added to the water. Examples of carbon black include SuperP (MTI Japan) and carbon black (Sigma Aldrich).

[0034] As for the carbon black, Ketjenblack with a large specific surface area and a hollow structure is preferred. Regarding the properties of the Ketjenblack, Ketjenblack dispersed in water containing a dispersant with an average particle size (secondary particle diameter) of 10 nm to 600 nm is preferred, and Ketjenblack with an average particle size of 20 nm to 400 nm is more preferred. An example of Ketjenblack is ECP-600JD (Lion Specialty Chemicals Co., Ltd.).

[0035] Examples of carbon nanotubes include single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. Single-walled carbon nanotubes are preferred because they have excellent conductivity, and when bundled, they become long and have a width that allows highly active single-nanometer-sized catalyst nanoparticles to adhere to them.

[0036] The first carbon particles may have functional groups such as hydroxyl groups, carboxyl groups, nitrogen-containing groups, silicon-containing groups, phosphorus-containing groups such as phosphate groups, and sulfur-containing groups such as sulfonic acid groups, and preferably have carboxyl groups. Having carboxyl groups makes it easier for NiFe Prussian blue analogs, NiFe layered double hydroxides, or combinations thereof to be adsorbed onto the surface of the first carbon particles, thereby improving the OER catalytic activity and the durability of the cathode.

[0037] The carboxyl group content that may be contained in the first carbon particles is preferably 1% to 20% by mass, more preferably 5% to 15% by mass, and even more preferably 8% to 10% by mass, based on 100% by mass of the first carbon particles. By keeping the carboxyl group content within the above preferred range, it is possible to further improve the OER catalytic activity and the durability of the cathode while suppressing the manufacturing cost of the catalyst. The carboxyl group content can be measured by elemental analysis or X-ray photoelectron spectroscopy, etc.

[0038] The first carbon particle may contain heteroatoms. Examples of heteroatoms include oxygen atoms, nitrogen atoms, phosphorus atoms, sulfur atoms, silicon atoms, etc. The first carbon particle may contain one or more types of heteroatoms. The first carbon particle may be oxidized, hydroxylated, nitrided, phosphated, sulfurized, or silicified.

[0039] The specific surface area of ​​the first carbon particle is 0.8 m². 2 Preferably 1.0 m 2 More preferably 1.1m / g or more, 2 More preferably 1.5m / g or more. 2 More preferably 2.0m / g or more. 2 A value of 1 / g or more is even more preferable. Having the above-mentioned preferred specific surface area of ​​the first carbon particles makes it easier to prevent catalyst aggregation and further improves oxygen evolution catalytic activity. The upper limit of the specific surface area is not particularly limited; for example, 2000 m². 2 / g is also acceptable. Specific surface area can be measured using a specific surface area measuring device employing the nitrogen adsorption BET method.

[0040] The average particle size of the first carbon particles is not particularly limited and may have an average particle size (diameter) of, for example, 5 nm to 1000 μm. The average particle size of the first carbon particles can be measured by scanning electron microscope (SEM) or transmission electron microscope (TEM).

[0041] The NiFe layered double hydroxide supported on the first carbon particles may have an average diameter equal to or smaller than that of the NiFe Prussian blue analog. The average diameter of the NiFe Prussian blue analog and / or the NiFe layered double hydroxide can be measured by transmission electron microscopy (TEM). Having the average diameter of the NiFe Prussian blue analog and / or the NiFe layered double hydroxide within the above preferred range allows for a further reduction in the OER overpotential.

[0042] The OER catalyst may contain a binder. Including a binder in the OER catalyst can improve the durability of the cathode. The binder contained in the OER catalyst may be a water-soluble binder, preferably an ion-conducting binder, such as Nafion®.

[0043] The OER catalyst, the precursor of the OER catalyst, or a combination thereof (such as the OER catalyst) and the ORR catalyst may each be in a layered form, or the layered OER catalyst and layered ORR catalyst may be positioned on a porous support film, and the cathode may be a laminate including a porous support film, a layer of the OER catalyst, and a layer of the ORR catalyst. The cathode may also include a metal mesh such as a Ni mesh as a current collector.

[0044] The thickness of the OER catalyst layer and the ORR catalyst layer may be, for example, 0.01 μm or more and 3000 μm or less.

[0045] The stacking order of the laminate of the porous support film, the ORR catalyst layer, and the OER catalyst layer is not particularly limited. For example, the laminate may consist of the porous support film, the ORR catalyst layer, and the OER catalyst layer from bottom to top, or the porous support film, the OER catalyst layer, and the ORR catalyst layer from bottom to top, or the porous support film may be located between the ORR catalyst layer and the OER catalyst layer.

[0046] The number of layers in the laminate, such as the porous support film, the ORR catalyst layer, and the OER catalyst layer, can be one or multiple.

[0047] The laminate of the porous support film, the ORR catalyst layer, and the OER catalyst layer may include other layers between each layer or at any position in the outermost layer, as long as they do not obstruct air and electrolyte. The laminate of the porous support film, the ORR catalyst layer, and the OER catalyst layer may have a diffusion layer between the ORR catalyst layer and the OER catalyst layer in which the components of the ORR catalyst and the components of the OER catalyst are diffused.

[0048] The layers of the OER catalyst and the ORR catalyst may not be in a stacked structure, but rather form a single catalyst layer by combining each layer in the same plane. That is, a single catalyst layer containing the OER catalyst and the ORR catalyst, combined in the same plane, may be located on a porous support film.

[0049] The OER catalyst and the ORR catalyst may be a mixture, and the mixture may be located on a porous support film. In other words, a catalyst mixture layer of the OER catalyst and the ORR catalyst may be located on a porous support film.

[0050] The OER catalyst and ORR catalyst may be the laminate, the catalyst layer of the single layer, the catalyst mixed layer, or a combination thereof. Figure 2 shows the lamination sequence of one embodiment of this positive electrode, which includes a Ni mesh as a current collector and carbon paper (CP) as a porous support film. Figure 2-A is an example of Ni mesh / CP / ORR / OER, Figure 2-B is an example of Ni mesh / ORR / CP / OER, Figure 2-C is an example of Ni mesh / CP / OER / ORR, and Figure 2-D is an example of a Ni mesh / CP / ORR&OER mixed layer. This positive electrode can function well in any of the configurations illustrated in Figure 2, and may function even better when it includes the catalyst mixed layer shown in Figure 2-D. In Figure 2, OER means an OER catalyst, an OER catalyst precursor, or a combination thereof.

[0051] In this cathode, NiFe Prussian blue analog, NiFe layered double hydroxide, or a combination thereof is supported on first carbon particles, however, not all of the NiFe Prussian blue analog, NiFe layered double hydroxide, or a combination thereof is supported on the first carbon particles. The amount of NiFe Prussian blue analog, NiFe layered double hydroxide, or a combination thereof supported on the first carbon particles per unit area of ​​the cathode may be small, preferably 0.001 μmol / cm³. 2 More than 1000μmol / cm 2 More preferably, 0.01 μmol / cm³ 2 More than 500μmol / cm 2 More preferably, 0.1 μmol / cm³ 2 More than 100μmol / cm 2 The following is true: The preferred loading amount described above reduces interaction with the combined ORR catalyst, suppressing interference and allowing the ORR catalyst to perform more effectively. By minimizing the loading amount of the OER catalyst in this cathode, an excellent catalyst turnover rate can be achieved. Furthermore, the reduced loading amount of the OER catalyst reduces the amount of material used, thus minimizing geopolitical risks.

[0052] The ORR catalyst comprises a second carbon particle and iron azaphthalocyanine supported on the second carbon particle. The iron azaphthalocyanine molecules can be molecularly adsorbed onto the surface of the second carbon particle. By molecularly adsorbing the iron azaphthalocyanine molecules onto the surface of the second carbon particle, a molecular film of iron azaphthalocyanine can be formed on the surface of the first carbon particle.

[0053] Iron azaphthalocyanine is preferably represented by the following formula (1): [ka] It is a metal complex represented by, In formula (1), X1 to X8 are each independently a hydrogen atom or a halogen atom, D1, D3, D5, and D7 are each independently a nitrogen atom or a carbon atom, at least one of D1, D3, D5, and D7 is a carbon atom to which a hydrogen atom or a halogen atom is bonded, and M is an iron atom.

[0054] The metal complex of formula (1) exhibits excellent oxygen reduction catalytic activity and high solubility in solvents. Therefore, its affinity for the second carbon particle is improved, and the metal complex is easily adsorbed uniformly onto the surface of the second carbon particle.

[0055] A specific example of a metal complex of formula (1) is the metal complex of formula (1-1). However, specific examples of metal complexes of formula (1) are not limited to this example.

[0056] [ka] In equation (1-1), M is an iron atom.

[0057] The metal complex of formula (1) may have isomers, such as the metal complex of formula (1-2). [ka] In formula (1-2), X1 to X8 are each independently a hydrogen atom or a halogen atom, D1, D3, D5, and D7 are each a nitrogen atom or a carbon atom, at least one of D1, D3, D5, and D7 is a carbon atom to which a hydrogen atom or a halogen atom is bonded, and M is an iron atom.

[0058] While metal complexes are a concept that includes isomers as shown in formula (1-2) above, the isomers of metal complexes are not limited to those shown in formula (1-2). For example, in formula (1-2), at least one selected from each of the cyclic structures containing D1, D3, D5, and D7 may have the position of the nitrogen atom swapped with any of the positions of D1, D3, D5, and D7 within the same cyclic structure.

[0059] In metal complexes, four nitrogen atoms coordinated around the iron atom form part of the pyridine ring structure, and an FeN4 structure containing these four nitrogen atoms and the iron atom is locally formed within the molecule of the metal complex. Because the metal complex has an FeN4 structure, it can exhibit good oxygen reduction catalytic activity.

[0060] The second carbon particles are a conductive carbon material, similar to the first carbon particles, and may consist of one type of carbon material or contain two or more types of carbon materials. The type of carbon material contained in the second carbon particles, the average diameter of the second carbon particles, and the method for measuring the average diameter can be the same as those for the first carbon particles. The second carbon particles may be the same carbon particles as the first carbon particles or different carbon particles. The first and second carbon particles may be the same carbon particles without distinction. The first and second carbon particles may share a single core particle. The OER catalyst and the ORR catalyst may be supported on one of the carbon particles. For example, if the OER catalyst and the ORR catalyst are separate layered layers, the first and second carbon particles are contained in separate layers. If the OER catalyst and the ORR catalyst are a mixed catalyst layer, the first and second carbon particles may exist indistinguishably within the mixed catalyst layer. Even if the OER catalyst and the ORR catalyst are in separate layers, in the diffusion layer at the interface between the OER catalyst layer and the ORR catalyst layer, the first carbon particles and the second carbon particles may exist indistinguishably within the diffusion layer.

[0061] The second carbon particles may have functional groups such as hydroxyl groups, carboxyl groups, nitrogen-containing groups, silicon-containing groups, phosphorus-containing groups such as phosphate groups, and sulfur-containing groups such as sulfonic acid groups, and preferably have carboxyl groups. Having carboxyl groups makes it easier for iron azaphthalocyanine to adsorb onto the surface of the second carbon particles, which can further improve the ORR catalytic activity and the durability of the cathode.

[0062] The carboxyl group content that may be contained in the second carbon particles is preferably 1% to 20% by mass, more preferably 5% to 15% by mass, and even more preferably 8% to 10% by mass, based on 100% by mass of the second carbon particles. By keeping the carboxyl group content within the above preferred range, it is possible to further improve the ORR catalytic activity and the durability of the cathode while suppressing the manufacturing cost of the catalyst. The carboxyl group content can be measured by elemental analysis or X-ray photoelectron spectroscopy, etc.

[0063] The specific surface area of ​​the second carbon particle is 0.8 m². 2 Preferably 1.0 m 2 More preferably 1.1m / g or more, 2 More preferably 1.5m / g or more. 2 More preferably 2.0m / g or more. 2 A value of 1 / g or more is even more preferable. Having the above-mentioned preferred specific surface area of ​​the second carbon particles makes it easier to prevent catalyst aggregation and further improves the ORR catalytic performance. The upper limit of the specific surface area is not particularly limited; for example, 2000 m². 2 / g is also acceptable. Specific surface area can be measured using a specific surface area measuring device employing the nitrogen adsorption BET method.

[0064] The ORR catalyst may contain a binder. The inclusion of a binder in the ORR catalyst can improve the durability of the cathode. The binder contained in the ORR catalyst can be a water-soluble binder, preferably an ion-conducting binder, such as Nafion®.

[0065] The amount of iron azaphthalocyanine supported on the second carbon particle per unit area of ​​the positive electrode may be small, preferably 10 μg / cm³. 2 The above 5.0 × 10 3 μg / cm 2 below Therefore, the above preferred loading amount reduces interaction with the composite OER catalyst, thereby suppressing interference and allowing the OER catalyst to perform more effectively. The ORR catalyst in this cathode can exhibit excellent catalytic turnover speed by keeping the loading amount to a minimum. In addition, the small loading amount of the OER catalyst reduces the amount of material used, thus lowering geopolitical risks. The loading amount of iron azaphthalocyanine on the second carbon particle is 0.45 wt% or more relative to the carbon mass of the carbon particle, and is 2.3 × 10⁻⁶ 2 wt% or less is also acceptable.

[0066] In both the OER catalyst and the ORR catalyst, having the supported amount within the preferred range further reduces interference between them, making it easier for each to exhibit its respective performance.

[0067] This cathode can be manufactured using a simple method, as described later, enabling low-cost production and making it suitable for industrial applications.

[0068] This disclosure also applies to a zinc-air secondary battery (also known as the zinc-air secondary battery) comprising the positive electrode. The zinc-air secondary battery may include the positive electrode, electrolyte, and negative electrode, which may contain an OER catalyst and an ORR catalyst. The zinc-air secondary battery may have a separator between the positive electrode and the negative electrode.

[0069] Examples of negative electrodes include metallic zinc, conductive zinc oxide, zinc-containing alloys, and composite materials such as nickel foam or carbon electrodes supporting copper nanowires. Preferably, zinc-plated nickel foam or copper nanowire composite materials can be used.

[0070] The electrolyte can be an aqueous electrolyte containing zinc ions. Examples of zinc-containing aqueous electrolytes include aqueous solutions obtained by dissolving an alkali such as potassium hydroxide or sodium hydroxide in an aqueous solution of zinc-containing material such as zinc chloride, zinc nitrate, zinc acetate, zinc trifluoromethanesulfonate, zinc methanesulfonate, zinc oxide, zinc perchlorate, zinc tetrafluoroborate, or zinc hexanefluorophosphate as an auxiliary electrolyte. The electrolyte may be used alone or in combination of two or more types.

[0071] If the cathode contains an OER catalyst precursor that has not undergone hydrolysis treatment, it is necessary to hydrolyze the precursor in the electrolyte used when manufacturing the zinc-air secondary battery. Therefore, an alkaline aqueous solution such as potassium hydroxide aqueous solution or sodium hydroxide aqueous solution is used as the electrolyte.

[0072] A separator is a component that separates the positive electrode and the negative electrode, holds the electrolyte, and ensures ionic conductivity between the positive and negative electrodes. Examples of separators include polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, cellulose, cellulose acetate, hydroxyalkylcellulose, carboxymethylcellulose, polyvinyl alcohol, cellophane, polystyrene, polyacrylonitrile, polyacrylamide, polyvinyl chloride, polyamide, vinylon, polymers having micropores such as poly(meth)acrylic acid, gel compounds, ion exchange membranes, cyclized polymers, polymers containing poly(meth)acrylates, polymers containing sulfonates, polymers containing quaternary ammonium salts, and polymers containing quaternary phosphonium salts.

[0073] This zinc-air rechargeable battery has a power output of 10 mA / cm². 2 In terms of current density, the discharge voltage (vs. Zn / Zn) is preferably 1.16V or higher, more preferably 1.18V or higher, and even more preferably 1.20V or higher. 2+ It also shows 20mA / cm². 2 At a constant current density, the discharge voltage (vs. Zn / Zn) is preferably 1.14V or higher, more preferably 1.16V or higher, and even more preferably 1.18V or higher. 2+ ) indicates.

[0074] This zinc-air secondary battery allows the ORR catalyst and OER catalyst to function within the same positive electrode. Conventionally, during OER operation (charging), the carbon contained in the positive electrode can oxidize, a problem known as carbon corrosion. The charging voltage during OER operation is Zn / Zn 2+ While carbon corrosion can become significant if the voltage significantly exceeds 2V, this zinc-air secondary battery can suppress carbon corrosion because the overvoltage of the OER catalyst, i.e., the charging voltage, is low. This zinc-air secondary battery has a charging voltage of 10mA / cm². 2 or 20mA / cm 2 At a constant current density, the charging voltage (vs.Zn / Zn) is preferably 2.2V or less, more preferably 2.1V or less, even more preferably 2.05V or less, and even more preferably 2.0V or less. 2+ This demonstrates the following. By having the above-mentioned preferred charging voltage, this zinc-air secondary battery can suppress the corrosion of carbon in the positive electrode (carbon corrosion). This makes it possible to suppress the corrosion of carbon that may be contained in the porous support film, and the carbon particles contained in the OER catalyst and ORR catalyst.

[0075] The zinc-air secondary battery containing this positive electrode exhibits a small charge-discharge voltage difference due to the high activity of both the OER catalyst and the ORR catalyst. The zinc-air secondary battery containing this positive electrode exhibits a voltage difference of 10 mA / cm². 2 or 20mA / cm 2 At a constant current density, the charge-discharge voltage difference is preferably 1.0V or less, more preferably 0.95V or less, even more preferably 0.90V or less, even more preferably 0.85V or less, even more preferably 0.80V or less, and even more preferably 0.75V or less. Generally, the smaller the voltage difference, the higher the secondary battery performance, and the voltage difference increases as the current increases, but the zinc-air secondary battery including this positive electrode has a charge-discharge voltage difference of 10mA / cm². 2 Preferably 20 mA / cm² 2 Even at a constant current density, the above-mentioned preferred charge-discharge voltage difference can be achieved.

[0076] While carbon paper is resistant to carbon corrosion, carbon black is relatively susceptible. However, the OER catalyst in this cathode is highly active, resulting in a low OER overpotential, which can be kept below a potential that suppresses carbon black corrosion. Therefore, in zinc-air secondary batteries containing this cathode, carbon corrosion can be suppressed, thereby inhibiting electrolyte degradation and extending battery life.

[0077] Zinc-air rechargeable batteries have a capacity, i.e., a current density (mA / cm²). 2 Carbon corrosion occurs when the charging voltage changes rapidly and significantly as the temperature rises, but the charging voltage of this zinc-air secondary battery remains almost constant regardless of the capacity, thereby suppressing carbon corrosion.

[0078] This disclosure also, Prepare a first dispersion by dispersing a NiFe Prussian blue analog in a first solvent. Prepare a solution by dissolving iron azaphthalocyanine in a second solvent. Mixing the first dispersion, the solution, and the carbon particles, To obtain a precursor liquid containing the NiFe Prussian blue analog as a precursor of an OER catalyst supported on carbon particles, and the iron azaphthalocyanine as a precursor of an ORR catalyst supported on carbon particles, and The precursor solution is applied to the porous support film, and the first and second solvents are removed to form a mixture of the OER catalyst precursor and the ORR catalyst on the porous support film. This invention relates to a method for manufacturing a positive electrode for a zinc-air secondary battery, including (hereinafter also referred to as "this method").

[0079] The first solvent is a solvent (dispersion medium) for dispersing the NiFe Prussian blue analog, and can be water, alcohol, or a combination thereof, with water being preferred from an environmental standpoint. The alcohol can be methanol, ethanol, butanol, isopropyl alcohol, ethylene glycol, methoxyethanol, hexafluoro-2-propanol, etc. The first solvent may be a single solvent or a mixture of two or more solvents. The concentration of NiFePBA in the dispersion obtained by dispersing NiFePBA in the first solvent is preferably 0.5 to 200 g / L, more preferably 2 to 100 g / L, and even more preferably 20 to 60 g / L. By having the NiFePBA concentration within the above preferred range, the adsorption rate of NiFePBA is increased, and the NiFePBA in the dispersion is more uniformly adsorbed onto the surface of the carbon particles, further improving the OER catalytic activity and durability. The concentration of NiFePBA can be measured, for example, based on the absorbance coefficient and molar extinction coefficient using a spectrophotometer. The amount of metal may also be measured by atomic absorption spectrometry.

[0080] NiFePBA can be prepared by mixing an aqueous solution of K3[Fe(CN)6] with an aqueous mixture of FeSO4·7H2O and Ni(NO3)2·6H2O. By changing the concentrations of FeSO4·7H2O and Ni(NO3)2·6H2O, Ni x Fe 1-x [Fe(CN)6] 0.67 The range of x in yH2O can be changed from greater than 0 to less than 1. The hydration number y is not particularly limited, but for example, it is in the range of 3 to 5.

[0081] NiFePBA can be supported on carbon particles simply by mixing a dispersion of NiFePBA in water, alcohol, or a combination thereof with carbon particles.

[0082] The temperature, pressure, and other conditions for dissolving iron azaphthalocyanine in the second solvent are not particularly limited, as long as the conditions allow iron azaphthalocyanine to dissolve in the second solvent. For example, the temperature when preparing the solution can be below the boiling point of the second solvent, and may be, for example, room temperature (e.g., 25°C).

[0083] The second solvent is not particularly limited as long as it can dissolve iron azaphthalocyanine, and can be, for example, water, alcohol, or a combination thereof. The alcohol can be methanol, ethanol, isopropyl alcohol, hexafluoro-2-propanol, etc. The second solvent may be one type or a mixture of two or more solvents. The second solvent may be the same as or different from the first solvent. Another solvent may be added when mixing the carbon particles.

[0084] The concentration of iron azaphthalocyanine in the solution obtained by dissolving iron azaphthalocyanine in a second solvent is preferably 0.0001 g / L to 5 g / L, more preferably 0.01 g / L to 1 g / L, and even more preferably 0.1 g / L to 1 g / L. By having the iron azaphthalocyanine concentration within the above preferred range, the adsorption efficiency and adsorption rate of iron azaphthalocyanine are increased, and the iron azaphthalocyanine in the solution is more easily adsorbed uniformly onto the surface of the carbon particles. This allows for the formation of a uniform monolayer consisting of single molecules of iron azaphthalocyanine on the surface of the carbon particles, further improving the oxygen reduction catalytic activity and durability. The concentration of iron azaphthalocyanine can be measured, for example, based on the absorbance coefficient and molar extinction coefficient using a spectrophotometer.

[0085] This method allows for the simple and environmentally friendly production of a positive electrode using water, alcohol, or a combination thereof, without requiring high-temperature processes that necessitate thermal energy. When hydrolyzing NiFePBA using an alkaline aqueous electrolyte during the production of zinc-air secondary batteries, no waste liquid is produced, further reducing the environmental impact.

[0086] By mixing a first dispersion, in which a NiFe Prussian blue analog is dispersed in a first solvent, with carbon particles, NiFePBA can be relatively uniformly adsorbed and supported on the surface of the carbon particles.

[0087] By mixing a solution of iron azaphthalocyanine dissolved in a second solvent with carbon particles, the iron azaphthalocyanine can be relatively uniformly adsorbed and supported on the surface of the carbon particles. The iron azaphthalocyanine may be adsorbed on a portion of the surface of the carbon particles, or it may be adsorbed in a film-like manner on the surface of the carbon particles.

[0088] Iron azaphthalocyanine can dissolve in the second solvent, and the dissolved iron azaphthalocyanine molecules can be relatively uniformly adsorbed onto the surface of carbon particles. By molecularly adsorbing iron azaphthalocyanine onto the surface of carbon particles, excellent chemical interaction ability can be obtained between the iron azaphthalocyanine and carbon particles, resulting in a catalyst with excellent efficiency in electron transfer between iron azaphthalocyanine and carbon particles and excellent redox catalytic activity.

[0089] The method for mixing the first dispersion and carbon particles is not particularly limited. For example, the first dispersion and carbon particles may be mixed, and the resulting mixture may be stirred using, for example, a mixer, ultrasonic device, magnetic stirrer, or agitator. Alternatively, the first dispersion and carbon particles may be mixed, and the resulting mixture may be dispersed using a homogenizer or other disperser. The method for mixing the solution in which iron azaphthalocyanine is dissolved in the second solvent with the carbon particles can be the same as described above.

[0090] The surface of a carbon particle includes not only the outer surface of the particle but also the inner surface of a hollow-structured particle. For example, if the carbon particle has a hollow structure like Ketjenblack, the surface of the carbon particle refers to both the outer and inner surfaces of the Ketjenblack particle.

[0091] The order in which the first dispersion, the solution, and the carbon particles are mixed can be arbitrary. For example, the first dispersion, the solution, and the carbon particles may be mixed simultaneously; the first dispersion and the solution may be mixed first, and then the carbon particles may be mixed; the carbon particles may be mixed into the first dispersion first, and then the solution may be mixed; the carbon particles may be mixed when preparing the solution, and then the first dispersion may be mixed; the first dispersion and the carbon particles may be mixed; the solution and the carbon particles may be mixed; and a mixture of the first dispersion and the carbon particles may be mixed with a mixture of the solution and the carbon particles. The carbon particles may be of one type or more types.

[0092] Methods for applying the precursor liquid onto the porous support film include, for example, drop casting, spray coating, dipping, or spin coating.

[0093] By removing the first and second solvents, a mixture of the OER catalyst precursor and the ORR catalyst can be formed on the porous support film.

[0094] The method for removing the first and second solvents is not particularly limited and examples include filtration such as solid-liquid separation, vacuum drying, heat drying, and room temperature drying. The temperature for the solvent removal step is preferably, for example, 200°C or less, 100°C or less, or 50°C or less, from the viewpoint of the durability of the positive electrode, but it may also be between 100°C and 140°C, or even at room temperature.

[0095] Preferably, the precursor of the OER catalyst is hydrolyzed to form the OER catalyst, and a mixed catalyst of the OER catalyst and the ORR catalyst is formed.

[0096] By hydrolyzing NiFePBA, a precursor of the OER catalyst supported on carbon particles, a layered NiFe double hydroxide supported on carbon particles can be formed.

[0097] Hydrolysis can be carried out using an alkaline aqueous solution. The alkaline aqueous solution can be an aqueous solution of potassium hydroxide, an aqueous solution of sodium hydroxide, a combination thereof, or an aqueous electrolyte solution obtained by dissolving the above-mentioned alkali and zinc. The concentration of the aqueous potassium hydroxide solution is preferably 0.1 to 15 mol / L. The concentration of the aqueous sodium hydroxide solution is preferably 0.1 to 20 mol / L. By using the above-preferred concentrations of the alkaline aqueous solution, the hydrolysis treatment can be carried out more effectively.

[0098] Hydrolysis treatment can be performed during the manufacturing of the positive electrode, after the manufacturing of the positive electrode, or during the manufacturing of a zinc-air secondary battery containing the positive electrode.

[0099] A binder may be added to a first dispersion obtained by dispersing NiFePBA in a first solvent, a solution obtained by dissolving iron azaphthalocyanine in a second solvent, or a mixture of the first dispersion and the aforementioned solution. The binder can be a water-soluble binder soluble in the first and second solvents, preferably an ion-conducting binder, such as Nafion®.

[0100] This disclosure also, To prepare a first dispersion by dispersing a NiFe Prussian blue analog in a first solvent, Mixing the first carbon particles into the first dispersion, To obtain a precursor liquid of an OER catalyst in which the NiFe Prussian blue analog is supported on the first carbon particles, and The first solvent is removed from the precursor liquid to form a precursor of the OER catalyst in which the NiFe Prussian blue analog is supported on the first carbon particles. Prepare a solution by dissolving iron azaphthalocyanine in a second solvent. To prepare a second dispersion by dispersing second carbon particles in the aforementioned solution, and The second solvent is removed from the second dispersion to form an ORR catalyst in which the iron azaphthalocyanine is supported on the second carbon particles. Combining a porous support film, a precursor of the OER catalyst, and an ORR catalyst. This invention relates to a method for manufacturing a positive electrode for a zinc-air secondary battery, including (hereinafter also referred to as "this method").

[0101] Preferably, the precursor of the OER catalyst is formed. The precursor solution is applied onto the porous support film, and the first solvent is removed to form a layer of the OER catalyst precursor on the porous support film. Includes, Forming the aforementioned ORR catalyst The second dispersion is applied onto the precursor layer, and the second solvent is removed to form an ORR catalyst layer on the precursor layer. Includes.

[0102] Preferably, the ORR catalyst is formed The second dispersion is applied onto the porous support film, and the second solvent is removed to form an ORR catalyst layer on the porous support film. Includes, Forming the precursor of the OER catalyst The precursor solution is applied onto the ORR catalyst layer, and the first solvent is removed to form a layer of the OER catalyst precursor on the ORR catalyst layer. Includes.

[0103] After removing the first and second solvents, the cathode, which is a combination of the porous support film, the precursor of the OER catalyst, and the ORR catalyst, may be pressed.

[0104] Preferably, the precursor of the OER catalyst is formed. The precursor solution is applied to the first substrate, and the first solvent is removed from the precursor solution to form a layer of the OER catalyst precursor on the porous support film. Includes, Forming the aforementioned ORR catalyst The second dispersion is applied to the second substrate, and the second solvent is removed from the second dispersion to form an ORR catalyst layer on the second substrate. Includes, The OER catalyst precursor layer is peeled off from the first substrate, the ORR catalyst layer is peeled off from the second substrate, and the laminate of the OER catalyst precursor layer and the ORR catalyst layer is placed on a porous support film. Includes.

[0105] This method preferably includes hydrolyzing an OER catalyst precursor to form an OER catalyst. NiFe-LDH can be obtained by hydrolyzing NiFePBA supported on carbon particles, which are the precursor of the OER catalyst. The hydrolysis of the OER catalyst precursor may be performed following the formation of the OER catalyst precursor, following the production of the positive electrode, or during the production of a zinc-air secondary battery including the positive electrode, electrolyte, and negative electrode.

[0106] This disclosure also relates to a method for manufacturing a zinc-air secondary battery, comprising the positive electrode, electrolyte, and negative electrode manufactured by the present method. The manufacture of a zinc-air secondary battery can be carried out by conventional methods, except for the inclusion of the present positive electrode. [Examples]

[0107] (Example 1) (Preparation of ORR catalyst) 258 mg of pyridine-2,3-dicarbonitride, 135 mg of iron(III) chloride hexahydrate, and 20 mg of diazabicycloundecene (DBU) were mixed in a test tube and dissolved in a mixed solvent containing 10 mL of methanol and 10 mL of dimethyl sulfoxide (DMSO).

[0108] Next, the mixture was heated at 180°C for 3 hours under nitrogen purging to obtain a reaction product containing iron tetrapyridopolyphylazine (FeTPP). The reaction product was centrifuged three times with acetone and dried. The precipitate after centrifugation was dissolved in concentrated sulfuric acid and added dropwise to water to precipitate FeTPP. The precipitated FeTPP was recovered by centrifugation and washed with methanol to obtain FeTPP.

[0109] Next, 0.1 mg of the obtained FeTPP was dissolved in 1.0 mL of DMSO to prepare a solution with an FeTPP concentration of 0.1 g / L. The solution was a bluish, transparent liquid, confirming that the FeTPP was dissolved in DMSO.

[0110] 5 mg of Ketjenblack (ECP600JD, manufactured by Lion Specialty Chemicals Co., Ltd.), which has carboxyl groups and an average diameter of 30-40 nm, was dispersed in the obtained solution. For dispersion, sonication (20 kHz) was performed for 15 minutes. The dispersion was uniformly black and cloudy, confirming a substantially uniform dispersion state.

[0111] The obtained dispersion was subjected to solid-liquid separation and methanol washing to remove the solvent, DMSO, and dried at room temperature for 24 hours to obtain the ORR catalyst. The amount of FeTPP supported on Ketjenbrak was 19.1 wt% relative to the carbon mass of the carbon particles.

[0112] 0.82 mg of the obtained ORR catalyst, 84 μL of Milli-Q water, 336 μL of isopropyl alcohol, and 6 μL of 0.5% by mass Nafion aqueous solution were mixed in an ultrasonic stirrer to prepare the ORR catalyst solution. As schematically shown in Figure 8, a 5 × 5 cm sample was placed on an aluminum plate heated to 120°C on a hot plate. 2 A carbon paper (Toray Industries, TGP-H-120) was placed, and an ORR catalyst solution, prepared by spraying it six times across the heated carbon paper, was used to form an ORR catalyst layer on the carbon paper. The amount of FeTPP supported per unit area of ​​carbon paper (per unit area of ​​positive electrode) was 414 μg / cm². 2 That was the case.

[0113] (Preparation of OER catalyst) 2.0 mmol of K3[Fe(CN)6] (manufactured by Kanto Chemical Co., Ltd.) aqueous solution (30 mL) is added to an aqueous mixture of 1.20 mmol of FeSO4·7H2O (manufactured by Kanto Chemical Co., Ltd.) and 1.80 mmol of Ni(NO3)2·6H2O (manufactured by Fujifilm Wako Chemical Co., Ltd.) 0.6 Fe 0.4 [Fe(CN)6] 0.67 NiFePBA particles having the composition yH2O were formed. The formed NiFePBA particles were centrifuged at 4000 rpm (2600 G), washed with water, and then dried under reduced pressure to obtain NiFePBA powder. 0.6 Fe 0.4 [Fe(CN)6] 0.67 The hydration number y of yH2O was determined by thermogravimetric differential thermal analysis (TG-DTA) using a Rigaku Thermo plus EVO2, and the result was y = 3.6.

[0114] [Fe(CN)6] is present on the surface of NiFePBA powder nanoparticles. 4- To prepare an aqueous dispersion of NiFePBA nanoparticles by modifying them, the formed NiFePBA particle powder was mixed with an aqueous solution of Na4[Fe(CN)6]·10H2O (Kanto Chemical Special Grade), and the mixture was stirred for 3 weeks. As a result, 1.50 × 10⁻⁶ -1 A stable aqueous dispersion of surface-modified NiFePBA nanoparticles was obtained in mol / L. The average particle size of the NiFePBA nanoparticles was 10 nm.

[0115] The composition includes 63.4 mg of Ketjenblack (manufactured by Lion Specialty Chemicals, ECP600JD) with an average diameter of 30-40 nm as carbon particles, 890.1 mg of Nafion (registered trademark) (a mixed solution of lower aliphatic alcohols and water, 5.0% by mass, manufactured by Sigma-Aldrich) as a binder, and 1.50 × 10⁻⁶ as a catalyst precursor. -1A precursor solution for the OER catalyst was prepared by mixing 1.406 mL of an aqueous dispersion of mol / L surface-modified NiFePBA nanoparticles, 2.00 g of water, and 6.28 g of isopropyl alcohol in a ball mill for 20 minutes. As schematically shown in Figure 8, the prepared precursor solution was spray-coated six times onto the ORR catalyst layer formed on the carbon paper, which was placed on an aluminum plate heated to 120°C, to form a carbon paper / ORR catalyst layer / OER catalyst precursor layer. At this time, the amount of NiFePBA nanoparticles supported on the Ketjenblack particles per unit area of ​​carbon paper (unit area of ​​the positive electrode) was 1.17 μmol / cm². 2 That was the case.

[0116] A commercially available nickel mesh was placed as a current collector for the positive electrode on the formed carbon paper / ORR catalyst layer / OER catalyst precursor layer to fabricate a positive electrode containing the nickel mesh / carbon paper / ORR catalyst layer / OER catalyst precursor layer schematically shown in Figure 2-A.

[0117] The prepared cathode consists of 6.0 mol / L KOH as the electrolyte and a secondary electrolyte (Zn 2+ A zinc-air secondary battery with a capacity of 300 mAh / g (Zn) was fabricated using a mixed electrolyte aqueous solution of 0.20 mol / L zinc chloride (ZnCl2, Kanto Chemical Special Grade) as the salt, and commercially available metallic zinc foil with a thickness of 120 μm as the negative electrode. At this time, NiFePBA nanoparticles supported on Ketjenblack in the precursor layer were converted to NiFe-LDH upon contact with the electrolyte aqueous solution, forming an OER catalyst layer, with a supported amount of 1.17 μmol / cm³, the same as that of the NiFePBA nanoparticles. 2 It was. Also, the Ni FePBA nanoparticles, which are precursors, 0.6 Fe 0.4 [Fe(CN)6] 0.67 From [Fe(CN)6] 0.67 After removal, the composition ratio of Ni to Fe was 0.6:0.4.

[0118] (Example 2) Similar to Example 1, an ORR catalyst layer was formed on carbon paper. An OER catalyst precursor solution, prepared in the same manner as in Example 1, was applied to the opposite side of the carbon paper on which the ORR catalyst layer was formed to form an OER catalyst precursor layer, thus creating an ORR catalyst layer / carbon paper / OER catalyst precursor layer. A commercially available nickel mesh was placed on the formed ORR catalyst layer / carbon paper / OER catalyst precursor layer as a current collector for the positive electrode to fabricate a positive electrode containing the nickel mesh / ORR catalyst layer / carbon paper / OER catalyst precursor layer schematically shown in Figure 2-B. Next, a zinc-air secondary battery was fabricated using the fabricated positive electrode in the same manner as in Example 1, and the NiFePBA nanoparticles in the precursor layer were converted to NiFe-LDH to form an OER catalyst layer.

[0119] (Example 3) A precursor solution of the OER catalyst, prepared in the same manner as in Example 1, was applied to carbon paper to form a precursor layer of the OER catalyst layer. An ORR catalyst layer was then formed on the OER catalyst precursor layer to form a carbon paper / OER catalyst precursor layer / ORR catalyst layer. A commercially available nickel mesh was placed on the formed carbon paper / OER catalyst precursor layer / ORR catalyst layer as a current collector for the positive electrode to fabricate a positive electrode containing the nickel mesh / carbon paper / OER catalyst precursor layer / ORR catalyst layer as schematically shown in Figure 2-C. Next, a zinc-air secondary battery was fabricated using the fabricated positive electrode in the same manner as in Example 1, and the NiFePBA nanoparticles in the precursor layer were converted to NiFe-LDH to form the OER catalyst layer.

[0120] (Example 4) An ORR catalyst solution prepared in the same manner as in Example 1 and an OER catalyst precursor solution prepared in the same manner as in Example 1 were mixed to prepare a catalyst mixture of the ORR catalyst and the OER catalyst precursor. The prepared catalyst mixture was applied to carbon paper to form a catalyst mixture layer of carbon paper / ORR catalyst and OER catalyst precursor. A commercially available nickel mesh was placed on the formed carbon paper / catalyst mixture layer as a current collector for the positive electrode to fabricate a positive electrode containing the nickel mesh / carbon paper / catalyst mixture layer schematically shown in Figure 2-D. Next, a zinc-air secondary battery was fabricated using the fabricated positive electrode in the same manner as in Example 1, and NiFePBA in the catalyst mixture layer was converted to NiFe-LDH to form an OER catalyst.

[0121] (Example 5) The electrolyte is 6.0 mol / L KOH and the auxiliary electrolyte (Zn 2+ A zinc-air secondary battery was prepared in the same manner as in Example 4, except that a mixed electrolyte aqueous solution of 0.20 mol / L zinc methanesulfonate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the salt, and NiFePBA in the catalyst mixed layer was converted to NiFe-LDH to form an OER catalyst.

[0122] (Example 6) The electrolyte is 6.0 mol / L KOH and the auxiliary electrolyte (Zn 2+ A zinc-air secondary battery was prepared in the same manner as in Example 4, except that a mixed electrolyte aqueous solution of 0.20 mol / L zinc oxide (manufactured by Koshu Chemical) was used as the salt, and NiFePBA in the catalyst mixed layer was converted to NiFe-LDH to form an OER catalyst.

[0123] (Example 7) The electrolyte is 6.0 mol / L KOH and the auxiliary electrolyte (Zn 2+ A zinc-air secondary battery was prepared in the same manner as in Example 4, except that a mixed electrolyte aqueous solution of 0.20 mol / L zinc acetate (Zn(CH3COO)2, Kanto Chemical Special Grade) was used as the salt, and NiFePBA in the catalyst mixed layer was converted to NiFe-LDH to form an OER catalyst.

[0124] (Example 8) The electrolyte is 6.0 mol / L KOH and the auxiliary electrolyte (Zn 2+ A zinc-air secondary battery was prepared in the same manner as in Example 4, except that a mixed electrolyte aqueous solution of 0.20 mol / L zinc trifluoromethanesulfonate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the salt, and NiFePBA in the catalyst mixed layer was converted to NiFe-LDH to form an OER catalyst.

[0125] (Example 9) The electrolyte is 6.0 mol / L KOH and the auxiliary electrolyte (Zn 2+ A zinc-air secondary battery was prepared in the same manner as in Example 4, except that a mixed electrolyte aqueous solution of 0.30 mol / L zinc chloride was used as the salt, and NiFePBA in the catalyst mixed layer was converted to NiFe-LDH to form an OER catalyst.

[0126] (Example 10) An ORR catalyst solution prepared in the same manner as in Example 1 was mixed with a stable aqueous dispersion of surface-modified NiFePBA nanoparticles (without Ketjenblack) prepared in the same manner as in Example 1 to prepare a catalyst mixture of the ORR catalyst and the OER catalyst precursor. A zinc-air secondary battery was then constructed in the same manner as in Example 4, and the NiFePBA in the catalyst mixture layer was converted to NiFe-LDH to form the OER catalyst layer.

[0127] (Charge / Discharge Measurement and Evaluation) The zinc-air secondary batteries prepared in Examples 1-10 had a power output of 10 mA / cm². 2 The charge-discharge characteristics at a constant current density were measured (using EC Frontier's ECstat-302 and ECstat-4002), and the average charging voltage was determined. OER ), the average discharge voltage (Average V ORR ), and the average value of the charge / discharge voltage difference (V GAP The following values ​​were calculated. The average values ​​of the charging voltage and discharge voltage are average values ​​in the range of 50 to 150 mAh / g (Zn). Table 1 shows a list of the manufacturing conditions and comparison results for each catalyst tested.

[0128] [Table 1]

[0129] (Evaluation of the influence of stacking sequence and catalyst mixed layer on charge / discharge characteristics) Figure 3 shows the 10 mA / cm² output of zinc-air secondary batteries fabricated in Example 1 (CP / ORR layer / OER layer), Example 2 (ORR layer / CP / OER layer), Example 3 (CP / OER layer / ORR layer), Example 4 (CP / OER and ORR mixed layer), and Example 10 (CP / OER and ORR mixed layer). 2 The charge-discharge curves (curves showing changes in charge-discharge voltage and battery capacity) at a constant current density are shown. The lower line represents the discharge voltage, reflecting the performance of the ORR catalyst, and the upper line represents the charge voltage, reflecting the performance of the OER catalyst. The fabricated zinc-air secondary batteries showed excellent charge-discharge voltages regardless of the stacking order of the ORR catalyst and the OER catalyst relative to the carbon paper (CP) in the positive electrode. Furthermore, the zinc-air secondary batteries equipped with positive electrodes containing the catalyst mixed layer fabricated in Examples 4 and 10 also showed excellent charge-discharge voltages for both the ORR catalyst and the OER catalyst. The average charge voltage of the zinc-air secondary battery equipped with the positive electrode containing the catalyst mixed layer fabricated in Example 4 was 1.95V vs. Zn / Zn 2+ The voltage was significantly below 2V. Furthermore, the average discharge voltage was 1.24V, resulting in a small charge-discharge voltage difference of 0.71V.

[0130] (Evaluation of the effect of auxiliary electrolytes on charge / discharge characteristics) Figure 4 shows a zinc-air secondary battery with a positive electrode containing a catalyst mixture layer prepared using zinc chloride (Example 4) and zinc acetate (Example 7) as auxiliary electrolytes, exhibiting a power output of 10 mA / cm². 2 The charge-discharge curves at a constant current density are shown. The fabricated zinc-air secondary batteries showed excellent charging performance in both cases where zinc chloride and zinc acetate were used as auxiliary electrolytes, with zinc chloride showing even better charging performance compared to zinc acetate.

[0131] (Evaluation of the impact of different types of auxiliary electrolytes on charge-discharge characteristics) Figure 5 shows the graphs of charge-discharge characteristics of zinc-air secondary batteries for each type of auxiliary electrolyte (each concentration is 0.2 M) fabricated in Examples 4 to 8 at a constant current density of 10 mA / cm 2 All of them showed good battery performance, and the zinc-air secondary battery fabricated using zinc chloride in Example 4 showed better battery performance.

[0132] (Evaluation of the influence of the concentration of the auxiliary electrolyte on the charge-discharge characteristics) Figure 6 shows the graphs of charge-discharge characteristics of zinc-air secondary batteries according to the concentration of the auxiliary electrolyte fabricated in Examples 4 and 9 at a constant current density of 10 mA / cm 2 All of them showed good battery performance, and the zinc-air secondary battery containing 0.2 M zinc chloride fabricated in Example 4 showed better battery performance.

[0133] [[ID=I4]](Evaluation of the influence of the current density on the charge-discharge characteristics) Figure 7 shows the charge-discharge curves of the zinc-air secondary battery fabricated in Example 4 at constant current densities of 10 mA / cm 2 and 20 mA / cm 2 The voltage difference at a current density of 10 mA / cm 2 was 0.71 V, and even in the case of a larger current density of 20 mA / cm 2 the voltage difference was 0.74 V. Thus, the ORR catalyst and OER catalyst of this zinc-air secondary battery have comprehensively excellent performance.

[0134] (Reference Example) Ni[[ID=S1]] 0.6 I Fe 0.4 [Fe(CN)6] 0.67 nanoparticles were surface-modified with Na4[Fe(CN)6] to obtain its aqueous dispersion. A single-layer carbon nanotube film was transferred onto carbon paper, and an aqueous dispersion of Ni 0.6 Fe 0.4 [Fe(CN)6] 0.67 nanoparticles was dropped thereon and then converted into NiFe-LDH.

[0135] TEM observation revealed that single-nanometer NiFe-LDH nanodots with a particle size of 1.75 ± 0.25 nm were attached to the surface of single-walled carbon nanotubes. The current density used for charge evaluation of typical zinc-air secondary batteries was 10 mA / cm². 2 The OER overvoltage, calculated by linear sweep voltammetry with no iR compensation, was 260 mV. Current density: 10 mA / cm² 2 A stable 2.2V (vs.Zn / Zn) 2+ It was found that the effects of carbon corrosion can be avoided by maintaining a low charging voltage below this level.

Claims

1. The mixture comprises a porous support film, an oxygen evolution reaction catalyst, a precursor of the oxygen evolution reaction catalyst, or a combination thereof, and an oxygen reduction reaction catalyst. The oxygen evolution catalyst, the precursor of the oxygen evolution catalyst, or a combination thereof comprises first carbon particles, and a NiFe Prussian blue analog, a NiFe layered double hydroxide, or a combination thereof supported on the first carbon particles. The oxygen reduction reaction catalyst comprises a second carbon particle and iron azaphthalocyanine supported on the second carbon particle. Positive electrode for zinc-air rechargeable batteries.

2. The positive electrode according to claim 1, wherein the oxygen evolution catalyst, the precursor of the oxygen evolution catalyst, or a combination thereof and the oxygen reduction catalyst are each arranged in layers, and a laminate of the layered oxygen evolution catalyst, the precursor of the oxygen evolution catalyst, or a combination thereof and the layered oxygen reduction catalyst is located on the porous support film.

3. The positive electrode according to claim 1, wherein the oxygen evolution reaction catalyst, a precursor of the oxygen evolution reaction catalyst, or a combination thereof is a mixture of the oxygen reduction reaction catalyst, and the mixture is located on the porous support film.

4. The amount of NiFe Prussian blue analog, NiFe layered double hydroxide, or a combination thereof supported on the first carbon particles per unit area of ​​the positive electrode is 0.001 μmol / cm³. ２ 1000μmol / cm or more ２ The positive electrode according to claim 1, which is as follows:

5. The amount of iron azaphthalocyanine supported on the second carbon particles per unit area of ​​the positive electrode is 10 μg / cm³. ２ The above 5.0 x 10 ３ μg / cm³ ２ The positive electrode according to claim 1, which is as follows:

6. A zinc-air secondary battery comprising the positive electrode described in any one of claims 1 to 5.

7. Charge / discharge voltage at a constant current density (vs. Zn / Zn) ２＋ The zinc-air secondary battery according to claim 6, wherein the difference between the voltages is 1.0V or less.

8. Charging voltage at a constant current density (vs. Zn / Zn) ２＋ The zinc-air secondary battery according to claim 6, wherein the voltage is 2.2V or less.

9. Prepare a first dispersion by dispersing a NiFe Prussian blue analog in a first solvent. Prepare a solution by dissolving iron azaphthalocyanine in a second solvent. Mixing the first dispersion, the solution, and the carbon particles, To obtain a precursor liquid containing the NiFe Prussian blue analog as a precursor of an oxygen evolution reaction catalyst supported on carbon particles, and the iron azaphthalocyanine as an oxygen reduction reaction catalyst supported on carbon particles, and The precursor solution is applied to the porous support film, and the first and second solvents are removed to form a mixture of the oxygen evolution catalyst precursor and the oxygen reduction catalyst on the porous support film. A method for manufacturing a positive electrode for a zinc-air secondary battery, including the method described above.

10. A method for producing a positive electrode for a zinc-air secondary battery according to claim 9, wherein forming the mixture includes hydrolyzing a precursor of the oxygen evolution reaction catalyst to form the oxygen evolution reaction catalyst, thereby forming a mixed catalyst of the oxygen evolution reaction catalyst and the oxygen reduction reaction catalyst.

11. Prepare a first dispersion by dispersing a NiFe Prussian blue analog in a first solvent. Mixing the first carbon particles into the first dispersion, To obtain a precursor liquid of an oxygen evolution reaction catalyst in which the NiFe Prussian blue analog is supported on the first carbon particles, and The first solvent is removed from the precursor liquid to form a precursor for an oxygen evolution reaction catalyst in which the NiFe Prussian blue analog is supported on the first carbon particles. Prepare a solution by dissolving iron azaphthalocyanine in a second solvent. To prepare a second dispersion by dispersing second carbon particles in the aforementioned solution, and The second solvent is removed from the second dispersion to form an oxygen reduction reaction catalyst on which the iron azaphthalocyanine is supported on the second carbon particles. Combining a porous support film, a precursor of the oxygen evolution reaction catalyst, and an oxygen reduction reaction catalyst. A method for manufacturing a positive electrode for a zinc-air secondary battery, including the method described above.

12. Forming the precursor of the oxygen evolution reaction catalyst is The precursor solution is applied onto the porous support film, the first solvent is removed, and a layer of the oxygen evolution reaction catalyst precursor is formed on the porous support film. Includes, Forming the oxygen reduction reaction catalyst is The second dispersion is applied onto the precursor layer, and the second solvent is removed to form an oxygen reduction reaction catalyst layer on the precursor layer. including, A method for manufacturing a positive electrode for a zinc-air secondary battery according to claim 11.

13. Forming the oxygen reduction reaction catalyst is The second dispersion is applied onto the porous support film, and the second solvent is removed to form an oxygen reduction reaction catalyst layer on the porous support film. Includes, Forming a precursor for the oxygen evolution reaction catalyst The precursor solution is applied onto the oxygen reduction reaction catalyst layer, and the first solvent is removed to form a layer of the precursor of the oxygen evolution reaction catalyst on the oxygen reduction reaction catalyst layer. including, A method for manufacturing a positive electrode for a zinc-air secondary battery according to claim 11.

14. A method for producing a positive electrode for a zinc-air secondary battery according to any one of claims 11 to 13, comprising hydrolyzing a precursor of the oxygen evolution reaction catalyst to form the oxygen evolution reaction catalyst.

15. A method for manufacturing a zinc-air secondary battery, comprising a positive electrode, an electrolyte, and a negative electrode manufactured by the manufacturing method described in any one of claims 9 to 13.

16. A method for manufacturing a zinc-air secondary battery, comprising a positive electrode, an electrolyte, and a negative electrode manufactured by the manufacturing method described in claim 14.

Images