Metal-air battery anode, metal-air battery, and method for manufacturing metal-air battery anode

Abstract

To provide a negative electrode for a metal air battery, a method for manufacturing the same, and a metal air battery using the same, which suppress the growth of dendritic crystals of metal in the negative electrode of the metal air battery and suppress side reactions.SOLUTION: A negative electrode for an air battery has a metal substrate comprising one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe), and a thin film comprising a titanium oxide nanosheet monolayer film located on the metal substrate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a negative electrode for a metal-air battery and a metal-air battery using the same. [Background technology]

[0002] Energy storage technology using zinc electrodes has attracted attention due to its abundant reserves, low cost, high stability, and high capacity, and is expected to be put to practical use in portable power sources, electric vehicles, large-scale energy storage, etc. However, there are problems such as the growth of dendrites due to uneven precipitation / elution of zinc, which penetrate the separator and short-circuit with the counter electrode. In addition, side reactions such as zinc corrosion and hydrogen generation occur, which significantly reduce energy efficiency, and the formation of an oxide film reduces the reversibility of the zinc electrode and gas generation causes battery expansion (see, for example, Non-Patent Document 1).

[0003] Various efforts have been made to address this problem. In particular, a method of modifying the zinc electrode surface with other substances and controlling the interface with the electrolyte is promising for improving current efficiency and cycle stability, because it directly controls the precipitation / dissolution process on the zinc electrode surface, improves the reaction rate, and suppresses side reactions (see, for example, non-patent document 2).

[0004] Various interfacial layers have been studied, ranging from inorganic materials to organic materials and inorganic-organic hybrids. These interfacial layers have achieved high current efficiency and stability by physically separating the zinc electrode and the electrolyte to suppress side reactions and by controlling the transport, distribution, and interaction of ions and electrons. However, many interfacial layers have a thickness on the micrometer scale, which increases the proportion of inactive materials in the electrode and increases the distance of movement of ions and electrons. As a result, the charge capacity is greatly reduced due to increased resistance, and this also leads to increased costs. Recently, very thin interfaces have been produced by the ALD method, but there are problems such as high equipment costs and limited materials that can be applied (see, for example, Non-Patent Document 3).

[0005] On the other hand, a technology is known in which a metal oxide nanosheet is used as an anode material for a metal secondary battery to suppress dendrite formation (see, for example, Patent Document 1). Patent Document 1 discloses an anode material for a secondary battery in which a nanosheet of an oxide of a metal such as titanium, ruthenium, or niobium is supported on a carbon-based conductive support. Patent Document 1 reports that metal cations are attracted along the surface of the metal oxide nanosheet, and the metal precipitates in a plate shape rather than in a needle-like dendrite. However, in Patent Document 1, since the metal oxide nanosheet is held by a powder that is a carbon-based conductive support, when this is used on a negative electrode active material, the interface layer between the electrolyte and the electrode needs to be as thick as or thicker than the carbon-based conductive support, which causes a problem of increased interface resistance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2014 / 069541 [Non-patent literature]

[0007] [Non-Patent Document 1] Campeng Li et al.,Energy Environ.Mater.,2020,3,146 [Non-Patent Document 2] Changjiu Li et al.,Energy Stor.Mater.,2021,35,19 [Non-Patent Document 3] Kangning Zhao et al., Adv. Mater. Interfaces, 2018, 5, 1800848 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above, an object of the present invention is to provide a negative electrode for a metal-air battery that suppresses the growth of metal dendrites in the negative electrode of the metal-air battery and suppresses side reactions, a method for manufacturing the same, and a metal-air battery using the same. [Means for solving the problem]

[0009] The negative electrode for a metal-air battery according to the present invention comprises a metal substrate made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe), and a thin film made of a titanium oxide nanosheet monolayer film located on the metal substrate, thereby solving the above-mentioned problems. The contact angle of water with respect to the surface of the thin film may be in the range of 0° or more and 10° or less. The thickness of the monolayer may be in the range of 0.5 nm to 1.5 nm. The thickness of the thin film may be in the range of 0.5 nm to 10 nm. The titanium oxide nanosheet constituting the titanium oxide nanosheet monolayer film is Ti 0.87 O2, Ti 0.91 O2, Ti3O7, Ti4O9, and Ti5O 11 may be selected from the group consisting of: The titanium oxide nanosheet constituting the titanium oxide nanosheet monolayer film may have a thickness of 0.5 nm to 1.5 nm and a longitudinal length of 5 μm to 30 μm. The metal substrate may have a thickness in the range of 10 μm to 1 mm. The surface roughness Ra of the metal substrate may be 10 nm or less. The titanium oxide nanosheet may have an alkylammonium cation having an alkyl group having 1 to 20 carbon atoms. The alkyl ammonium cation may be at least one selected from the group consisting of tetramethyl ammonium ion, tetraethyl ammonium ion, tetrapropyl ammonium ion, tetrabutyl ammonium ion, and benzylmethyl ammonium ion. The method for producing the above-mentioned metal-air battery negative electrode according to the present invention comprises applying a dispersion liquid containing titanium oxide nanosheets to the surface of a metal substrate made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe), thereby solving the above-mentioned problem. The applying method may be selected from the group consisting of a spin coating method, a dip coating method, a LB method, a dropping method, a layer-by-layer adsorption method, and a spray method. The metal-air battery according to the present invention includes a negative electrode, an air electrode, and an electrolyte located between the negative electrode and the air electrode, and the negative electrode is the above-mentioned metal-air battery negative electrode, thereby solving the above-mentioned problems. The cathode may contain a catalyst selected from the group consisting of metals, metal oxides, metal oxynitrides, metal nitrides, metal borides, metal silicides, and metal sulfides. The battery may further include a separator, and the electrolyte may be impregnated in the separator. Effect of the Invention

[0010] The negative electrode for a metal-air battery of the present invention comprises a metal substrate made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe), and a thin film made of a titanium oxide nanosheet monolayer film located thereon. Metal ions are uniformly distributed on the surface of the negative electrode due to the negative charge of the titanium oxide nanosheet monolayer film. As a result, the generation of dendrites from the surface of the negative electrode can be suppressed. Furthermore, hydrogen generation activity is low on the titanium oxide nanosheet monolayer film, and side reactions such as hydrogen generation and corrosion are suppressed. By using such a negative electrode, a metal-air battery with excellent cycle life can be provided.

[0011] The negative electrode for a metal-air battery of the present invention can be produced by simply applying a dispersion liquid containing a titanium oxide nanosheet onto a metal substrate, and is therefore advantageous in practice since it does not require a complicated process, expensive equipment, or skilled techniques. [Brief description of the drawings]

[0012] [Figure 1] Schematic diagram showing the negative electrode for a metal-air battery of the present invention. [Diagram 2] Schematic diagram explaining the mechanism for suppressing dendrite growth [Diagram 3] A flowchart showing the steps of manufacturing the negative electrode for a metal-air battery of the present invention. [Figure 4] Schematic diagram showing a metal-air battery of the present invention. [Diagram 5] XRD patterns of K0.8Ti1.73Li0.27O4 powder and H1.07Ti1.73O4·H2O powder. [Figure 6] SEM image of K0.8Ti1.73Li0.27O4 powder [Figure 7] SEM image of H1.07Ti1.73O4·H2O powder [Figure 8] Zeta potential of titanium oxide nanosheet dispersion [Figure 9] FIG. 1 shows SEM images of samples of Examples 1 to 3. [Figure 10] 1 shows SEM and AFM images of the sample in Example 1. [Figure 11] FIG. 1 shows the XRD pattern of the sample of Example 1. [Figure 12] FIG. 1 shows XRD patterns of samples of Examples 4 and 5. [Figure 13] FIG. 1 shows an in-plane XRD pattern of the sample of Example 1. [Figure 14] Figures showing TEM images, electron diffraction patterns, STEM images and EDS mapping of the sample in Example 1. [Figure 15] FIG. 1 shows the XPS spectrum of the sample in Example 1. [Figure 16] FIG. 1 shows the TOF-SIMS spectrum of the sample in Example 1. [Figure 17] FIG. 1 shows charge / discharge curves for symmetric coin cells of Examples 1 and 7. [Figure 18] FIG. 1 shows the results of cycling tests of the symmetric coin cells of Example 1 for various periods of time. [Figure 19] FIG. 1 shows the results of cycling tests of symmetric coin cells of Example 7 for various periods of time. [Figure 20] FIG. 1 shows an SEM image of the sample of Example 1 after a charge / discharge test. [Figure 21] FIG. 13 shows an SEM image of the sample of Example 7 after a charge / discharge test. [Figure 22] FIG. 1 shows LSV curves of samples of Examples 1 and 7. [Figure 23] FIG. 1 shows the potential change during zinc deposition under a constant current (1 mA / cm2) in a battery using the samples of Examples 6 and 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that like elements are given like reference numerals and their description will be omitted.

[0014] In this specification, the term "nanosheet monolayer film" refers to a monolayer film formed by densely arranging titanium oxide nanosheets obtained by exfoliating layered titanium oxide into single layers. The term "thin film consisting of nanosheet monolayer film" is used when referring to the nanosheet monolayer film itself, or when referring to a multilayer film (also called nanosheet multilayer film) in which the nanosheet monolayer film is multilayered. When observed with an electron microscope, titanium oxide nanosheets are considered to be densely arranged when they are gathered to form a film.

[0015] (Embodiment 1) In the first embodiment, the negative electrode for a metal-air battery and a method for producing the same of the present invention will be described in detail. FIG. 1 is a schematic diagram showing the negative electrode for a metal-air battery of the present invention.

[0016] The metal-air battery negative electrode 100 of the present invention comprises a metal substrate 110 made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe), and a thin film 140 made of a titanium oxide nanosheet monolayer film 130 formed by densely arranging titanium oxide nanosheets 120 located on the metal substrate 110. Although Fig. 1 shows a case where the thin film 140 is made of one titanium oxide nanosheet monolayer film 130, the thin film 140 may be made of a nanosheet multilayer film in which the titanium oxide nanosheet monolayer films 130 are multilayered.

[0017] The metal substrate 110 made of the above-mentioned metals functions as a negative electrode for a metal-air battery using these metals as the negative electrode active material. The use of the metal substrate 110 makes it possible to eliminate the need for a current collector for collecting current from the negative electrode 100. However, it is also possible to use a current collector. When a current collector is used, a material having electrical conductivity can be used for the current collector, and it may be, for example, copper, stainless steel, nickel, carbon, or the like, and its shape may be a foil, plate, or mesh. Alternatively, the battery case that houses the metal-air battery of the present invention may have the function of a current collector.

[0018] The thickness of the metal substrate 110 varies depending on the application of the battery, but may be, for example, in the range of 10 μm to 1 mm, and preferably in the range of 0.1 mm to 0.5 mm. If the thickness is within this range, it is easy to handle.

[0019] The surface roughness Ra of the metal substrate 110 may preferably be 0 nm or more and 10 nm or less. Within this range, a uniform titanium oxide nanosheet monolayer film 130 can be formed. The surface roughness Ra of the metal substrate 110 may be in the range of 3 nm or more and 5 nm or less. Within this range, a denser titanium oxide nanosheet monolayer film 130 without gaps can be obtained, and the metal substrate 110 and the titanium oxide nanosheet monolayer film 130 can be in good contact with each other, resulting in excellent electrical properties.

[0020] The titanium oxide nanosheet 120 is not particularly limited as long as it is a single layer exfoliated from a layered titanium oxide, and varies depending on the composition of the selected layered titanium oxide. Preferably, the titanium oxide nanosheet 120 is 0.87 O2, Ti 0.91 O2, Ti3O7, Ti4O9, and Ti5O 11 These are all negatively charged and can attract metal ions. For example, Ti 0.87 O2 0.52- , Ti 0.91 O2 0.36- , Ti3O7 2- , Ti4O9 2- , and TiO 11 2- Among them, the titanium oxide nanosheet 120 is preferably TiO 2 , because larger nanosheets can be used and the metal substrate 110 can be efficiently covered with the titanium oxide nanosheet 120. 0.87 It's O2.

[0021] For example, layered titanium oxide is 0.8 Ti 1.73 Li 0.27 When expressed as O4, the layer is peeled off and becomes Ti 0.87 Titanium oxide nanosheets represented by the formula CsO2 are obtained. For example, layered titanium oxide is 0.7 Ti 1.825 □ 0.175 When the layer is peeled off, Ti 0.91 Titanium oxide nanosheets represented by TiO2 are obtained. For example, when the layered titanium oxide is represented by NaTiO7, a titanium oxide nanosheet represented by TiO7 is obtained by exfoliating the single layer. Thus, a person skilled in the art can easily understand the composition of the original layered titanium oxide in order to obtain a desired titanium oxide nanosheet.

[0022] The titanium oxide nanosheets 120 have a thickness of 0.5 nm to 1.5 nm and a longitudinal length of 5 μm to 30 μm. Such dimensions allow electrostatic repulsion between the titanium oxide nanosheets 120, resulting in excellent dispersibility, and a dense monolayer film can be obtained when applied.

[0023] The titanium oxide nanosheet 120 may have an alkylammonium cation having an alkyl group having 1 to 20 carbon atoms on its surface. In a dispersion liquid containing the titanium oxide nanosheet 120 used in the production method described below, the titanium oxide nanosheet 120 is dispersed due to the presence of the alkylammonium cations, and may have an alkylammonium cation on its surface. Even in this case, the performance of the negative electrode is not deteriorated.

[0024] Illustratively, such alkylammonium cations are at least one selected from the group consisting of tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, and benzylmethylammonium ion.

[0025] In particular, when the thin film 140 is made of a titanium oxide nanosheet multilayer film (not shown), the presence of alkylammonium cations between the titanium oxide nanosheet monolayer films having negative charges facilitates multilayering.

[0026] The thickness of the titanium oxide nanosheet monolayer film 130 made of such a titanium oxide nanosheet 120 is the same as the thickness of the titanium oxide nanosheet 120, and is in the range of 0.5 nm or more and 1.5 nm or less.

[0027] The thickness of the thin film 140 is preferably 0.5 nm to 10 nm, taking into consideration the case where the thin film 140 is made of the titanium oxide nanosheet monolayer film 130 and the case where the thin film 140 is made of the titanium oxide nanosheet multilayer film. That is, the thin film 140 may have 1 to 10 titanium oxide nanosheet monolayer films 130. Within this range, the generation of metal dendrites and side reactions can be efficiently suppressed. In particular, when the thin film 140 is made of the titanium oxide nanosheet monolayer film 130, the thickness is significantly thinner at about 1 nm compared to the interface layer in Non-Patent Document 3, so that the amount of substance of the required elements is small, and costs can be reduced.

[0028] The surface of the thin film 140 is preferably hydrophilic. As a result, the anode 100 of the present invention exhibits low contact resistance to an aqueous electrolyte, and is therefore effective for a metal-air battery using an aqueous electrolyte. The contact angle of water with the surface of the thin film 140 is more preferably in the range of 0° or more and 10° or less. As a result, excellent battery characteristics are achieved even in a metal-air battery using an aqueous electrolyte. The contact angle is measured in accordance with JIS R 3257. More preferably, the contact angle is 0° or more and 5° or less.

[0029] 1 shows the thin film 140 made of the titanium oxide nanosheet monolayer film 130 completely covering the metal substrate 110, but from the viewpoint of suppressing dendrite growth, it is sufficient that the thin film 140 covers at least a part of the metal substrate 110. However, in order to achieve the effect of suppressing dendrite growth and to minimize the occurrence of side reactions, the coverage rate of the titanium oxide nanosheet monolayer film 130 (titanium oxide nanosheet relative to the total surface area of ​​the substrate) is preferably 30% or more, more preferably 50% or more, and even more preferably 80% or more and 100% or less.

[0030] Next, the mechanism by which the growth of dendrites is suppressed when the metal-air battery negative electrode 100 of the present invention is used will be described. FIG. 2 is a schematic diagram illustrating the mechanism for suppressing dendrite growth.

[0031] The upper part of Figure 2 shows an example in which a zinc substrate without a titanium oxide nanosheet monolayer film was used as the negative electrode, and the lower part of Figure 2 shows an example in which a zinc substrate with a titanium oxide nanosheet monolayer film was used as the negative electrode.

[0032] On a zinc substrate that does not have a thin film 140 made of the titanium oxide nanosheet monolayer film 130, dendrites grow due to non-uniform deposition / elution of zinc, which penetrates the separator and shorts out with the counter electrode. In addition, side reactions such as hydrogen generation and zinc corrosion occur, which significantly impair energy efficiency (upper part of FIG. 2). On the other hand, on a zinc substrate that has a thin film 140 made of the titanium oxide nanosheet monolayer film 130, the zinc ions in the aqueous solution are uniformly distributed on the substrate due to the negative charge of the titanium oxide nanosheet monolayer film 130, so zinc is uniformly deposited and the generation of dendrites is suppressed. In addition, the hydrogen generation activity is low, and side reactions such as hydrogen generation and corrosion are suppressed (lower part of FIG. 2). Here, a zinc substrate is used as the metal substrate 110 for ease of understanding, but it goes without saying that the present invention is not limited to zinc substrates.

[0033] Next, a method for producing the metal-air battery negative electrode 100 of the present invention will be described. FIG. 3 is a flow chart showing the steps of producing the negative electrode for a metal-air battery of the present invention.

[0034] The metal-air battery negative electrode 100 of the present invention includes step S310. Step S310: A dispersion liquid containing titanium oxide nanosheets (hereinafter simply referred to as titanium oxide nanosheet dispersion liquid) is applied to the surface of a metal substrate made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe). The manufacturing method of the present invention is advantageous in practice since it does not involve complicated processes and does not require expensive equipment or skilled techniques.

[0035] In step S310, the metal substrate is as described above, and therefore the description will be omitted. Prior to step S310, a step of polishing the surface of the metal substrate may be performed. This allows the surface roughness of the metal substrate to be controlled within the above-mentioned range. Such polishing may be any of mechanical polishing, chemical polishing, and chemical mechanical polishing. In addition, following polishing of the surface of the metal substrate, a hydrophilization treatment may be performed. This allows the subsequent application of the titanium oxide nanosheet dispersion liquid to be performed uniformly. The hydrophilization treatment may be, for example, oxygen plasma treatment or ultraviolet irradiation for about 10 to 30 minutes in an ozone atmosphere.

[0036] The titanium oxide nanosheet dispersion may be prepared by, for example, the method for preparing a colloidal suspension described in JP 2006-96897 A, but can be obtained by the following method, for example. A layered titanium oxide powder is contacted with an aqueous acid solution such as hydrochloric acid to obtain a hydrogen ion exchanger in which the metal ions between the layers are replaced with hydrogen ions or oxonium ions. The hydrogen ion exchanger is then placed in an aqueous solution containing the above-mentioned alkylammonium cations and stirred. The titanium oxide nanosheet dispersion thus obtained is prepared by replacing the solvent in the suspension in which the single layers of the exfoliated titanium oxide nanosheets are obtained with an organic solvent.

[0037] The organic solvent for the titanium oxide nanosheet dispersion is not particularly limited, but is preferably selected from the group consisting of dimethyl sulfoxide (DMSO), formamide, propanol, dimethylformamide, tetrahydrofuran, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, and N,N'-dimethylpropyleneurea. These organic solvents are polar solvents, and titanium oxide nanosheets are easily dispersed in them. Among them, DMSO is preferred from the viewpoints of moderate viscosity (easy to stretch and form a thin liquid film) and vapor pressure (easy to control because it dries relatively slowly).

[0038] The concentration of the titanium oxide nanosheets in the titanium oxide nanosheet dispersion is preferably in the range of 0.05 wt% to 5 wt%. Within this range, a uniform titanium oxide nanosheet monolayer film can be obtained. The concentration of the titanium oxide nanosheets is more preferably in the range of 0.08 wt% to 0.12 wt%. This makes it easier to obtain a dense nanosheet monolayer film.

[0039] In step S310, the method of application is not particularly limited as long as the titanium oxide nanosheet dispersion liquid can be applied to the metal substrate, but illustrative methods are selected from the group consisting of spin coating, dip coating, LB (Langmuir-Blodgett) method, dropping method, alternate adsorption method, and spray method. Among these, the spin coating method is advantageous in that a very uniform titanium oxide nanosheet monolayer film can be obtained.

[0040] For example, when using the spin coating method, the concentration of the titanium oxide nanosheet dispersion liquid and the size of the metal substrate will vary, but within the above-mentioned concentration range, the concentration is 5 μL / cm 2 More than 50μL / cm 2 The titanium oxide nanosheet dispersion liquid is dropped in the following range, and the rotation speed is in the range of 500 rpm to 8000 rpm, and the spin coating time is in the range of 1 minute to 15 minutes. From the viewpoint of the coverage rate on the metal substrate, it is more preferable to use 20 μL / cm 2 More than 40μL / cm 2 The titanium oxide nanosheet dispersion liquid may be dropped in the following range, and the rotation speed may be in the range of 1000 rpm to 1350 rpm, and the spin coating time may be in the range of 2 minutes to 10 minutes.

[0041] In this manner, it is possible to provide a negative electrode for a metal-air battery, which comprises a thin film made of a monolayer film of a titanium oxide nanosheet (titanium oxide nanosheet monolayer film) on a metal substrate.

[0042] By repeating step S310, a thin film made of a titanium oxide nanosheet multilayer film in which the titanium oxide nanosheet monolayer film is multilayered can be obtained. The number of repetitions is not particularly limited, but may be preferably 10 times or less.

[0043] Following step S310, a current collector as described above may be applied to the side of the metal substrate facing the thin film.

[0044] (Embodiment 2) In the second embodiment, a metal-air battery using the negative electrode for a metal-air battery of the present invention will be described in detail. FIG. 4 is a schematic diagram showing a metal-air battery of the present invention.

[0045] The metal-air battery 400 of the present invention includes a negative electrode 410, an air electrode 420 which is a positive electrode, and an electrolyte 430 located between the negative electrode 410 and the air electrode 420. The negative electrode 410 is the metal-air battery negative electrode 100 described in the first embodiment, and therefore a description thereof will be omitted. The metal-air battery 400 of the present invention not only suppresses the generation of dendrites from the surface of the negative electrode due to the titanium oxide nanosheet monolayer film of the negative electrode 410, but also has low hydrogen generating activity and suppresses side reactions such as hydrogen generation and corrosion, resulting in an excellent cycle life.

[0046] A known cathode that uses oxygen as an active material can be used as the cathode 420. The cathode 420 preferably includes a catalyst that absorbs oxygen from the air and reacts it with oxygen. The catalyst is preferably selected from the group consisting of metals, metal oxides, metal oxynitrides, metal nitrides, metal borides, metal silicides, and metal sulfides.

[0047] The metal is at least one selected from the group consisting of titanium, zirconium, sodium, calcium, barium, magnesium, aluminum, silicon, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, yttrium, niobium, tin, tungsten, tantalum, indium, lanthanum, lead, strontium, bismuth, cerium, molybdenum, and hafnium. Metal oxides, metal oxynitrides, metal nitrides, metal borides, metal silicides, and metal sulfides may be compounds of the selected metals. These are preferred because they suppress the generation of by-products at the air electrode.

[0048] The air electrode 420 may contain a conductive material to improve the conductivity. The conductive material may be carbon black such as Ketjen black or acetylene black, a carbonaceous material such as carbon nanotubes, or a conductive polymer. The conductive material may be contained in the range of 1% by mass to 10% by mass with respect to the catalyst.

[0049] The catalyst may be processed into a layer shape together with a conductive material using a binder, which may be an olefin resin such as polyethylene or polypropylene, a fluorine-based resin such as polyvinylidene fluoride or polytetrafluoroethylene, or a rubber-based resin such as styrene-butadiene rubber.

[0050] The air electrode 420 may further include a current collector. The current collector may be made of a material having electrical conductivity, such as copper, stainless steel, nickel, or carbon, and may be in the form of a foil, plate, or mesh. From the viewpoint of oxygen supply performance, it is preferable for the current collector to have a porous structure such as carbon paper or a metal mesh.

[0051] When the air electrode 420 comprises the above-mentioned layered catalyst and current collector, these can be set appropriately depending on the application, but for example, the layered catalyst may have a thickness in the range of 2 μm to 500 μm, and the current collector may have a thickness in the range of 10 μm to 1 mm.

[0052] The air electrode 420 can be manufactured by a known method, but for example, the air electrode 420 can be obtained by mixing the above-mentioned catalyst together with a conductive material and a binder in a solvent as necessary, applying the mixture to a current collector, and drying the mixture.

[0053] The electrolyte 430 is located between the negative electrode 410 and the air electrode 420, and any electrolyte used in metal-air batteries can be used. Such electrolytes include aqueous electrolytes, non-aqueous electrolytes, ionic liquids, and solid electrolytes. When an aqueous electrolyte, non-aqueous electrolyte, or ionic liquid is used, it is preferable to impregnate and hold the electrolyte in a separator (not shown). The separator is a porous membrane made of a resin such as polyethylene or polypropylene.

[0054] The aqueous electrolyte may be any electrolyte that has electrical conductivity, and may be an electrolyte solution in which an alkali metal salt such as lithium, sodium, or potassium, or a zinc salt is dissolved in water.Specific examples of the electrolyte include an aqueous solution of lithium chloride, an aqueous solution of potassium chloride, an aqueous solution of sodium chloride, an aqueous solution of lithium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of sodium hydroxide, an aqueous solution of lithium nitrate, an aqueous solution of potassium nitrate, an aqueous solution of sodium nitrate, an aqueous solution of lithium acetate, an aqueous solution of potassium acetate, an aqueous solution of sodium acetate, an aqueous solution of zinc sulfate, an aqueous solution of zinc nitrate, an aqueous solution of zinc phosphate, and an aqueous solution of zinc acetate.

[0055] Non-aqueous electrolytes include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, dimethoxymethane, diethoxymethane, dimethoxyethane, tetrahydrofuran, methyltetrahydrofuran, diethoxyethane, dimethylsulfoxide, sulfolane, acetonitrile, benzonitrile, ionic liquids, fluorine-containing carbonates, fluorine-containing ethers, polyethylene glycols, and fluorine-containing polyethylene glycols.

[0056] Ionic liquids are substances that consist of a combination of anions and cations and are liquid at room temperature. Representative anions include halide anions, BF4 - Boronide anions such as (CN)2N - Amide anion, sulfate anion, PF6 -Representative cations include imidazoliums such as 2-ethylimidazolium, ammoniums such as diethylmethylammonium, pyridiniums such as alkylpyridiniums, pyrrolidiniums such as dialkylpyrrolidiniums, phosphoniums, sulfoniums, etc. The ionic liquid may further contain a known supporting salt.

[0057] The solid electrolyte may be a known solid electrolyte that allows metal ions of the negative electrode active material to pass therethrough when a voltage is applied. Examples of such solid electrolytes include glass ceramics. The solid electrolyte may also be combined with a non-aqueous electrolyte solution.

[0058] The metal-air battery 400 of the present invention may be housed in a case (not shown). The case may be made of aluminum (Al), stainless steel, nickel-plated steel, or the like. The shape of the metal-air battery 400 may be a coin type, a button type, a sheet type, a cylindrical type, a square type, or the like. The case may be an open-to-air type or a sealed type. In the sealed type, an oxygen (air) inlet pipe and a drain pipe may be provided for the air electrode 420. In FIG. 4, the metal-air battery 400 of the present invention shows a set of the negative electrode 410, the air electrode 420, and the electrolyte 430, but a plurality of these may be integrated. Such modifications are within the scope of the present invention and will be understood by those skilled in the art.

[0059] The metal-air battery 400 of the present invention is charged by connecting it to an external power source and applying a positive potential to the air electrode 420 and a negative potential to the negative electrode 410. The metal-air battery 400 is discharged by connecting a discharge circuit to the negative electrode 410 and the air electrode 420 and passing electricity through the discharge circuit of an electronic device, an electric vehicle, or the like.

[0060] Next, a method for producing the metal-air battery 400 of the present invention will be described. The metal-air battery 400 may be prepared, for example, by laminating the negative electrode 410, the air electrode 420, and the electrolyte 430. In particular, when the electrolyte 430 is an aqueous electrolyte, a non-aqueous electrolyte, or an ionic liquid, a separator may be disposed on the negative electrode 410, the separator may be impregnated with the electrolytic solution, and then the air electrode 420 may be laminated.

[0061] The present invention will now be described in detail with reference to specific examples, but it should be noted that the present invention is not limited to these examples. EXAMPLES

[0062] [reagent] The following reagents were used: Potassium carbonate (K2CO3, 99.9%, Rare Metallic Co., Ltd.), titanium dioxide (TiO2, 99.99%, Rare Metallic Co., Ltd.), lithium carbonate (Li2CO3, 99.99%, Rare Metallic Co., Ltd.), hydrochloric acid (HCl, 35 wt%, Kishida Chemical Co., Ltd.), tetrabutylammonium hydroxide solution (TBAOH, 10 wt%, Wako special grade, Fujifilm Wako Pure Chemical Co., Ltd.), dimethyl sulfoxide (DMSO, reagent grade, Fujifilm Wako Pure Chemical Co., Ltd.), zinc sulfate (ZnSO4, Wako grade 1, Fujifilm Wako Pure Chemical Co., Ltd.), and sodium sulfate (Na2SO4, reagent grade, Fujifilm Wako Pure Chemical Co., Ltd.) were obtained and used as is.

[0063] [Substrate etc.] Zinc substrates (Zn, 2cm x 2cm x 0.25mm, 99.98%, Alfa Aesar), silicon substrates (Si, 2cm x 2cm x 0.525mm, SUMCO), and stainless steel (SS, 2cm x 2cm x 0.025mm, Type 304, Alfa Aesar) were used. The zinc substrates were polished before use. The surface roughness after polishing was measured with an atomic force microscope (AFM, AFM5000II, Hitachi High-Tech Science), and was found to be Ra = 3.7nm.

[0064] [Preparation of titanium oxide nanosheets] A mixture of K2CO3, TiO2 and Li2CO3 (molar ratio 0.42:1.73:0.135) was sintered at 1000℃ for 20 hours to obtain layered titanate K 0.8 Ti 1.73 Li 0.27 O4 was obtained. This (15 g) was treated with HCl (1 mol / L, 1 L) for 3 days, and K + H + H exchanged for 1.07 Ti 1.73 O4·H2O was derived. K 0.8 Ti 1.73 Li 0.27 O4 powder and H 1.07 Ti 1.73 The O4·H2O powder was subjected to powder X-ray diffraction measurement (Rigaku Corporation, Rint-2200, Cu Kα radiation (λ=1.5405 Å)) and observation with a scanning electron microscope (SEM, JSM-6010LA, JEOL Ltd.). The results are shown in Figures 5 to 7.

[0065] Figure 5 shows the K 0.8 Ti 1.73 Li 0.27 O4 powder and H 1.07 Ti 1.73 Figure 1 shows the XRD pattern of O4·H2O powder.

[0066] According to Figure 5, K 0.8 Ti 1.73 Li 0.27 The O4 powder has a crystalline phase with an orthorhombic crystal system with lattice constants a = 0.3818(1) nm, b = 1.5471(6) nm, and c = 0.29972(2) nm. 1.07 Ti 1.73 The O4·H2O powder was also confirmed to be a crystalline phase having an orthorhombic system with lattice constants a = 0.37839(9) nm, b = 1.8363(4) nm, and c = 0.2966(2) nm.

[0067] Figure 6 shows the 0.8 Ti 1.73 Li 0.27 FIG. 1 shows an SEM image of O4 powder. Figure 7 shows the H 1.07 Ti 1.73Figure 1 shows an SEM image of O4·H2O powder.

[0068] 6 and 7, it was found that the plate-like layers were composed of stacked particles, with particle sizes of several tens of micrometers.

[0069] H 1.07 Ti 1.73 O4·H2O powder (4 g) was mixed with TBA + / H + When the specimen was immersed in a TBAOH (1 L) solution with a concentration of 0.01% and shaken intermittently for 30 days, the Ti was peeled off into a single layer. 0.87 A titanium oxide nanosheet dispersion liquid in which O2 was dispersed was obtained. This dispersion liquid was centrifuged at 10,000 rpm for 30 minutes, and the resulting precipitate was redispersed in DMSO to obtain a titanium oxide nanosheet DMSO dispersion liquid. 0.87 The concentration of the O2 nanosheets was adjusted to 0.1 wt%. In the following, when discussing the dispersion or monolayer film, we will refer to them as "titanium oxide nanosheets," and when discussing the properties of the nanosheets, such as their concentration and zeta potential, we will refer to them as "Ti 0.87 They call it "O2 nanosheet."

[0070] The zeta potential in the dispersion was measured using a zeta potential / particle size measurement system (ELSZ-2, manufactured by Otsuka Electronics Co., Ltd.) The results are shown in FIG.

[0071] FIG. 8 is a diagram showing the zeta potential of a titanium oxide nanosheet dispersion liquid.

[0072] According to FIG. 8, the zeta potential of the titanium oxide nanosheet dispersion is −27 mV. 0.87 It was confirmed that the O2 nanosheets were negatively charged. When ZnSO4 electrolyte, which is commonly used as an electrolyte for zinc-ion batteries, was added to this colloidal dispersion, Zn 2+ and Ti 0.87 The electrostatic attraction between the O2 nanosheets caused them to aggregate and become cloudy. In the following, a titanium oxide nanosheet dispersion was used.

[0073] [Example 1] In Example 1, an electrode including a zinc substrate having a monolayer film made of a titanium oxide nanosheet (hereinafter referred to as a titanium oxide nanosheet monolayer film) was prepared according to the procedure of FIG.

[0074] In detail, the zinc substrate was subjected to oxygen (O2) plasma treatment for 2 minutes using a surface treatment device (PIB-20, manufactured by Vacuum Device Co., Ltd.) to clean the surface. A titanium oxide nanosheet dispersion (Ti 0.87 O2 nanosheet concentration: 0.1wt%, 120μL, 30μL / cm 2 The sample was spin-coated using a spin coater (MS-B100, manufactured by Mikasa Co., Ltd.). The spin-coating conditions were a rotation speed of 100 rpm for 5 seconds and 1200 rpm for 300 seconds. 0.87 The sample is called O2@Zn. In order to observe the thin film and observe the in-plane diffraction, a single layer of titanium oxide nanosheet was also formed on a silicon substrate. 0.87 For simplicity, these samples may be collectively referred to as the sample of Example 1.

[0075] The morphology of the surface of the sample of Example 1 was observed using an SEM. The results are shown in Figures 9 and 10. Powder X-ray diffraction and in-plane X-ray diffraction were performed on the sample of Example 1. The in-plane X-ray diffraction pattern was obtained using BL-6C: X-ray diffraction and scattering experimental station (synchrotron X-ray (λ = 1.1991 Å)) at the Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Inter-University Research Institute Corporation. The cross section of the sample of Example 1 was observed and elemental analysis was performed using a transmission electron microscope (TEM, JEM-2100F, manufactured by JEOL Ltd.) equipped with energy dispersive X-ray spectroscopy (EDS). The sample for TEM was prepared using a FIB-SEM double beam device (Xvision200DB, manufactured by Hitachi High-Tech Science Corporation). These results are shown in Figures 11 to 14.

[0076] The surface condition of the sample of Example 1 was examined using an X-ray photoelectron spectrometer (XPS, PHI 680, manufactured by ULVAC-PHI, Inc.) and a time-of-flight secondary ion mass spectrometer (TOF-SIMS, PHI TRIFT V nanoTOF, manufactured by ULVAC-PHI, Inc.). The results are shown in Figures 15 and 16. In addition, the contact angle of the surface of the sample of Example 1 was measured using a contact angle meter (CA-XP, manufactured by Kyowa Interface Science Co., Ltd.).

[0077] The electrolyte was 1M Na2SO4 or 1M ZnSO4, and the working electrode was the sample of Example 1 (Ti 0.87 Linear sweep voltammetry (LSV) was measured using an electrochemical station (AUT87433, Autolab) in a three-electrode system with a 1M ZnSO4 electrolyte, a glass fiber filter paper (Whatman) as a separator, and the sample of Example 1 as a negative electrode. A 2032-type symmetric coin cell was assembled using 1M ZnSO4 as an electrolyte, glass fiber filter paper (Whatman) as a separator, and the sample of Example 1 as a negative electrode. The performance of zinc deposition / dissolution in the symmetric coin cell of Example 1 was evaluated using a battery charge / discharge device (HJ1001SD8, Hokuto Denko Corporation). The state of the sample of Example 1 after the charge / discharge measurement was observed by SEM. These results are shown in Figures 17, 18, 20, and 22.

[0078] [Example 2] In Example 2, an electrode including a zinc substrate having a titanium oxide nanosheet monolayer film was prepared in the same manner as in Example 1, except that the rotation speed was set to 1400 rpm. The obtained sample was called the sample of Example 2 and was evaluated in the same manner as in Example 1. The results are shown in FIG.

[0079] [Example 3] In Example 3, an electrode including a zinc substrate having a titanium oxide nanosheet monolayer film was prepared in the same manner as in Example 1, except that the rotation speed was set to 2000 rpm. The obtained sample was called the sample of Example 3 and was evaluated in the same manner as in Example 1. The results are shown in FIG.

[0080] [Example 4] In Example 4, an electrode having a zinc substrate with a multilayer film made of titanium oxide nanosheets (hereinafter referred to as a titanium oxide nanosheet multilayer film) was prepared in the same manner as in Example 1, except that the operation of Example 1 was repeated twice. The obtained sample was treated as the sample of Example 4 or Ti 0.87 This was called O2@Zn-2T and was evaluated in the same manner as in Example 1. The results are shown in Figure 12.

[0081] [Example 5] In Example 5, an electrode having a zinc substrate with a titanium oxide nanosheet multilayer film was prepared in the same manner as in Example 1, except that the operation of Example 1 was repeated five times. The obtained sample was called the sample of Example 5 or Ti 0.87 This was called O2@Zn-5T and was evaluated in the same manner as in Example 1. The results are shown in Figure 12.

[0082] [Example 6] In Example 6, an electrode having a stainless steel substrate with a titanium oxide nanosheet monolayer film was prepared in the same manner as in Example 1, except that the substrate was stainless steel. 0.87 This was called O2@SS and was evaluated in the same manner as in Example 1. The results are shown in Figure 23.

[0083] [Examples 7 and 8] In Examples 7 and 8, a zinc substrate and stainless steel were used as they were for the electrodes, respectively, and were evaluated in the same manner as in Example 1. The results are shown in Figs. 11, 15, 19, and 21 to 23.

[0084] For simplicity, the samples of Examples 1 to 8 are summarized in Table 1, and the results are explained.

[0085] [Table 1]

[0086] FIG. 9 is a diagram showing SEM images of the samples of Examples 1 to 3. FIG. 10 shows an SEM image and an AFM image of the sample of Example 1.

[0087] In the SEM image, the dark areas correspond to areas where titanium dioxide nanosheets are densely deposited in a single layer, and the bright areas correspond to areas where titanium dioxide nanosheets are not deposited.

[0088] Figures 9(a) to (c) are SEM images of the samples of Example 3 to Example 1, respectively. As shown in Figure 9, in the samples of Example 2 and Example 3 obtained by spin coating at high speeds of 1400 rpm and 2000 rpm, the titanium oxide nanosheet was not deposited in the center of the zinc substrate, leaving a portion exposed. In this case, the SEM images show that the coverage (the coverage of the titanium oxide nanosheet with respect to the total surface area of ​​the substrate) was 47% for the sample of Example 2 and 37% for the sample of Example 3.

[0089] On the other hand, in the sample of Example 1 obtained by spin coating at 1200 rpm, it was found that a uniform, high-quality film made of titanium oxide nanosheets was produced that completely covered the centimeter-scale area of ​​the substrate (coverage rate 100%). Although it depends on the concentration of the titanium oxide nanosheet dispersion, if the concentration of the titanium oxide nanosheets is in the range of 0.08 wt% to 0.12 wt%, it is possible to obtain a film of 20 μL / cm. 2 More than 40μL / cm 2 It was shown that it is effective to drop the titanium oxide nanosheet dispersion liquid in the range below, and to adopt a rotation speed in the range of 1000 rpm or more and 1350 rpm or less and a spin coating time in the range of 2 minutes or more and 10 minutes or less.

[0090] FIG. 10(a) shows the sample of Example 1 (Ti 0.87 A more enlarged SEM image of O2@Zn is shown in Figure 10(a). Titanium oxide nanosheets with sizes ranging from several micrometers to several tens of micrometers are densely arranged on the zinc substrate with no gaps.

[0091] FIG. 10(b) shows the sample of Example 1 (Ti 0.87Figure 10(b) shows an AFM image of the titanium oxide nanosheet (O2@Si). The AFM image in Figure 10(b) is a smooth and dense film with a thickness of about 1 nm, similar to the SEM image in Figure 10(a), and is a titanium oxide nanosheet monolayer film. From this, it can be said that the thin film on the zinc substrate is also a titanium oxide nanosheet monolayer film.

[0092] Although not shown, the thin films of the samples of Examples 4 and 5 were also smooth and dense films, but their thicknesses were about 2 nm and about 5 nm, respectively. From this, it was confirmed that the thin films of the samples of Examples 4 and 5 were titanium oxide nanosheet multilayer films in which the single-layer films were multilayered.

[0093] FIG. 11 shows the XRD pattern of the sample of Example 1. FIG. 12 shows the XRD patterns of the samples of Examples 4 and 5. FIG. 13 is a diagram showing an in-plane XRD pattern of the sample of Example 1.

[0094] FIG. 11 also shows the XRD pattern of the zinc substrate having a hexagonal crystal structure. According to FIG. 11, the sample of Example 1 (Ti 0.87 The XRD pattern of O2@Zn) coincided with that of the zinc substrate and showed no new peaks after spin-coating.

[0095] On the other hand, according to Fig. 12, the XRD patterns of the samples of Examples 4 and 5 showed a new peak at 2θ = 5.8°. This peak corresponds to an interlayer distance of 1.5 nm, and the peak intensity of the sample of Example 5 was greater than that of the sample of Example 4. This is because the titanium oxide nanosheets have TBA between the layers. + The thin films of the samples in Examples 4 and 5 are titanium oxide nanosheet multilayer films. By laminating the layers layer by layer, a high-quality multilayer film that maintains the denseness and smoothness of a single layer film is realized.

[0096] FIG. 13 shows the results of the sample of Example 1 (Ti 0.87 The in-plane XRD pattern of TiO2@Si with unit cell size (a=0.3760nm and c=0.2976nm) is shown.0.87 The indexing was achieved by a two-dimensional rectangular lattice of O2 nanosheets, indicating the presence of a monolayer of nanosheets on the silicon substrate surface.

[0097] FIG. 14 shows a TEM image, an electron diffraction pattern, a STEM image and an EDS mapping of the sample of Example 1.

[0098] FIG. 14(a) shows the sample of Example 1 (Ti 0.87 The cross-sectional TEM image of O2@Zn clearly shows a 1 nm-thick monolayer of nanosheets laminated on the surface of the zinc substrate. The electron diffraction pattern from the zinc substrate in Figure 14(b) is consistent with zinc metal with a hexagonal crystal structure, and no other diffraction patterns were observed.

[0099] Figure 14(c) is a STEM image of the sample of Example 1, and Figures 14(d)-(f) show EDS mappings of oxygen (O), zinc (Zn) and titanium (Ti), respectively. Figures 14(d)-(f) are shown in grayscale, with each element present in the bright areas. Figures 14(d)-(f) confirm that Zn is uniformly distributed in the area corresponding to the zinc substrate, and that a thin layer of O and Ti elements is formed on the zinc substrate.

[0100] FIG. 15 shows the XPS spectrum of the sample of Example 1.

[0101] FIG. 15(a) shows the sample of Example 1 (Ti 0.87 In addition to the XPS spectrum of O2@Zn, the XPS spectrum of the zinc substrate is also shown. According to FIG. 15(a), the sample of Example 1 showed a titanium (Ti) peak in addition to the zinc (Zn), carbon (C) and oxygen (O) peaks. Since the zinc peak intensity did not decrease significantly before and after coating with the titanium oxide nanosheet, this suggests that the sample of Example 1 has a titanium oxide nanosheet present on the zinc substrate as a monolayer film with a thickness of 1 nm.

[0102] 15(b) to (d) show the Zn2p 3 / 2 , O1s, Ti2p1 / 2 and Ti2p 3 / 2 According to FIG. 15(b), the peak observed at 1021.8 eV is due to Zn2p in the metallic state. 3 / 2 This corresponds to the bond energy of 531.7 eV, which indicates that the zinc on the substrate is in a metallic state. The O1s peak shown in Fig. 15(a) can be separated into two peaks, 531.7 eV due to the C-O bond and 530.3 eV due to the TO bond, as shown in Fig. 15(c). According to Fig. 15(d), the peaks at 464.3 eV and 458.7 eV correspond to the Ti2p peaks of the Ti-O bond, respectively. 1 / 2 and Ti2p 3 / 2 This indicates that the titanium in the titanium oxide nanosheets is tetravalent.

[0103] FIG. 16 shows a TOF-SIMS spectrum of the sample of Example 1.

[0104] Figure 16(a) shows the TOF-SIMS spectra of zinc (Zn) and titanium (Ti) in the range of the surface depth of the sample of Example 1 of 2 nm or less. Figures 16(b) to (d) show enlarged TOF-SIMS spectra of Zn with mass numbers of 64, 66, and 68. According to Figures 16(b) to (d), the peak intensity of Ti was much greater than that of Zn. This indicates that in the sample of Example 1, the titanium oxide nanosheet monolayer film covers the entire surface of the zinc substrate.

[0105] Figures 16(e)-(g) show the distribution of all fragment cations, Ti ions, and Zn ions, respectively, for the sample of Example 1. In the figures, the arrows indicate scratches that occurred during sample preparation. According to Figures 16(e)-(g), the Ti ions and Zn ions are uniformly distributed, and the interface between the zinc substrate and the titanium oxide nanosheet monolayer film was kept clean without any reaction occurring.

[0106] From the above, it has been demonstrated that the method of the present invention shown in FIG. 3 can provide a metal substrate provided with a thin film which is a titanium oxide nanosheet monolayer film or multilayer film.

[0107] FIG. 17 shows the charge / discharge curves of the symmetric coin cells of Examples 1 and 7. FIG. 18 shows the results of cycling tests of the symmetric coin cells of Example 1 for various periods of time. FIG. 19 shows the results of cycling tests of the symmetric coin cells of Example 7 for various periods of time.

[0108] 17(A) and (B) show the charge / discharge curves at different current densities in the symmetric coin cells of Example 1 and Example 7, respectively. According to FIG. 17, the voltage hysteresis (i.e., the potential difference between charge and discharge) of the symmetric coin cells of Example 1 and Example 7 both increased with increasing current density. This confirmed that the polarization of zinc deposition / dissolution occurred in the symmetric coin cells.

[0109] More specifically, the voltage hysteresis of the symmetric coin cell of Example 1 is measured at a current density of 0.5 mA / cm 2 to 10mA / cm 2 and then increased stepwise to 0.5 mA / cm 2 On the other hand, the symmetric coin cell of Example 7 changed its current density at a current density of 0.5 mA / cm 2 to 10mA / cm 2 Specifically, the current increases stepwise to 5 mA / cm 2 A short circuit occurred when the capacitance increased to 1. This is believed to be due to dendritic growth.

[0110] Figures 18 and 19 show the results for a current density of 1 mA / cm 2 , capacity 1mhA / cm 2 The results of cycle tests of the symmetric coin cells of Examples 1 and 7 in the above are shown. As shown in Fig. 19, the symmetric coin cell of Example 7 using an electrode without a titanium oxide nanosheet shorted out after a cycle of 105 hours, whereas, as shown in Fig. 18, the symmetric coin cell of Example 1 using an electrode with a titanium oxide nanosheet monolayer film operated stably without shorting up to 1400 hours. In other words, it was found that the use of an electrode with a titanium oxide nanosheet monolayer film improved cycle stability by 13 times or more.

[0111] Although not shown, the cycle stability of symmetric coin cells using the samples of Examples 2 and 3 was improved over that of Example 7, but not as good as that of Example 1. This suggests that by covering a portion of the metal substrate with a titanium oxide nanosheet monolayer film, dendrite growth is suppressed and battery characteristics are improved, and a coverage rate of 50% or more is preferable.

[0112] In addition, the symmetric coin cells using the samples of Examples 4 and 5 showed cycle stability similar to that of Example 1. This suggests that the titanium oxide nanosheet multilayer film is advantageous in suppressing dendrite growth.

[0113] According to Fig. 19(a), the voltage hysteresis of both the symmetric coin cells of Example 1 and Example 7 decreased in the first few cycles, indicating a decrease in the polarization of the battery. However, according to Fig. 19(b) and (c), the symmetric coin cell of Example 1 showed a smaller voltage hysteresis than the symmetric coin cell of Example 7, reaching a low stable value of 67 mV and maintaining it up to 1400 hours.

[0114] FIG. 20 is a diagram showing an SEM image of the sample of Example 1 after the charge-discharge test. FIG. 21 is a diagram showing an SEM image of the sample of Example 7 after the charge-discharge test.

[0115] As shown in Fig. 20, it was found that the sample of Example 1 having the titanium oxide nanosheet monolayer film maintained a relatively flat surface even after 1400 hours of charge-discharge testing. This is because, as described with reference to Figs. 2 and 8, the titanium oxide nanosheet monolayer film is oxidized by electrostatic interaction with Zn 2+ Attracted Zn 2+ This is because the zinc is uniformly distributed over the entire surface of the monolayer film, thereby making it possible to suppress the zinc from growing in a dendritic form.

[0116] On the other hand, the sample of Example 7, which did not have a titanium oxide nanosheet monolayer film, had dendrites on the surface (the area indicated by the dotted line in the figure) as shown in Figure 21. Furthermore, the fiber shown in Figure 21 is a separator, and it is believed that the zinc that broke through the separator (the area indicated by the arrow in the figure) caused the short circuit.

[0117] From the above, it has been demonstrated that a metal substrate provided with a thin film, which is a single-layer film or a multilayer film, made of the titanium oxide nanosheet of the present invention can function as a negative electrode of a metal-air battery, and in particular, can suppress the formation of dendrites.

[0118] The results of the wettability of the sample of Example 1 will be described. The contact angle when a drop of water was dropped on the surface of the sample of Example 1 was 4.5°, and that of the surface of the sample of Example 7 was 90°. In other words, it was found that the titanium oxide nanosheet monolayer film dramatically improves the wettability of the surface. This suggests that the negative electrode of the present invention is also effective for metal-air batteries because it can reduce the contact resistance when an aqueous electrolyte is used.

[0119] FIG. 22 is a diagram showing the LSV curves of the samples of Examples 1 and 7.

[0120] Fig. 22(a) is an LSV curve when Na2SO4 electrolyte is used, and Fig. 22(b) is an LSV curve when ZnSO4 electrolyte is used. The LSV curve for Na2SO4 electrolyte reflects the generation of hydrogen (H2), and the LSV curve for ZnSO4 electrolyte reflects the combined activity of hydrogen generation and zinc deposition.

[0121] According to Fig. 22(a), the sample of Example 7 showed a higher current density and higher hydrogen generation activity than the sample of Example 1. A spike was observed in the curve of the sample of Example 7, and intense hydrogen gas generation was observed. On the other hand, according to Fig. 22(b), the samples of Example 1 and Example 7 showed similar current densities, and it was found that the combined activities of zinc deposition and hydrogen generation were comparable.

[0122] From the above, it was found that the sample of Example 1 having the titanium oxide nanosheet monolayer film had higher zinc deposition reaction activity and lower hydrogen generation activity than the sample of Example 7 not having the titanium oxide nanosheet monolayer film. This indicates that if the sample of Example 1 is used as an electrode, it is possible to promote zinc deposition while suppressing hydrogen generation, and that zinc ions (Zn 2+ ) is strongly supported as the preferred adsorption site.

[0123] FIG. 23 shows the constant current (1 mA / cm 2 3 shows the potential change during zinc deposition under a 0.2 V condition.

[0124] 23, the nucleation overpotentials of zinc in the samples of Example 6 and Example 8 were found to be 85 mV and 90 mV, respectively. The fact that the nucleation overpotential of the sample of Example 6 was smaller than that of Example 8 suggests that the titanium oxide nanosheet monolayer film effectively promoted the nucleation of zinc and effectively reduced the electrochemical polarization of the zinc electrode.

[0125] Although the above description has been given using zinc as the metal substrate, it goes without saying that the effects of the titanium oxide nanosheet monolayer film are not limited to zinc, and those skilled in the art will understand that similar effects can be obtained with various metal substrates used in the negative electrodes of metal-air batteries.

[0126] As described above, the negative electrode of the present invention comprises a metal substrate made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe), and a thin film made of a titanium oxide nanosheet monolayer film or multilayer film located thereon, and can be used as the negative electrode of a metal-air battery. In particular, since dendrite growth in the negative electrode is suppressed, a metal-air battery with excellent cycle life can be provided. [Industrial Applicability]

[0127] The negative electrode for a metal-air battery of the present invention can suppress dendrite growth and side reactions, and therefore, by applying such a negative electrode, a metal-air battery with a large capacity and excellent cycle life can be provided, which can contribute to portable power sources for drones and unmanned aerial vehicles, storage batteries for electric vehicles, large-scale storage systems for renewable energy power generation, and storage batteries used in conjunction with home solar power generation. [Explanation of symbols]

[0128] 100 Negative electrode for metal-air battery 110 Metal Substrate 120 Titanium oxide nanosheet 130 Titanium oxide nanosheet monolayer film 140 Thin Film 400 Metal-air battery 410 negative electrode 420 Air pole 430 Electrolytes

Claims

1. a metal substrate made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe); a thin film consisting of a titanium oxide nanosheet monolayer film located on the metal substrate; A metal-air battery negative electrode comprising:

2. 2. The metal-air battery negative electrode according to claim 1, wherein the contact angle of water with the surface of the thin film is in the range of 0° to 10°.

3. 2. The metal-air battery negative electrode according to claim 1, wherein the titanium oxide nanosheet monolayer film has a thickness in the range of 0.5 nm to 1.5 nm.

4. 4. The metal-air battery negative electrode according to claim 3, wherein the thickness of the thin film is in the range of 0.5 nm to 10 nm.

5. The titanium oxide nanosheets constituting the titanium oxide nanosheet monolayer film are Ti ０．８７ O ２ , Ti ０．９１ O ２ , Ti ３ O ７ , Ti ４ O ９ , and Ti ５ O １１ The negative electrode for a metal-air battery according to claim 1 , selected from the group consisting of:

6. 2. The metal-air battery negative electrode according to claim 1, wherein the titanium oxide nanosheet constituting the titanium oxide nanosheet monolayer film has a thickness of 0.5 nm to 1.5 nm and a longitudinal length of 5 μm to 30 μm.

7. 2. The negative electrode for a metal-air battery according to claim 1, wherein the metal substrate has a thickness in the range of 10 μm to 1 mm.

8. 2. The negative electrode for a metal-air battery according to claim 1, wherein the metal substrate has a surface roughness Ra of 10 nm or less.

9. 2. The metal-air battery negative electrode according to claim 1, wherein the titanium oxide nanosheet has an alkylammonium cation having an alkyl group having 1 to 20 carbon atoms.

10. 10. The metal-air battery negative electrode according to claim 9, wherein the alkylammonium cation is at least one selected from the group consisting of a tetramethylammonium ion, a tetraethylammonium ion, a tetrapropylammonium ion, a tetrabutylammonium ion, and a benzylmethylammonium ion.

11. 11. The method for producing a metal-air battery negative electrode according to claim 1, comprising applying a dispersion liquid containing titanium oxide nanosheets to the surface of a metal substrate made of one metal selected from the group consisting of zinc (Zn), lithium (Li), magnesium (Mg), aluminum (Al), and iron (Fe).

12. The method of claim 11 , wherein the applying is selected from the group consisting of a spin coating method, a dip coating method, an LB method, a dropping method, a layer-by-layer adsorption method, and a spray method.

13. A metal-air battery comprising a negative electrode, an air electrode, and an electrolyte located between the negative electrode and the air electrode, The metal-air battery, wherein the negative electrode is the metal-air battery negative electrode according to any one of claims 1 to 10.

14. 14. The metal-air battery according to claim 13, wherein the air electrode contains a catalyst selected from the group consisting of a metal, a metal oxide, a metal oxynitride, a metal nitride, a metal boride, a metal silicide, and a metal sulfide.

15. Further comprising a separator, 14. The metal-air battery according to claim 13, wherein the electrolyte is impregnated in the separator.

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