Redox mediator coated porous carbon sheet, positive electrode for air battery, air battery, and method for manufacturing redox mediator coated porous carbon sheet

Abstract

To provide a redox mediator coated porous carbon sheet that can effectively suppress charging overvoltage while increasing the cycle capacity of an air battery, a positive electrode for an air battery, an air battery, and a method for manufacturing the redox mediator coated porous carbon sheet.SOLUTION: In a redox mediator coated porous carbon sheet according to an embodiment of the present invention, a redox mediator that mediates the oxidative decomposition of a metal oxide through its own redox reaction is fixed to the surface of the porous carbon sheet, and the fixed amount of the redox mediator is 0.2 mg / cm2 or more and less than 2.9 mg / cm2.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a redox mediator-coated porous carbon sheet, a positive electrode for an air battery, an air battery, and a method for producing a redox mediator-coated porous carbon sheet. [Background technology]

[0002] The spread of renewable energy and the demand for electrified vehicles have necessitated the development of lightweight, high-capacity storage batteries, i.e., batteries with higher energy density. Among the secondary batteries that can be envisioned for realization, the lithium-air battery has the highest theoretical energy density, and it is expected that storage batteries will become significantly smaller, lighter, and have higher capacities.

[0003] Lithium-air batteries use lithium metal as the negative electrode active material and oxygen in the air as the positive electrode active material in an electrochemical reaction. During discharge, lithium metal dissolves into the electrolyte at the negative electrode (Li → Li + +e - ), at the positive electrode, lithium ions undergo a reduction reaction with electrons from the external circuit and oxygen (O2) absorbed from the air, and lithium peroxide is precipitated (2Li + +2e - +O2→Li2O2). During charging, the reverse reaction occurs, with lithium peroxide decomposing at the positive electrode, turning into lithium ions and oxygen. Lithium-air batteries charge and discharge by repeating this process. The positive electrode is also called the air electrode, since it is an electrode that absorbs and releases oxygen from the air as it is charged and discharged.

[0004] In order to improve the output and capacity of a lithium-air battery cell, the positive electrode must have sufficient electrical conductivity as an electrode, a wide electrochemically active surface where the battery reaction occurs, and a diffusion path for supplying the battery reactants oxygen and lithium ions to the electrochemically active surface. During discharge, this diffusion path also serves to provide a space for accumulating lithium peroxide (Li2O2) without inhibiting the growth of the solid deposit of lithium peroxide (Li2O2). For this reason, it is preferable that the positive electrode has a continuous pore structure inside that allows easy diffusion of substances, and has as large a pore volume and surface area as possible.

[0005] As materials for producing such porous positive electrodes, conductive carbon materials with nanostructures that have large surface areas and pore volumes, specifically carbon black, graphene, carbon nanotubes (CNTs), etc., have been considered.

[0006] In Patent Document 1, a large specific surface area (1,000 m) called Ketjen Black (KB) is 2 A porous carbon positive electrode is produced by kneading carbon black (approximately 1000 g / g) with a binder, coating and solidifying the mixture. The porous carbon positive electrode of Patent Document 1 is said to be capable of improving the energy efficiency and capacity retention characteristics of a lithium-air battery.

[0007] In addition, in Non-Patent Document 1, a binder-free nonwoven CNT sheet electrode is produced by using fibrous carbon nanotubes (CNTs) as a raw material. The porous carbon sheet in Non-Patent Document 1 has high porosity and yet is self-supporting, and when used as a positive electrode for a lithium-air battery, it is said that an oxygen diffusion path is secured, and the capacity and rate characteristics can be significantly improved. The positive electrode produced in Non-Patent Document 1 has a capacity of 4 mAh / cm 2 This allows for a charge / discharge cycle capacity of more than 2mAh / cm2, which is larger than the cycle capacity of a lithium-ion battery (approximately 2mAh / cm2). 2 This is more than twice the amount of [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2020-149819 A [Non-patent literature]

[0009] [Non-Patent Document 1] Akihiro Nomura et.al., Highly-porous Super-Growth carbon nanotube sheet cathode developshigh-power Lithium-Air Batteries, Electrochimica Acta 400 (2021) 139415 Summary of the Invention [Problem to be solved by the invention]

[0010] When charging a lithium-air battery, lithium peroxide decomposes into oxygen and lithium ions at the positive electrode (Li2O2→2Li + +2e - +O2). The decomposition of lithium peroxide occurs from the surface of the positive electrode, so as charging progresses, the spatial distance between the lithium peroxide and the surface of the positive electrode increases, causing the overvoltage to rise toward the latter half of charging. As the charging overvoltage increases, the decomposition and deterioration of the electrolyte and electrodes progresses.

[0011] According to the non-woven CNT sheet electrode prepared in Non-Patent Document 1, the capacity is 4 mAh / cm 2 Although this allows for a high charge / discharge cycle capacity of more than twice that of a lithium-ion battery, the overvoltage during charging is high.

[0012] A method to suppress the rise in charging overvoltage is to add a redox mediator (RM). RM mediates the oxidative decomposition of lithium peroxide (RM → RM + +e - , 2RM+ +Li2O2→2Li + +2RM+O2). The intermediation of RM makes it possible to efficiently oxidize and decompose lithium peroxide that is far from the surface of the positive electrode, thereby suppressing the increase in charging overvoltage.

[0013] Generally, RM is introduced into a battery by dissolving it in an electrolyte. However, with this method, the RM in the electrolyte comes into direct contact with the lithium metal negative electrode and is reduced and decomposed (shuttle effect), making it difficult to obtain a long-term continuous overvoltage suppression effect.

[0014] In Patent Document 1, when preparing a positive electrode using Ketjen Black, RM is kneaded with Ketjen Black, and the resulting mixture is applied and solidified to introduce RM into the positive electrode. A positive electrode incorporating RM can suppress the shuttle effect and can suppress charging overvoltage for a long period of time, compared to a case where RM is dissolved in an electrolyte.

[0015] However, in Patent Document 1, there is a limit to the amount of Ketjen black that can be effectively supported as an electrode (<1 mg / cm 2 ), and therefore the surface area and pore volume of the positive electrode itself are limited, so the charge / discharge cycle capacity is limited to 0.5 mAh / cm. 2 It was small, less than 1.

[0016] In view of the above circumstances, the present invention aims to increase the cycle capacity of an air battery (for example, 4 mAh / cm 2 The object of the present invention is to provide a redox mediator-coated porous carbon sheet, a positive electrode for an air battery, an air battery, and a method for producing a redox mediator-coated porous carbon sheet, which are capable of effectively suppressing charging overvoltage while satisfying the above requirements. [Means for solving the problem]

[0017] The present inventors have conducted extensive research to solve the above problems, and have found that by fixing a specific amount of a redox mediator to the surface of a porous carbon sheet and using the sheet as the positive electrode of an air battery, charging overvoltage can be effectively suppressed, which has led to the completion of the present invention.

[0018] That is, the means for solving the above problems include the following aspects. [1] A redox mediator that mediates the oxidative decomposition of a metal oxide by its own redox reaction is fixed to the surface of the porous carbon sheet; The amount of the redox mediator adhered is 0.2 mg / cm 2 More than 2.9mg / cm 2 The redox mediator-coated porous carbon sheet has a molecular weight of less than 10000. [2] BET specific surface area is 200m 2 / g or more 1100m 2 / g or less. [3] The redox mediator-coated porous carbon sheet according to [1] or [2], which is self-supporting. [4] The redox mediator-coated porous carbon sheet according to any one of [1] to [3], which has a thickness of 40 μm or more and 300 μm or less. [5] The redox mediator-coated porous carbon sheet according to any one of [1] to [4], wherein an oxidation potential of the redox mediator is higher than an equilibrium potential of the metal oxide. [6] The redox mediator-coated porous carbon sheet according to any one of [1] to [5], wherein the metal oxide is lithium peroxide. [7] The redox mediator-coated porous carbon sheet according to any one of [1] to [6], wherein the redox mediator is at least one selected from the group consisting of nitrites, nitrates, bromides, iodides, and phenothiazine-based compounds. [8] The redox mediator-coated porous carbon sheet according to any one of [1] to [7], wherein the redox mediator is at least one selected from the group consisting of lithium nitrite, lithium nitrate, lithium bromide, and 10-methylphenothiazine. [9] The redox mediator-coated porous carbon sheet according to any one of the aspects [1] to [8], wherein the specific surface area of ​​the redox mediator-coated porous carbon sheet is 70% or more of the specific surface area of ​​the porous carbon sheet.

[10] The redox mediator-coated porous carbon sheet according to any one of the aspects [1] to [9], wherein the electric resistance of the redox mediator-coated porous carbon sheet is smaller than the electric resistance of the porous carbon sheet.

[11] A positive electrode for an air battery, comprising the redox mediator-coated porous carbon sheet according to any one of the above aspects [1] to

[10] .

[12] A positive electrode comprising the redox mediator-coated porous carbon sheet according to

[11] ; A negative electrode; an electrolyte present between the positive electrode and the negative electrode; An air battery comprising:

[13] The air battery according to

[12] , wherein the negative electrode contains lithium metal.

[14] preparing a redox mediator solution by dissolving a redox mediator that mediates the oxidative decomposition of a metal oxide by its own redox reaction in a solvent; contacting the redox mediator solution with a porous carbon sheet so that the redox mediator solution is present on the surface and within the pores of the porous carbon sheet; drying the redox mediator solution to remove the solvent and adhere the redox mediator to the porous carbon sheet; The method for producing a redox mediator-coated porous carbon sheet comprises the steps of:

[15] The method for producing a redox mediator-coated porous carbon sheet according to

[14] , wherein the contact is at least one method selected from the group consisting of impregnation, dripping, spray coating, and inkjet coating.

[16] The method for producing a redox mediator-coated porous carbon sheet according to

[14] or

[15] , wherein the redox mediator is an inorganic salt, and the solvent is a high-polarity solvent or a medium-polarity solvent.

[17] The method for producing a redox mediator-coated porous carbon sheet according to any one of

[14] to

[16] , wherein the redox mediator is at least one selected from the group consisting of lithium nitrite, lithium nitrate, and lithium bromide, and the solvent is 1-propanol.

[18] The method for producing a redox mediator-coated porous carbon sheet according to

[14] or

[15] , wherein the redox mediator is an organic compound, and the solvent is a medium polarity solvent or a low polarity solvent.

[19] The method for producing a redox mediator-coated porous carbon sheet according to any one of the embodiments of the group consisting of

[14] ,

[15] , and

[18] , wherein the redox mediator is 10-methylphenothiazine and the solvent is anisole.

[20] The method for producing a redox mediator-coated porous carbon sheet according to any one of

[14] to

[20] , wherein the redox mediator-coated porous carbon sheet is a positive electrode for an air battery. Effect of the Invention

[0019] The redox mediator-coated porous carbon sheet of the present disclosure has a large capacity (e.g., 4 mAh / cm 2 It is possible to realize an air battery having the above-mentioned structure and in which charging overvoltage is effectively suppressed. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic cross-sectional view of an air battery according to one embodiment. [Diagram 2]FIG. 1 is a schematic cross-sectional view of an air battery according to one embodiment. [Diagram 3] FIG. 1 is a diagram showing a method for introducing a redox mediator into a porous carbon sheet. [Figure 4] 2 is a scanning electron microscope photograph of the sheet of Comparative Example 1. [Diagram 5] 1 is a scanning electron microscope photograph of the sheet of Example 2. [Figure 6] 1 is an elemental mapping of carbon in the sheet of Example 2. [Figure 7] Elemental mapping of bromine for the sheet of Example 2. [Figure 8] FIG. 1 is a diagram showing a method for measuring electrical resistance. [Figure 9] This is the charge and discharge curve of air battery 1. [Figure 10] This is the charge / discharge curve of air battery 2. [Figure 11] Charging and discharging curves of air battery 3. [Figure 12] FIG. 1 is a diagram showing the discharge end voltage and the charge end voltage of air batteries 1, 2, and 3. [Figure 13] Charging and discharging curves of air battery 4. [Figure 14] 5 shows a charge / discharge curve of the air battery 5. [Figure 15] 5 shows the charge and discharge curve of the air battery 6. [Figure 16] 5 shows a charge / discharge curve of the air battery 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. Furthermore, among the components in the following embodiments, components that are not described in the claims showing the highest concept will be described as optional components.

[0022] <Porous carbon sheet coated with redox mediator> The redox mediator-coated porous carbon sheet of the present disclosure has a specific amount of a redox mediator that mediates the oxidative decomposition of a metal oxide by its own redox reaction fixed to the surface of the porous carbon sheet. The redox mediator may be fixed to the surface of the porous carbon sheet, and may be fixed not only to the outermost surface of the porous carbon sheet but also to the inner surfaces of the pores.

[0023] <Amount of Redox Mediator (RM)> The redox mediator-coated porous carbon sheet of the present disclosure has a redox mediator (RM) adhering to the porous carbon sheet in an amount of 0.2 mg / cm 2 More than 2.9mg / cm 2 The range is less than.

[0024] When the porous carbon sheet before the redox mediator was fixed was available, the amount of the fixed redox mediator was measured by punching out a circle having a diameter (φ) of 16 mm from the porous carbon sheet coated with the redox mediator and the porous carbon sheet before the redox mediator was fixed, measuring the mass (mg) of each circle, and calculating the difference between the masses. 2 On the other hand, when it is difficult to obtain a porous carbon sheet before the redox mediator is fixed thereto, such as when a completed air battery is disassembled, the mass of the redox mediator-coated porous carbon sheet is measured, and then the sheet is thoroughly washed with a solvent capable of dissolving the redox mediator to remove the redox mediator, and the mass of the dried sheet is measured and used as the mass of the porous carbon sheet before the redox mediator is fixed thereto.

[0025] For example, when a redox mediator is dissolved in an electrolyte and introduced into a lithium-air battery, the redox mediator oxidized at the positive electrode may diffuse to the negative electrode without decomposing lithium peroxide during charging, and may react directly with the lithium peroxide, resulting in self-discharge, a so-called shuttle effect.

[0026] However, when the redox mediator-coated porous carbon sheet of the present invention is used as a positive electrode, the presence of the redox mediator in the positive electrode makes it possible to suppress the influence of the shuttle effect, thereby further improving the capacity retention of the battery.

[0027] The amount of redox mediator adhered to the porous carbon sheet was 0.2 mg / cm 2 If the amount of the redox mediator adhering to the porous carbon sheet is 2.9 mg / cm or more, the charge voltage can be suppressed without affecting the discharge voltage. 2 If this occurs, the electrical resistance of the redox mediator-coated porous carbon sheet will increase and the pores in the porous carbon sheet will become blocked, causing the oxygen diffusibility necessary for discharge to be lost, resulting in a significant decrease in the discharge capacity of the battery.

[0028] The amount of the redox mediator adhered to the porous carbon sheet is preferably 0.3 mg / cm 2 More than 0.4g / cm 2 More than 0.6mg / cm 2 Above 0.9 mg / cm 2 More than 1.2mg / cm 2 More than 1.6mg / cm 2 or more than 2.0g / cm 2 On the other hand, the amount of the redox mediator adhered to the porous carbon sheet is preferably 2.8 mg / cm. 2 Below, 2.6mg / cm 2 Below, 2.4mg / cm 2 Below, 2.2mg / cm 2 Below 2.0mg / cm 2 Below 1.8mg / cm 2 or less than 1.6 mg / cm 2 It may be the following:

[0029] <Specific surface area of ​​redox mediator-coated porous carbon sheet relative to specific surface area of ​​porous carbon sheet> The specific surface area of ​​the redox mediator-coated porous carbon sheet of the present disclosure is preferably 70% or more of the specific surface area of ​​the porous carbon sheet before the redox mediator is fixed thereto.

[0030] If the specific surface area of ​​the redox mediator-coated porous carbon sheet is 70% or more of the specific surface area of ​​the raw material porous carbon sheet, the pore volume of the porous carbon sheet is reduced little before and after the redox mediator is fixed to the surface of the porous carbon sheet, so that the pore structure remains the same as before the fixation of the redox mediator, and the pores are not blocked. As a result, when the redox mediator-coated porous carbon sheet of the present disclosure is used as the positive electrode of an air battery, the discharge capacity of the battery formed can be maintained.

[0031] The ratio of the specific surface area of ​​the redox mediator-coated porous carbon sheet to the specific surface area of ​​the porous carbon sheet may more preferably be 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more.

[0032] <Electrical resistance> The electrical resistance of the redox mediator-coated porous carbon sheet of the present disclosure is preferably smaller than the electrical resistance of the porous carbon sheet before the redox mediator is fixed thereto. If the electrical resistance of the redox mediator-coated porous carbon sheet is smaller than the electrical resistance of the raw material porous carbon sheet, the fixation of the redox mediator can suppress charging overvoltage.

[0033] <Properties of redox mediator-coated porous carbon sheet> (BET specific surface area) The redox mediator-coated porous carbon sheet of the present disclosure has a BET specific surface area of ​​200 m 2 / g or more 1100m 2 The BET specific surface area is preferably in the range of 0.1 to 1.0 μm / g or less. Note that the BET specific surface area is calculated by rounding off to the first decimal place.

[0034] The BET specific surface area of ​​the redox mediator-coated porous carbon sheet is 200 m 2 / g or more, when the sheet is used as the positive electrode of an air battery, the efficiency of ion transport is increased, and a battery with a large discharge capacity can be formed. For example, when lithium ions react with oxygen to generate lithium peroxide, a reaction field necessary for oxygen to receive electrons supplied from the positive electrode can be secured, resulting in a large discharge capacity. On the other hand, 2 When the capacitance is 0.1 to 1.0 W / g or less, the contribution of side reactions in the battery on the surface of the positive electrode can be suppressed, and therefore favorable charge / discharge characteristics can be obtained.

[0035] The BET specific surface area of ​​the redox mediator-coated porous carbon sheet is more preferably 250 m 2 / g or more, 300m 2 / g or more, 350m 2 / g or more, 400m 2 / g or more, 450m 2 / g or more, or 500m 2 / g or more, 2 / g or less, 900m 2 / g or less, 850m 2 / g or less, 800m 2 / g or less, 750m 2 / g or less, or 700m 2 / g or less.

[0036] (Pore volume of pores with diameters between 2nm and 1000nm) The redox mediator-coated porous carbon sheet of the present disclosure has a pore volume of pores with diameters of 2 nm to 1000 nm of 0.5 cm 3 / g or more 5.0cm 3 / g or less. The pore volume of pores with a diameter of 2 nm to 1000 nm is obtained by the BJH (Barrett-Joyner-Hallenda) method from an adsorption isotherm obtained by nitrogen adsorption measurement. The pore volume of pores with a diameter of 2 nm to 1000 nm is rounded off to one decimal place.

[0037] Pores having a diameter in the range of 2 nm to 1000 nm function as a battery reaction surface (reaction field). Therefore, if the volume of the pores in this range is large, when the sheet is used as the positive electrode of a lithium-air battery, the amount of lithium ions, oxygen, and electrons that can react per unit time in the discharge reaction increases. This results in excellent high-speed discharge characteristics. In addition, in the charge reaction, the reaction field for lithium peroxide to transfer electrons to the positive electrode and decompose into lithium ions and oxygen increases, making it possible to transfer more electrons. Therefore, if the volume of the pores having a diameter in the range of 2 nm to 1000 nm is large, an air battery with better charge and discharge characteristics can be provided.

[0038] The pore volume of the pores having a diameter of 2 nm or more and 1000 nm or less in the redox mediator-coated porous carbon sheet is preferably 0.8 cm or less in order to provide a battery having superior charge / discharge characteristics. 3 / g or more, 1.0cm 3 / g or more, 1.5cm 3 / g or more, 2.0cm 3 / g or more, or 2.5 cm 3 On the other hand, the pore volume of the pores having a diameter of 2 nm or more and 1000 nm or less is more preferably 4.5 cm3 / g or more, so that the redox mediator-coated porous carbon sheet has sufficient strength and is self-supporting. 3 / g or less, 4.0cm 3 / g or less, 3.5cm 3 / g or less, or 3.0 cm 3 / g or less.

[0039] (Pore volume of pores with diameters between 0.1 μm and 10 μm) The redox mediator-coated porous carbon sheet of the present disclosure has a pore volume of 0.5 cm for pores with diameters of 0.1 μm or more and 10 μm or less. 3 / g or more 10.0cm 3 / g or less. The pore volume of pores having a diameter of 0.1 μm or more and 10 μm or less is obtained using a value measured by mercury intrusion porosimetry. The pore volume of pores having a diameter of 0.1 μm or more and 10 μm or less is rounded off to one decimal place.

[0040] When the redox mediator-coated porous carbon sheet is used as a positive electrode of an air battery, the pores having a diameter in the range of 0.1 μm to 10 μm mainly function as a path for oxygen outside the battery to penetrate into the redox mediator-coated porous carbon sheet. If the pore volume of the pores having a diameter in the range of 0.1 μm to 10 μm satisfies the above range, when the sheet is used as a positive electrode of a lithium-air battery, oxygen that reacts with lithium ions to generate lithium peroxide during discharge can be penetrated in a sufficient amount and at a high speed. This makes it possible to provide a battery with a large discharge capacity at a high current density, that is, excellent high-speed discharge characteristics. In addition, when lithium peroxide decomposes into lithium ions and oxygen during charging, the oxygen generated is easily released from the positive electrode sheet, making it possible to charge at a high speed.

[0041] The pore volume of the pores of the redox mediator-coated porous carbon having a diameter of 0.1 μm or more and 10 μm or less is preferably 1.0 cm, since this enables faster charging and discharging when the sheet is used as the positive electrode of a lithium-air battery. 3 / g or more, 1.5cm 3 / g or more, 2.0cm 3 / g or more, or preferably 2.5 cm 3 On the other hand, the pore volume of the pores having a diameter of 0.1 μm or more and 10 μm or less is more preferably 9.0 cm3 / g, in order that the redox mediator-coated porous carbon sheet has sufficient strength and is self-supporting. 3 / g or less, 8.0cm 3 / g or less, 7.0cm 3 / g or less, or 6.0 cm 3 / g or less.

[0042] (porosity) The redox mediator-coated porous carbon sheet of the present disclosure preferably has a porosity in the range of 60% or more and 95% or less. If the porosity is 60% or more, when the redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, it can store a large amount of metal oxides such as lithium peroxide that are generated during discharge, and the resistance to the intrusion of oxygen or air containing oxygen into the inside is low. As a result, it is possible to provide a battery that has a high discharge capacity and is capable of high-speed discharge. On the other hand, if the porosity is 95% or less, the redox mediator-coated porous carbon sheet has excellent strength.

[0043] Here, the porosity is calculated from the apparent density and true density of the sheet by the following formula. [1-(apparent density of sheet / true density of material that composes sheet)] x 100

[0044] The porosity of the redox mediator-coated porous carbon sheet may be more preferably 65% ​​or more, 70% or more, 75% or more, 80% or more, or 85% or more, from the viewpoint of obtaining a battery having a higher discharge capacity and capable of discharging at a higher rate when the redox mediator-coated porous carbon sheet is used as the positive electrode of a lithium-air battery. On the other hand, the porosity of the redox mediator-coated porous carbon sheet may be more preferably 94% or less, 93% or less, 92% or less, 91% or less, or 90% or less, from the viewpoint of obtaining superior strength.

[0045] (Met) The redox mediator-coated porous carbon sheet of the present disclosure has a basis weight of 1.7 mg / cm 2 More than 6.4mg / cm 2 If the basis weight is within this range, when the redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, it is possible to obtain an air battery that has a high discharge capacity and is capable of high-speed discharge. The basis weight is determined by punching out the target sheet into a circle with a diameter (φ) of 16 mm, measuring the mass (mg), and calculating the area (cm) of the circle. 2 ) to obtain the mass per area.

[0046] The weight of the redox mediator-coated porous carbon sheet is more preferably 1.9 mg / cm 2 More than 2.1mg / cm 2 More than 2.3mg / cm 2 More than 2.5mg / cm 2 More than 3.0mg / cm 2 or more than 3.7 mg / cm 2 or more, 6.0 mg / cm 2 Below 5.5mg / cm 2 Below, 5.0mg / cm 2 Below, 4.5mg / cm 2 Below, 4.0mg / cm 2 or less than 3.7 mg / cm 2 It may be the following:

[0047] (density) The redox mediator-coated porous carbon sheet of the present disclosure has a sheet density (also referred to as apparent density) of 0.05 g / cm 3 More than 0.50g / cm 3 The density of the sheet is preferably in the following range: When the redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, the sheet has a sufficient number of pores necessary for oxygen to permeate and diffuse, and has excellent strength.

[0048] The density of the redox mediator-coated porous carbon sheet is preferably 0.07 g / cm3 in order to provide a superior sheet strength. 3 More than 0.10g / cm 3 More than 0.12g / cm 3 More than 0.14g / cm 3 or more than 0.16g / cm 3 On the other hand, the density of the redox mediator-coated porous carbon sheet is more preferably 0.40 g / cm3 in order to provide a sheet having sufficient voids. 3 Below, 0.35g / cm 3 Below, 0.30g / cm 3 Below 0.25g / cm 3 or less than 0.20g / cm 3 It may be the following:

[0049] (G / D ratio) The redox mediator-coated porous carbon sheet of the present disclosure preferably has an intensity ratio (G / D ratio) of the peak intensity G derived from crystalline carbon to the peak intensity D derived from turbostratic carbon, as determined by Raman spectroscopy, of 10,000 or less. By including a certain amount of turbostratic carbon in the crystalline carbon, the carbon sheet has a high affinity with the electrolyte, and an air battery with excellent discharge characteristics can be obtained. The G / D ratio is rounded off to one decimal place.

[0050] The G / D ratio of the redox mediator-coated porous carbon sheet may be more preferably 1000 or less, 500 or less, 200 or less, 100 or less, 50 or less, 20 or less, 10 or less, or 5 or less, in that when the redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, an air battery having more excellent cycle characteristics can be obtained.

[0051] On the other hand, the G / D ratio of the redox mediator-coated porous carbon sheet is preferably 0.5 or more. By forming the carbon sheet mainly from crystalline carbon, the oxidation resistance is increased, and an air battery with excellent cycle characteristics can be obtained. The G / D ratio of the redox mediator-coated porous carbon sheet may more preferably be 0.7 or more, 1.0 or more, or 1.5 or more.

[0052] (Thickness) The redox mediator-coated porous carbon sheet of the present disclosure preferably has a thickness in the range of 40 μm or more and 300 μm or less. If the thickness is 40 μm or more, the redox mediator-coated porous carbon sheet has self-supporting properties, making it possible to manufacture a small and lightweight air battery at low cost. On the other hand, if the thickness is 300 μm or less, a sufficiently small and lightweight air battery can be obtained.

[0053] The thickness of the redox mediator-coated porous carbon sheet may more preferably be 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, 175 μm or more, or 200 μm or more, and may be 280 μm or less, 260 μm or less, 240 μm or less, 220 μm or less, or 200 μm or less.

[0054] <Applications of redox mediator-coated porous carbon sheet> The redox mediator-coated porous carbon sheet of the present disclosure is suitable for use as a positive electrode for an air battery, although the use is not particularly limited. The redox mediator-coated porous carbon sheet of the present disclosure can effectively suppress charging overvoltage while maintaining a large cycle capacity, which is a feature of air batteries. The redox mediator-coated porous carbon sheet of the present disclosure exerts excellent effects, particularly when used as a positive electrode for a lithium-air battery.

[0055] <Redox Mediator (RM)> The redox mediator (RM) attached to the surface of the porous carbon sheet is a compound that mediates the oxidative decomposition of metal oxides by its own redox reaction. + ) and the reductant (RM), and when introduced into an air battery, + ) oxidizes and decomposes metal oxides such as lithium peroxide, forming Li + It generates metal ions such as

[0056] More specifically, the redox mediator introduced into the air battery is first oxidized to an oxidant (RM + ) and the resulting oxidized product (RM + ) attacks the surface of metal oxides such as lithium peroxide that are deposited during discharge. This results in the formation of oxidants (RM + ) catalyzes the decomposition of metal oxides and is itself reduced to a reduced form (RM).

[0057] For example, in an air battery that generates lithium peroxide as a metal oxide, the decomposition reaction of lithium peroxide during charging is as follows in the presence of a redox mediator (RM). First, the redox mediator (RM) itself is oxidized to become an oxidant (RM + ) and then the oxidized form (RM + ) reacts with the lithium peroxide formed during discharge to decompose the lithium peroxide, generating lithium ions and oxygen, while being reduced back to the reduced form (RM). RM → RM + +e - , 2RM + +Li2O2→2Li + +2RM+O2

[0058] In air batteries, the redox mediator (RM) allows for efficient oxidative decomposition of metal oxides such as lithium peroxide that are far from the positive electrode surface, which can suppress the rise in charging overvoltage.

[0059] The redox mediator (RM) is preferably a chemical species whose oxidation potential is greater than the equilibrium potential of the metal oxide to be oxidized and decomposed, so that the RM is oxidized prior to the metal oxide to be oxidized and decomposed during charging, allowing the RM to fully exert its function.

[0060] For example, when the metal oxide to be oxidatively decomposed is lithium peroxide, it is preferable that the chemical species has an oxidation potential higher than 2.96 V, which is the theoretical value of the equilibrium potential of lithium peroxide. From the viewpoint of effectively suppressing an increase in overvoltage, it is more preferable that the oxidation potential is greater than 2.96 V and not greater than 5.00 V, even more preferable that the oxidation potential is greater than 2.96 V and not greater than 4.00 V, even more preferable that the oxidation potential is greater than 2.96 V and not greater than 3.80 V, and particularly preferable that the oxidation potential is greater than 2.96 V and not greater than 3.50 V.

[0061] The redox mediator may be an inorganic salt or an organic salt. Examples of inorganic salts include bromides, nitrites, nitrates, and iodides. More specifically, examples of the salt include LiNO2, NaNO2, KNO2, RbNO2, CsNO2, LiNO3, NaNO3, KNO3, RbNO3, CsNO3, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, and CsI.

[0062] Examples of organic salts include tetrathiafulvalene (TTF), ferrocene, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), tetramethyl-p-phenylenediamine (TMPD), 5,10-dimethylphenazine (DMPZ), 1,5-naphthalenediamine (NDA), 4,N,N-trimethylaniline (TMA), 1-phenylpyrrolidine (PPD), 10-methylphenothiazine (MPT), 2,5-di-t-butyl-1,4-benzoquinone (DBBQ), etc. Redox mediators may be used alone or in combination of two or more.

[0063] Among them, the redox mediator is preferably at least one selected from the group consisting of nitrites, nitrates, bromides, iodides, and phenothiazine compounds.

[0064] Furthermore, the redox mediator is preferably at least one selected from the group consisting of lithium nitrite, lithium nitrate, lithium bromide, and 10-methylphenothiazine (MPT).

[0065] <Porous carbon sheet> The porous carbon sheet to which the redox mediator (RM) is attached is a sheet made of carbon as a raw material and has a plurality of pores. In the redox mediator-coated porous carbon sheet of the present disclosure, the redox mediator is attached inside the pores of the porous carbon sheet and on the surface of the sheet.

[0066] (raw materials) The carbon material used to make the porous carbon sheet may be a carbon material that is generally used as a conductive assistant. Examples include 'n black and 'ketchen black. The shape of the carbon used as the raw material for the porous carbon sheet is not particularly limited as long as it can form a porous sheet having voids. The shape of the carbon used as the raw material for the porous carbon sheet may be, for example, powder or fiber.

[0067] When powdered carbon is used as the raw material, for example, porous carbon particles may be used. Porous carbon particles are particles whose main component is carbon and have many fine holes on the surface. Examples of porous carbon particles include carbon black such as Ketjen Black (registered trademark) and other carbon particles formed by a template method.

[0068] When fibrous carbon is used as the raw material, it is preferable to select it from the group consisting of carbon nanotubes, carbon nanohorns, and carbon nanofibers. All of these fibrous carbons are commercially available, and among them, carbon nanotubes are preferable because they are cylindrical and, when formed into a sheet, tend to satisfy the BET specific surface area and pore volume required for the positive electrode of an air battery.

[0069] (BET specific surface area) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure has a BET specific surface area of ​​300 m 2 / g or more 1200m 2 The BET specific surface area is preferably in the range of 0.1 to 1.0 μm / g or less. Note that the BET specific surface area is calculated by rounding off to the first decimal place.

[0070] The BET specific surface area of ​​the raw material porous carbon sheet is 300m 2 / g or more, when the resulting redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, a battery with high ion transport efficiency can be formed. For example, when lithium ions react with oxygen to generate lithium peroxide, a reaction field necessary for oxygen to receive electrons supplied from the positive electrode can be secured, resulting in a large discharge capacity. On the other hand, 2 When the positive electrode has a surface area of ​​100 μm or less, the contribution of side reactions in the battery on the surface of the positive electrode can be suppressed, and thus favorable charge / discharge characteristics can be obtained.

[0071] The BET specific surface area of ​​the porous carbon sheet is more preferably 350 m 2 / g or more, 400m 2 / g or more, 450m 2 / g or more, 500m 2 / g or more, 550m 2 / g or more, 600m 2 / g or more, or 650m 2 / g or more, 2 / g or less, 1000m 2 / g or less, 900m 2 / g or less, 850m 2 / g or less, 800m 2 / g or less, 750m 2 / g or less, or 700m 2 / g or less.

[0072] (Pore volume of pores with diameters between 2nm and 1000nm) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure has a pore volume of pores with diameters of 2 nm to 1000 nm of 0.5 cm 3 / g or more 5.0cm 3 The pore volume of pores having a diameter of 2 nm or more and 1000 nm or less is determined by rounding off to one decimal place.

[0073] The pore volume of the pores having a diameter of 2 nm or more and 1000 nm or less in the raw material porous carbon sheet is preferably 0.8 cm or less, in order to provide a battery having superior charge / discharge characteristics.3 / g or more, 1.0cm 3 / g or more, 1.5cm 3 / g or more, 2.0cm 3 / g or more, or 2.5 cm 3 On the other hand, the pore volume of the pores having a diameter of 2 nm or more and 1000 nm or less is more preferably 4.5 cm3 / g, in order to ensure that the obtained redox mediator-coated porous carbon sheet has sufficient strength while maintaining its self-supporting property. 3 / g or less, 4.0cm 3 / g or less, 3.5cm 3 / g or less, or 3.0 cm 3 / g or less.

[0074] (Pore volume of pores with diameters between 0.1 μm and 10 μm) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure has a pore volume of pores with diameters of 0.1 μm or more and 10 μm or less of 0.5 cm 3 / g or more 10.0cm 3 The pore volume of pores having a diameter of 0.1 μm or more and 10 μm or less is determined by rounding off to one decimal place.

[0075] The pore volume of the pores of the raw material porous carbon sheet having a diameter of 0.1 μm or more and 10 μm or less is preferably 1.0 cm, since this enables faster charging and discharging when the resulting redox mediator-coated porous carbon sheet is used as the positive electrode of a lithium-air battery. 3 / g or more, 1.5cm 3 / g or more, 2.0cm 3 / g or more, or preferably 2.5 cm 3 On the other hand, the pore volume of the pores having a diameter of 0.1 μm or more and 10 μm or less is more preferably 9.0 cm3 / g, in order to ensure that the obtained redox mediator-coated porous carbon sheet has sufficient strength while maintaining its self-supporting property. 3 / g or less, 8.0cm 3 / g or less, 7.0cm 3 / g or less, or 6.0 cm 3 / g or less.

[0076] (porosity) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure preferably has a porosity in the range of 60% or more and 95% or less. If the porosity is 60% or more, when the redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, it is possible to store a large amount of metal oxides such as lithium peroxide that are generated during discharge, and the resistance to the intrusion of oxygen or air containing oxygen into the inside is low. As a result, it is possible to provide a battery that has a high discharge capacity and is capable of high-speed discharge. On the other hand, if the porosity is 95% or less, the obtained redox mediator-coated porous carbon sheet has excellent strength.

[0077] The porosity of the porous carbon sheet may be more preferably 65% ​​or more, 70% or more, 75% or more, 80% or more, or 85% or more, from the viewpoint of obtaining a battery having a higher discharge capacity and capable of faster discharge when the resulting redox mediator-coated porous carbon sheet is used as the positive electrode of a lithium-air battery. On the other hand, the porosity of the porous carbon sheet may be more preferably 94% or less, 93% or less, 92% or less, 91% or less, or 90% or less, from the viewpoint of imparting superior strength to the resulting redox mediator-coated porous carbon sheet.

[0078] (Met) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure has a basis weight of 1.5 mg / cm 2 More than 3.5mg / cm 2 If the basis weight is within this range, when the obtained redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, an air battery having a high discharge capacity and capable of high-speed discharge can be obtained.

[0079] The basis weight of the porous carbon sheet is more preferably 1.6 mg / cm 2 More than 1.7mg / cm 2 Above 1.8 mg / cm 2 Above 1.9 mg / cm 2 or more than 2.0 mg / cm2 or more, 3.2 mg / cm 2 Below 3.0mg / cm 2 Below, 2.8mg / cm 2 Below, 2.6mg / cm 2 or less than 2.4 mg / cm 2 It may be the following:

[0080] (density) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure has a sheet density (also referred to as apparent density) of 0.05 g / cm 3 More than 0.50g / cm 3 It is preferable that the density of the sheet is in the following range. When the obtained redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, the sheet has a sufficient number of pores necessary for oxygen to permeate and diffuse, and has excellent strength.

[0081] The density of the porous carbon sheet is preferably 0.07 g / cm in order to provide a porous carbon sheet coated with a redox mediator having superior strength. 3 More than 0.10g / cm 3 More than 0.12g / cm 3 More than 0.14g / cm 3 or more than 0.16g / cm 3 On the other hand, the density of the porous carbon sheet is more preferably 0.40 g / cm3 or more in order to provide a redox mediator-coated porous carbon sheet having sufficient voids. 3 Below, 0.35g / cm 3 Below, 0.30g / cm 3 Below 0.25g / cm 3 or less than 0.20g / cm 3 It may be the following:

[0082] (G / D ratio) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure preferably has an intensity ratio (G / D ratio) of the peak intensity G derived from crystalline carbon to the peak intensity D derived from turbostratic carbon, as determined by Raman spectroscopy, of 10,000 or less. When the carbon sheet contains a certain amount of turbostratic carbon in the crystalline carbon, it is possible to obtain an air battery with improved affinity for the electrolyte and excellent discharge characteristics. The G / D ratio is rounded off to one decimal place.

[0083] The G / D ratio of the porous carbon sheet may be more preferably 1000 or less, 500 or less, 200 or less, 100 or less, 50 or less, 20 or less, 10 or less, or 5 or less, in that when the resulting redox mediator-coated porous carbon sheet is used as the positive electrode of an air battery, an air battery having superior cycle characteristics can be obtained.

[0084] On the other hand, the G / D ratio of the porous carbon sheet is preferably 0.5 or more. The carbon sheet is mainly composed of crystalline carbon, so that the oxidation resistance is increased and an air battery with excellent cycle characteristics can be obtained. The G / D ratio of the porous carbon sheet may more preferably be 0.7 or more, 1.0 or more, or 1.5 or more.

[0085] (Thickness) The porous carbon sheet used as the raw material for the redox mediator-coated porous carbon sheet of the present disclosure preferably has a thickness in the range of 40 μm to 300 μm. If the thickness is 40 μm or more, the resulting redox mediator-coated porous carbon sheet will be self-supporting, making it possible to manufacture a small and lightweight air battery at low cost. On the other hand, if the thickness is 300 μm or less, a sufficiently small and lightweight air battery can be obtained.

[0086] The thickness of the porous carbon sheet may more preferably be 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, 175 μm or more, or 200 μm or more, and may be 280 μm or less, 260 μm or less, 240 μm or less, 220 μm or less, or 200 μm or less.

[0087] The above-mentioned porous carbon sheet can be produced by the method described in Non-Patent Document 1, for example.

[0088] <Method for producing a redox mediator-coated porous carbon sheet> The redox mediator-coated porous carbon sheet of the present disclosure can be obtained by a production method including the following steps. (1) A redox mediator that mediates the oxidative decomposition of a metal oxide by its own redox reaction is dissolved in a solvent to prepare a redox mediator solution. (2) The prepared redox mediator solution is brought into contact with a porous carbon sheet, so that the redox mediator solution is present on the surface and inside the pores of the porous carbon sheet. (3) The redox mediator solution is dried to remove the solvent, and the redox mediator is fixed to the porous carbon sheet.

[0089] <(1) Preparation of redox mediator solution> In order to adhere the redox mediator to the porous carbon sheet, first, the redox mediator is dissolved in a solvent to prepare a redox mediator solution.

[0090] (Redox mediator) As the redox mediator, the various compounds described above can be used.

[0091] (solvent) The solvent for dissolving the redox mediator is not particularly limited, and may be any solvent that can dissolve the redox mediator used and allows the resulting solution to permeate the porous carbon sheet.

[0092] When the redox mediator is an inorganic salt, the solvent is preferably a high polarity solvent or a medium polarity solvent, which dissolves the inorganic salt and allows the resulting solution to permeate the porous carbon sheet.

[0093] Among these, a combination in which the redox mediator is at least one selected from the group consisting of lithium bromide, lithium nitrite, and lithium nitrate, and 1-propanol is used as the solvent, is preferred in terms of the solubility of the redox mediator and the permeability of the resulting redox mediator solution.

[0094] When the redox mediator is an organic compound, the solvent is preferably a medium polarity solvent or a low polarity solvent, which dissolves the organic compound and allows the resulting solution to permeate the porous carbon sheet.

[0095] Among these, a combination in which the redox mediator is 10-methylphenothiazine and anisole is used as the solvent is preferred in terms of the solubility of the redox mediator and the permeability of the resulting redox mediator solution.

[0096] <(2) Contact with redox mediator solution> Next, the prepared redox mediator solution is brought into contact with the porous carbon sheet, so that the redox mediator solution is present on the surface and inside the pores of the porous carbon sheet.

[0097] (Porous carbon sheet) As the porous carbon sheet, the above-mentioned porous carbon sheet can be used.

[0098] (Contact method) The method for contacting the redox mediator solution with the porous carbon sheet is not particularly limited, as long as the redox mediator solution can be present on the surface and inside the pores of the porous carbon sheet.

[0099] The contact method may be, for example, at least one method selected from the group consisting of impregnation, dripping, spray coating, and inkjet coating.

[0100] (3) Adhesion of redox mediators The redox mediator solution is then dried to remove the solvent and to adhere the redox mediator to the porous carbon sheet.

[0101] (Drying method) The drying method is not particularly limited and can be appropriately selected depending on the type of solvent used. For example, a method of vacuum drying for a certain period of time at a temperature at which the solvent used volatilizes can be used.

[0102] <Air battery> The air battery of the present disclosure comprises a positive electrode containing the above-mentioned redox mediator-coated porous carbon sheet, a negative electrode, and an electrolyte present between the positive electrode and the negative electrode.

[0103] <Coin cell type air battery> A schematic cross-sectional view of an air battery according to one embodiment is shown in Fig. 1. The air battery 600 is an air battery generally called a "coin cell type" that includes an electrode laminate in which a negative electrode structure 610 and a positive electrode structure 620 are laminated with a separator 660 interposed therebetween, and a restraining device 630 that restrains the electrode laminate. The positive electrode structure 620 has a metal mesh 680 on the surface on the side of the restraining device 630, and an insulating O-ring is disposed between the restraining device 630 and the metal mesh 680 (not shown), thereby ensuring insulation between the restraining device 630 and the positive electrode structure 620.

[0104] The negative electrode structure 610 is composed of a current collector 635, a metal layer 640 disposed on the current collector 635, and columnar spacers 650 disposed on both ends of the current collector 635. A space 670 is provided between the metal layer 640 and a separator 660, and the space 670 is filled with an electrolyte.

[0105] As the material constituting the metal layer 640, it is preferable to contain an alkali metal and / or an alkaline earth metal. Among them, a layer containing lithium metal is preferable.

[0106] The positive electrode structure 620 includes the redox mediator-coated porous carbon sheet 690 of the present disclosure that is mechanically and electrically in contact with a metal mesh 680 containing a metal that is a current collector. The metal mesh 680 serves as a positive electrode substrate and also has a function of serving as a flow path through which air or oxygen passes.

[0107] A separator 660 is disposed between the negative electrode structure 610 and the positive electrode structure 620.

[0108] Hereinafter, an example of a method for manufacturing the air battery 600 will be described. First, the negative electrode structure 610 is prepared. A metal layer 640 made of lithium or the like in a disk shape that is concentric with the current collector 635 and has a smaller diameter than the current collector 635 is laminated on the disk-shaped current collector 635. Subsequently, a columnar spacer 650 is pressed onto the current collector 635 to obtain the negative electrode structure 610.

[0109] The spacer 650 is an insulator. The material may be a metal oxide, a metal nitride, a metal oxynitride, or the like. For example, Al2O3, Ta2O5, TiO2, ZnO, ZrO2, SiO2, B2O3, P2O5, GeO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, Si3N4, AlN, and AlO x N 1-x (0 < x < 1) may be used. Among them, Al2O3 and SiO2 are preferable because they are easily available and have excellent processability.

[0110] The spacer 650 may be made of a resin. Examples of the resin include polyolefin resin, polyester resin, polyimide resin, and polyether ether ketone (PEEK) resin. Examples of the polyolefin resin include polyethylene and polypropylene. Examples of the polyester resin include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polytributylene terephthalate (PTT). These resins are preferred because they are easily available and have excellent processability.

[0111] Next, the separator 660 is pressed onto the spacer 650. At this time, a space 670 is provided between the metal layer 640, the spacer 650, and the separator 660.

[0112] The separator 660 is a porous insulator that allows alkali metal ions and / or alkaline earth metal ions to pass through. The material of the separator 660 may be any inorganic material (including metallic materials) and organic material that is not reactive with the metal layer 640 and the electrolyte.

[0113] Examples of materials for separator 660 include resins such as polyethylene, polypropylene, and polyolefin, and glass. Separator 660 may be a woven fabric or a nonwoven fabric.

[0114] Thereafter, the separator 660 is filled with the electrolyte. At this time, the space 670 is also filled with the electrolyte.

[0115] The electrolyte may be any aqueous or non-aqueous electrolyte containing an alkali metal salt and / or an alkaline earth metal salt. When the aqueous electrolyte contains a lithium salt, the lithium salt may be, for example, LiOH, LiCl, LiNO3, or Li2SO4, and the solvent may be water or a water-soluble solvent.

[0116] When the non-aqueous electrolyte (nonaqueous electrolyte) contains a lithium salt, examples of the lithium salt that can be used include LiPF6, LiBF4, LiSbF6, LiSiF6, LiAsF6, LiN(SO2C2F5)2, Li(FSO2)2N, LiCF3SO3(LiTfO), Li(CF3SO2)2N(LiTFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiB(C2O4)2.

[0117] Examples of non-aqueous solvents used in non-aqueous electrolytes include glymes (monoglyme, diglyme, triglyme, and tetraglyme), methyl butyl ether, diethyl ether, ethyl butyl ether, dibutyl ether, polyethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, cyclohexanone, dioxane, dimethoxyethane, 2-methyltetrahydrofuran, 2,2-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, methyl formate, ethyl formate, dimethyl carbonate, and diethyl carbonate. Examples of suitable organic solvents include ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, polyethylene carbonate, gamma-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, acetonitrile, benzonitrile, nitromethane, nitrobenzene, triethylamine, triphenylamine, tetraethylene glycol diamine, dimethylformamide, diethylformamide, N-methylpyrrolidone, dimethylsulfone, tetramethylene sulfone, triethylphosphine oxide, 1,3-dioxolane, and sulfolane.

[0118] Thereafter, a positive electrode structure 620 is prepared in which a metal mesh 680 is disposed on a redox mediator-coated porous carbon sheet 690 .

[0119] As the metal mesh 680, for example, a mesh containing at least one metal selected from the group consisting of copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), titanium (Ti), gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) can be used. That is, examples of the mesh include a simple metal selected from this group, an alloy containing a metal selected from this group, and a compound of a metal selected from this group and carbon (C), nitrogen (N), or the like. In the case of an alloy, it may also contain iron (Fe) and chromium (Cr). The mesh may have a thickness of 0.2 mm and a mesh size of 1 mm, for example.

[0120] Thereafter, the positive electrode structure 620 is attached to the negative electrode structure 610 filled with the electrolyte via a separator 660, and the assembly is restrained with a restraining device 630 to obtain an air battery 600. Here, the assembly is preferably performed in dry air, for example, in dry air with a dew point temperature of −50° C. or lower.

[0121] The air battery 600 has a redox mediator-coated porous carbon sheet 690 and a metal mesh 680 as the positive electrode structure 620, but the air battery of the present disclosure is not limited to the above, and the positive electrode structure 620 may consist solely of the redox mediator-coated porous carbon sheet 690.

[0122] The air battery 600 is capable of taking in a large amount of oxygen because the positive electrode structure 620 using the redox mediator-coated porous carbon sheet 690 has excellent air or oxygen permeability, and also has high ion transport efficiency and a wide reaction field. Therefore, it is an excellent air battery that has a large capacity even though it is small and lightweight.

[0123] <Stacked air battery> A schematic cross-sectional view of an air battery according to another embodiment is shown in Fig. 2. Fig. 2 is a schematic view showing a layered type air battery.

[0124] The air battery 500 has a laminated structure in which a positive electrode structure 510 and a negative electrode structure 100 are laminated via a separator 540. The number of laminated pairs may be one or more pairs, with one positive electrode structure 510 and one negative electrode structure 100 being regarded as one pair, and there is no particular upper limit to the number of pairs.

[0125] The negative electrode structure 100 is composed of a pair of negative electrode active material layers (metal layers) and a negative electrode current collector 520 sandwiched between them.

[0126] On the other hand, the positive electrode structure 510 is arranged such that a pair of laminates each composed of a redox mediator-coated porous carbon sheet 550 and a gas diffusion layer 560 sandwich a positive electrode current collector 525. The gas diffusion layer 560 and the redox mediator-coated porous carbon sheet 550 are arranged in this order from the positive electrode current collector 525 side.

[0127] The gas diffusion layer 560 of the positive electrode structure 510 allows air, oxygen, and other gases to pass between the outside of the battery and the redox mediator-coated porous carbon sheet 550. The gas diffusion layer 560 also functions as a path for electrons to move between the redox mediator-coated porous carbon sheet 550 and the positive electrode current collector 525. Since the gas diffusion layer 560 functions as a path for the gases to move, it is necessary for it to have air-permeable communicating holes and to have electronic conductivity. For example, carbon paper TGP-H (Toray Industries, Inc.) and KRECA (registered trademark) E704 (Kureha Corporation) can be used as the gas diffusion layer 560.

[0128] Since the positive electrode current collector 525 has a function of electrical connection with the outside as well as a function of a flow path for air or oxygen, the air battery 500 can have a larger capacity with a simpler structure.

[0129] For example, metals such as copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), titanium (Ti), gold (Au), silver (Ag), platinum (Pt), and palladium (Pd), as well as alloys and compounds (e.g., compounds with carbon and / or nitrogen) thereof can be used for the negative electrode current collector 520 and the positive electrode current collector 525. In the case of alloys, iron (Fe) and chromium (Cr) can also be included.

[0130] Next, a method for manufacturing the air battery 500 will be described. First, the negative electrode structure 100 is constructed from a pair of negative electrode metals and a negative electrode current collector 520 sandwiched between them, and the negative electrode current collector 520 is surrounded by a separator 540 so as to extend to the outside, and the space within the separator is filled with an electrolyte.

[0131] Next, the positive electrode structure 510 is constructed from a pair of laminates each consisting of a redox mediator-coated porous carbon sheet 550 and a gas diffusion layer 560, and a positive electrode current collector 525 sandwiched between them. Note that, from the positive electrode current collector 525 side, the gas diffusion layer 560 and the redox mediator-coated porous carbon sheet 550 are arranged in this order.

[0132] The negative electrode structure 100 and the positive electrode structure 510 are laminated with a separator 540 interposed therebetween to produce an air battery 500. The air battery 500 may be housed in a storage container (not shown). EXAMPLES

[0133] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these.

[0134] <Measurement method> Various measurement methods carried out in the examples and comparative examples are as follows.

[0135] (1)BET specific surface area The adsorption isotherm was obtained by nitrogen adsorption using 3Flex (Micromeritics Instrument Corp.) according to the BET method.

[0136] (2) Pore volume of pores with diameters of 2 nm to 1,000 nm The adsorption isotherm was obtained by nitrogen adsorption using 3Flex (Micromeritics Instrument Corp.) and the BJH method.

[0137] (3) Pore volume of pores with diameters of 0.1 μm to 10 μm The pore volumes in the pore diameter range of 10 nm to 200,000 nm (0.01 μm to 200 μm) were measured by mercury intrusion using an AutoPoreIV (Micromeritics Instrument Corp.), and the values ​​of the pore volumes in the pore diameter range of 0.1 μm to 10 μm were used.

[0138] (4) Metsuke The porous carbon sheet and the redox mediator-coated porous carbon sheet were each punched out into a circle having a diameter (φ) of 16 mm, and their masses (mg) were measured. The masses (mg) of the porous carbon sheet and the redox mediator-coated porous carbon sheet were calculated based on the area (cm 2 ) to obtain the mass per area, and then calculate the basis weight (mg / cm 2 ) was decided.

[0139] (5) Sheet density (ρ sheet ) Sheet density (ρ sheet ) was calculated by dividing the basis weight of the sheet by the thickness of the sheet.

[0140] (6)Porosity The porosity was calculated according to the following formula. Porosity = [1-(ρ sheet / ρ)] × 100 In the formula, ρ is the true density of the sheet constituent, and the true density of carbon nanotubes 1, 2, and 3 described later is 1.3 g / cm 3 This was calculated assuming the following.

[0141] (7)G / D ratio The Raman spectrum was obtained using a Touch-VIS-NIR Raman spectrometer (Nanophoton Corporation) with a 10x objective lens, an excitation wavelength of 532 nm, and an irradiation laser power of 1 mW. The peak intensity due to crystalline carbon was calculated as G (1580 cm -1 ), and the peak intensity due to turbostratic carbon is D (1350 cm -1 ) and the G / D peak intensity ratio was calculated.

[0142] (8) Amount of redox mediator attached The amount of the redox mediator adhered was measured by punching out a circle having a diameter (φ) of 16 mm from the porous carbon sheet coated with the redox mediator and the porous carbon sheet before the redox mediator was adhered, measuring the mass (mg) of each circle, and calculating the difference between the masses. 2 ) to obtain the mass per area.

[0143] <Carbon materials> The carbon materials used as the raw material for the porous carbon sheet are shown in Table 1. Carbon nanotube 1 (CNT1) was a single-walled carbon nanotube ZEONANO SG101 (Zeon Corporation). Carbon nanotube 2 (CNT2) was a single-walled carbon nanotube produced by the super-gloss method (chemical vapor deposition method) according to the description in Non-Patent Document 1. Specifically, a silicon substrate on which Fe (2 nm) / Al2O3 (40 nm) was deposited by sputter deposition was sealed in a circular furnace, and annealed at 750°C for 6 minutes under 1 atmospheric pressure while supplying a He / H2 mixed gas (mixture ratio 1 / 9) at a flow rate of 1000 sccm. Next, a He / H2 mixed gas containing 150 ppm water and 10% ethylene was supplied at a flow rate of 1000 sccm for 10 minutes to grow a carbon nanotube aggregate on the silicon substrate, which was used as CNT2. The carbon nanotubes (CNT3) used were single-walled carbon nanotubes MEIJO eDIPS2.0 (Meijo Nano Carbon Co., Ltd.).

[0144] [Table 1]

[0145] <Preparation of porous carbon sheet> Porous carbon sheets were produced using the carbon materials (CNT1 to CNT3) shown in Table 1. Table 2 shows the physical properties of the obtained porous carbon sheets.

[0146] CNT1 and CNT2 were mixed in a small amount of pure water and pre-dispersed by stirring with a mixer (High Flex Homogenizer, SMT Corporation, Model: HF93, Rotational speed: 9000 rpm, Time: 3 minutes), and then pure water was added to adjust the carbon nanotube concentration to 0.05 mass% to prepare a CNT aqueous dispersion. The obtained CNT aqueous dispersion was subjected to ultrasonic treatment at room temperature (Branson ultrasonic homogenizer, EMERSON Corporation, Model: 450D, Output: 50 W, Time: 50 seconds), filtered on a filter (Omnipore membrane filter, 1.0 μm pore size), and vacuum dried to obtain self-supporting porous carbon sheets (Sheets 1 and 2).

[0147] CNT3 was mixed in a small amount of isopropanol and pre-dispersed by mixing with a mixer (Highflex homogenizer, SMT Corporation, HF93, rotation speed 9000 rpm, 3 minutes), and then isopropanol was added to adjust the carbon nanotube concentration to 0.05 mass% to prepare a CNT isopropanol dispersion. The obtained CNT isopropanol dispersion was ultrasonicated in an ice bath (Branson ultrasonic homogenizer, EMERSON Corporation, model: 450D, output: 20 W, time: 180 minutes), filtered on a filter (Omnipore membrane filter, 1.0 μm pore size), and vacuum dried to obtain a self-supporting porous carbon sheet (sheet 3).

[0148] [Table 2]

[0149] <Combination of redox mediator and solvent> In order to find a suitable combination of a redox mediator and a solvent, a redox mediator was combined with a solvent to confirm whether the redox mediator was soluble in the solvent and whether the resulting solution was capable of penetrating a porous carbon sheet.

[0150] The redox mediators used were lithium bromide (LiBr), lithium nitrite (LiNO2), sodium nitrite (NaNO2), lithium nitrate (LiNO3), and 10-methylphenothiazine (MPT).The solvents used were water, 1-propanol, and anisole.

[0151] The dissolution was judged by adding a redox mediator to a solvent and determining whether a 1 wt % solution of the redox mediator could be prepared. The penetration was judged by applying the obtained solution to a porous carbon sheet at a rate of 10 μl / cm per application. 2 to 25μl / cm 2 After dropping the solution and leaving it for one minute or more, it was judged whether the solution had penetrated into the sheet or not. Next, the sheet was vacuum dried at 100°C for one hour or more to produce a redox mediator-coated porous carbon sheet in which the redox mediator was fixed to the surface of the porous carbon sheet.

[0152] The results of the combination of the redox mediator and the solvent are shown in Table 3. The symbols shown in Table 3 have the following meanings. ◯: The redox mediator was dissolved in the solvent and the solution permeated the porous carbon sheet. Xa: The redox mediator was dissolved in the solvent, but the solution did not penetrate the porous carbon sheet and was repelled. Xb: The redox mediator was not dissolved in the solvent.

[0153] [Table 3]

[0154] In the case of the combination Xa in Table 3, in which the solvent is water, the aqueous solution could be permeated into the porous carbon sheet for sheets 1 and 2, which contain a large amount of turbostratic carbon components and have a G / D ratio of approximately less than 10, by applying mechanical stimulation such as kneading or rubbing the aqueous solution onto the sheet rather than leaving it on the sheet. However, when the aqueous solution was permeated by mechanical stimulation, the sheet shrunk after drying, and twisting or shrinking became evident. Furthermore, the aqueous solution could not be permeated into sheet 3, which has a G / D ratio of more than 100, even by mechanical stimulation.

[0155] From the results in Table 3, it is evident that the solvent for forming the solution used for adhering the redox mediator to the porous carbon sheet can be selected based on the following requirements. (1) Having sufficient solubility in the redox mediator; (2) It has affinity with the porous carbon sheet and has good wettability; and (3) It is volatile and the solvent must be easily removed.

[0156] Specifically, in the case of an inorganic salt redox mediator, a high-medium polarity solvent or a medium polarity solvent can be used, such as a short-chain alcohol such as 1-propanol, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), etc. In the case of an organic compound redox mediator such as MPT, a medium polarity solvent or a low polarity solvent can be used, such as anisole, toluene, and acetonitrile.

[0157] By selecting a suitable combination of a redox mediator and a solvent and adjusting the concentration of the resulting solution, the amount and site of adhesion of the redox mediator can be freely selected by dropping the solution onto the porous carbon sheet and allowing it to penetrate, or by spraying or inkjet coating the solution.

[0158] <Examples 1 to 9, Comparative Examples 2, 3, 5, and 7> [Preparation of redox mediator-coated porous carbon sheet] A redox mediator shown in Table 4 was attached to the surface of a porous carbon sheet (Sheet 1 to Sheet 3) described in Table 2 by the method shown in Figure 3 to prepare a redox mediator-coated porous carbon sheet.

[0159] The redox mediators used were lithium bromide (LiBr), lithium nitrite (LiNO2), lithium nitrate (LiNO3), and 10-methylphenothiazine (MPT). The solvent used was anisole for 10-methylphenothiazine (MPT), and 1-propanol for the other redox mediators.

[0160] The redox mediator was added to the solvent to prepare a 1 wt % solution of the redox mediator. The obtained solution was applied to the porous carbon sheet at a rate of 10 μl / cm 2 to 25μl / cm 2 The solution was dripped onto the porous carbon sheet, left for at least one minute to allow the solution to penetrate into the sheet, and then vacuum dried at 100° C. for at least one hour to produce a redox mediator-coated porous carbon sheet in which the redox mediator was adhered to the surface of the porous carbon sheet. The amount of redox mediator adhered was adjusted by adjusting the amount of redox mediator solution dripped and the number of drips.

[0161] [Preparation of lithium-air battery cells] Examples 1 to 9 and Comparative Examples 2, 3, 5, and 7 were used as the redox mediator-coated porous carbon sheets, and as the porous carbon sheets to which no redox mediator was attached, Sheet 1 was used as is in Comparative Example 1, Sheet 2 was used as is in Comparative Example 4, and Sheet 3 was used as is in Comparative Example 6, to prepare lithium-air batteries using these sheets as the positive electrodes.

[0162] Specifically, each sheet was cut into a circle with a diameter (φ) of 16 mm and vacuum dried at 100°C for more than 12 hours. The sheets were then stacked in the following order: [lithium metal foil (φ16 mm) / separator for lithium ion secondary battery / (redox mediator-coated porous carbon sheet or porous carbon sheet) (φ16 mm)], and then an electrolyte (a tetraethylene glycol dimethyl ether (TEGDME) solution containing 1 M lithium bistrifluoromethanesulfonylimide (LiTFSI)) was permeated into the sheets to produce a lithium-air battery cell.

[0163] (Measurement of discharge and charge voltage) The discharge and charge voltages of the fabricated lithium-air battery cells were measured. Specifically, a battery charge-discharge system (Hokuto Denko, model: HJ1001SD8) was used in a pure oxygen flow environment at room temperature and at a constant current (0.4 mA / cm 2 ), discharged for 10 hours under 2.0-4.5V cutoff conditions, rested for 10 minutes, then charged for 10 hours (4mAh / cm 2 ) were discharged and charged for 5 hours (2mAh / cm 2 The intermediate voltages at which the discharge and charge voltages were measured were recorded as the discharge and charge voltages. The results are shown in Table 4. The symbols shown in Table 4 have the following meanings. Xa: Default capacity (4mAh / cm 2 ) The intermediate voltage could not be recorded because the 2.0 V cutoff voltage was reached before discharging. Xb: Default capacity (4mAh / cm 2 ) The 4.5V cutoff voltage was reached before charging, so intermediate voltages could not be recorded.

[0164] [Table 4]

[0165] LiBr was used as a redox mediator at 0.2 mg / cm 2 to 1.6 mg / cm 2 (Molar amount: 2 μmol / cm 2 to 20 μmol / cm 2It can be seen that the redox mediator-coated porous carbon sheets of Examples 1 to 4 to which LiBr was fixed had almost no effect on the discharge voltage, while significantly suppressing the charge voltage, as compared with the porous carbon sheet of Comparative Example 1 to which LiBr was not fixed.

[0166] It can be seen that the redox mediator-coated porous carbon sheets of Examples 5 to 7, in which LiNO2, LiNO3, or MPT was fixed to the same extent as the redox mediator, were also able to significantly suppress the charge voltage with almost no effect on the discharge voltage.

[0167] The redox mediator-coated porous carbon sheets prepared using the sheets 2 and 3 were also coated with 0.4 mg / cm LiBr as a redox mediator. 2 (4μmol / cm 2 It can be seen that in Examples 8 and 9 in which the electrode was fixed, the charge voltage was significantly reduced with almost no effect on the discharge voltage.

[0168] LiBr was used as a redox mediator at 2.9 mg / cm 2 The porous carbon sheets coated with a redox mediator of Comparative Examples 3, 5, and 7 to which LiBr was fixed showed a significantly reduced discharge amount and were unable to discharge the specified amount, compared with the porous carbon sheets to which LiBr was not fixed of Comparative Examples 1, 4, and 6. This is thought to be because when an excessive amount of the redox mediator is fixed, the electrical resistance of the porous carbon sheet increases and the pores are blocked, resulting in a loss of oxygen diffusivity necessary for discharge.

[0169] [Scanning electron microscope photographs and elemental mapping] A scanning electron microscope photograph of the porous carbon sheet of Comparative Example 1 to which LiBr was not fixed is shown in FIG. 2 A scanning electron micrograph of the adhered redox mediator-coated porous carbon sheet of Example 2 is shown in FIG.

[0170] The redox mediator-coated porous carbon sheet of Example 2 has the same appearance as the porous carbon sheet of Comparative Example 1 as a nonwoven fabric-like fibrous carbon aggregate, and it is clear that LiBr is fixed without impairing the porosity of the sheet.

[0171] LiBr at 0.4 mg / cm 2 With respect to the adhering redox mediator-coated porous carbon sheet of Example 2, elemental mapping of carbon (C) is shown in Figure 6. Elemental mapping of bromine (Br) is shown in Figure 7. From Figures 6 and 7, it can be seen that bromine (Br), which is a constituent element of the redox mediator, is uniformly adhered around the carbon (C) of the carbon nanotubes forming the porous carbon sheet.

[0172] [Measurement of various physical properties] Table 5 shows the results of various measurements on the redox mediator-coated porous carbon sheets of Examples 1, 2, and 5, and the porous carbon sheets of Comparative Examples 1 and 3. It can be seen that the thickness and pore volume of the redox mediator-coated porous carbon sheets are almost unchanged by the fixation of the redox mediator, and the pore structure is maintained similar to that before the fixation of the redox mediator. LiBr was used as the redox mediator at 2.9 mg / cm. 2 Comparative Example 3, which was fixed, had a specific surface area of ​​490 m 2 / g, and the capacity was reduced to the default capacity (4 mAh / cm 3 ) due to pore blockage, as shown in Table 4. 2 ) was no longer able to discharge.

[0173] [Table 5]

[0174] [Measurement of membrane resistance (electrical resistance)] The membrane resistances of the porous carbon sheet and the redox mediator-coated porous carbon sheet, measured before and after the fixation of the redox mediator, are shown in Table 6. As the membrane resistance, the electrical resistance passing through each sheet was measured by the method described in Fig. 3. Specifically, a sheet cut into a circle with a diameter of 16 mm was sandwiched between two copper foils, a surface pressure of 118 kPa was applied, and the AC impedance between the copper plates was measured (Biologic, model: SP-200), and the real impedance component at a frequency of 1 Hz was recorded as the membrane resistance.

[0175] [Table 6]

[0176] LiBr was used as a redox mediator at 0.4 mg / cm 2 The porous carbon sheet coated with the redox mediator of Example 2, to which the redox mediator was fixed, had a lower membrane resistance (electrical resistance) than the porous carbon sheet of Comparative Example 1 to which the redox mediator was not fixed, which is considered to be effective in suppressing the overvoltage of the lithium-air battery cell. 2 When the redox mediator is adhered to the porous carbon sheet to a large extent, the membrane resistance (electrical resistance) increases. It is considered that it becomes difficult to discharge the specified amount of electricity in the case of a redox mediator-coated porous carbon sheet to which a large amount of the redox mediator is adhered, because the membrane resistance (electrical resistance) increases.

[0177] [Preparation of lithium-air battery cells] Examples 2, 8, and 9 were used as coated porous carbon sheets, and Comparative Examples 1, 4, and 6 were used as porous carbon sheets to which no redox mediator was attached, and lithium-air batteries were fabricated using these as the positive electrodes.

[0178] Specifically, each sheet was cut into a circle with a diameter (φ) of 16 mm, and vacuum dried at 100°C for 12 hours or more. The sheets were then stacked in the order of [lithium metal foil (φ16 mm) / separator for lithium ion secondary battery / (redox mediator-coated porous carbon sheet or porous carbon sheet) (φ16 mm)], and the electrolyte was then permeated to prepare a lithium-air battery cell. As the electrolyte, a tetraethylene glycol dimethyl ether (TEGDME) solution containing 1M lithium bistrifluoromethanesulfonylimide (LiTFSI), or a TEGDME solution containing 0.5M LiTFSI, 0.5M LiNO3 (redox mediator), and 0.2M LiBr (redox mediator) was used. The properties of the prepared air batteries are shown in Table 7.

[0179] [Table 7]

[0180] (Measurement of discharge and charge voltage) A charge-discharge cycle test was carried out on the fabricated lithium-air battery cell. Using a battery charge-discharge system (Hokuto Denko, model: HJ1001SD8), the cells were charged at room temperature under a pure oxygen flow environment at a constant current (0.4 mA / cm 2 ), 10 hours of discharge and charge under 2.0-4.5V cutoff condition (4mAh / cm 2 ) was repeated three times.

[0181] The charge / discharge curves of air batteries 1, 2, and 3 are shown in Figures 9, 10, and 11, respectively. Air battery 1, which uses a porous carbon sheet to which no redox mediator is fixed, shows a gradual increase in charge voltage toward the end of charging, whereas air battery 2, which contains the redox mediator LiBr in the electrolyte, shows a flat charge voltage near 3.6 V and then the charge voltage increases slowly toward the end of charging. Air battery 3, which uses a redox mediator porous carbon sheet to which the redox mediator LiBr is fixed, shows a flat charge voltage near 3.6 V and then increases toward the end of charging, just like air battery 2, but the increase is more suppressed than in air battery 2, indicating that overvoltage can be effectively suppressed.

[0182] FIG. 12 shows the voltages at the end of discharge and the end of charge for each of the air batteries 1, 2, and 3. Although all the air batteries show almost the same discharge end voltage (about 2.6 V), the charge voltage of the air battery 1 using the porous carbon sheet to which the redox mediator is not fixed reaches the 4.5 V cutoff voltage and cannot be fully charged. The air battery 2 containing the redox mediator LiBr in the electrolyte has a lower charge voltage than the air battery 1, but the effect disappears after three cycles and the 4.5 V cutoff voltage is reached. The air battery 3 using the redox mediator porous carbon sheet to which the redox mediator LiBr is fixed does not reach the 4.5 V cutoff voltage even in the third cycle, and it is found that the effect of suppressing the charge overvoltage is sustained more than that of the air battery 2.

[0183] The charge / discharge curves of air batteries 4 and 5 are shown in Figures 13 and 14. Air battery 4, which uses a porous carbon sheet to which no redox mediator is fixed, reaches the 4.5 V cutoff voltage at less than half the charge capacity and is barely chargeable, whereas air battery 5, which uses a redox mediator porous carbon sheet to which the redox mediator LiBr is fixed, can be charged while effectively suppressing charging overvoltage.

[0184] The charge / discharge curves of the air batteries 6 and 7 are shown in Figures 15 and 16. It can be seen that the air battery 6 using a porous carbon sheet to which no redox mediator is fixed exhibits a high charging overvoltage of about 4.2 V, whereas the air battery 7 using a redox mediator porous carbon sheet to which the redox mediator LiBr is fixed can be charged while effectively suppressing the charging overvoltage. [Industrial Applicability]

[0185] According to the present invention, the cycle capacity can be increased to a large value (e.g., 4 mAh / cm 2As a result, an air battery having a large cycle capacity and improved charge / discharge cycle characteristics can be obtained. [Explanation of symbols]

[0186] 600 Air battery 610 Negative electrode structure 620 Positive electrode structure 630 Restraints 635 Current collector 640 Metal layer 650 Spacer 660 Separator 670 Space 680 Metal Mesh 690 Porous carbon sheet coated with redox mediator 500 Air battery 100 Negative electrode structure 510 Positive electrode structure 520 Negative electrode current collector 525 Positive electrode current collector 540 Separator 550 Redox mediator-coated porous carbon sheet 560 Gas diffusion layer

Claims

1. A redox mediator that mediates the oxidative decomposition of a metal oxide by its own redox reaction is fixed to the surface of the porous carbon sheet; The amount of the redox mediator adhered is 0.2 mg / cm ２ More than 2.9 mg / cm ２ The redox mediator-coated porous carbon sheet has a molecular weight of less than 10000.

2. BET specific surface area is 200m ２ / g or more 1100m ２ 2. The redox mediator-coated porous carbon sheet according to claim 1, wherein the surface area of ​​the porous carbon sheet is 0.1 μm or less.

3. 2. The redox mediator-coated porous carbon sheet of claim 1, which is self-supporting.

4. 2. The redox mediator-coated porous carbon sheet according to claim 1, which has a thickness of 40 μm or more and 300 μm or less.

5. 2. The redox mediator-coated porous carbon sheet according to claim 1, wherein the oxidation potential of the redox mediator is greater than an equilibrium potential of the metal oxide.

6. 2. The redox mediator-coated porous carbon sheet according to claim 1, wherein the metal oxide is lithium peroxide.

7. 2. The redox mediator-coated porous carbon sheet according to claim 1, wherein the redox mediator is at least one selected from the group consisting of nitrites, nitrates, bromides, iodides, and phenothiazine-based compounds.

8. 8. The redox mediator-coated porous carbon sheet according to claim 7, wherein the redox mediator is at least one selected from the group consisting of lithium nitrite, lithium nitrate, lithium bromide, and 10-methylphenothiazine.

9. 2. The redox mediator-coated porous carbon sheet according to claim 1, wherein the specific surface area of ​​the redox mediator-coated porous carbon sheet is 70% or more of the specific surface area of ​​the porous carbon sheet.

10. 2. The redox mediator-coated porous carbon sheet according to claim 1, wherein the electric resistance of the redox mediator-coated porous carbon sheet is smaller than the electric resistance of the porous carbon sheet.

11. A positive electrode for an air battery, comprising the redox mediator-coated porous carbon sheet according to claim 1 .

12. A positive electrode comprising the redox mediator-coated porous carbon sheet according to claim 11; A negative electrode; an electrolyte present between the positive electrode and the negative electrode; An air battery comprising:

13. 13. The air battery of claim 12, wherein the negative electrode comprises lithium metal.

14. preparing a redox mediator solution by dissolving a redox mediator that mediates the oxidative decomposition of a metal oxide by its own redox reaction in a solvent; contacting the redox mediator solution with a porous carbon sheet so that the redox mediator solution is present on the surface and within the pores of the porous carbon sheet; drying the redox mediator solution to remove the solvent and adhere the redox mediator to the porous carbon sheet; A method for producing a redox mediator-coated porous carbon sheet, comprising:

15. 15. The method for producing a redox mediator-coated porous carbon sheet according to claim 14, wherein the contact is at least one selected from the group consisting of impregnation, dripping, spray coating, and inkjet coating.

16. The method for producing a redox mediator-coated porous carbon sheet according to claim 14, wherein the redox mediator is an inorganic salt, and the solvent is a high polarity solvent or a medium polarity solvent.

17. 17. The method for producing a redox mediator-coated porous carbon sheet according to claim 16, wherein the redox mediator is at least one selected from the group consisting of lithium nitrite, lithium nitrate, and lithium bromide, and the solvent is 1-propanol.

18. The method for producing a redox mediator-coated porous carbon sheet according to claim 14, wherein the redox mediator is an organic compound, and the solvent is a medium polarity solvent or a low polarity solvent.

19. 19. The method for producing a redox mediator-coated porous carbon sheet according to claim 18, wherein the redox mediator is 10-methylphenothiazine, and the solvent is anisole.

20. The method for producing a redox mediator-coated porous carbon sheet according to claim 14 , wherein the redox mediator-coated porous carbon sheet is a positive electrode for an air battery.

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