Porous carbon material for positive electrode of air battery

Abstract

This invention provides a porous carbon material for air battery cathodes that has high energy density and improved cycle characteristics. [Solution] The present invention relates to a porous carbon material for the positive electrode of an air battery, wherein, in a heating gas mass spectrometry, the ratio of the amount of carbon dioxide desorbed in the temperature range of 700°C to 1000°C to the amount of carbon dioxide desorbed in the temperature range of 30°C to 1000°C is 70% or more, at a heating rate of 10°C / min.

Description

[Technical Field]

[0001] This disclosure relates to porous carbon materials for the cathode of air batteries. [Background technology]

[0002] Air batteries, which use oxygen as the positive electrode and a metal as the negative electrode, are generally known. For example, when the metal is zinc, the following battery reaction is known. In order to use such an air battery as a secondary battery, a reverse reaction with oxygen molecules is required, which necessitates high catalytic activity. Therefore, generally, rare metals such as Pt, Pd, and Ni are supported on a carbon material and used as a catalyst for the positive electrode. (Positive electrode) O2+2H2O+4e - → 4OH - (Negative electrode) 2Zn+4OH - → 2ZnO + 2H2O + 4e - (Overall) 2Zn + O2 → 2ZnO

[0003] However, the reaction is rate-limiting for oxygen, resulting in low energy density and cycle characteristics. Therefore, further improvements in the catalytic performance of cathode catalysts are needed. Furthermore, if the catalytic performance of carbon can be increased, it will be possible to reduce the amount of rare metals used. One indicator of the catalytic performance of porous carbon materials is their ability to efficiently retain oxygen involved in the cathode reaction, water as the electrolyte, and reaction intermediates such as OOH radical ions, OH radical ions, and O radical ions that are generated during the reaction, within the pores. This makes it possible to efficiently advance the cathode reaction.

[0004] Patent Document 1 describes a pore size with a peak intensity ratio (G / D ratio) of 1.6 or more and 2.2 or less, measured by Raman spectroscopy, and a pore volume of 0.18 cm³. 3 A technology has been disclosed in which Pt is supported on a carbon material with a pore size of 2.6 nm to 2.8 nm and a peak top pore diameter of the pore distribution curve, and used as a cathode catalyst for fuel cells. However, the energy density and cycle characteristics are not at a sufficient level. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-88828 [Overview of the project] [Problems that the invention aims to solve]

[0006] The purpose of this disclosure is to provide a porous carbon material for air battery cathodes that has high energy density and improved cycle characteristics. [Means for solving the problem]

[0007] In one embodiment of the present disclosure, the porous carbon material for the positive electrode of an air battery exhibits, in a heating-generated gas mass spectrometry, a ratio of the amount of carbon dioxide desorbed in the temperature range of 700°C to 1000°C to the amount of carbon dioxide desorbed in the temperature range of 30°C to 1000°C is 70% or more at a heating rate of 10°C / min.

[0008] An air battery positive electrode according to one embodiment of the present disclosure includes a porous permeable material as an electrode and a porous carbon material for the air battery positive electrode. [Effects of the Invention]

[0009] According to the porous carbon material for the positive electrode of an air battery of this disclosure, an air battery with high energy density and improved cycle characteristics can be obtained. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows the amount of carbon dioxide gas generated by the porous carbon materials for the positive electrode of air batteries prepared in Examples 1 to 4, measured in a temperature range from room temperature to 1000°C, and plotted against temperature. [Figure 2]It is a diagram showing the amount of carbon dioxide gas generated in the temperature range from room temperature to 1000 °C for the porous carbon material for the air battery positive electrode of Comparative Example 1, plotted against temperature. [Figure 3] It is a diagram showing the amount of carbon monoxide gas generated in the temperature range from room temperature to 1000 °C for the porous carbon material for the air battery positive electrode prepared in Example 1, plotted against temperature. [Figure 4] It is a diagram showing the cumulative particle size distribution of the pore diameters of the porous carbon materials for the air battery positive electrodes prepared in Examples 1 to 4. [Figure 5] It is a diagram showing the charge-discharge voltage plotted against the charge-discharge time for the zinc-air secondary battery prepared using the porous carbon materials for the air battery positive electrodes prepared in Examples 1 to 4. [Figure 6] It is a diagram showing the charge-discharge voltage plotted against the charge-discharge time for the zinc-air secondary battery prepared using the porous carbon material for the air battery positive electrode of Comparative Example 1.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. However, the embodiments shown below are an example for embodying the technical idea of the present disclosure, and the present disclosure is not limited to the following. In this specification, the term "step" includes not only an independent step but also the case where it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0012] <<Porous Carbon Material for Air Battery Positive Electrode>> The porous carbon material for the air battery positive electrode of the present disclosure is characterized in that in the heating-generated gas mass analysis, the ratio of the amount of carbon dioxide desorbed in the temperature range from 700 °C to 1000 °C to the amount of carbon dioxide desorbed in the temperature range from 30 °C to 1000 °C at a heating rate of 10 °C / min is 70% or more.

[0013] The porous carbon material used for the air battery positive electrode of the present disclosure is not particularly limited, and examples thereof include mesoporous carbon, Ketjen black, acetylene black, activated carbon, carbon nanotubes, multi-layer graphene, graphite, and the like. Among these carbon materials, a carbon material having voids inside the secondary particles is preferable. For example, mesoporous carbon, Ketjen black, acetylene black, etc. may be mentioned, and it may contain at least one selected from the group consisting of these. The carbon material may be used alone or in combination of two or more.

[0014] By subjecting the porous carbon material to surface treatment, a functional group is formed on the surface of the carbon material. When the carbon material having the functional group formed thereon is heated, the functional group present on the surface decomposes according to the heating temperature, and decomposition gases such as carbon monoxide and carbon dioxide are generated. Examples of such functional groups that generate decomposition gases include a carboxyl group, a functional group having a lactone ring, an acid anhydride group, a phenolic hydroxyl group, a carbonyl group, an ether group, and a group having a quinone structure. Carbon dioxide is generated at 100°C to 400°C for the carboxyl group, and at 190°C to 650°C for the functional group having a lactone ring. The acid anhydride group decomposes at 350°C to 620°C, and carbon monoxide is generated together with carbon dioxide. On the other hand, the phenolic hydroxyl group decomposes at 600°C to 700°C, and carbon monoxide and water are generated. The carbonyl group decomposes at 700°C to 980°C, the ether group decomposes at 700°C, and the group having a quinone structure decomposes at 700°C to 980°C, generating carbon monoxide. The carbon dioxide desorbed in the temperature range of 700°C to 1000°C is considered to be derived from the carbon monoxide generated from the carbonyl group, ether group, and quinone structure. Therefore, the desorption amount of carbon dioxide desorbed in the temperature range of 700°C to 1000°C is a physical property related to the abundance of functional groups having a carbonyl group, quinone, ether, etc. And the ratio of the desorption amount of carbon dioxide represents the abundance ratio of the carbon material having a carbonyl group, quinone, ether, etc.

[0015] The ratio of carbon dioxide desorbed in the temperature range of 700°C to 1000°C to the amount of carbon dioxide desorbed in the temperature range of 30°C to 1000°C is 70% or more, preferably 75% or more, and more preferably 80% or more. If it is less than 70%, the proportion of carbon material having carbonyl groups and quinone structures among the functional groups present on the surface of the carbon material will be small. Carbonyl groups and quinone structures are functional groups that have only a C=O double bond in the carbon-oxygen bond, and it is thought that this bonding state allows other reaction intermediates such as oxygen, hydroxide ions, and radical ions to be appropriately attracted to the functional group and retained in the pore, thereby enabling the cathode reaction to proceed efficiently.

[0016] The ratio of the amount of carbon monoxide desorbed in the temperature range of 400°C to 1000°C to the amount of carbon monoxide desorbed in the temperature range of 30°C to 1000°C is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0017] The total amount of acidic functional groups in the porous carbon material for the positive electrode of an air battery is preferably 0.3 mmol / g or more, more preferably 0.5 mmol / g or more, and even more preferably 1.0 mmol / g or more. There is no particular upper limit, but 4 mmol / g or less is preferred. Below 0.3 mmol / g, the initial discharge capacity tends to be lower. This is thought to be because a higher total amount of acidic functional groups increases the efficiency of retaining oxygen and intermediates in the battery reaction, reducing overpotential and improving cycle characteristics. In the positive electrode of an air battery, as the number of charge-discharge cycles increases, the carbon material undergoes side reactions with the electrolyte and oxygen, causing deterioration such as surface oxidation. This is thought to reduce the ability to retain reaction intermediates, thereby reducing catalytic activity and causing a decrease in capacity. In other words, improving the ability to retain reaction intermediates can improve cycle characteristics.

[0018] Here, the total amount of acidic functional groups is measured by the Boehm method. The Boehm method is a method for quantifying the amount of acidic functional groups present on the surface of a sample by adding an alkali to the sample, reacting it, and then back-titrating the alkali concentration with an acid. The total amount of acidic functional groups is a physical property related to the abundance of carboxyl groups, phenolic hydroxyl groups, lactone groups, acid anhydride groups, and other functional groups that generate decomposition gases such as carbon monoxide and carbon dioxide, as mentioned above.

[0019] Porous carbon material for the positive electrode of air batteries can be oxidized as needed. One method of oxidation is heating in air. The heating temperature is not particularly limited, but is preferably between 100°C and 500°C, and more preferably between 200°C and 400°C. Below 100°C, the amount of target acidic functional groups does not increase, and above 500°C, carbon is burned by oxygen, and weight loss tends to be significant. The heating time is also not particularly limited, but is preferably between 1 hour and 24 hours, and more preferably between 3 hours and 12 hours. Below 1 hour, the amount of modified acidic functional groups is small, so the effect on battery characteristics is small. On the other hand, even if heat treatment is performed in air for a long period of time of 24 hours or more, the increase in the amount of acidic functional groups is small, which is undesirable from the viewpoint of low yield.

[0020] The pore diameter at a volume-based cumulative of 70% obtained by the QSDFT method for the porous carbon material for the air battery positive electrode is 1 nm or more and 5 nm or less, preferably 2 nm or more and 4 nm or less. Also, the pore diameter at a volume-based cumulative of 80% may be 1 nm or more and 5 nm or less, preferably 2 nm or more and 4 nm or less. Further, it is preferable that the volume ratio of pores having a pore diameter of 1.5 nm or more and 4 nm or less is 50% or more, more preferably 60% or more, and even more preferably 70% or more. Also, it is preferable that the ratio of pores having a pore diameter of 1.5 nm or more and 5 nm or less is 70% or more based on volume, and it is also preferable that the ratio of pores having a pore diameter of 2 nm or more and 4 nm or less is 60% or more based on volume. When within the above-described range, in addition to the tendency for the cycle characteristics to improve due to the high retention efficiency of the electrolyte, oxygen, reaction intermediates, etc. in the pores, the effects of the present disclosure can be easily obtained. Here, the QSDFT method is the quenched solid density functional theory method. The QSDFT method is applied to the measured adsorption isotherm to calculate the pore distribution, and the pore diameter at a predetermined volume-based cumulative is calculated.

[0021] The specific surface area of the porous carbon material for the air battery positive electrode is preferably 500 m 2 / g or more, more preferably 1000 m 2 / g or more, and even more preferably 1500 m 2 / g or more. The upper limit is not particularly limited, but it may be 3000 m 2 / g or less. The specific surface area may be calculated, for example, from the gas adsorption method. From the nitrogen adsorption / desorption curve obtained by the nitrogen adsorption / desorption measurement method, a value measured by the single-point method or multi-point method using nitrogen gas based on the BET (Brunauer, Emmett, Teller) theory may be used. Generally, a porous carbon material with a large specific surface area has high catalytic activity and tends to have high cycle characteristics when used as a positive electrode catalyst.

[0022] The porous carbon material for the positive electrode of an air battery may be secondary particles formed by the aggregation of primary particles. From the viewpoint of packing, it is preferable that the secondary particles do not have connecting pores where voids are connected internally. The 50% particle size D50 in the volume-based cumulative particle size distribution of the secondary particles of the porous carbon material may be 0.1 μm or more and 30 μm or less. The 50% particle size D50 is preferably 1 μm or more, more preferably 2 μm or more. The 50% particle size D50 is preferably 15 μm or less, more preferably 10 μm or less. D50 is measured, for example, using a laser diffraction particle size distribution analyzer.

[0023] The particle size of the primary particles constituting the secondary particles of the porous carbon material for the positive electrode of an air battery may be, for example, 1 nm to 30 μm. Preferably, the particle size of the primary particles is 2 nm or more, more preferably 5 nm or more. Preferably, the particle size of the primary particles is 30 μm or less, more preferably 10 μm or less. The particle size of the primary particles is calculated, for example, by calculating the equivalent spherical diameter from the contour lengths of 20 primary particles for each of 10 selected secondary particles in an image observed using a scanning electron microscope (SEM), transmission electron microscope (TEM), or scanning transmission electron microscope (STEM), and taking the arithmetic mean of these values ​​to determine the particle size of the primary particles.

[0024] The aspect ratio of the porous carbon material for the positive electrode of an air battery is preferably between 1 and 5, and more preferably between 1 and 3. The closer the aspect ratio is to 1, the higher the degree of sphericity, making it preferable for a porous carbon material for an air battery.

[0025] <<Air battery positive electrode>> The positive electrode of the air battery according to this disclosure is characterized by comprising a porous permeable material as a current collector and a porous carbon material for the positive electrode of a zinc-air battery according to this disclosure.

[0026] Porous permeable materials function as current collectors, and examples include carbon paper and nickel foam. A porous carbon material for the positive electrode of an air battery is combined with a liquid medium, binder, conductive additive, etc., as needed, and the resulting electrode-forming composition is applied to the porous permeable material, dried, and pressure-molded to produce the positive electrode of an air battery.

[0027] Porous permeable materials can also enhance adhesion to positive electrode composition layers by forming fine irregularities on their surface. Furthermore, if they are porous and permeable, they can take on a variety of forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics. The thickness of a current collector made of a porous permeable material may be, for example, 3 μm to 500 μm.

[0028] The liquid medium may be an organic solvent, water, or the like, depending on the application. Examples of organic solvents include amide solvents such as isopropanol and N-methyl-2-pyrrolidone (NMP), ketone solvents such as diisopropyl ketone, diisobutyl ketone, and methyl ethyl ketone, hydrocarbon solvents such as heptane, ether solvents such as tetrahydrofuran, dimethoxyethane, and dioxolane, amine solvents such as diethylenetriamine, and ester solvents. The organic solvent may be used alone or in combination of two or more. The content of the liquid medium may be, for example, 10% to 90% by mass in the total mass of the electrode-forming composition.

[0029] A binder is a material that helps adhere to conductive additives, for example, and to the electrode composition to the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butylene rubber, fluororubber, and various copolymers. The binder content may be, for example, 0.05% by mass or more and 50% by mass or less in the electrode-forming composition.

[0030] Conductive additives are materials that improve the electrical conductivity of the positive electrode composition layer, for example. Examples of conductive additives include graphite such as modified graphene, natural graphite, and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; and carbon materials such as graphene and carbon nanotubes. The content of the conductive additive may be, for example, 0.5% by mass or more and 30% by mass or less in the total mass of the electrode forming composition.

[0031] <<Zinc-air battery>> The zinc-air battery of this disclosure is characterized by comprising a positive electrode of the air battery of this disclosure, an electrolyte, and a negative electrode containing zinc. The zinc-air battery may optionally include a separator. The electrolyte may be contained in the positive electrode, negative electrode, and separator of the air battery.

[0032] Any known material can be used as the negative electrode in a zinc-air battery. Examples of negative electrode materials include Zn metal, zinc-nickel alloy, zinc-alumina mixture, and alumina-coated zinc. In these negative electrode materials, some of the Zn may be replaced with other alkali metals. Zn metal is preferred as the negative electrode material. With these materials, a high voltage can be obtained from the zinc-air battery.

[0033] The separator can be made from any known material, such as glass fiber discs, porous polyethylene, polypropylene, cellulose nanofibers, nonwoven fabrics, ceramics, or paper. Alternatively, a known separator may be used after being coated.

[0034] The pH of the electrolyte is not particularly limited, but it is preferable to have a pH close to neutral from the viewpoint of preventing electrode corrosion. A preferred pH is between 4 and 7.

[0035] When using an electrolyte with a pH of 4 to 7, the electrolyte preferably contains a zinc salt, and can be appropriately selected from zinc salts used in conventional zinc-air batteries. Specifically, examples include ZnSO4, Zn(CH3COO)2, and ZnCl2. One of these can be used alone, or two or more can be used in combination. When using a basic electrolyte, for example, KOH can be used as the electrolyte.

[0036] The solvent of the electrolyte may contain water and may also contain an organic solvent. As the organic solvent, carbonate solvents, ether solvents, ester solvents, amide solvents, nitrile solvents, and sulfur-containing solvents may be used, or an organic solvent in which some elements of the above organic solvents are substituted with fluorine may be used. Examples of organic solvents include carbonate solvents such as propionate carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, and vinylene carbonate; ether solvents such as 1,3-dioxolane, 1,2-dimethoxyethane, 1,3-dimethoxypropane, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, and tetrahydrofuran; ester solvents such as methyl formate, methyl acetate, and γ-butyllactone; amide solvents such as N,N-dimethylacetamide and N,N-dimethylformamide; and sulfur-containing solvents such as sulfolane, dimethyl sulfoxide, and 1,3-propanesalton. The water content in the electrolyte solvent may be 90% by mass or more, 95% by mass or more, 99% by mass or more, or 100% by mass. [Examples]

[0037] Examples are described below. Unless otherwise specified, "%" refers to mass.

[0038] Example 1 70g of Bellpearl R100 (Air Water Performance Chemical Co., Ltd.) was heat-treated at 1000°C for 5 hours under a nitrogen atmosphere to obtain a carbide. 30g of the obtained carbide was heat-treated for 3 hours in an air stream of nitrogen and carbon dioxide mixed in a volume ratio of approximately 1:4 to activate it and obtain an activated product. 1g of the obtained activated product was placed in an alumina crucible and heat-treated at 350°C in air for 10 hours to produce the carbon material for the positive electrode of the air battery in Example 1.

[0039] Example 2 The carbon material for the positive electrode of the air battery in Example 2 was prepared in the same manner as in Example 1, except that the heat treatment time in the activation was changed to 5.5 hours.

[0040] Example 3 The carbon material for the positive electrode of the air battery in Example 3 was prepared in the same manner as in Example 1, except that the heat treatment time in the activation was changed to 6.5 hours.

[0041] Example 4 The carbon material for the positive electrode of the air battery in Example 4 was prepared in the same manner as in Example 1, except that the heat treatment time in the activation was changed to 7.5 hours.

[0042] Comparative Example 1 Knobel MH-00 pulverized product (manufactured by Toyo Tanso Co., Ltd.) was used as the carbon material for the positive electrode of the air battery.

[0043] The following evaluations were performed using the porous carbon materials of Examples 1-4 and Comparative Example 1.

[0044] <Total acidic functional group amount> The measurement was carried out referring to the Boehm method (H.P. Boehm, Adzan. Catal, 16, 179 (1966)). Specifically, 50 mL of an aqueous sodium hydroxide solution (0.05 mol / L) was added to 1 g of the porous carbon material, and it was stirred with a roller for 4 hours. After stirring, 10 mL of the filtrate obtained by filtration separation was taken, an aqueous sulfuric acid solution (0.025 mol / L) was added dropwise, and the titration volume when the pH reached around 8.4 was measured. As a blank test, 10 mL of an aqueous sodium hydroxide solution (0.05 mol / L) was taken, an aqueous sulfuric acid solution (0.025 mol / L) was added dropwise, and the titration volume when the pH reached around 8.4 was measured. The total amount of acidic functional groups was calculated by the following formula. The evaluation results are shown in Table 1. Total amount of acidic functional groups (mmol / g) = {(a - b) × 0.025 × 2 × 50 / 10} / S a: Titration volume of sulfuric acid in the blank test (mL) b: Titration volume of sulfuric acid when the sample was reacted (mL) S: Sample mass (g)

[0045] <Ratio of CO2 desorption amount and ratio of CO desorption amount> Using the porous carbon material, the amount of carbon dioxide gas generated in the temperature range from room temperature to 1000 °C was measured by a temperature-programmed desorption gas photoionization mass spectrometer (manufactured by Rigaku Corporation, TPD type R). Specifically, 4 mg to 15 mg of the sample was collected, introduced into the glass tube of the temperature-programmed desorption gas photoionization mass spectrometer, He gas was passed through at 300 mL / min, and the temperature was raised to 1000 °C at a heating rate of 10 °C / min. The generated gas was taken as carbon dioxide gas that generated a profile corresponding to m / z = 44 by a quadrupole mass spectrometer. The ratio of the total amount of generated carbon dioxide gas to the amount of carbon dioxide gas generated from 700 °C to 1000 °C was calculated from the obtained profile. The measurement results are shown in Table 1, and FIGS. 1 and 2.

[0046] Also, as carbon monoxide gas that generated a profile corresponding to m / z = 28, the ratio of the total amount of generated carbon monoxide gas to the amount of carbon monoxide gas generated from 700 °C to 1000 °C was also calculated from the obtained profile. The measurement results for Example 1 are shown in FIG. 3.

[0047] <Pore diameter, pore volume, and specific surface area at 70% cumulative volume> Using porous carbon materials, the volume of open pores (pore diameters between 0.4 nm and 100 nm) into which gas can enter was measured using a surface area / pore analyzer (product name: Nova Touch, manufactured by Anton Paar). Specifically, after dehydration treatment at 150°C for 1 hour under vacuum evacuation, nitrogen adsorption was measured at 77 K and a pressure range of 0.0001 Torr to 760 Torr, and the nitrogen adsorption amount was defined as the volume of the open pores. Furthermore, the pore distribution was calculated by applying the rapid solid density functional theory (QSDFT method) to the obtained adsorption isotherms. In the QSDFT method, a cylindrical pore model was used for fitting, and the pore diameter, pore volume, and specific surface area at 70% cumulative volume were calculated. The measurement results are shown in Table 1 and Figure 4.

[0048] <d50> Using a porous carbon material, the volume-based particle size distribution was measured with a laser diffraction particle size distribution analyzer (MASTERSIZER 3000 manufactured by Malvern). The measurement sample was prepared as follows. 2 mL of a dispersant (ADEKA Pluronic (registered trademark) L-44; manufactured by ADEKA) was diluted with 170 mL of an aqueous solvent and dispersed with a touch mixer to obtain a diluted dispersant. An appropriate amount of the porous carbon material, 2.5 mL of water, and 2.5 mL of the diluted dispersant were put into a test tube, dispersed with a touch mixer for several seconds, and then dispersed by ultrasonic treatment for 120 seconds to obtain a measurement sample so that the laser intensity of the measuring device was within an appropriate range. The volume average particle size was calculated as the 50% particle size D50 at which the volume integration value from the small particle size side in the volume-based particle size distribution was 50%. The measurement results are shown in Table 1.

[0049] <<Cycle characteristics>> <Fabrication of air battery positive electrode> 90 mg of the porous carbon material for air batteries in each example and comparative example was mixed with 120 μL of water and 5 μL of polytetrafluoroethylene (60% dispersion in H2O) in an agate mortar. 240 μL of isopropanol was added and mixed to obtain a slurry. The obtained slurry was applied to the microporous surface of Sigracet 39BB carbon paper (thickness 315 μm). The electrode was dried in an oven at 100 °C, roll-pressed at room temperature, and cut into a disk shape with a diameter of 11 mm to fabricate an air battery positive electrode.

[0050] <Assembly and electrochemical measurement of Zn air battery> 16 mL of air (-0.13 mm -2 corresponding) was used in a custom-made two-electrode cell (equivalent to -0.13 mmol of O2 in room temperature air). The cell was assembled and tested in room temperature air.

[0051] To prevent evaporation of the electrolyte, the valve was closed during the test. A zinc foil disc (d=13mm) was used as the negative electrode, a glass fiber disc (d=21mm) as the separator, and 120 μL of 1 M ZnSO4 was used as the electrolyte. Before the cycling evaluation, the cell electrodes were left to stand for 5 hours to allow them to immerse. The cell was discharged, and discharge and charge cycles of 1.0 mAh cm were performed using BioLogic VMP3 in galvanostatic mode. -2 The test was performed at a current density of 1 mAhcm² during charging. -2 (Positive electrode disk area (0.95 cm²) 2 When a current of (calculated at approximately ) flows or the voltage reaches 2V, charging ends and the system switches to discharging, with a discharge rate of 1mAhcm. -2 The charge and discharge cycles were performed under the condition that discharge would end and charging would switch when a certain current flowed or the voltage became 0V. The number of cycles at which the discharge termination voltage fell to 50% or less of the initial cycle value was used as the evaluation index for the cycle characteristics. The evaluation results are shown in Figures 5 and 6.

[0052] [Table 1]

[0053] The porous carbon materials for air battery cathodes in Examples 1-4 showed a higher ratio of carbon dioxide gas desorption between 700°C and 1000°C and a lower ratio of carbon dioxide gas desorption below 700°C compared to the porous carbon material for air battery cathodes in Comparative Example 1. From this, it can be inferred that the porous carbon materials for air battery cathodes prepared in Examples 1-4 have a low proportion of surface functional groups such as lactones, carboxyl groups, and acid anhydrides, and a high proportion of functional groups such as ethers, quinones, and carbonyl groups. The high ratio of carbon monoxide gas desorption above 700°C supports the above inference.

[0054] As shown in Examples 1-4, zinc-air batteries fabricated using the porous carbon material for the positive electrode of air batteries according to this disclosure exhibited a high number of cycles and excellent cycle characteristics. On the other hand, the zinc-air battery shown in Comparative Example 1 had only 3 cycles, and its performance as a secondary battery was significantly inferior. [Industrial applicability]

[0055] The positive electrode material for air batteries disclosed herein exhibits excellent cycle characteristics and can be used in applications such as small electrical devices like hearing aids and aerospace applications such as drones.

[0056] This disclosure includes the following forms: (Section 1) A porous carbon material for the cathode of an air battery, wherein, in mass spectrometry of the generated gas, the ratio of carbon dioxide desorbed in the temperature range of 700°C to 1000°C to the amount of carbon dioxide desorbed in the temperature range of 30°C to 1000°C is 70% or more, at a heating rate of 10°C / min. (Section 2) A porous carbon material for the cathode of an air battery as described in item 1, wherein the volume-based cumulative 70% pore diameter is 1 nm or more and 5 nm or less. (Section 3) Specific surface area of ​​500 m 2 A porous carbon material for the positive electrode of an air battery as described in item 1 or 2, which is 1 / g or more. (Section 4) A porous carbon material for a positive electrode of an air battery according to any one of items 1 to 3, wherein the 50% particle size D50 in the cumulative particle size distribution is 0.1 μm or more and 30 μm or less. (Section 5) A porous carbon material for the positive electrode of an air battery, as described in any of items 1 to 4, wherein the aspect ratio is between 1 and 5. (Section 6) A positive electrode for an air battery comprising a porous permeable material as an electrode and a porous carbon material for an air battery positive electrode as described in any one of items 1 to 5. (Section 7) A zinc-air battery comprising the positive electrode of an air battery described in item 6, an electrolyte, and a negative electrode containing zinc. (Section 8) The zinc-air battery according to item 7, wherein the electrolyte is an electrolyte solution with a pH of 4 or higher and 7 or lower.

Claims

1. A porous carbon material for the cathode of an air battery, wherein, in mass spectrometry of the generated gas, the ratio of carbon dioxide desorbed in the temperature range of 700°C to 1000°C to the amount of carbon dioxide desorbed in the temperature range of 30°C to 1000°C is 70% or more, at a heating rate of 10°C / min.

2. A porous carbon material for a positive electrode of an air battery according to claim 1, wherein the volume-based cumulative 70% pore diameter is 1 nm or more and 5 nm or less.

3. Specific surface area of ​​500 m ２ A porous carbon material for the positive electrode of an air battery according to claim 1, wherein the material is 1g or more.

4. The porous carbon material for the positive electrode of an air battery according to claim 1, wherein the 50% particle size D50 in the cumulative particle size distribution is 0.1 μm or more and 30 μm or less.

5. A porous carbon material for a positive electrode of an air battery according to claim 1, wherein the aspect ratio is 1 or more and 5 or less.

6. A positive electrode for an air battery comprising a porous permeable material as an electrode and a porous carbon material for an air battery positive electrode according to any one of claims 1 to 5.

7. A zinc-air battery comprising the positive electrode of an air battery according to claim 6, an electrolyte, and a negative electrode containing zinc.

8. The zinc-air battery according to claim 7, wherein the electrolyte is an electrolyte solution with a pH of 4 or higher and 7 or lower.

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