JP2023079085A - Composition for producing porous carbon film, sheet for producing porous carbon film, method for producing porous carbon film for positive electrode of air battery, and method for producing air battery using porous carbon film obtained by the method for positive electrode - Google Patents

Abstract

To provide a composition capable of producing a porous carbon film with high capacity when used as a positive electrode of an air battery without using oxygen for carbonization treatment, a sheet formed from the composition, a method for producing a porous carbon film using the composition, and a method for producing an air battery using the porous carbon film as a positive electrode.SOLUTION: A mixture containing porous carbon particles, a polymer material for binders having a mass loss rate of less than 90% when heated to 800°C in an inert atmosphere, a pyrolytic organic compound having a mass loss rate of 90% or more when heated to 800°C in an inert atmosphere, and at least one optional component selected from carbon fibers and carbon nanotubes is formed into a film, and the film is fired in an inert atmosphere to obtain a carbon film with controlled pore distribution.SELECTED DRAWING: Figure 1

Description

The present invention provides a composition for producing a porous carbon film, a sheet for producing a porous carbon film, a method for producing a porous carbon film for an air battery positive electrode, and a method for producing an air battery using the porous carbon film obtained by the method as a positive electrode. Regarding.

Batteries are attracting attention as a driving force that supports the smart society, and the demand for them is increasing rapidly. Among various types of batteries, air batteries are attracting a great deal of attention because of their structure suitable for small size, light weight and large capacity.
An air battery is a battery that uses oxygen in the air as a positive electrode active material and a metal as a negative electrode active material, is also called a metal-air battery, and is positioned as a type of fuel cell. One example is a lithium-air battery using a metal or compound capable of intercalating and deintercalating lithium ions as a negative electrode active material. Reaction at each electrode in a lithium-air battery is represented by the following equation.

In air batteries, the positive electrode active material is oxygen in the air, which can be taken in from the outside of the battery. This structure is suitable for In addition, since the positive electrode active material can be taken in from the outside, the amount of the positive electrode active material that can be used is not limited.

However, current air batteries have not fully exploited their potential for small size, light weight, and large capacity. One of the reasons for this is that the discharge capacity of the positive electrode is not yet sufficiently high.
In an air battery, oxygen in the air is the positive electrode active material, and the reaction at the positive electrode during discharge is such that metal ions moving from the negative electrode combine with oxygen and electrons to form oxides. For this reason, in order to increase the capacity of the air battery, the metal ions moving from the negative electrode should be able to move easily to all corners of the positive electrode (high ion transport efficiency), and the air containing oxygen that reacts with the metal ions should be It is easy to permeate and diffuse into the inner reaction field (high oxygen permeability), there are many reaction fields in the positive electrode where metal ions and oxygen react to form oxides, and the pore volume for storing this oxide is large. need to be big. In addition, in order to manufacture a compact and lightweight air battery at low cost, it is desired that the positive electrode be self-supporting as a structure.

In response to such problems, in Patent Document 1, porous carbon used for the positive electrode is provided with pores including mesopores and micropores, and the carbonaceous walls constituting the outer shell of the mesopores have a three-dimensional network structure. wherein the micropores are formed in the carbonaceous wall, the mesopores are open pores, the pore portions are continuous to form connected pores, and the pores are fine The half-value width of the pore size distribution is 2 nm or less, the half-value width of the connected pore size distribution of the connected pores is 50 nm or more, and the pore volume occupied by the pores having a pore size of 1 nm or more is 1.0 ml/g or more, or 4.0 ml/g. g or less has been proposed (claim 1). Here, the pore diameter means a value measured by a nitrogen adsorption method (paragraph [0021]), and a carbon material having many pores in the mesopore region with a pore diameter of 1 nm or more has a high capacity as a positive electrode. applying (paragraph [0023]), and applying a paint in which a composition containing the porous carbon and a binder that fixes the porous carbon is dispersed in a solvent on the positive electrode current collector, or It is described that the positive electrode layer can be formed by molding the composition by compression pressing (paragraphs [0033] and [0035]).

In Patent Document 2, in a positive electrode layer containing a conductive porous body containing carbon, the first pore volume occupied by pores having a pore diameter of 1 nm or more and 200 nm or less has a pore diameter of more than 200 nm and 10,000 nm or less. A lithium-air battery is proposed in which the pores are larger than the second pore volume (claim 1). Since the lithium oxide produced during discharge is produced in the pores of the positive electrode layer, the larger the number of first pores having a smaller pore size, the more small particles are produced. Since the decomposition reaction of lithium oxide, which sometimes occurs, tends to occur not only on the surface but also on the entire surface, it is possible to improve charge-discharge cycle characteristics (paragraph [0035]), ensuring high capacity and improving charge-discharge cycle characteristics. Then, it is described that the preferable range of the first pore volume is 0.1 to 2.4 cm ³ /g (paragraph [0037]). Further, in Patent Document 2, as a method for manufacturing the positive electrode layer, a paint in which a composition containing a conductive porous material, a binder, etc. is dispersed in a solvent is applied on the positive electrode current collector by a doctor blade method or the like. method, or a method of molding the above composition by compression pressing (paragraph [0042]).

Patent Document 3 discloses a porous carbon structure (claims 1 to 11) having specific pore structures and physical properties, and the porous carbon structure is composed of porous carbon particles and a polymer material as raw materials and contains more than 0.03% A manufacturing method (claims 13 to 15) in which carbonization is performed in an oxidizing gas atmosphere having an oxygen concentration in the range of less than 5%, and a battery including a positive electrode structure having the porous carbon structure (claim 22). is suggesting.

Japanese Patent No. 5852548 Japanese Unexamined Patent Application Publication No. 2018-133168 WO2020/235638

As described above, various attempts have been made on the positive electrode to increase the capacity of the air battery, and certain results have been obtained.
However, in the positive electrode using porous carbon in which the pore volume occupied by pores with a pore size of 1 nm or more described in Patent Document 1 is 1.0 ml / g or more and 4.0 ml / g or less, a binder is used. Since the pores of the porous carbon are partly filled with the binder and the pore volume of the positive electrode becomes smaller than the pore volume of the porous carbon, there is a limit to increasing the capacity.
In Patent Document 2, in order to improve the charge-discharge cycle characteristics while ensuring a high capacity of the air battery, the first pore volume with a pore diameter of 1 nm or more and 200 nm or less is the second pore volume of more than 200 nm and 10000 nm or less It is described that a conductive porous body containing carbon larger than its volume is used as a positive electrode layer. However, the preferred range of the first pore volume is 0.1 to 2.4 cm ³ /g. A layer and method of making the same are desired.
The present inventors have found that by performing a carbonization treatment in an oxidizing gas atmosphere having an oxygen concentration in the range of more than 0.03% and less than 5%, a porous material having a high pore volume suitable for the positive electrode of an air battery can be obtained. It was previously proposed to manufacture a carbon structure (Patent Document 3). However, if oxygen with high oxidative combustion power is used for the treatment, the porous film mainly composed of carbon particles may disappear due to oxidative combustion depending on the treatment conditions. It was necessary to control and manufacture.

The present invention provides a composition capable of producing a porous carbon film that can obtain a high capacity when used as a positive electrode of an air battery without using oxygen for carbonization, a sheet formed of the composition, and the composition An object of the present invention is to provide a method for producing a porous carbon membrane using a material and a method for producing an air battery using the porous carbon membrane as a positive electrode.

The present inventor conducted various studies to solve the above problems, and found that a composition for producing a porous carbon film, together with porous carbon particles and a polymer material for a binder, was subjected to infusibilization treatment or carbonization. The inventors have found that a porous carbon film with a large pore volume can be obtained by incorporating a thermally decomposable organic compound that decomposes during treatment, and have completed the present invention.

That is, one aspect of the present invention for solving the above problems is porous carbon particles, a polymer material for a binder having a mass reduction rate of less than 90% when heated to 800 ° C. in an inert atmosphere, and an inert atmosphere A composition for producing a porous carbon film containing at least one selected from a thermally decomposable organic compound having a mass reduction rate of 90% or more when heated to 800° C. in a medium, and optionally carbon fibers and carbon nanotubes. It is a thing.

Another aspect of the present invention for solving the above problems is a porous carbon membrane-producing sheet formed from the porous carbon membrane-producing composition.

Another aspect of the present invention for solving the above problems is a method for producing a porous carbon film for an air battery positive electrode, comprising preparing a mixture slurry containing the composition for producing a porous carbon film. molding the mixture slurry; immersing the molded body obtained by the molding in a solvent in which the polymer material for a binder has a low solubility; and drying the sample obtained by the immersion. and carbonizing the dried sample in an inert gas atmosphere.

Furthermore, another aspect of the present invention for solving the above problems is a method for manufacturing an air battery, comprising manufacturing a porous carbon film by the method for manufacturing a porous carbon film, and forming a positive electrode from the porous carbon film. A method for manufacturing an air battery, comprising: forming an air battery, preparing a negative electrode and a separator, laminating the positive electrode and the negative electrode with the separator interposed therebetween, and filling the separator with an electrolytic solution.

According to the present invention, a porous carbon membrane for an air battery positive electrode having a large pore volume can be obtained, so that high oxygen permeability and high ion transport efficiency can be obtained, and many reaction fields and reactant storage spaces can be obtained. Therefore, it is possible to provide an air battery that is compact, lightweight, and suitable for increasing the capacity.

FIG. 1 is a flow chart diagram of a method for producing a porous carbon membrane according to one aspect of the present invention. A cross-sectional schematic diagram showing the structure of a coin cell, which is an example of an air battery with a porous carbon membrane. Schematic cross-sectional view showing the structure of a laminated air battery, which is another example of an air battery with a porous carbon membrane.

Hereinafter, with reference to the drawings, the configuration and effects of the present invention will be described along with technical ideas. However, the mechanism of action is presumed, and whether it is correct or not does not limit the present invention. In addition, among the constituent elements in the following embodiments, those constituent elements that are not described in the claims representing the highest concept will be described as optional constituent elements. It should be noted that the description of a numerical range (a description in which two numerical values are connected by "-") is meant to include numerical values described as lower and upper limits.

[Composition for producing porous carbon membrane]
The composition for producing a porous carbon film according to one aspect of the present invention (hereinafter sometimes simply referred to as the "composition according to the first aspect") consists of porous carbon particles heated to 800°C in an inert atmosphere. A polymer material for a binder having a weight loss rate of less than 90% when heated, a thermally decomposable organic compound having a weight loss rate of 90% or more when heated to 800°C in an inert atmosphere, and optional components It contains at least one selected from carbon fibers and carbon nanotubes. Hereinafter, each component and optional components other than these will be described in detail.

(Porous carbon particles)
A porous carbon particle is a particle containing carbon as a main component and has a large number of fine pores on its surface. Examples of porous carbon particles include carbon black such as Ketjenblack (registered trademark), carbon particles formed by a template method, and the like.

(Polymer material for binder)
The polymeric binder material functions as a binder that binds the porous carbon particles together. In addition, a carbonized product is produced by a carbonization treatment in the method for producing a porous carbon film to be described later, and in the porous carbon film obtained through the treatment, the porous carbon particles are bonded to each other to exhibit the function of maintaining the shape of the film. do. In order to exhibit the function of retaining the shape of the porous carbon film, a binder polymer having a mass reduction rate of less than 90% when heated to 800° C. in an inert atmosphere is used. The mass reduction rate is preferably 85% or less, more preferably 80% or less, from the viewpoint of obtaining a self-supporting and high-strength porous carbon film. Although the lower limit of the mass reduction rate is not particularly limited, it is usually about 70% in industrially used binder polymeric materials. Examples of binder polymeric materials include polyacrylonitrile (PAN), polyvinylidene fluoride, polysulfone, and solvent-soluble polyimide.

(thermally decomposable organic compound)
The thermally decomposable organic compound adheres to the surface of the porous carbon particles, and is thermally decomposed by the infusibilization treatment or carbonization treatment in the method for producing a porous carbon film described later, thereby reducing the surface of the porous carbon particles to the voids between the particles. Alternatively, it exhibits the function of exposing on the surface of the porous carbon membrane. As a result, the pore volume of the porous carbon membrane increases by the amount of pores present on the exposed surface. In order to exhibit the function of exposing the surfaces of the porous carbon particles, a thermally decomposable organic compound having a mass reduction rate of 90% or more when heated to 800° C. in an inert atmosphere is used. The mass reduction rate is preferably 95% or more, more preferably 98% or more, from the viewpoint of exposing more of the surface of the porous carbon particles. Since the mass reduction rate is preferably as high as possible, it may be 100%, that is, the thermally decomposable organic compound may be completely decomposed when heated to 800° C. in an inert atmosphere.

In addition, the thermally decomposable organic compound preferably has a temperature of 100° C. or higher and 700° C. or lower at which the mass reduction rate becomes 90%. When the temperature is 100° C. or higher, deformation or the like due to decomposition of the thermally decomposable organic compound can be suppressed in each treatment such as drying performed before the infusibilization treatment or carbonization treatment. From this point of view, the temperature is more preferably 150° C. or higher. Further, when the temperature is 200° C. or higher, the remaining amount of the binder polymer softened by the infusibility treatment or carbonization treatment increases, and the binder polymer flows to coat the surface of the porous carbon particles. It is further preferable because it is possible to effectively suppress the clogging of pores caused by the From this point of view, it is particularly preferable that the temperature is 250° C. or higher. On the other hand, when the temperature is 700° C. or less, the thermally decomposable organic compound is decomposed before the binder polymer is carbonized in the carbonization treatment, and the gas generated by the decomposition causes the airway to open in the binder polymer. The formation increases the voids of the resulting porous carbon film. From this point of view, the temperature is more preferably 650° C. or lower, and even more preferably 600° C. or lower.

Thermal analysis equipment such as thermogravimetric analysis (TGA) and differential thermogravimetric analysis (TG-DTA) equipment is used to determine the mass reduction rate at each temperature in an inert atmosphere for polymer materials for binders and thermally decomposable organic compounds. The temperature is raised to about 800° C. in an atmosphere of an inert gas such as nitrogen or argon, and the measurement is performed.

However, if the thermal analysis equipment described above cannot be used, the value obtained by the following method may be used as the mass reduction rate.
First, the mass at room temperature of a polymer material for binder or a thermally decomposable organic compound to be measured (hereinafter referred to as "material to be measured" in this paragraph) is measured.
Next, using a heating device capable of heat treatment in an inert atmosphere, the material to be measured is heated to a predetermined temperature in an atmosphere of an inert gas such as nitrogen or argon, and maintained at that temperature for about 30 minutes. After holding, the temperature is lowered. The predetermined temperature is set to 800° C. when obtaining the mass reduction rate when the material to be measured is heated to 800° C. On the other hand, in the case of confirming that the temperature at which the mass reduction rate of the material to be measured reaches 90% is equal to or lower than a specific temperature, the predetermined temperature is the specific temperature.
Next, the mass of the material to be measured after cooling is measured.
Then, the value obtained by the following calculation from the mass of the material to be measured at room temperature and the mass after cooling is taken as the mass reduction rate (%) at the predetermined temperature in an inert gas atmosphere. .
(mass at room temperature (g) - mass after cooling (g))/mass at room temperature (g) x 100
Note that the mass reduction rate (%) in this specification has the following relationship with the residual carbon rate (%), which is the percentage of carbon remaining in the material to be measured.
Mass reduction rate (%) = 100 - residual coal rate (%)

The thermally decomposable organic compound can also act as a binder that binds between porous carbon particles or between porous carbon particles and at least one selected from carbon fibers and carbon nanotubes, which are optional components described later. This makes it possible to reduce the amount of the polymer material for the binder and increase the ratio of the porous carbon particles in the resulting porous carbon film.

Examples of thermally decomposable organic compounds include polyethylene oxide (PEO), polyethylene glycol (PEG), polyethylene (PE), polyisobutylene (PIB), styrene butadiene rubber (SBR), polystyrene (PS), polytetrafluoroethylene ( PTFE) and the like. Among them, polyethylene oxide (PEO) is preferred. Polyethylene oxide (PEO) is available with various molecular weights, and although the molecular weight is not particularly limited, it preferably has a viscosity average molecular weight of 10,000 or more and 100,000 or less. When the viscosity-average molecular weight is 10,000 or more, thermal decomposition at low temperatures is sufficiently suppressed. On the other hand, when the viscosity-average molecular weight is 100,000 or less, good dispersibility can be obtained when the mixture slurry is prepared.

The amount of the thermally decomposable organic compound to be added is not particularly limited, but it is preferably 0.001 or more and 10 or less in mass ratio with respect to the porous carbon particles. When the mass ratio is equal to or higher than the lower limit, the amount of pores on the surface of the porous carbon particles exposed by decomposition of the thermally decomposable organic compound in the infusibilization treatment or carbonization treatment, and the amount of pores for the binder formed by the decomposition The amount of airways in carbonized molecular materials tends to be both sufficient. From this point of view, the mass ratio is more preferably 0.005 or more, more preferably 0.01 or more, and particularly preferably 0.02 or more. On the other hand, since the mass ratio is equal to or less than the upper limit, the raw material cost can be reduced, and the amount of gas generated by the decomposition of the thermally decomposable organic compound in the infusibilization treatment or carbonization treatment is suppressed, which is required for exhaust gas treatment. Costs can also be reduced. From these points, the mass ratio is more preferably 5 or less, more preferably 2 or less.

In addition, the amount of the thermally decomposable organic compound to be blended is, from the viewpoint of sufficiently exhibiting the action of the organic compound as a binder, for example, the porous carbon particles and the polymeric material for the binder described above, and the optional components described later. It may be 0.5 parts by mass or more and 90 parts by mass or less with respect to a total of 100 parts by mass of certain carbon fibers and carbon nanotubes. In this case, the content of the thermally decomposable organic compound is preferably 1 part by mass or more and 80 parts by mass or less, more preferably 3 parts by mass or more and 70 parts by mass or less with respect to a total of 100 parts by mass of the above components.

(Carbon nanofibers and carbon nanotubes)
The composition according to the first aspect may optionally contain at least one selected from carbon fibers and carbon nanotubes. By containing at least one selected from carbon fibers and carbon nanotubes, the resulting porous carbon film can have high strength. For example, carbon fibers having a diameter of 0.1 μm or more and 20 μm or less and a length of 1 mm or more and 20 mm or less can be used. Carbon nanotubes having a diameter of 0.5 nm or more and 20 nm or less and a length of 1 μm or more and 20 μm or less can be used, for example.

The blending amounts of the porous carbon particles, the polymer material for the binder, the carbon fibers and the carbon nanotubes described above are, for example, 50% by mass or more and 90% by mass or less of the porous carbon particles and 5% by mass or more and 49% by mass or less of the binder binder. It can be a molecular material, 0% to 15% by weight carbon fiber, and 0% to 10% by weight carbon nanotube. As described above, the amount of the thermally decomposable organic compound is 0.001 or more and 10 or less with respect to the porous carbon particles, or the ratio of the porous carbon particles, the polymer material for the binder, the carbon fiber, and the carbon nanotube. It can be 0.5 parts by mass or more and 90 parts by mass or less with respect to a total of 100 parts by mass.

(solvent)
The composition according to the first aspect may contain a solvent for dispersing the components described above.
As a solvent for dispersing the porous carbon particles and the polymeric binder material, for example, dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), etc. can be used.

[Sheet for producing porous carbon membrane]
A sheet for producing a porous carbon membrane according to another aspect of the present invention (hereinafter sometimes simply referred to as "a sheet according to the second aspect") is formed from the composition for producing a porous carbon membrane according to the first aspect. be done. Forming the composition for producing a porous carbon membrane according to the first aspect into a sheet facilitates mass production of porous carbon membranes having a uniform thickness.

The thickness of the sheet relating to the second side is not particularly limited, but is exemplified from 50 μm to 1 mm. When the sheet thickness is 50 μm or more, the resulting porous carbon membrane has excellent handleability. From this point of view, the sheet thickness is preferably 100 μm or more, more preferably 150 μm or more. On the other hand, since the sheet thickness is 1 mm or less, it is possible to miniaturize the air battery using the resulting porous carbon film as the positive electrode. From this point of view, the sheet thickness is preferably 900 μm or less, more preferably 800 μm or less.

The method for producing the sheet according to the second aspect is not particularly limited, but the mixture slurry containing the composition according to the first aspect is coated by a doctor blade method, a roll coater method, a die coater method, a spin coat method, or a spray coating method. A method of molding by a wet film-forming method such as the above is exemplified.

[Manufacturing method of porous carbon membrane for positive electrode of air battery]
A method for producing a porous carbon film for an air battery positive electrode according to another aspect of the present invention (hereinafter sometimes simply referred to as "a production method according to the third aspect") comprises, as shown in FIG. Preparing a mixture slurry containing the composition for producing a porous carbon film according to one aspect (S1), molding the mixture slurry (S2), forming a molded body obtained by the molding, immersing in a solvent in which the polymer material for a binder has a low solubility (S3); drying the sample obtained by the immersion (S4); (S6). The manufacturing method according to the third aspect may further include making the sample obtained in S4 infusible in air (S5) before S6.
Each step will be described in detail below.

(S1: mixture slurry preparation)
The mixture slurry contains the porous carbon membrane-producing composition according to the first aspect. The method of mixing each component of the composition to prepare a slurry is not particularly limited, and a mixer having an impeller or blades, a mixer in which the container itself revolves, a ball mill mixer, or the like can be employed.

(S2: molding)
The method for molding the mixture slurry is not limited as long as a molded body having a predetermined size can be obtained. A wet film-forming method can be employed.
The shape of the molded body after molding may be any shape as long as it meets the purpose. In order to miniaturize the air battery, it is preferable to form a sheet having a uniform thickness.

(S3: solvent immersion)
Solvent immersion is performed by a non-solvent induced phase separation method in which the molded body molded in step S2 is immersed in a solvent in which the polymer material for a binder has a low solubility. The non-solvent-induced phase separation method is a method in which a polymer solution is immersed in a poor solvent for the polymer to phase-separate and precipitate the polymer. By the non-solvent-induced phase separation method, the polymer material for the binder phase-separates and deposits in a state where the porous carbon particles are bonded to each other, and a porous carbon film with a framework of porous carbon particles and optionally carbon fibers and carbon nanotubes is produced. can do. At this time, most of the solvent of the mixture slurry is compatible with the poor solvent.
Examples of the solvent in which the binder polymeric material has low solubility include water, alcohol such as ethyl alcohol, methyl alcohol, isopropyl alcohol, and butyl alcohol, and mixed solvents thereof.

(S4: drying)
The drying step is performed to evaporate and remove the solvent used in preparing the mixture slurry and the poor solvent used in step S3. Examples of the drying method include a method of placing in a dry air environment, a reduced pressure drying method, a vacuum drying method, and the like. In this drying step, in order to increase the drying speed, the temperature may be increased to a temperature exceeding the boiling points of the solvent and the poor solvent.

(S5: infusibilization)
The infusibilizing treatment is performed for the purpose of preventing the polymer material for binder from being melted and separated in the carbonization treatment in the next step S6 to impair the bonding between the carbon particles and to prevent the shape of the molded body from collapsing. The infusibilizing treatment may be omitted depending on the type of binder polymeric material used. Polymer materials for binders that require infusibility treatment are polymers with a structure that melts and liquefies when heated as they are. It is necessary to change to a structure that does not Polyvinyl chloride (PVC), polyvinyl acetate, and the like are examples of polymeric materials for binders that require infusibilizing treatment. On the other hand, polymer materials for binders, which do not require infusibility treatment, can be softened by intermolecular cross-linking due to their own functional groups when heated without the introduction of oxygen, but they do not become liquid. carbonization progresses in Examples of polymeric materials for binders that do not require infusibilization include phenol formaldehyde resin (PF), polyvinylidene chloride (PVDC), polyphenylene (PP) and cellulose. Among polymer materials for binders, polyacrylonitrile (PAN) is a polymer that is softened by heating but does not become liquid and carbonizes. In order to promote the cross-linking reaction, infusibilization treatment is carried out at 200 to 400° C. in the air to convert the fibers into fibers that do not melt even at high temperatures, and then carbonization is carried out. In the examples described later, PAN is used because of the ease of preparation of mixture slurry and the ease of non-solvent-induced phase separation, and the infusibilization is carried out according to the industrial manufacturing method of carbon fibers.

The atmosphere for the infusibilization treatment is preferably air circulation or air circulation in terms of cost, but it is also possible to use a mixture of oxygen with an inert gas such as nitrogen or argon. The flow rate when the air is circulated is preferably 0.1 mL/min or more, more preferably 1 mL/min or more, from the viewpoint of sufficiently advancing the infusibilization. From the viewpoint of reducing manufacturing costs, it is preferably 100 m ³ /min or less, more preferably 50 m ³ /min or less, and even more preferably 10 m ³ /min or less.

The temperature at which the infusibilization treatment is performed is preferably 250° C. or higher, more preferably 260° C. or higher, and even more preferably 270° C. or higher, in order to sufficiently progress the infusibilization. When the infusibilization treatment temperature is at least the above lower limit, sufficient infusibilization prevents the polymeric binder material from melting and separating from the carbon particles in the subsequent carbonization step, thereby increasing the strength of the porous carbon film. can be maintained. The temperature of the infusibilization treatment is preferably 350° C. or lower, more preferably 340° C. or lower, and even more preferably 330° C. or lower. When the temperature of the infusibilization treatment is equal to or lower than the above upper limit, a moderate cross-linking reaction can occur, and the binder polymeric material is oxidized and burned through the cross-linking reaction due to the oxidation reaction with oxygen present at 21% in the air. , and the situation in which the porous membrane is damaged is less likely to occur.
The lower limit of the retention time at the predetermined treatment temperature for infusibilization is preferably 1 min or longer, more preferably 10 min or longer, and even more preferably 20 min or longer, from the viewpoint of sufficiently advancing the infusibilizing. The upper limit of the holding time is preferably 100 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less, from the viewpoint of reducing manufacturing costs.
The upper limit of the temperature increase rate in the infusibilization treatment is preferably 100° C./min or less, more preferably 50° C./min or less, in order to sufficiently progress the infusibilization of the polymer material for the binder. It is preferably 30° C./min or less, more preferably 30° C./min or less. Although the lower limit of the heating rate is not particularly limited, it is preferably 0.01° C./min or more from the viewpoint of shortening the heating time and finishing the infusibilization treatment in a short time.

An oven furnace, a tubular furnace, a box furnace, an infrared furnace and the like are exemplified as apparatuses used for the infusibilization treatment.

(S6: Carbonization)
The purpose of the carbonization treatment is to convert the polymeric binder material into carbon. By carbonizing the polymer material for the binder, the electrical conductivity is improved, and furthermore, the adhesiveness to porous carbon particles, carbon fibers, and carbon nanotubes is increased, and the strength of the porous carbon film is increased.
Carbonization treatment can be performed using, for example, an oven furnace, a tubular furnace, a box furnace, an infrared furnace, a baking furnace, or the like. The temperature of the carbonization treatment is preferably 600° C. or higher, more preferably 700° C. or higher, and even more preferably 800° C. or higher, from the viewpoint of sufficiently carbonizing the polymeric binder material. On the other hand, the temperature of the carbonation treatment is preferably 3,000° C. or lower, more preferably 2,000° C. or lower, and even more preferably 1,500° C. or lower, from the viewpoint of using a general-purpose treatment apparatus and reducing the treatment cost.
The rate of temperature increase in the carbonization treatment is preferably 100° C./min or less, more preferably 50° C./min or less, and even more preferably 30° C./min or less, from the viewpoint of sufficiently carbonizing the binder polymer material. . Although the lower limit of the heating rate is not specified, it is preferably 0.01° C./min or more from the viewpoint of shortening the processing time and reducing the processing cost.
The atmosphere for the carbonization treatment is preferably an inert atmosphere such as argon (Ar) gas or nitrogen (N ₂ ) gas. The inert gas may be in a state of being sealed in the furnace, or may be processed while flowing. When the inert gas is flowed, the flow rate is not particularly limited, but from the viewpoint of suppressing the influence of outside air contamination due to the structure of the furnace, it is preferably 0.1 mL / min or more, and more preferably 1 mL / min or more. 10 mL/min or more is more preferable. On the other hand, from the viewpoint of reducing treatment costs, the flow rate of the inert gas is preferably 100 m ³ /min or less, more preferably 50 m ³ /min or less, and even more preferably 10 m ³ /min or less.

In the manufacturing method according to the third aspect, the thermally decomposable organic compound is decomposed during the infusibilization treatment (S5) or the carbonization treatment (S6). As a result, the surfaces of the porous carbon particles that have been in contact with the thermally decomposable organic compound are exposed in the voids between the particles or on the surface of the porous carbon film, and the pores existing on the exposed particle surfaces The pore volume of the membrane increases. In addition, when the gas generated by the decomposition of the thermally decomposable organic compound is released to the outside, air passages are formed in the softened polymer material for binder, so that pores are also formed in the carbonized material. It is formed. As a result, the pores of the entire porous carbon membrane increase. Decomposition of the thermally decomposable organic compound occurs simply by raising the temperature to the decomposition temperature of the organic compound or higher, and strict control of atmosphere and temperature is not required. Therefore, the manufacturing method according to the third aspect has the advantage of not requiring equipment for precisely controlling the oxygen concentration in the atmosphere and the processing temperature. Moreover, the manufactured porous carbon structure has sufficient mechanical strength for practical use so that it can stand on its own.

[Physical properties of porous carbon membrane]
The porous carbon membrane obtained by the manufacturing method according to the third aspect preferably has a large number of pores and satisfies all of the following conditions (a) to (c).
(a) Pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less is 3.6 cm ³ /g or more and 7.0 cm ³ /g or less (b) Pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less is 2 .8 cm ³ /g or more and 7.0 cm ³ /g or less (c) The pore specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less is 1000 m ² /g or more and 2000 m ² /g or less, from condition (a) to ( c) will be described in detail.

Condition (a) expresses that the pore volume in the pore diameter range of 1 nm or more and 1000 nm or less is considerably large. This pore volume is obtained from the adsorption isotherm obtained from the nitrogen adsorption measurement using the BJH (Barrett-Joyner-Hallenda) method.
When a porous carbon film that satisfies the condition (a) is used as the positive electrode of an air battery, it can store a larger amount of metal oxide (lithium peroxide in a lithium-air battery) generated during discharge, resulting in high discharge capacity characteristics. Batteries can be provided. In addition, since the total amount of oxygen passing through pores within this range of pore diameters increases in proportion to the pore volume, permeation and diffusion of air within the porous carbon membrane is facilitated. Therefore, the oxygen introduced into the positive electrode from the outside of the battery can spread to every corner of the carbon particles forming the carbon skeleton at high speed. Furthermore, since the pores in this pore diameter range serve as a migration path for metal ions (Li ions in lithium-air batteries), the large volume allows the metal ions to move smoothly, allowing air and oxygen to permeate. Combined with high diffusivity, it is possible to provide an air battery with excellent high-speed discharge characteristics, that is, high-load characteristics.
Therefore, from the viewpoint of obtaining an air battery having a larger discharge capacity and excellent high-load characteristics, the pore volume is preferably 3.6 cm ³ /g or more, more preferably 3.7 cm ³ /g or more. is more preferable, and 3.8 cm ³ /g or more is even more preferable. From the viewpoint of maintaining the strength of the porous carbon membrane, the pore volume is preferably 7.0 cm ³ /g or less, more preferably 6.0 cm ³ /g or less.

Condition (b) indicates that the pore volume occupied by relatively small pores having a diameter of 1 nm or more and 200 nm or less is large and the number of smaller pores is large. This pore volume is also obtained using the BJH (Barrett-Joyner-Hallenda) method from the adsorption isotherm obtained from the nitrogen adsorption measurement.
When a porous carbon film that satisfies the condition (b) is used for the positive electrode of an air battery, it becomes possible to store a large amount of oxide produced by the reaction of metal ions, oxygen, and electrons during discharge, resulting in a battery exhibiting high discharge capacity. can provide.
Therefore, from the viewpoint of obtaining a large discharge capacity, the pore volume in the above pore diameter range is preferably 2.8 cm ³ /g or more, more preferably 2.9 cm ³ /g or more. It is more preferably 0 cm ³ /g or more.
In addition, from the viewpoint of securing a volume of pores having a diameter of more than 200 nm with higher oxygen permeation and diffusibility and excellent discharge characteristics at high load, that is, a large discharge capacity at high speed, the above pore diameter The pore volume in the range is preferably 7.0 cm ³ /g or less, more preferably 6.0 cm ³ /g or less, and even more preferably 5.0 cm ³ /g or less.

Condition (c) indicates that the specific surface area of pores in a relatively small range of 1 m or more and 200 nm or less in diameter is large. By satisfying this condition, when metal ions and oxygen react in a discharge reaction, there are many reaction fields where oxygen receives electrons supplied from the positive electrode, and more electrons can be transferred. In this condition (c), when the above condition (b) “pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less is 2.8 cm ³ /g or more and 7.0 cm ³ /g or less” is satisfied, discharge is possible. It is possible to provide a battery exhibiting a high discharge capacity coupled with the ability to store a large amount of the metal oxide produced. Similarly, in the charging reaction, the metal oxide provides a large number of reaction sites for transferring electrons to the positive electrode to become metal ions and oxygen, enabling transfer of more electrons.
The above specific surface area is preferably 1000 m ² /g or more in order to secure a reaction field for transferring electrons. In order to allow metal ions and oxygen to enter smoothly, the specific surface area is preferably 1700 m ² /g or less, more preferably 1400 m ² /g or less.

The porous carbon membrane obtained by the manufacturing method according to the third aspect may satisfy the following condition (d) in addition to the above conditions (a) to (c).
(d) The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less is 900 m ² /g or more and 1700 m ² /g or less This condition indicates that the specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less is large. there is In the positive electrode reaction during discharge of an air battery, metal ions that have migrated from the negative electrode and oxygen that has migrated and diffused from the outside air side of the positive electrode receive electrons from the inner surface of the pores inside the positive electrode and undergo metal oxidation. It is a reaction that produces a substance. Therefore, the large specific surface area increases the number of places where this reaction occurs when it is used as the positive electrode of an air battery, and as a result, discharge is performed more smoothly, resulting in a battery with excellent high-load characteristics.
The lower limit of the specific surface area is preferably 900 m ² /g or more, more preferably 1000 m ² /g or more, from the viewpoint of securing a reaction field. The upper limit of the specific surface area is preferably 1700 m ² /g or less, more preferably 1400 m ² /g or less, from the viewpoint of maintaining the strength of the porous carbon membrane.

The porous carbon membrane obtained by the manufacturing method according to the third aspect preferably satisfies the following condition (e) in addition to the conditions (a) to (c) or the conditions (a) to (d). .
(e) Apparent density of 0.10 g/cm ³ or more and 0.20 cm ³ /g or less If the apparent density of the porous carbon film is within this range, the porous carbon film has pores necessary for permeation and diffusion of oxygen. and sufficient strength. Therefore, a self-supporting porous carbon film can be obtained, and the positive electrode of an air battery can be provided without using a metal mesh or the like. This makes it possible to reduce the weight and size of the battery, improve productivity, and reduce the cost. The apparent density can be determined by dividing the mass of the porous carbon membrane by its volume.
When the apparent density is not too low, the strength of the porous carbon film increases, and it can be used as a positive electrode without adhering to a current collector such as a metal mesh. From this point, the lower limit of the apparent density is preferably 0.10 g/cm ³ or more, more preferably 0.11 g/cm ³ or more, and further preferably 0.12 g/cm ³ or more. preferable. As a result, a porous carbon film having pores and high strength can be obtained.
Also, when the apparent density is low, the amount of pores present in the porous carbon film increases, and an air battery with a large capacity and excellent load characteristics can be obtained. From this point, the upper limit of the apparent density is preferably 0.20 g/cm ³ or less, more preferably 0.19 g/cm ³ or less, and further preferably 0.18 g/cm ³ or less. preferable.

The porous carbon film obtained by the manufacturing method according to the third aspect has the following conditions in addition to the above conditions (a) to (c), (a) to (d), or the above conditions (a) to (e) (f) is preferably satisfied.
(f) Porosity is 90% or more and 99% or less The porosity of the porous carbon membrane is calculated from the apparent density and the true density by (1-apparent density of the porous carbon membrane / true density of the constituent material of the porous carbon membrane). can ask. A porosity equal to or higher than the above lower limit means having a sufficiently large porosity. When such a porous carbon film is used for the positive electrode of an air battery, it is possible to store a large amount of the metal oxide generated by discharge, and the intrusion of air and oxygen from the outside of the battery into the positive electrode occurs smoothly with little resistance. , it is possible to provide a battery that has a high discharge capacity and can be discharged at a high speed.
Further, when the porosity is equal to or less than the above upper limit, the rigidity and strength of the porous carbon membrane can be secured and the membrane can stand on its own. More preferably, the upper limit of the porosity is 98% or less.

[Method for manufacturing air battery]
A method for manufacturing an air battery according to another aspect of the present invention (hereinafter sometimes simply referred to as a “method for manufacturing according to the fourth aspect”) comprises manufacturing a porous carbon membrane by the method described above, A method for manufacturing an air battery, comprising forming a positive electrode from a carbon film, preparing a negative electrode and a separator, stacking the positive electrode and the negative electrode with the separator interposed therebetween, and filling the separator with an electrolytic solution. . Hereinafter, the manufacturing method according to the fourth aspect will be described with reference to the drawings, taking the case of manufacturing a coin cell and a laminated battery as an example.

(coin cell)
FIG. 2 is a schematic diagram showing an example of a coin cell.
The coin cell 600 is composed of a laminated structure in which a negative electrode structure 610 and a positive electrode structure 620 are laminated with a separator 660 interposed therebetween. This laminated structure is then restrained by a coin cell type restraint 630 . An insulating O-ring (not shown) is arranged between the coin cell restraint 630 and the metal mesh 680 to ensure insulation between the restraint 630 and the positive electrode structure 620 .

The negative electrode structure 610 includes a current collector 635, a metal layer 640 arranged on the current collector 635, and columnar spacers 650 arranged at both ends thereof. A space 670 is provided between them and is filled with an electrolytic solution.
Metal layer 640 preferably contains an alkali metal and/or an alkaline earth metal. Among them, a layer made of lithium metal is preferable.

The positive electrode structure 620 comprises a porous carbon membrane 690 in mechanical and electrical contact with a current collector metal containing mesh (metal mesh) 680 . In this case, the metal mesh 680 serves as a positive electrode base material and also functions as a channel through which air or oxygen passes.
A separator 660 is disposed between the negative electrode structure 610 and the positive electrode structure 620 .

An example of a method for manufacturing the coin cell 600 will be described below.
First, the negative electrode structure 610 is prepared. A disk-shaped metal layer 640 made of lithium or the like, which is concentric with the current collector 635 and has a diameter smaller than that of the current collector 635 , is stacked on the disk-shaped current collector 635 , and a columnar spacer is formed on the current collector 635 . 650 is pressed to obtain the negative electrode structure 610 .

Spacer 650 is an insulator. The material may be metal oxide, metal nitride, metal oxynitride, or the like. For example, _Al2O3 , _{Ta2O5 , TiO2 , ZnO} , ZrO2, _{SiO2 , B2O3} , _{P2O5 ,} GeO2, _Li2O , _Na2O , _{K2O ,} MgO, CaO, SrO, BaO, Si ₃ N ₄ , AlN, AlO _x N _1-x (0<x<1), and the like. Among them, Al ₂ O ₃ and SiO ₂ are preferable because they are easily available and excellent in workability.

The spacer 650 may be resin. Examples of resins include polyolefin-based resins, polyester-based resins, polyimide-based resins, and polyetheretherketone (PEEK)-based resins. Examples of polyolefin-based resins include polyethylene and polypropylene. Polyester-based resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polytributylene terephthalate (PTT). These resins are easily available and excellent in workability, and thus are preferable.

Separator 660 is then pressed onto spacer 650 .
A space 670 is provided between the metal layer 640 , the spacer 650 and the separator 660 .
Separator 660 is a porous insulator that allows the passage of alkali metal ions and/or alkaline earth metal ions. Separator 660 is any inorganic material (including metallic materials) and organic material that does not have reactivity with metal layer 640 and the electrolyte.
The material of the separator 660 may be a resin such as polyethylene, polypropylene, or polyolefin, glass, or the like. Separator 660 may be woven or non-woven.

After that, the separator 660 is filled with an electrolytic solution. At this time, the space 670 is also filled with the electrolytic solution.

As the electrolytic solution, any aqueous or non-aqueous electrolytic solution containing an alkali metal salt and/or an alkaline earth metal salt can be used. When the aqueous electrolyte contains a lithium salt, examples of the lithium salt that can be used include LiOH, LiCl, LiNO ₃ , and Li ₂ SO ₄ , and water or a water-soluble solvent can be used as the solvent. can.

When the non-aqueous electrolytic solution (non-aqueous electrolytic solution) contains a lithium salt, examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiSiF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li( _FSO2 ) _2N , _LiCF3SO3 ( _{LiTfO )} , Li( _CF3SO2 ) _2N (LiTFSI), _{LiC4F9SO3 , LiClO4} , _{LiAlO2 , LiAlCl4} , and LiB(C ₂ O ₄ ) ₂ and the like can be used.

Non-aqueous solvents used in the non-aqueous electrolyte include glymes (monoglyme, diglyme, triglyme, tetraglyme), methylbutyl ether, diethyl ether, ethylbutyl 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, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, polyethylene carbonate, γ-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 and the like.

After that, a positive electrode structure 620 having a metal mesh 680 arranged on a porous carbon film 690 is prepared.
Examples of the metal mesh 680 include copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), titanium (Ti), gold (Au), silver (Ag), platinum (Pt), and palladium. A mesh having at least one metal selected from the group consisting of (Pd) can be used. That is, a metal element selected from this group, an alloy containing a metal selected from this group, and a mesh composed of a compound of a metal selected from this group and carbon (C) or nitrogen (N) can be mentioned. In the case of alloys, iron (Fe) and chromium (Cr) may also be included. The mesh can have a thickness of 0.2 mm and an opening of 1 mm, for example.

After that, the positive electrode structure 620 is attached to the negative electrode structure 610 filled with the electrolytic solution with the separator 660 interposed therebetween, and is restrained by the restraint 630 to obtain the coin cell 600 . Here, the mounting is preferably performed under dry air, for example, under dry air with a dew point temperature of −50° C. or less.
Through the above steps, the coin cell 600 is manufactured.
The coin cell 600 has the porous carbon film 690 and the metal mesh 680 as the positive electrode structure 620, but the air battery of the present invention is not limited to the above, and the positive electrode structure 620 is composed of: It may have only the porous carbon film 690 .

In the manufactured coin cell 600, the positive electrode structure 620 using the porous carbon film 690 has excellent high air or oxygen permeability, can take in a large amount of oxygen, and has high ion transport efficiency. Since it has a wide reaction field, it can be an excellent air battery having a small size and light weight and a large capacity.

(Layered air battery)
FIG. 3 is a schematic diagram showing an example of a stacked air battery.
The laminated air battery 500 has a laminated structure in which a positive electrode structure 510 and a negative electrode structure 100 are laminated with a separator 540 interposed therebetween. The number of laminations may be one or more pairs, with each positive electrode structure 510 and negative electrode structure 100 being one pair as a unit, and there is no particular upper limit to the logarithm.

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.

On the other hand, the positive electrode structure 510 is configured such that a pair of laminated bodies each including a porous carbon film 550 and a gas diffusion layer 560 sandwich a positive electrode current collector 525 . A gas diffusion layer 560 and a porous carbon film 550 are arranged in this order from the positive electrode current collector 525 side.

Gas diffusion layer 560 of cathode structure 510 allows air, oxygen, and other gases to move between the cell exterior and porous carbon membrane 550 through it. The gas diffusion layer also functions as an electron migration path between the porous carbon film 550 and the positive electrode current collector 525 . Since the gas diffusion layer functions as a movement path for the gas, it is necessary to have communication holes with air permeability, and it is also necessary to have electronic conductivity. As the gas diffusion layer, for example, Toray's carbon paper TGP-H, Kureha's Kureka (registered trademark) E704, or the like can be used.

Since the positive electrode current collector 525 has a function of electrical connection with the outside and a function of a flow path for air or oxygen, the present air battery 500 can obtain a larger capacity with a simpler structure. ing.

Examples of the negative electrode current collector 520 and the positive electrode current collector 525 include copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), titanium (Ti), gold (Au), and silver. (Ag), platinum (Pt), and palladium (Pd), as well as alloys thereof and compounds thereof (eg, compounds with carbon and/or nitrogen) can be used. In the case of alloys, iron (Fe) and chromium (Cr) may also be included.

Next, a method for manufacturing the laminated air battery 500 will be described.
The negative electrode structure 100 is composed of a pair of negative electrode metals and a negative electrode current collector 520 sandwiched between them. to fill.
The positive electrode structure 510 is composed of a pair of laminates composed of a porous carbon film 550 and a gas diffusion layer 560 and a positive electrode current collector 525 sandwiched between them. Note that the gas diffusion layer 560 and the porous carbon film 550 are arranged in order from the positive electrode current collector 525 side.
The negative electrode structure 100 and the positive electrode structure 510 are laminated via the separator 540 to fabricate the laminated air battery 500 . Note that the stacked air battery 500 may be housed in a housing (not shown).

In this specification, the manufacturing method according to the fourth aspect has been described in detail with reference to FIGS. can be applied to

EXAMPLES The present embodiment will be described in detail below with reference to Examples, but the present embodiment is not limited to these.

The physical properties of the porous carbon particles and the obtained porous carbon films used in the following examples and comparative examples were measured by the following methods.
(1) Pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less Using 3Flex (manufactured by Micromeritics Instrument Corp.), the BJH (Barrett-Joyner-Hallenda) method is used from the adsorption isotherm obtained by the nitrogen adsorption method. I asked.
(2) Pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less It was obtained by the BJH method from the adsorption isotherm obtained by the nitrogen adsorption method using 3Flex (manufactured by Micromeritics Instrument Corp.).
(3) Specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less It was determined using the BJH method from the adsorption isotherm obtained by the nitrogen adsorption method using 3Flex (manufactured by Micromeritics Instrument Corp.).
(4) Specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less It was determined using the BJH method from the adsorption isotherm obtained by the nitrogen adsorption method using 3Flex (manufactured by Micromeritics Instrument Corp.).
(5) BET method specific surface area It was obtained according to the BET (Brunauer-Emmett-Teller) method from the adsorption isotherm obtained by the nitrogen adsorption method using 3Flex (manufactured by Micromeritics Instrument Corp.).
(6) Apparent density It was obtained by dividing the mass of the porous carbon membrane by its volume.
(7) Porosity (%)
It was obtained by the following calculation.
(1-apparent density of porous carbon membrane/true density of constituent material of porous carbon membrane) x 100
(8) Infusibilization yield (%)
It was obtained from the following calculation.
Porous membrane mass after infusibility (g)/Porous membrane mass before infusibility (g) x 100
(9) Carbonization yield (%)
It was obtained from the following calculation.
Mass of porous carbon membrane after carbonization (g)/mass of porous membrane after infusibility (g) x 100
(10) Carbon film thickness retention rate (%)
It was obtained from the following calculation.
Porous carbon film thickness after carbonization (μm)/coated sheet thickness (μm)×100

In addition, the battery characteristics of the air battery using the porous carbon film as the positive electrode in the following examples and comparative examples were evaluated by the discharge capacity obtained under the following conditions for the coin cells produced by the following method.
A positive electrode obtained by cutting a porous carbon film into φ16 mm, metallic lithium (φ16 mm, thickness 0.2 mm) as a negative electrode, and a separator immersed in 100 μL of a 1M-tetraethylene glycol dimethyl ether solution of electrolyte LiTFS (lithium trifluoromethanesulfonate). Glass fiber paper (Whatman (registered trademark), GF / A) is mounted in a coin cell case (CR2032 type) in a dry room (in dry air) with a dew point temperature of -50 ° C. or less, as shown in FIG. A coin cell 600 was produced.
This coin cell 600 was discharged in a pure oxygen atmosphere at a current density of 0.4 mA/cm ² , and the discharge capacity obtained was taken as the discharge end point when the voltage dropped to 2.3 V. The porous carbon membrane used as the positive electrode The discharge capacity per mass of the positive electrode (hereinafter referred to as "discharge capacity of the porous carbon film") was calculated by dividing by the mass of .

[Example 1]
A porous carbon film for an air battery positive electrode was produced by the following method, and evaluated by the method described above.

(Mixture slurry preparation process)
75 parts by mass of Ketjenblack EC600JD as porous carbon particles, 5 parts by mass of carbon fibers with an average fiber diameter of 6 μm and an average length of 3 mm, 5 parts by mass of carbon nanotubes with an average diameter of 1.6 nm and a length of about 5 μm, and a binder 3 parts by mass of polyacrylonitrile (PAN) and 12 parts by mass of polyethylene oxide (PEO) manufactured by ALDRICH with a viscosity average molecular weight of 600,000 are used as the polymer material, and N-methylpyrrolidone is used as a solvent to uniformly disperse them. was added and mixed with a rotating and revolving kneader ARE310 manufactured by Thinky to prepare a mixture slurry. At this time, the mass ratio of polyethylene oxide (PEO) to porous carbon particles is 0.16. Table 1 shows the properties of the Ketjenblack EC600JD used.

(Molding process)
The mixture slurry was molded into a sheet having a thickness of 550 μm by a wet film forming method using a doctor blade.

(Solvent immersion step)
The molded sheet was placed in a tray, and 220 g of methanol was added and allowed to stand. After 2 hours, the methanol in the tray was discharged, 220 g of methanol was newly added, and after standing still for 17 hours, the methanol in the tray was discharged to convert the molded sheet into a porous film.
In this step, the molded sheet in which porous carbon particles and carbon fibers are dispersed in an N-methylpyrrolidone solution of PAN is immersed in methanol, which is a non-solvent (poor solvent) for PAN. The carbon particles and the carbon fibers are bound together and phase-separated to form a porous film with the carbon particles as a skeleton. On the other hand, most of the N-methylpyrrolidone in the molded sheet is compatible with methanol and removed.

(Drying process)
The porous membrane after immersion in the solvent was taken out from the tray and dried at 50° C. for 2 hours and at 80° C. for 10 hours to remove the volatile solvent contained in the porous membrane.

(Infusibilization step)
The dried porous film was subjected to infusibilization treatment at 320° C. for 3 hours in an air circulation atmosphere using a Yamato Inert Oven DN411 to convert PAN in the porous carbon film into an infusible resin. Most of the PEO in the porous membrane is decomposed and dissipated in this infusibilization step. The porous film yield in this infusibilization step was 86.4%.

(Carbonization process)
An infusible porous film having a length of 90 mm and a width of 80 mm obtained by the infusible treatment was heated to 1050°C at a temperature elevation rate of 10°C/min using a box-type furnace manufactured by Denken High Dental Co., while flowing nitrogen gas at a rate of 600 mL/min. C., held at 1050.degree. C. for 3 hours, and then allowed to cool to room temperature to carbonize the infusibilized PAN to obtain a porous carbon film composed entirely of carbon. In this carbonization step, the PEO remaining in the porous membrane after the infusibilization treatment is further decomposed and dissipated. The porous film yield in this carbonization step was 94.7%.
The thickness retention rate of the porous carbon membrane, which is the percentage of the thickness of the porous carbon membrane relative to the thickness of the molded sheet, was 51%.
Furthermore, the amount of porous carbon particles in the porous carbon film calculated from the mix slurry was 87%.

(Physical properties of porous carbon membrane)
In the obtained porous carbon membrane, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 3.6 cm ³ /g, and the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less was 2.9 cm ³ /g. The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 1066 cm ² /g, and the specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less was 1056 cm ² /g. The obtained porous carbon film had a BET specific surface area of 1102 m ² /g, an apparent density of 0.17 g/cm ³ and a porosity of 91.2%.

(Discharge capacity of air battery using porous carbon film as positive electrode)
Next, a coin cell using this porous carbon film as a positive electrode was produced by the method described above, and the discharge capacity of the porous carbon film was calculated. As a result, the discharge capacity showed a large value of 3350 mAh/g.

[Comparative Example 1]
The procedure of Example 1 was repeated except that PEO was not added and the amount of PAN was changed to 15 parts by mass (the same amount as the total amount of PAN and PEO in Example 1). The porous membrane yield in the infusibilizing step was 92.3%, which was higher than the 86.4% of Example 1. It is considered that this is because in Example 1, a mass reduction corresponding to the decomposition and dissipation of PEO occurs in the infusibilization step, whereas in Comparative Example 1, since PEO is not included, the mass reduction does not occur. Table 2 shows the yield of the porous carbon membrane, the thickness retention rate of the porous carbon membrane, and the amount of porous carbon particles in the porous carbon membrane calculated from the mixture slurry composition in the carbonization step.

In the obtained porous carbon membrane, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 3.4 cm ³ /g, and the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less was 2.8 cm ³ /g. The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 984 cm ² /g, and the specific surface area occupied by pores with a diameter of 1 nm or more and ²⁰⁰ nm or less was 975 cm 2 /g. Also, the discharge capacity of the air battery using this porous carbon film as the positive electrode was 2671 mAh/g, which was smaller than that of Example 1. The BET specific surface area, apparent density and porosity of this porous carbon film were as shown in Table 3, respectively.

[Example 2]
Same as Example 1, except that the amount of PAN used when preparing the mixture slurry was 7 parts by mass, the amount of PEO used was 8 parts by mass, and the thickness of the sheet formed from the mixture slurry was 200 μm. went to At this time, the mass ratio of PEO to porous carbon particles is 0.107. The porous membrane yield in the infusibilizing step was 90.3%. In addition, the yield of the porous carbon film in the carbonization step, the thickness retention rate of the porous carbon film, and the amount of porous carbon particles in the porous carbon film calculated from the mixture slurry mixture were as shown in Table 2. .

In the obtained porous carbon membrane, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less is 3.9 cm ³ /g, the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less is 3.0 cm ³ /g, The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 1049 cm ² /g, and the specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less was 1038 cm ² /g. In addition, the discharge capacity of the air battery using this porous carbon film as the positive electrode showed a large value of 3512 mAh/g. The BET specific surface area, apparent density and porosity of this porous carbon film were as shown in Table 3, respectively.

[Comparative Example 2]
Example 2 was repeated except that PEO was not added and the amount of PAN was changed to 15 parts by mass (the same amount as the total amount of PAN and PEO in Example 1). The porous film yield in the infusibilizing step was 95.1%, which was higher than the 90.3% of Example 1. This is presumably because in Example 2, a mass decrease corresponding to the decomposition and dissipation of PEO occurs in the infusibilizing step, whereas in Comparative Example 2, since PEO is not included, the mass decrease does not occur. In addition, the porous membrane yield in the carbonization step, the thickness retention rate of the porous carbon membrane, and the amount of porous carbon particles in the porous carbon membrane calculated from the blending of the mixture slurry were as shown in Table 2, respectively. .

In the obtained porous carbon membrane, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 3.8 cm ³ /g, and the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less was 2.6 cm ³ /g. The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less is 1010 cm ² /g, the specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less is 995 cm ² /g, and the BET specific surface area is 1054 m ² /g. A smaller value than Example 2 was obtained. Also, the discharge capacity of the air battery using this porous carbon film as the positive electrode was 2630 mAh/g, which was smaller than that of Example 2. The apparent density and porosity of this porous carbon film were as shown in Table 3, respectively.

[Example 3]
The procedure was carried out in the same manner as in Example 2, except that 10 parts by mass of PAN and 5 parts by mass of PEO were used when preparing the mixture slurry. At this time, the mass ratio of PEO to porous carbon particles is 0.067. The porous membrane yield in the infusibilizing step was 92.4%. In addition, the yield of the porous carbon film in the carbonization step, the thickness retention rate of the porous carbon film, and the amount of porous carbon particles in the porous carbon film calculated from the mixture slurry mixture were as shown in Table 2. .

In the obtained porous carbon membrane, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 3.8 cm ³ /g, and the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less was 2.9 cm ³ /g. The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 1016 cm ² /g, and the specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less was 1004 cm ² /g. Also, the discharge capacity of the air battery using this porous carbon film as the positive electrode showed a large value of 3563 mAh/g. The BET specific surface area, apparent density and porosity of this porous carbon film were as shown in Table 3, respectively.

[Example 4]
85 parts by mass of porous carbon particles, 4 parts by mass of carbon nanofibers and 4 parts by mass of carbon nanotubes, 3 parts by mass of PAN, and 4 parts by mass of PEO when preparing the mixture slurry. The same procedure as in Example 1 was carried out, except that the thickness of the sheet formed from the mixture slurry was 300 μm. At this time, the mass ratio of PEO to porous carbon particles is 0.047. The porous membrane yield in the infusibilizing step was 93.4%. In addition, the yield of the porous carbon film in the carbonization step, the thickness retention rate of the porous carbon film, and the amount of porous carbon particles in the porous carbon film calculated from the mixture slurry mixture were as shown in Table 2. .

In the obtained porous carbon membrane, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 3.8 cm ³ /g, and the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less was 2.9 cm ³ /g. The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 1096 cm ² /g, and the specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less was 1084 cm ² /g. In addition, the discharge capacity of the air battery using this porous carbon film as the positive electrode showed a large value of 3912 mAh/g. The BET specific surface area, apparent density and porosity of this porous carbon film were as shown in Table 3, respectively.

[Comparative Example 3]
The procedure of Example 4 was repeated except that PEO was not added and the amount of PAN was changed to 7 parts by mass (the same amount as the total amount of PAN and PEO in Example 4). The porous film yield in the infusibilizing step was 97.2%, which was higher than the 93.4% of Example 4. This is probably because in Example 4, a mass decrease corresponding to the decomposition and dissipation of PEO occurs in the infusibilizing step, whereas in Comparative Example 3, since PEO is not included, the mass decrease does not occur. In addition, the yield of the porous carbon film in the carbonization step, the thickness retention rate of the porous carbon film, and the amount of porous carbon particles in the porous carbon film calculated from the mixture slurry mixture were as shown in Table 2. .

In the obtained porous carbon membrane, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less was 3.6 cm ³ /g, and the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less was 2.7 cm ³ /g. The specific surface area occupied by pores with a diameter of 1 nm or more and 1000 nm or less is 994 ^{cm 2} /g, the specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less is 983 cm 2 /g, and the BET specific surface area is 1029 m ² /g. A smaller value than Example 4 was obtained. Also, the discharge capacity of the air battery using this porous carbon film as the positive electrode was 3372 mAh/g, which was smaller than that of Example 4. The apparent density and porosity of this porous carbon film were as shown in Table 3, respectively.

Regarding the examples and comparative examples described above, Table 2 summarizes the manufacturing conditions of the porous carbon membranes, and Table 3 summarizes the physical properties of the obtained porous carbon membranes and the discharge capacities of the batteries.

From the above results, the porous carbon membrane produced by blending a thermally decomposable organic compound such as polyethylene oxide (PEO) as a component of the mixture slurry was finer than that produced without blending it. The pore volume, pore specific surface area and BET specific surface area are increased, and it can be said that the discharge capacity of the battery when used for the positive electrode of the air battery is also increased. This is because the thermally decomposable organic compound in the mixture slurry and the sheet formed from the same is decomposed and dissipated by heating in the infusibilization step and the carbonization step, and voids are formed in the porous carbon film. When the gas generated by the decomposition of the thermally decomposable organic compound is dissipated outside the membrane, some of the bonds in the binder polymeric material covering the porous carbon particles are peeled off, and airways are formed in the binder polymeric material. It is speculated that this is due to the increase in pores of the porous carbon membrane due to the formation of

According to the present invention, it is possible to achieve a high discharge capacity that could not be achieved conventionally when compared with air batteries having the same structure and size. Therefore, the present invention is useful in that it can provide a high-capacity air battery that could not be obtained conventionally, and in that it can make a battery with the same discharge capacity smaller.

600 coin cell 610 negative electrode structure 620 positive electrode structure 630 coin cell type restraint 635 current collector 640 metal layer 650 spacer 660 separator 670 space (electrolyte filling space)
680 Metal mesh 690 Porous carbon film 100 Negative electrode structure 500 Laminated air battery 510 Positive electrode structure 520 Negative electrode current collector 525 Positive electrode current collector 540 Separator 550 Porous carbon film 560 Gas diffusion layer

Claims (10)

porous carbon particles,
A polymeric material for a binder having a mass reduction rate of less than 90% when heated to 800°C in an inert atmosphere;
Porous carbon containing at least one selected from a thermally decomposable organic compound having a mass reduction rate of 90% or more when heated to 800° C. in an inert atmosphere, and carbon fibers and carbon nanotubes as optional components. A composition for producing membranes. 2. The composition for producing a porous carbon film according to claim 1, wherein said thermally decomposable organic compound is polyethylene oxide (PEO). The content of the thermally decomposable organic compound is 0.5 parts by mass or more and 90 parts by mass when the total of the porous carbon particles, the binder polymer material, the carbon nanofibers, and the carbon nanotubes is 100 parts by mass. 3. The composition for producing a porous carbon membrane according to claim 1 or 2, wherein the composition is at most parts. A porous carbon membrane-producing sheet formed from the porous carbon membrane-producing composition according to any one of claims 1 to 3. A method for producing a porous carbon film for an air battery positive electrode, comprising:
preparing a mixture slurry containing the composition for producing a porous carbon membrane according to any one of claims 1 to 3;
molding the mixture slurry;
immersing the molded body obtained by molding in a solvent in which the polymer material for a binder has a low solubility;
A method for producing a porous carbon film for an air battery positive electrode, comprising drying the sample obtained by immersion, and carbonizing the sample obtained by drying in an inert gas atmosphere. 6. The method for producing a porous carbon membrane according to claim 5, comprising making the sample obtained by drying infusible in the air before the carbonization. 7. The method for producing a porous carbon membrane according to claim 5, wherein said porous carbon membrane satisfies all of the following conditions (a) to (c).
(a) The pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less is 3.6 cm ³ /g or more and 7.0 cm ³ /g or less (b) The pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less is 2.8 cm ³ /g or more and 7.0 cm ³ /g or less (c) The specific surface area occupied by pores with a diameter of 1 nm or more and 200 nm or less is 1000 m ² /g or more and 2000 m ² /g or less The method for producing a porous carbon membrane according to claim 7, wherein the porous carbon membrane further satisfies the following condition (e).
(e) Apparent density of 0.10 g/cm ³ or more and 0.20 g/cm ³ or less 9. The method for producing a porous carbon membrane according to claim 7, wherein said porous carbon base membrane further satisfies the following condition (f).
(f) Porosity is 90% or more and 99% or less A method for manufacturing an air battery,
producing a porous carbon membrane by the method for producing a porous carbon membrane according to any one of claims 5 to 9;
forming a positive electrode from the porous carbon film and preparing a negative electrode and a separator;
A method for manufacturing an air battery, comprising: laminating the positive electrode and the negative electrode with a separator interposed therebetween; and filling the separator with an electrolytic solution.

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