JP2014053269A - Carbon material for air electrode of air cell, air cell containing the same, and process of manufacturing carbon material for air electrode of air cell - Google Patents

Abstract

A carbon material for an air electrode of an air battery, an air battery including the carbon material, and an air battery having a reaction starting point of an oxygen reduction reaction more than that of a conventional carbon material that has been used for an air electrode of an air battery. A method for producing a carbon material for an air electrode is provided.
A carbon material used for an air electrode of an air battery, wherein the carbon material contains an amino group at least on a surface thereof.
[Selection] Figure 3

Description

  The present invention relates to a carbon material for an air electrode of an air battery, an air battery including the carbon material, and an air battery having more reaction starting points for an oxygen reduction reaction than a conventional carbon material that has been used for an air electrode of an air battery. The present invention relates to a method for producing an air electrode carbon material.

  An air battery is a chargeable / dischargeable battery using a single metal or a metal compound as a negative electrode active material and oxygen as a positive electrode active material. Since oxygen, which is a positive electrode active material, is obtained from air, it is not necessary to enclose the positive electrode active material in the battery. Therefore, in theory, an air battery has a larger capacity than a secondary battery using a solid positive electrode active material. realizable.

In a lithium-air battery, which is a type of air battery, the reaction of formula (I) proceeds at the negative electrode during discharge.
2Li → 2Li ⁺ + 2e ⁻ (I)
The electrons generated in the formula (I) reach the air electrode after working with an external load via an external circuit. Then, lithium ions (Li ⁺ ) generated in the formula (I) move by electroosmosis from the negative electrode side to the air electrode side in the electrolyte sandwiched between the negative electrode and the air electrode.

Further, during discharge, the reactions of the formulas (II) and (III) proceed at the air electrode.
2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (II)
2Li ⁺ + 1 / 2O ₂ + 2e ⁻ → Li ₂ O (III)
The generated lithium peroxide (Li ₂ O ₂ ) and lithium oxide (Li ₂ O) are accumulated in the air electrode as solids.
At the time of charging, the reverse reaction of the above formula (I) proceeds at the negative electrode, and the reverse reaction of the above formulas (II) and (III) proceeds at the air electrode, respectively. Become.

  A carbon material has been conventionally used for an air electrode of an air battery. However, knowledge about what characteristics of the carbon material determine the capacity of the positive electrode has not yet been obtained. Therefore, there has been no decisive guide on how to improve the carbon material blended in the air electrode to increase the capacity of the air battery. As a technique for obtaining a high-capacity nonaqueous electrolyte battery, Patent Document 1 discloses a positive electrode mainly composed of a carbonaceous material having a pore volume of 1.0 mL / g or more, which is occupied by pores having a diameter of 1 nm or more, A nonaqueous electrolyte battery comprising a negative electrode including a negative electrode active material that occludes and releases metal ions, and a nonaqueous electrolyte layer sandwiched between the positive electrode and the negative electrode is disclosed.

JP 2002-015737 A

Paragraphs [0056]-[0064] of Patent Document 1 describe examples of non-aqueous electrolyte batteries using ketjen black for the air electrode. However, when the present inventors further examined the nonaqueous electrolyte battery disclosed in Patent Document 1, it was found that the capacity was still low when Ketjen Black was used for the air electrode.
The present invention has been accomplished in view of the above circumstances, and has a carbon starting material for an air electrode of an air battery that has more reaction starting points for an oxygen reduction reaction than a conventional carbon material that has been used for an air electrode of an air battery. An object of the present invention is to provide an air battery containing the carbon material and a method for producing a carbon material for an air electrode of the air battery.

  The carbon material of the present invention is a carbon material used for an air electrode of an air battery, and the carbon material contains an amino group at least on the surface.

In the present invention, the ratio of the nitrogen atom number concentration to the carbon atom number concentration per specific surface area is preferably 2 × 10 ⁻⁵ m ^{−2 to} 7.5 × 10 ⁻³ m ⁻² .

  A first air battery according to the present invention is an air battery including at least an air electrode, a negative electrode, and an electrolyte layer interposed between the air electrode and the negative electrode, wherein the air electrode is an air electrode of the air battery. It contains carbon materials for use.

  In the first air battery of the present invention, the negative electrode may contain lithium metal or a lithium compound.

  The method for producing a carbon material for an air electrode of an air battery according to the present invention includes a carbon containing at least one linker selected from the group consisting of a functional group itself serving as a linker and a group having a functional group serving as the linker. By preparing a raw material and an amino compound containing a bond-forming functional group and an amino group that form a bond by a chemical reaction with the functional group serving as the linker, and by causing the amino compound to act on the carbon raw material The linker contained in the carbon raw material and the bond-forming functional group contained in the amino compound cause a chemical reaction to form a bond between the carbon raw material and the amino compound, and at least an amino group And a synthesis step of synthesizing a carbon material for an air electrode of an air battery contained on the surface.

In the production method of an air electrode carbon material of the air battery of the present invention, wherein the _{linker, -W-CO 2 H, -W} -CO 2 R, -W-OH, -W-OR, -W-CHO, And -W-OCOR (W represents a divalent organic group or a single bond, and R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms. .) May be at least one functional group selected from the group consisting of:

In the production method of an air electrode carbon material of the air battery of the present invention, the bond forming functional group, -Z-OH, -Z-OR , -Z-CHO, -Z-CO 2 H, -Z-CO ₂ R, —Z—OCOR, —Z—X, and —Z—NH ₂ (wherein Z represents a divalent organic group or a single bond, and R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms) Alternatively, it represents an aromatic hydrocarbon group having 6 to 10 carbon atoms, and X represents a halogen atom selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). And at least one functional group selected from the group consisting of:

  The second air battery of the present invention is an air battery in which an electrolyte is interposed between an air positive electrode and a lithium metal or lithium compound negative electrode, and the air positive electrode has a porous three-phase interface site in communication. And an amino group bonded to an edge carbon atom of the three-phase interface site.

In the second air battery of the present invention, the ratio of the number of nitrogen atoms to the number of carbon atoms per specific surface area in the carbon fiber material is 2 × 10 ⁻⁵ m ^{−2 to} 7.5 × 10 ^−3. m- ² is preferred.

  The method for producing an air cathode of the present invention uses a porous carbon fiber material having a three-phase interface site in communication as a raw material, and forms a bond containing a linker functional group on an edge carbon atom and an amino compound at the three-phase interface site. An amino group is bonded to the edge carbon atom by chemically reacting with a functional group.

In the method for manufacturing an air cathode of the present invention, the linker functional groups on the edge carbon _{atoms, -W-CO 2 H, -W} -CO 2 R, -W-OH, -W-OR, -W-CHO, And -W-OCOR (W represents a divalent organic group or a single bond, and R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms. .) May be at least one functional group selected from the group consisting of:

In the method for manufacturing an air cathode of the present invention, the bond-forming functional _{group, -Z-OH, -Z-OR} , -Z-CHO, -Z-CO 2 H, -Z-CO 2 R, -Z-OCOR , -Z-X, and -Z-NH ₂ (however, Z represents a divalent organic group or a single bond, and, R represents an aliphatic hydrocarbon group or a C 6-10 having 1 to 10 carbon atoms Represents an aromatic hydrocarbon group, and X represents a halogen atom selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). There may be at least one functional group.

  According to the present invention, since the amino group is contained at least on the surface, the carbon material has a larger number of reaction starting points for the oxygen reduction reaction than the conventional carbon material. As a result, such a carbon material is used for the air electrode of an air battery. In this case, electrons can be exchanged between the carbon material and a larger number of oxygen molecules, and higher capacity can be realized than the conventional air battery.

It is a figure which shows an example of the laminated constitution of the air battery of this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. It is the expansion schematic diagram of the structure of an expanded carbon fiber, and the schematic diagram of the chemical structure of the carbon atom layer. It is a SEM image of the expanded carbon fiber aminated product of Example 1, and an SEM image of the expanded carbon fiber aminated product contained in the air electrode layer of the air battery of Example 5 after discharge. Example 5-Example 6 and Comparative Example 9-Comparative Example 9-Charge capacity of air batteries of Comparative Example 12 and nitrogen atom number concentration relative to carbon atom number concentration per specific surface area in carbon materials used in these air batteries It is the graph which showed the relationship of ratio. It is a schematic diagram of a constant current electrochemical treatment apparatus. It is the SEM image of the carbon material for air electrodes of the air battery of the comparative example 4, and the SEM image of the carbon material contained in the air electrode layer of the air battery of the comparative example 12 after discharge.

1. The carbon material for the air electrode of an air battery The carbon material of this invention is a carbon material used for the air electrode of an air battery, Comprising: The said carbon material contains an amino group at least on the surface, It is characterized by the above-mentioned.

  As described above, the air battery using ketjen black for the air electrode layer has a low capacity and has a significant deterioration in durability, and therefore cannot withstand repeated use. This is because, in the prior art, sufficient study on the surface structure of the carbon material has not been made, and the types of functional groups added to the surface of the carbon material and the concentration of the number of atoms, which improve the capacity of the air battery, This is because almost no knowledge about the ratio was obtained.

  The present inventors paid attention to the functional group on the surface of the carbon material and repeated studies. As a result, the present inventors can increase the number of reaction starting points of the oxygen reduction reaction by using a carbon material containing an amino group at least on the surface for the air electrode. The present invention has been completed by finding that it can be improved.

When a conventional carbon material such as ketjen black is used, the reason why the discharge capacity of the air battery is still low is that the number of reaction starting points in the carbon material and the area of the reaction site are, for example, expanded carbon fibers described later It is thought that it is much smaller than an aminated product. The reaction here is mainly an oxygen reduction reaction represented by at least one of the above formulas (II) and (III).
As an index of the number of reaction starting points, the amount of amino groups contained on the surface of the carbon material can be exemplified. Examples of the physical property value indicating the amount of amino groups contained on the surface of the carbon material include the amino group content and the ratio of the nitrogen atom number concentration to the carbon atom number concentration. Carbon materials vary in shape and size depending on the material, and the amino group content is also different.In the present invention, the carbon material is widely applicable to carbon materials, and is an index that can be compared with other carbon materials. It is appropriate to employ the ratio of the number of nitrogen atoms to the number of carbon atoms.
As one of the grounds on which the amino group on the surface of the carbon material becomes the starting point of the oxygen reduction reaction, as shown in the examples described later, in an air battery using a carbon material containing a specific amount of amino group on the surface for the air electrode, It is mentioned that the solids of lithium peroxide (Li ₂ O ₂ ) and lithium oxide (Li ₂ O) deposited on the air electrode surface after discharge become extremely small. As described above, the reason why discharge deposits are extremely small by containing a specific amount of amino groups is not clear in detail, but amino groups introduced with a high degree of dispersion on the carbon material surface supplement lithium ions. In addition, it is presumed that this is for forming nucleation sites of lithium oxide as discharge deposits.

In the present invention, the ratio of the number of nitrogen atoms to the number of carbon atoms per specific surface area (hereinafter sometimes referred to as the ratio) is 2 × 10 ⁻⁵ m ^{−2 to} 7.5 × 10 ^−. It is preferably ³ m ^-2 . When the ratio is less than 2 × 10 ⁻⁵ m ⁻² , the amount of amino groups on the surface of the carbon material becomes too small, resulting in fewer starting points for the oxygen reduction reaction, and the charge / discharge capacity that is an effect of the present invention. There is a possibility that the effect of the increase in the amount cannot be fully enjoyed. On the other hand, when the ratio exceeds 7.5 × 10 ⁻³ m ⁻² , the number of amino groups on the surface of the carbon material becomes too large, and thus the lithium oxide having a high polarity that is a discharge deposit is an amino group on the surface of the carbon material. As a result of competing and adsorbing to the base and closing the pores of the carbon material, the battery characteristics may be deteriorated.
In the present invention, the ratio of the nitrogen atom number concentration to the carbon atom number concentration per specific surface area is more preferably 5 × 10 ⁻⁴ m ⁻² or more, and more preferably 1 × 10 ⁻³ m ⁻² or more. More preferably. In the present invention, the ratio of the nitrogen atom number concentration to the carbon atom number concentration per specific surface area is more preferably 6 × 10 ⁻³ m ⁻² or less, and 4 × 10 ⁻³ m ⁻² or less. More preferably.

As a method for measuring the ratio of the nitrogen atom number concentration to the carbon atom number concentration per specific surface area, a known method can be adopted. For example, the carbon atom number concentration and the nitrogen atom number concentration on the surface of the carbon material are measured by X-ray photoelectron spectroscopy (XPS), and the BET method (Brunauer-Emmett-Teller method) Examples include a method for measuring the specific surface area of the material. The measured nitrogen atom number concentration is divided by the carbon atom number concentration, and the ratio of the nitrogen atom number concentration to the carbon atom number concentration is calculated. Furthermore, the ratio of the nitrogen atom number concentration to the carbon atom number concentration per specific surface area can be calculated by dividing the ratio of the calculated nitrogen atom number concentration to the carbon atom number concentration by the specific surface area of the carbon material.
It should be noted that the mixing ratio of the raw materials when producing the carbon material according to the present invention, for example, the mixing ratio of the carbon raw material and the amino compound, is the number of nitrogen atoms relative to the carbon atom number concentration per specific surface area as it is. It may be a concentration ratio.

As a typical example of the carbon material that satisfies the above-described condition of the ratio of the number of nitrogen atoms to the number of carbon atoms per specific surface area, an expanded carbon fiber having at least a surface aminated under appropriate conditions can be exemplified. The carbon material for the air electrode of the air battery of the present invention is preferably such an expanded carbon fiber aminated product.
An expanded carbon fiber refers to a fine carbon fiber obtained by further heat-treating a graphite intercalation compound synthesized using a carbon fiber raw material. Although the manufacturing method of expanded carbon fiber is not specifically limited, For example, a chemical processing method, an electrochemical processing method, etc. are mentioned. Depending on the physical properties required for the air electrode carbon material of the air battery, the expanded carbon fiber may be appropriately classified or ground.

FIG. 2A is an enlarged schematic view of the structure of the expanded carbon fiber, and FIG. 2B is a schematic view of the chemical structure of the carbon atom layer of the expanded carbon fiber. FIG. 2B is a schematic diagram further enlarging the inside of the circle of the broken line part of FIG.
In the expanded carbon fiber, the area occupied by the edge portion with respect to the total surface area of the carbon material is larger than that of the conventional carbon material. The edge part here refers to a part occupied by edge carbon atoms. An edge carbon atom refers to a carbon atom that is located at the end of a carbon atom layer and can be bonded to atoms other than carbon atoms. In many cases, a functional group that can be modified is added to the edge carbon atom present in the edge portion of the expanded carbon fiber so as to serve as a linker described later. Therefore, there is an advantage that more amino groups can be easily added to the edge portion of the expanded carbon fiber than other carbon materials through the linker.
A method for producing the expanded carbon fiber and an aminated product thereof will be described later.

  The carbon material for an air electrode of an air battery according to the present invention contains an amino group at least on the surface thereof, so that when it is used for the air electrode of an air battery, a solid that deposits on the air electrode surface during discharge is present. It becomes extremely smaller than the conventional air battery. Such an air battery has a larger charge capacity than an air battery using a conventional carbon material because the discharge deposit is easily decomposed and reduced to metal ions during charging.

2. Manufacturing method of carbon material for air electrode of air battery The manufacturing method of the carbon material for air electrode of the air battery of the present invention is at least selected from the group consisting of a functional group itself serving as a linker and a group having a functional group serving as the linker. A preparation step of preparing an amino compound containing a carbon raw material containing at least one linker at least on the surface, a bond-forming functional group that forms a bond by a chemical reaction with the functional group serving as the linker, and an amino group; and By causing the amino compound to act on a carbon raw material, the linker contained in the carbon raw material and the bond-forming functional group contained in the amino compound cause a chemical reaction, whereby the carbon raw material and the amino compound A synthetic engineer that synthesizes a carbon material for an air electrode of an air battery that forms a bond between them and contains at least an amino group on the surface It is characterized by having.

The method for producing an air cathode according to one embodiment of the present invention uses a porous carbon fiber material having a three-phase interface site in communication as a raw material, and the linker functional group and amino compound on the edge carbon atom in the three-phase interface site are An amino group is bonded to the edge carbon atom by chemically reacting with the contained bond-forming functional group.
As used herein, “connected three-phase interface site” refers to a site where an electrode reaction proceeds in the presence of a carbon electrode, lithium ions, and oxygen gas. Moreover, it is preferable that the porous carbon fiber material here is an expanded carbon fiber material.

The present invention includes (1) a preparation step of preparing a carbon raw material and an amino compound, and (2) a synthesis step of synthesizing a carbon material for an air electrode of an air battery containing at least an amino group on the surface. The present invention is not necessarily limited to the above two steps, and may have other steps in addition to the above two steps.
Hereinafter, the steps (1) to (2) will be described in order.

2-1. Preparation Step This step is a step of preparing a carbon raw material and an amino compound.
The carbon raw material that can be used in the present invention contains at least the surface of at least one linker selected from the group consisting of a functional group itself serving as a linker and a group having a functional group serving as the linker.

  In the present invention, the linker contained in the carbon raw material refers to an atom, a functional group, or an organic group that plays a role of bonding the carbon atom of the carbon raw material and the amino compound to each other. As an aspect of a linker, the functional group itself used as a linker may be sufficient, and the group which has the said functional group may be sufficient. That is, in this step, a group having at least one functional group serving as a linker is used as the linker.

In the present invention, the linker included in the carbon raw material is not particularly limited as long as it is a group capable of forming a chemical bond by a known chemical reaction. Depending on the kind described amino compound is different from the type of linker with the carbon raw material, _{linker, -W-CO 2 H, -W} -CO 2 R, -W-OH, -W-OR, -W- CHO, and -W-OCOR (W represents a divalent organic group or a single bond, and R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms. It may be at least one functional group selected from the group consisting of:

The divalent organic group W in the linker is not particularly limited as long as the chemical structure can be maintained during the reaction between the carbon raw material and the amino compound, but a lower carbon chain, specifically having 1 to 5 carbon atoms. Carbon chain or a single bond is preferable, and a carbon chain having 1 to 3 carbon atoms or a single bond is particularly preferable.
Specific linkers, for _{example, -CO 2 H, - (CH} 2) n -CO 2 H, -CO 2 CH 3, -OH, - (CH 2) n -OH, -O-CH 2 CH 2 _{-OH, -O-CH 3, -O} -CH 2 CH 3, -CHO, - (CH 2) n -CHO, -OCOCH 3, - (CH 2) n -OCOCH 3 , etc. (more, n represents 1 A natural number of 5). Among these, as a _linker, -CO 2 H, it is preferable to employ -CHO, and -OH.

Examples of the carbon material containing a linker containing a carboxyl group (—CO ₂ H), an aldehyde group (—CHO), and / or a hydroxyl group (—OH) on the surface include the above-mentioned expanded carbon fibers.

The amino compound that can be used in the present invention is an amino compound containing an amino group and a bond-forming functional group that forms a bond by a chemical reaction with the above-described linker on the surface of the carbon material. The amino compound that can be used in the present invention is not particularly limited as long as it can leave an amino group after the reaction with the carbon raw material.
The bond-forming functional group that forms a bond by a chemical reaction with a functional group that serves as a linker is not particularly limited and can be appropriately selected depending on the type of the carbon raw material. For example, -Z-OH, -Z-OR,- Z—CHO, —Z—CO ₂ H, —Z—CO ₂ R, —Z—OCOR, —Z—X, and —Z—NH ₂ (wherein Z represents a divalent organic group or a single bond, R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, and X represents fluorine (F), chlorine (Cl), bromine (Br), and It may be at least one functional group selected from the group consisting of iodine (I) and a halogen atom selected from the group consisting of iodine (I).

The divalent organic group Z in the bond-forming functional group is not particularly limited as long as the chemical structure can be maintained during the reaction between the carbon raw material and the amino compound, but the lower carbon chain, specifically the number of carbon atoms A carbon chain or a single bond having 1 to 5 carbon atoms is preferable, and a carbon chain or a single bond having 1 to 3 carbon atoms is particularly preferable.
Specific binding functional groups include, for example, —OH, — (CH ₂ ) _n —OH, —O—CH ₂ CH ₂ —OH, —O—CH ₃ , —O—CH ₂ CH ₃ , —CHO. , — (CH ₂ ) _n —CHO, —CO ₂ H, — (CH ₂ ) _n —CO ₂ H, —CO ₂ CH ₃ , —OCOCH ₃ , — (CH ₂ ) _n —OCOCH ₃ , —Cl, — CH ₂ —Cl, —Br, —CH ₂ —Br, —CH ₂ —NH ₂ , and the like (where n is a natural number of 1 to 5) can be exemplified. Among these, it is preferable to employ —OH, —NH ₂ , —Br, and —CH ₂ —Br as the binding functional group.

Examples of amino compounds that can be used in the present invention include 2-aminoethanol (structural formula: HOCH ₂ CH ₂ NH ₂ , CAS No. 141-43-5), 3-aminopropanol (HOCH ₂ CH ₂ CH ₂ NH _2). , CAS No.156-87-6), 4- aminobutanol _{(HOCH 2 CH 2 CH 2 CH} 2 NH 2, CAS No.13325-10-5), diethanolamine _{(HN (CH 2 CH 2 OH} ) 2, CAS Nanba111-42-2), triethanolamine _{(N (CH 2 CH 2 OH} ) 3, CAS No.102-71-6), N- (1- naphthyl) ethanol amine _((C 10 H 7) HNCH _{2 CH 2 OH), N- (} 2- naphthyl) ethanol amine, phenyl ethanol amine _{((C 6} H 5) CH _{OH) CH 2 NH 2, CAS} No.7568-93-6), include Arno roll (CAS No.87129-71-3) and the like.

Examples of bonds formed by the linker and the binding functional group include, for example, the linker containing a carboxyl group (—CO ₂ H) and the binding functional group containing a hydroxyl group (—OH). An ester bond (—CO ₂ —); an amide bond (wherein the linker contains a carboxylic acid ester group (—CO ₂ R) and the binding functional group contains an amino group (—NH ₂ )) -C (O) NH-); when the linker contains a hydroxyl group (-OH) and the binding functional group contains a halogen atom (-X); Can be mentioned.

Hereinafter, the manufacturing method is demonstrated about the expanded carbon fiber which is an example of the carbon raw material which can be used for this invention.
Carbon fiber raw materials used for the production of expanded carbon fibers include pitch-based carbon fibers, PAN-based carbon fibers, and non-graphitizable carbon fibers such as phenol resin carbon fibers; graphitizable carbon fibers such as mesophase pitch-based carbon fibers Carbon nanotubes such as carbon nanotubes and carbon nanohorns are preferred. Many of these carbon fibers have sp ² hybrid orbitals similar to graphite. For example, pitch-based carbon fibers that have been heat-treated at a high temperature have extremely high crystallinity compared to simple graphite, and the strong bonds between carbon atoms derived from them affect the strength and elasticity of the pitch-based carbon fibers. It is exerting. In general, PAN-based carbon fibers and pitch-based carbon fibers are greatly affected by the infusibilization treatment method and heat treatment temperature in improving strength and elastic modulus, and the excellent physical properties of these carbon fiber raw materials are obtained after expansion. It is maintained even in fibrillar microfibers.

  In graphite and carbon fibers having a layered structure, carbon atoms in the a-axis direction and the b-axis direction, which are crystallographically substantially parallel to the carbon atom layer, are connected by a strong covalent bond. The carbon atoms in the c-axis direction, which are perpendicular, are only bonded with a weak van der Waals force. Accordingly, graphite intercalation compounds are produced by incorporating various types of atoms, molecules, ions, and the like between the carbon atomic layers.

  Examples of a method for synthesizing a graphite intercalation compound using a carbon fiber raw material include a chemical treatment method and an electrochemical treatment method. Among these, according to the chemical oxidation method, which is one of the chemical treatment methods, an oxidizing agent such as concentrated sulfuric acid, nitric acid, potassium permanganate, or a base such as potassium hydroxide or sodium hydroxide is added to the carbon material. By doing so, the molecule of the oxidizing agent or the molecule of the base is taken in between the carbon atom layers, and the graphite intercalation compound can be synthesized. On the other hand, for example, according to an electrochemical oxidation method which is one of electrochemical treatment methods, a graphite intercalation compound is obtained by electrochemically oxidizing a carbon fiber raw material in an acid electrolyte such as nitric acid or sulfuric acid. Can be synthesized. The obtained graphite intercalation compound becomes a small fiber shape having an average particle size of 1 μm or less after pyrolysis. This is because when the atoms, molecules, ions, etc. inserted between the carbon atom layers are decomposed by heat treatment and the decomposition products are released out of the carbon atom layer, the laminated structure of the carbon atom layer is partially broken. As a result of expanding the carbon atom layer, the carbon fiber raw material is changed from a simple carbon fiber shape to a fine fiber shape.

Hereinafter, an electrochemical treatment method and a chemical treatment method for the expanded carbon fiber will be described. In addition, the manufacturing method of the expanded carbon fiber which can be used suitably for this invention is not limited only to the method described below.
The electrochemical treatment method for the expanded carbon fiber preferably includes an electrochemical treatment step, a cleaning step, and a carbonization treatment step. The electrochemical treatment step is a step of producing a graphite intercalation compound by inserting at least one of atoms, molecules and ions (hereinafter sometimes referred to as atoms) between carbon atom layers by electrochemical treatment. It is. The washing step is a step of washing away excess electrolyte components and atoms adhering to the surface of the graphite intercalation compound. The carbonization treatment step is a step of removing atoms inserted between carbon atom layers of the graphite intercalation compound and expanding the carbon atom layer. Note that the electrochemical treatment method is not limited to the above three steps. For example, a drying step for removing the solvent used for washing or the like between the washing step and the carbonization treatment step, In addition, a grinding step or the like for efficiently advancing the carbonization treatment may be provided, or a classification step or the like for obtaining a carbon material having a particle size within a predetermined range may be used after the carbonization treatment step. .

As the electrochemical treatment apparatus used for the electrochemical treatment method, a known apparatus used for electrolytic oxidation can be appropriately used. Examples of electrochemical processing devices include current and voltage control devices such as electrochemical cells and potentiostats / galvanostats. As the electrochemical cell, for example, a triode cell having a working electrode, a counter electrode, and a reference electrode can be used. As an example of the configuration inside the triode cell, for example, a working electrode, a counter electrode, and a reference electrode to which a carbon fiber raw material is fixed are all immersed in an electrolytic solution. Although depending on the capacity of the triode cell, the amount of the electrolyte is preferably such that the carbon fiber raw material is sufficiently immersed.
As the electrolytic solution, an acid can usually be used. The type of acid is not particularly limited as long as it causes electrolysis when energized. Examples of the acid include organic acids, inorganic acids, and mixtures thereof. Examples of inorganic acids include sulfuric acid, concentrated sulfuric acid, nitric acid, concentrated nitric acid, and phosphoric acid. Examples of the organic acid include formic acid and acetic acid. Among these acids, concentrated nitric acid, formic acid, and dilute sulfuric acid having a concentration of 9 mol / dm ³ or less are preferable, and concentrated nitric acid is more preferable.
The working electrode, the counter electrode, and the reference electrode are connected to a current and voltage control device such as a potentiostat / galvanostat and an electrochemical process is performed to insert atoms and the like between the carbon atom layers. When acid is used as the electrolyte, acid molecules are inserted between the carbon atom layers. The current value and the treatment time during the electrochemical treatment can be appropriately selected depending on the amount of the carbon fiber raw material used for the electrochemical treatment and the type and concentration of the electrolytic solution. For example, when 0.01 to 1 g of pitch-based carbon fiber raw material is used as the carbon fiber raw material, constant current energization is performed at a current density of 5 to 15 A / g until the applied charge amount becomes 2,000 to 3,000 C. It is preferable to do.
By such an electrochemical treatment, an interlayer reaction is performed over the inside of the fiber, and the carbon fiber can be given a multi-fiber property, that is, a property as a bundle in which a large number of microfibers are twisted together.

The cleaning solution that can be used in the cleaning step is not particularly limited as long as it can remove the electrolyte component, atoms, and the like that are excessively attached to the surface of the graphite intercalation compound. Examples of the cleaning liquid include water, organic acids, organic acid esters, and mixed liquids thereof. Examples of organic acids that can be used include formic acid, acetic acid, and oxalic acid. As the organic acid ester, an ester of the above organic acid or the like can be used. The graphite intercalation compound washed with the washing liquid may be further subjected to an alkali treatment with a basic solution such as aqueous ammonia, aqueous sodium hydroxide or aqueous potassium hydroxide, or a basic gas such as ammonia, if necessary. These graphite intercalation compounds that have been alkali-treated with a basic solution or a basic gas may be further washed with water or the like, if necessary.
After the washing step, the obtained graphite intercalation compound is preferably dehydrated and dried appropriately. In preparation for the carbonization treatment, the graphite intercalation compound after the washing step may be appropriately ground.

  The carbonization treatment is a step of performing a carbon fiber expansion treatment by decomposing the graphite intercalation compound after the washing treatment by heat treatment. Specifically, first, the graphite intercalation compound after the cleaning treatment is placed in a heating apparatus, and heat treatment is performed at 800 to 1,200 ° C. for 3 to 10 seconds. Thus, by performing heat processing rapidly in a very short time, a carbon atom layer can be expanded and a desired expanded carbon fiber can be manufactured.

  Expanded carbon fibers obtained by an electrochemical treatment method usually have normal edges on the surface. The normal edge as used herein refers to an end portion of the expanded carbon fiber that contains an edge carbon atom that maintains an angular shape without being rounded and can participate in an oxygen reduction reaction. For this reason, the expanded carbon fiber obtained by the electrochemical treatment method has a surface edge area wider than that of the conventional carbon fiber. As a result, the reaction resistance is smaller than that of the conventional carbon material and the charge capacity is large.

  An example of the chemical treatment method for the expanded carbon fiber is an alkali activation method. In the alkali activation method, an alkaline solution such as an alkaline aqueous solution and a known reaction apparatus can be appropriately used. The alkaline aqueous solution that can be used in the alkali activation method is preferably strongly alkaline, and is preferably a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution having a concentration of 6 mol / L or more, or a tetramethylammonium hydroxide aqueous solution having a concentration of 20% by mass or more. The alkali treatment time and the alkali treatment temperature can be appropriately selected depending on the amount and size of the carbon fiber raw material used for the alkali treatment and the type and concentration of the alkali solution. For example, when 0.1 to 10 g of pitch-based carbon fiber material is used as the carbon fiber material, it is preferable to perform an alkali treatment at a processing temperature of 60 to 95 ° C. for 1 to 10 hours.

2-2. Synthetic Step This step involves reacting the carbon raw material described above with a chemical reaction between the linker contained in the carbon raw material and the bond-forming functional group contained in the amino compound by causing the amino compound to act on the carbon raw material. This is a step of synthesizing a carbon material for an air electrode of an air battery that forms a bond with the amino compound and contains at least the amino group on the surface.
In this step, “to make the amino compound act on the carbon raw material” means that the amino compound is sufficiently brought into contact with the carbon raw material so that a bond is formed between the carbon raw material and the amino compound. As an example of the aspect which makes an amino compound act on a carbon raw material, the aspect etc. which mix a carbon raw material and an amino compound are mentioned, for example.

In this step, a catalyst may be appropriately used to promote the reaction. For example, when the linker contains a carboxyl group (—CO ₂ H) and the binding functional group contains a hydroxyl group (—OH), when an ester bond (—CO ₂ —) is formed, An acid catalyst such as p-toluenesulfonic acid may be used. When the linker contains a hydroxyl group (—OH) and the binding functional group contains a halogen atom (—X), when forming an ether bond (—O—), sodium hydroxide A base catalyst such as an aqueous solution may be used.

Hereinafter, this process will be described in detail by taking as an example the case where the carbon raw material is a material containing a carboxyl group (—CO ₂ H) and the amino compound is an amino alcohol containing a hydroxyl group (—OH). To do.
First, a carbon raw material, amino alcohol, and an appropriate acid catalyst are added to a reaction vessel and stirred. A suitable solvent may be further added to the reaction vessel. In order to promote the esterification reaction, the reaction solution may be appropriately heated. In addition, since the esterification reaction is a dehydration condensation reaction, the reaction vessel may be appropriately equipped with a water collecting device such as a Dean-Stark trap, and the reaction equilibrium may be shifted in the direction of forming an ester bond to promote the reaction. .
Examples of the acid catalyst that can be used include organic acids, inorganic acids, and mixtures thereof. Examples of inorganic acids include sulfuric acid, concentrated sulfuric acid, nitric acid, concentrated nitric acid, and phosphoric acid. Examples of the organic acid include formic acid and acetic acid.
After the esterification reaction is completed, the reaction solution is filtered to take out the filtrate, and the filtrate is appropriately washed and dried to obtain a carbon material for an air electrode of an air battery containing at least an amino group on the surface. It is done. For washing the filtrate, a low-boiling and polar protic solvent such as methanol and ethanol; a low-boiling and nonpolar solvent such as diethyl ether; a low-boiling and polar aprotic solvent such as acetone; Etc. can be used. Among these, it is preferable to use a protic solvent having a low boiling point and polarity such as methanol and ethanol as an organic solvent for washing.

The mixing ratio of the carbon raw material and the amino compound is preferably adjusted as appropriate according to the amount and type of the linker on the surface of the carbon raw material and the amount and type of the binding functional group contained in the amino compound.
In addition, when using expanded carbon fiber as a carbon raw material and amino alcohol as an amino compound, the ratio of the number of nitrogen atoms to the number of carbon atoms per specific surface area is 2 × 10 ⁻⁵ m ^{−2 to} 7.5 ×. In the case of 10 ⁻³ m ⁻² , for example, the mixing ratio (mass ratio) of the expanded carbon fiber and amino alcohol is expanded carbon fiber: amino alcohol = 20 mass%: 80 mass% to 99 mass%: It is preferable to set it as 1 mass%.

  Thus, the carbon material for an air electrode of the air battery according to the present invention described above can be manufactured by causing an amino compound to act on the carbon raw material and adding an amino group to the surface of the carbon raw material. Moreover, this manufacturing method can manufacture the carbon material for air electrodes of the target air battery in one step by making a carbon raw material and an amino compound react on comparatively simple conditions.

3. Air battery The air battery of the present invention is an air battery comprising at least an air electrode, a negative electrode, and an electrolyte layer interposed between the air electrode and the negative electrode, wherein the air electrode is a carbon for an air electrode of the air battery. Including material.

  An air battery according to one embodiment of the present invention is an air battery in which an electrolyte is interposed between an air positive electrode and a lithium metal or lithium compound negative electrode, and the air positive electrode has a porous three-phase interface site in communication. It is characterized in that an amino group is bonded to an edge carbon atom of the three-phase interface site.

FIG. 1 is a diagram showing an example of a layer configuration of an air battery according to the present invention, and is a diagram schematically showing a cross section cut in a stacking direction. The air battery of the present invention is not necessarily limited to this example.
The air battery 100 is sandwiched between the air electrode 6 including the air electrode layer 2 and the air electrode current collector 4, the negative electrode 7 including the negative electrode active material layer 3 and the negative electrode current collector 5, and the air electrode 6 and the negative electrode 7. An electrolyte layer 1 is provided.
Hereinafter, an air electrode, a negative electrode, an electrolyte layer, and a separator and a battery case that are preferably used for the air battery of the present invention, which constitute the air battery of the present invention, will be described in detail.

  The air electrode used in the present invention includes an air electrode layer, and generally further includes an air electrode current collector and an air electrode lead connected to the air electrode current collector.

  The air electrode layer contains at least the carbon material for an air electrode of the air battery according to the present invention described above. Furthermore, you may contain a catalyst, a binder, etc. as needed.

  The content ratio of the carbon material in the air electrode layer is preferably 10 to 99% by mass and more preferably 20 to 95% by mass when the mass of the entire air electrode layer is 100% by mass. . If the content ratio of the carbon material is too low, the reaction field is reduced, and the battery capacity may be reduced. On the other hand, if the content ratio of the carbon material is too high, the content ratio of the catalyst described later is relatively reduced, and there is a possibility that a sufficient catalyst function cannot be exhibited.

Examples of the catalyst used for the air electrode layer include an oxygen active catalyst. Examples of oxygen active catalysts include, for example, platinum groups such as nickel, palladium and platinum; perovskite oxides containing transition metals such as cobalt, manganese or iron; inorganic compounds containing noble metal oxides such as ruthenium, iridium or palladium A metal coordination organic compound having a porphyrin skeleton or a phthalocyanine skeleton; manganese oxide and the like.
From the viewpoint that the electrode reaction is performed more smoothly, a catalyst may be supported on the carbon material described above.

  Although the said air electrode layer should just contain the said carbon material at least, it is preferable to contain the binder which fixes the said carbon material further. Examples of the binder include rubber resins such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and styrene / butadiene rubber (SBR rubber). Although it does not specifically limit as a content rate of the binder in an air electrode layer, For example, when the mass of the whole air electrode layer is 100 mass%, 1-40 mass%, Especially 1-10 mass% It is preferable that

As a method for producing the air electrode layer, for example, a method of mixing and rolling the air electrode layer raw material containing the carbon material, a slurry is prepared by adding a solvent to the raw material, and an air electrode current collector described later Although the method etc. which apply | coat to a body are mentioned, it is not necessarily limited to these methods. Examples of a method for applying the slurry to the air electrode current collector include known methods such as a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method.
The thickness of the air electrode layer varies depending on the use of the air battery and the like, but is preferably 2 to 500 μm, and more preferably 5 to 300 μm.

The air electrode current collector used in the present invention collects current in the air electrode layer. The material for the air electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, aluminum, iron, titanium, and carbon. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. In particular, in the present invention, the air electrode current collector is preferably mesh-shaped from the viewpoint of excellent current collection efficiency. In this case, usually, a mesh-shaped air electrode current collector is disposed inside the air electrode layer. Furthermore, the air battery of the present invention may include another air electrode current collector (for example, a foil-shaped current collector) that collects electric charges collected by the mesh-shaped air electrode current collector. In the present invention, a battery case to be described later may also have the function of an air electrode current collector.
The thickness of the air electrode current collector is, for example, preferably 10 to 1000 μm, and more preferably 20 to 400 μm.

  The negative electrode used in the present invention preferably includes a negative electrode active material layer containing a negative electrode active material, and generally further includes a negative electrode current collector and a negative electrode lead connected to the negative electrode current collector. In the present invention, the negative electrode may contain lithium metal or a lithium compound.

The negative electrode active material layer used in the present invention contains a negative electrode active material containing at least one selected from the group consisting of metal materials, alloy materials, and carbon materials. Specific examples of metals and alloy materials that can be used for the negative electrode active material include alkali metals such as lithium, sodium, and potassium; group 2 elements such as magnesium and calcium; group 13 elements such as aluminum; zinc, Examples include transition metals such as iron; or alloy materials and compounds containing these metals.
Examples of the alloy containing lithium element include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy. Moreover, as a metal oxide containing a lithium element, lithium titanium oxide etc. can be mentioned, for example. Examples of the metal nitride containing a lithium element include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. In addition, lithium coated with a solid electrolyte can also be used for the negative electrode active material layer.

  The negative electrode active material layer may contain only the negative electrode active material, or may contain at least one of a conductive material and a binder in addition to the negative electrode active material. For example, when the negative electrode active material has a foil shape, a negative electrode active material layer containing only the negative electrode active material can be obtained. On the other hand, when the negative electrode active material is in a powder form, a negative electrode active material layer containing a negative electrode active material and a binder can be obtained. In addition, about the kind and content rate of a binder, it is as above-mentioned.

  The conductive material contained in the negative electrode active material layer is not particularly limited as long as it has conductivity. For example, a carbon material, a perovskite-type conductive material, a porous conductive polymer, a metal porous body, etc. Can be mentioned. The carbon material may have a porous structure or may not have a porous structure. Specific examples of the carbon material having a porous structure include mesoporous carbon. On the other hand, specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon nanotube, and carbon fiber.

  The material for the negative electrode current collector used in the present invention is not particularly limited as long as it has conductivity, and examples thereof include copper, stainless steel, nickel, and carbon. Of these, SUS and Ni are preferably used for the negative electrode current collector. Examples of the shape of the negative electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. In the present invention, a battery case, which will be described later, may have the function of a negative electrode current collector.

The electrolyte layer used in the present invention is held between the air electrode layer and the negative electrode active material layer and functions to exchange metal ions between the air electrode layer and the negative electrode active material layer.
For the electrolyte layer, an electrolytic solution, a gel electrolyte, a solid electrolyte, or the like can be used. These may be used alone or in combination of two or more.

As the electrolytic solution, an aqueous electrolytic solution and a non-aqueous electrolytic solution can be used.
The type of non-aqueous electrolyte is preferably selected as appropriate according to the type of conductive metal ion. For example, as a non-aqueous electrolyte used for a lithium-air battery, a solution containing a lithium salt and a non-aqueous solvent is usually used. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO _4, and LiAsF ₆ ; LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ (Li-TFSA), LiN (SO ₂ C ₂ F ₅ ) Organic lithium salts such as ₂ and LiC (SO ₂ CF ₃ ) ₃ can be mentioned. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl carbonate, butylene carbonate, γ-butyrolactone, and sulfolane. , Acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO) and A mixture thereof can be exemplified. The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 to 3 mol / L.

In this invention, it is preferable to use a highly viscous thing as a non-aqueous electrolyte solution or a non-aqueous solvent. Examples of the highly viscous non-aqueous electrolyte or non-aqueous solvent include ionic liquids. Examples of the ionic liquid include N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) amide (PP13TFSA), N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) amide (P13TFSA), N-butyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) amide (P14TFSA), N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) amide (DEMETFSA) N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) amide (TMPATFSA) and the like.
Among the non-aqueous solvents, in order to advance the oxygen reduction reaction represented by the formula (II) or (III), it is more preferable to use an electrolyte solution that is stable to oxygen radicals. Examples of such non-aqueous solvents include acetonitrile (AcN), 1,2-dimethoxyethane (DME), dimethyl sulfoxide (DMSO), N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) amide ( PP13TFSA), N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) amide (P13TFSA), N-butyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) amide (P14TFSA) and the like.

It is preferable that the type of the aqueous electrolyte is appropriately selected according to the type of the conductive metal ion. For example, as an aqueous electrolyte used for a lithium air battery, a solution containing a lithium salt and water is usually used. Examples of the lithium salt include lithium salts such as LiOH, LiCl, LiNO ₃ , and CH ₃ CO ₂ Li.

The gel electrolyte used in the present invention is usually gelled by adding a polymer to a non-aqueous electrolyte solution. For example, a non-aqueous gel electrolyte of a lithium-air battery is obtained by adding a polymer such as polyethylene oxide (PEO), polyacrylonitrile (PAN), or polymethyl methacrylate (PMMA) to the non-aqueous electrolyte solution described above, and gelling. can get. In the present invention, a LiTFSA (LiN (CF ₃ SO ₂ ) ₂ ) -PEO-based non-aqueous gel electrolyte is preferable.

As the solid electrolyte, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer electrolyte, or the like can be used.
Specific examples of the sulfide-based solid electrolyte include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₃ , Li ₂ S—P ₂ S ₃ —P ₂ S ₅ , and Li ₂ S—SiS. _{2, Li 2 S-Si 2} S, Li 2 S-B 2 S 3, Li 2 S-GeS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 S-SiS 2 -P 2 S 5 _{, Li 2 S-SiS 2 -Li} 4 SiO 4, Li 2 S-SiS 2 -Li 3 PO 4, Li 3 PS 4 -Li 4 GeS 4, Li 3.4 P 0.6 Si 0.4 S 4, Examples include Li _3.25 P _0.25 Ge _0.76 S ₄ , Li _4-x Ge _1-x P _x S _{4, and the} like.
Specifically, as the oxide-based solid electrolyte, LiPON (lithium phosphate oxynitride), Li _1.3 Al _0.3 Ti _0.7 (PO ₄ ) ₃ , La _0.51 Li _0.34 TiO Examples include _0.74 , Li ₃ PO ₄ , Li ₂ SiO ₂ , Li ₂ SiO _{4 and the} like.
The polymer electrolyte is preferably selected as appropriate depending on the type of metal ion to be conducted. For example, a polymer electrolyte of a lithium air battery usually contains a lithium salt and a polymer. As the lithium salt, at least one of the above-described inorganic lithium salt and organic lithium salt can be used. The polymer is not particularly limited as long as it forms a complex with a lithium salt, and examples thereof include polyethylene oxide.

The air battery of the present invention may include a separator between the air electrode and the negative electrode. Examples of the separator include porous membranes such as polyethylene and polypropylene; and nonwoven fabrics made of resin such as polypropylene and nonwoven fabrics such as glass fiber nonwoven fabric.
These materials that can be used for the separator can also be used as a support material for the electrolytic solution by impregnating the above-described electrolytic solution.

The air battery of the present invention usually includes a battery case that houses an air electrode, a negative electrode, an electrolyte layer, and the like. Specific examples of the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminate type. The battery case may be an open-air battery case or a sealed battery case. An open-air battery case is a battery case having a structure in which at least the air electrode layer can sufficiently come into contact with the atmosphere. On the other hand, when the battery case is a sealed battery case, it is preferable that a gas (air) introduction pipe and an exhaust pipe are provided in the sealed battery case. In this case, the gas to be introduced and exhausted preferably has a high oxygen concentration, and more preferably is dry air or pure oxygen. In addition, it is preferable to increase the oxygen concentration during discharging and decrease the oxygen concentration during charging.
An oxygen permeable film or a water repellent film may be provided in the battery case according to the structure of the battery case.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited only to these examples.

1. Production of expanded carbon fiber [Example 1]
1-1. Electrochemical treatment A pitch-based carbon fiber was fixed to the tips of both platinum electrodes, immersed in a concentrated nitric acid electrolyte, and subjected to constant-current electrochemical treatment to synthesize a nitric acid-graphite intercalation compound.
FIG. 5 is a schematic diagram of a constant current electrochemical treatment apparatus. The constant current electrochemical treatment apparatus 200 used in the present invention includes a potentiostat / galvanostat (manufactured by Solartron, model 1287) and an electrochemical cell.
The outline of the electrochemical cell is as follows. A reaction vessel 11 having a volume of 300 mL is equipped with a platinum plate 12 and a platinum plate 13 (length 50 mm × width 10 mm × thickness 0.2 mm) as electrodes, and a lower end of the anode (working electrode) platinum plate 12 is 5 cm long. Pitch-based carbon fibers 14 (manufactured by Nippon Graphite Fiber Co., Ltd., product name “YS-95”, fiber diameter: 5 μm, mass: 0.1 g) were fixed with tape. As a reference electrode, a silver / silver chloride electrode 15 was attached in the vicinity of the anode. In order that the pitch-based carbon fiber 14 was sufficiently crushed, 100 mL of 13 mol / dm ³ nitric acid (16 in FIG. 5) was added as an electrolytic solution.
The electrochemical cell platinum plate 12, platinum plate 13, and silver / silver chloride electrode 15 are all connected to a potentiostat / galvanostat, and the electric current applied to the pitch-based carbon fiber 14 reaches 2,400C. A constant current was applied at a density of 10 A / g to synthesize a nitric acid-graphite intercalation compound.

1-2. Washing The obtained nitric acid-graphite intercalation compound was taken out of the electrochemical cell, and the nitric acid-graphite intercalation compound was repeatedly washed with a sufficient amount of water in order to remove the nitric acid adhering to the surface of the nitric acid-graphite intercalation compound. Thereafter, the nitric acid-graphite intercalation compound was dehydrated and dried in a desiccator for 24 hours.

1-3. Carbonization treatment The nitric acid-graphite intercalation compound after drying was decomposed by a heat treatment to expand the carbon fiber. Specifically, the nitric acid-graphite intercalation compound after drying is inserted into an electric furnace and subjected to rapid heating treatment at 1,000 ° C. for 5 seconds in the air, thereby expanding and expanding the carbon atomic layer. Carbonized fiber was prepared.

1-4. Addition of Amino Group to Expanded Carbon Fiber An amino group was added to the expanded carbon fiber by Fischer's esterification reaction. This reaction is an esterification reaction between a carboxyl group mainly having an edge carbon atom in the expanded carbon fiber and a hydroxyl group of ethanolamine by allowing ethanolamine to act on the expanded carbon fiber. In a reaction vessel, 0.2 g of expanded carbon fiber obtained through a carbonization treatment, 0.4 mL of ethanolamine (manufactured by Kishida Chemical Co., Ltd., purity 99.0% or more), p-toluenesulfonic acid (Kishida) as an acid catalyst Chemical Co., Ltd. (purity 99.0% or more) 1.5 g, toluene (Kishida Chemical Co., Ltd., purity 99.0% or more) 200 mL was added as a solvent, and a stirrer chip was further added. A Dean-Stark trap and a condenser were connected to the reaction vessel, and the reaction solution was stirred at about 110 ° C. for 9 hours and reacted while refluxing. Then, after filtering the reaction solution and obtaining the solid of a filtrate, washing | cleaning was repeated using the saturated sodium hydrogencarbonate aqueous solution and distilled water suitably about the solid of the said filtrate. The solid after the washing is further washed with methanol and then dried in a vacuum for 15 hours, and the carbon material for an air electrode of the air battery of Example 1 (hereinafter referred to as the expanded carbon fiber aminated product of Example 1) Was made.

[Example 2]
In the same manner as in Example 1, electrochemical treatment, washing, and carbonization treatment were performed to produce expanded carbon fibers. In addition of the amino group to the expanded carbon fiber in Example 1, the amino group was added to the expanded carbon fiber in the same manner as in Example 1 except that the addition amount of ethanolamine was changed from 0.4 mL to 2.0 μL. The carbon material for an air electrode of the air battery of Example 2 (hereinafter, sometimes referred to as an expanded carbon fiber aminated product of Example 2) was produced.

[Comparative Example 1]
In the same manner as in Example 1, electrochemical treatment, washing, and carbonization treatment were performed to produce expanded carbon fibers. In addition of the amino group to the expanded carbon fiber in Example 1, the amino group was added to the expanded carbon fiber in the same manner as in Example 1 except that the addition amount of ethanolamine was changed from 0.4 mL to 0.8 mL. The carbon material for an air electrode of the air battery of Comparative Example 1 (hereinafter, sometimes referred to as an expanded carbon fiber aminated product of Comparative Example 1) was prepared.

[Comparative Example 2]
In the same manner as in Example 1, electrochemical treatment, washing, and carbonization treatment were performed to produce expanded carbon fibers. In addition of the amino group to the expanded carbon fiber in Example 1, the amino group was added to the expanded carbon fiber in the same manner as in Example 1 except that the addition amount of ethanolamine was changed from 0.4 mL to 0.5 μL. The carbon material for an air electrode of the air battery of Comparative Example 2 (hereinafter, sometimes referred to as an expanded carbon fiber aminated product of Comparative Example 2) was prepared.

[Comparative Example 3]
In the same manner as in Example 1, electrochemical treatment, cleaning, and carbonization treatment were performed, and the carbon material for the air electrode of the air battery of Comparative Example 3 (hereinafter sometimes referred to as expanded carbon fiber of Comparative Example 3). Was made. That is, in Comparative Example 3, no amino group was added to the expanded carbon fiber.

[Reference Example 1]
A 500 mL reaction vessel equipped with a Liebig condenser was installed in the oil bath. 200 mL of a 8 mol / L KOH aqueous solution was added to the reaction vessel, 5 g of a carbon material was added, and the mixture was stirred with a magnetic stirrer. The temperature of the oil bath was set to 80 ° C., and cooling water was allowed to flow through the Liebig condenser, whereby the alkaline aqueous solution was refluxed for 6 hours, and the alkali activation treatment was performed on the carbon material. A carbon material for an air electrode was produced.

2. 2. Evaluation of carbon material 2-1. SEM Observation of Carbon Material The expanded carbon fiber aminated product of Example 1 and ketjen black (Ketjen-EC600JD; hereinafter may be referred to as the air electrode carbon material of the air battery of Comparative Example 4) are described below. Under the conditions, a scanning electron microscope (hereinafter referred to as SEM) was observed. That is, using a scanning electron microscope (Hitachi, S-5500), SEM observation was performed at an acceleration voltage of 10 kV or 3 kV and a magnification of 500 to 10,000 times.
6A is an SEM image at a magnification of 500 times of the carbon material for the air electrode of the air battery of Comparative Example 4. FIG. As can be seen from FIG. 6, the air electrode carbon material of the air battery of Comparative Example 4 has a very fine chemical structure. On the other hand, FIG. 3A is an SEM image of the expanded carbon fiber aminated product of Example 1 at a magnification of 5,000. As can be seen from FIG. 3A, the expanded carbon fiber aminated product of Example 1 is a flaky solid having a major axis of 1 to 10 μm, a minor axis of 0.5 to 5 μm, and an aspect ratio of 2 to 9. .

2-2. Measurement of the number concentration ratio per specific surface area Example 1-Example 2 and Comparative Example 1-Expanded carbon fiber aminated product of Comparative Example 2, expanded carbon fiber of Comparative Example 3, and air battery of Comparative Example 4 For the air electrode carbon material, the ratio of the nitrogen atom number concentration to the carbon atom number concentration per specific surface area was measured.
Using an X-ray photoelectron spectrometer (manufactured by ULVAC-PHI, product number: PHI5700), X-ray photoelectron spectroscopy was performed in accordance with JIS K0167, and the carbon atom number concentration and the nitrogen atom number concentration were measured. Moreover, the BET method was performed based on JISZ8830 using the gas adsorption amount measuring apparatus (Bell Japan, product number: Belsorb max), and the specific surface area of the carbon material was measured.
The measured nitrogen atom number concentration was divided by the carbon atom concentration, and the ratio of the nitrogen atom concentration to the carbon atom concentration was calculated. Furthermore, the ratio of the nitrogen atom number concentration to the carbon atom number concentration per specific surface area was calculated by dividing the ratio of the calculated nitrogen atom number concentration to the carbon atom number concentration by the specific surface area of the carbon material.

3. Production of air electrode [Example 3]
First, the expanded carbon fiber aminated product of Example 1 and the PTFE binder (manufactured by Daikin) were mixed at a ratio of expanded carbon fiber aminated product: PTFE = 90% by mass: 10% by mass, and further added to the mixture as a solvent. A predetermined amount of ethanol was added. Next, the mixture was rolled by a roll press and pre-dried under a temperature condition of 60 ° C. and a vacuum condition. Subsequently, the dried mixture was appropriately cut out, and further finally dried under a temperature condition of 120 ° C. and a vacuum condition, whereby an air electrode of Example 3 was produced.

[Example 4]
In Example 3, in place of the expanded carbon fiber aminated product of Example 1, the expanded carbon fiber aminated product of Example 2 was used, except that the materials were mixed, pre-dried and cut out in the same manner as in Example 3. Then, final drying was performed to produce the air electrode of Example 4.

[Comparative Example 5]
In Example 3, in place of the expanded carbon fiber aminated product of Example 1, the expanded carbon fiber aminated product of Comparative Example 1 was used, except that the materials were mixed, pre-dried, and cut out in the same manner as in Example 3. Then, final drying was performed to produce an air electrode of Comparative Example 5.

[Comparative Example 6]
In Example 3, in place of the expanded carbon fiber aminated product of Example 1, the expanded carbon fiber aminated product of Comparative Example 2 was used except that the material was mixed, pre-dried, and cut out in the same manner as in Example 3. Then, final drying was performed to produce an air electrode of Comparative Example 6.

[Comparative Example 7]
In Example 3, in place of the expanded carbon fiber aminated product of Example 1, the expanded carbon fiber of Comparative Example 3 was used, except that the materials were mixed, pre-dried, cut out, and finally, as in Example 3. It dried and produced the air electrode of the comparative example 7.

[Comparative Example 8]
In Example 3, in place of the expanded carbon fiber aminated product of Example 1, the carbon material for the air electrode of the air battery of Comparative Example 4 was used, and the materials were mixed and pre-dried in the same manner as in Example 3. Then, cutting and final drying were performed to produce an air electrode of Comparative Example 8.

4). Preparation of air battery [Example 5]
The air electrode of Example 3 was used as the air electrode.
As an electrolytic solution, N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) amide (manufactured by Kanto Chemical Co., PP13TFSA), lithium bis (trifluoromethanesulfonyl) amide (manufactured by Kishida Chemical Co., Ltd.) at 0.32 mol / Dissolved to a concentration of kg and prepared by stirring and mixing overnight under an argon atmosphere. In addition, a polypropylene nonwoven fabric (JH1004N) was prepared as a separator.
Metal lithium (manufactured by Kyokuto Metal, thickness: 200 μm, φ15 mm) was prepared as the negative electrode.
An F-type cell (made by Hokuto Denko) was prepared as a battery case.

Each member is housed in the battery case so as to be laminated in the order of metallic lithium, a separator impregnated with an electrolytic solution, and an air electrode containing an expanded carbon fiber amination from the bottom of the battery case. Was made. Furthermore, the entire battery case was housed in a 500 mL glass desiccator with a gas replacement cock so that the atmosphere inside the battery case could be controlled.
All the above steps were performed in a glove box under a nitrogen atmosphere.

[Example 6]
In Example 5, the air battery of Example 6 was produced using the same member as Example 5 except that the air electrode of Example 4 was used instead of the air electrode of Example 3.

[Comparative Example 9]
In Example 5, an air battery of Comparative Example 9 was produced using the same members as in Example 5 except that the air electrode of Comparative Example 5 was used instead of the air electrode of Example 3.

[Comparative Example 10]
In Example 5, an air battery of Comparative Example 10 was produced using the same members as in Example 5 except that the air electrode of Comparative Example 6 was used instead of the air electrode of Example 3.

[Comparative Example 11]
In Example 5, an air battery of Comparative Example 11 was produced using the same members as in Example 5 except that the air electrode of Comparative Example 7 was used instead of the air electrode of Example 3.

[Comparative Example 12]
In Example 5, an air battery of Comparative Example 12 was produced using the same members as in Example 5 except that the air electrode of Comparative Example 8 was used instead of the air electrode of Example 3.

5. Charge / Discharge Test of Air Battery The charge / discharge test was performed on the air batteries of Example 5 to Example 6 and Comparative Example 9 to Comparative Example 12, and the charge capacity and reaction resistance were measured.
First, each air battery was left under a temperature condition of 60 ° C. for 3 hours. Then, using a charge / discharge test apparatus (manufactured by Nagano, BTS2004H), while supplying pure oxygen (Taiyo Nippon Sanso, 99.9%) to the air electrode layer of each air battery, A charge / discharge test was conducted under the conditions of a current density of 0.05 mA / cm ² , a discharge start voltage of 2.0 V, and a charge start voltage of 3.8 V, and the charge capacity was measured.

6). SEM observation of carbon material after charge / discharge test About the air battery of Example 5 and Comparative Example 12 after the charge / discharge test, the carbon material was taken out from the air electrode and subjected to SEM observation under the following conditions. That is, using a scanning electron microscope (Hitachi, S-5500), SEM observation was performed at an acceleration voltage of 10 kV or 3 kV and a magnification of 500 to 10,000 times.
FIG. 6B is an SEM image at a magnification of 5,000 times of the carbon material contained in the air electrode layer of the air battery of Comparative Example 12 after discharge. White arrows in FIG. 6 (b) shows the discharge precipitate _(Li 2 _{O 2} solid, Li ₂ O solid, or solid mixtures thereof). As can be seen from FIG. 6B, discharge deposits having a major axis of about 2 to 4 μm are deposited on the surface of the carbon material in the air battery of Comparative Example 12 after discharge. On the other hand, FIG. 3B is an SEM image at a magnification of 10,000 times of the expanded carbon fiber amination contained in the air electrode layer of the air battery of Example 5 after discharge. As can be seen from FIG. 3B, a very small discharge deposit having a major axis of less than about 1 μm is deposited on the surface of the expanded carbon fiber aminated product in the air battery of Example 5 after discharge.

7). Summary of Evaluation FIG. 4 shows the charge capacity of the air cells of Example 5 to Example 6 and Comparative Example 9 to Comparative Example 12, and carbon atoms per specific surface area in the carbon material used in these air cells. 3 is a graph showing the relationship of the ratio of the number concentration of nitrogen atoms to the number concentration (hereinafter sometimes referred to as the N / C ratio per specific surface area). FIG. 4 is a graph in which the vertical axis represents the charge capacity (mAh / g) and the horizontal axis represents the N / C ratio per specific surface area (10 ⁻³ m ⁻² ). In FIG. 4, the black circle plot is a plot showing the result of using expanded carbon fiber or an aminated product thereof as the carbon material, and the black triangle plot is the result of using ketjen black as the carbon material. It is a plot.
As can be seen from FIG. 4, the charge capacity of the air battery of Comparative Example 12 using ketjen black for the air electrode is 600 mAh / g, and the N / C ratio per specific surface area is 0.5 × 10 ⁻³ m ^{−. 2} .
On the other hand, as can be seen from FIG. 4, the charge capacity of the air battery of Example 5 using the expanded carbon fiber aminated product of Example 1 for the air electrode is 1,826 mAh / g, and N / C per specific surface area. The ratio is 3.8 × 10 ⁻³ m ⁻² . Moreover, the charge capacity of the air battery of Example 6 using the expanded carbon fiber amination product of Example 2 for the air electrode is 1,130 mAh / g, and the N / C ratio per specific surface area is 1.6 × 10 6. ^-3 m ^-2 .
The air battery of Comparative Example 12 using a conventional carbon material has a charge capacity of 600 mAh / g, whereas Example 5-Example using an expanded carbon fiber aminated product (Example 1-Example 2). As for the air battery of Example 6, all charge capacity exceeds 1,000 mAh / g. In particular, the air battery of Example 5 using the expanded carbon fiber aminated product (Example 1) having an N / C ratio per specific surface area of 3.8 × 10 ⁻³ m ⁻² is the air of Comparative Example 12. It has a charge capacity that is more than three times that of a battery. Therefore, compared with the air battery of Comparative Example 12 using a conventional carbon material, the air batteries of Examples 5 and 6 use the expanded carbon fiber amination product having an appropriate atomic number concentration ratio for the air electrode. It can be seen that the charging capacity has improved.

On the other hand, the charge capacity of the air battery of Comparative Example 10 using the expanded carbon fiber aminated product of Comparative Example 2 for the air electrode is 832 mAh / g, and the N / C ratio per specific surface area is 2 × 10 ^−5. m- ² . Further, the charge capacity of the air battery of Comparative Example 11 using the expanded carbon fiber of Comparative Example 3 for the air electrode is 375 mAh / g, and the N / C ratio per specific surface area is 1 × 10 ⁻⁵ m ⁻² . is there.
Thus, the charge capacity of the air battery of Comparative Example 10 using the expanded carbon fiber aminated product (Comparative Example 2) having an N / C ratio per specific surface area of 2 × 10 ⁻⁵ m ⁻² is 1,000 mAh. / G. Moreover, the charge capacity of the air battery of Comparative Example 11 using the expanded carbon fiber (Comparative Example 3) is lower than the charge capacity of the air battery of Comparative Example 12 using a conventional carbon material. These results indicate that when the N / C ratio per specific surface area is 0 or too low, the charging capacity is reduced because the starting point of the oxygen reduction reaction is too small.

Moreover, the charge capacity of the air battery of Comparative Example 9 using the expanded carbon fiber aminated product of Comparative Example 1 for the air electrode is 320 mAh / g, and the N / C ratio per specific surface area is 7.6 × 10 ^−3. m- ² .
Thus, the charge capacity of the air battery of Comparative Example 9 using the expanded carbon fiber aminated product (Comparative Example 1) having an N / C ratio per specific surface area of 7.6 × 10 ⁻³ m ⁻² is It is lower than the charge capacity of the air battery of Comparative Example 12 using a conventional carbon material. This result shows that when the N / C ratio per specific surface area is too high, the lithium oxide, which is a discharge deposit, has a high polarity. This indicates that the charge capacity is reduced as a result of clogging the pores and insufficient decomposition of the discharge deposits during charging.
Moreover, as shown in FIG. 4, the approximate curve represented by the following formula | equation (A) is derived from the data of Example 5- Example 6 and Comparative Example 9-Comparative Example 11.
y = −86.3x ² + 629x + 550 Formula (A)
(In the above formula (A), y represents the charge capacity (mAh / g), and x represents the N / C ratio per specific surface area (10 ⁻³ m ⁻² ).)
From the above formula (A), the expanded carbon fiber aminated product having an N / C ratio per specific surface area of 1 × 10 ⁻⁵ m ^{−2 to} 7.6 × 10 ⁻³ m ⁻² is theoretically defined as an air electrode. As a result, an air battery capable of exhibiting a higher charge capacity than an air battery using a conventional carbon material is produced.

FIG. 6A, which is an SEM image of a carbon material before charging / discharging, and FIG. 6B, which is an SEM image of a carbon material after discharge, are compared for an air battery using a conventional carbon material. It can be seen that coarse discharge deposits having a major axis of about 2 to 4 μm are deposited on the later carbon material surface.
On the other hand, about the air battery using the carbon material which concerns on this invention, Fig.3 (a) which is a SEM image of the carbon material before charging / discharging, and FIG.3 (b) which is the SEM image of the carbon material after discharge are shown. By comparison, it can be seen that very minute discharge deposits having a major axis of less than about 1 μm are deposited on the surface of the carbon material after discharge.
From these results, on the surface of a conventional carbon material containing no amino group, coarse discharge deposits that are difficult to be decomposed during charging and difficult to be reduced to lithium ions are generated after discharge. Therefore, it is considered that the charge capacity is reduced as a result of coarse discharge deposits being accumulated on the surface of the air electrode at every discharge.
On the other hand, on the surface of the carbon material according to the present invention containing an amino group, minute discharge deposits that are relatively easily decomposed during charging and easily reduced to lithium ions are generated after discharging. For this reason, it is considered that discharge deposits are easily eliminated during charging, and as a result, a charge capacity comparable to that of an unused carbon material can be maintained.

DESCRIPTION OF SYMBOLS 1 Electrolyte layer 2 Air electrode layer 3 Negative electrode active material layer 4 Air electrode current collector 5 Negative electrode current collector 6 Air electrode 7 Negative electrode 11 Container 12 Platinum plate of anode (working electrode) 13 Platinum plate of cathode (counter electrode) Pitch system Carbon fiber 15 Silver / silver chloride electrode 16 13 mol / dm ³ Nitric acid 100 Air battery 200 Constant current electrochemical treatment device

Claims (12)

A carbon material used for an air electrode of an air battery,
The carbon material for an air electrode of an air battery, wherein the carbon material contains an amino group at least on a surface thereof. 2. The air of the air battery according to claim 1, wherein a ratio of a nitrogen atom number concentration to a carbon atom number concentration per specific surface area is 2 × 10 ⁻⁵ m ^{−2 to} 7.5 × 10 ⁻³ m ^−2. Carbon material for poles. An air battery comprising at least an air electrode, a negative electrode, and an electrolyte layer interposed between the air electrode and the negative electrode,
An air battery, wherein the air electrode includes the carbon material for an air electrode of the air battery according to claim 1 or 2.   The air battery according to claim 3, wherein the negative electrode contains lithium metal or a lithium compound. At least one linker selected from the group consisting of a functional group itself serving as a linker and a group having a functional group serving as the linker is bonded by a chemical reaction with the carbon raw material containing at least the surface and the functional group serving as the linker. A preparation step of preparing an amino compound containing a bond-forming functional group and an amino group to be formed; and
By causing the amino compound to act on the carbon raw material, the linker contained in the carbon raw material and the bond-forming functional group contained in the amino compound cause a chemical reaction, whereby the carbon raw material and the amino compound And a synthesis step of synthesizing a carbon material for an air electrode of an air battery containing an amino group at least on the surface thereof. A method for producing a carbon material for an air electrode of an air battery, comprising: Wherein the _{linker, -W-CO 2 H, -W} -CO 2 R, -W-OH, -W-OR, -W-CHO, and -W-OCOR (although, W is a divalent organic group or a single And R represents at least one functional group selected from the group consisting of an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms). Item 6. A method for producing a carbon material for an air electrode of an air battery according to Item 5. The bond forming functional _{group, -Z-OH, -Z-OR} , -Z-CHO, -Z-CO 2 H, -Z-CO 2 R, -Z-OCOR, -Z-X, and -Z- NH ₂ (wherein Z represents a divalent organic group or a single bond, and R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, and X represents at least one functional group selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). A method for producing a carbon material for an air electrode of an air battery according to 5 or 6. An air battery having an electrolyte interposed between an air positive electrode and a lithium metal or lithium compound negative electrode,
The air positive electrode includes a porous carbon fiber material having three-phase interface sites in communication with each other, and an amino group is bonded to an edge carbon atom of the three-phase interface site. . The ratio of the nitrogen atom number concentration with respect to the carbon atom number concentration per specific surface area in the carbon fiber material is 2 × 10 ⁻⁵ m ^{−2 to} 7.5 × 10 ⁻³ m ^−2. Air battery.   By using a porous carbon fiber material having a three-phase interface site in communication as a raw material, by chemically reacting the linker functional group on the edge carbon atom at the three-phase interface site and the bond-forming functional group contained in the amino compound, A method for producing an air cathode, wherein an amino group is bonded to the edge carbon atom. Linker functional groups on the edge carbon _{atoms, -W-CO 2 H, -W} -CO 2 R, -W-OH, -W-OR, -W-CHO, and -W-OCOR (although, W is Represents a divalent organic group or a single bond, and R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms). The manufacturing method of the air positive electrode of Claim 10 which is two functional groups. The bond forming functional _{group, -Z-OH, -Z-OR} , -Z-CHO, -Z-CO 2 H, -Z-CO 2 R, -Z-OCOR, -Z-X, and -Z- NH ₂ (wherein Z represents a divalent organic group or a single bond, and R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, and X represents at least one functional group selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The manufacturing method of the air positive electrode of 10 or 11.