Carbon structure, air battery, and method for producing carbon structure

Abstract

Provided is a carbon structure for a positive electrode of an air battery, the carbon structure including carbon nanotubes as a carbon material, the carbon nanotubes having an average diameter of 1 nm to 10 nm, an average length of 1 [mu] m to 100 [mu] m, and an aspect ratio of 1000 to 10000.

Description

Technical Field

[0001] The present invention relates to a carbon structure used in a positive electrode of an air battery, an air battery using the carbon structure, and a method for manufacturing the carbon structure. Background Art

[0002] Batteries have attracted attention as a driving force for supporting a smart society, and the demand for them has been growing rapidly. There are various types of batteries. Among them, air batteries have received high attention because they are small, lightweight, and suitable for a large-capacity structure.

[0003] 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, and is also called a metal-air battery, which is a type of fuel cell. As a representative example, there is a lithium-air battery that uses a metal or compound capable of occluding and releasing lithium ions as a negative electrode active material. In a lithium-air battery, the reactions at each electrode are represented by the following formulas.

[0004] Negative electrode:

[0005] Positive electrode:

[0006] In an air battery, the positive electrode active material is oxygen, and the positive electrode has a function of absorbing and discharging oxygen in the air in cooperation with charge and discharge. Therefore, for the carbon structure used in the positive electrode, a structure that can inhale a large amount of oxygen from the air is required. That is, high air or oxygen permeability is required for the carbon structure for the positive electrode.

[0007] In addition, in order to improve the output and capacity of a single lithium-air battery, for the carbon structure used in the positive electrode, high ion transport efficiency and a wide reaction field are required, which are characteristics generally required for batteries.

[0008] Furthermore, in order to make an air battery small and lightweight and reduce costs, the carbon structure for the positive electrode is preferably self-supporting.

[0009] Under such circumstances, Patent Document 1 proposes a lithium-air battery using the following positive electrode layer, in which the first pore volume ratio of pores having a pore diameter of 1 nm or more and 200 nm or less is larger than the second pore volume of pores having a pore diameter of more than 200 nm and 1000 nm or less.

[0010] In Patent Document 1, as a method for forming a positive electrode layer, the following methods are described: a method of coating a composition containing a conductive porous body, a binder, etc. dispersed in a solvent on a positive electrode current collector, for example, by a doctor blade method; or a method of molding the above composition by press bonding; and so on. In addition, as the current collector, stainless steel, nickel, aluminum, carbon, etc. can be exemplified, and as its shape, foil shape, plate shape, mesh shape, etc. can be exemplified, and it is described that a mesh shape is particularly preferred.

[0011] In Patent Document 2, a proposal is made to use a carbon structure body having a specific pore structure and physical properties and having self-supporting properties as the positive electrode of an air battery. The carbon structure body described in Patent Document 2 has a high pore volume and can be self-supporting.

[0012] Prior Art Documents

[0013] Patent Documents

[0014] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-133168

[0015] Patent Document 2: International Publication No. 2020 / 235638 Summary of the Invention

[0016] Problems to be Solved by the Invention

[0017] The positive electrode layer described in Patent Document 1 includes a current collector. In the positive electrode layer described in Patent Document 1, the current collector can hold a composition containing a conductive porous body, a binder, etc. However, the current collector does not function as a generation field where lithium ions, oxygen, and electrons react to generate lithium peroxide during the discharge process. Therefore, when aiming for the light weight of the battery, a positive electrode structure that does not require a current collector is preferred.

[0018] The carbon structure body described in Patent Document 2 has self-supporting properties and shows a large discharge capacity due to the high pore capacity of the carbon structure body when used as the positive electrode of an air battery. However, in order to maintain the shape of the carbon structure body, it is necessary to contain carbon fiber as a reinforcing material.

[0019] Carbon fiber as a reinforcing material helps to maintain the shape of the carbon structure body, but carbon fiber itself does not contribute to the generation field where lithium ions, oxygen, and electrons react to generate lithium peroxide during the discharge process. Therefore, by containing carbon fiber, the discharge capacity of the air battery decreases with its content.

[0020] In addition, the carbon structure described in Patent Document 2 is manufactured by carbonization in an oxidizing gas atmosphere. Specifically, it is manufactured by carbonization at a temperature in the range of 350°C to 3000°C in an oxidizing gas atmosphere with an oxygen concentration of 0.03% or more and less than 5%. Carbonization in an oxidizing gas atmosphere requires fine control of the oxygen concentration and temperature, and it is not easy to manufacture the carbon structure described in Patent Document 2. In addition, carbonization in an oxidizing gas atmosphere requires oxidation-resistant equipment, and the manufacturing cost also increases.

[0021] It should be noted that Patent Document 2 shows that, in the examples, the carbon structure carbonized in an oxidizing gas atmosphere exhibits a high discharge capacity. On the other hand, the carbon structure that was not carbonized in an oxidizing gas atmosphere but only carbonized in an inert atmosphere remained at a low capacity.

[0022] The present invention has been completed in view of the above circumstances, and its object is to provide a carbon structure for a positive electrode of an air battery, which can maintain its shape and has self-supportability even without containing a current collector and carbon fibers as a reinforcing material, and can also realize an air battery that exhibits a large discharge capacity even without undergoing a carbonization process in an oxidizing gas atmosphere.

[0023] Means for Solving the Problem

[0024] The inventors of the present invention conducted in-depth research to solve the above problems. And it was found that by using a carbon material having carbon nanotubes with specific physical properties as a raw material, the shape can be maintained, self-supportability can be achieved, and even without undergoing a carbonization process in an oxidizing gas atmosphere, a carbon structure capable of realizing an air battery that exhibits a high capacity can be obtained, thus completing the present invention.

[0025] That is, the present invention includes the following aspects. [1]

[0027] A carbon structure, which is a carbon structure for a positive electrode of an air battery, wherein,

[0028] The above carbon structure contains carbon nanotubes as a carbon material,

[0029] The average diameter of the above carbon nanotubes is 1 nm or more and 10 nm or less, the average length is 1 μm or more and 100 μm or less, and the aspect ratio is 1000 or more and 10000 or less. [2]

[0031] The carbon structure as described in aspect [1], which is composed only of the above carbon material and carbon derived from a binder polymer that binds the carbon materials to each other. [3]

[0033] The carbon structure as described in Method [1] or [2], wherein,

[0034] (a) The pore volume of pores with a diameter of 1 nm or more and 1000 nm or less based on the nitrogen adsorption method is 1.0 cm 3 / g or more and 3.0 cm 3 / g or less,

[0035] (b) The pore volume of pores with a diameter of 1 nm or more and 200 nm or less based on the nitrogen adsorption method is 1.0 cm 3 / g or more and 2.3 cm 3 / g or less,

[0036] (c) The pore volume of pores with a diameter of 200 nm or more and 10000 nm or less based on the mercury intrusion method is 1.0 cm 3 / g or more and 3.3 cm 3 / g or less,

[0037] (d) The external specific surface area of the t-curve based on the nitrogen adsorption method is 100 m 2 / g or more and 300 m 2 / g or less,

[0038] (e) The apparent density is 0.15 g / cm 3 or more and 0.30 g / cm 3 or less,

[0039] (f) The porosity is 70% or more and 90% or less. [4]

[0041] The carbon structure as described in any one of Methods [1] to [3], which has self-supporting properties. [5]

[0043] A positive electrode for an air battery, which contains the carbon structure as described in any one of Methods [1] to [4]. [6]

[0045] An air battery, which comprises:

[0046] The positive electrode for an air battery as described in Method [5],

[0047] a negative electrode, and

[0048] an electrolytic solution existing between the positive electrode for an air battery and the negative electrode. [7]

[0050] The air battery as described in Method [6], wherein the negative electrode contains lithium metal. [8]

[0052] The manufacturing method of the carbon structure according to any one of the methods [2] to [4], comprising:

[0053] Preparing a binder slurry containing the above carbon material and the above binder polymer;

[0054] Molding the above binder slurry to obtain a binder molded body;

[0055] Immersing the above binder molded body in a solvent having a low solubility for the above binder polymer to obtain a porous structure;

[0056] Drying the above porous structure to obtain a carbon structure precursor; and

[0057] Carbonizing the above carbon structure precursor in an inert atmosphere to obtain a carbon structure. [9]

[0059] The manufacturing method of the carbon structure according to the method [8], wherein the temperature of the above carbonization treatment is in the range of 500°C or more and 3000°C or less.

[10]

[0061] The manufacturing method of the carbon structure according to the method [8] or [9], wherein

[0062] The method further includes: after drying the above porous structure to obtain the above carbon structure precursor and before performing the above carbonization treatment, performing an infusibilization treatment on the above carbon structure precursor to obtain an infusibilized carbon structure,

[0063] Performing the above carbonization treatment on the above infusibilized carbon structure.

[0064] Effects of the Invention

[0065] In the carbon structure of the present invention, only the material obtained by carbonizing the carbon material and the binder polymer can maintain its shape and has self-supporting properties. In the carbon structure of the present invention, current collectors, reinforcing materials such as carbon fibers, which are used to maintain the shape, are not necessary. Therefore, it is possible to reduce the area that does not contribute to the charge-discharge reaction field, that is, the area that does not contribute to the discharge capacity. Therefore, it is possible to increase the discharge capacity of each carbon structure, and it is possible to provide a small and lightweight air battery with a large discharge capacity.

[0066] In addition, although the carbon structure of the present invention is manufactured without undergoing a carbonization process in an oxidizing gas atmosphere, it is still possible to realize an air battery with a high discharge capacity. Therefore, when realizing an air battery with a high discharge capacity, the carbon structure of the present invention is easier to produce and can reduce the manufacturing cost compared with the carbon structure obtained by carbonization treatment in an oxidizing gas atmosphere. Description of the Drawings

[0067] Figure 1 is a flowchart showing the manufacturing process of the carbon structure of the present invention.

[0068] Figure 2 is a schematic cross-sectional view of an air battery according to an embodiment of the present invention.

[0069] Figure 3 is a schematic cross-sectional view of an air battery according to another embodiment of the present invention.

[0070] Figure 4 is a schematic cross-sectional view of an air battery according to another embodiment of the present invention.

[0071] Figure 5 is a schematic cross-sectional view of a button battery fabricated in Examples and Comparative Examples. Detailed Embodiments

[0072] Embodiments of the present invention will be described below with reference to the accompanying drawings. The same elements are denoted by the same reference numerals, and their descriptions are omitted. It should be noted that the present invention is not limited to these embodiments.

[0073] 《Carbon Structure》

[0074] The carbon structure of the present invention is a carbon structure for a positive electrode of an air battery and includes carbon nanotubes as a carbon material. The carbon structure of the present invention is a carbon structure having self-supporting properties or capable of being self-supporting, and can form a positive electrode structure of an air battery by itself alone.

[0075] In the present invention, "having self-supporting properties or capable of being self-supporting" means a film-like structure (which may also be referred to as a "self-supporting film" in this application) that can maintain the shape of a self-supporting film even without using a support. The carbon structure of the present invention has a carbon-based skeleton, and the thickness is preferably in the range of 20 μm to 800 μm, more preferably in the range of 30 μm to 500 μm.

[0076] More specifically, the carbon structure (i.e., the self-supporting film) of the present invention can form a positive electrode structure of an air battery by itself alone without being supported by a current collector such as a metal mesh formed of a metal element such as copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), titanium (Ti), gold (Au), silver (Ag), platinum (Pt), palladium (Pd), stainless steel (SUS), or an alloy containing a metal-containing component, or a substrate formed of a metal foil such as aluminum foil, nickel foil, or SUS foil.

[0077] <Carbon Material>

[0078] The carbon structure of the present invention comprises a carbon material containing carbon nanotubes as a constituent raw material, the average diameter of the carbon nanotubes being 1 nm or more and 10 nm or less, the average length being 1 μm or more and 100 μm or less, and the ratio of the length to the diameter, i.e., the aspect ratio, being 1000 or more and 10000 or less.

[0079] It should be noted that the carbon structure of the present invention may also contain other carbon materials within the range that does not impair the effects of the present invention as long as it contains the above carbon material containing carbon nanotubes as a constituent raw material.

[0080] By making the average diameter, average length, and aspect ratio of the carbon nanotubes that make up the carbon material fall within the above ranges, in the manufacturing method of the carbon structure described later, even without adding reinforcing materials such as carbon fibers, a carbon structure for an air battery that can maintain its shape, has self-supporting properties, and exhibits a high discharge capacity can be obtained.

[0081] In the carbon structure of the present invention, by using carbon nanotubes within the above characteristic range as the carbon material of the constituent raw material and implementing the manufacturing method of the carbon structure described later, the shape can be maintained only by the carbon nanotubes and the carbon from the polymer binder that binds the carbon nanotubes to each other, and it has self-supporting properties.

[0082] (Average diameter)

[0083] The average diameter of the carbon nanotubes as the raw material of the carbon structure of the present invention is 1 nm or more and 10 nm or less. When the average diameter of the carbon nanotubes is greater than 10 nm, the number of carbon nanotubes in the carbon structure decreases, and the generation field of lithium peroxide generated in the discharge reaction decreases, so the discharge capacity of the obtained air battery becomes smaller. Carbon nanotubes with a diameter less than 1 nm are difficult to manufacture and obtain.

[0084] The average diameter of the carbon nanotubes can be 1.2 nm or more, 1.4 nm or more, or 1.5 nm or more, and can be 7 nm or less, 5 nm or less, or 3 nm or less.

[0085] (Average length)

[0086] The average length of the carbon nanotubes used as the raw material of the carbon structure of the present invention is 1 μm or more and 100 μm or less. When the average length of the carbon nanotubes is less than 1 μm, the carbon nanotubes become powdery. Therefore, according to the manufacturing method of the carbon structure described later, a binder slurry is prepared by mixing with a binder polymer and a solvent. Even when the binder slurry is coated and dried for forming, the binding force between the carbon nanotubes is weak, and the coating film will be damaged. In this case, if carbon fibers or the like as reinforcing materials are mixed, a carbon structure that can maintain its shape and has self-supporting properties can be obtained. However, since reinforcing materials such as carbon fibers do not contribute to the discharge capacity, the capacity of the obtained air battery decreases accordingly. As a result, the mass of the battery increases, and miniaturization is difficult to achieve.

[0087] On the other hand, when the average length of the carbon nanotubes exceeds 100 μm, the dispersion of the carbon nanotubes is poor at the stage of mixing with the binder polymer and the solvent to prepare the binder slurry. Even when the binder slurry is coated for forming, it will become lumpy and it is difficult to form a formed body. In this case, if carbon fibers or the like as reinforcing materials are mixed, a carbon structure that can maintain its shape and has self-supporting properties can be obtained. However, as described above, since reinforcing materials such as carbon fibers do not contribute to the discharge capacity, the capacity of the obtained air battery decreases accordingly. As a result, the mass of the battery increases, and miniaturization is difficult to achieve.

[0088] The average length of the carbon nanotubes can be 2 μm or more, 3 μm or more, or 4 μm or more, and can be 70 μm or less, 40 μm or less, or 20 μm or less.

[0089] (Aspect ratio)

[0090] The aspect ratio of the carbon nanotubes used as the raw material of the carbon structure of the present invention is 1000 or more and 10000 or less. When the aspect ratio of the carbon nanotubes is less than 1000, the length of the carbon nanotubes is relatively short, and thus the carbon nanotubes become powdery. When a binder slurry is prepared by mixing with a binder polymer and a solvent, at the stage of coating and drying for forming the binder slurry, the binding force between the carbon nanotubes becomes weak, and the coating film will be damaged.

[0091] On the other hand, when the aspect ratio of the carbon nanotubes is greater than 10000, the length of the carbon nanotubes is relatively long. Therefore, at the stage of mixing with the binder polymer and the solvent to prepare the binder slurry, the dispersion of the carbon nanotubes is poor. Even when the binder slurry is coated for forming, it will become lumpy and it is difficult to form a formed body.

[0092] The aspect ratio of the carbon nanotubes can be 2000 or more, 2500 or more, or 3000 or more, and can be 8000 or less, 7000 or less, or 6000 or less.

[0093] <Physical properties of the carbon structure>

[0094] The carbon structure of the present invention preferably has the following physical properties.

[0095] (a) The pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less based on the nitrogen adsorption method is 1.0 cm 3 / g or more and 3.0 cm 3 / g or less,

[0096] (b) The pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less based on the nitrogen adsorption method is 1.0 cm 3 / g or more and 2.3 cm 3 / g or less,

[0097] (c) The pore volume occupied by pores with a diameter of 200 nm or more and 10000 nm or less based on the mercury intrusion method is 1.0 cm 3 / g or more and 3.3 cm 3 / g or less,

[0098] (d) The external specific surface area of the t-curve based on the nitrogen adsorption method is 100 m 2 / g or more and 300 m 2 / g or less,

[0099] (e) The apparent density is 0.15 g / cm 3 or more and 0.30 g / cm 3 or less,

[0100] (f) The porosity is 70% or more and 90% or less.

[0101] ((a) Pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less)

[0102] In the carbon structure of the present invention, (a) the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less based on the nitrogen adsorption method is preferably 1.0 cm 3 / g or more and 3.0 cm 3 / g or less. It should be noted that (a) the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less based on the nitrogen adsorption method is obtained by rounding off the second decimal place.

[0103] By making the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less based on the nitrogen adsorption method in the carbon structure within the above range, when the carbon structure is used as the positive electrode of an air battery, more lithium peroxide generated by discharging can be accumulated, and a battery with high discharge capacity characteristics can be provided. In addition, by increasing the pore volume in this pore region, the permeation and diffusion of air or oxygen within the carbon structure become easier. Therefore, air or oxygen introduced from outside the battery into the positive electrode can be rapidly distributed to every corner of the carbon nanotubes forming the carbon skeleton. Furthermore, by increasing the pore volume in this pore region, the movement of lithium (Li) ions becomes smooth, and with a high degree of synergistic effect with the permeation and diffusibility of air and oxygen, an air battery with excellent high-speed discharge characteristics, that is, high load characteristics, can be provided.

[0104] From the aspect of being able to provide a battery with more excellent charge-discharge characteristics, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less based on the nitrogen adsorption method in the carbon structure is more preferably 1.2 cm 3 / g or more, 1.4 cm 3 / g or more, 1.6 cm 3 / g or more, or 2.0 cm 3 / g or more. On the other hand, from the aspect of making the strength of the carbon structure sufficient and capable of maintaining self-supportability, the pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less based on the nitrogen adsorption method is more preferably 2.9 cm 3 / g or less, 2.8 cm 3 / g or less, 2.7 cm 3 / g or less, or 2.0 cm 3 / g or less.

[0105] ((b) The pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less)

[0106] In the carbon structure of the present invention, the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less based on the nitrogen adsorption method is preferably 1.0 cm 3 / g or more and 2.3 cm 3 / g or less. It should be noted that the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less based on the nitrogen adsorption method is obtained by rounding the second decimal place.

[0107] In the carbon structure, the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less based on the nitrogen adsorption method in (b) being in the above range means that although the pore diameter is in a relatively small range, the pore volume is large, which indicates a large number of pores. That is, when such a carbon structure forms an air battery, during the discharge process, it provides more fields for lithium ions to react with oxygen, and can provide a battery with a high discharge capacity.

[0108] When the carbon structure is used as the positive electrode of an air battery, from the aspect of enabling faster charge and discharge, the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less based on the nitrogen adsorption method in (b) of the carbon structure is more preferably 1.1 cm 3 / g or more, 1.5 cm 3 / g or more, 1.8 cm 3 / g or more, or preferably 2.0 cm 3 / g or more. On the other hand, from the aspect of making the strength of the carbon structure sufficient and capable of maintaining self-supporting properties, the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less based on the nitrogen adsorption method in (b) is more preferably 2.2 cm 3 / g or less, 1.8 cm 3 / g or less, 1.5 cm 3 / g or less, or 1.2 cm 3 / g or less.

[0109] ((c) Pore volume occupied by pores with a diameter of 200 nm or more and 10,000 nm or less)

[0110] In the carbon structure of the present invention, the pore volume occupied by pores with a diameter of 200 nm or more and 10,000 nm or less based on the mercury intrusion method in (c) is preferably 1.0 cm 3 / g or more and 3.3 cm 3 / g or less. It should be noted that the pore volume occupied by pores with a diameter of 200 nm or more and 10,000 nm or less based on the mercury intrusion method in (c) is obtained by rounding the first digit after the decimal point.

[0111] In the carbon structure, (c) the pores with a diameter of 200 nm or more and 10,000 nm or less based on the mercury intrusion method mainly function due to oxygen outside the battery invading the inside of the carbon structure as the positive electrode. Therefore, if the pore volume in the above range is large, it implies that when lithium ions react with oxygen to form lithium peroxide, a sufficient amount of oxygen can invade and can invade at high speed. Thus, an air battery using the carbon structure of the present invention as the positive electrode becomes a battery with a large discharge capacity at high current density, that is, excellent high-load characteristics. In addition, during the charging process, lithium peroxide transfers electrons to the electrode to become Li ions and oxygen, but by making the pore volume occupied by the pores with a diameter of 200 nm or more and 10,000 nm or less in the above range, the release of oxygen from the carbon structure is improved, and high-speed charging can be performed.

[0112] From the aspect of realizing the invasion and release of oxygen to the positive electrode at high speed, the pore volume occupied by the pores with a diameter of 200 nm or more and 10,000 nm or less in the carbon structure (c) based on the mercury intrusion method is more preferably 1.1 cm 3 / g or more, 1.5 cm 3 / g or more, 2.0 cm 3 / g or more, or 2.5 cm 3 / g or more. On the other hand, regarding the pore volume occupied by the pores with a diameter of 200 nm or more and 10,000 nm or less in the carbon structure (c) based on the mercury intrusion method, for the reason that it should not be too large to maintain the strength of the carbon structure, it can be 3.0 cm 3 / g or less, 2.0 cm 3 / g or less, or 1.5 cm 3 / g or less.

[0113] ((d) External specific surface area of the t-curve based on the nitrogen adsorption method)

[0114] In the carbon structure of the present invention, the external specific surface area of the t-curve based on the nitrogen adsorption method (d) is preferably 100 m 2 / g or more and 300 m 2 / g or less. It should be noted that the external specific surface area of the t-curve based on the nitrogen adsorption method (d) is obtained by rounding the first digit after the decimal point.

[0115] Regarding the external specific surface area of the t-curve, based on the adsorption isotherm obtained by nitrogen adsorption measurement, the specific surface area is determined from a graph obtained by plotting the thickness of the nitrogen adsorption layer on the horizontal axis and the adsorption amount on the vertical axis. The value obtained by subtracting the external specific surface area of the t-curve from the specific surface area determined by the BET (Brunauer-Emmett-Teller) method, which is also obtained by nitrogen adsorption measurement, is defined as the micropore specific surface area of the t-curve. Regarding the pores represented by the t-curve micropores, since the pores are too small for lithium ions and oxygen to penetrate, they hardly contribute to the discharge reaction. That is, the external specific surface area of the t-curve represents the specific surface area of the pores that are effective for the discharge reaction and, furthermore, for the charge reaction.

[0116] In the carbon structure, (d) the external specific surface area of the t-curve based on the nitrogen adsorption method is in the range of 100 m 2 / g or more and 300 m 2 / g or less. This is due to the external specific surface area of the carbon nanotubes used as raw materials. In the carbon structure, since the carbon from the polymer binder binds to the carbon nanotubes, the value becomes smaller than that of the carbon nanotubes used as raw materials.

[0117] In the carbon structure, if (d) the external specific surface area of the t-curve based on the nitrogen adsorption method is 100 m 2 / g or more, when the carbon structure is used as the positive electrode of an air battery, in the case where lithium ions and oxygen react to form lithium peroxide, a reaction field required for oxygen to accept electrons supplied from the positive electrode can be ensured, and thus a large discharge capacity can be obtained. On the other hand, if (d) the external specific surface area of the t-curve based on the nitrogen adsorption method is 300 m 2 / g or less, the contribution of side reactions on the surface of the positive electrode can be suppressed, and thus preferable charge-discharge characteristics can be obtained.

[0118] From the aspect of providing more reaction fields, (d) the external specific surface area of the t-curve of the carbon structure is more preferably 120 m 2 / g or more, 140 m 2 / g or more, 160 m 2 / g or more, 180 m 2 / g or more, or 200 m 2 / g or more. On the other hand, for the reason of being able to more effectively suppress side reactions on the electrode surface, (d) the external specific surface area of the t-curve based on the nitrogen adsorption method can be 280 m 2 / g or less, 250 m 2 / g or less, 200 m 2 / g or less, or 180 m 2 / g or less.

[0119] ((e) Apparent density)

[0120] In the carbon structure of the present invention, the (e) apparent density is preferably 0.15 g / cm 3 or more and 0.30 g / cm 3 or less. If the (e) apparent density of the carbon structure is within this range, the carbon structure has sufficient pores required for air and oxygen to permeate and diffuse, and has sufficient strength. If the apparent density is lower than the above range, the strength of the carbon structure may decrease. If it is higher than the above range, there is a risk of reduction in the pores required for air and oxygen to permeate and diffuse.

[0121] From the aspect of making the strength of the carbon structure more excellent, the (e) apparent density of the carbon structure can be more preferably 0.16 g / cm 3 or more, 0.18 g / cm 3 or more, 0.20 g / cm 3 or more, or 0.22 g / cm 3 or more. On the other hand, from the aspect of providing a carbon structure with sufficient voids, the (e) apparent density of the carbon structure can be more preferably 0.29 g / cm 3 or less, 0.28 g / cm 3 or less, 0.25 g / cm 3 or less, or 0.22 g / cm 3 or less.

[0122] ((f) Porosity)

[0123] In the carbon structure of the present invention, the (f) porosity is preferably 70% or more and 90% or less. If the (f) porosity of the carbon structure is within this range, the carbon structure has sufficient pores required for air and oxygen to permeate and diffuse, and has sufficient strength. If the porosity is higher than the above range, there is a possibility of reduction in the strength of the carbon structure. If it is lower than the above range, there is a risk of reduction in the pores required for air and oxygen to permeate and diffuse.

[0124] When the carbon structure is used as the positive electrode of a lithium-air battery, from the aspect of obtaining a battery with a higher discharge capacity and capable of discharging at a higher speed, the (f) porosity of the carbon structure can be more preferably 72% or more, 74% or more, 76% or more, or 78% or more. On the other hand, from the aspect of being able to impart more excellent strength to the carbon structure, the (f) porosity of the carbon structure can be more preferably 89% or less, 88% or less, 87% or less, or 86% or less.

[0125] 《Manufacturing Method of Carbon Structure》

[0126] The carbon structure of the present invention can be obtained by implementing a manufacturing method including the following steps:

[0127] Prepare a binder slurry containing a carbon material and a binder polymer;

[0128] Mold the binder slurry to obtain a binder molded body;

[0129] Immerse the binder molded body in a solvent having a low solubility for the binder polymer to obtain a porous structure;

[0130] Dry the porous structure to obtain a carbon structure precursor; and

[0131] Carbonize the carbon structure precursor under an inert atmosphere to obtain a carbon structure.

[0132] Figure 1 is a flowchart showing the manufacturing process of the carbon structure of the present invention.

[0133] First, prepare a binder slurry containing a carbon material and a binder polymer (step S1).

[0134] The binder slurry preferably contains a carbon material in a mass percentage of 60% by mass or more and 95% by mass or less in the solid component, a binder polymer of 5% by mass or more and 40% by mass or less, and a solvent for uniformly dispersing them.

[0135] The carbon material used in the preparation of the binder slurry is a carbon nanotube having the above physical properties.

[0136] Examples of the binder polymer used in the preparation of the binder slurry include polymer materials such as polyacrylonitrile (PAN), polysulfone, and solvent-soluble polyimide.

[0137] Examples of the solvent used in the preparation of the binder slurry include dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), etc.

[0138] Next, mold the binder slurry to obtain a binder molded body (step S2).

[0139] The molding method is not particularly limited. For example, a wet film forming method using a known doctor blade for coating can be cited. In addition, a roll coating method, a die coating method, a spin coating method, a spraying method, etc. can also be applied.

[0140] The shape of the molded body can be set in various ways according to the purpose. For example, it can be a sheet with a uniform thickness.

[0141] Thereafter, solvent impregnation is performed (step S3). Specifically, the binder molded body obtained in step S2 is immersed in a solvent having a low solubility for the binder polymer to obtain a porous structure.

[0142] In this solvent impregnation step, the binder molded body formed in Step S2 is impregnated in a solvent with low solubility for the binder polymer by the nonsolvent-induced phase separation method. Through this step, the binder polymer precipitates between the carbon materials, thereby bonding the carbon materials to each other and forming a porous structure composed of carbon materials and the binder polymer.

[0143] Examples of the solvent with low solubility for the binder polymer used in the solvent impregnation step include water and alcohols such as ethanol, methanol, and isopropyl alcohol, as well as their mixed solvents.

[0144] Next, drying (Step S4) is performed. Specifically, the porous structure obtained in Step S3 is dried to obtain a carbon structure precursor.

[0145] In this drying step, various solvents are volatilized from the molded body obtained in Step S3. The drying method is not particularly limited, and examples include a method of placing it in a dry air environment, a vacuum drying method, a vacuum drying method, etc. In order to accelerate the drying speed, heating can be performed at a temperature higher than the boiling point of the solvent.

[0146] Next, carbonization treatment (Step S6) is performed. Specifically, the carbon structure precursor obtained in Step S4 is carbonized in an inert atmosphere to obtain a carbon structure.

[0147] Through this carbonization treatment, the binder polymer is condensed and turned into carbon, and the generated carbon firmly binds the carbon materials to each other. By undergoing this carbonization treatment, a self-supporting carbon structure can be manufactured.

[0148] The carbonization treatment is carried out in an inert gas atmosphere. The furnace used in the carbonization treatment is not particularly limited, and examples include an oven furnace, a tubular furnace, a box furnace, an infrared irradiation furnace, a graphite heating furnace, an induction heating furnace, a lead hammer furnace, an Acheson furnace, etc.

[0149] The temperature of the carbonization treatment is preferably in the range of 500 °C or higher and 3000 °C or lower. If it is in this temperature range, a sufficient carbonization effect can be obtained. The temperature of the carbonization treatment is more preferably in the range of 800 °C or higher and 2500 °C or lower.

[0150] The upper limit of the heating rate in the carbonization treatment is preferably 100 °C / min or lower, more preferably 50 °C / min or lower, and further preferably 30 °C / min or lower. When the upper limit of the heating rate is greater than the above value, the carbon structure may not be sufficiently carbonized. There is no particular limitation on the lower limit of the heating rate, and it is preferably 0.01 °C / min or higher in terms of cost.

[0151] The carbonization treatment is usually carried out in an inert atmosphere. As the inert gas, for example, rare gases such as argon (Ar) and nitrogen (N2) can be used.

[0152] Through the above processes, a carbon structure having self-supportability and thus sufficient practical mechanical strength can be manufactured. According to the above manufacturing method, a carbon structure obtained by carbonizing the entire formed body can be obtained. Therefore, a carbon structure having self-supportability and electron conductivity required as an electrode can be formed without using reinforcing materials such as carbon fibers and current collectors that do not directly participate in the battery reaction. In addition, the carbon structure obtained by the above manufacturing method has self-supportability and also has high air or oxygen permeability, high ion transport efficiency, and a wide reaction field when used as an air battery.

[0153] In the manufacturing method of the carbon structure of the present invention, a non-melting treatment (process S5) can be optionally performed. Specifically, after the process of drying the porous structure to obtain the above carbon structure precursor (process S4) and before the above carbonization treatment (process S6), it may optionally include a process of performing a non-melting treatment on the carbon structure precursor obtained in process S4 to obtain a non-melted carbon structure. By performing the above carbonization treatment on the non-melted carbon structure obtained from the non-melting treatment process, a carbon structure can be obtained.

[0154] This non-melting treatment is performed for the purpose of preventing the binder polymer from undergoing melt separation and the shape of the porous structure from being damaged in the subsequent carbonization treatment process. Specifically, in the non-melting treatment, the binder polymer is oxidized and crosslinked to be solidified, thereby preventing the binder polymer from undergoing melt separation in the subsequent carbonization treatment process.

[0155] The non-melting treatment is carried out by heating using an oven furnace, infrared irradiation, etc. under air circulation. There is no particular limitation on the treatment temperature, and it is preferably 250 °C or higher and 350 °C or lower. By being 250 °C or higher, the oxidation crosslinking of the binder polymer material can be sufficiently carried out, and melting in the subsequent carbonization process can be avoided. By being 350 °C or lower, decomposition of the binder polymer material can be avoided. Depending on the type of binder polymer used, this non-melting treatment process can also be omitted and is an optional process in the manufacturing method of the carbon structure of the present invention.

[0156] Positive Electrode for Air Battery

[0157] The carbon structure of the present invention can be used as a positive electrode for an air battery. Since the carbon structure of the present invention has self-supportability, it does not require a support such as a current collector and can be directly applied as a positive electrode.

[0158] Air Battery

[0159] The air battery of the present invention includes a positive electrode for an air battery, a negative electrode, and an electrolyte existing between the positive electrode for an air battery and the negative electrode, which include the above carbon structure of the present invention.

[0160] <Button cell type air battery>

[0161] Figure 2 Schematic cross-sectional view of an air battery showing an embodiment of the present invention. Figure 3 It is a schematic cross-sectional view of an air battery according to another embodiment of the present invention. The air battery 601 is an air battery generally called a "button cell type" having an electrode laminate in which a negative electrode structure body 610 and a positive electrode structure body 621 are laminated with a separator 660 interposed therebetween, and a restraint member 630 for restraining the electrode laminate.

[0162] Figure 2 In the shown air battery 601, the positive electrode structure body 621 itself is the carbon structure body 690 of the present invention, and as the positive electrode structure body 621, only the carbon structure body 690 of the present invention is provided. Since the carbon structure body of the present invention has self-supporting properties, it can be used alone as a positive electrode structure body.

[0163] Composed only of the carbon structure body 690 Figure 2 In the shown positive electrode structure body 621, there is no metal net or the like constituting a current collector, so the air battery 601 becomes an air battery with a high mass energy density. In addition, since the structure of the carbon structure body 690 is simple, the number of manufacturing processes can be reduced, and the air battery can be manufactured efficiently.

[0164] An insulating O-ring (not shown) is disposed between the restraint member 630 and the carbon structure body 690 serving as the positive electrode structure body 621 to ensure insulation between the restraint member 630 and the positive electrode structure body 621.

[0165] The negative electrode structure body 610 is composed of a current collector 635, a metal layer 640 disposed on the current collector 635, and a spacer 650 disposed on the current collector 635 so as to surround the outer periphery of the metal layer 640. A space 670 is provided between the metal layer 640 and the separator 660, and the electrolyte is filled in the space 670.

[0166] The material constituting the metal layer 640 preferably contains an alkali metal and / or an alkaline earth metal. Among them, a layer containing lithium metal is preferred.

[0167] A separator 660 is disposed between the negative electrode structure body 610 and the positive electrode structure body 621.

[0168] In addition, an air battery of another embodiment is shown in Figure 3 . Figure 3In the air battery 600 shown, the positive electrode structure 620 is composed of the carbon structure 690 of the present invention and the metal mesh 680. Specifically, in the positive electrode structure 620 of the air battery 600, the carbon structure 690 of the present invention is mechanically and electrically contacted with the metal mesh 680 that serves both as a flow path for air or oxygen to flow through and as a current collector.

[0169] Here, Figure 2 The difference between the air battery 601 shown and Figure 3 the air battery 600 shown is only the presence or absence of the metal mesh 680. The carbon structure of the present invention has self-supporting properties, so it can form the positive electrode structure by itself, but according to the physical properties required for the air battery, it can be provided with a current collector such as a metal mesh.

[0170] In the Figure 3 positive electrode structure 620 shown that has the metal mesh 680, due to the presence of the metal mesh 680, the conductivity increases, and a sufficient flow path for air or oxygen can be ensured, so it becomes an air battery suitable for high output.

[0171] It should be noted that an insulating O-ring (not shown) is arranged between the restraint member 630 and the metal mesh 680, thereby ensuring the insulation between the restraint member 630 and the positive electrode structure 620.

[0172] A separator 660 is arranged between the negative electrode structure 610 and the positive electrode structure 620.

[0173] An example of the manufacturing method of the air battery 601 will be described below. First, the negative electrode structure 610 is prepared. A metal layer 640 based on lithium or the like is laminated on the disk-shaped current collector 635. The metal layer 640 is concentric with the current collector 635, has a diameter smaller than that of the current collector 635, and is disk-shaped. Then, the spacer 650 is pressed against the periphery of the metal layer 640 on the current collector 635 to obtain the negative electrode structure 610.

[0174] The spacer 650 is an insulator. As materials, they can be metal oxides, metal nitrides, metal oxynitrides, etc. For example, they can be Al2O3, Ta2O5, TiO2, ZnO, ZrO2, SiO2, B2O3, P2O5, GeO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, Si3N4, AlN, and AlO x N 1-x (0 < x < 1). Among them, Al2O3 and SiO2 are preferred because they are easily obtained and have excellent processability.

[0175] The spacer 650 can be a resin. Examples of the resin include polyolefin resins, polyester resins, polyimide resins, and polyether ether ketone (PEEK) resins. Examples of the polyolefin resins include polyethylene and polypropylene. Examples of the polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polytrimethylene terephthalate (PTT). These resins are preferred because they are easily available and have excellent processability.

[0176] Next, the separator 660 is pressed against the spacer 650. At this time, it is preferable to provide a space 670 between the metal layer 640, the spacer 650, and the separator 660.

[0177] The separator 660 is a porous insulator that allows alkali metal ions and / or alkaline earth metal ions to pass through. The material of the separator 660 can be any inorganic material (including metal materials) and organic materials that are non-reactive with the metal layer 640 and the electrolyte.

[0178] As the separator 660, a separator used in an existing metal battery can also be used. For example, it can be a porous membrane made of a synthetic resin such as polyolefin such as polyethylene and polypropylene, or a sheet made of glass fiber. The separator 660 can be a woven fabric or a non-woven fabric.

[0179] After that, the electrolyte is filled into the separator 660. At this time, it is preferable to fill the electrolyte into the space 670 as well.

[0180] As the electrolyte, any aqueous or non-aqueous electrolyte containing an alkali metal salt and / or an alkaline earth metal salt can be used.

[0181] When the aqueous electrolyte contains a lithium salt as the alkali metal salt and / or the alkaline earth metal salt, examples of the lithium salt include LiOH, LiCl, LiNO3, and Li2SO4, and examples of the solvent include water or a water-soluble solvent.

[0182] When the non-aqueous electrolyte (non-aqueous electrolyte) contains a lithium salt as the alkali metal salt and / or the alkaline earth metal salt, examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiSiF6, LiAsF6, LiN(SO2C2F5)2, Li(FSO2)2N, LiCF3SO3 (LiTfO), Li(CF3SO2)2N (LiTFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiB(C2O4)2.

[0183] Examples of the nonaqueous solvent used in the nonaqueous electrolyte include glycol dimethyl ethers (ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether), methyl butyl ether, diethyl ether, ethyl butyl ether, dibutyl ether, polyethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, cyclohexanone, dioxane, dimethoxyethane, 2-methyltetrahydrofuran, 2,2-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate , methyl formate, ethyl formate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, polyethylene carbonate, gamma-butyrolactone, decanoic acid, valerolactone, mevalerolactone, caprolactone, acetonitrile, benzonitrile, nitromethane, nitrobenzene, triethylamine, triphenylamine, tetraethylene glycol diamine, dimethylformamide, diethylformamide, N-methylpyrrolidone, dimethyl sulfone, tetramethylene sulfone, triethylphosphine oxide, 1,3-dioxolane and sulfolane.

[0184] Then, the carbon structure 690 of the present invention as the positive electrode structure 621 is attached to the negative electrode structure 610 filled with the electrolyte via the separator 660 and restrained with a button cell type restraint 630 to obtain the air battery 601. The assembly is preferably performed under dry air, for example, dry air with a dew point temperature of -50°C or less.

[0185] In the making Figure 3 In the case of the air battery 600 shown, a positive electrode structure 620 in which a metal mesh 680 is arranged on a carbon structure 690 is prepared and assembled as described above.

[0186] As the metal mesh 680, for example, a mesh containing at least one metal selected from the group consisting of copper (Cu), tungsten (W), aluminum (Al), nickel (Ni), titanium (Ti), gold (Au), silver (Ag), platinum (Pt) and palladium (Pd) can be used. For example, a mesh formed by a metal single substance selected from the group, an alloy containing a metal selected from the group, and a compound of a metal selected from the group and carbon (C), nitrogen (N), etc. can be cited. In the case of an alloy, iron (Fe) and chromium (Cr) may also be included. The mesh may be set to, for example, a thickness of 0.2 mm and a mesh opening of 1 mm.

[0187] In air batteries 601 and 600, since the positive electrode structure 621 or 620 using the carbon structure of the present invention has high air or oxygen permeability, it can absorb a large amount of oxygen. Furthermore, by having both high ion transmission efficiency and a wide reaction field, and a simple structure of only a carbon structure or only a carbon structure and a metal mesh, it can become an air battery that can be small and lightweight and suitable for large capacity.

[0188] <Stacked air battery>

[0189] Figure 4 The schematic cross-sectional view of an air battery showing another embodiment of the present invention is shown. Figure 4 It is a schematic diagram showing a stacked air battery (stacked metal battery).

[0190] The air battery 500 has a stacked structure in which a positive electrode laminate 510 and a negative electrode laminate 100 are stacked with a separator 540 interposed therebetween. Taking one pair consisting of one positive electrode laminate 510 and one negative electrode laminate 100 as a unit, the number of stacked pairs can be multiple pairs of one or more, and there is no particular upper limit on the number of pairs.

[0191] The negative electrode laminate 100 is composed of a pair of negative electrode active material layers (metal layers) and a negative electrode current collector 520 sandwiched therebetween.

[0192] On the other hand, the positive electrode laminate 510 is composed of a pair of positive electrode structures 621 which are carbon structures of the present invention, and a positive electrode current collector 525 sandwiched therebetween. The positive electrode current collector 525 in the air battery 500 becomes a current collector that also serves as a flow path for air or oxygen.

[0193] Since the carbon structure of the present invention has self-supporting properties, in the stacked air battery 500, by arranging the positive electrode current collector 525 between the positive electrode structures 621 which are the carbon structures of the present invention itself, the positive electrode laminate 510 can be formed. Therefore, a stacked air battery can be formed using a simple stacked structure, and a larger-capacity air battery can be realized.

[0194] It should be noted that in the air battery 500, the carbon structure of the present invention is directly used as the positive electrode structure, but the positive electrode structure can also be a structure in which the carbon structure of the present invention and a current collector such as a metal mesh are stacked. Since the carbon structure of the present invention has self-supporting properties, it can form the positive electrode structure only by itself, but can have a current collector such as a metal mesh according to the physical properties required for the air battery.

[0195] As the negative electrode current collector 520, for example, at least one metal selected from the group consisting of copper (Cu), tungsten (W), nickel (Ni), titanium (Ti), gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) can be used.

[0196] As the positive electrode current collector 525, for example, at least one metal selected from the group consisting of stainless steel (SUS), tungsten (W), aluminum (Al), nickel (Ni), titanium (Ti), gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) can be used.

[0197] That is, as the negative electrode current collector 520 and the positive electrode current collector 525, for example, a metal single substance selected from this group, an alloy containing a metal selected from this group, and a compound of a metal selected from this group and carbon (C), nitrogen (N), etc. can be used.

[0198] It should be noted that since the positive electrode current collector 525 forms a flow path for air or oxygen, for example, it needs to be a porous material such as a net, a grille, or a sponge.

[0199] The laminated air battery 500 can be manufactured by laminating the negative electrode structure 100 and the positive electrode structure 510 with a separator 540 interposed therebetween. The air battery 500 can be housed in a housing container (not shown).

[0200] In the air battery 500, since the positive electrode structure 510 using the carbon structure of the present invention has high air or oxygen permeability, a large amount of oxygen can be inhaled. Furthermore, by having both high ion transport efficiency and a wide reaction field and being a simple structure such as only a carbon structure or only a carbon structure and a metal net, it can be an air battery that can achieve miniaturization and light weight and is suitable for large capacity.

[0201] Examples

[0202] The present invention will be described in detail below by way of examples and the like, but the present invention is not limited to these.

[0203] <Measurement method>

[0204] The physical properties of the carbon material used as a raw material and the carbon structure produced are measured by the following methods.

[0205] (1) Pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less

[0206] Using 3Flex (Micromeritics Instrument Corp.), based on the adsorption isotherm obtained by the nitrogen adsorption method, the BJH (Barrett-Joyner-Hallenda) method is used to calculate.

[0207] (2) Pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less

[0208] Using 3Flex (Micromeritics Instrument Corp.), based on the adsorption isotherm obtained by the nitrogen adsorption method, the BJH method is used to calculate.

[0209] (3) Specific surface area occupied by pores with a diameter of 200 nm or more and 1000 nm or less

[0210] Using 3Flex (Micromeritics Instrument Corp.), it was determined by the BJH method based on the adsorption isotherm obtained by the nitrogen adsorption method.

[0211] (4) BET specific surface area

[0212] Using 3Flex (Micromeritics Instrument Corp.), based on the adsorption isotherm obtained by the nitrogen adsorption method, it was determined according to the BET (Brunauer - Emmett - Teller) method.

[0213] (5) t - curve external specific surface area

[0214] Using 3Flex (Micromeritics Instrument Corp.), based on the adsorption isotherm obtained by the nitrogen adsorption method, from the graph obtained by plotting the thickness of the nitrogen adsorption layer on the horizontal axis and the adsorption amount on the vertical axis, it was determined by the t - curve method.

[0215] (6) t - curve micropore specific surface area

[0216] It is defined as the value obtained by subtracting the above - mentioned t - curve external specific surface area from the specific surface area of the above - mentioned BET method.

[0217] (7) Pore volume occupied by pores with diameters above 200 nm and below 10000 nm

[0218] The pore volume in the range of pore diameters from 10 nm to 200000 nm (0.01 μm to 200 μm) was measured by mercury intrusion porosimetry using AutoPoreIV (Micromeritics Instrument Corp.), and the value of the pore volume of pores with diameters from 200 nm to 10000 nm was used.

[0219] (8) Apparent density

[0220] It was determined by dividing the mass of the carbon structure by its volume.

[0221] (9) Porosity

[0222] It was determined according to the following formula.

[0223] (1 - apparent density of carbon structure / true density of carbon structure) × 100

[0224] <Carbon material>

[0225] The carbon materials used in the raw materials of the carbon structure are shown in Table 1.

[0226] [Table 1]

[0227]

[0228] <Example 1>

[0229] (Carbon material)

[0230] As the carbon material, carbon nanotubes “TUBALL-CNT 01RW03” (OCSiAl Corporation) (CNT1) were used. As shown in Table 1, TUBALL-CNT 01RW03 had an average diameter of 1.6 nm, an average length of 5 μm, and an aspect ratio of 3100.

[0231] [Fabrication of carbon structure]

[0232] (Preparation process of binder slurry)

[0233] N-methylpyrrolidone, which is a solvent for uniformly dispersing them, was added to 80 parts by mass of TUBALL-CNT 01RW03 and 20 parts by mass of polyacrylonitrile (PAN) as a binder polymer, and they were mixed using a planetary mixer (Thinky Corporation, model: ARE310) to prepare a binder slurry.

[0234] (Forming process)

[0235] The binder slurry was coated to a thickness of 300 μm using a doctor blade method to fabricate a binder formed sheet (binder formed body).

[0236] (Solvent impregnation process)

[0237] The binder formed sheet obtained through the forming process was impregnated in methanol (poor solvent), and porous membrane formation was carried out by the nonsolvent-induced phase separation method.

[0238] The nonsolvent-induced phase separation method is a method of impregnating a polymer solution in a nonsolvent to cause phase separation and precipitation of the polymer. In this example, by impregnating the binder formed sheet (in a state where carbon materials are dispersed in an N-methylpyrrolidone solution in which polyacrylonitrile (PAN) as a binder polymer is dissolved) formed from the binder slurry in methanol as a nonsolvent (poor solvent), N-methylpyrrolidone dissolved into the methanol, and polyacrylonitrile (PAN) precipitated between the carbon materials. And, through the precipitation of polyacrylonitrile (PAN), a porous structure with carbon materials as the framework was formed.

[0239] Specifically, in the solvent impregnation process, the binder formed sheet was placed in a tray, 220 g of methanol was poured into it, and it was left standing. After 2 hours, the methanol in the tray was drained, 220 g of methanol was poured in again, and it was left standing for 17 hours. Then, the methanol in the tray was drained, and thus a phase separation sheet (porous structure) with porous membrane formation was obtained.

[0240] (Drying process)

[0241] The phase-separated sheet (porous structure) that has been subjected to porous membrane formation is taken out of the tray. In order to remove the volatile solvent contained in the phase-separated sheet (porous structure), drying is carried out at 50 °C for 2 hours and at 80 °C for 10 hours to obtain a dried sheet (precursor of carbon structure).

[0242] (Infusibilization process)

[0243] For the obtained dried sheet (precursor of carbon structure), using a Yamato Inert Oven DN411, infusibilization heat treatment is carried out at 320 °C for 3 hours in an atmospheric circulation atmosphere, and the polyacrylonitrile (PAN) of the dried sheet (precursor of carbon structure) is oxidized and crosslinked and cyclized to change into an infusible resin, thereby obtaining an infusibilized sheet (infusibilized carbon structure) with a length of 90 mm and a width of 80 mm.

[0244] (Carbonization process)

[0245] For the infusibilized sheet (infusibilized carbon structure) obtained in the infusibilization process, using a box furnace (Denken-Highdental Co., Ltd.), while flowing nitrogen at 600 mL / min, the temperature is raised to 1050 °C at a heating rate of 10 °C / min, held at 1050 °C for 3 hours, and then naturally cooled to room temperature, thereby carbonizing the infusibilized polyacrylonitrile (PAN) to obtain a porous carbon structure composed entirely of carbon. The manufacturing conditions and manufacturing results are shown in Table 2.

[0246]

[0247] [Measurement of physical properties of carbon structure]

[0248] Various measurements are carried out on the obtained carbon structure. The pore volume occupied by pores with a diameter of 1 nm or more and 1000 nm or less is 1.2 cm 3 / g, the pore volume occupied by pores with a diameter of 1 nm or more and 200 nm or less is 1.1 cm 3 / g, the pore volume occupied by pores with a diameter of 200 nm or more and 10000 nm or less is 2.9 cm 3 / g, and the external specific surface area of the t-curve is 161 m 2 / g. Regarding the basis weight (mg / cm 2 ), it is obtained by punching the carbon structure into a diameter and dividing its mass by its area. The physical properties of the carbon structure are shown in Table 3.

[0249] [Table 3]

[0250]

[0251] [Fabrication of Lithium-Air Battery]

[0252] The carbon structure is punched into a diameter of The fabricated carbon structure with a diameter of is used as the positive electrode to fabricate Figure 5 the button cell 800 of the CR2032 type as shown.

[0253] Specifically, in a drying chamber (dry air) with a dew point temperature of -50 °C or lower, the positive electrode 840, which is a carbon structure with a diameter of , the negative electrode 860 made of metallic lithium (with a diameter of and a thickness of 0.2 mm), the separator impregnated with 100 μL of a 1 M - tetraethylene glycol dimethyl ether solution of LiTFS (lithium trifluoromethanesulfonate) as the electrolyte (glass fiber paper (Whatman (registered trademark), GF / A) 850), and the stainless steel-made circular plate 870 and disc spring 875 are assembled using a button cell can (positive electrode can 810 and negative electrode can 815) (CR2032 type) to fabricate this button cell. Figure 5 In this case, the gasket 880 is sandwiched between the positive electrode can 810 and the negative electrode can 815, serving to fix the positive electrode can 810 and the negative electrode can 815 and ensure insulation. The external gas (oxygen in this evaluation) is directly inhaled into the positive electrode 840.

[0254] [Measurement of Discharge Capacity]

[0255] For the fabricated button cell as a lithium-air battery, the measurement of the discharge capacity is carried out at a current density of 0.4 mA / cm² in a pure oxygen atmosphere. 2 The moment when the voltage drops to 2.3 V is taken as the discharge end point, and the obtained discharge capacity is divided by the mass of the carbon structure used as the positive electrode, thereby calculating the discharge capacity (specific capacity) per unit mass of the positive electrode. As a result, the discharge capacity per unit mass of the positive electrode is 3476 mAh / g. The discharge capacity is shown in Table 3.

[0256] [Example 2]

[0257] (Carbon Material)

[0258] The same carbon material (CNT1) as in Example 1 is used.

[0259] [Fabrication of Carbon Structure]

[0260] (Binder Slurry Preparation Process)

[0261] A binder slurry was prepared in the same manner as in Example 1, except that 90 parts by mass of TUBALL-CNT 01RW03 (CNT1) and 10 parts by mass of polyacrylonitrile (PAN) as a binder polymer material were used.

[0262] (Forming process) (Solvent impregnation process) (Drying process) (Infusibilization process) (Carbonization process)

[0263] The forming process, solvent impregnation process, drying process, infusibilization process, and carbonization process were carried out in the same manner as in Example 1 to obtain a carbon structure. The manufacturing conditions and results are shown in Table 2.

[0264] [Physical property measurement of carbon structure]

[0265] For the obtained carbon structure, various physical properties were measured in the same manner as in Example 1. The results are shown in Table 3.

[0266] [Measurement of discharge capacity]

[0267] A lithium-air battery was fabricated in the same manner as in Example 1, and the discharge capacity was measured. The discharge capacity of the positive electrode per unit mass was 4219 mAh / g. The results are shown in Table 3.

[0268] <Example 3>

[0269] (Carbon material)

[0270] Carbon nanotube "eDIPS EC2.0P" (Meishin Co., Ltd.) (CNT2) was used as the carbon material. As shown in Table 1, the average diameter of DIPSEC2.0P is 2 nm, the average length is 10 μm, and the aspect ratio is 5100.

[0271] [Fabrication of carbon structure]

[0272] (Binder slurry preparation process) (Forming process) (Solvent impregnation process) (Drying process) (Infusibilization process) (Carbonization process)

[0273] Using "eDIPS EC2.0P" (CNT2) as the carbon material and setting the coating thickness in the forming process to 550 μm, the binder slurry preparation process, forming process, solvent impregnation process, drying process, infusibilization process, and carbonization process were carried out in the same manner as in Example 1 to obtain a carbon structure. The manufacturing conditions and results are shown in Table 2.

[0274] [Physical property measurement of carbon structure]

[0275] For the obtained carbon structure, various physical properties were measured in the same manner as in Example 1. The results are shown in Table 3.

[0276] [Measurement of discharge capacity]

[0277] A lithium-air battery was fabricated in the same manner as in Example 1, and its discharge capacity was measured. The discharge capacity of the positive electrode per unit mass was 4928 mAh / g. The results are shown in Table 3.

[0278] <Comparative Example 1>

[0279] (Carbon material)

[0280] "Ketjenblack EC600JD" (LION Specialty Chemicals Co., Ltd.) (KB) was used as the carbon material. In Ketjenblack EC600JD (KB), carbon particles with a primary particle size of about 34 nm are bonded in a grape-like shape to form secondary particles, and the particle size of the secondary particles is 4.2 μm in terms of the 50% particle size. Other properties of Ketjenblack EC600JD are also shown in Table 1. Note that for the 50% particle size, a laser particle size distribution analyzer LA950V2 (Horiba) was used, ethanol was used as the dispersion medium, and after dispersing for 3 min at a circulation speed of 3 and an ultrasonic intensity of 7, the measurement was carried out, and the particle size value corresponding to 50% cumulative by volume was used.

[0281] [Fabrication of carbon structure]

[0282] (Binder slurry preparation process) (Forming process) (Solvent impregnation process)

[0283] Ketjenblack EC600JD (KB) was used as the carbon material, and the binder slurry preparation process, forming process, and solvent impregnation process were carried out in the same manner as in Example 1 except for this. However, the strength of the phase separation sheet (porous structure) obtained in the solvent impregnation process was weak and was damaged during processing, and the subsequent drying process could not be carried out. The manufacturing conditions and manufacturing results are shown in Table 2.

[0284] <Comparative Example 2>

[0285] (Raw materials)

[0286] The same "Ketjenblack EC600JD" (LION Specialty Chemicals) (KB) as in Comparative Example 1 was used as the carbon material.

[0287] [Fabrication of carbon structure]

[0288] (Binder slurry production process)

[0289] 65 parts by mass of Ketjenblack EC600JD (KB), 12 parts by mass of carbon fiber as a reinforcing material, and 23 parts by mass of polyacrylonitrile (PAN) as a binder polymer were used, and the binder slurry was prepared in the same manner as in Example 1 except for this. The carbon fiber used as the reinforcing material was chopped fiber (Japan Polymer Industry, fiber average diameter 6 μm, average length 3 mm).

[0290] (Forming process) (Solvent impregnation process) (Drying process) (Infusibilization process) (Carbonization process)

[0291] The forming process, solvent impregnation process, drying process, infusibilization process, and carbonization process were carried out in the same manner as in Example 1 to obtain a carbon structure. The manufacturing conditions and manufacturing results are shown in Table 2.

[0292] It should be noted that in Comparative Example 1, since carbon fiber as a reinforcing material was not added, the strength of the phase-separated sheet (porous structure) obtained in the solvent impregnation process was weak and it was damaged. However, in Comparative Example 2, since carbon fiber as a reinforcing material was added, a phase-separated sheet (porous structure) with maintained strength was obtained.

[0293] [Measurement of physical properties of carbon structure]

[0294] For the obtained carbon structure, various physical properties were measured in the same manner as in Example 1. The results are shown in Table 3.

[0295] [Measurement of discharge capacity]

[0296] A lithium-air battery was fabricated in the same manner as in Example 1, and the discharge capacity was measured. The discharge capacity of the positive electrode per unit mass was 2824 mAh / g. The results are shown in Table 3.

[0297] <Comparative Example 3>

[0298] (Carbon material)

[0299] Carbon nanotube "ZEON-CNT-SG101" (Zeon Corporation, Japan) (CNT3) was used as the carbon material. As shown in Table 1, the average diameter of ZEON-CNT-SG101 is 4 nm, the average length is 400 μm, and the aspect ratio is 100,000.

[0300] [Fabrication of carbon structure]

[0301] (Binder slurry preparation process) (Forming process) (Solvent impregnation process)

[0302] ZEON-CNT-SG101 (CNT3) was used as the carbon material, and the binder slurry preparation process, forming process, and solvent impregnation process were carried out in the same manner as in Example 1 except for this. However, the phase-separated sheet (porous structure) obtained in the solvent impregnation process was non-uniform, in an island shape, and had weak strength, so the subsequent drying process could not be carried out. The manufacturing conditions and manufacturing results are shown in Table 2.

[0303] <Comparative Example 4>

[0304] (Carbon material)

[0305] Carbon nanotubes “Cnano-CNT FT6120” (Cnano Corporation) (CNT4) are used as the carbon material. As shown in Table 1, the average diameter of Cnano-CNT FT6120 is 8 nm, the average length is 150 μm, and the aspect ratio is 19,000.

[0306] [Fabrication of Carbon Structure]

[0307] (Binder Slurry Preparation Process) (Forming Process) (Solvent Impregnation Process)

[0308] Carbon nanotubes “Cnano-CNT FT6120” (CNT4) are used as the carbon material, and the binder slurry preparation process, forming process, and solvent impregnation process are carried out in the same manner as in Example 1. However, the strength of the phase separation sheet (porous structure) obtained in the solvent impregnation process is weak and is damaged during processing, making it impossible to carry out the subsequent drying process. The manufacturing conditions and manufacturing results are shown in Table 2.

[0309] [Comparative Example 5]

[0310] (Carbon Material)

[0311] The same carbon nanotubes “Cnano-CNT FT6120” (Cnano Corporation) (CNT4) as in Comparative Example 4 are used as the carbon material.

[0312] (Binder Slurry Preparation Process)

[0313] [Fabrication of Carbon Structure]

[0314] 75 parts by mass of Cnano-CNT FT6120, 10 parts by mass of carbon fiber as the reinforcing material, and 15 parts by mass of polyacrylonitrile (PAN) as the binder polymer material are used, and the binder slurry is prepared in the same manner as in Example 1. The carbon fiber as the reinforcing material is chopped fiber (Japan Polymer Industry, fiber average diameter 6 μm, average length 3 mm).

[0315] (Forming Process) (Solvent Impregnation Process) (Drying Process) (Infusibilization Process) (Carbonization Process)

[0316] The forming process, solvent impregnation process, drying process, infusibilization process, and carbonization process are carried out in the same manner as in Example 1 to obtain a carbon structure. The manufacturing conditions and manufacturing results are shown in Table 2.

[0317] Note that in Comparative Example 4, since carbon fiber as a reinforcing material was not added, the strength of the phase separation sheet (porous structure) obtained in the solvent impregnation step was weak and it was damaged. However, in Comparative Example 5, since carbon fiber as a reinforcing material was added, a phase separation sheet (porous structure) with maintained strength was obtained.

[0318] [Physical Property Measurement of Carbon Structure]

[0319] For the obtained carbon structure, various physical properties were measured in the same manner as in Example 1. The results are shown in Table 3.

[0320] [Measurement of Discharge Capacity]

[0321] A lithium-air battery was fabricated in the same manner as in Example 1, and the discharge capacity was measured. The discharge capacity of the positive electrode per unit mass was 1976 mAh / g. The results are shown in Table 3.

[0322] Industrial Applicability

[0323] The carbon structure according to the present invention enables a small and lightweight air battery with a large discharge capacity. In addition, the carbon structure of the present invention is manufactured without undergoing a carbonization process in an oxidizing gas atmosphere. Therefore, when realizing a high-discharge-capacity air battery, it is easier to produce compared to a carbon structure subjected to carbonization treatment in an oxidizing gas atmosphere, and a reduction in manufacturing cost can be achieved.

[0324] Explanation of Symbols

[0325] 600, 601 Air battery

[0326] 610 Negative electrode structure

[0327] 620, 621 Positive electrode structure

[0328] 630 Constraint member

[0329] 635 Current collector

[0330] 640 Metal layer

[0331] 650 Spacer

[0332] 660 Separator

[0333] 670 Space

[0334] 680 Metal mesh

[0335] 500 Air battery

[0336] 100 Negative electrode laminate

[0337] 510 Positive electrode laminate

[0338] 520 Negative current collector

[0339] 525 Positive current collector

[0340] 540 Separator

[0341] 800 Button cell

[0342] 810 Positive can

[0343] 815 Negative can

[0344] 840 Positive electrode

[0345] 850 Separator

[0346] 860 Negative electrode

[0347] 870 Circular plate

[0348] 875 Belleville spring

[0349] 880 Spacer

Claims

1. A carbon structure, which is a carbon structure for the positive electrode of an air battery, wherein, the carbon structure contains carbon nanotubes as a carbon material, the average diameter of the carbon nanotubes is 1 nm or more and 10 nm or less, the average length is 1 μm or more and 100 μm or less, and the aspect ratio is 1000 or more and 10000 or less.

2. The carbon structure according to claim 1, which is composed only of the carbon material and carbon derived from a binder polymer that binds the carbon materials to each other.

3. The carbon structure according to claim 1 or 2, wherein, (a) The pore volume occupied by pores with diameters above 1 nm and below 1000 nm based on the nitrogen adsorption method is 1.0 cm 3 / g or more and 3.0 cm 3 / g or less, (b) The pore volume occupied by pores with a diameter of more than 1 nm and less than 200 nm based on the nitrogen adsorption method is 1.0 cm 3 / g or more and 2.3 cm 3 / g or less, (c) The pore volume occupied by pores with a diameter of more than 200 nm and less than 10,000 nm based on mercury intrusion porosimetry is 1.0 cm 3 / g or more and 3.3 cm 3 / g or less, (d) The external specific surface area of the t-curve based on the nitrogen adsorption method is 100 m 2 / g or more and 300 m 2 / g or less, (e) The apparent density is 0.15 g / cm 3 or more and 0.30 g / cm 3 or less. (f) the porosity is 70% or more and 90% or less.

4. The carbon structure according to any one of claims 1 to 3, which has self-supportability.

5. A positive electrode for an air battery, which contains the carbon structure according to any one of claims 1 to 4.

6. An air battery, which includes: the positive electrode for an air battery according to claim 5, a negative electrode, and an electrolyte present between the positive electrode for an air battery and the negative electrode.

7. The air battery according to claim 6, wherein The negative electrode contains lithium metal.

8. A method for manufacturing the carbon structure according to any one of claims 2 to 4, which includes: preparing a binder slurry containing the carbon material and the binder polymer; forming the binder slurry to obtain a binder formed body; immersing the binder formed body in a solvent having low solubility for the binder polymer to obtain a porous structure; drying the porous structure to obtain a carbon structure precursor; and carbonizing the carbon structure precursor under an inert atmosphere to obtain a carbon structure.

9. The method for manufacturing a carbon structure according to claim 8, wherein, The temperature of the carbonization treatment is in the range of 500 °C or more and 3000 °C or less.

10. The method for manufacturing the carbon structure according to claim 8 or 9, wherein, the method further includes: after drying the porous structure to obtain the carbon structure precursor and before performing the carbonization treatment, performing an infusibilization treatment on the carbon structure precursor to obtain an infusibilized carbon structure, and performing the carbonization treatment on the infusibilized carbon structure.

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