JP2013191284A - Air battery - Google Patents

Abstract

An air battery including a carbon material, which has more reaction starting points for oxygen reduction reaction than a conventional carbon material, in an air electrode layer.
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 includes at least an air electrode layer, and the air electrode layer includes: An air battery comprising a carbon material having a D / G ratio of 0.8 to 0.9.
[Selection] Figure 2

Description

  The present invention relates to an air battery including, in an air electrode layer, a carbon material having more reaction starting points for oxygen reduction reaction than a conventional 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.

  Conventionally, ketjen black has been used as a conductive material in the air electrode. However, when ketjen black is used, although the initial capacity is high, there is a problem that the capacity after repeated charge and discharge is greatly reduced. As a technique for solving such a problem, Patent Literature 1 discloses a metal-air secondary battery including an air electrode including an air electrode layer containing a conductive material, a negative electrode, and a nonaqueous electrolyte, A technique relating to a metal-air secondary battery, wherein the conductive material is acicular carbon having an average aspect ratio of 10 or more is disclosed.

JP 2010-287390 A

When the inventor further examined the metal-air secondary battery disclosed in Patent Document 1, it was found that the discharge capacity that can be taken out per discharge was extremely low.
The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide an air battery including, in an air electrode layer, a carbon material having more reaction starting points for an oxygen reduction reaction than a conventional carbon material.

  The air battery of 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 includes at least an air electrode layer, and the air The extreme layer includes a carbon material having a D / G ratio of 0.8 to 0.9.

  In the present invention, the carbon material is preferably spherical.

  In the present invention, it is preferable that an average interplanar spacing of the (002) plane of the carbon material is 0.335 nm or more and less than 0.370 nm.

In the present invention, the carbon material may have a BET specific surface area of 10 to 3000 m ² / g.

  According to the present invention, the air electrode layer includes a carbon material having a D / G ratio of 0.8 or more, that is, a carbon material having a higher reaction starting point for the oxygen reduction reaction than the conventional carbon material. As a result of being able to exchange electrons with a larger number of oxygen molecules, it is possible to realize a higher voltage than conventional air batteries.

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 graph which piled up and showed the constant current discharge curve of the air battery of Example 1, Example 2, and Comparative Example 1. FIG.

  The air battery of 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 includes at least an air electrode layer, and the air The extreme layer includes a carbon material having a D / G ratio of 0.8 to 0.9.

  As described above, an air battery using ketjen black for the air electrode layer has a high initial capacity but has a significant deterioration in durability, and therefore cannot be used repeatedly. On the other hand, as disclosed in the above-mentioned Patent Document 1, an air battery using an acicular carbon material such as VGCF for the air electrode layer has been endured for repeated use as a result of the study by the present inventors. It was found that the discharge capacity that can be taken out per discharge was extremely low.

When a needle-shaped carbon material such as VGCF is used, the reason why the discharge capacity per one time is significantly low is that the number of reaction starting points in the needle-shaped carbon material, the interval, and the area of the reaction site are It is thought that it is much smaller than conventional carbon materials. 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, a D / G ratio can be exemplified. The D / G ratio refers to the ratio of the peak intensity at 1360 cm ⁻¹ (D band) to the peak intensity at 1580 cm ⁻¹ (G band) in the Raman spectrum of the carbon material. The D band is a peak corresponding to a defect portion that is likely to be a reaction starting point in the carbon material, such as a carbon edge portion or a strained portion. On the other hand, the G band is a peak corresponding to a graphitized part that is unlikely to be a reaction starting point in a carbon material, such as a carbon network surface. Therefore, it is considered that the number of reaction starting points increases as the D / G ratio value increases.
Note that the defect portion corresponding to the D band is considered to be a place where oxygen molecules first receive electrons from the carbon material. When oxygen radicals generated as a result of oxygen molecules receiving electrons and metal ions conducted through the electrolyte layer react with each other, and a metal oxide is deposited on a defect portion corresponding to the D band and a graphitization portion corresponding to the G band. Conceivable.

As an index of the distance between reaction starting points, an average interplanar distance d ₀₀₂ of the (002) plane of the carbon material, which is obtained by an X-ray diffraction method or a powder X-ray diffraction method, can be exemplified. In general, it is considered that the smaller the value of _d002, the smaller the distance between the carbon edge portions that are reaction starting points.
As an index of the area of the reaction site, the BET specific surface area obtained by the N ₂ adsorption method can be exemplified. Although the BET specific surface area is not necessarily an electrochemically effective surface area, it is considered that the discharge capacity increases as the BET specific surface area increases. The BET specific surface area corresponds to the sum of the area of the defect portion corresponding to the D band and the area of the graphitized portion corresponding to the G band.

  On the other hand, the present inventor also examined the increase in voltage in addition to the increase in capacity. Since the energy density of a battery is defined by the product of capacity and voltage, coexistence of higher capacity and higher voltage is one of the conditions for improving the energy density. However, no examples have been confirmed that have been studied so far on increasing the voltage of the air battery within the range of the discharge voltage actually used.

The present inventor has found that a carbon material having a D / G ratio of 0.8 to 0.9 has a surface of a carbon defect portion on which O ₂ adsorption is likely to occur as compared with conventional carbon materials such as ketjen black and VGCF. We focused on including more. The present inventor uses a carbon material having a D / G ratio of 0.8 to 0.9 for an air electrode layer of an air battery, thereby causing a discharge reaction including O ₂ adsorption and O ₂ reduction on the surface of the carbon material. As a result, the discharge voltage on the surface of the carbon material increases, and the discharge mid-voltage, that is, the effective discharge voltage is also improved. As a result, the reaction overvoltage of the air battery is reduced compared to the conventional air battery, and the discharge reaction is reduced. As a result, the inventors have found that a high voltage can be realized and completed the present invention.

In the carbon material used in the present invention, the ratio of the defect portion to the graphitized portion obtained by Raman shift, that is, the D / G ratio is 0.8 to 0.9. When the D / G ratio of the carbon material is less than 0.8, as described above, the proportion of defects (reaction starting points related to oxygen reduction) in the carbon material surface is too low, and graphite occupies the carbon material surface. Since the ratio of the conversion part is too high, when the carbon material is used for the air electrode of the air battery, the effective discharge voltage of the air battery may be reduced. On the other hand, when the D / G ratio of the carbon material exceeds 0.9, an undesirable side reaction may occur because the ratio of the defective portion in the surface of the carbon material is too high.
The D / G ratio of the carbon material used in the present invention is preferably 0.81 to 0.89, and more preferably 0.82 to 0.88.
In the present invention, as a method for measuring the D / G ratio of the carbon material, for example, as described above, a method of calculating from the peak intensities of the G band and the D band in the Raman spectrum of the carbon material can be mentioned.

Mean spacing of (002) plane of the carbon material used in the present invention, i.e. _{d 002} is preferably less than or 0.335nm 0.370nm. There is theoretically no carbon material with d ₀₀₂ less than 0.335 nm. When d _{002 of} the carbon material is 0.370 nm or more, the carbon material is too low in crystallinity, so that carbon may be consumed by an undesirable side reaction.
The d ₀₀₂ of the carbon material used in the present invention is more preferably 0.335 to 0.365 nm, and further preferably 0.335 to 0.360 nm.
In the present invention, as a method for measuring d ₀₀₂ of the carbon material, for example, a method of calculating from the half width of the diffraction peak of the (002) plane in the XRD spectrum of the carbon material can be mentioned.

The BET specific surface area of the carbon material used in the present invention is preferably as large as possible, but may be, for example, 10 to 3000 m ² / g. If the BET specific surface area is too small, the reaction area involved in oxygen reduction is too small, so that when the carbon material is used for the air electrode of an air battery, the discharge capacity of the air battery may be too small.
The BET specific surface area of the carbon material used in the present invention is preferably 10 to 1600 m ² / g.
In the present invention, as a method for measuring the BET specific surface area of the carbon material, for example, a method of performing N ₂ adsorption measurement under a temperature condition of 77 K on the carbon material and calculating by the BET method can be mentioned.

As a typical example of the carbon material that satisfies all the conditions of the D / G ratio, d ₀₀₂ , and BET specific surface area, a spherical carbon material can be exemplified. The carbon material used in the present invention is preferably spherical from the viewpoint that it is easy to close-pack in the air electrode layer, and as a result, the density of the air electrode can be increased and the number of electrode reaction sites can be increased. More preferably (CNS).
The spherical carbon material used in the present invention preferably has a carbon content measured by a thermal conductivity method of 98% or more. The carbon content is also related to the degree of graphitization. On the other hand, the ketjen black described above usually has a carbon content of less than 98%.
The spherical carbon material used in the present invention is preferably a non-hollow particle. On the other hand, the ketjen black described above is usually hollow particles.
It is preferable that the spherical carbon material used in the present invention does not substantially have a structure structure (a structure in which carbon is connected like a bead), that is, has a non-structure structure. On the other hand, the ketjen black described above usually has a structure structure.

  The carbon material used in the present invention may be an unfired product or a fired product. The firing temperature of the carbon material is preferably 2000 ° C. or less, and more preferably 1500 ° C. or less.

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 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.

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 the present invention, as the non-aqueous electrolyte or non-aqueous solvent, for example, 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 Low volatile liquids such as ionic liquids such as (trifluoromethanesulfonyl) amide (DEMETFSA), N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) amide (TMPATFSA) are used. May be
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 / exhausted preferably has a high oxygen concentration, more preferably 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 air electrode [Production Example 1]
First, carbon microspheres (manufactured by Tokai Carbon; hereinafter referred to as CNS) and a non-fired product and PTFE binder (manufactured by Daikin) were mixed in a ratio of CNS: PTFE = 90% by mass: 10% by mass. Next, the mixture was rolled by a roll press, dried, and appropriately cut to produce an air electrode layer. Subsequently, as an air electrode current collector, SUS mesh (manufactured by Niraco, 100 mesh made of SUS304) was attached to one surface side of the air electrode layer to obtain an air electrode of Production Example 1.

[Production Example 2]
First, CNS (manufactured by Tokai Carbon) was fired under a temperature condition of 1100 ° C. Next, the CNS after firing and the PTFE binder (manufactured by Daikin) were mixed at a ratio of CNS: PTFE = 90% by mass: 10% by mass. Thereafter, in the same manner as in Production Example 1, rolling, drying and the like were performed to produce an air electrode layer. Subsequently, as an air electrode current collector, SUS mesh (manufactured by Niraco, 100 mesh made of SUS304) was attached to one surface side of the air electrode layer to obtain an air electrode of Production Example 2.

[Production Example 3]
First, CNS (manufactured by Tokai Carbon) was fired under a temperature condition of 2600 ° C. Next, the CNS after firing and the PTFE binder (manufactured by Daikin) were mixed at a ratio of CNS: PTFE = 90% by mass: 10% by mass. Thereafter, in the same manner as in Production Example 1, rolling, drying and the like were performed to produce an air electrode layer. Subsequently, as an air electrode current collector, SUS mesh (manufactured by Niraco, 100 mesh made of SUS304) was attached to one surface side of the air electrode layer to obtain an air electrode of Production Example 3.

2. Evaluation of carbon material D / G ratio, BET specific surface area, (002) surface for CNS unfired product used in Production Example 1, CNS fired product used in Production Example 2, and CNS fired product used in Production Example 3 The average inter-surface distance d ₀₀₂ and pH were measured.

2-1. Measurement of D / G ratio The above carbon materials were subjected to Raman measurement using a laser light source of 488 nm with a laser Raman spectrophotometer. About the obtained Raman spectrum of each carbon material, the peak intensity of 1360 cm ⁻¹ (D band) and 1580 cm ⁻¹ (G band) obtained by subtracting the baseline is calculated, and the peak intensity of the D band with respect to the peak intensity of the G band is calculated. Calculated.
Each carbon material was measured at three points at an arbitrary location, each peak intensity ratio was calculated, and the average of the three peak intensity ratios was taken as the D / G ratio of the carbon material.

2-2. Measurement of BET specific surface area For each of the above carbon materials, N ₂ adsorption measurement was performed under a temperature condition of 77 K, and the BET specific surface area was calculated by the BET method.

2-3. Measurement of average plane distance d ₀₀₂ of (002) plane For each of the above carbon materials, an XRD pattern was measured by a powder X-ray diffraction method, and the average plane of (002) plane from the half-width position of the peak of (002) plane The interval d ₀₀₂ was calculated. Detailed measurement conditions and analysis methods of powder X-ray diffraction measurement are as follows.
Radiation source: CuK _α
Tube voltage: 40 kV
Tube current: 40 mA
Analysis method: FT method

2-4. Measurement of pH In order to quantitatively evaluate the amount of functional groups on the surface of each carbon material, the pH of each carbon material was measured based on the measurement method described in JIS K1474 6.10. A pH meter according to JIS Z8802 was used.
First, 1.0 g of each carbon material was weighed in terms of dry mass and added to the container. Next, 100 mL of water was added to the container and heated for 5 minutes so that boiling continued gently. Subsequently, after cooling to room temperature and adding water to 100 mL and stirring well, the pH of the suspension was measured using a pH meter.

Table 1 below shows the D / G ratio, BET specific surface area, (002) for the CNS unfired product used in Production Example 1, the CNS fired product used in Production Example 2, and the CNS fired product used in Production Example 3. It is the table _| surface which compared average surface space _| interval _{d002 of} a surface, and pH.

3. Production of air battery [Example 1]
The air electrode of Production Example 1 was used as the air electrode.
As an electrolytic solution, 0.32 mol / kg of N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) amide (manufactured by Kanto Chemical Co., Ltd., PP13TFSA), lithium bis (trifluoromethanesulfonyl) amide (manufactured by Kishida Chemical Co., Ltd.) A solution was prepared so as to have a concentration and stirred and mixed overnight under an argon atmosphere. Moreover, the nonwoven fabric made from a polypropylene was prepared as a separator.
A SUS foil (manufactured by Niraco, SUS304) was prepared as a negative electrode current collector, and metal lithium (manufactured by Honjo Metal) was bonded to one side of the SUS foil to prepare a negative electrode.
As a battery case, a case having an oxygen uptake hole on the air electrode side was prepared.

In the battery case, the negative electrode current collector, the metallic lithium, the separator impregnated with the electrolyte, the air electrode layer containing the CNS unfired product, and the air electrode current collector are stacked in this order from the bottom of the battery case. The member was accommodated and the air battery of Example 1 was produced.
All the above steps were performed in a glove box under a nitrogen atmosphere.

[Example 2]
In Example 1, the air battery of Example 2 was produced using the same member as Example 1 except that the air electrode of Production Example 2 was used instead of the air electrode of Production Example 1.

[Comparative Example 1]
In Example 1, an air battery of Comparative Example 1 was produced using the same members as in Example 1 except that the air electrode of Production Example 3 was used instead of the air electrode of Production Example 1.

4). Measurement of effective discharge voltage of air battery The effective discharge voltage of the air battery of Example 1, Example 2, and Comparative Example 1 was 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, Constant current discharge measurement was performed under the condition of a current density of 0.02 mA / cm ² . The voltage corresponding to half of the discharge capacity obtained by measurement was defined as the effective discharge voltage of the air battery.

  Table 2 below is a table comparing the effective discharge voltages of the air batteries of Example 1, Example 2, and Comparative Example 1.

5. Summary of Evaluation FIG. 2 is a graph in which the constant current discharge curves of the air cells of Example 1, Example 2, and Comparative Example 1 are superimposed.
As shown in Table 1 and Table 2, the air battery of Comparative Example 1 has a D / G ratio of 0.168, a BET specific surface area of 12 m ² / g, d ₀₀₂ of 0.340 nm, and a pH of 6.46. CNS (fired product at 2600 ° C.) is included in the air electrode layer. As shown in Table 2, the effective discharge voltage of the air battery of Comparative Example 1 is 2.50V. Therefore, the air battery of Comparative Example 1 using a carbon material having a D / G ratio of less than 0.2 has a lower discharge effective voltage than the air batteries of Examples 1 and 2 described later.

On the other hand, as shown in Tables 1 and 2, the air batteries of Example 1 and Example 2 had a D / G ratio of 0.858 or 0.823, a BET specific surface area of 15 m ² / g, d _002. Is an air battery including CNS of 0.356 nm or 0.357 nm and pH of 6.62 or 6.34 in the air electrode layer. As shown in Table 2, the effective discharge voltage of the air battery of Example 1 is 2.57V, and the effective discharge voltage of the air battery of Example 2 is 2.51V. Therefore, the air battery of Example 1 and Example 2 using the carbon material having a D / G ratio of 0.8 to 0.9 is 0 at the maximum as compared with the air battery using the conventional carbon material. It can be seen that the effective discharge voltage is improved by 0.07V.
In addition, pH of the carbon material used for Example 1, Example 2, and the comparative example 1 was all 6-7 (weakly acidic). This shows that there is almost no difference in the state of the functional group on the surface among the three types of carbon materials. Therefore, the amount of the functional group on the surface of the carbon material does not substantially contribute to the above-described difference in effective discharge voltage of the air battery, and only the difference in the D / G ratio, that is, the difference in the structure of the end of the carbon material, This is considered to contribute to the difference in the effective discharge voltage.

  According to the inventor's calculation, an increase in discharge effective voltage of 0.05 V in a lithium-air battery means that the output is increased by 1.5 times. Further, according to the trial calculation, in the lithium-air battery, similarly, an increase in the effective discharge voltage of 0.1 V means that the output is doubled. Therefore, it can be considered that the air battery of Example 1 has a discharge effective voltage as high as 0.07 V as compared with the air battery of Comparative Example 1, which is an extremely remarkable advance from the viewpoint of practical use of the air battery. .

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 100 Air battery

Claims (4)

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,
The air electrode comprises at least an air electrode layer;
The air battery, wherein the air electrode layer includes a carbon material having a D / G ratio of 0.8 to 0.9.   The air battery according to claim 1, wherein the carbon material is spherical.   The air battery according to claim 1 or 2, wherein an average interplanar spacing of the (002) plane of the carbon material is 0.335 nm or more and less than 0.370 nm. The air battery according to claim 1, wherein the carbon material has a BET specific surface area of 10 to 3000 m ² / g.

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