JP2015076125A - Porous carbon and metal-air battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a porous carbon that can provide a metal-air battery the cycle characteristics of which are enhanced while ensuring high output characteristics, and to provide a metal-air battery including this porous carbon in the positive electrode.SOLUTION: A porous carbon for use in the positive electrode of a metal-air battery includes meso holes and pores including micro holes having a bore smaller than that of the meso hole. A carbonaceous wall composing the outline of the meso hole has a three-dimensional mesh structure, and the micro hole is formed in the carbonaceous wall. The meso hole is an open pore, and the pore parts continue to form a coupling hole. The amount of CO and COdetected after discharge by temperature-programmed desorption is 1000 μmol/g or less.

Description

  The present invention relates to porous carbon and a metal-air battery including the porous carbon in a positive electrode.

  A metal-air battery is a battery that uses oxygen in the air as the positive electrode active material and metal as the negative electrode active material, and has a high energy density (the amount of electric power that can be discharged with respect to weight), and can be easily reduced in size and weight. As a battery having an energy density exceeding that of a lithium ion battery which has an advantage of being present and is considered to have the highest energy density at present.

  Such a metal-air battery includes a positive electrode, a negative electrode, an electrolyte layer disposed between the positive electrode and the negative electrode, and an oxygen permeable membrane laminated on the positive electrode. A conductive material is used for the positive electrode, and a carbon material such as graphite or acetylene black is used.

  In such a metal-air battery, it has been reported that a carbon material having a porous structure, specifically, mesoporous carbon is used as the positive electrode (see, for example, Patent Documents 1 and 2).

JP 2011-178588 A JP 2011-146283 A

  As described above, when a metal-air battery is manufactured using a carbon material having a predetermined pore volume and pore size distribution, such as ketjen black or conventional mesoporous carbon, and its discharge is evaluated, a large output characteristic is obtained. However, there is a problem that the capacity retention rate (cycle characteristics) after repeating the charge / discharge cycle is low.

  The present invention has been made in order to solve such problems. Porous carbon capable of providing a metal-air battery having improved cycle characteristics while ensuring high output characteristics, and porous carbon An object is to provide a metal-air battery included in a positive electrode.

In order to solve the above problems, according to the present invention, porous carbon used for a positive electrode of a metal-air battery, comprising mesopores and micropores having a pore size smaller than the mesopores, The carbonaceous wall that forms the outline of the mesopores has a three-dimensional network structure, the micropores are formed in the carbonaceous wall, the mesopores are open pores, and the pore portions are continuously connected. Porous carbon is provided in which pores are formed and the amount of CO and CO ₂ detected by a temperature programmed desorption method after discharge is 1000 μmol / g or less.

  Moreover, according to this invention, the metal air battery which comprises the said porous carbon in a positive electrode is provided.

  In the porous carbon of the present invention, by simultaneously controlling the distribution state of pores and the difficulty of being oxidized on the surface, the metal-air battery using this porous carbon can achieve both output characteristics and cycle characteristics.

It is a schematic sectional drawing which shows the structure of the metal air battery of this invention. It is a schematic sectional drawing which shows the structure of the porous carbon of this invention. It is a graph which shows the cycling characteristics of porous carbon. It is a graph which shows the measurement result by the Raman spectroscopy of porous carbon.

The metal-air battery of the present invention collects a positive electrode having a positive electrode layer containing porous carbon and a positive electrode current collector that collects the positive electrode, a negative electrode layer containing a negative electrode active material, and the negative electrode layer. A porous carbon comprising: a negative electrode having a negative electrode current collector; a separator disposed between the positive electrode layer and the negative electrode layer; and an electrolyte layer that conducts metal ions between the positive electrode layer and the negative electrode layer. Is provided with pores including mesopores and micropores having a diameter smaller than that of the mesopores, and the carbonaceous wall constituting the outline of the mesopores has a three-dimensional network structure, and the micropores are formed in the carbonaceous walls. Formed, the mesopores are open pores, the pore portions continuously form connection holes, and the amount of CO and CO ₂ detected by the temperature programmed desorption method after discharge is 1000 μmol / g. It is characterized by the following.

  As an example of such a metal-air battery, FIG. 1 shows a cross-sectional view of a lithium-air battery, and the present invention will be described in detail with reference to this drawing.

  As illustrated in FIG. 1, a lithium-air battery 10 includes a battery case 1 including a lower insulating case 1a and an upper insulating case 1b having a microporous film 7 provided to supply oxygen, and the lower insulating case 1a. Of the negative electrode current collector 2 formed on the inner bottom surface and the negative electrode layer 3 formed on the negative electrode current collector 2 and made of metal Li, the positive electrode layer 4 containing porous carbon, and the positive electrode layer 4 A positive electrode including a positive electrode current collector 5 for collecting current, a negative electrode lead 2 ′ connected to the negative electrode current collector 2, a positive electrode lead 5 ′ connected to the positive electrode current collector 5, a negative electrode layer 3, and a positive electrode layer 4 and the electrolyte layer 6 disposed between the four. In this figure, the electrolyte layer 6 has a structure including a separator.

The battery reaction in the lithium-air battery having such a configuration is as follows.
Discharge reaction (when using batteries)
Negative electrode: 2Li → 2Li ⁺ + 2e ⁻ (1)
Positive electrode: 2Li ⁺ + 2e ⁻ + O ₂ → Li ₂ O ₂ (2)
Charging reaction (during battery charging)
Negative electrode: 2Li ⁺ + 2e ⁻ → 2Li (3)
Positive electrode: Li ₂ O ₂ → 2Li ⁺ + 2e ⁻ + O ₂ (4)

  At the time of discharging, as shown in the formulas (1) and (2), electrons and lithium ions are released from the negative electrode, while at the positive electrode, oxygen and lithium ions taken in from the outside of the battery react to react with lithium oxide. Produces. At the time of charging, as shown in equations (4) and (5), lithium ions are taken together with electrons in the negative electrode, and lithium ions and oxygen are released together with electrons in the positive electrode.

  Next, each configuration of such a lithium-air battery will be described in detail.

1. The positive electrode is composed of a positive electrode layer containing porous carbon and a positive electrode current collector that collects current from the positive electrode layer. In the present invention, as shown in FIG. 2, the porous carbon 20 includes pores including mesopores 11 and micropores 12 having a smaller diameter than the mesopores, and constitutes the outline of the mesopores. The carbonaceous wall 13 has a three-dimensional network structure, the micropores are formed in the carbonaceous wall, the mesopores are open pores, and the pore portions continuously form connection holes, The amount of CO and CO ₂ detected by the temperature programmed desorption method after discharge is 1000 μmol / g or less.

  As in the above configuration, if the carbonaceous wall that forms the outline of the mesopores has a three-dimensional network structure and micropores are formed in the carbonaceous wall, the surface area per unit amount, that is, the specific surface area is large. Therefore, many reaction fields can be provided. In addition, since the mesopores are open pores and the pore portions continuously form connection holes, the diffusibility of lithium ions and oxygen is improved, and the output characteristics of the battery are improved.

  In the present specification, those having a pore diameter of less than 2 nm are referred to as micropores, those having a pore diameter of 2 to 50 nm are referred to as mesopores, and those having a pore diameter exceeding 50 nm are referred to as macropores, and these pores are collectively referred to. May be referred to as pores. In the present specification, the pore diameter means a value measured by a nitrogen adsorption method. Further, the pore size distribution is obtained by performing nitrogen adsorption measurement of porous carbon and using the BJH method from the obtained adsorption isotherm.

  In the present invention, the proportion of pores having a pore diameter of 20 nm or more with respect to the total pore volume is preferably 70% or more.

  The pore diameter (pore diameter) in the pores including the mesopores and micropores is preferably 0.3 to 100 nm. While it is difficult to produce a material having a pore diameter of less than 0.3 nm, when the pore diameter exceeds 100 nm, the amount of carbonaceous wall per unit volume is reduced, and there is a possibility that the three-dimensional network structure cannot be maintained. .

The pore volume occupied by pores having a pore diameter of 1 nm or more is preferably 1 ml / g or more. In the lithium air battery, lithium oxides such as Li ₂ O and Li ₂ O ₂ accumulate in the pores of the positive electrode carbon material as the discharge reaction proceeds. The so-called micropores having a pore diameter of 1 nm or less in the carbon material are quickly blocked by the accumulation of the oxide and inhibit the discharge reaction, so that the contribution to the capacity is very small. Therefore, a carbon material having many pores in a mesopore region having a pore diameter of 1 nm or more gives a high capacity as a positive electrode of a nonaqueous electrolyte battery, and gives a high capacity exceeding 1600 mAh / g per unit weight. For this purpose, it is necessary to have a pore volume of 1.0 ml / g or more in the mesopore region. However, when the pore volume exceeds 4.0 ml / g, the bulk density of the carbon material becomes extremely large, and the capacity per unit volume decreases. Therefore, it is more preferable to have a pore volume of 1.0 ml / g or more and 4.0 ml / g or less in a mesopore region of 1 nm or more.

The specific surface area is measured by the BET method and is preferably 600 to 2000 m ² / g. When the specific surface area is less than 600 m ² / g, there is a problem that the formation amount of pores is insufficient and a three-dimensional network structure is not formed. On the other hand, when the specific surface area exceeds 2000 m ² / g, the shape of the carbon wall cannot be maintained. There is a problem that it will collapse.

  Furthermore, the carbon wall is composed of a carbon portion and a void portion, and the ratio of the volume of the carbon portion to the total volume of the carbon wall is preferably 40% or more. If the ratio of the volume of the carbon portion to the volume of the entire carbon wall is 40% or more, the micropores are more easily developed, so that fine pores are generated in the carbon wall.

Thus, the optimization of the pore distribution contributes to the improvement of the temperament (oxygen, lithium) diffusion and as a result is effective for the improvement of the output, but on the other hand, the contribution to the cycle characteristics is small. In order to improve cycle characteristics, it is important to control the generation / disappearance behavior of Li ₂ O _{2 on} the surface of the positive electrode, but it is difficult to achieve this only by controlling the pore distribution.

Therefore, in the present invention, the surface of the porous carbon is hardly oxidized, and specifically, the amount of CO and CO ₂ detected by the temperature programmed desorption method after discharge is 1000 μmol / g or less, preferably 100 μmol / g or less. Yes.

  Such porous carbon of the present invention includes, for example, a fluid material containing an organic resin and having a carbon yield of 40% or more and 85% or less, and an oxide, hydroxide, carbonic acid of a metal (for example, alkaline earth metal). A step of mixing at least one metal compound selected from the group consisting of a salt and an organic acid salt and template particles having substantially the same diameter to produce a mixture, and heating the mixture in a non-oxidizing atmosphere It can be manufactured by a method having a step of firing to produce a fired product and a step of removing the template particles in the fired product.

  If template particles having substantially the same particle size are used as described above, the template particles are uniformly dispersed in the matrix (in the fired product), so that variations in the spacing between the template particles are reduced. Therefore, a three-dimensional network structure in which the thickness of the carbonaceous wall is almost uniform is obtained. However, if the carbon yield of the flowable material is too small or large (specifically, if the carbon yield of the flowable material is less than 40% or exceeds 85%), the three-dimensional network structure is A three-dimensional network structure in which the location where the template particles exist becomes continuous pores after removing the template particles by using a flowable material having a carbon yield of 40% or more and 85% or less. The porous carbon which has can be obtained. Further, if the same particle size is used as the template particle, continuous pores of the same size are formed, so that sponge-like and substantially yielding porous carbon can be produced.

  Further, the diameter of the pores, the pore distribution of the porous carbon, and the thickness of the carbonaceous wall can be adjusted by changing the diameter of the template particles and the kind of the organic resin. Accordingly, by appropriately selecting the diameter of the template particles and the type of the organic resin, it is possible to produce porous carbon having a more uniform pore diameter and a larger pore capacity. Furthermore, since the porous carbon can be produced without using the flowable material containing the organic resin as the carbon source and without undergoing the activation treatment step, the obtained porous carbon has a very high purity.

  In addition, it is preferable to use an alkaline earth metal compound as the template particle, but it is possible to remove the alkaline earth metal compound with a weak acid or hot water (that is, the template particle can be removed without using a strong acid). Therefore, in the step of removing the template particles, it is possible to suppress changes in the properties of the porous carbon itself. In addition, when weak acid is used, there is an advantage that the removal speed is increased. On the other hand, when hot water is used, there is an advantage that the disadvantage that the acid remains and becomes an impurity can be prevented. In the step of removing the template particles, the eluted oxide solution can be used again as a raw material, and the production cost of porous carbon can be reduced.

  On the other hand, the raw material used as the oxide is not only an alkaline earth metal oxide (magnesium oxide, calcium oxide, etc.) but also a metal organic acid (magnesium citrate, Magnesium oxide, calcium citrate, calcium oxalate, etc. In addition, common inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, citric acid, acetic acid, and formic acid are used as cleaning solutions for removing oxides. It is preferably used as a dilute acid of 2 mol / l or less, and hot water at 80 ° C. or higher can also be used.

Furthermore, in the porous carbon of the present invention, in order to reduce the amount of CO and CO ₂ detected by the temperature programmed desorption method after discharge to 1000 μmol / g or less, it is necessary to make the surface difficult to be oxidized. Graphitization is performed at a temperature of 2000 ° C. or higher, preferably 2500 ° C. or higher in an oxidizing atmosphere.

  The positive electrode layer in the present invention may contain at least the above porous carbon, but preferably further contains a binder for fixing the porous carbon. Examples of the binder include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). Although it does not specifically limit as content of the binder in a positive electrode layer, It is preferable to exist in the range of 1 weight%-40 weight%.

  The thickness of the positive electrode layer in the present invention varies depending on the use of the lithium-air battery, but is preferably in the range of 2 μm to 500 μm, and more preferably in the range of 5 μm to 300 μm.

  Further, as a method for forming the positive electrode layer, on the positive electrode current collector described below, a method in which a paint in which a composition composed of the porous carbon and a binder is dispersed in a solvent is applied by a doctor blade method or the like, A method of molding the composition by a pressure press can be used.

  The positive electrode current collector used in the present invention collects current from the positive electrode layer. The material of the positive 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 positive electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. Especially, in this invention, it is preferable that the shape of a positive electrode electrical power collector is a mesh form. This is because the current collection efficiency is excellent. In this case, usually, a mesh-like positive electrode current collector is disposed inside the positive electrode layer. Furthermore, the lithium-air battery of the present invention may have another positive electrode current collector (for example, a foil-shaped current collector) that collects charges collected by the mesh-shaped positive electrode current collector. In the present invention, a battery case to be described later may have the function of a positive electrode current collector.

  The thickness of the positive electrode current collector in the present invention is, for example, preferably in the range of 10 μm to 1000 μm, and more preferably in the range of 20 μm to 400 μm.

2. Next, the negative electrode used in the metal-air battery of the present invention will be described. The negative electrode used in the present invention has a negative electrode layer containing a negative electrode active material and a negative electrode current collector that collects current from the negative electrode layer.

  The negative electrode layer used in the present invention contains at least a negative electrode active material having lithium. The negative electrode active material used in the present invention is preferably capable of occluding and releasing lithium ions. Such a negative electrode active material is not particularly limited as long as it has lithium, and examples thereof include a simple metal, an alloy, a metal oxide, and a metal nitride. Furthermore, examples of the alloy having a 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 which has 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.

  Further, the negative electrode layer in the present invention may contain only the negative electrode active material, or may contain a binder in addition to the negative electrode active material. For example, when the negative electrode active material is in the form of a foil, a negative electrode 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 layer having a negative electrode active material and a binder can be obtained. Since this binder is the same as the contents described in “2. Positive electrode” described above, description thereof is omitted here. In addition, as a method for forming the negative electrode layer using the powdered negative electrode active material, a doctor blade method, a molding method using a pressure press, or the like can be used similarly to the positive electrode layer.

  The material for the negative electrode current collector in the present invention is not particularly limited as long as it has conductivity, and examples thereof include copper, stainless steel, nickel, and carbon. 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.

3. Separator The separator used in the present invention is installed between the positive electrode layer and the negative electrode layer. The separator is not particularly limited as long as it has a function of electrically separating the positive electrode layer and the negative electrode layer. For example, a porous film such as polyethylene (PE) or polypropylene (PP), PE, Examples thereof include porous insulating materials such as resin nonwoven fabrics such as PP and nonwoven fabrics such as glass fiber nonwoven fabrics.

  The separator preferably has a porosity in the range of 30 to 90%. If the porosity is less than 30%, it may be difficult to sufficiently hold the electrolyte in the separator. On the other hand, if the porosity exceeds 90%, sufficient separator strength cannot be obtained. Because there is a fear. A more preferable range of the porosity is 35 to 60%.

4). Electrolyte layer In the present invention, the electrolyte layer may be in the form of either a solution system represented by an organic solvent system containing a lithium salt or a solid film system represented by a polymer solid electrolyte system containing a lithium salt. . In the case of a solution system, as the electrolyte layer, a liquid electrolyte solution prepared by dissolving a lithium salt in a nonaqueous solvent can be used. As the non-aqueous solvent, a known non-aqueous solvent can be used as a solvent for the lithium secondary battery. For example, propylene carbonate (PC), ethylene carbonate (EC), or a mixed solvent of both of them (referred to as a first solvent) and one or more non-solvents having a viscosity lower than that of the PC or EC and a donor number of 18 or less. It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent with an aqueous solvent (hereinafter referred to as a second solvent).

  As the second solvent, a carbonate ester bond or a chain carbonate containing an ester bond in the molecule is preferable. Among them, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), Examples include isopropiomethyl carbonate, ethyl propionate, methyl propionate, γ-butyrolactone (γ-BL), ethyl acetate, and methyl acetate. These second solvents can be used alone or in the form of a mixture of two or more. In particular, the second type solvent preferably has a boiling point of 90 ° C. or higher.

  The blending amount of the EC or PC in the mixed solvent is preferably 10 to 80% by volume ratio. A more preferable blending amount of EC or PC is 20 to 75% by volume ratio. Specific examples of the mixed solvent include EC and PC, EC and DEC, EC and PC and DEC, EC and γ-BL, EC and γ-BL and DEC, EC and PC and γ-BL, EC and PC, and A mixed solvent of γ-BL and DEC, preferably having a volume ratio of EC of 10 to 80%. A more preferred EC volume ratio is in the range of 25-65%.

Examples of the electrolyte contained in the nonaqueous electrolytic solution include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), and lithium trifluoromethanesulfonate (LiCF _3). SO ₃ ), lithium salts (electrolytes) such as bistrifluoromethanesulfonylamidolithium [LiN (CF ₃ SO ₂ ) ₂ ], and the like, but are not limited thereto.

  The amount of electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2.5 mol / l. When using a liquid nonaqueous electrolyte layer, as described above, the nonaqueous electrolyte layer is formed by impregnating and holding the nonaqueous electrolyte in the separator.

When using a solid electrolyte nonaqueous electrolyte layer, a film containing a polymer material in which a lithium salt is dissolved can be used as the polymer solid electrolyte. Examples of the polymer material include polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and the like. As the lithium salt, for example, lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ] and the like. Moreover, it is preferable to add an organic solvent to the solid electrolyte layer in order to improve ionic conductivity. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), fluorine-containing carbonates, chain carbonates, and the like. These organic solvents may be used alone or in combination of two or more.

  As described above, the air lithium secondary battery has been described as an example of the nonaqueous electrolyte battery of the present invention. However, as the negative electrode active material, a material capable of inserting and extracting metal ions composed of sodium, aluminum, magnesium, cesium, or the like is used. It can also be used as another air metal secondary battery. In preparing other air metal secondary batteries, metal salts such as sodium, aluminum, magnesium, cesium, etc. may be used as the above-mentioned electrolyte.

5. Battery Case The battery case is not particularly limited as long as it can accommodate the above-described positive electrode, negative electrode, and electrolyte layer, and specific examples include a coin type, a flat plate type, a cylindrical type, and a laminate type. it can. The battery case may be an open-air battery case or a sealed battery case. In the case of a battery case that is open to the atmosphere, the battery case has a vent hole through which air can enter and exit, and the air can be in contact with the positive electrode. On the other hand, when the battery case is a sealed battery case, it is preferable to provide a gas (air) supply pipe and a discharge pipe in the sealed battery case. In this case, the gas to be supplied / exhausted is preferably a dry gas, in particular, preferably has a high oxygen concentration, and more preferably pure oxygen (99.99%). In addition, it is preferable to increase the oxygen concentration during discharging and decrease the oxygen concentration during charging.

  Further, the metal-air battery of the present invention may be one in which a plurality of power generating elements in which a positive electrode layer, an electrolyte layer, and a negative electrode layer are arranged in this order are stacked via an intermediate current collector. The metal-air battery of the present invention may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because the effects of the present invention can be more effectively exhibited. Further, the use of the metal-air battery of the present invention is not particularly limited, and examples thereof include a vehicle-mounted application, a stationary power supply application, and a household power supply application.

  Next, the method for producing a lithium-air battery of the present invention is not particularly limited as long as it can obtain the above-described lithium-air battery, and is the same method as the method for producing a general lithium-air battery. Can be used. For example, when manufacturing a coin-cell type lithium-air battery, under an inert gas atmosphere, first, a negative electrode having a negative electrode layer and a negative electrode current collector is placed in the negative electrode side battery case, and then on the negative electrode layer. A separator is disposed, and then the electrolyte is injected from above the separator. Next, a positive electrode having a positive electrode layer and a positive electrode current collector is disposed with the positive electrode layer facing the separator side, and then the positive electrode side. Examples of the method include arranging the battery case and finally caulking them.

Example 1
Graphitized MgO template mesoporous carbon (made by Toyo Tanso, maximum pore size of 4 nm) and PTFE binder (made by Daikin) heat-treated at 2500 ° C. and kneaded with ethanol solvent at a weight ratio of 90:10. The electrode sheet was produced by rolling with a roll press. As an electrolyte, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bistrifluoromethanesulfonylamide (DEMETFSA, manufactured by Kanto Chemical) and LiTFSA (lithium bistrifluoromethanesulfonylamide, manufactured by Kishida Chemical) are used. What was stirred, mixed and dissolved overnight under an Ar atmosphere so as to have a concentration of 0.32 mol / kg was used. Further, a polyolefin separator as a separator, a metal Li (manufactured by Honjo Kagaku) as a negative electrode and a SUS304 plate (manufactured by Niraco) attached as a current collector plate are arranged as shown in FIG. Manufactured.

Comparative Example 1
A lithium-air battery was produced in the same manner as in Example 1 except that the heat treatment temperature was 1000 ° C. or less and non-graphitized MgO-templated mesoporous carbon (Toyo Tanso, maximum pore size of 200 m distribution) was used. .

Comparative Example 2
A lithium-air battery was produced in the same manner as in Example 1 except that Ketjen Black ECP600JD (manufactured by Ketjen Black International) was used instead of MgO-templated mesoporous carbon.

Regarding these metal-air batteries, batteries that were held at 60 ° C. for 3 hours after fabrication were discharged to 2.3 V under a current density of 0.2 mA / cm ² . Thereafter, the battery was charged to 3.85 V under a current density of 0.12 mA / cm ² . The following is repeated.

The temperature programmed desorption method was performed according to the following procedure.
(1) The sample after discharge was linearized with pure water to remove discharge products.
(2) The sample was put in a quartz tube and heated to 1100 ° C. in a He atmosphere.
(3) Since the carbon surface functional group was eliminated as CO and CO ₂ , this was quantified using micro GC. In addition, the influence of the peak accompanying decomposition | disassembly of a binder (a PTFE in a present Example) was excluded.

  Regarding the pore size distribution, nitrogen adsorption measurement was performed on the positive electrodes of Examples and Comparative Examples, and the BJH method was determined from the obtained adsorption isotherms. Further, the positive electrodes of Example 1 and Comparative Example 2 were measured by Raman spectroscopy. The above results are shown in FIGS.

From the results of FIG. 4, it can be seen that the porous carbon of Example 1 is certainly graphitized. Also, as shown in FIG. 3, by using graphitized carbon in which the amount of CO and CO ₂ detected by the temperature programmed desorption method after discharge is 1000 μmol / g or less as porous carbon as the positive electrode, Compared to the case of using non-graphitized carbon or ketjen black in which the amount of CO and CO ₂ detected by the temperature programmed desorption method is more than 1000 μmol / g, a higher capacity is maintained after 5 cycles of charge and discharge. It was.

DESCRIPTION OF SYMBOLS 1 Battery case 2 Negative electrode collector 3 Negative electrode layer 4 Positive electrode layer 5 Positive electrode collector 6 Electrolyte layer 7 Microporous film 10 Lithium air battery 11 Mesopore 12 Micropore 13 Carbonaceous wall

Claims (4)

Porous carbon used for a positive electrode of a metal-air battery, comprising pores including mesopores and micropores having a pore diameter smaller than the mesopores, and a carbonaceous wall constituting the outline of the mesopores is three-dimensional It has a network structure, the micropores are formed in the carbonaceous wall, the mesopores are open pores, and the pore portions continuously form connection holes, and temperature rising and desorption after discharge Porous carbon, wherein the amount of CO and CO ₂ detected by the method is 1000 μmol / g or less.   The porous carbon according to claim 1, wherein the proportion of pores having a pore diameter of 20 nm or more is 70% or more with respect to the total pore volume. The porous carbon according to claim 1 or 2, wherein the amount of CO and CO ₂ detected by the temperature programmed desorption method is 100 µmol / g or less.   The metal-air battery which comprises the porous carbon of any one of Claims 1-3 in a positive electrode.

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