JP2014017230A - Porous carbon and metal air battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide porous carbon capable of providing a metal air battery improved in output characteristics while securing high capacity, and a metal air battery including the porous carbon in a positive electrode.SOLUTION: Porous carbon used for a positive electrode of a metal air battery includes a pore containing a meso pore and a micro pore having a pore size smaller than that of the meso pore. A carbonaceous wall configuring an outer shell of the meso pore forms a three dimensional network structure, and the micro pore is formed in the carbonaceous wall. The meso pore is an open pore, and pore portions are continuous to form a connection hole. A half-value width of a pore size distribution of the pore is 2 nm or less, and a half-value width of a connection hole size distributing of the connection hole is 50 nm or more.

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.

  Such a metal-air battery has a problem in that the positive electrode capacity is not sufficient and the high-capacity characteristic inherent in the metal-air battery is not utilized. In order to solve this, Patent Document 1 reports that a positive electrode having a high capacity can be obtained by using a carbon material having a pore volume of 1.0 ml / g or more occupied by a pore diameter of 1 nm or more in diameter as the positive electrode. Yes.

JP 2002-015737 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, and its discharge evaluation is performed, a large discharge capacity can be obtained, but a higher discharge capacity can be obtained. It has been found that the voltage at the potential flat portion is low and the output performance is not sufficient for the development to the output application.

  The present invention has been made to solve such problems, and can provide a metal-air battery with improved output characteristics while securing a high capacity, and this porous carbon as a positive electrode. It aims at providing the metal air battery which comprises.

  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 constituting 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 to the pores. The porous carbon is characterized in that the half-value width of the pore diameter distribution of the pores is 2 nm or less, and the half-value width of the connection pore diameter distribution of the connection holes is 50 nm or more.

  Moreover, according to this invention, it consists of 1st porous carbon and 2nd porous carbon, 1st porous carbon is said porous carbon, and 2nd porous carbon is said porous carbon. The mesopores of the first porous carbon contain a metal oxide, and the amount of the second porous carbon is more than 0 wt% and not more than 25 wt% with respect to the total weight of the first porous carbon and the second porous carbon. A porous carbon is provided.

  Furthermore, 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, since the pore portions continuously form the connecting holes, the diffusibility of lithium ions and oxygen is improved, so that the output characteristics of the battery are improved.

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 pore diameter distribution of porous carbon. It is a graph which shows the connection hole diameter distribution of porous carbon. It is a graph which shows the current-voltage characteristic of a metal air battery. It is a graph which shows the relationship between the pore diameter distribution of the porous carbon of the positive electrode of a metal air battery, and the maximum output. It is a graph which shows the relationship between the connection hole diameter distribution of the porous carbon of the positive electrode of a metal air battery, and the maximum output. It is a graph which shows the relationship between the ratio of the porous carbon which contains a metal oxide in a mesopore, and discharge voltage.

  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, the half-value width of the pore diameter distribution of the pores is 2 nm or less, and the connection of the connection holes The half width of the pore size distribution is 50 nm or more. That.

  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 full width at half maximum of the pore diameter distribution of the pores is 2 nm or less, and the full width at half maximum of the connection hole diameter distribution of the connection holes is 50 nm or more.

  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. Furthermore, the half-value width of the pore diameter distribution of the pores is 2 nm or less, and the half-value width of the connection hole diameter distribution of the connection holes is 50 nm or more, thereby further improving the output characteristics while maintaining a high capacity. Can do.

  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. Furthermore, the pore size distribution is determined by measuring the nitrogen adsorption of porous carbon, using the BJH method from the obtained adsorption isotherm, and the width from the pore size at which the distribution is maximum to the pore size at which the distribution value is halved. Is the half-value width of the pore size distribution, and the half-value width of the connected pore size distribution is obtained by performing a palm porometry measurement of porous carbon and obtained from the bubble point method. The width up to the hole diameter is defined as the half width of the connection hole diameter distribution.

  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.

  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 template particles having substantially the same particle diameter are used, continuous pores having the same size are formed, so that sponge-like and substantially bowl-like 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 order to obtain the porous carbon of the present invention, carbonization is preferably performed at a temperature of 500 ° C. or higher and 1500 ° C. or lower in a non-oxidizing atmosphere. Since the resin with a high carbon yield is a polymer, carbonization may be insufficient at less than 600 ° C. and pore development may not be sufficient, while shrinkage is large at 1500 ° C. or more, and the oxide may sinter. This is because coarsening causes the pore size to be reduced and the specific surface area to be reduced.

  The porous carbon of the present invention comprises the first porous carbon that is the porous carbon and the second porous carbon that contains a metal oxide in the mesopores of the porous carbon. It is preferable that the amount of the second porous carbon is greater than 0 wt% and not more than 25 wt% with respect to the total weight of the porous carbon and the second porous carbon. The second porous carbon is left in the mesopores without removing the metal oxide that is the template particle in the production process of the first porous carbon. As this metal oxide, it can be used as said template particle, It is preferable to use a thing with high affinity with oxygen and lithium. By containing a small amount of the second porous carbon, the affinity between lithium and oxygen is high, and a highly active nano-sized metal oxide is highly dispersed in the electrode. It is considered that the oxygen adsorption ability is improved and the output characteristics of the battery are improved. However, if the amount of the second porous carbon exceeds 25 wt%, the effect of the first porous carbon is canceled and the characteristics are deteriorated.

  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
MgO template mesoporous carbon (manufactured by Toyo Tanso, maximum pore size of 4 nm) and PTFE binder (manufactured by Daikin) were kneaded with an ethanol solvent at a weight ratio of 90:10, rolled by a roll press, and an electrode sheet Was made. 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 MgO-templated mesoporous carbon (manufactured by Toyo Tanso, maximum pore size of distribution 200 m) 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.

Comparative Example 3
A lithium air battery was produced in the same manner as in Example 1 except that acid-treated ketjen black ECP600JD was used.

  The mesoporous carbon used in Example 1 and the ketjen black used in Comparative Example 2 were subjected to nitrogen adsorption measurement, and the pore diameter was determined from the obtained adsorption isotherm using the BJH method. The half-width of the pore size distribution is the half-width of the pore size distribution, and the palm porometry measurement is performed to obtain the connected pore size from the bubble point method. The width up to the half pore diameter is defined as the half-value width of the connected pore diameter distribution, and the results are shown in FIG. 3 and FIG.

Regarding these metal-air batteries, batteries that were held at 60 ° C. for 3 hours after production were discharged to 2.3 V under a current density of 0.1 mA / cm ² . Regarding the current-voltage characteristics, the voltage was measured after holding the battery at 60 ° C. for 3 hours and then holding it at each current density for 30 minutes. The above results are shown in Table 1 and FIGS.

Example 2
Instead of the MgO-templated mesoporous carbon of Example 1, MgO-templated mesoporous carbon containing 0 wt%, 20 wt%, 40 wt% and 60 wt% of the mesoporous carbon from which the MgO as the template particles have not been removed is used. A lithium air battery was manufactured in the same manner as described above. Regarding these metal-air batteries, the batteries maintained at 60 ° C. for 3 hours after the production were discharged under a current density of 0.1 mA / cm ² , and the discharge voltage at the time of constant capacity regulation was measured. The result is shown in FIG.

  As is clear from the above results, high capacity is maintained by using porous carbon having a half-value width of the pore size distribution of 2 nm or less and a half-value width of the connected pore size distribution of 50 nm or more for the positive electrode layer of the metal-air battery. However, it was confirmed that the output characteristics were improved.

  As in Comparative Example 2, when ketjen black was used for the positive electrode layer, the discharge characteristics were low, but this low discharge characteristic means that a rate-limiting process exists on the electrode surface during the discharge reaction. Suggests. For the reaction of the metal-air battery, it is essential that oxygen and metal ions exist in the reaction field. Porous carbon such as ketjen black has a hollow structure with pores in the primary particles and has a very large pore volume, which greatly contributes to the discharge capacity of the battery. However, since the intra-particle pores are independent and closed, it is difficult for metal ions and oxygen to diffuse into the pores. For this reason, the overvoltage increases due to the rate of material supply during the reaction, and the discharge potential decreases. Ketjen black has irregular pore diameters and a wide pore diameter distribution. For this reason, if the reaction occurs in a certain pore size region, the other pore size region is not used, which also causes a low pore utilization rate.

  On the other hand, in the porous carbon of the present invention, the carbonaceous wall constituting the outline of the mesopores has a three-dimensional network structure, and micropores are formed in the carbonaceous wall, and the surface area per unit amount That is, the specific surface area is increased, and 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. Furthermore, the half-value width of the pore diameter distribution of the pores is 2 nm or less, and the half-value width of the connection hole diameter distribution of the connection holes is 50 nm or more, thereby further improving the output characteristics while maintaining a high capacity. Can do.

  In addition, the mesopores have affinity for oxygen and lithium, and by containing a predetermined amount of porous carbon containing a highly active metal oxide, the ability to adsorb lithium ions and oxygen on the carbon surface is improved, and the battery discharge The voltage is improved.

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 (6)

  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 A mesh structure is formed, the micropores are formed in the carbonaceous wall, the mesopores are open pores, and the pore portions continuously form connection pores, and the pore size distribution of the pores The porous carbon is characterized in that the half-value width of is 2 nm or less, and the half-value width of the connection hole diameter distribution of the connection holes is 50 nm or more.   The porous carbon according to claim 1, wherein the pore diameter in the pore is 0.3 to 100 nm.   The porous carbon according to claim 1, wherein the pore volume occupied by pores having a pore diameter of 1 nm or more is 1 ml / g or more. The porous carbon according to claim 1, which has a specific surface area of 600 to 2000 m ² / g. Consisting of a first porous carbon and a second porous carbon,
The first porous carbon is the porous carbon according to any one of claims 1 to 4,
The second porous carbon contains metal oxide in the mesopores of the porous carbon according to any one of claims 1 to 4,
A porous carbon in which the amount of the second porous carbon is more than 0 wt% and not more than 25 wt% with respect to the total weight of the first porous carbon and the second porous carbon.   The metal air battery which comprises the porous carbon of any one of Claims 1-5 in a positive electrode.

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