JP6717681B2 - Method for producing catalyst sheet and method for producing air electrode - Google Patents

Description

The present invention relates to a method for manufacturing a catalyst sheet used for a battery electrode and a method for manufacturing an air electrode.

Various types of oxygen reduction catalysts for air electrodes have been studied so far. For example, those in which a precious metal such as a platinum group element or silver is deposited and supported on activated carbon or carbon powder, those in which activated carbon and a metal conversion product are mixed, and further, a mixture of an organometallic complex such as metal porphyrin and carbon powder, Alternatively, those heat-treated products are being studied. In general, noble metals such as platinum group elements and silver have a large catalytic effect, but since it is difficult to recycle the air electrode especially in a primary battery, it is not realistic to use an expensive material in terms of cost. Then, manganese oxide is tried as one of the cheap catalysts (for example, refer patent document 1).

Patent No. 5373966

However, as a method of applying a catalyst to the electrode, in the case of a method of producing an electrode by mixing the powder mixed with the catalyst powder to the carbon powder or the powder supported on the carbon powder together with a binder to produce an electrode, It has a drawback that the electrical connection is broken and the important electrical connection in the electrode is poor. Therefore, in the electrode, the electron transfer from the reaction field on the catalyst surface is not smooth and the charge transfer resistance increases, so that the actual performance of the air electrode is not fully obtained.
Therefore, an object of the present invention is to improve the polarization characteristics by smoothing the movement of electrons with a structure using a manganese catalyst, and to manufacture and provide an inexpensive catalyst sheet and air electrode.

In order to achieve the above object, the present invention, in a method for producing a catalyst sheet used for a battery electrode, after kneading a conductive material and an organic binder in a solution of water and a manganese catalyst precursor, followed by molding and drying. A sheet member is prepared, and the sheet member is heat-treated at a temperature at which a catalyst is obtained in the air to form a catalyst sheet, and the organic binder is a polymer dispersion having a higher melting point than the temperature at which the heat treatment is performed. There is a fluororesin such as polytetrafluoroethylene (PTFE, also referred to as Teflon (registered trademark)) or a thermoplastic resin such as a polyolefin resin such as polypropylene (PP), and the solution is manganese nitrate (II ) hexahydrate, or characterized by manganese (II) acetate tetrahydrate der Rukoto.

In the above method for producing a catalyst sheet, the catalyst sheet may be impregnated with a solution of a manganese catalyst precursor, and then dried and heat-treated.

Further, the present invention, in the method for producing an air electrode used in an air battery, after kneading a conductive material and an organic binder in a solution of water and a manganese catalyst precursor, it is molded and dried to produce a sheet member, said sheet member, to obtain a catalyst sheet by heat treatment at a temperature at which the catalyst is obtained in the atmosphere, the catalyst sheet, resulting et been by crimping the current collector, wherein the organic binder at the time of the heat treatment A polymer dispersion having a melting point higher than temperature, such as a fluororesin such as polytetrafluoroethylene (also referred to as PTFE or Teflon (registered trademark)), or a thermoplastic resin such as a polyolefin resin such as polypropylene (PP). , and the said solution is characterized manganese nitrate (II) hexahydrate, or manganese acetate (II) is tetrahydrate der Rukoto.
The catalyst sheet may be impregnated with a solution of a manganese catalyst precursor, and then dried and heat-treated.

In the present invention, a conductive material and an organic binder are kneaded in a solution of water and a manganese catalyst precursor, and then molded and dried to produce a sheet member, and the sheet member is heat-treated at a temperature at which a catalyst is obtained in the atmosphere. Then, a catalyst sheet is formed. This makes it possible to improve the polarization characteristics by smoothing the movement of electrons and obtain an inexpensive catalyst sheet. In addition, since the air electrode can be obtained by pressure-bonding this catalyst sheet to the current collector, it is possible to improve the polarization characteristics by smoothing the movement of electrons with the structure using the manganese catalyst, and to provide an inexpensive air electrode. It is easy to manufacture.

It is the figure which showed typically the cross-section of an air battery. It is the figure which showed the test result.

An embodiment of the present invention will be described below.
The example which used the catalyst sheet which concerns on embodiment of this invention for the air electrode of an air cell is shown.
FIG. 1 is a diagram schematically showing a cross-sectional structure of an air battery.
The air battery 10 includes an exterior body 11 formed of a plastic case made of resin, and an air electrode 13 and a metal electrode 15 that form a pair of electrodes are arranged to face the exterior body 11 with a gap. The air battery 10 is a primary battery in which the air electrode 13 acts as a positive electrode and the metal electrode 15 acts as a negative electrode by injecting an electrolytic solution into the outer casing 11. In FIG. 1, the symbol UL indicates the liquid level of the electrolytic solution.

The exterior body 11 is formed in a hollow box shape, and a rectangular opening 11K is provided on the front surface that constitutes the largest surface of the exterior body 11. The air electrode 13 is attached to the exterior body 11 so as to cover the opening 11K. Further, the metal electrode 15 is inserted through the metal electrode insertion opening formed on the upper surface of the exterior body 11, and is fixed by the sandwiching member 11A and the support member 11B formed inside the exterior body 11.

Note that it is also possible to use the sheet material containing paper as the exterior body 11 and use a sheet material having a film on the surface of the paper constituting the base material as the sheet material. As the sheet material, paper having at least the inner surface laminated with a heat-fusible resin (for example, polyethylene (PE)), that is, laminated paper can be used.

The air electrode 13 includes a current collector and a catalyst sheet that forms a catalyst layer for oxygen reduction, and is fixed to the exterior body 11 by adhesion or the like. The air electrode 13 has a gas permeability that allows outside air to pass through the exterior body 11, and a liquid impermeability that does not leak the electrolytic solution.
The metal electrode 15 is supported in the exterior body 11 so as to face the air electrode 13. The structure for supporting the metal electrode 15 may be fixed by the sandwiching member 11A and the supporting member 11B arranged in the exterior body 11 as described above, or by a lid portion of the exterior body 11 formed separately. Various supporting structures such as supporting the metal electrode 15 can be applied.

The metal electrode 15 is formed of a plate material made of magnesium alloy and is arranged in parallel with the air electrode 13. An aqueous solution of sodium chloride is used as the electrolytic solution. That is, the air battery 10 of this embodiment is a magnesium air battery (metal air battery).
The magnesium-air battery can use seawater as an electrolytic solution or a liquid obtained by mixing salt with tap water, so that the electrolytic solution can be easily procured. A bag body containing sodium chloride, which is an electrolyte, may be arranged in advance inside the exterior body 11, and power may be generated only by injecting water such as tap water.

The metal electrode 15 is not limited to a magnesium alloy, and a metal such as zinc, iron, or aluminum, or an alloy thereof may be used. When zinc is used for the metal electrode 15, an aqueous potassium hydroxide solution may be used for the electrolytic solution, and when iron is used for the metal electrode 15, an alkaline aqueous solution may be used for the electrolytic solution. When aluminum is used for the metal electrode 15, an electrolytic solution containing sodium hydroxide or potassium hydroxide may be used.

The air electrode 13 will be described.
The collector of the air electrode 13 is a rectangular copper mesh (copper mesh). Note that the present invention is not limited to the copper mesh, and a porous current collector having a porous structure other than the copper mesh, such as a metal mesh using a metal other than copper, can be widely applied.
The catalyst sheet is prepared by kneading a conductive material (conductive material) and an organic binder in a dispersion medium in which water and a manganese catalyst precursor are dispersed, molding and drying the mixture into a sheet, and heat-treating at a temperature at which a catalyst is obtained. It is made by This catalyst sheet is cut into a sheet of a predetermined size and then pressure-bonded to both surfaces of the copper mesh to be integrated with the copper mesh.

The step of forming the catalyst sheet into a sheet shape is performed by, for example, sandwiching a paste obtained by kneading a conductive material and an organic binder in a solution of water and a manganese catalyst precursor in a PET film and pressing the paste using a roller press machine. The step of pressure-bonding the catalyst sheet to the copper mesh (current collector) is performed by pressing with a pressing machine. Various known devices may be applied to these steps. For example, for crimping, a dedicated crimping device (including jigs and tools) suitable for crimping the catalyst sheet and the copper mesh is manufactured, and the crimping device is manufactured. You may crimp using.
As will be described later, the catalyst sheet is a product obtained by kneading and firing a granular redox catalyst, a binder, etc., so that it has unevenness on the surface and has some unevenness even after being pressed by a roller press. Have Since the catalyst sheet has irregularities, the surface area is increased, and the adhesion can be improved when the copper mesh and the catalyst sheet are pressure-bonded.

The conductive material is carbon powder. More specifically, it is a powder of carbon black such as Ketjen black (KB), carbon whiskers, graphite, graphite whiskers, activated carbon, carbon nanotubes, carbon nanowires, and carbon nanohorns. The conductive material may be a conductive material other than carbon, such as a metal material such as copper or aluminum, or an organic conductive material such as a polyphenylene derivative.
The organic binder is a polymer dispersion, specifically, a fluororesin such as polytetrafluoroethylene (also referred to as PTFE or Teflon (registered trademark)) or a polyolefin resin such as polypropylene (PP). It is a thermoplastic resin.

The dispersion medium comprises a solution of manganese catalyst precursor. This solution is not particularly limited as long as the desired manganese catalyst (manganese oxide) can be obtained. In the present embodiment, the target manganese catalyst is manganese dioxide, and the manganese catalyst precursor is manganese (II) nitrate hexahydrate or manganese (II) acetate tetrahydrate. Instead of manganese (II) nitrate hexahydrate or manganese (II) acetate tetrahydrate, an aqueous solution of another divalent manganese salt may be used.

1. (Example)
Next, examples and comparative examples will be described. Each example and comparative example have the same configuration except that the catalyst sheet is different, and the catalyst sheet will be described below. Information on each catalyst sheet is given in Table 1.

(Example 1)
KB as a conductive material and PTFE as an organic binder were kneaded in a 1M manganese nitrate aqueous solution in which water and manganese(II) nitrate hexahydrate were dissolved. At this time, fibrillation of PTFE occurred, and kneading was continued until the change in viscosity became stable to prepare a paste having a predetermined viscosity. When preparing the catalyst sheet, 1M manganese nitrate aqueous solution in which manganese(II) nitrate hexahydrate was dissolved was added so that carbon:manganese dioxide=9:1 so that the amount of water was the same. did.
Next, after being formed into a sheet and dried, a heat treatment was performed at 120° C. for one hour as a firing process. This heat treatment was performed in the presence of air and in an environment of atmospheric pressure (in air). 120° C. is the temperature at which the catalyst is obtained. By this heat treatment, manganese dioxide was obtained by thermal decomposition of manganese (II) nitrate, and fixing and supporting of manganese dioxide were completed. Then, as a sintering process of PTFE, a heat treatment was performed at 200° C. for 30 minutes. Through the above steps, a catalyst sheet containing 10% by weight of manganese dioxide with respect to the conductive material (KB) was produced.

(Example 2)
KB as a conductive material and polypropylene as a binder were kneaded in a 1M manganese nitrate aqueous solution in which water and manganese(II) nitrate hexahydrate were dissolved. At this time, kneading was continued until the viscosity change became stable, and a paste having a predetermined viscosity was produced. When preparing the catalyst sheet, 1M manganese nitrate aqueous solution in which manganese(II) nitrate hexahydrate was dissolved was added so that carbon:manganese dioxide=9:1 so that the amount of water was the same. did.
Next, after being formed into a sheet and dried, a heat treatment was performed at 120° C. for one hour as a firing process. This heat treatment was carried out in the presence of air and at atmospheric pressure, as in Example 1. Through the above steps, a catalyst sheet containing 10% by weight of manganese dioxide with respect to the conductive material (KB) was produced.

(Example 3)
KB as a conductive material and PTFE as an organic binder were kneaded in a 1M manganese acetate aqueous solution in which water and manganese (II) acetate tetrahydrate were dissolved. At this time, fibrillation of PTFE occurred, and kneading was continued until the change in viscosity became stable to prepare a paste having a predetermined viscosity. When preparing the catalyst sheet, a 1M manganese acetate aqueous solution in which manganese (II) acetate tetrahydrate was dissolved was added so that carbon:manganese dioxide=9:1 and the amount of water was the same. did.
Next, after being formed into a sheet and dried, a heat treatment was performed at 200° C. for one hour as a firing process. This heat treatment was carried out in the presence of air and at atmospheric pressure, as in Examples 1 and 2 above. Through the above steps, a catalyst sheet containing 10% by weight of manganese dioxide with respect to the conductive material (KB) was produced.

(Comparative Example 1)
A catalyst sheet was prepared by kneading KB as a conductive material and PTFE binder as an organic binder with water and molding and drying. That is, the catalyst sheet of Comparative Example 1 does not contain a manganese catalyst.

(Comparative example 2)
A catalyst sheet was prepared by mixing KB as a conductive material and manganese dioxide powder as a catalyst in a ratio of 9:1, kneading PTFE and water as an organic binder, and molding and drying the mixture. That is, a catalyst sheet containing 10% of manganese dioxide was produced by a method of simply adding manganese dioxide powder. As the manganese dioxide powder, dry battery grade electrolytic manganese dioxide (EMD) powder was used.

(Comparative example 3)
KB and 1M manganese nitrate aqueous solution in which manganese (II) nitrate hexahydrate was dissolved were kneaded so that KB as a conductive material and manganese dioxide as a catalyst had a ratio of 9:1, and the kneaded material was heated at 80°C. After being dried for 24 hours, heat-treated at 120° C. for 24 hours and then pulverized to prepare a catalyst powder having KB supported on its surface. This heat treatment was performed in the presence of air and at atmospheric pressure.
Next, this catalyst powder, PTFE and water were kneaded, and molded and dried. Thus, a catalyst sheet containing 10% manganese dioxide was produced. That is, the catalyst sheet of Comparative Example 3 is formed of powder in which manganese dioxide is deposited and carried on the surface of carbon.

(Comparative Example 4)
KB as a conductive material, polyethylene as a binder and water were kneaded to prepare a paste having a predetermined viscosity. Next, a 1M aqueous solution of manganese nitrate in which manganese(II) nitrate hexahydrate was dissolved was adjusted to have the same amount of water so that carbon:manganese dioxide=9:1, and the paste prepared above was prepared. After kneading and forming into a molded and dried sheet, as a baking treatment, a heat treatment was carried out at 120° C. for one hour in the presence of air at atmospheric pressure.
Attempts were made to produce a catalyst sheet through the above steps, but since polyethylene had a low melting point, polyethylene melted and agglomerated, strength was not obtained, and a catalyst sheet could not be produced.
The melting point of polyethylene is 95 to 130° C. for low density polyethylene and 120 to 140° C. for high density polyethylene. On the other hand, the melting point of PTFE is 327°C, and the melting point of PP is about 165°C.

2. (Evaluation test)
Each catalyst sheet except for Comparative Example 4 was cut (sized) into a predetermined size, and pressure-bonded to both surfaces of a copper mesh to prepare an air electrode 13. Next, the air battery 10 was produced using each air electrode 13 and the metal electrode 15 made of a magnesium alloy, and a polarization test by discharge was performed. The test results are shown in FIG. In FIG. 2, the horizontal axis represents the current density (mA/square centimeter), and the vertical axis represents the battery voltage (V).

As shown in FIG. 2, Examples 1 to 3 were all good results as compared with Comparative Examples 1 to 3. This indicates that by using the catalyst sheets used in Examples 1 to 3, the movement of electrons can be made smooth with the configuration using the manganese catalyst. Among the examples, good results were obtained in the order of Example 1, Example 2 and Example 3.
As for the comparative example, compared with the comparative example 1 containing no manganese catalyst, the comparative examples 2 and 3 showed some decrease in polarization, but the sufficient effect was not obtained.

The inventors have confirmed that when manganese nitrate is used as in Examples 1 and 2, manganese dioxide can be obtained at a baking temperature of about 120° C. or higher. In Examples 1 and 2, the decomposition of PTFE is avoided by performing the heat treatment at a relatively low temperature (120° C.) within the range where firing is possible.
Further, in Example 3 using manganese acetate, the baking treatment was performed at 200°C. Even at 200° C., it is sufficiently lower than the melting point of PTFE (327° C.), so that the decomposition of PTFE can be avoided.
The temperature of the heat treatment may be a temperature that avoids the decomposition of PTFE, and is preferably 320° C. or lower from the viewpoint of considering the temperature rise due to the heat of reaction. More preferably, the temperature is 120° C. or higher and 280° C. or lower. The heat treatment time may be appropriately adjusted depending on the type of binder and the heat treatment temperature.

Further, in Example 1, the sintering process is performed at 200°C. This 200° C. is a temperature that avoids the decomposition of PTFE, as described above. It should be noted that the temperature may be other than 200° C. as long as the temperature avoids the decomposition of PTFE.
Furthermore, since the present inventors perform the above heat treatment in the presence of air in an environment of atmospheric pressure, it is possible to efficiently perform thermal decomposition of the manganese catalyst precursor dispersed in the aqueous dispersion of the organic binder. is there. That is, as compared with the case where the heat treatment is performed under reduced pressure, the surrounding oxygen content is large, and the thermal decomposition reaction can be promoted.

According to the present embodiment, in the preformed sheet, the carbon powder is fixed by the polymer binder, and by impregnating the solution of the manganese catalyst precursor, drying and heat treatment, the carbon powder and the binder surface are oxidized with manganese. The physical catalyst is deposited and formed. For example, by repeating this operation a plurality of times, a dense and sufficient amount of catalyst is supported inside the sheet. Eventually, a conductive matrix of carbon supporting a catalyst, which is a reaction field, is formed in the sheet, which facilitates electron transfer in the sheet, and an air electrode composed of this sheet and a current collector. The performance of 13 is improved dramatically.

Further, the catalyst sheet is formed by heat treatment in the atmosphere at a temperature at which the catalyst can be obtained, so that the thermal decomposition reaction can be accelerated. Therefore, an inexpensive manganese-based catalyst can be efficiently operated, and an inexpensive and high-performance air battery can be obtained. In particular, when an aqueous solution of manganese nitrate is used as the solution of the manganese catalyst precursor, thermal decomposition such as the chemical formula (Formula (1)) occurs at around 120°C, so the heat treatment temperature is set to 120°C and the melting point is higher than this. When the organic binder, which is the polymer binder of (1), is used, the manganese oxide-based catalyst can be deposited without causing the sheet to break.
Mn(NO ₃ ) ₂ →MnO ₂ +2(NO ₂ )... Formula (1)

As the manganese catalyst precursor, it is necessary to consider the combination of the treatment temperature and the melting point of the organic binder, and for example, manganese (II) nitrate, manganese (II) acetate, or manganese (II) bisacetate can be used. The organic binder is not limited to a fluorine resin such as PTFE and a polyolefin resin such as polypropylene, but a polyimide resin, an aramid resin, or the like can be used.
In addition, since the organic binder has thermoplasticity, sintering of the binders occurs when the heat treatment temperature is near these sintering temperatures, and the effect of increasing the mechanical strength of the catalyst sheet can also be obtained.

That is, the catalyst sheet of the present embodiment, after kneading the carbon powder as the conductive material and the organic binder in the solution of water and the manganese catalyst precursor, it is molded and dried to produce a sheet member, the sheet member, Heat treatment is performed in the atmosphere at a temperature at which the catalyst is obtained to form a catalyst sheet. This makes it possible to improve the polarization characteristics by smoothing the movement of electrons and to manufacture an inexpensive catalyst sheet. In this case, since the sheet member is heat-treated in the atmosphere at a temperature at which the catalyst is obtained, it becomes easy to promote the thermal decomposition reaction at the time of manufacturing the sheet.

Moreover, as shown in Examples 1 and 2, since the manganese nitrate aqueous solution is used as the solution of the manganese catalyst precursor, the manganese oxide-based catalyst can be deposited and formed at a relatively low temperature. Therefore, it becomes easy to select an organic binder which is a polymer binder having a melting point higher than this.
Furthermore, since a polymer dispersion having a melting point higher than the temperature during the heat treatment is used as the organic binder, decomposition of the organic binder can be avoided and destruction of the sheet can be avoided. Moreover, the mechanical strength of the catalyst sheet can be increased by using a thermoplastic resin for the organic binder.

Further, since the air electrode 13 is obtained by pressure-bonding the catalyst sheet manufactured by the above-described manufacturing method to the current collector, the air electrode 13 capable of smoothing the movement of electrons with the structure using the manganese catalyst is obtained. It can be manufactured. Further, in the method for manufacturing the sheet and the air electrode 13 of the present embodiment, since local stress (for example, shearing force) does not act on the catalyst sheet and the air electrode 13, the quality of the catalyst sheet and the air electrode 13 is stabilized. It will be easier.

The present invention is not limited to the above-described embodiment, and various modifications and changes can be made based on the technical idea of the present invention.
For example, the catalyst sheet of the above-mentioned embodiment can be used for the air electrode of various air batteries. Further, this catalyst sheet may be used as an electrode plate of batteries other than air batteries.

10 Air Battery 11 Exterior Body 11A Holding Member 11B Supporting Member 11K Opening 13 Air Pole 15 Metal Pole

Claims (4)

In a method for producing a catalyst sheet used for a battery electrode,
A conductive material and an organic binder are kneaded in a solution of water and a manganese catalyst precursor, and then molded and dried to produce a sheet member, and the sheet member is heat-treated at a temperature at which a catalyst can be obtained in the atmosphere to form a catalyst sheet. to form,
The organic binder is a polymer dispersion having a melting point higher than the temperature during the heat treatment, and is a fluororesin such as polytetrafluoroethylene (PTFE, also called Teflon (registered trademark)), or polypropylene (PP). It is a thermoplastic resin such as a polyolefin resin such as
The solution, the catalyst sheet manufacturing method, wherein the manganese (II) nitrate hexahydrate, or manganese acetate (II) is tetrahydrate der Rukoto. The method for producing a catalyst sheet according to claim 1, wherein the catalyst sheet is impregnated with a solution of a manganese catalyst precursor, which is then dried and heat-treated. In the manufacturing method of the air electrode used in the air battery,
After kneading a conductive material and an organic binder in a solution of water and a manganese catalyst precursor, a sheet member is prepared by molding and drying, and the sheet member is heat-treated at a temperature at which a catalyst is obtained in the atmosphere to form a catalyst. A sheet is obtained, which is obtained by pressing the catalyst sheet onto a current collector,
The organic binder is a polymer dispersion having a melting point higher than the temperature during the heat treatment, and is a fluororesin such as polytetrafluoroethylene (PTFE, also called Teflon (registered trademark)), or polypropylene (PP). It is a thermoplastic resin such as a polyolefin resin such as
The method for producing an air electrode, wherein the solution is manganese (II) nitrate hexahydrate or manganese (II) acetate tetrahydrate. The method for producing an air electrode according to claim 3, wherein the catalyst sheet is impregnated with a solution of a manganese catalyst precursor, which is then dried and heat-treated.

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