JP3172852B2 - Air electrode, method of manufacturing the air electrode, and air battery having the air electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical air electrode such as a cylindrical or rectangular cylinder having a gas diffusion electrode using oxygen as an active material, and having excellent high rate (high load) discharge characteristics and liquid leakage resistance. The present invention relates to a method for manufacturing an air electrode and an air battery having the air electrode.

[0002]

2. Description of the Related Art Conventionally, a cylindrical air electrode is made of a polytetrafluoroethylene (hereinafter referred to as PTFE), a water-repellent fluororesin porous membrane having oxygen gas permeability and a conductive current collector such as a nickel net or an expanded metal. And a porous catalyst layer obtained by mixing various metal oxides, activated carbon, and PTFE dispersion, and a three-layer electrode, which is formed by pressing and pressing the whole, into a cylindrical shape, is curved. Both end portions were formed by bonding with synthetic rubber or epoxy resin adhesive. For example, as a water-repellent fluororesin porous membrane, a sheet having oxygen gas permeability, such as PTFE, a copolymer of tetrafluoroethylene and hexafluoropropylene (hereinafter, referred to as FEP), and a nickel wire netting as a current collector, By using an expanded metal or the like, a water-repellent fluororesin porous membrane, a catalyst layer, and a current collector are laminated in this order and pressed to form a three-layer electrode.

The electrode is curved so that the current collector is on the inside, and both ends of the current collector are partially overlapped to form a cylinder. Next, the overlapped portion of the fluororesin porous membrane and the current collector exposed by removing the catalyst layer portion are welded by welding means such as spot welding or beam welding, and the joint is filled with fluororesin and liquid-tight. (See Japanese Patent Application Laid-Open No. 58-75773) or after the current collector is joined in a cylindrical shape using spot welding or the like in advance, and a sheet serving as a catalyst layer is slightly overlapped on both ends of the outside of the cylinder. A method of winding together, and further wrapping the fluororesin porous membrane slightly at both ends, winding and press-fitting to integrate them (Japanese Patent Application Laid-Open No.
198862) is known.

In any of the above-mentioned known electrodes, leakage of the electrolyte is prevented by a fluororesin porous membrane made of PTFE or FEP on the outermost periphery.

[0005] However, these fluororesin materials are excellent in water repellency due to the lowest surface energy among various films, but are very poor in tackiness. Therefore, even if these films are wound around a current collector or a catalyst layer, the binding force is very weak. In such an electrode, the electrolyte penetrates into the interface between the water-repellent fluororesin porous membrane and the current collector or the catalyst layer during discharge to form a liquid film, and as a result, this liquid film prevents the supply of oxygen. And the discharge performance is not good.

On the other hand, at both ends of the wound water-repellent fluororesin porous film, a method of heat-sealing the PTFE or FEP porous film to a temperature higher than the melting point of the PTFE or FEP as in the above-mentioned known example. Is conventionally performed. However, in the case of a porous PTFE membrane,
Even if the temperature is raised to 80 ° C., the melt viscosity is extremely high at 10 ¹¹ to 10 ¹³ poise, so that it is necessary to apply pressure to cool and combine the PTFE porous membranes in order to join the porous PTFE membranes.
In order to eliminate the pinholes in the FE porous membrane to obtain an electrode with less liquid leakage, there is a problem that a very complicated and sophisticated technique is required.

On the other hand, in the case of a FEP porous membrane, the melt viscosity is extremely small, 10 ⁴ to 10 ⁵ , so that when the FEP is melted,
There is a problem that P flows out and is deformed, and does not function as a porous film because it blocks pores. As described above, in the case of the cylindrical electrode, of the two points of the bonding of the bonding interface between the water-repellent fluororesin porous membrane and the current collector or the catalyst layer and the joining of both ends of the water-repellent fluororesin porous membrane, If the bonding at one of the two points is poor, a problem occurs in the discharge characteristics or liquid leakage resistance.

[0008]

SUMMARY OF THE INVENTION The present invention is to stabilize discharge characteristics by preventing the formation of a liquid film at the interface between electrode components by passing a current as in the above-mentioned conventional example, and to stabilize discharge characteristics. It is an object of the present invention to provide an air electrode and an air battery having excellent liquid leakage resistance by solving the weak point of the joining of the water repellent sheet.

[0009]

According to the first aspect of the present invention, at least three of a current collector, a catalyst layer, and a fluororesin porous membrane are overlapped, and both end portions thereof come into contact with or approach each other. In the air electrode formed in a cylindrical shape as described above, a dispersion containing a fluororesin having a melting point lower than the melting point of the fluororesin porous membrane is attached to the surface of the fluororesin porous membrane, and the fluororesin in the dispersion is melted. With a temperature treatment above the temperature,
An air electrode is formed by binding the fluororesin porous membranes or the fluororesin porous membrane and the catalyst layer.

The invention according to claim 2 is the same as the invention according to claim 1, except that the fluororesin porous film is a PTFE porous film, and the invention according to claim 3 is according to claim 1. A dispersion obtained by emulsion polymerization as a dispersion containing a fluororesin in addition to the invention according to the invention described in (2) or (2).
This is a dispersion containing a liquid in which hydrophobic colloidal resin particles of EP are suspended using a nonionic surfactant or an anionic surfactant.

The invention according to claim 4 is the first invention.
The method for manufacturing an air electrode according to the invention according to the description, the invention according to claim 5 is the method for manufacturing the air electrode according to claim 2, and the invention according to claim 6 is the invention according to claim 3. This is a method for manufacturing an air electrode.

The invention according to claim 7 is the first invention.
An air battery provided with the air electrode according to any one of claims 1 to 3 as a positive electrode. The invention according to claim 8 is manufactured by the method for manufacturing an air electrode according to any of claims 4 to 6. An air battery provided with the air electrode as a positive electrode.

Further, according to the ninth aspect of the present invention, at least four members of a current collector, a catalyst layer, a gas diffusion layer having carbon black and a fluororesin, and a fluororesin porous film are mutually connected at both sides. At least one of the gas diffusion layer and the fluororesin porous membrane adheres a dispersion containing a fluororesin having a melting point lower than that of the fluororesin porous membrane to an air electrode formed in a cylindrical shape so as to be in contact with or approaching. The air electrode is heat-treated at a temperature equal to or higher than the melting temperature of the fluororesin in the dispersion.

According to a tenth aspect of the present invention, in addition to the ninth aspect, the fluororesin porous membrane is made of PTF.
The invention according to claim 11 is an E porous membrane, and the invention according to claim 11 is claim 9.
Or a liquid in which a fluororesin dispersion is obtained by suspending hydrophobic colloidal resin particles of FEP obtained by emulsion polymerization using a nonionic surfactant or an anionic surfactant. The invention according to claim 12 is an air battery provided with the air electrode according to any one of claims 9 to 11 as a positive electrode.

[0015]

According to the above construction, a fluororesin porous membrane having a high melting point and a high melt viscosity maintains its shape as a porous membrane, and a dispersion in which a fluororesin having a melting point lower than the melting point of the fluororesin porous membrane is dispersed. Since the liquid has adhered to the porous membrane, the fluororesin is melted by a temperature treatment higher than its melting point and strongly binds the fluororesin porous membranes or the fluororesin porous membrane and the catalyst layer. This prevents the electrolyte from penetrating into the interface between the fluororesin porous membrane and the current collector or the catalyst layer due to the discharge, and therefore prevents the supply of oxygen by the liquid film of the permeated electrolyte, resulting in poor discharge. Phenomenon can be prevented.

Further, in addition to the above-mentioned functions, claims 9 to 1
The air electrode described in No. 2 and the air battery provided with the air electrode have a gas diffusion layer that has carbon black, and has a bulky gas diffusion layer that can sufficiently hold air. Load) A fall in the battery voltage due to insufficient air supply at the beginning of discharge can be prevented by supplying air from the gas diffusion layer.

[0017]

【Example】

(Embodiment 1) Hereinafter, the present invention will be described along with specific embodiments with reference to the drawings.

FIG. 1 is a sectional view of a cylindrical zinc-air battery to which the present invention is applied. From the inside, 1 is a catalyst layer, 2 is a current collector, 3 is a water-repellent fluororesin porous film, and these three-layer cylindrical molded bodies are 4A.

The air electrode is formed by pressing a sheet-like catalyst layer 1 onto a net-like current collector 2 covered with a conductive paint. The catalyst layer 1 was prepared by mixing 3 kg of activated carbon, 4 kg of manganese oxide, 1.5 kg of carbon black and 0.7 kg of fluororesin powder, adding ethyl alcohol to the mixed mixture, kneading the mixture, and extruding to form a flat belt. Rolled into a 0.6 mm sheet by passing between two rollers heated to about 60 ° C. For the current collector 2, a so-called seamless cylindrical wire mesh in which the weft is woven into the warp spirally,
When the sheet-shaped catalyst layer 1 is pressed and pressed from the inside of the current collector 2 to the outside, a cylindrical molded body 4A having a seamless three-layer structure can be obtained. Next, a dispersion containing a fluororesin having a lower melting point is applied to the surface of the water-repellent fluororesin porous film 3 having gas permeability, and the fluororesin porous film 3 is applied to the cylindrical molded body 4A having the three-layer structure. After the winding, heat treatment is performed at 280 ° C. for 2 hours. At this time, a 50 μm thick PTFE porous membrane was used as the fluororesin porous membrane 3, and FEP was used as the fluororesin in the dispersion liquid to be applied.
5 is a separator and 6 is a gelled zinc negative electrode. The gelled zinc negative electrode 6 was prepared as follows. That is, 3% by weight of sodium polyacrylate and 1% by weight of carboxymethylcellulose are added to a 40% by weight aqueous solution of potassium hydroxide (containing 3% by weight of zinc oxide) to gel. Next, zinc powder having a weight ratio twice that of the gel electrolyte was added and mixed to obtain a gel zinc negative electrode. 7 is an air diffusion paper, 8 is a positive electrode can, and 9 is an insulating tube. 10 is an air intake hole, 11 is a hermetic seal to be removed before using the battery, 1
2 is a plate. 13 and 14 are metal caps.
14 and 14, a cylindrical air electrode is sandwiched and pressed, and the current is collected by spot welding with the positive electrode can 8. Reference numeral 15 denotes an organic sealant, 16A and 16B denote resin sealing members, 17 denotes a negative electrode terminal cap, and 18 denotes a negative electrode current collector.

The above-mentioned 10 cylindrical zinc-air batteries of 60
(Table 1) shows the number of leaked batteries and the 100 mA constant-current discharge capacity after sealed storage at 20 ° C for 20 days.

[0021]

[Table 1]

As shown in Table 1, the battery type No. 1
No. 4 shows that the dispersion liquid was not applied to the surface of the porous PTFE membrane and the end of the porous membrane winding end was not heat-sealed. No. 2 was obtained by heat-sealing only the end of the PTFE porous membrane winding end. No. 3 is obtained by applying a fluororesin dispersion of PTFE, which is the same component as the porous film, to the surface of the PTFE porous film and performing a heat treatment. In this case, the heat treatment was performed at 340 ° C., which is higher than the PTFE melting point. Battery type No. Reference numeral 4 denotes a battery according to an example of the present invention, in which an FEP dispersion is applied to the surface of a PTFE porous film. Battery type No. 5 is the battery type N
o. 4 is a battery in which the end of the winding end of the porous PTFE membrane is further heat-sealed. As is clear from Table 1, when the dispersion is not applied, even if the winding end of the porous film is heat-sealed, the liquid leakage resistance cannot be secured, and the liquid film is formed at the interface between the porous film and the catalyst layer due to the discharge. It is generated and reduces the discharge characteristics. When PTFE is used for the dispersion, the battery type N
o. Since the melt viscosity of PTFE is high as in 3, the clogging of the porous film itself does not occur, but the binding property by the application of the dispersion is not obtained, and the leakage resistance and discharge characteristics are not good. On the other hand, the battery type No. 4 and battery type No. In the battery according to the fifth embodiment of the present invention, PTFE has a melting point of 327 ° C. and a high melt viscosity, so that the porous membrane is maintained without change.
Melts at 0 ° C. due to low melt viscosity and melts by heat treatment. Therefore, due to the adhesive effect of the melted FEP, the porous PTFE membranes or the porous PTFE membrane and the catalyst layer are strongly bonded. As a result, it is possible to improve the liquid leakage resistance and prevent the electrolyte from penetrating into the interface between the porous membrane and the catalyst layer due to the discharge, thereby preventing the supply of oxygen and deteriorating the discharge. In the above, the electrode of each battery type was wound around the porous membrane three times, but the same result was obtained when the electrode was wound one or more times. In the examples of the present invention, the FEP dispersion was applied to the PTFE porous membrane. However, the same good results were obtained when the FEP dispersion was further applied to the cylindrical catalyst layer side.

In the first embodiment, the electrode and the battery are formed in a cylindrical shape. However, the present invention is not limited to the cylindrical shape, but may be a cylindrical shape such as a rectangular tube type.

Further, in Example 1, a dispersion of PTFE porous membrane and FEP was used, but the point is that a porous membrane was formed by a fluororesin having a high melting point, and a fluororesin having a melting point lower than the melting point was dispersed. Any dispersion may be used. And among the fluororesins that can be used in the present invention, there are copolymers of ethylene and tetrafluoroethylene, polyperfluoromonofluoromethoxypentane, polyperfluorodifluoroethoxyhexane, polyperfluorodifluoroethoxyhexane, and other alkyl fluoride groups such as polyperfluorodifluoroethoxyhexane. There are various conventionally known fluororesins such as a perfluoroalkoxy resin having a chain, polyfluorinated ethylene and polyhexafluoropropylene.

(Example 2) FIG. 2 is a sectional view of a battery employing a four-layer cylindrical air electrode having a gas diffusion layer provided between a fluororesin porous membrane and a catalyst layer. 4B in the figure is a cylindrical molded body having a four-layer structure including a catalyst layer. From inside, 1 is a catalyst layer, 2 is a current collector, 3A is a gas diffusion layer made of carbon black and fluororesin, and 3B is a water repellent. It is a fluororesin porous membrane.

For the air electrode, a sheet-like catalyst layer 1 is pressed onto a net-like current collector 2 covered with a conductive paint. This sheet-like catalyst layer 1 is composed of 3 kg of activated carbon and 4 k of manganese oxide.
g, 1.5 kg of carbon black and 0.7 kg of fluororesin powder, ethyl alcohol was added to this mixture, and the mixture was kneaded.
The sheet was further passed through two rollers heated to about 60 ° C. and rolled to form a 0.6 mm sheet. A seamless cylinder is formed by pressing a sheet-like catalyst layer 1 from the inside to the outside of the current collector 2 using a so-called seamless cylindrical wire mesh in which the weft is woven into the current collector 2 in a spiral manner. It can be formed into a molded body 4B. Next, 4 kg of carbon black and 6 kg of PTFE powder are mixed, and a sheet-shaped gas diffusion layer formed to a thickness of 200 μm in the same manner as the catalyst layer 1 is wound around the cylindrical molded body two times. Further, a dispersion containing a fluororesin having a lower melting point is applied to the surface of the water-repellent fluororesin porous membrane 3B having gas permeability, wound around the cylindrical molded body three times, and then heat-treated at 280 ° C. for 2 hours. At this time, a 50 μm thick PTFE porous membrane was used as the fluororesin porous membrane 3B, and FEP was used as the fluororesin in the dispersion liquid to be applied. 5 is a separator and 6 is a gelled zinc negative electrode. The gelled zinc negative electrode was prepared as follows. A 40% by weight aqueous solution of potassium hydroxide (containing 3% by weight of zinc oxide) is mixed with 3% by weight of sodium polyacrylate and 1% by weight of carboxymethylcellulose to gel. Next, zinc powder having a weight ratio twice that of the gel electrolyte was added and mixed to obtain a gel zinc negative electrode. 7 is an air diffusion paper, 8 is a positive electrode can, and 9 is an insulating tube. 1
0 is an air intake hole, 11 is a hermetic seal to be peeled off before using the battery, and 12 is a dish paper. Reference numerals 13 and 14 denote metal caps, in which a cylindrical air electrode is sandwiched between 13 and 14 for pressure bonding, and current is collected by spot welding with the positive electrode can 8. Reference numeral 15 denotes an organic sealant, 16A and 16B denote resin sealing members, 17 denotes a negative electrode terminal cap, and 18 denotes a negative electrode current collector.

The above-mentioned 10 cylindrical zinc-air batteries of 100
(Table 2) shows the number of leaked batteries which were sealed and stored at 60 ° C. for 10 days after the mA constant current discharge, the 100 mA constant current discharge capacity, and the minimum falling voltage at the start of the 500 mA constant current discharge.
The reason for using the battery after discharge in the liquid leakage test is that it is considered that the zinc expands due to the discharge, so that it is easy for the liquid to leak after the discharge and a difference easily appears in the liquid leakage resistance evaluation.

[0028]

[Table 2]

As shown in Table 2, the battery type No. 1
No gas diffusion layer was applied, and no dispersion was applied to the surface of the PTFE porous membrane. No. 2 does not apply a gas diffusion layer, but has a FPTFE dispersion applied to the surface of a PTFE porous membrane. 3 to the battery type No. The battery type No. 5 applies the gas diffusion layer. No. 3 is the one in which the FEP dispersion is applied only to the surface of the gas diffusion layer, battery type N
o. No. 4 is a PTFE porous membrane coated with an FEP dispersion liquid. No. 5 is applied to both. As is clear from Table 2, when the FEP dispersion liquid was applied to the PTFE porous membrane or the gas diffusion layer, the battery type No. when the FEP dispersion liquid was not applied. Compared with No. 1, the discharge characteristics and the resistance to liquid leakage after the discharge are dramatically improved. This is considered to be the same as the operation described in the first embodiment. Furthermore, in the battery using the gas diffusion layer, an improvement was confirmed in the initial fall of the battery voltage at the time of heavy load discharge, which indicates that the sheet-like diffusion layer has a porous shape that can sufficiently hold air due to the height of the carbon black. It is considered that the fall of the battery voltage due to insufficient air supply was prevented by supplying air from the gas diffusion layer at the beginning of high-rate discharge. In this example, three rounds of the PTFE porous membrane were wound, but the same result was obtained with one or more rounds. Also, in the case of the gas diffusion layer, a similar effect of suppressing the fall of the battery voltage was observed in one or more turns.

[0030]

As is clear from the above description, in the cylindrical air electrode, a dispersion containing a fluororesin having a lower melting point than that of the fluororesin porous film is applied to the surface of the fluororesin porous film, and the fluorine in the dispersion is By joining the fluororesin porous film by heat treatment at a temperature not lower than the melting temperature of the resin, it is possible to provide a cylindrical air electrode excellent in high-rate discharge characteristics and liquid leakage resistance, and a battery having the same.

[Brief description of the drawings]

FIG. 1A is a half sectional view of a cylindrical zinc-air battery according to a first embodiment of the present invention. FIG. 1B is an enlarged explanatory view of a circle in FIG.

FIG. 2A is a half sectional view of a cylindrical zinc-air battery according to Embodiment 2 of the present invention. FIG. 2B is an enlarged explanatory view of a circle in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Catalyst layer 2 Current collector 3 Fluororesin porous film 3A Gas diffusion layer 3B Fluororesin porous film 4A Three-layer cylindrical molded body 4B Four-layer cylindrical molded body 5 Separator 6 Gelled zinc negative electrode 8 Positive electrode can 10 Air intake

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-144482 (JP, A) JP-A-63-94565 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/86-4/98 H01M 12/06

Claims (12)

(57) [Claims] An air electrode formed in a cylindrical shape such that at least three members of a current collector, a catalyst layer, and a fluororesin porous membrane are overlapped and both end portions thereof come into contact with or approach each other. A dispersion containing a fluororesin having a melting point lower than the melting point of the fluororesin porous membrane is adhered to the surface of the resinous porous membrane, and the fluororesins in the dispersion are subjected to a temperature treatment at a temperature equal to or higher than the melting temperature of the fluororesin. An air electrode that binds the fluororesin porous membrane and the catalyst layer. 2. The air electrode according to claim 1, wherein the fluororesin porous membrane is a polytetrafluoroethylene porous membrane. 3. A dispersion containing a fluororesin is prepared by subjecting a hydrophobic colloidal resin particle of a copolymer of tetrafluoroethylene and hexafluoropropylene obtained by emulsion polymerization to a nonionic surfactant or an anionic surfactant. 3. A dispersion containing a liquid suspended by using the method described in claim 1.
The air electrode as described. 4. A method for manufacturing an air electrode, comprising: a current collector, a catalyst layer, and a fluororesin porous membrane, wherein at least three members are overlapped, and a cylindrical shape is formed such that both end portions thereof come into contact with or approach each other. Attaching a dispersion containing a fluororesin having a melting point lower than the melting point of the fluororesin porous membrane to the surface of the fluororesin porous membrane, and a heat treatment step of treating at a temperature equal to or higher than the melting temperature of the fluororesin in the dispersion. And bonding the fluororesin porous membranes or the fluororesin porous membrane and the catalyst layer to each other. 5. The method for producing an air electrode according to claim 4, wherein a polytetrafluoroethylene porous membrane is used as the fluororesin porous membrane. 6. A nonionic surfactant or an anionic surfactant, wherein hydrophobic colloidal resin particles of a copolymer of tetrafluoroethylene and hexafluoropropylene obtained by emulsion polymerization are added to a dispersion containing a fluororesin. The method for producing an air electrode according to claim 4 or 5, wherein a dispersion containing a liquid suspended by using a liquid is used. 7. An air battery comprising the air electrode according to claim 1 as a positive electrode. 8. An air battery provided with an air electrode produced by the method for producing an air electrode according to claim 4 as a positive electrode. 9. A tube in which at least four sides of a current collector, a catalyst layer, a gas diffusion layer having carbon black and a fluororesin, and a fluororesin porous membrane are contacted or approached to each other at both end portions thereof. In the air electrode formed in the mold,
A dispersion containing a fluororesin having a melting point lower than that of the fluororesin porous film is attached to at least one of the gas diffusion layer and the fluororesin porous film, and the temperature is equal to or higher than the melting temperature of the fluororesin in the dispersion. Air electrode heat treated at 10. The air electrode according to claim 9, wherein the fluororesin porous membrane is a polytetrafluoroethylene porous membrane. 11. A fluororesin dispersion is prepared by using a hydrophobic colloidal resin particle of a copolymer of tetrafluoroethylene and hexafluoropropylene obtained by emulsion polymerization using a nonionic surfactant or an anionic surfactant. The air electrode according to claim 9, wherein the air electrode is a dispersion containing a liquid suspended by the method. 12. An air battery comprising the air electrode according to claim 9 as a positive electrode.