JPH07211323A - Air electrode, manufacture thereof, and air battery using the electrode - Google Patents

Abstract

PURPOSE:To provide an air positive electrode for an air battery with excellent high rate performance and high leakage resistance. CONSTITUTION:An air positive electrode 1 is constituted with a three-layer stack formed by arranging a catalyst layer 2 on the side facing to a gelled zinc negative electrode 6 through a cellophane separator 5, a gas diffusion layer 4 comprising a porous film made of polychlorotrifluoroethylene on an air taking-in side, and a current collecting layer 3 between these layers 2, 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air electrode which uses oxygen as an active material and is excellent in discharge characteristics under high load (high rate) and resistance to liquid leakage, a method for producing the same, and an air battery having the electrode.

[0002]

2. Description of the Related Art In a conventional cylindrical air electrode, a three-layer laminate having a gas permeable and water-repellent gas diffusion layer, a catalyst layer and a current collector layer is pressure bonded to form an electrode body. The electrode body is curved, and both ends of the electrode body are adhered with a synthetic rubber or an epoxy adhesive or welded by spot welding to form a cylindrical body.

For example, as the water repellent gas diffusion layer, an oxygen gas permeable water repellent sheet made of a fluorine resin such as polytetrafluoroethylene or polytetrafluoroethylene-hexafluoropropylene copolymer is used, and a current collector is used. As the layer, a conductive sheet made of nickel mesh, expanded metal or the like is used, and as the catalyst layer, a metal oxide, activated carbon, and a polytetrafluoroethylene dispersion medium are mixed to form a porous sheet. Was used as a sheet-shaped laminated electrode body, and this electrode body was cylindrically curved so that the current collector layer was on the inside, and both ends were overlapped to form a cylindrical air electrode (JP-A-57-208074). JP-A-59-98479, JP-A-60-13616
No. 8).

Further, the gas diffusion layer and the catalyst layer at both ends of the overlapping are removed to expose the current collector layer, and the exposed current collector layers are welded by spot welding, beam welding or the like, and the welding is performed. In order to make the portion liquid-tight, the welded portion was filled with a fluororesin to make it liquid-tight, and the overlapping portion was reinforced (JP-A-58-7577).
(See Japanese Patent Publication No. 3).

Further, in order to obtain an air electrode which is liquid-tight and has high mechanical strength, the current collector layer is first curved and both ends thereof are welded to each other in advance to form a cylinder without using the sheet-like laminated electrode body as described above. The current collector layer is formed, and a porous catalyst layer is formed on the outer circumference of the cylindrical current collector layer, and the outer circumference of the catalyst layer is further overlapped by a gas diffusion layer having water repellency such as polypropylene. In some cases, the air was wound together, and then the gas diffusion layer was heat-pressed to form a cylindrical air electrode (Japanese Patent Laid-Open No. Sho 5).
No. 8-198862).

[0006]

In the conventional cylindrical air electrode, the mechanical strength is increased by the water-repellent gas diffusion layer existing on the outermost periphery to prevent liquid leakage.

However, polytetrafluoroethylene, polytetrafluoroethylene-that constitutes the gas diffusion layer
Materials such as hexafluoropropylene copolymer and polypropylene are excellent in water repellency because of their low surface energy among films, but their adhesiveness is very poor. The binding force with the body layer and the catalyst layer was very weak.

Therefore, when an air battery is formed by using the air electrode thus constructed, an electrolytic solution is formed at the interface between the gas diffusion layer and the catalyst layer or at the interface between the gas diffusion layer and the current collector layer due to discharge. However, there is a problem in that there is a possibility that discharge will become impossible due to the permeation of oxygen and the formation of a liquid film at that portion, and this liquid film interrupts the supply of oxygen.

In an air electrode used in a battery that does not flow a large current such as a button type air battery, a fluororesin dispersion is formed at the interface between the gas diffusion layer and the catalyst layer or the interface between the gas diffusion layer and the current collector layer. The formation of a liquid film can be easily prevented simply by applying it to improve the water repellency, but in the case of an air electrode used for a battery that requires a large current such as a cylindrical air battery, the above water repellency treatment is applied. However, there is a problem in that a liquid film is still formed by simply performing.

When a gas diffusion layer such as polytetrafluoroethylene is used to heat above the melting point and the interface with the catalyst layer or the like is joined by heat welding to prevent the formation of a liquid film, polytetrafluoroethylene is used. Fluoroethylene is 340-3
Since the melt viscosity is as high as 10 ¹¹ to 10 ¹³ poise even if the temperature is raised to 80 ° C., it is necessary to cool and bond under pressure in order to bond the interface, and as a result, pinholes are formed. However, when assembling an air electrode that does not leak from this portion into a cylindrical shape, there is a problem that it is very complicated and requires a high degree of technology.

When a polytetrafluoroethylene-hexafluoropropylene copolymer is used for the gas diffusion layer, on the contrary, the melt viscosity is very low at 10 ⁴ to 10 ⁵ poises, and when melted for bonding, the flow Dashi, transform,
There is a problem that the gas permeability is lost by closing the pores of the porous catalyst layer and the porous gas diffusion layer to deteriorate the function.

Therefore, in the case of an air electrode used in a battery requiring a large current such as a cylindrical air battery, it is necessary to secure the bonding property at the interface between the gas diffusion layer and the catalyst layer in order to secure the discharge characteristics or the leakage resistance. This is an important issue in terms of points.

The present invention prevents the formation of a liquid film at the interface between a gas diffusion layer and a catalyst layer, which is generated by passing a large current, and has an air electrode excellent in heavy load discharge characteristics and liquid leakage resistance, and an air electrode thereof. An object is to provide a manufacturing method and an air battery having the electrode.

[0014]

In order to achieve the above object, in the air electrode of the present invention, a current collector layer and a gas diffusion layer having gas permeability which is disposed on one side of the current collector layer. And a catalyst layer disposed on the other side of the current collector layer to form an electrode body, and the gas diffusion layer is formed of a polychlorotrifluoroethylene porous film.

Further, a cylindrical air electrode can be obtained by curving the catalyst layer inside with a cylindrical shape.

Further, in order to achieve the above object, in the method for producing an air electrode of the present invention, a laminate of a current collector layer and a catalyst layer is formed into a cylindrical body with the catalyst layer inside. A porous membrane of polychlorotrifluoroethylene is wound around the outer periphery of this cylindrical body, and then heat treated to bond the porous membrane to the cylindrical body.

It is effective to set the heat treatment conditions such that the heat treatment is performed at a temperature of 220 ° C. for 2 hours.

Further, to achieve the above object, in the air battery of the present invention, a current collector layer and a gas-permeable polychlorotrifluoroethylene porous layer disposed on one side of the current collector layer. A positive electrode is composed of a laminate of a gas diffusion layer of the membrane and a catalyst layer arranged on the other side of the current collector, and the negative electrode is provided on the positive electrode via a separator.

Further, the negative electrode can be positioned inside the cylindrical positive electrode having the catalyst layer inside with a separator interposed therebetween to form a cylindrical air battery.

[0020]

The air electrode constructed as described above and the air battery using the air electrode as a positive electrode operate as described below.

The polychlorotrifluoroethylene used in the gas diffusion layer has a high water repellency because it belongs to a fluorine-based synthetic resin, and has a melting point of 210 to 212 ° C., and polytetrafluoroethylene and polytetrafluoroethylene-hexafluoropropylene Since it is lower than the melting point of the polymer, it melts at a low temperature and has a melt viscosity of 10 ⁷ poise, which is smaller than that of polytetrafluoroethylene and larger than that of polytetrafluoroethylene-hexafluoropropylene copolymer. Has become.

Therefore, when the gas diffusion layer is joined to the catalyst layer or the current collector layer in order to prevent the formation of the liquid film at the interface, the heat fusion can be performed at a relatively low temperature, and the melt viscosity is increased. Since it is smaller than that of polytetrafluoroethylene, it is not necessary to cool and join while applying pressure for joining, and since it is larger than the melt viscosity of polytetrafluoroethylene-hexafluoropropylene copolymer, Then, it starts to flow, and it does not obstruct the function by blocking the hole.

Therefore, when polychlorotrifluoroethylene having water repellency is used as the gas diffusion layer, it can be bonded well to the catalyst layer or the current collector layer only by heat treatment at a relatively low temperature, and the high load discharge characteristics and It has excellent leakage resistance.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a cross-sectional view of a cylindrical zinc-air battery,
In FIG. 1, reference numeral 1 is a cylindrical air positive electrode, and as shown in FIG. 2, a catalyst layer 2 and a current collector layer 3 pressure-bonded to the catalyst layer 2,
A three-layer laminate with a water-repellent and porous gas diffusion layer 4 is formed into a cylindrical shape with the catalyst layer 2 inside. Reference numeral 5 is a cellophane separator in contact with the inner surface of the air positive electrode 1, 6 is a gel-like zinc negative electrode existing via the catalyst layer 2 of the air positive electrode 1 and the separator 5, and 7 is an outer periphery of the air positive electrode 1, that is, a gas diffusion layer 4
An air diffusion paper in contact with 8; a cylindrical positive electrode can 8 containing a power generating element such as the air positive electrode 1 and the gelled zinc negative electrode 6; 9 an insulating tube covering the outer periphery of the positive electrode can 8; A through hole provided in the tube 9 for taking in air, 1
Reference numeral 1 denotes a hermetic seal that closes the through hole 10 and is removed when the battery is used. 12 is a dish paper, 13 is a positive electrode cap made of metal, 14 is a current collecting cap made of metal, and the positive electrode cap 13
The end of the air positive electrode 1 is pressed and sandwiched by the current collecting cap 14 to contact the current collector layer 3, and the positive electrode can 8 is integrally conductively connected by spot welding. Reference numeral 15 is a sealant made of an organic component, 16 is a synthetic resin sealing body, 17 is a negative electrode terminal cap, and 18 is a negative electrode current collector embedded in the gel zinc negative electrode 6.

As the current collector layer 3, a net formed by weaving stainless wire having a wire diameter of 0.15 mm to a size of 40 mesh is used, and as the catalyst layer 2, 3 kg of activated carbon, 4 kg of manganese oxide, 1.5 kg of carbon black, 0.7 kg of fluororesin powder was mixed, ethyl alcohol was added to this mixture and kneaded, and then flattened into a flat band by extrusion molding.
Further, it is passed through two rollers heated to about 60 ° C. and rolled to form a sheet having a thickness of 0.6 mm.

A two-layer laminated sheet formed by press-bonding the catalyst layer 2 to the current collector layer 3 by pressing is curved into a cylindrical shape with the catalyst layer 2 on the inside, and the two end portions are overlapped. The catalyst layer 2 is removed, and the exposed current collector layers 3 are spot-welded into a cylindrical shape. As the gas diffusion layer 4, polychlorotrifluoroethylene formed into a porous film having gas permeability is used, and it is wound around the outer circumference of a cylinder made of a laminate of the catalyst layer 2 and the current collector layer 3 at 220 ° C. By heat treatment for 2 hours, the gas diffusion layer 4 is bonded to the outer periphery of the cylinder, that is, a part of the catalyst layer 2 and the current collector layer 3 to form the cylindrical air positive electrode 1 composed of a three-layer laminate. The number of times the gas diffusion layer 4 is wound around the outer circumference of the cylinder is preferably 2 or more in terms of mechanical strength and liquid tightness.

The gelled zinc negative electrode 6 is a gelled gel obtained by adding 3% by weight of sodium polyacrylate and 1% by weight of carboxymethylcellulose to a 40% by weight potassium hydroxide aqueous solution (containing 3% by weight of zinc oxide). An electrolytic solution was prepared, and then, zinc powder was added and mixed in a weight ratio of 2 to the gel electrolytic solution, and mixed.

The result of measuring the polarization state of the cylindrical zinc-air battery constructed as described above is as shown in FIG. 3, and the measurement test was carried out by measuring the sustain voltage of the battery when discharged at a predetermined current. Indicates the value. In addition, in FIG. No. 1 is the sustain voltage of the zinc-air battery according to the above-mentioned embodiment using a porous membrane of polychlorotrifluoroethylene for the gas diffusion layer. No. 2 is the sustain voltage of a conventional air zinc battery using a porous film of polytetrafluoroethylene for the gas diffusion layer, No. 2 Reference numeral 3 is the sustaining voltage of a conventional air zinc battery using a porous film of polytetrafluoroethylene-hexafluoropropylene copolymer for the gas diffusion layer.
o. 2 and No. In the case of 3, the heat treatment for joining the gas diffusion layers was not performed. No. No. 4 is No. In No. 2, the sustain voltage when heat-treated at 340 ° C., which is higher than the melting point of polytetrafluoroethylene, for 2 hours. No. 5 is No. Three
Is the sustain voltage when heat-treated at 280 ° C. for 2 hours at or above the melting point of the polytetrafluoroethylene-hexafluoropropylene copolymer.

In FIG. 2 and No. In the case of 3, the current value was 100 mA and the sustain voltage was less than 1.0 V, but this was because the bond between the catalyst layer and the gas diffusion layer was weak,
It is considered that the electrolytic solution permeated into this joint portion due to the discharge to form a liquid film, and it was difficult to supply oxygen to the catalyst layer, so that the sustain voltage was lowered. No. In the case of No. 4, No. Although it is slightly improved as compared with the case of 2, it is insufficient as a battery requiring a large current. No. In the case of 5, the heat treatment melted the porous film of the polytetrafluoroethylene-hexafluoropropylene copolymer, which started to flow due to the low melt viscosity, blocking the pores of the porous film and making it impossible to supply oxygen. I think that the.

However, no. In the case of No. 1, good polarization characteristics are exhibited, and since the bonding between the catalyst layer and the gas diffusion layer is strong, the electrolytic solution permeates into this bonding portion due to discharge, and a liquid film is formed. It is believed that the above can be prevented and oxygen can be sufficiently supplied to the catalyst layer.

[0031]

Since the present invention is constituted as described above, it has the following effects.

The air electrode is a stack of a current collector layer, a gas diffusion layer having gas permeability which is arranged on one side of the current collector layer, and a catalyst layer arranged on the other side of the current collector layer. The electrode body is constituted by a body, and the gas diffusion layer is formed of a porous film of polychlorotrifluoroethylene having water repellency and bonding properties, so that the gas diffusion layer can be satisfactorily used as a catalyst layer or a collector layer. And is excellent in heavy load discharge characteristics and liquid leakage resistance.

[Brief description of drawings]

FIG. 1 is a sectional view of a cylindrical zinc-air battery according to an embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of a portion A in FIG.

[Fig. 3] Polarization characteristic diagram of cylindrical zinc-air battery

[Explanation of symbols]

 1 Cylindrical Air Positive Electrode 2 Catalyst Layer 3 Current Collector Layer 4 Gas Diffusion Layer 5 Cellophane Separator 6 Gel Zinc Negative Electrode

Claims (6)

[Claims] 1. A laminate of a current collector layer, a gas diffusion layer having gas permeability which is disposed on one side of the current collector layer, and a catalyst layer disposed on the other side of the current collector layer. An air electrode which constitutes an electrode body and in which the gas diffusion layer is formed of a porous membrane of polychlorotrifluoroethylene. 2. The air electrode according to claim 1, which has a cylindrical shape with the catalyst layer inside. 3. A laminated body of a current collector layer and a catalyst layer is formed into a cylindrical body with the catalyst layer inside, and a porous membrane of polychlorotrifluoroethylene is wound around the outer periphery of the cylindrical body,
Then, a method of manufacturing an air electrode in which the porous membrane is joined to the cylindrical body by heat treatment. 4. The method for producing an air electrode according to claim 3, wherein the heat treatment is performed at a temperature of 220 ° C. for 2 hours. 5. A current collector layer, a gas diffusion layer of polychlorotrifluoroethylene porous membrane having gas permeability which is disposed on one side of the current collector layer, and a gas diffusion layer on the other side of the current collector. An air battery in which a positive electrode is constituted by a laminate with the catalyst layer, and a negative electrode is provided on the positive electrode via a separator. 6. The air battery according to claim 5, wherein a negative electrode is provided inside a cylindrical positive electrode having a catalyst layer inside with a separator interposed therebetween.