BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an air electrode, a metal-air battery including an air electrode, and an air electrode production method.

Description of the Background Art

A metal-air battery uses atmospheric oxygen as a positive electrode active substance of the battery. In the structure of such metal-air battery, one face of an air electrode is in contact with an electrolytic solution and the other face is in contact with air. Generally, the air electrode is provided with air holes for the intake of air and has a porous structure inside. As an electrolytic solution, an alkaline aqueous solution for reducing the surface tension of water to enhance the osmosis is used, for instance.

Conventionally, there is a problem in that an electrolytic solution may permeate an air electrode and further leak out of the air electrode depending on the structure of the air electrode, the properties of the electrolytic solution, and the like. Leakage of an electrolytic solution causes a deterioration in battery performance that makes a long-lasting reliability and a long lifetime unobtainable, and also raises problems of safety, such as touching the electrolytic solution.

In order to address such problems, it is thinkable that an air electrode61includes, apart from a catalyst layer62and a current collector63, a water repellent membrane65provided outside the catalyst layer62, as illustrated inFIG. 10. The water repellent membrane65makes it possible to briefly suppress the leakage of an electrolytic solution64indeed, but the electrolytic solution64, which has permeated the catalyst layer62, may be collected between the water repellent membrane65and the catalyst layer62to generate a gap at an interface between the water repellent membrane65and the catalyst layer62even if the measures as illustrated inFIG. 10are taken. If such gap is generated, the electrolytic solution64collected between the catalyst layer62and the water repellent membrane65may reduce the amount of the air fed to the catalyst layer62to inhibit the electrode reaction of the catalyst layer62.

JP 2002-110182 A, for instance, discloses an air electrode including a catalyst layer that is provided with a plurality of through holes formed by sticking a needle from one face to the other face of the catalyst layer. It is intended that the disclosed air electrode has a gas permeability enhanced by the through holes.

In JP 2002-110182 A, the gas permeability of the disclosed air electrode is taken into consideration, but no discussion is made about the possibility of leakage of an electrolytic solution through the through holes. As a consequence, the surface of the catalyst layer is covered with the electrolytic solution, so that the air required for the reaction is hardly fed to the catalyst layer and the reduction in battery lifetime is incurred. In addition, problems of safety are still remaining.

The present invention is made in view of the problems as above, and an object of the present invention is to prevent the detachment of a water repellent membrane and a catalyst layer from each other and the leakage of an electrolytic solution as well to enhance the battery performance, so as to provide an air electrode excellent in reliability and safety, a metal-air battery including such an air electrode, and a method of producing such an air electrode.

SUMMARY OF THE INVENTION

A means for solution according to an aspect of the present invention as a means for achieving the above object is an air electrode including a current collector, a water repellent membrane, and a catalyst layer arranged between the current collector and the water repellent membrane. The catalyst layer includes a first face in contact with either one of the current collector and the water repellent membrane, a second face in contact with either other of the current collector or the water repellent membrane, and a plurality of through holes, through which the first face and the second face communicate with each other. The plurality of through holes each have a constriction with an inner diameter smaller than either of an opening diameter in the first face and an opening diameter in the second face.

In the air electrode with the configuration as above, it is preferable that the plurality of through holes each have a cross section in a piercing direction that is a constricted shape having an inner diameter sequentially reduced from the first face toward inside of the catalyst layer and from the second face toward the inside of the catalyst layer.

A metal-air battery including the air electrode as above is also within the scope of technical ideas of the present invention. In other words, a metal-air battery according to another aspect of the present invention includes the air electrode with the configuration as above, a metal electrode, and an electrolyte.

Further, a method of producing the air electrode as above is also within the scope of technical ideas of the present invention. According to yet another aspect of the present invention, a method of producing an air electrode including a current collector, a water repellent membrane, and a catalyst layer arranged between the current collector and the water repellent membrane, the catalyst layer including a plurality of through holes each piercing to a first face and a second face of the catalyst layer, includes forming a plurality of first through holes in the catalyst layer before formation of the plurality of through holes, each first through hole piercing the catalyst layer in a thickness direction, and pressing the catalyst layer provided with the plurality of first through holes. The pressing is performed in a piercing direction of the plurality of first through holes to form, in the catalyst layer, through holes each having a constriction with an inner diameter smaller than either of an opening diameter in the first face and the opening diameter in the second face.

According to the present invention, the leakage of an electrolytic solution is successfully prevented and the battery performance is enhanced, which allows an air electrode excellent in reliability and safety and a metal-air battery including such an air electrode to be provided. In addition, an air electrode production method according to the present invention makes it possible to easily form an air electrode including a catalyst layer provided with through holes.

