JPH0745296A - Electrolyte plate for molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To increasingly improve a cell life characteristic by providing a hole part for moving an ion and reaction gas and holed nickel plate for impeding growth of a nickel metal precipitated from a cathode side, in an electrolytic plate. CONSTITUTION:An electrolytic plate 1 comprises three sheets of porous electrolytic holding sheets 1a for holding a molten carbonate electrolyte and a holed nickel plate 1b, and the plate 1b is interposed between the first/second sheets 1a as viewed from a side of an anode 2. The anode 2 is formed of a nickel sintered unit, and in the other surface of the plate 1, a cathode 3 formed of a lithium peroxide nickel sintered unit is provided. By providing the plate 1b in the plate 1, dendrite-shaped metal nickel, made to grow from a side of the cathode 3 to cause a short-circuit, can be impeded. Further, moving an ion and reaction gas in the plate 1 for electrochemical reaction is prevented from interfering because of passing through a hole part of the plate 1b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten carbonate fuel cell, and more particularly to an electrolyte plate thereof.

[0002]

2. Description of the Related Art Generally, a molten carbonate fuel cell has a structure in which a reaction gas supply / discharge manifold is attached to each peripheral surface of a battery stack formed by alternately stacking single cells and gas separation plates. . The single cell comprises an anode made of a nickel sintered body and a nickel oxide sintered body via an electrolyte plate in which a mixed alkali metal carbonate such as lithium carbonate or potassium carbonate as an electrolyte is held in a porous ceramic material. This is a structure in which a cathode mainly composed of is arranged. During operation, the fuel gas mainly containing hydrogen is supplied to the anode, and the mixed gas of air and carbon dioxide gas is supplied to the cathode.

When the above-mentioned gas is supplied to the battery having the above structure, the following reactions (1) to (3) occur in the anode, the cathode and the battery as a whole. _{1 / 2O 2 + CO 2 +} 2e - → CO 3 2- ···· (1) H 2 + CO 3 2- → H 2 O + CO 2 + 2e - ···· (2) H 2 + 1 / 2O 2 → H 2 O ... (3) As is clear from the above three chemical formulas, oxygen and carbon dioxide are consumed at the cathode to generate carbonate ions, and the carbonate ions are transferred to the anode to react with hydrogen to form water. It is a reaction that produces carbon dioxide.

[0004]

When the above reaction occurs, a part of nickel oxide, which is an electrode material, reacts with carbon dioxide at the cathode, as shown in the following reaction formula (4), to generate nickel ions. And elutes in the electrolyte. NiO + CO ₂ → Ni ²⁺ + CO ₃ ^2- (4) The nickel ions eluted in the electrolyte in this way react with the hydrogen that has diffused from the anode side, are reduced to metallic nickel, and near the cathode. It begins to precipitate. The deposited metallic nickel grows like a dendrite. If this growth continues, finally the dendrite-like metallic nickel grown from the cathode side reaches the anode side, causing a short circuit between the anode and the cathode, degrading the battery characteristics and shortening the battery life. There was a problem that it would end up.

In view of the above problems, the present invention provides an electrolyte plate for a molten carbonate fuel cell which can suppress deterioration of cell characteristics and can dramatically improve cell life characteristics. With the goal.

[0006]

In order to achieve the above object, the present invention provides an electrolyte plate interposed between an anode and a cathode of a molten carbonate fuel cell, wherein the electrolyte of the electrolyte plate contains ions, A hole for moving the reaction gas,
The present invention is characterized in that there is a perforated nickel plate having a nickel portion that prevents the growth of nickel metal deposited from the cathode side.

[0007]

As described above, by providing a perforated nickel electrode plate in the electrolyte plate, it exists so as to hinder the growth of dendrite-like metallic nickel that has grown from the cathode side in the electrolyte of the electrolyte plate. Therefore, further growth is suppressed, and dendrite-like precipitates of metallic nickel are prevented from forming near the anode.

Since the ions and the reaction gas move in the electrolyte plate for the electrochemical reaction by passing through the holes of the perforated nickel plate, there is no problem in the battery reaction.

[0009]

EXAMPLES An electrolyte according to an example of the present invention will be described below. FIG. 1 is a perspective view of a main part of fuel ionization using an electrolyte plate according to an example of the present invention. An anode 2 made of a nickel sintered body is provided on one surface of the electrolyte plate 1, and the electrolyte plate 1 is provided. A cathode 3 made of a lithiated nickel oxide sintered body is provided on the other surface of the. On the other surface side of the cathode 3, a first current collector plate 4, a first corrugated plate 5 having a corrugated plate shape and forming a passage for an oxidant gas, and a gas separation plate 6 made of a stainless steel plate are sequentially arranged. It is provided. On the other hand, the second current collecting plate 7 is provided on the other surface side of the anode 2.
And a corrugated plate-like second corrugate 8 which is provided with a passage for fuel gas in a direction perpendicular to the first corrugate 5
And the gas separation 6 plate are laminated.

A battery stack is constructed by tightening the above-structured ones with upper and lower end plates (not shown) in the stacking direction. Electrolyte plate 1 of the fuel cell having the above structure
2 shows that the molten carbonate electrolyte was retained as shown in FIG.
It is composed of a porous electrolyte holding sheet 1a and a perforated nickel plate 1b, and the perforated nickel plate 1b is an anode 2
It is provided so as to be sandwiched between the first and second electrolyte holding sheets 1a when viewed from the side.

The electrolyte plate 1 having the above structure was manufactured as follows. First, the production of the electrolyte holding sheet 1a will be described. First, γ− having an average particle size of 0.1 μm
100 parts by weight of lithium aluminate, diameter 100 μm
20 parts by weight of alumina, 30 parts by weight of polyvinyl butyral resin as a binder, 20 parts by weight of dioctyl phthalate as a plasticizer, and 300 parts by weight of ethanol as a solvent are weighed. Next, the above materials are sufficiently mixed by a ball mill to prepare a slurry. Further, minute bubbles contained in the slurry were removed by stirring under reduced pressure. The slurry thus obtained was subjected to a usual tape casting method to have a thickness of about 0.3 mm and a width of 2 mm.
It was formed into a tape shape of 00 mm. The length of this tape is 2
The electrolyte holding sheet 1a was produced by cutting the sheet into a square with a side of 200 mm by cutting it into a piece of 00 mm. The porosity of this electrolyte holding sheet was about 50%.

Subsequently, an electrolyte plate 1 was produced as follows. Two electrolyte holding sheets 1a produced as described above are laminated, and then a perforated nickel plate 1b (pore diameter: 70 μm,
A thickness: 50 μm, a porosity: 45%) was placed thereon, and one sheet of electrolyte holding sheet 1a was further laminated thereon. Next, with respect to the laminated body composed of the electrolyte holding sheet 1a and the perforated nickel plate 1b, 50 to 150 ° C. and a pressure of 50 to 300 k.
g / cm ² (preferably 100 to 200 kg / cm ² )
Pressure was applied under the conditions described above, and the above-mentioned laminated body was integrated by pressure formation.

Next, the laminated body integrated by the above pressure was heated to 800 ° C. in an oxygen / nitrogen atmosphere. In this temperature rising process, the binder and the plasticizer in the electrolyte holding sheet are decomposed, and finally the γ-lithium aluminate is sintered. K ₂ CO _3: Li2CO ₃ in the sintered body
= 62: 38 mol% of mixed carbonate was impregnated to prepare the electrolyte plate 1. The thickness of the electrolyte plate 1 is 0.5 ± 0.
It was 05 mm.

An anode 2 made of a nickel sintered body and a cathode 3 made of a lithium nickel oxide sintered body were arranged on both sides of the electrolyte plate 1 to assemble the unit cell shown in FIG. 1 as described above. Hereinafter, this unit cell is referred to as (a) cell. (Comparative Example) An electrolyte plate was prepared in the same manner as in the above-described example except that a perforated nickel plate was not used, and a single cell was prepared in the same manner.

The battery thus manufactured is hereinafter referred to as (x) battery. (Experiment) Using the battery (a) of the present invention and the battery of Comparative Example (x), continuous discharge was performed, and the battery life at this time was examined.
The result is shown in FIG. The experimental conditions are as shown below.

Oxidant gas: mixed gas of air and carbon dioxide Fuel gas: mixed gas of humidified hydrogen and carbon dioxide Operating temperature: 650 ° C. load: 150 mA / cm ² or no load (open circuit voltage) As is clear from FIG. 3, the initial characteristics are (a) the battery of the present invention and (x) the comparative battery regardless of whether the load is 150 mA / cm ² or no load (open circuit voltage). Both are almost the same. However, in the battery (x), the voltage drops remarkably with time.

On the other hand, in the case of the battery (a), it is recognized that the voltage is slightly decreased as compared with the initial value, it hardly changes even after 4000 hours, and the battery performance does not decrease for a long time. In the battery (a), this is because metallic nickel deposited in the electrolyte plate and growing from the cathode side in the electrolyte is
It is considered that since the perforated nickel plate suppressed further growth, no dendrite-like precipitate of metallic nickel was formed in the vicinity of the anode. (Other matters) In the above embodiment, the perforated nickel plate has a hole diameter of 70 μm, a thickness of 50 μm, and a porosity of 45%.
Although the thing of what was used was not limited to this.

As for the hole diameter, if the hole diameter is too large, the grown dendrite-like metallic nickel easily passes through the holes of the nickel plate, and it becomes impossible to effectively suppress the growth. On the other hand, the smallest hole diameter of the perforated nickel plate at present is 50 μm. Taking the above into consideration, it is desirable that the pore size is 50 μm to 80 μm.

Further, the thickness is preferably 100 μm or less because if it is too thick, it will hinder the movement of ions and the like in the electrolyte, which will increase the resistance value and deteriorate the battery characteristics. However, as a processing problem, if the thickness is too thin, the nickel plate will be broken when the holes are opened, so a thickness of 50 μm or more is considered appropriate. Further, the porosity of the nickel plate is preferably smaller than that of the electrolyte. This is because when the openness of the nickel plate is larger than that of the electrolyte, the grown dendrite-like nickel metal easily passes through the holes of the nickel plate,
This is because it is difficult to interfere with the growth of nickel metal. However, if the porosity is too low, the nickel plate portion increases, which hinders the movement of ions and the like in the electrolyte and raises the resistance value.
When an electrolyte holding sheet having a porosity of 100% is used, the porosity of perforated nickel is preferably about 45% to 50%.

[0020]

As described above, according to the present invention, since the perforated nickel plate is provided in the electrolyte, the growth of the dendrite-like nickel metal grown from the cathode side is obstructed by the nickel plate. And growth is suppressed. As a result, it is possible to prevent the deterioration of the battery characteristics caused by the short circuit of the electrodes and to prolong the battery life.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of a fuel cell using an electrolyte plate according to an example of the present invention.

FIG. 2 is a schematic diagram of an electrolyte plate according to an example of the present invention.

FIG. 3 is a graph showing the relationship between discharge time and battery voltage in the battery (a) of the present invention and the battery (x) of the comparative example.

[Explanation of symbols]

 1 Electrolyte Plate 1a Electrolyte Holding Sheet 1b Perforated Nickel Plate

Claims (1)

[Claims] 1. An electrolyte plate interposed between an anode and a cathode of a molten carbonate fuel cell, wherein the electrolyte plate has holes for moving ions and reaction gas, and nickel deposited from the cathode side. An electrolyte plate for a molten carbonate fuel cell, characterized in that there is a perforated nickel plate having a nickel portion that inhibits metal growth.