JPS6174262A - Manufacture of cathode for fused salt fuel cell - Google Patents

Abstract

PURPOSE:To obtain a cathode which has superior property, a long life and easy manufacturing by including a metal in a cell, which works as a cathode, together with a binding agent adhered by coating to a conductive porous material, if necessary, pressurized without sintering. CONSTITUTION:A layer made of a metal such as nickel and a binding agent is formed at least on one of the faces of a conductive porous material consisting of screen, expanding metal, panting metal or foaming metal etc. and is included in a cell without sintering process. If more strength is needed, it may well be pressurized after it is dried. Highpolymer materials, for example,car boxymethlcellulose, polyvinylalcohol, polyvinyl chloride and polyethlene etc. are used as binding agents. Thereby, it enables to get a enough strength as a pole and enables also to keep a good efficiency for a long time because it is not sintered at high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a cathode for a molten salt fuel cell that operates at about 600 to 700°C.

Conventional technology Fuel cells that use molten salts such as molten carbonate as electrolytes, along with phosphoric acid and solid electrolyte systems, are being used to reform power generation methods as part of energy diversification, oil conservation measures, and energy conservation. It is expected that this technology will make a significant contribution, and vigorous development efforts are underway. Among these, molten carbonate fuel cells have the advantage that they do not require platinum group catalysts such as phosphoric acid-based catalysts, and do not require high temperatures compared to solid electrolyte-based fuel cells. Furthermore, since it operates at around 600°C, the waste heat used for the purpose of improving efficiency is of high quality, and the recovery and use of this waste heat can be said to be extremely significant from the standpoint of energy conservation. However, many issues remain, such as further improving the performance of the electrode, especially extending its life, improving the corrosion resistance of other constituent materials, and ensuring economic efficiency.

Lithiated nickel oxide is most commonly utilized in sintered form as the cathode in molten carbonate fuel cells. A sintered body of nickel is used as the anode, and an alkali carbonate held in a so-called tile is used as the electrolyte.

The cathode is assembled into the battery as a nickel sintered body, and lithium and oxidation are carried out by keeping the battery at operating temperature or higher using lithium carbonate contained in the electrolyte and oxygen in the atmosphere. There is a way to do both at the same time. As an improved method, a nickel sintered body and lithium hydroxide are heated in advance to form a lithiated nickel oxide sintered body,
A method has been proposed in which lithiated nickel oxide powder is produced using nickel powder and lithium hydroxide, and this is sintered.

Lithiated nickel oxide exhibits excellent electrical conductivity that nickel oxide does not have, and also has corrosion resistance against carbonates in oxidizing atmospheres, and has the property of smoothly performing oxygen ionization reactions. It has been adopted since.

Problems to be Solved by the Invention In the conventional cathode manufacturing method described above, the shape of the electrode is maintained by bonding lithiated nickel oxide through sintering, so there are almost no problems in terms of conductivity or reactivity. However, since the manufacturing methods of both methods are somewhat complicated and have been studied mainly to improve strength, sintering progresses further due to the temperature during operation, and the amount of oxidizing gas supplied is reduced. Problems arise in diffusion and rapid removal of reaction products from the reaction part, leading to problems such as a decrease in battery performance.

The present invention solves these problems with cathodes and provides a cathode that has excellent characteristics, has a long life, and is easy to manufacture.

SUMMARY OF THE INVENTION The present invention provides a method of screening materials that act as cathodes, such as nickel, manganese, copper, cobalt, iron, and particularly preferably nickel, together with a binder.

It is characterized by being applied to porous materials such as expanded metal, punched metal, and foamed metal, and if necessary, being incorporated into batteries without applying pressure and sintering.

Function The simplest process of the present invention is to apply a paste of nickel and a binder solution to the core material, smooth the surface by passing it through a slit, and dry it. If further strength is required, pressure may be applied after drying.

In addition, if additional strength is required for handling,
It is also preferable to add a thermoplastic resin powder as a binder and heat the resin powder to a temperature higher than the temperature at which the resin powder melts after the surface is smoothed or pressurized. As the binder, known polymeric materials such as carhoki/methyl cellulose, polyvinyl alcohol, polyvinyl chloride, and polyethylene are used.

However, as the battery undergoes further sintering during operation, the porosity decreases, creating problems in terms of gas diffusion and electrolyte distribution within the power node, thereby reducing battery performance. No sintering was performed during the first assembly, and the production
By converting into lithiated nickel oxide and causing light sintering during heating to a degree or at operating temperature, it is possible to simplify the manufacturing process and extend the lifespan. .

In the electrode according to the present invention, the layer mainly composed of nickel powder applied to the porous conductor is able to absorb the crystals present inside when the temperature is raised to 600 to 70oC, which is the preferred operating temperature of the battery. The adhesive decomposes and loses its binding function. Therefore, the role of the binder is to provide strength to the electrodes during operation prior to battery assembly.

Therefore, although the binding function is lost by heating, the nickel now becomes lithiated nickel oxide, and this work! Sintering begins slowly at vJ temperature, which provides sufficient strength as an electrode, and because it is not sintered in high humidity, sintering progresses extremely slowly compared to conventional sintered electrodes. Therefore, it maintains good performance over a long period of time.

In this way, in the present invention, the 6
Powders of cobalt, manganese, iron, copper, etc. can also be used as long as they are lightly sintered at temperatures of 00 to 700°C.
Nickel is the best in terms of performance and corrosion resistance.

Furthermore, in order to facilitate the formation of lithiated metal oxides after assembly into a battery, lithium hydroxide or lithium carbonate may be added to these metals.

Example Carbonyl nickel powder 50g and polyethylene powder 4
0g were mixed thoroughly, and a 2% by weight aqueous solution of carboxymethyl cellulose was added thereto to form a paste.

This paste has a thickness of 0.11mm and a pore size of 2mm. Own,
Coat it on both sides of nickel punching metal with a hole spacing of 2.5 m, and smooth the surface by passing it through the slits of 1.3+ m. This is lightly pressurized at a pressure of 100 Kp/crd and then heated at 140° C. for 20 minutes to dissolve the added polyethylene. The atmosphere during this heating may be air.

The porous nickel material obtained through such a simple process is incorporated into a battery as it is. Note that this nickel porous body has sufficient strength, and no phenomena such as breakage are observed during handling.

This electrode was used as a cathode, and a known sintered electrode mainly made of nickel was used as a fuel electrode. In addition, as the electrolyte and its carrier, 56% by weight of a mixed salt of lithium carbonate and potassium carbonate and 45% by weight of lithium aluminate powder were used.
A paste-type structure containing the following was used.

As the fuel gas, a mixed gas of 80% hydrogen and 20% carbon dioxide was used, and as the oxidizing agent, a mixture of 65% air and 35% carbon dioxide was used. Note that all figures are volume ratios. Also,
The operating temperature is 660-660°C.

A battery using the cathode according to the present invention was referred to as A, and a conventional fuel cell B using a nickel sintered porous body impregnated with lithium hydroxide was compared under the following conditions.

Figure 1 shows the results of the operation test at a current density of 100 mA/d. As shown in FIG. 1, there is no significant difference in the characteristics up to 500 hours of operation, but after that, a difference is seen in the characteristics. Battery A using the cathode according to the present invention shows a terminal voltage of 0.82 V/cell until 1 o○○ hours have elapsed, whereas conventional type B has a terminal voltage of 0.82 V/cell, showing deterioration in performance. Furthermore, at 2000 hours, they are 0.74 and 0.7v, respectively. The cause of this is B
Since the cathode is a sintered body of nickel doped with lithium, sintering progresses more easily over time than the electrode of the present invention, resulting in a decrease in electrode area,
This leads to a reduction in the so-called three-phase interface, resulting in a voltage drop. This phenomenon is increasing over time.

On the other hand, in the cathode of the present invention, the nickel powder is supported on foamed nickel and is not sintered, so over-sintering is difficult to achieve over time, and therefore the voltage drop is lower than that of B. It seems that the degree is decreasing. In other words, in the cathode of the present invention, the electric pupil is working with light sintering during this operation, so unlike the case where the cathode is already sufficiently sintered at a high temperature like a known sintered body, there is no oversintering. It can be pointed out that this progresses only extremely slowly. In other words, if sintering progresses too much, both the porosity and the pore diameter become small, which impedes the diffusion of gas and electrolyte, and also reduces the third F zone between the electrode, electrolyte, and gas, resulting in performance deterioration. Therefore, the degree of such adverse effects is small.

Figure 2 shows the operation of these batteries A and H for 200 hours (100 hours).
This is the current-voltage characteristic examined after continuous discharge (mA/, i continuous discharge). As is clear from the figure, even if a cathode made by a simple method without adding a sintering process as in the present invention is used, the initial characteristics are not inferior to those of the conventional sintering method.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a cathode for a molten salt fuel cell with a long life by suppressing excessive sintering during operation through a simple process.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a comparison of voltages during continuous discharge of fuel cells using different cathodes, and FIG. 2 is a diagram showing a comparison of current-voltage characteristics.

Claims (2)

[Claims] (1) Production of a cathode for a molten salt fuel cell, characterized in that a layer made of metal and a binder is formed on at least one surface of a conductive porous body, and the cathode is incorporated into a battery without going through a sintering process. Law. (2) The method for producing a cathode for a molten salt fuel cell according to claim 1, wherein the conductive porous body is a screen, expanded metal, punched metal, or foamed metal.