JPS58119161A - Manufacture of electrode for fused salt fuel battery - Google Patents

Abstract

PURPOSE:To obtain an electrode having superior mechanical strength, electric conductivity, and electric discharge characteristic by mixing at least one kind among lithium hydroxide, lithium carbonate, and lithium chloride with nickel oxide powder and treating said mixture with press molding and firing. CONSTITUTION:Lithium hydroxide is added in a molar ratio of 1:0.5 into the nickel oxide powder having an average particle diameter of 20mum or less, and a proper amount of water is further added into the above mixture so that an uniform mixture can be obtained. The slurry consisting of aqueous solution of lithium hydroxide and nickel oxide dispersed is dried and coagulated, and then molded to a plate form having a thickness of about 1mm. under a pressure of 300kg/cm<2>, and then said plate is baked at 1,100 deg.C in air for 4hr. Thus, the electrode having a sufficient corrosion resistance enough to stand the use over a long period, high mechanical strength, and superior electric discharge characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an alkali metal carbonate such as lithium carbonate, potassium carbonate, or sodium carbonate as an electrolyte, and uses
00'(:, relates to electrodes of molten salt fuel cells operated at 00').

At present, fuel cells that use acidic or alkaline solutions as electrolytes and operate at relatively low temperatures of room temperature to 200'C are widely known. Carbon, corrosion-resistant metals, and the like are used as electrode materials. - In fuel cells using power tank molten salt as an electrolyte, especially in molten carbon dioxide fuel cells, the operating temperature is as high as about 660° C., so there are major restrictions on the materials that can be used as electrodes. Furthermore, since molten salt is generally very corrosive, it is difficult to select an electrode material that can be used for a long period of time. In particular, the cathode is exposed to a strong oxidizing atmosphere as it reaches a high temperature in the presence of oxygen, and also comes into direct contact with molten salt, so the electrode materials must be very limited, such as oxides.

Conventionally, the electrodes of fuel cells using molten salt as an electrolyte, especially molten carbonate fuel cells, are generally considered to be porous nickel for the anode (fuel electrode) and porous nickel oxide for the cathode (air electrode). I've been exposed to it.

The porous nickel oxide material serving as the cathode was manufactured by the following method. That is, first, a nickel porous body is manufactured by a method such as sintering nickel powder, and this is incorporated into a fuel cell as a cathode. After assembling the fuel cell, the temperature is raised to around the operating temperature, and a fuel gas (natural gas, hydrogen, etc.) is flowed to the anode side and an oxidizer (-element, air, etc.) to the cathode side. A Niracle porous material is oxidized to an oxidized Niracle porous material, which is used as a cathode.

When oxidizing electrochemically in this way, some lithium is doped into the nickel oxide from the lithium carbonate in the electrolyte, which is said to maintain electrical conductivity.

Before being oxidized, Niracle porous material has high mechanical strength and electrical conductivity due to sintering between metal particles, but once it is oxidized and changes to Niracle oxide porous material, which has almost no conductivity, nickel particles In the sintered portion between the two, the bond becomes weaker due to a change in the volume of the crystal structure from nickel to nickel oxide. As a result, the mechanical strength of the Niracle oxide porous material is extremely reduced, and even after several tens of hours of operation, the electrode becomes extremely brittle and weak, and cannot be handled without retaining its shape. deteriorate as much as possible. Furthermore, the resistance of the electrode itself increases because the lithium doping during oxidation is not sufficient and uniform and the bonding force between particles is weak. If the resistance of the electrode increases, the battery performance will decrease due to resistance loss. As described above, the conventional method of oxidizing a two-cell porous material in an operating state and using it as an electrode cannot be said to be excellent in terms of the mechanical strength and discharge characteristics of the electrode.

The object of the present invention is to obtain sufficient corrosion resistance, mechanical strength, and good discharge characteristics to withstand long-term use by improving the electrodes of a fuel cell using such a molten salt as an electrolyte.

That is, it provides a porous nickel oxide electrode that is uniformly and sufficiently doped with lithium and has high conductivity, in which Niracle oxide powder is mixed with at least one member selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium chloride. The method is characterized in that the electrodes are manufactured by mixing, adding an organic binder and the like as necessary, press-molding, and then firing the mixture at, for example, 600 to 1200'C.

Next, the present invention will be explained based on examples.

Add lithium hydroxide to nickel oxide (NIP) powder with an average particle size of 20 μm or less at a molar ratio of 1:0.6+7), add an appropriate amount of water to mix evenly, and add water. Make a slurry of lithium oxide dispersed in an aqueous lithium oxide solution and mix well with stirring. This is dried, and the solidified product is turned into a powder, and an organic binder such as cellulose or synthetic resin is added to it for 300 g.
It is molded into a plate shape with a thickness of about 1 mm under a pressure of kg/ctM. This is baked in air at 1000° C. for 4 hours.

The greenish-gray color before firing turns black after firing.
A porous nickel oxide electrode containing lithium with strong mechanical strength was obtained. As a result of X-ray diffraction, it was found that the main component of this material was lithium nickel oxide (for example, Li2Ni5014).

Next, in order to find out the electrical conductivity of this electrode, we applied silver paste to both sides of the electrode sample piece and measured the electrical conductivity, and as shown in the following table, we confirmed that it exhibited high electrical conductivity at high temperatures.

In order to evaluate the discharge performance of the nickel oxide porous electrode containing lithium thus obtained, a fuel cell was constructed using the above electrode as a cathode and a known cloth-added nickel porous electrode as an anode. The electrolyte was prepared by molding a mixture of 60 parts by weight of fine alumina powder as a support and 50 parts by weight of a mixture of lithium carbonate and potassium carbonate in a molar ratio of 1':1 at a pressure of 200 kg/-.
The electrode was fired for 1 hour at ℃, and the active area of the electrode was 4
It was set as X 5 c4. Then, hydrogen at 1 atm is used as the fuel gas, and a mixture of air and carbon dioxide is used as the oxidizing gas.
An operation test was conducted at a temperature of 650°C.

The above battery is designated as A, and the battery in which the conventional electrode is used as a cathode is designated as B. The test results for these batteries are shown in the figure.

It can be seen that the performance of the fuel cell B of the comparative example deteriorates as the operating time increases, but the performance deterioration of the fuel cell A according to the present invention is greatly improved. Further, when this cand was taken out after the discharge test, it was found that the electrode of the present invention had a solid shape and the strength had not changed from before use. On the other hand, conventional cands cause electrode breakage, which causes deterioration of characteristics. These results show that the electrode manufactured according to the present invention exhibits excellent performance as a cand for molten carbonate fuel cells.

In addition, in the above example, an example was shown in which lithium hydroxide was used as the lithium compound, but similar results were obtained when lithium carbonate and lithium chloride were used.

Furthermore, if the molar ratio of lithium compound added to nickel oxide is 0.1 lithium to 1 nickel, alloying with lithium will be insufficient and good conductivity will not be exhibited, resulting in large resistance polarization due to NiO. Become. Conversely, if lithium is added in an amount of 1.5 or more, a large amount of lithium compounds that do not participate in the reaction with nickel oxide will remain in the electrode, preventing sintering between nickel oxide particles and increasing the strength. decreases. Therefore, the ratio of the lithium compound added is 1 nickel to 0.1 to 1 lithium.
．． A range of 5 is the optimal condition. In addition, if the lithium compound to be added is made into a slurry by adding water,
Although the particle size may be somewhat large, when using lithium carbonate that is insoluble in water, it is necessary to use particles with a particle size as small as possible and to perform sufficient stirring and grinding.

Firing is performed in air, but a temperature of 1000° C. or higher is required because sintering does not occur at low temperatures.

During firing, it depends on the type of lithium compound, but about 500~
A reaction between the lithium compound and nickel oxide occurs at 800°C, and the resulting lithium nickel oxide is sintered at a temperature of 1000°C or higher. Therefore, firing starts at 500~
It is best to carry out the reaction at a temperature of s o o'C for about 3 hours, and then sinter at a temperature of 1000 to 1200'C for about 1 hour.
When the particle size is 20 μm or less, sintering between particles is strongly formed. 2oI
If it becomes rougher than im, the sintering strength will be low and a substrate with a large surface area will not be produced. In this respect, when the thickness is 20 μm or less, an excellent electrode can be obtained.

As described above, the electrode manufactured according to the present invention has lithium nickel oxide obtained by uniformly and sufficiently doping the aluminum oxide as the main component, and the sintered part between the particles is placed in a strong oxidizing atmosphere. It is stable even when exposed to direct contact with molten carbonate, etc., and has high mechanical strength. Also electrically conductive.

It has excellent discharge characteristics and these properties are stable over a long period of time.

[Brief Description of the Drawings] The drawings are diagrams showing the discharge characteristics of a molten carbonate fuel cell according to an embodiment of the present invention and the discharge characteristics of a molten carbonate fuel cell using a type of electrode that is oxidized under conventional operating conditions. It is.

Claims (2)

[Claims] (1) For a molten salt fuel cell, characterized in that nickel oxide powder is mixed with at least one lithium compound selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium chloride, and the mixture is pressure-molded and then fired. Electrode manufacturing method. (2) The nickel oxide powder has an average particle size of 20 μm or less, and the mixing ratio of nickel oxide and the lithium compound is 1:0.1 to 1:0.1 in molar ratio of nickel to lithium.
1.5, the method for producing an electrode for a molten salt fuel cell according to claim 1.