JPH0831431A - Method for producing lithium negative electrode for thermal battery - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent molten lithium from reacting with oxygen, nitrogen and water when a molten lithium is impregnated and held in a molded body of iron powder to prepare a lithium negative electrode for a thermal battery. . [Structure] Lithium is melted and impregnated into a molded body of iron powder in an inert gas atmosphere containing both oxygen content and water content of 2 ppm or less and containing carbon dioxide of 1 to 10%.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermal battery in which molten lithium is used as a negative electrode.

[0002]

2. Description of the Related Art A thermal battery is a type of high temperature battery that uses a molten salt, which is solid at room temperature, as an electrolyte, and heats it at a high temperature of about 400 to 700 ° C. to liquefy it to generate electricity. In conventional thermal batteries, metallic calcium and metallic magnesium were used as the negative electrode active material,
In these negative electrode active materials, a large current density discharge which has been recently demanded for thermal batteries, for example, a requirement of a discharge life of several minutes at 500 mA / cm ³ or 1000 to 3000 mA / cm ³
It was impossible to satisfy the requirement such as the pulse discharge of large current density. Therefore, in order to solve such a problem, a new lithium-based negative electrode has been developed. There are various types of lithium-based negative electrodes, for example, one using molten lithium as shown in US Pat. No. 4,221,849.

In the case of producing a negative electrode using molten lithium, in order to prevent molten lithium from flowing into the positive electrode side, after heating and melting the lithium, the molten lithium is pressed into iron powder to form iron powder. The body was kept impregnated.

On the other hand, since molten lithium has a very high reactivity, it easily reacts with oxygen, nitrogen and moisture in the atmosphere. Therefore, it was necessary to remove oxygen, nitrogen, and water as much as possible while using an inert gas such as argon gas as the atmosphere during the production of the negative electrode.

[0005]

However, although oxygen and moisture in the atmosphere during the production of the negative electrode can be removed by respective simple removing devices, it is difficult to remove nitrogen, and further, under the condition that oxygen and moisture are low. Then, molten lithium was more likely to react with nitrogen.

Since the crystal lattice of lithium nitride produced by the reaction of lithium and nitrogen is smaller than that of lithium, active points of the reaction are successively generated, and the production reaction of lithium nitride proceeds from the surface of lithium to the inside. do it,
Finally, there was a problem that all the lithium was nitrided and the ability as a negative electrode active material was lost.

The present invention is intended to solve such a problem. When a molten lithium is impregnated and held in a molded body of iron powder to produce a lithium negative electrode for a thermal battery, the molten lithium contains oxygen, nitrogen and water. It is to prevent it from reacting with.

[0008]

In order to solve the above-mentioned problems, the method for producing a lithium negative electrode for a thermal battery according to the present invention is such that the oxygen content and the water content are both 2 ppm or less and carbon dioxide is 1
In an atmosphere of an inert gas containing 10% to 10%, lithium is melted and impregnated into a molded body of iron powder.

[0009]

In the present invention, since the amounts of oxygen and water are set to 2 ppm or less in the atmosphere of an inert gas such as argon gas, the molten lithium does not react with oxygen or water to be deteriorated.

Although carbon dioxide is contained in an inert gas atmosphere in an amount of 1 to 10%, lithium reacts with carbon dioxide and changes to lithium carbonate. This lithium carbonate is much more stable than lithium nitride, and even if nitrogen is present in an inert gas atmosphere, lithium reacts with carbon dioxide rather than with nitrogen and lithium is not nitrided. Absent.

On the other hand, since the crystal lattice of lithium carbonate is larger than that of lithium, the activity of the reaction is low, and the reaction for producing lithium carbonate is limited to the surface layer of lithium. And, when carbon dioxide is in the range of 1 to 10%, lithium carbonate does not adversely affect the electrode reaction of lithium.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

A method of manufacturing the lithium negative electrode for a thermal battery of the present invention will be described with reference to FIGS.

FIG. 1A is a diagram showing a state before the production of the lithium negative electrode, and FIG. 1B is a diagram showing a state after the production of the negative electrode.

In FIG. 1A, 1 is a sheet of metallic lithium punched out in a circular shape, 2 is an average particle size of 20 μm, and 2 is a specific surface area.
A molded body made of sponge-like iron powder of ˜5 m ² / g, which is 10 t after the iron powder is uniformly dispersed on the lithium sheet 1.
It is pressure-molded at on / cm ² . Reference numeral 3 is a metal cup that accommodates the lithium sheet 1 inside.

Then, as shown in FIG. 1B, the upper surface of the iron powder molded body 2 and the lower surface of the metal cup 3 are sandwiched by a hot plate 4 heated to 550 ° C., and the lithium sheet 1 is melted.
Negative electrode 5 was obtained by impregnating and holding molten lithium in the gap in iron powder molded body 2. At this time, the gas atmosphere was a mixed gas in which argon gas and carbon dioxide were mixed at a ratio of 95: 5, and the amount of oxygen and water in this mixed gas was 2 ppm or less. The lithium negative electrode thus manufactured was used as the negative electrode of the present invention.

A lithium negative electrode was prepared in the same manner as in the present invention except that carbon dioxide was not included, and this was used as a negative electrode for comparison.

Then, 1, 5, 10, 15% of nitrogen was introduced into each atmosphere of the negative electrodes of the present invention and the comparison, and the progress of nitriding of each negative electrode was observed when the negative electrodes were stored in the same atmosphere.

The results are shown in (Table 1).

[0020]

[Table 1]

As shown in (Table 1), when the amount of oxygen and the amount of water are 2 ppm or less, the amount of nitrogen is 1, 5, 10, 1
Even if it is as small as 5%, nitriding of lithium easily proceeds,
In the comparative negative electrode, the time until all the lithium was nitrided became shorter as the amount of nitrogen increased.

On the other hand, in the negative electrode of the present invention, since lithium reacts with carbon dioxide before reacting with nitrogen, nitridation of lithium did not occur at all.

Further, in the gas atmosphere of the present invention, argon gas is replaced with nitrogen, and assuming that the amount of nitrogen is large, the ratio of nitrogen to carbon dioxide is 95: 5 and 9.
Even in the case of 9: 1, the nitridation of lithium could be prevented by the presence of carbon dioxide.

[0024]

INDUSTRIAL APPLICABILITY As described above, in the method for producing a lithium negative electrode for a thermal battery according to the present invention, the amounts of oxygen and water are both 2 ppm.
As described below, since lithium is melted and impregnated and held in a molded body of iron powder in an atmosphere of an inert gas containing carbon dioxide in an amount of 1 to 10%, even if nitrogen is present in the atmosphere, lithium is not converted to nitrogen. Since it reacts with carbon dioxide rather than with reaction, nitridation of lithium can be prevented.

Further, by setting the amounts of oxygen and water to 2 ppm or less, it is possible to prevent the lithium from reacting with oxygen and water and being deteriorated.

[Brief description of drawings]

FIG. 1A is a diagram showing a state before producing a lithium negative electrode. FIG. 1B is a diagram showing a state after producing the same negative electrode.

[Explanation of symbols]

 1 Metal Lithium Sheet 2 Iron Powder Molded Body 3 Metal Cup 4 Hot Plate 5 Negative Electrode

Claims (2)

[Claims] 1. A lithium negative electrode for a thermal battery in which a molded body of iron powder is melted and impregnated with lithium in an atmosphere of an inert gas having an oxygen content and a water content of 2 ppm or less and containing 1 to 10% of carbon dioxide. Manufacturing method. 2. The inert gas is argon gas.
A method for producing a lithium negative electrode for a thermal battery as described above.