JPH0414463B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for producing lead iodide useful as a positive electrode active material in solid electrolyte batteries.

As one method for producing this type of lead iodide, a method is known in which lead nitrate and potassium iodide are reacted in water. This reaction is expressed by the following reaction formula: Pb(NO ₃ ) ₂ +2KI→PbI ₂ +2KNO ₃ , but the amount of lead nitrate used is determined by effectively utilizing the harmful lead salt and reducing the amount of lead in the solution after the reaction. Conventionally, from the viewpoint of preventing potassium iodide from remaining in potassium iodide, the ratio was set at a theoretical molar ratio (1/2) or less. However, the solid electrolyte battery using lead iodide as an anode active material obtained by this method is
The disadvantage was that the discharge capacity tended to vary and was low overall.

This invention was made based on the knowledge that a high and stable discharge capacity can be obtained by increasing the amount of lead nitrate used in the reaction compared to the conventional method. That is, in producing water-soluble lead salt and lead iodide, this invention makes the reaction molar ratio of water-soluble lead salt to hydroiodic acid or its alkali metal salt larger than the theoretical molar ratio (1/2). The present invention relates to a method for producing lead iodide for solid electrolyte batteries, characterized by:

Figure 1 shows the discharge characteristics of lead iodide (curves 1a to 3a) obtained by the method of this invention using lead nitrate and potassium iodide as starting materials, compared to commercially available lead iodide (curves 1b to 3b). This is a comparison.
That is, curves 1a to 3a each have a molar ratio of lead nitrate to potassium iodide of 8/2.
(Curve-1a), 6/2 (Curve-2a), and 4/2 (Curve-3a) are the results for lead iodide, while curves 1b to 3b are the results for lead nitrate relative to potassium iodide. These are the results for three types of commercially available lead iodide from different manufacturers and manufacturing lots, each using a molar ratio of the theoretical molar ratio (1/2) or lower.

The solid electrolyte battery was manufactured using lithium foil as the cathode and yLi ₃ N-(1-y)LiI compound (y=
0.88), a mixture of lead iodide and nickel powder with a volume ratio of 4:1 was used as the anode, and the anode diameter was 10 mm. The discharge characteristics are shown as the relationship between the closed circuit voltage and the discharge capacity when a constant current discharge of 30 μA is performed at 20°C.

As is clear from this figure, commercially available lead iodide has a discharge capacity of 2 to 7 mAh at a final voltage of 1.4 V, while lead iodide obtained using the method of this invention has a discharge capacity of approximately 7.5 mAh.
~11mAh, indicating a significant increase in discharge capacity. In addition, by appropriately setting the molar ratio of lead nitrate used, a more stable discharge capacity can be obtained compared to commercially available products, just as the discharge capacity is obtained according to the molar ratio of lead nitrate used. .

A typical water-soluble lead salt used in this invention is lead nitrate, but other water-soluble lead salts such as lead acetate and Pb
(SO ₃ NH ₂ ) ₂ , PbSiF ₆ etc. can be used. In addition, as hydroiodic acid or its alkali metal salt,
Hydroiodic acid, potassium iodide, sodium iodide, etc. are used.

The molar ratio of the water-soluble lead salt to hydroiodic acid or its alkali metal salt is usually 2/2 to 20/2.
It is preferable to set the ratio to be 3/2 to 9/2, particularly preferably from 3/2 to 9/2, and by using such an excessive amount, the above-mentioned discharge characteristics can be improved.

The reaction generally proceeds rapidly at room temperature by mixing an aqueous solution of a water-soluble lead salt with an aqueous solution of hydriodic acid or an alkali metal salt thereof.
At this time, it is preferable to add an aqueous solution of hydroiodic acid or an alkali metal salt thereof to the aqueous solution of the water-soluble lead salt in order to carry out the reaction in an excess state of the water-soluble lead salt. However, depending on the case, a reverse addition method to the above may be used.

Next, embodiments of this invention will be described.

Example An aqueous solution prepared by dissolving 20 g of potassium iodide in 200 g of ion-exchanged water was poured at once into an aqueous solution prepared by dissolving 80 g of lead nitrate in 200 g of ion-exchanged water at room temperature while stirring the aqueous solution vigorously. The reaction was completed quickly. After the solution was allowed to stand for 2 to 3 minutes, it was separated and thoroughly washed with a large amount of ion-exchanged water. Thereafter, it was vacuum dried at 180° C. for 10 hours to obtain lead iodide for solid electrolyte batteries of the present invention.

The molar ratio of lead nitrate to potassium iodide in the above reaction was 8/2.

Test Example 50 mg of a solid electrolyte consisting of yLi ₃ N-(1-y)LiI compound (y = 0.88) was pre-molded at 1 ton/cm ² in a mold with an inner diameter of 10 mm, and then a 150 mg of the resulting mixture consisting of 3 g of lead iodide and 1 g of nickel powder was charged and molded at 7 tons/cm ² . On the solid electrolyte side of the obtained molded pellet, a 0.21 mm thick
A lithium foil with a diameter of 8 mm was pressed and crimped, and a solid electrolyte battery as shown in FIG. 2 was fabricated using a conventional method.

In Fig. 2, 1 is a cathode, 2 is an anode, 3 is a solid electrolyte, 4 is a cathode plate, 5 is an anode plate, and 6 is an insulator, which is fixed to the cathode and anode plates 4 and 5 by a brazing material 7. .

When this solid electrolyte battery was subjected to a constant current discharge of 30μA at 20℃, the discharge capacity was 11mAh at a final voltage of 1.4V, as shown in curve 1a in Figure 1 above.
It was hot. In addition, the amount of lead nitrate used in the above example was 6/2 and 4/2 with respect to potassium iodide.
The discharge capacity similar to the above when expressed as (molar ratio) is:
Curves 2a and 3a of FIG. 1 mentioned above, respectively.
It was as shown.

[Brief explanation of drawings]

Figure 1 shows the relationship between closed circuit voltage and discharge capacity of solid electrolyte batteries using lead iodide obtained by this invention method and commercially available lead iodide as positive electrode active materials, and Figure 2 shows the relationship between closed circuit voltage and discharge capacity of solid electrolyte batteries obtained by this invention method. 1 is a cross-sectional view showing an example of a solid electrolyte battery using lead iodide as an anode active material.

Claims (1)

[Claims] 1. In producing lead iodide by reacting a water-soluble lead salt with hydroiodic acid or an alkali metal salt thereof, the reaction of a water-soluble lead salt with hydroiodic acid or an alkali metal salt thereof A method for producing lead iodide for solid electrolyte batteries, characterized in that the molar ratio is larger than the theoretical molar ratio (1/2). 2. The method for producing lead iodide for solid electrolyte batteries according to claim 1, wherein the reaction molar ratio of water-soluble lead salt to hydroiodic acid or its alkali metal salt is from 2/2 to 20/2.