JPS6045129B2 - Production method of divalent silver oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing stable divalent silver oxide.

Currently, monovalent silver oxide A&0-zinc Zn-based batteries have been commercialized and put into practical use as power sources for small electronic devices, such as electronic wristwatches and electronic desktop calculators.

As electronic devices become smaller, there is a demand for the development and practical use of smaller power batteries. Along with this, batteries using divalent silver oxide (AgO) as a positive electrode active material, which has a higher energy density per unit weight and volume than monovalent silver oxide (A&O), are attracting attention. This Ag0 is ~0
The energy density per unit weight is 1.8 compared to 0.
7 times, and the energy density per unit volume is 1.94 times.

Therefore, by replacing this AgO with Ag2O, Ag0-
When a Zn-based alkaline battery is formed, it is possible to increase the capacity by about 40% with the same size and shape. Currently available AgO releases oxygen gas and changes into stable Ag and O when it comes into contact with an alkaline electrolyte.

Further, when a battery is formed, the discharge voltage produces a two-stage curve of potentials Ag0 and Aomio. Unless the battery has a function to absorb the generated oxygen gas inside the battery, it is extremely dangerous due to leakage and explosion due to increased internal pressure. If an oxygen gas absorption function were applied inside the battery as a gas removal measure, the efficiency of the molten liquid inside the battery would decrease, making it impossible to fully utilize the high energy of AgO. The intended purpose of increasing capacity could not be achieved.
In order to achieve the above-mentioned desires and objectives, the present inventors
After conducting a study on Ag0 that is stable in an alkaline solution, we discovered ~ρ, which has an X-ray diffraction pattern different from that of previously reported Ag0, and a method for producing the same, and filed a patent application for this.

The present invention is based on the previously applied AgO production method, and as a result of research into a more stable AgO production method, the present invention was developed by adding cadmium salt or cadmium oxide to the AgO solution synthesized by the previous production method. By synthesizing AgO, which generates less gas, and as a new effect, Ag
AgO with high open-circuit voltage maintenance property when configured as an O-Zn battery was obtained.

A specific example will be shown below. Oxidize silver nitrate (AgNO3) in an alkaline solution using potassium persulfate (K2S2O$) as an oxidizing agent. Methods for obtaining AgO have been reported in the past.

Although this method is good for simply producing AgO,
As the 8ρ used as the positive electrode active material of alkaline batteries,
The reaction from AgO to Ag2O described above, ie, the reaction of the following formula, proceeds extremely easily and is unsuitable. Therefore,
After examining various synthesis conditions for AgO, we found that the intensity of the X-ray diffraction pattern reported previously was significantly different from that of AgO.
was obtained, and it was confirmed that this was stable in an alkaline solution.

The conventionally reported method for synthesizing ρ is to add 72y of sodium hydroxide (NaOH) to 11g of hot water kept at a temperature of about 85°C.
1 with stirring, then to this solution was added 75y of potassium persulfate (K2S2O8), an oxidizing agent, in a suspension state using water as a dispersion medium, and then silver nitrate (AgNO3)
Add 51y dissolved in as little water as possible.
This entire solution was heated to a temperature of 90°C. Stir at a constant temperature.
After this stirring process, a black AgO precipitate is taken out from the solution left still, washed with water, and dried to obtain ~ρ. The reaction formula in this case is as follows. At this time, K used to synthesize 35lg of AgNO into AgO
2S2O875y is 1.85 times the theoretical reaction amount in formula (1), and NaOH72y is 3.0 times the reaction theoretical amount. Based on this condition, we investigated the stabilizing factors of Nρ and found that even at a synthesis temperature of 90°C or lower, Ag
It has become clear that O is produced and that more stable AgO can be obtained if synthesized at a temperature lower than 90°C.

In addition, the necessary amount of NaOH, which is an alkali, basically only needs to be present in an amount that does not lower the pH of the reaction system to 9 or less,
The amount of K2S2O8, which is an oxidizing agent, is
It has become clear that the minimum amount necessary is enough to make the change. Based on this result, we investigated a new method for synthesizing AgO, and were able to synthesize AgO that is stable in an alkaline solution. In the present invention, the effect on gas generation when cadmium nitrate is added at the final stage of synthesis under these synthesis conditions and the voltage stability of a battery used as a positive electrode active material will be explained in Examples together with Comparative Examples. (Comparative example) Dissolve NaOH48y in water 1e, then K2S2O84
8.8y was dissolved and maintained at a temperature of 60°C, AgNO35
A solution of ly dissolved in 0.1' of water is gradually added dropwise over 2 to 5 minutes.

At this time, the reaction solution is stirred at a constant speed, and the synthesis is completed after 10 minutes.After the synthesis is completed, the supernatant liquid is discarded and washed with distilled water to sufficiently remove the alkaline content. AgO was obtained by drying at a drying temperature of 60°C or lower. (Example 1) ~9 was produced under the conditions and synthesis procedure shown in the comparative example, and then (1) Cd(NO3)2 was added to this solution.・4H200.044
y/50ml solution, (2) Cd(NO3)2・4H20
0.089y/50ml solution, (3) Cd(NO3)2
・4H204.45y/50ml solution, (4) Cd(N
Prepare O3)2.4H2017.78y/50ml solution, drop each of the cadmium nitrate solutions (1) to (4) into the above stirring solution over a period of about 1 minute, and after the dropwise addition is complete, add 1 ml of cadmium nitrate solution. Make it react.

After completion of the synthesis, the supernatant was discarded and washed with distilled water to sufficiently remove the alkaline content, followed by drying at a drying temperature of 60° C. or lower to obtain AgO with different amounts of cadmium added. The gas generation performance of the AgO obtained in the comparative example (blank) and the four types of AgO added with cadmium obtained in Example 1 was measured at 1'' at 70°C.
The figure shows a comparison of the amount of gas generated when tested in a 0M KOH aqueous solution for 16 hours.

In this case, the amount of Cd(NO3)2・4H20 added (1)
- (4) is (1
) is 0.05 parts by weight, (2) is 1 part by weight, (3) is 5 parts by weight, and (4) is 2 parts by weight.
It is thought that the Cd present therein is in the state of CdO. Therefore, even if cadmium oxide was added after AgO synthesis, the effect was observed, but the effect was worse than the results shown in the figure.

In the results shown in the figure, the patent application was filed first. AgO synthesis method 1
By making AgO using Cd(NO3)2 and then adding and synthesizing Cd(NO3)2, stable ~
It became clear that ρ could be obtained. Also, the amount added is A
It is sufficient if the amount is 0.5 parts or more per 1 (4) parts by weight of g.
Considering the energy density of AgO, it is meaningless to add more than 1 part. Next, the inventors et al.
The results of a study regarding the timing of addition of d(NO3)2 are shown.

As for the AgO synthesis method, Cd(NO
The simplest method is to synthesize using a mixed solution with 3) added, but in this case, there is no effect of adding cadmium,
On the contrary, it has a negative effect and accelerates gas generation. This means that
This does not mean that cadmium should be added, but that Ag
This shows that it is important at what stage in the O crystal growth stage it is added. (Example 2) Dissolve 48g of NaOH in water 1e, then K2S2O84
8.8y was dissolved and kept at a temperature of 60℃, AgNO35l
yI:. Cd(NO3)・4H201.79y and water 0.
1e is added dropwise over 2 minutes.

At this time, the reaction solution was stirred at a constant speed, and the synthesis was completed at 11 particles.
...(4) Dissolve 48y of NaOH in 1e of water,
Next, melt K2S2O848.8y at a temperature of 60'C.
A solution of AgNO35ly dissolved in 0.1f of water was added dropwise over 2 minutes. At this time, the reaction solution was stirred at a constant speed and reacted for 10 minutes. Then, 0.1.79 g of Cd(NO3).4H was added to the above stirring solution.
A solution of 05e dissolved in water is added dropwise within 1 minute to cause a one-powder reaction.
...(B) After discarding the supernatant liquid of AgO synthesized in the reactions of A and B and washing with distilled water to sufficiently remove the alkaline content, dry at a drying temperature of 60°C or less. ,AgO
I got it. The gas generation test of AgO obtained in A and B above was carried out in 7
The results obtained in a 10M KOH aqueous solution at 0°C are as follows. As is clear from the results above, AgO
If cadmium is present during the crystal growth stage, stable growth of AgO will be inhibited, and its addition will have an adverse effect.

Looking at the SEM photograph, it was confirmed that the AgO particles in A were extremely fine. Therefore, the present inventors have found that the method of adding cadmium after ~ρ crystal growth has the greatest addition effect, and provides a method for producing more stable ~ρ. Even when 0.05 to 20 parts by weight of CdO powder was mixed into AgO prepared by the method for which the present inventor previously applied for a patent, the effect was observed, but the effect was less than that of the method of the present invention. It was confirmed that the present invention is the best method.

Another effect of cadmium addition is on the voltage stability of AgO-Zn based cells. AgO-Zn battery has an open circuit voltage of 1.8
It is well known that the discharge voltage is as high as 5V and takes a two-step curve. This is not preferable as a power source for electronic equipment, and many methods have been proposed in which discharge is performed at one level of voltage. Basically, one-stage discharge cannot occur unless the Ag porous layer or layer is electrically conductive through the Ag2O porous layer or layer in all parts of the current collector that are in contact with AgO. In the test, the IEC standard diameter was 11.9 mm and height was 4.2 mm.
It was held at R-44 pond in Tm1n. The positive electrode is made by mixing 2% by weight of polyfluoroethylene powder into AgO, press-molding a certain amount into a pellet, and insulating everything except the surface facing the negative electrode.
Current collection from the AgO pellets was carried out by a nickel-plated iron ring with an inner diameter of 87rOn, which was in electrical continuity with the positive electrode case. Known negative electrodes, separators, electrolytes, etc. were used. In the battery with the above configuration, AgO obtained in Example 1 and Cd in (2) in Example 2 are calculated as 0
．． Cd in (4) of AgOl Example 2 added with 05 parts by weight
Using a positive electrode active material of AgO containing 20 parts by weight, the battery was pre-discharged to 5 mAH and the voltage stability was examined when the battery was stored at 70°C.

The results are as follows. An Ag layer is formed on the surface of the positive electrode active material and around the ring by preliminary discharge of 5 mAH. As a result, although the battery voltage could be set to AlO-Zn potential, it became clear that after storage at 70OC, there was a difference in voltage stability depending on whether cadmium was added or not. As explained above, in the synthesis method previously proposed by the present inventor, by adding cadmium salt or cadmium oxide at the final stage of synthesis, AgO can be produced with unprecedented stability and less gas generation. It has become possible to add and synthesize Cd, and it has also become possible to provide a new effect in terms of voltage stability of the battery.

[Brief explanation of the drawing]

The figure shows the amount of gas generated from AgO with cadmium added at the final stage of AgO synthesis.

Claims (1)

[Scope of Claims] 1. A method for synthesizing divalent silver oxide from silver salt or silver oxide by reacting silver salt or silver oxide, persulfate, and alkali metal hydroxide, wherein the persulfate is The amount used is 1.0 to 1.85 times the theoretical reaction amount and the concentration of the aqueous solution is 0.
．． 04 to 0.72 mol/l, the amount of alkali metal hydroxide used is 1.05 to 6.0 times the theoretical reaction amount, and the aqueous solution concentration is 0.3 to 4.8 mol/l. ~8
A method for producing divalent silver oxide, which comprises carrying out a synthesis reaction at a temperature of 0° C., and adding cadmium salt or cadmium oxide to the reaction solution after the synthesis reaction is completed. 2. The method for producing divalent silver oxide according to claim 1, wherein 0.05 to 20 parts by weight of cadmium salt or cadmium oxide is added to 100 times the weight of silver during synthesis. 3. The method for producing divalent silver oxide according to claim 1, wherein the cadmium salt is any one selected from the group consisting of cadmium nitrate, cadmium sulfate, and cadmium halide.