JPS6141850B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing silver oxide suitable as an anode active material for alkaline batteries. In recent years, various studies have been made on using silver oxide (AgO) as an anode active material for alkaline batteries. The discharge capacity per unit volume of silver oxide (Ag ₂ O), which has been commonly used, is approximately 1680 mA.
H/cm ³ , whereas silver oxide is about 3330mA
It has a discharge capacity of about 2.0 times H/cm ³ and is suitable as an anode active material. A method for producing ferric oxide is an anodizing method in which silver nitrate solution is used as an electrolytic bath, electrolysis is performed using platinum mesh as the anode and cathode, and silver oxide is electrodeposited on the anode. Ozone oxidation method involves blowing ozone into a silver nitrate solution to oxidize it and generate colloidal particles. Chemical oxidation methods are known in which a silver nitrate solution is oxidized using an oxidizing agent in the presence of an alkali.
In the anodic oxidation method and ozone oxidation method, _{Ag6O8 ・}
Because silver oxylates such as AgNO ₃ are mainly produced,
It is necessary to heat-treat the product to convert it into silver oxide, which makes the work complicated, making it difficult to mass-produce, and the yield is low. Furthermore, the silver oxide obtained by these manufacturing methods decomposes in an electrolyte consisting of an alkaline solution and generates a large amount of gas, and the discharge capacity of the active material decreases, so it is not suitable as an active material for batteries. do not have. The present invention relates to a chemical oxidation method that has a simple manufacturing process and is suitable for mass production with high yield.The present invention relates to a chemical oxidation method that has a simple manufacturing process and is suitable for mass production with high yield. It provides: Persulfates such as potassium persulfate (K ₂ S ₂ O ₈ ) and permanganese such as potassium permanganate (KMnO ₄ ) are used as oxidizing agents to oxidize silver nitrate, which is the main raw material when producing silver oxide. These include acid salts and chlorates such as sodium chlorite (NaClO ₂ ). The various oxidizing agents mentioned above were added to a 1.2 mol/aqueous sodium hydroxide solution, and a 3 mol/aqueous silver nitrate solution was gradually added dropwise to the solution, and silver nitrate was oxidized with the various oxidizing agents to obtain 0.5 g of ferric oxide. the anode active material,
A GS12 type silver oxide battery was made using zinc as the cathode active material and a 25% by weight aqueous sodium hydroxide solution as the electrolyte, and the open circuit voltage and terminal voltage of each sample battery were 1.4V.
The following table 1 shows the discharge capacity and discharge utilization rate until
Shown below.

[Table] As is clear from this table, those oxidized with potassium permanganate have a low open circuit voltage and small discharge capacity, and those oxidized with sodium zinc oxide have a small discharge capacity and a low discharge utilization rate. low.
Compared to these, those using ferric oxide obtained by oxidation with potassium persulfate have a large discharge capacity and a high discharge utilization rate, and are thus found to be suitable as an oxidizing agent. Next, the present inventors investigated the conditions for synthesizing silver oxide with good yield, high purity, and low decomposition rate in alkaline solutions. , the ratio of persulfate and alkali usage was clarified. The other synthesis conditions were found to be suitable: reaction temperature of 80° C., reaction time of 60 minutes, and aging time of 60 minutes, so the experiment was conducted under the same conditions. Figure 1 shows the relationship between the purity of silver oxide and the amount of potassium persulfate used when synthesizing silver oxide using 1 mole of silver nitrate and varying the amount of potassium persulfate used. show. We also investigated the relationship between the daily average amount of gas generated and the amount of potassium persulfate used when silver oxide synthesized under these conditions was immersed in a 25% by weight aqueous sodium hydroxide solution maintained at 45°C. Shown in Figure 2. An excess of 10 moles of alkali was added in each case. As is clear from FIG. 1, the silver oxide produced under synthesis conditions in which the amount of potassium persulfate is 0.7 mol or more has a high purity, that is, it has a large discharge energy per unit weight as an anode active material. Also, as is clear from Figure 2, the amount of potassium persulfate
Silver oxide produced under the synthesis conditions of 0.7 mol to 2.0 mol generates less gas in an alkaline solution, that is, has less decomposition. The decomposition of silver oxide reduces the discharge capacity of the active material, and the gas generated during decomposition may promote leakage or cause deformation or rupture of the battery. must be suppressed as much as possible. Next, 1 mol of silver nitrate and potassium persulfate were synthesized within the range of 0.7 mol to 2.0 mol, and the relationship between the yield and the amount of alkali used was investigated, as shown in Figure 3. Curve A is when using 1 mole of silver nitrate and 0.7 mole of potassium persulfate, curve B is when using 1 mole of silver nitrate and 1.0 mole of potassium persulfate, and curve B is when using 1 mole of silver nitrate and 2.0 mole of potassium persulfate. Let the curve be C. As shown in FIG. 3, the amount of alkali required to achieve a yield close to 100% is 2.4 moles of A, 3 moles of B, and 5 moles or more of C, but it is not necessary to use a large excess. From Figures 1, 2, and 3, the number of moles of potassium persulfate used relative to the number of moles of silver nitrate used is
By setting the number of moles of alkali to be in the range of 0.7 to 2.0 times the number of moles of silver nitrate used, and the number of moles of alkali to be greater than the sum of the number of moles of silver nitrate and twice the number of moles of potassium persulfate used. It is possible to synthesize silver oxide with a yield of 98% or more, a purity of 98% or more, and less decomposition in an alkaline solution. The present inventors further determined the molar ratios of the amounts of silver nitrate, potassium persulfate, and alkali to be within the above-mentioned ranges, and further investigated the concentrations of silver nitrate and alkali, and Table 2 shows the results.

【table】

[Table] As is clear from this table, the silver nitrate concentration is approximately
0.2 to 5 mol/, alkaline concentration approximately 0.8 to 2.0 mo
Silver oxide produced under the conditions of 1/20% has high purity and generates a small amount of gas in an alkaline solution, that is, it decomposes slowly. By controlling the synthesis conditions within a certain range as described above, it was possible to obtain silver oxide with high yield, high purity, and slow decomposition. In the above synthesis example, sodium hydroxide was used as the alkali and potassium persulfate was used as the oxidizing agent, but other materials such as potassium hydroxide and sodium persulfate can also be used.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the amount of potassium persulfate and the purity of silver oxide, Figure 2 shows the relationship between the amount of potassium persulfate and the amount of gas generated, and Figure 3 shows the relationship between the amount of alkali and the yield. It is a relationship diagram.

Claims (1)

[Claims] 1. When producing silver oxide for batteries by oxidizing silver salt with an oxidizing agent consisting of persulfate in an alkaline solution, the number of moles of persulfate used is equal to the number of moles of silver salt used. The number of moles of alkali used should be within the range of 0.7 to 2.0 times the number of moles of salt used, and the number of moles of alkali used should be regulated to a range of more than the sum of the number of moles of silver salt used and twice the number of moles of persulfate used. , and a method for producing ferric oxide for batteries, characterized in that the concentration of the silver salt solution is regulated in the range of 0.2 mol/ to 5 mol/, and the concentration of the alkaline solution is regulated in the range of 0.8 mol/ to 2.0 mol/.