JPS6121382B2 - - Google Patents

Description

[Detailed description of the invention]

The invention relates to a button-type air battery, and aims to improve storage characteristics. With the recent spread of hearing aids, there has been a demand for inexpensive and high capacity batteries. Traditionally, mercury batteries have been mainly used as a power source for hearing aids, but because these batteries have a small capacity, they need to be replaced about once every two weeks, and mercury itself is a polluting substance. , there is a growing demand for batteries that can replace these batteries. Therefore, air-zinc batteries, which use oxygen in the air as the positive electrode active material and zinc as the negative electrode, have been attracting attention. The positive electrode of this battery is mainly composed of activated carbon as a catalyst, a conductive material, and manganese dioxide, and is coated on a current collector using a water-repellent binder. The reaction of this battery is theoretically expressed as follows. Positive electrode 1/2O ₂ +H ₂ O+2e→2OH ^- E ₀ =0.401V Negative electrode Zn+2OH ^- →ZnO+H ₂ O E ₀ =1.245V Bipolar reaction 1/2O ₂ +Zn →ZnO E ₀ =1.646V However, the actual battery voltage is The amount of manganese dioxide added to the
It will look like a table. Table 1 shows the open circuit voltage of the battery when the amount of manganese dioxide as the main component of the positive electrode was changed.

[Table] In other words, the voltage is 40% when the addition rate of manganese dioxide is 40
There is no significant change when the amount exceeds % by weight. Moreover,
Since the standard voltage of this battery is 1.35V or higher, at least 20 to 40% by weight of manganese dioxide is required. However, when a battery using this positive electrode is stored, it has the disadvantage that the voltage gradually decreases. For example, when stored at 60°C for 20 days, the open-circuit voltage decreases from 1.364V to 1.340V for the product containing 40% MnO ₂ by weight. By the way, in the case of no MnO ₂ addition, it does not change much at 1.329V. As a result of various studies on the cause of this voltage drop due to storage, it was found that it largely depends on the amount of activated carbon added, and that if the amount added does not exceed 40% by weight, it will affect the discharge characteristics. For example, the initial closed circuit voltage when discharging at 620Ω is
1.09V, 1.23V with 20wt% addition, 1.27V with 40wt% addition
, and adding more than that will not have a significant effect. On the other hand, when a large amount of activated carbon is added, manganese dioxide is oxidized depending on the activity of the activated carbon, and its potential is lowered. In this way, the effects of activated carbon and MnO ₂ addition are in opposite directions. As a result of further investigation into this problem, the present inventors found that by using activated carbon with an appropriate value of methylene blue decolorizing power, which is one evaluation method for indicating the activity of activated carbon, the open circuit voltage decreases due to storage. succeeded in obtaining an air battery with almost no Here, methylene blue decolorization power is specified in JISK1470, and methylene blue solution A is added to the activated carbon sample, shaken and filtered, and the color of the filtrate is compared with methylene blue solution B to find that it matches the color of solution B. It is determined from the amount of solution A required for this. Solution A is 0.120 g of methylene blue dissolved in phosphate-potassium-disodium phosphate buffer solution at Hz7 to make 100 ml, and solution B is solution A10.
ml, add water to make 500 ml, and add a buffer solution to 5 ml to make 500 ml. The greater the methylene blue decolorizing power, the higher the activity. In the present invention, the activated carbon for the positive electrode, which is mainly composed of activated carbon, manganese dioxide, and a conductive material and contains a water-repellent binder, has a methylene blue decolorizing power of 100 to 250.
ml is used. If the decolorizing power of methylene blue is smaller than this, the closed circuit voltage will decrease due to the low activity.For example, if the decolorizing power of methylene blue is 50ml, a load of 620Ω
It becomes 1.20V. Furthermore, when the decolorizing power of methylene blue increases, the activity is high, and MnO ₂ is oxidized by activated carbon during storage, resulting in a significant decrease in open circuit voltage. Table 2 shows 620 Ω batteries with positive electrodes made by blending activated carbon with various methylene blue decolorizing powers with manganese dioxide and graphite as a conductive material.
Initial flat voltage (intermediate voltage) at load and 40 at 60°C
It shows the flat voltage (intermediate voltage) after storage for days. On the other hand, when using this battery as a power source for hearing aids, etc.
It is necessary to maintain a closed circuit voltage of approximately 1.25V, and it is required that this 1.25V can be maintained even after storage.

【table】

[Table] As is clear from Table 2, the preferred initial flat voltage is the composition enclosed by the double box in the table, but due to the difference in the activity of activated carbon due to storage, the preferred range is as follows: The decolorizing power of the methylene blue of the active carbon used is limited due to the blending composition. The present invention will be explained below using examples. Figure 1 shows A44 type (diameter 11.6φ, height 5.4mm)
shows an air battery. 1 is a positive electrode case, 2 is an air intake hole, 3 is a diffusion paper, 4 is a water-repellent film made of fluororesin, and 5 is a positive electrode. The positive electrode is manganese dioxide 40
Part by weight, 40 parts by weight of activated carbon and graphite as a conductive material
Add 20 parts by weight of polytetrafluoroethylene as a water repellent to 100 parts by weight of the 20 parts by weight mixture, apply it on a current collector, dry it, and heat to 320 to 340°C, which is the melting point of polytetrafluoroethylene. It was heat treated. Various methylene blue decolorizing powers were used as the activated carbon. 6 is a separator, 7 is a liquid-containing material, 8 is a nylon gasket, 9 is a sealing plate, and 10 is a zinc negative electrode. The electrolyte used was a 10 mol/KOH aqueous solution saturated with ZnO. Figure 2 shows the relationship between the methylene blue decolorizing power of the activated carbon used in the positive electrode and the open circuit voltage of the battery. Characteristics after storage for days are shown. As is clear from the figure, methylene blue decolorizing power
No significant difference was observed for items smaller than 250ml. However, when it exceeds 260ml, it suddenly decreases to 60ml.
When stored at ℃ for 20 days, the decrease was large;
Both will no longer maintain even 1.35V. Therefore, anything with methylene blue decolorizing power of 250 ml or more will not meet the specifications. FIG. 3 shows the flattening voltages C and D at discharge rates of 180Ω and 620Ω, respectively. As a result, when the methylene blue decolorizing power is 100ml or more, high rate load (180Ω),
It can be seen that although the general load (620Ω) is not affected greatly, it suddenly decreases when the load is lower than that. From the above, the methylene blue decolorizing power of activated carbon is 100~
If a 250 ml bottle is used, the ability of manganese dioxide will not be lost during storage and the stability of the flat voltage during discharge can be maintained. As described above, according to the present invention, a button-type air battery with stable voltage and excellent storage characteristics can be obtained.

[Brief explanation of the drawing]

Figure 1 is a side view with essential parts cut out showing an embodiment of the battery of the present invention, Figure 2 is a diagram showing the relationship between the methylene blue decolorizing power of activated carbon used in the positive electrode and the open circuit voltage, and Figure 3 is the same. The relationship between methylene blue decolorizing power and closed circuit voltage is shown. 5... Positive electrode, 6... Separator, 10... Negative electrode.

Claims (1)

[Claims] 1. A button-shaped button-shaped body comprising a positive electrode mainly composed of activated carbon, manganese dioxide, and a conductive material and containing a water-repellent binder, a zinc negative electrode, and a separator, and characterized in that the activated carbon of the positive electrode has a methylene blue decolorizing power of 100 to 250 ml. air battery.