JPH0430153B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a button-type zinc-air battery used as a power source for hearing aids, etc. Conventional configurations and their problems In recent years, the field of medical devices has been attracting attention as the population ages. Under these circumstances, the demand for hearing aids as a countermeasure for hearing loss is rapidly increasing, and along with this, the demand for power batteries is also increasing. Conventionally, mercury batteries have often been used as a power source for hearing aids. Advantages of mercury batteries include low cost per capacity and stable discharge voltage. However, on the other hand, it is relatively heavy as a power source for a hearing aid, for example, a power source with a diameter of 11.6 mm and a height of 5.4 mm weighs about 3 g. Another problem was that the battery had to be replaced every two weeks due to its low capacity, and the positive electrode active material used in the mercury battery itself could cause pollution. A button-type zinc-air battery is a battery that has received attention in response to these problems. A feature of this battery is that since oxygen in the air is used as the active material of the positive electrode, it is possible to increase the internal volume of the sealing plate for the negative electrode, thereby increasing the capacity of the battery. In addition, the discharge pressure is relatively stable. It has the advantages of being low pollution and lightweight. However, compared to conventional batteries, this battery has
Due to the presence of air holes, liquid may leak from the air holes during discharge or after over-discharge, or liquid may leak from the air holes when stored in high humidity or during discharge in high humidity. . The reason for this is that oxygen, which is a positive electrode active material, is taken in from the outside, and due to the reaction form of the negative electrode, the constitution of the negative electrode increases as the discharge progresses, and the final 10~
Increase by 20%. Therefore, as the discharge progresses, the volume expands, liberating the electrolyte, and further compressing the air electrode, which is thought to eventually cause leakage from the air holes. Furthermore, under high humidity conditions, moisture is absorbed into the battery system, resulting in the same state as described above. Purpose of the Invention The present invention provides a method for controlling the amount of electrolyte, the filling rate within the volume of the sealing plate, and the concentration of the electrolyte.
The purpose is to solve the conventional problems and provide a highly reliable button-type zinc-air battery with improved storage characteristics. Structure of the Invention In order to achieve the above object, the present invention is characterized in that the amount of the caustic alkaline electrolyte is regulated to 0.24 to 0.23 μ per 1 mAh of the negative electrode active material made of zinc chloride. This makes it possible to improve storage characteristics and increase capacity. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described as R44 type (diameter 11.6
An example of this is an air button battery with a diameter of 5.4 mm, a height of 5.4 mm, and a nominal capacity of 400 mAh. FIG. 1 shows a half-sectional view of a button-type zinc-air battery including this embodiment. In the figure, 1 is a positive electrode case, and 2 is an air intake hole provided in the positive electrode case with a diameter of
Two 0.5mm holes are drilled. 3 is a cellulose-based porous paper placed in the air chamber to diffuse air and absorb the electrolyte coming out from the air electrode. 4 is a water-repellent film based on tetrafluoroethylene that works to suppress liquid leakage. 5 is an air electrode formed by using a nickel porous body as a current collector and coating this with a catalyst made of manganese dioxide, activated carbon, and a conductive material; 6;
7 is a separator, and 7 is an electrolyte-containing material. 8 is a gasket made of nylon that is coupled to the sealing plate 9. 10 is a zinc negative electrode that is a feature of the present invention. The internal volume of the sealing plate 9 coupled with the gasket 8 is 250μ, and is filled with zinc oxide powder or alkaline electrolyte. At this time, the ratio of zinc to electrolyte is important. In other words, the amount of electrolyte per 1mAh of zinc is 0.24~
0.28μ is optimal. When the amount is less than 0.24μ, the amount of electrolyte is small, so the utilization rate of zinc is low and the battery capacity is small. Moreover, the utilization rate of zinc becomes even lower in the low-temperature test. On the other hand, if the amount is larger than 0.78 μ, the utilization rate of the negative electrode improves, but there is a free electrolyte in the sealing plate, which causes a leakage phenomenon during storage or at the end of discharge. Regarding this leakage phenomenon, the filling rate of zinc and electrolyte into the sealing plate,
It was found that the concentration of the electrolyte had an effect. The filling rate in the sealing plate is 75-85%, and the electrolyte concentration is 28-32%.
was found to be the most preferable. The mechanism of liquid leakage from the positive electrode air hole is that the reaction process of a button-type zinc-air battery is Zn+1/2O ₂ →ZnO, and oxygen for the positive electrode active material is taken in from the outside, but as the discharge progresses, the volume of the negative electrode expands. The catalyst layer is compressed, and furthermore, the electrolyte on the negative electrode side is pushed out, weakening the function of the water-repellent film and preventing oxygen from being supplied. As a result, the battery becomes suffocated, gas is generated from the positive electrode due to the potential of the negative electrode, and this eventually causes liquid leakage from the air holes. Therefore, the higher the filling rate of zinc or the like into the sealing plate, the shorter the time until leakage. When the filling rate of the sealing plate is 75% or less, as shown in Figure 2, there is no effect on the battery voltage, but
The internal resistance becomes extremely high and its variation is also extremely large, and is particularly susceptible to high rate discharge. There was almost no difference in this internal resistance when the filling rate was 75% or more. On the other hand, when the filling rate is 95%, almost all leaks occur immediately after assembly.
In addition, in batteries of 85% or more, there is no leakage immediately after discharge, but when the depth of discharge reaches 70% to 85% or more after discharge, leakage is observed from the air hole of the positive electrode. It was found that this degree increases as the filling rate within the sealing plate increases. Therefore, when the filling rate of the sealing plate is 75 to 85%, the battery characteristics and leakage resistance characteristics are excellent. Here it was set to 80%. Note that the sealing plate filling rate was calculated using the following formula. Filling rate (%) Volume of zinc powder + Volume of mercury used for oxidation + Electrolyte amount (volume) / Sealing plate internal volume x 100 On the other hand, the electrolyte concentration is an important point from the battery characteristics. That is, when the electrolyte concentration is higher than 32 wt%, it absorbs moisture in the air, accelerates wetting of the positive electrode catalyst, and the battery becomes suffocated, eventually causing leakage from the air holes. This tendency increases as the electrolyte concentration increases. In humid conditions of 70 to 90%, leakage from the air holes is observed even if the product is stored without the sticker paper. When the electrolyte concentration is lower than 28 wt%, the time until leakage from the air holes becomes longer, but the utilization rate of zinc decreases significantly. Therefore,
The appropriate electrolyte concentration is preferably 28 to 32 wt%. Here, a KOH aqueous solution with a concentration of 30 wt% was used. Next, the effects of the present invention will be described. As shown in Table 1, the battery configuration of the present invention is mainly based on the configuration in which the filling rate in the sealing plate is 80%, the electrolyte concentration is 30wt%, and the electrolyte amount is 0.27μ per 1mAh of negative electrode active material. It was evaluated as follows. The negative electrode filling capacity is 450mAh.
And so. For other configurations, the negative electrode capacitance and the amount of electrolyte were varied depending on the filling rate and electrolyte ratio.

[Table] Table 2 shows the internal resistance values after battery assembly and storage at 45°C for 4 hours. As a result, it was found that the internal resistance value was not influenced by the electrolyte concentration, but was greatly influenced by the electrolyte ratio and the sealing plate filling rate. When the filling rate is 70%, the internal resistance value is 2.7~
The value was 5.0Ω, and it can be said that not only is the value high, but the variation is also large. When the filling rate is 80% or more, the value is small and stable with little variation. However, the electrolyte ratio also has an influence, and tends to be particularly high when the filling rate is 80% or less and the electrolyte ratio is 0.22μ/1mAh or less. The reason for this is thought to be that the adhesion of the elements constituting the battery is affected by the filling rate and the electrolyte ratio.

【table】

[Table] Table 3 shows the table when discharging through a 620Ω resistor.
The capacity index is shown with the configuration of A-2 in 1 as 100.
Note that the final voltage was 0.9 V, and the capacity was calculated using the discharge voltage at 1/2 of the time until the end of discharge. As a result, at a filling rate of 70% in configurations B, C, and D, the internal resistance is high and the filling capacity of the negative electrode is small due to the relationship of the filling rate. Configurations A, E, and F with a filling rate of 80% have higher capacity indexes than those with other filling rates. Among them, the electrolyte ratio is
0.22μ/mAh has a small absolute amount of electrolyte, and
0.32μ/mAh has a small absolute amount of zinc. Therefore,
In the former case, the electrolytic solution is rate-limiting, and a stable discharge curve cannot be obtained because the flat voltage is low. In the latter case, a stable discharge curve can be obtained due to the large amount of electrolyte, but the rate is determined by zinc. Also, in a configuration with a filling rate of 90%, capacity decreases. That is, as mentioned earlier, oxygen is taken in from the outside air from the discharge reaction of Zn+1/2O ₂ →ZnO, so as the discharge progresses, the volume on the negative electrode side expands, and the catalyst layer is compressed. Furthermore, the electrolyte on the negative electrode side is pushed out, the function of the water-repellent film deteriorates, and eventually oxygen is no longer supplied. As a result, the battery becomes suffocated and ceases to function. This tendency increases as the filling rate increases.
Therefore, the discharge capacity index also becomes low. Judging comprehensively, a filling rate of 70% is problematic in terms of capacity, and
At 90%, the capacity is low and leakage (immediately after assembly,
(and during discharge or during overdischarge) are more likely to occur. At a filling rate of 90%, 7 to 9 leaks were observed immediately after. Moreover, as mentioned above, during discharge, even batteries that had not immediately leaked leaked from the air holes. By the way, in conventional mercury batteries and oxidation batteries, the filling rate of the sealing plate is 90 to 95%, but the aforementioned leakage immediately after discharge, during discharge, or during overdischarge is not observed. This problem is unique to button-type batteries, and this tendency was not observed when the sealing plate was filled with a filling rate of 75 to 85%. Furthermore, from the capacity index in Table 3, there is a tendency for the index to increase as the electrolyte concentration increases. However, when the concentration is 35wt% or more,
Due to the characteristics of the electrolyte, it absorbs moisture in the air, so if it is placed in a particularly humid environment, leakage from the air holes is observed during or after discharge. Table 4 shows the number of days from the start of discharge to leakage (air hole) in the configurations (E-1 to E3, A-1 to A3, F-1 to 3) with a sealing plate filling rate of 80%. It is something. The discharge resistance was 620Ω, and the discharge environment was 30°C and 70%. As a result, when the electrolyte concentration was 35%, a leakage phenomenon was observed after 5 to 8 days, and the discharge curve became unstable due to suffocation. Therefore, the discharge capacity index was also small. This trend was not observed for 25% and 30%.

[Table] Similar trends were observed for the filling rates of other sealing plates, although there were differences in the number of days until leakage. Effects of the Invention From these results, the filling rate of the sealing plate in the present invention is 76 to 85%, and the electrolyte ratio is 0.24 to 0.28μ.
/1mAh button type zinc-air battery has the best capacity and leakage performance.

[Brief explanation of drawings]

FIG. 1 is a half-sectional view of a button-type zinc-air battery, and FIG. 2 is a diagram showing the relationship between the filling rate of zinc or the like in the sealing plate and the internal resistance. 1... Positive electrode case, 5... Air electrode, 6... Separator, 7... Electrolyte impregnated material, 9... Sealing plate, 1
0...Zinc negative electrode.

Claims (1)

[Claims] 1. Oxygen as a positive electrode active material, zinc chloride as a negative electrode active material,
A caustic alkaline aqueous solution is used as the electrolyte, the amount of electrolyte is 0.24 to 0.28 μ per 1 mAh of the negative electrode active material, and the filling rate of the internal volume of the negative electrode sealing plate containing the negative electrode active material and the alkaline electrolyte is 75 to 85%. Button-type zinc-air batteries regulated by 2 The concentration of the caustic alkaline aqueous solution as the electrolyte is 28
The button-type zinc-air battery according to claim 1, which is regulated to ~32wt%.