JP2001068170A - Zinc air battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zinc air battery with high capacity, high high-rate discharging characteristics, high safety, and high reliability. SOLUTION: This zinc air battery has a positive electrode catalyst sheet 5 prepared by pressing a catalyst layer containing a manganese oxide against a current collector made of a metal screen for bonding, and as the manganese oxide, manganese dioxide having a nearly globular shape having a ratio of a major diameter to a minor diameter of 1.0-1.5, and a specific surface area by BET method of 30-100 m2/g is used. By using this manganese dioxide, fluidity of positive electrode catalyst powder is increased, and as a result, the density of the positive electrode catalyst sheet is made uniform, discharge characteristics are stabilized, and electrolyte leakage caused by over discharge can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved zinc-air battery.

[0002]

2. Description of the Related Art An air zinc battery using zinc as a negative electrode and oxygen in the air as a positive electrode does not need to be packed with a positive electrode active material in the battery. The feature is that more zinc can be packed and a larger capacity can be obtained as compared with alkaline manganese batteries and silver oxide batteries, and the demand is expanding.

Further, in recent years, there has been an increasing interest in environmental issues, and further higher capacity has been demanded. In addition, it has been applied to a hearing aid of a high output type for hearing loss, which has been using a mercury battery, and has been used for other purposes. Due to the multifunctionality of devices such as pagers, there is an increasing demand for higher output type batteries.

[0004] In the case of an air battery, the standard discharge capacity mainly depends on the amount of the negative electrode active material. As a technique for increasing the capacity, the thickness of the positive electrode catalyst sheet is reduced to increase the internal volume of the battery. Attempts have been made to increase the loading.

Conventionally, a cathode catalyst sheet used for an air battery is manufactured by the following method. First, activated carbon and manganese oxide serving as an oxygen reduction catalyst, artificial graphite as a conductive material, polytetrafluoroethylene (PTFE) powder as a binder and a water repellent are stirred at high speed, and PTFE is fiberized to form a fiber having a particle size of 0.1. A positive electrode catalyst powder of about 1.0 mm is used. The positive electrode catalyst powder was fed in a fixed amount between two parallel rollers to be formed into a sheet, and further pressed by a rolling roller onto a current collector made of a metal screen, and then filled into the gap to integrate the positive electrode catalyst. Had a sheet. Here, manganese dioxide (electrolytic manganese dioxide) by an electrolytic method was used as the manganese oxide.

[0006]

However, since electrolytic manganese dioxide is produced by collecting and pulverizing manganese dioxide deposited on the electrode and making it to have a predetermined particle size, the particle shape is polygonal. It is amorphous, has a very wide particle size distribution, and has low fluidity as a powder. For this reason, the cathode catalyst powder using this has very poor fluidity,
When the thickness of the cathode catalyst sheet is reduced using the catalyst powder, the density of the sheet becomes non-uniform, and the air permeability of the cathode itself varies. For this reason, in an air battery using the same, there were cases where variations in discharge characteristics and the occurrence of liquid leakage during overdischarge occurred. That is, when the density of the positive electrode catalyst sheet becomes higher than necessary, the air permeability of the catalyst sheet decreases, and it becomes impossible to secure the amount of oxygen necessary for discharge.
If the density was too low, the water repellency of the catalyst sheet was reduced, and the absorption of water from the outside of the battery was increased, and liquid leakage occurred during an overdischarge test under high humidity.

[0007] These problems have hindered the increase in capacity. However, if the specific surface area of electrolytic manganese dioxide is increased for the purpose of increasing the output, the true density is reduced. Sex was further reduced, increasing similar problems.

The present invention is intended to solve such a problem, and provides a safe and highly reliable air zinc battery which increases the battery capacity and improves the discharge characteristics under heavy load. The purpose is to:

[0009]

SUMMARY OF THE INVENTION The present invention relates to an air-zinc battery having a positive electrode catalyst sheet in which a catalyst layer containing manganese oxide is pressed and integrated with a current collector made of a metal screen, , Long diameter / short diameter = 1.
It is characterized by being manganese dioxide having a substantially spherical shape of 0 to 1.5 and a specific surface area of 30 to 100 m ² / g by a BET method.

Here, the manganese dioxide used in the present invention is preferably a chemical manganese dioxide produced by a chemical synthesis method. Chemical manganese dioxide generally has a substantially spherical particle shape after production, and the ratio of long diameter to short diameter is 1.
0 to 1.5. On the other hand, in the electrolytic manganese dioxide, the electrodeposits are pulverized in the production process and the particle size is adjusted, so that the particle shape does not become spherical but becomes polygonal and irregular. In this electrolytic manganese dioxide, it is also possible to suspend and precipitate in an electrolytic bath without changing the deposition on the electrode by changing the electrolysis conditions.In this case, the particle shape can be substantially spherical. In the method, it is necessary to greatly increase the current density at the time of electrolysis, and industrial productivity is greatly reduced. In this case, the particle diameter becomes small and the specific surface area exceeds 100 m ² / g, so that the contact resistance between the particles increases and the fluidity decreases. Therefore, even if such electrolytic manganese dioxide is used, the effect of the present invention cannot be obtained.

In the present invention, the manganese dioxide is used as a positive electrode catalyst, mixed with activated carbon, a conductive material, a binder and the like to form a positive electrode catalyst powder having a particle size of about 0.1 to 1.0 mm, formed into a sheet by a roller, A positive electrode catalyst sheet is integrated by pressing and filling the metal screen. In such a positive electrode catalyst sheet, the density is made uniform due to the high fluidity of the positive electrode catalyst powder, and the air permeability and water repellency are stabilized. Therefore, the air battery using the same has stable discharge characteristics and can prevent over-discharge leakage.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The zinc-air battery of the present invention will be described below with reference to FIG. A water-repellent film 8 made of a PTFE film, a positive electrode body, and a separator 3 are accommodated in an upper stage of a positive electrode case 7 having a step portion on the bottom surface having an air hole 10. The positive electrode body is prepared by mixing activated carbon and manganese oxide as an oxygen reduction catalyst, graphite as a conductive material, and PTFE powder as a binder, and stirring the mixture at a high speed to fibrillate the PTFE powder to obtain a particle diameter of 0.1 to 1%. A positive electrode catalyst powder having a thickness of about 0.0 mm was integrated with a nickel-plated positive electrode current collector 6 made of stainless steel by press-fitting to form a positive electrode catalyst sheet 5. The PTFE film is pressure-bonded to the surface of the positive electrode catalyst sheet 5 on the side opposite to the separator 3. Nickel-stainless steel-copper 3 is placed on the upper part of the separator 3 via an insulating gasket 4.
A negative electrode case 1 formed by processing a layer clad material is provided, and a sealant such as polyamide resin is usually applied between the insulating gasket 4 and the negative electrode case 1 to prevent leakage of an alkaline electrolyte. ing. Further, the inside of the negative electrode case 1 is filled with a gel zinc negative electrode 2 and is in contact with the separator.

The gelled zinc negative electrode is obtained by mixing and stirring a zinc alloy powder, an alkaline electrolyte and a gelling agent. Here, the zinc alloy powder has a particle size of about 100 to 300 μm, and is made of calcined or non-melted with addition of aluminum, bismuth, indium, lead, etc., and the alkaline electrolyte is 25 to 40 wt%.
Aqueous potassium hydroxide solution and gelling agent use polyacrylic acid or the like.

(Example 1) Manganese oxide is substantially spherical with a ratio of major axis to minor axis of 1.0 to 1.5 (average value 1.2), specific surface area of 40 m ² / g, average Particle size 25μ
m, a chemical manganese dioxide, which was blended with activated carbon. The compounding ratio of the chemical manganese dioxide was 50% by weight based on the total amount of the activated carbon and the manganese dioxide. Further, graphite and PTFE powder were added thereto. Graphite and PT
The amount of FE powder added is activated carbon, manganese dioxide, graphite,
5% by weight of graphite based on the total amount of PTFE powder, PTFE
The powder was 20 wt%. This mixture was stirred by a stirrer to obtain a particulate positive electrode catalyst powder of 0.1 to 1.0 mm. This positive electrode catalyst powder was supplied in a fixed amount to a roller press, and after being formed into a continuous sheet, the sheet was again supplied to a roller press together with a metal screen serving as a current collector, pressed and filled in the metal screen, and integrated. Thus, a cathode catalyst sheet having a thickness of 0.3 mm was prepared, and using this, a PR44 type air zinc battery shown in FIG. 1 was prepared.

At this time, the gelled zinc negative electrode has 500 pp of lead.
A 1% calcined zinc alloy powder to which m was added, a 30 wt% aqueous potassium hydroxide solution, and polyacrylic acid were mixed and used.

Examples 2 to 6 As manganese oxides,
The ratio of the major axis to the minor axis was the same as that of Example 1, and the specific surface area and the average particle size were chemical manganese dioxide having the values described in Table 1, and were blended with activated carbon at the blend ratio shown in Table 1. . Otherwise, a PR44 type air-zinc battery was fabricated in the same manner as in Example 1, and Examples 2 to 6 were made.

(Conventional example) Electrolytic manganese dioxide is used as a manganese oxide, the specific surface area, the average particle size, and the mixing ratio are set to the values shown in Table 1, and the thickness of the positive electrode catalyst sheet is set to 0.4.
mm. Other than that, PR44 was performed in the same manner as in Example 1.
A zinc-air battery was fabricated. In addition, in the case of electrolytic manganese dioxide, the shape is a polygonal indefinite shape, so it is not possible to specify the ratio of the long diameter to the short diameter, but if this is regarded as an approximate sphere and quantified, it will be about 2.2. .

(Comparative Examples 1-2) Electrolytic manganese dioxide was used as the manganese oxide, the specific surface area, the average particle size, and the mixing ratio were set to the values shown in Table 1, and the thickness of the positive electrode catalyst sheet was set to 0.3 mm. . Otherwise, a PR44 type zinc-air battery having the same configuration as in Example 1 was produced, and Comparative Examples 1 and 2 were made.

Comparative Example 3 Chemical manganese dioxide having the same ratio of the major axis to the minor axis as in Example 1 was used as the manganese oxide, but the average particle diameter was 5 μm and the specific surface area was 12%.
The material used was 0 m ² / g. Otherwise, Example 1
In the same manner as described above, a PR44 type zinc-air battery was produced.

[0020]

[Table 1]

The batteries of these examples, the conventional example, and the comparative example were subjected to a continuous discharge test and an overdischarge test of 620 Ω and 120 Ω. The overdischarge test was performed at a temperature of 25 ° C.
Discharge was performed under a load of 250 Ω in an atmosphere of a relative humidity of 85%, and the rate of occurrence of liquid leakage when the load was further applied for 100 hours after the discharge was examined. Table 2 shows the results. The numerical value of each discharge capacity indicates the average value and the variation σ (σ = standard deviation) of 20 batteries.

[0022]

[Table 2]

In the conventional example using electrolytic manganese dioxide, since the thickness of the positive electrode catalyst sheet is large, the supply amount of the positive electrode catalyst powder to the roller when forming the positive electrode catalyst sheet can be increased. It can be supplied substantially uniformly, and the density variation of the manufactured positive electrode catalyst sheet is reduced. Therefore, variation in discharge capacity is suppressed,
Although there was no occurrence of liquid leakage in the overdischarge test, the negative electrode filling amount was reduced as compared with the example because the positive electrode catalyst sheet was thicker,
The discharge capacity decreases.

Comparative Example 1 using the same electrolytic manganese dioxide as the conventional example and reducing the thickness of the positive electrode catalyst sheet, and Comparative Example 2 using the electrolytic manganese dioxide to further increase the specific surface area
However, although the discharge capacity and heavy load discharge were improved, the dispersion was extremely large, and liquid leakage occurred in the overdischarge test.

On the other hand, in Examples 1 to 6 of the present invention,
Even when the thickness of the cathode catalyst sheet is reduced and manganese dioxide with a high specific surface area is used, the density of the cathode catalyst sheet is made uniform, suppressing variations in discharge capacity and increasing the capacity, enabling heavy-load discharge. It became. Furthermore, there was no liquid leakage in the overdischarge test. However, when the specific surface area was increased to 120 m @ 2 / g and the average particle size was set to 5 .mu.m (Comparative Example 3), the discharge capacity was reduced, the dispersion was increased, and liquid leakage occurred in the overdischarge test.

Even when the chemical manganese dioxide of this embodiment is used, when the compounding ratio of the chemical manganese dioxide is low (for example, 10%), the discharge capacity in heavy load discharge decreases, and the generation of liquid leakage also occurs. Was seen. Therefore, in the present invention, the compounding ratio of the chemical manganese dioxide is preferably higher than 10%.

As described above, the product of the present invention poses a conventional problem when the thickness of the cathode catalyst sheet is reduced to increase the capacity of the zinc-air battery, or when manganese dioxide having a high specific surface area is used to cope with heavy load discharge. This solves the problem of the variation in the discharge capacity and the problem of the occurrence of the liquid leakage in the overdischarge test, and can secure the performance more than before.

The present invention is not limited by the above embodiment. Elements that do not directly affect the present invention, such as zinc alloy powder, gelling agent, electrolyte concentration, and positive electrode catalyst, may be changed without departing from the scope of the present invention.

[0029]

According to the present invention, in an air-zinc battery, even if the thickness of the cathode catalyst sheet is reduced to increase its capacity, the discharge performance is stabilized, the heavy-load discharge is improved, and the generation of liquid leakage is prevented. Can be prevented. Therefore, according to the present invention, a highly reliable high-capacity air zinc battery can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a zinc-air battery according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Negative electrode case, 2 ... Gel zinc negative electrode, 3 ... Separator, 4 ... Insulating gasket, 5 ... Positive electrode catalyst layer, 6 ... Positive electrode current collector, 7 ... Positive electrode case, 8 ... Water repellent film, 9 ... Air diffusion paper ,
10 air holes.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideyuki Ogata 3-4-1 Minamishinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Corporation (72) Inventor Machiko Ohashi 3-4-1 Minamishinagawa, Shinagawa-ku, Tokyo No. Toshiba Battery Corporation F-term (reference) 5H018 AA10 AS03 BB03 EE02 EE07 EE12 HH01 HH02 HH05 5H032 AA02 AS03 AS11 BB02 CC11 EE01 EE02 HH01 HH04

Claims (3)

[Claims] 1. An air zinc battery having a positive electrode catalyst sheet in which a catalyst layer containing a manganese oxide is pressure-bonded to a current collector made of a metal screen, wherein the manganese oxide has a long diameter / short diameter = 1. A manganese dioxide having a substantially spherical shape of 0.0 to 1.5 and a specific surface area of 30 to 100 m ² / g by a BET method, characterized by being manganese dioxide. 2. The zinc-air battery according to claim 1, wherein the manganese dioxide is a chemical manganese dioxide. 3. The air zinc battery according to claim 1, wherein the mixing ratio of manganese dioxide is 10% by weight or more based on the total amount of activated carbon and manganese dioxide.