JPS5826622B2 - silver oxide battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the improvement of a battery having an anode whose surface is composed of silver oxide and whose active material is ferric oxide, a cathode whose active material is zinc, and an alkaline solution as its electrolyte. Accordingly, an object of the present invention is to provide a battery having a large discharge capacity and excellent low-temperature characteristics.

In recent years, various studies have been made on the use of ferric oxide (Age) as an anode active material.

The discharge capacity per unit volume of conventionally commonly used silver oxide (Ag20) is approximately 1680 mA](/c4, while the discharge capacity of ferric oxide is approximately 3330 mARlcrd.
It has a discharge capacity about 2.0 times higher than that of 100%, making it suitable as an anode active material.

However, ferric oxide easily decomposes in alkaline electrolyte, resulting in significant performance deterioration during storage, and the oxygen gas generated during decomposition promotes electrolyte leakage, leading to deformation and rupture of the battery. There is.

As a result of various studies on the decomposition of silver oxide in an alkaline electrolyte, the present inventors found that the decomposition of silver oxide is suppressed when the concentration of the electrolyte is low.

Figure 1 shows the amount of gas generated per 12 particles when ferric oxide particles with an average particle size of about 1 to 3 μm were immersed in alkaline electrolytes of various concentrations maintained at 45° C. for 720 hours. show.

Curve A in the figure represents the amount of gas generated when an aqueous sodium hydroxide solution is used as the electrolyte, and curve B represents the amount of gas generated when an aqueous potassium hydroxide solution is used as the electrolyte.

As is clear from this figure, if any electrolyte has a weight ratio of 20 or less, decomposition of silver oxide is suppressed and the amount of gas generated is small.

A low electrolyte concentration is preferable for suppressing the decomposition of silver oxide, but if the electrolyte concentration is lower than 5% by weight, the ionic conductivity deteriorates and internal resistance increases.
Furthermore, when using an anode can made of a nickel-plated iron can, rust occurs from pinholes in the plating layer and thin parts of the plating layer, increasing the contact resistance between the anode can and the anode. The electrolyte concentration must be regulated within a range of about 5 to 20 parts by weight.

The table below shows that G-13 type alkaline batteries were made by varying the concentration of the electrolyte injected into the anode, which mainly consists of silver oxide, and by injecting 25 parts by weight of electrolyte into the cathode. 4
The change in total height was investigated after storage for 0 days.

As is clear from this table, when the electrolyte concentration is 5 to 20% by weight, the decomposition of silver oxide is suppressed and there is no significant difference in the total height change.

However, if the electrolyte concentration exceeds 30% by weight, the gas generated due to decomposition may promote leakage of the electrolyte.
The upper limit of the electrolyte concentration needs to be 20 weight or more to avoid deformation or rupture of the battery.

Phosphorous graphite is commonly used as a conductive agent for anodes because of its good conductivity, low bulk density, and lubrication that makes it easy to release the formed anode from the mold. The present inventors have discovered that when silver oxide and phosphorous graphite are mixed and wetted with an alkaline electrolyte, the decomposition of the silver oxide is promoted by the phosphorous graphite.

This tendency is shown in Figure 2. Phosphate graphite is mixed in various proportions with 0.5 t of silver oxide, and an anode is formed by pressure molding. The graph shows the change in discharge capacity of the anode after it was moistened with an electrolyte and stored at 60°C for 40 days.

As is clear from this figure, as the amount of phosphorous graphite added increases, the decomposition of silver oxide is promoted, resulting in a significant decrease in discharge capacity after storage.

It is presumed that the decomposition of silver oxide by phosphorous graphite is caused by functional groups such as carboxyl groups present on the surface of phosphorous graphite.

Therefore, it is better to use an electrolytic solution having the above-mentioned concentration range and to form the anode by pressure molding an anode active material made of ferric oxide in a state that does not contain phosphorous graphite to prevent the decomposition of ferric oxide. It is effective in suppressing

Since the filling amount of the anode active material increases to the extent that the cased phosphorous graphite is not added, the discharge capacity of the anode also increases.

Note that this type of silver battery is suitable for applications with extremely low load resistance, such as electronic watches, so there is no problem in its use even without the addition of a conductive additive.

The present inventors investigated a more stable treatment method for the anode active material, and as a result, as shown in Figure 3, ferric oxide particles 1
By reducing only the surface of
It has been found that forming the surface layer 2 consisting of 20) is effective.

Reduction methods include chemical reduction using a reducing agent such as formalin, glucose, or glycerin, reduction through heat treatment in a reducing atmosphere or inert atmosphere, and electrochemical reduction through electrical discharge. .

Note that the interface between the surface layer 2 of the silver oxide particle 10 and the inside 3 of the particle is not clear.

Depending on the conditions of the reduction, some metallic silver may be generated in the surface layer 2.

Although the decomposition of the anode active material is suppressed by the formation of a surface layer made of silver oxide, the discharge capacity of the anode active material decreases as the production ratio of silver oxide increases.

This tendency is shown in Figure 4, where 0.5 t of anode active material particles that have produced various proportions of silver oxide through reduction are collected and used as an anode. The graph shows the change in discharge capacity of the anode at the initial stage of manufacture (curve C) when wetted with an electrolyte solution, and the change in discharge capacity after storage at 60° C. for 40 days in a state moistened with the electrolyte solution (curve D).

As is clear from this figure, the production ratio of silver oxide is 3.
If it exceeds 0% by weight, the discharge capacity of the anode will be small from the beginning of production, while if the production ratio of ferrous oxide exceeds 10% by weight, the anode active material will partially decompose, especially when stored for a long period of time at high temperatures. There is capacity deterioration due to b1 storage.

Therefore, the production ratio of the surface layer consisting of silver oxide is preferably regulated to a range of about 10 to 30 parts by weight based on the total weight of the particles.

In order to suppress the decomposition of ferric oxide, the surface of the anode obtained by molding ferric oxide powder is reduced to coat the surface of the anode with ferric oxide.
It has been previously proposed to coat the surface of the anode with a thin layer of silver or the anode with an organic binder in which silver oxide is dispersed.

The thin layer of silver oxide in the former case is an aggregate of particles and has many micropores, so during storage of the battery, the alkaline electrolyte passes through the thin layer and penetrates into the inside of the anode. Therefore, the second silver oxide comes into contact with the electrolytic solution and disperses, resulting in a decrease in discharge capacity.

On the other hand, in the latter case, when a binder in which ferric oxide is dispersed is applied to the anode, pinholes and uneven coating occur, making it difficult to obtain a sufficient effect. If the binder has the following properties, when it comes into contact with silver oxide, it reduces it and causes a decrease in discharge capacity, which limits the range of binders that can be selected.

Furthermore, when preparing silver oxide and a binder, and when applying and drying this mixture, silver oxide reacts with carbon dioxide gas in the air to form silver carbonate, which is then loaded into a battery. This promotes deterioration of the alkaline electrolyte and passivation of the cathode active material, leading to greater variations in battery performance.

As mentioned above, the electrolyte concentration on the anode side, which is formed by molding an anode active material mainly composed of ferric oxide and containing no phosphorous graphite, and whose surface is composed of silver oxide, is set to about 5 to 20%. By regulating the amount within this range, the decomposition of silver oxide can be effectively suppressed.

However, when a battery is assembled using this electrolyte, sufficient battery performance can be obtained under normal conditions, but satisfactory performance cannot be obtained when used at low temperatures.

In other words, at low temperatures, when the electrolyte concentration is low on the catholyte side that uses zinc as the cathode active material, the electrolyte becomes insufficient for the cathode active material, and the cathode active material is likely to become passivated. Since the discharge utilization rate of the anode decreases, the electrolyte concentration on the anode side needs to be slightly higher.

A 20 weight electrolyte was injected into the anode mainly composed of silver oxide whose surface was composed of silver oxide, and the concentration of the electrolyte injected into the cathode mainly composed of zinc was varied to produce G-13. 6.5 at -10°C and -20°C.
Ni, 1;? Figure 5 shows the evolution of the discharge duration at 1 when the terminal voltage becomes 1.4V when continuous discharge is performed by connecting a load resistor of .

Curve E in the figure is the discharge duration at -10°C when a sodium hydroxide electrolyte is used, curve G is the discharge duration at -20°C, and curve F is when a potassium hydroxide aqueous electrolyte is used. One is the discharge duration at 10°C, and the other is the discharge duration at 20°C.

As is clear from this figure, when the electrolyte concentration is lower than about 23 times the electrolytic solution, the discharge utilization rate of the cathode active material is poor, so that sufficient discharge performance cannot be obtained, especially at low temperatures.

On the other hand, if the electrolyte concentration exceeds about 40% by weight, the electrolyte will easily absorb carbon dioxide gas in the air when handled, resulting in the formation of carbonates in the electrolyte and deterioration, resulting in the formation of a casing of dissolved carbon dioxide. As a result, the cathode active material becomes passivated, and the discharge performance of the battery deteriorates.

Therefore, in order to suppress the influence of carbon dioxide gas as much as possible and to allow the discharge reaction on the cathode side to proceed smoothly even at low temperatures, it is necessary to regulate the electrolyte concentration to a range of about 23 to 40 F. .

The present invention provides a silver oxide battery having an anode using silver oxide as an anode active material, a cathode using zinc as an active material, and an alkaline solution as an electrolyte, wherein the anode has an oxidized surface on the surface of the second silver oxide. The anode is made of active material particles with a surface layer of silver and is compression-molded without containing phosphorous graphite, and the electrolyte concentration on the anode side is regulated to 5 to 20% by weight, and the cathode side is The electrolyte concentration is regulated in the range of 23 to 40 wt.
An electrolyte absorber loaded with a gel agent added to the cathode side or coated on the single tube, or a non-hydrophilic thin layer placed between the anode and cathode material, can reduce the concentration of electrolyte between the anode and cathode sides. By maintaining uniformity, the drawbacks of the conventional method are solved.

Next, an example of the silver oxide battery of the present invention will be described with reference to FIG.

A ferric oxide powder having a particle size of about 1 to 3 μm is treated in a nitrogen atmosphere at about 120°C for 9 hours to form a surface layer of ferric oxide in an amount of about 30% of the total weight of the particles. The anode 4 is compression-molded at a pressure of about 5 ton/cm without adding phosphorous graphite to produce an anode 4 having a packing density of about 5.6 f/cr/1.

An electrolytic solution consisting of a 2.0 weight percent sodium hydroxide aqueous solution is injected into the bottom of an anode can 5 made of a nickel-plated iron can, the anode 4 is inserted into this, and the anode is heated with the electrolytic solution. 4 is wetted, and then an electrolytic film consisting of a non-hydrophilic microporous film 6 such as polyethylene or polypropylene that has not been hydrophilized with a surfactant or the like, a semipermeable membrane 7 such as cellophane, and a nonwoven polypropylene fabric is placed on the anode 4. The liquid holding bodies 8 are placed one after another.

Separately, on the inside of the cathode terminal plate 10 to which a polyamide cross-sectional gasket 9 was fitted on the periphery, 25 weight tons of hydroxide gel made of sodium polyacrylate was applied.
A cathode material 11 made of a mixture of an electrolyte made of a J-hydroxide solution and a zinc powder is loaded, and this cathode terminal plate 10 is inserted into the anode can 5.
The opening end of the anode can 5 is bent inward to seal the battery.

Reference numeral 12 denotes a stainless steel pedestal that is integrated when the anode 4 is compression molded.

In order to maintain a non-uniform state of electrolyte concentration on the anode side and the cathode side, there is a method of adding a gel agent that fixes the electrolyte to the cathode agent.

Among the gel agents, polyacrylic acid or its salt, carboxypolymethylene, and the like are particularly suitable because they maintain a stable gel state in the electrolytic solution.

Moreover, these gel agents can also be applied to one side of the electrolyte solution holder to form a gel agent layer.

Furthermore, as described in the examples, a non-hydrophilic thin layer that does not interfere with the discharge reaction can be interposed between the anode and the cathode agent to prevent the electrolyte from migrating. It is even more effective if used in combination with a gel agent.

[Brief explanation of the drawing]

Figure 1 is a relationship diagram between electrolyte concentration and gas generation amount, Figure 2 is a relationship diagram between phosphorous graphite addition rate and electrode performance, Figure 3 is an enlarged cross-sectional view of anode active material particles, and Figure 4 5 is a diagram showing the relationship between the production ratio of silver oxide and electrode performance, FIG. 5 is a diagram showing the relationship between electrolyte concentration and battery performance, and FIG. 6 is a sectional view of the silver oxide battery according to the present invention. DESCRIPTION OF SYMBOLS 1...Anode active material particle, 2...Surface layer, 3...Particle interior, 4...Anode, 11
...Cathode agent.

Claims (1)

[Claims] 1. In a ferric oxide battery having an anode using ferric oxide as an anode active material, a cathode using zinc as an active material, and an alkaline solution as an electrolyte, the anode has ferric oxide on the surface of the ferric oxide. An anode consisting of active material particles with a silver surface layer, compression molded without containing a conductive additive such as phosphorous graphite, and the electrolyte concentration on the anode side is regulated between 5 and 20 weight coefficients. At the same time, the electrolyte concentration on the cathode side is regulated to a range of 23 to 40% by weight, and a gel agent added to the cathode agent, an electrolyte absorber loaded with a gel agent or coated on one side, or an electrolyte absorber on the anode and cathode sides is used. A silver oxide battery that maintains non-uniform electrolyte concentration between the anode and cathode sides by a non-hydrophilic thin layer placed between them.