JP3235161B2 - Button type alkaline battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a button type alkaline battery. More specifically, the present invention relates to a laminated structure of a separator interposed between a negative electrode agent and a positive electrode agent.

[0002]

2. Description of the Related Art In recent years, alkaline batteries such as silver oxide batteries, mercury batteries, alkaline manganese batteries, and nickel zinc batteries have been developed.
It is used as a power source for various types of desktop devices and portable devices, and further miniaturization and higher performance are required. An alkaline battery basically has a structure in which a negative electrode agent and a positive electrode agent are separated by a separator, and the inside is filled with an electrolytic solution. With the progress of the electrochemical reaction in both electrode portions, only the electrolytic solution can move between the two electrodes via the separator. Therefore, the battery characteristics greatly depend on the performance of the separator.

Conventionally, a separator having a laminated structure has been used to improve the performance of the separator. This has a configuration in which various functional films are combined on the front and back surfaces based on a cellophane film. As the functional film, a polyethylene film, a nonwoven fabric, paper, or the like is used. As the laminated structure of the separator using these materials, those listed below have been conventionally used. That is, a three-layer laminate structure of a polyethylene film, a cellophane film, and a polyethylene film, a structure in which three sheets of a polyethylene film, a cellophane film, and a nonwoven fabric are combined, and a combination of a polyethylene film, a first cellophane film, a second cellophane film, and a nonwoven fabric This is a configuration in which four sheets are combined.

The cellophane film located in the intermediate layer is excellent in hydrophilicity and liquid retention, has a small electric resistance, and has an action of reducing a positive electrode active material such as silver ions, and thus has an excellent permeation suppression function. There is. However, since the cellophane film is of a cellulosic type, it is easily oxidized and deteriorated when it comes in contact with an oxidizing agent such as a depolarizer. For this reason, there is a disadvantage that ions and molecules between the positive electrode and the negative electrode are easily transmitted. To compensate for this drawback, a polyethylene film having oxidation resistance is generally laminated with a cellophane film and arranged so as to face at least the positive electrode side. This polyethylene membrane uses a material whose surface is modified in order to impart ion exchangeability and water retention. Specifically, a monomer having a carboxyl group such as acrylic acid or methacrylic acid is graft-polymerized using radiation.

[0005] The characteristics of such a surface-modified polyethylene film greatly depend on the graft ratio. For example, while the graft ratio increases, the hydrophilicity increases and the electrical resistance decreases,
The transmittance to the anode active material such as silver ions increases, and the storage stability of the battery capacity decreases. Conversely, when the graft ratio is small, the capacity preservation property is improved, but the electrical resistance of the membrane is increased, and the closed circuit voltage (hereinafter referred to as CCV; Closed Circuit).
It is an abbreviation of t Voltage. ) Decreases. As described above, the selection of the graft ratio of the polyethylene film, that is, the electric resistance greatly affects the battery performance and is extremely important.

[0006]

In the case of using a three-layered separator laminated on both sides of a cellophane film with a graft-polymerized polyethylene film, the polyethylene film facing the positive electrode side and the polyethylene film facing the negative electrode side are conventionally the same. And had the same electric resistance. Therefore, when a polyethylene film having a relatively low graft ratio is used, there is a problem or a problem that the electric resistance is increased and the capacity preservation property is improved, but the CCV characteristic is deteriorated. On the other hand, when a polyethylene film having a relatively high graft ratio is commonly used on both the front and back surfaces, there is a problem or a problem that while the electric resistance is reduced, the CCV characteristic is improved, and the capacity preservability is reduced. As described above, it has conventionally been very difficult to improve both the CCV characteristics and the capacity preservability.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a button-type alkaline battery separator having a three-layer laminate structure capable of improving both CCV characteristics and capacity preservation. The purpose is to do. The following measures were taken to achieve this purpose.
That is, as a separator interposed between a negative electrode agent and a positive electrode agent of an alkaline battery, a first polyethylene film having a relatively low graft ratio obtained by graft polymerization of acrylic acid or methacrylic acid and having a high electric resistance, a cellophane film, A laminate obtained by laminating a second polyethylene film having a relatively large ratio and a relatively small electric resistance and integrally forming the same was used. Then, a measure was taken to dispose the first graft-polymerized polyethylene film having a large electric resistance on the positive electrode agent side.
Specifically, the electric resistance of the first polyethylene film of the separator is set in a range of 150 to 500 mΩ · cm ² ,
The electric resistance of the second polyethylene film is 100 to 200 mΩ.
・ Set to the range of cm ² . Further, as the sealing plate, one having three bent portions in the positive electrode case side direction, the positive electrode case bottom surface direction, and the opposite direction to the positive electrode case bottom surface at an end portion fitted with the positive electrode case via the sealing gasket was used. .

[0008]

As described above, in the present invention, the electrical resistance of the polyethylene film facing the positive electrode agent side is increased, and the electrical resistance of the polyethylene film facing the negative electrode agent side is set small. Thereby, excellent capacity preservability can be obtained without lowering the CCV characteristics of the alkaline battery. In other words, by increasing the electrical resistance of the polyethylene film on the positive electrode agent side and reducing the electrical resistance of the polyethylene film on the negative electrode agent side, a battery having excellent CCV characteristics can be obtained without lowering the capacity storage stability. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing an embodiment of a button-type alkaline battery according to the present invention, in which the present invention is applied to a silver oxide battery SR616SW (outer diameter: 6.8 mm, height: 1.6 mm). It is. As shown in the figure, the silver oxide battery includes a negative electrode agent 1 and a sealing plate 2 containing the negative electrode agent 1. This sealing plate 2 also serves as a negative electrode terminal. A positive electrode case 4 is fitted to the sealing plate 2 via a sealing packing 3. The sealing gasket 3 is made of, for example, a nylon material, and electrically insulates a negative electrode terminal formed of the sealing plate 2 and a positive electrode terminal formed of the positive electrode case 4. At the inner bottom of the positive electrode case 4, a positive electrode material 5 in the form of pellets containing silver oxide as a main component is arranged. The inside of the battery thus sealed is filled with an electrolytic solution. In this example, an aqueous solution of caustic soda was used as the electrolytic solution. However, the present invention is not necessarily limited to this, and other alkaline aqueous solutions can be used. Further, it is needless to say that the present invention is not limited to silver oxide batteries, but can be applied to alkaline batteries using various types of negative electrode agents and positive electrode agents.

A separator 6 is interposed so as to separate the negative electrode agent 1 and the positive electrode agent 5 from each other. The separator 6 has a three-layer structure including a second polyethylene film 8 in contact with the negative electrode agent 1, a first polyethylene film 7 in contact with the positive electrode agent 5, and a cellophane film 9 laminated by both polyethylene films.

The first polyethylene film 7 is formed by graft polymerization of acrylic acid or methacrylic acid, and is made of a material having a relatively low graft ratio. For this reason, the electric resistance is relatively large, and is preferably set in the range of 150 to 500 mΩ · cm ² . The second polyethylene film 8 is also made of a material obtained by graft polymerization of acrylic acid or methacrylic acid. In this case, a material having a relatively large graft ratio is selected, and the electric resistance is relatively small. Preferably, the electric resistance is set in the range of 100 to 200 mΩ · cm ² . The laminated separator 6 is obtained by laminating the pair of the first polyethylene film 7 and the second polyethylene film 8 on the cellophane film 9 from both sides and integrally molding them.

In this embodiment, the lower limit of the electric resistance of the first polyethylene film 7 is set to 150 mΩ · cm ² . If the electric resistance of the first polyethylene film 7 is set to be equal to or lower than this lower limit, the permeation amount of silver ions increases remarkably, and it is difficult to obtain a desired capacity storage property. In this embodiment, the upper limit of the electric resistance of the first polyethylene film is set to 500 mΩ · cm.
Set to ² . If the electrical resistance of the first polyethylene film is set to exceed this upper limit, a desired CCV characteristic cannot be obtained due to an increase in internal resistance.

On the other hand, in this embodiment, the electric resistance of the second polyethylene film is set in the range of 100 to 200 mΩ · cm ² . The lower the electrical resistance of the second polyethylene film, the better the CCV characteristics. However, when the surface is modified by graft polymerization using acrylic acid or methacrylic acid, it is difficult to reduce the electric resistance to 100 mΩ · cm ² or less due to production technology. For this reason, 100 mΩ · cm ² was set as the lower limit of the electric resistance of the second polyethylene film. On the other hand, upper limit 2
The value of 00 mΩ · cm ² is a rough guide, and the CCV characteristic is improved by lowering the internal resistance as much as possible.

The electric resistance of the graft-polymerized polyethylene film was measured by an AC voltage drop method (1 kHz). The measurement atmosphere temperature was set to 20 ± 1 ° C., and the graft-polymerized polyethylene sample was subjected to 40% KOH (specific gravity 1.400).
± 0.005) After being immersed in an aqueous solution for 12 hours or more, it was taken out and measured for electric resistance.

[0015]

In order to confirm the effects of the present invention, samples were prepared and evaluated for capacity preservation and CCV characteristics. For comparison, one sample was the invention product and the other was 2 samples.
The types were made. Before describing the measurement results, the contents of each sample will be described below.

For the inventive sample, the electric resistance 20
The grafted polymer of thickness 27μm with 0mΩ · cm ² 1
As a separator, a polyethylene film, a cellophane film having a thickness of 21 μm, and a graft-polymerized second polyethylene film having an electric resistance of 100 mΩ · cm ² and a thickness of 27 μm were laminated in this order and integrally formed.
The button-type alkaline battery shown in (1) was produced. Note that a first polyethylene film having a large electric resistance is arranged on the positive electrode side.

The sample of Conventional product 1 has a graft-polymerized first polyethylene film having an electric resistance of 150 mΩ · cm ² and a thickness of 27 μm, a cellophane film having a thickness of 21 μm, and an electric resistance of 150 mΩ · cm ² and a thickness of 27 μm. A button-type alkaline battery shown in FIG. 1 was produced by using a separator obtained by laminating the graft-polymerized second polyethylene film in this order and integrally forming the laminated film. In the conventional product 1, the first polyethylene film has a lower electric resistance and the second polyethylene film has a higher electric resistance as compared with the invention product. Therefore, the electrical resistance as the separator total is equal to that of the invention.

The sample of the prior art 2 has a graft-polymerized first polyethylene film having an electric resistance of 200 mΩ · cm ² and a thickness of 27 μm, a cellophane film having a thickness of 21 μm, and an electric resistance of 200 mΩ · cm ² and a thickness of 27 μm. A button-type alkaline battery shown in FIG. 1 was produced by using a separator obtained by laminating the graft-polymerized second polyethylene film in this order and integrally forming the laminated film. In the conventional product 2, the second polyethylene film has a higher electrical resistance than the inventive sample, and the electrical resistance of the first polyethylene film is equal to that of the inventive product. Therefore, the electrical resistance of the separator as a whole is higher than that of the invention.

FIG. 2 is a graph showing the results of measuring the capacity retention of each of the samples described above. The horizontal axis shows the number of storage days, and the vertical axis shows the capacity storage rate. The samples were stored at a temperature of 60 ° C. for acceleration. The final voltage was set to 1.4V. The discharge load resistance used was 68 kΩ. Each measurement is the average of 10 samples. In the graph, curve A represents the measurement result of the product of the present invention, curve B represents the measurement result of conventional product 1, and curve C
Represents the measurement result of the conventional product 2. As is clear from this graph, in the conventional product 1 using the separator made of the first polyethylene film having a low electric resistance, the capacity preservation rate sharply decreases after 40 days. On the other hand, the product of the present invention and the conventional product 2 maintain a capacity storage ratio of 90% or more even when the storage days exceed 100 days.

FIG. 3 is a graph showing measurement results of CCV characteristics. The horizontal axis indicates the depth of discharge, and the vertical axis indicates CCV. The measurement condition of CCV was 5 seconds at 23 ° C. using a load resistance of 2 kΩ. The measured values represent the average of 10 samples. As in the graph of FIG. 2, curve A represents the invention, curve B represents the conventional product 1, and curve C represents the conventional product 2. As is clear from this graph,
The conventional product 2 using the separator made of the second polyethylene membrane having a high electric resistance has a CCV of 1.3 V or less, whereas the invention product and the conventional product 1 have a CCV of 1.3 V or more.

As is clear from the above measurement results, the invention product is clearly superior in the capacity preservation and the CCV characteristics are not inferior to the conventional product 1. Also, it can be seen that the product of the present invention is not inferior in capacity preservation in spite of having excellent CCV characteristics as compared with Conventional Product 2. From this result, it was found that the CCV characteristics depended on the electric resistance of the total laminated film of the separator, and the capacity preservation depended on the electric resistance of the first polyethylene film disposed on the positive electrode agent side. The reason for this is that by arranging a polyethylene film having a large electric resistance on the positive electrode material side, the amount of silver ions permeated can be reduced, and the cellophane film is less likely to be broken by silver ions. That is, by increasing the electrical resistance of the polyethylene film on the positive electrode material side and reducing the electrical resistance of the polyethylene film on the negative electrode material side, it is possible to provide an alkaline battery excellent in capacity storage without lowering CCV characteristics. it can. or,
By reducing the electric resistance of the polyethylene film on the side of the negative electrode, an alkaline battery having excellent CCV characteristics can be provided without lowering the capacity preservability.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a basic configuration of a button-type alkaline battery according to the present invention.

FIG. 2 is a graph showing the results of measuring the capacity retention of a button-type alkaline battery.

FIG. 3 is a graph showing a result of measuring CCV characteristics of a button-type alkaline battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode agent 2 Sealing plate 3 Sealing packing 4 Positive electrode case 5 Positive electrode agent 6 Separator 7 1st polyethylene film 8 2nd polyethylene film 9 Cellophane film

Continuation of the front page (56) References JP-A-57-95069 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 2/14-2/18 H01M 2/02-2 / 08 H01M 6/04-6/12

Claims (1)

(57) [Claims] 1. A separator interposed between a negative electrode agent and a positive electrode agent, a first polyethylene film obtained by graft polymerization of acrylic acid or methacrylic acid and having a relatively low graft ratio and a high electric resistance, a cellophane film, and a graft. A laminate formed by laminating a second polyethylene film having a relatively large electric resistance and a small electric resistance and integrally forming the same, and the first graft-polymerized polyethylene film having a large electric resistance is arranged on the positive electrode agent side, and The electrical resistance of the first polyethylene film of the separator is 150 to 500 mΩ · cm.
² , the electrical resistance of the second polyethylene film is 100 to 200.
in the range of milliohms · cm ^2, the sealing plate is, at the end of the positive electrode case and engageable via sealing packing, positive electrode case laterally, the positive electrode case bottom direction, and bending of three places of a direction opposite to that of the positive electrode case bottom An alkaline battery having a part.