HK1091323B - Alkaline cell and production method for same - Google Patents

Description

Alkaline battery and method for producing the same

Technical Field

The present invention relates to a coin-type alkaline battery or a button-type alkaline battery.

Background

As shown in fig. 3, an alkaline battery for a small-sized electronic device such as a wristwatch is configured such that the open end of a positive electrode can 2 is sealed with a negative electrode can 4 by a gasket 6. On the negative electrode case 4, a folded portion 4a and a folded bottom portion 4b are formed, and an open edge end of the folded portion 4a is folded back along an outer peripheral surface in a U-shape in cross section. At the folded portion 4a, the negative electrode can 4 is brought into close contact with the inner peripheral surface of the opening end edge of the positive electrode can 2 by the gasket 6, thereby achieving airtight sealing.

The negative electrode can 4 is press-formed into a cup shape from a three-layer clad material having a nickel layer 7 made of nickel, a stainless steel layer 8 made of stainless steel, and a current collector layer 9 made of copper.

The positive electrode can 2 contains a positive electrode 1, while the negative electrode can 4 contains a negative electrode 3, which in turn contains mercury-free zinc or zinc alloy powder as the negative electrode active material. The negative electrode 3 is separated from the positive electrode 1 by a separator 5, and the negative electrode 3 is filled with an alkaline electrolyte.

Allowing the negative electrode 3 to use the zinc or zinc alloy powder mixed with mercury instead of the zinc or zinc alloy powder, thereby suppressing the generation of hydrogen (H) from the zinc powder or zinc alloy powder₂) Or inhibit the generation of hydrogen gas from the current collector layer 9, which is typically caused by contacting zinc or zinc alloy powder with copper on the negative electrode can via an alkaline electrolyteHydrogen gas is generated. The generation of hydrogen is caused by a reaction of dissolving zinc or zinc alloy powder in an alkaline electrolyte while oxidizing zinc into zinc oxide. As described above, the generation of hydrogen can be suppressed by using zinc mixed with mercury. As a result, deterioration of capacity and deterioration of leakage resistance characteristics that may be caused by the generation of hydrogen, and swelling of the battery due to an increase in internal pressure are avoided.

Disclosure of Invention

The alkaline battery according to the present invention comprises: a positive electrode; a negative electrode containing zinc alloy powder; a separator separating the positive electrode from the negative electrode; an alkaline electrolyte; a positive electrode case accommodating the (insulated) positive electrode; a negative electrode case that houses a negative electrode, has a tin-plated layer that is heat-treated at a melting point (232 ℃) or higher, and is in contact with the negative electrode through the tin-plated layer; and a gasket interposed between the positive electrode can and the negative electrode can.

Further, the method for producing an alkaline battery according to the present invention comprises:

a first step of forming a tin plating layer on a negative electrode can;

a second step of subjecting the tin-plated layer to heat treatment at a melting point (232 ℃) of tin or higher; and

third, the positive electrode case and the negative electrode case are folded back so that a sealing gasket is interposed therebetween, which contains the positive electrode, the negative electrode, the separator, and the alkaline electrolyte, and then such folded portions are sealed tightly for hermetic sealing.

In order to effectively suppress the generation of hydrogen gas, a method for plating a plating layer containing tin, which is a metal having a higher hydrogen overpotential than copper, is desired.

By using the present invention, hydrogen gas to be generated by bringing zinc as a negative electrode active material into contact with a current collector (copper) layer of a negative electrode can be suppressed, corrosion of zinc can also be suppressed, and thus, the leakage resistance characteristics against the creep phenomenon of an alkaline electrolyte can be improved.

The tin plating layer before heat treatment has some defects such as pin holes or cracks that cause the current collector layer (copper layer) to be exposed. Since copper has a lower hydrogen overpotential than tin, hydrogen gas is generated when copper comes into contact with zinc powder as a negative electrode active material.

However, when the tin plating layer is heat-treated at the melting point of tin or higher, defects such as pin holes or cracks are repaired, and thus, the copper layer is no longer exposed, thereby preventing the generation of hydrogen gas.

Further, according to the present invention, since the peripheral portion 6b of the projecting portion 6a of the gasket on the center side is allowed to contact with the inner face of the negative electrode case 4, the leakage resistance characteristic is improved, even when a certain degree of accuracy variation occurs in the process of providing the tin-plated film on the inner face of the negative electrode case, since the peripheral portion 6b of the projecting portion of the gasket on the center side contacts with the inner face of the negative electrode case, the transfer of the alkaline electrolyte can be prevented, and further, since the gap between the peripheral portion 6b of the projecting portion 6a of the gasket 6 on the center side and the inner face of the negative electrode case 4 is 0.05mm or less, the transfer of the zinc powder in the negative electrode is prevented, and further, unlike the case where the end of the gasket and the inner face of the negative electrode case are in contact, since the projecting portion of the gasket on the center side is not used as a holder of the negative electrode case, then, the contact between the positive electrode and the negative electrode in the battery is not hindered, and the corrosion reaction of zinc of the negative electrode active material as the current collector (copper) layer of the negative electrode can does not proceed, thereby improving the deterioration of the capacity retention characteristics.

According to the present invention, an alkaline battery excellent in discharge characteristics can be realized without using mercury.

Drawings

Fig. 1 is a cross-sectional view of an alkaline cell according to the present invention;

fig. 2 is a cross-sectional view of a negative electrode can according to the present invention; and

fig. 3 is a cross-sectional view of a conventional alkaline battery.

Detailed Description

The alkaline cell of the present invention will now be described in detail with reference to the preferred embodiment shown in fig. 1 and 2.

Fig. 1 shows a cross-sectional view of a button-type alkaline cell. The open end edge of the positive electrode can 2 is sealed with the negative electrode can 4 by a gasket 6 having a U-shaped cross section.

The positive electrode can 2 is made of a stainless steel thin plate having a nickel plating layer. It also functions as a positive electrode terminal. The positive electrode can 2 contains a positive electrode formed in a form like a coin or like a button sheet. Then, a separator 5 is disposed on the positive electrode 1 contained in the positive electrode can 2. The separator 5 may be a three-layer laminate consisting of a nonwoven fabric, cellophane and a piece of graft polymerized polyethylene. The separator 5 is impregnated with an alkaline electrolyte. The alkaline electrolyte may be an aqueous solution of sodium hydroxide or potassium hydroxide, or a mixed aqueous solution of sodium hydroxide and potassium hydroxide.

An annular seal gasket 6 is disposed on the inner peripheral face of the open end edge of the positive electrode can 2. Then, the negative electrode 3 is placed on the separator 5. The negative electrode 3 is a gel-like substance composed of mercury-free zinc or zinc alloy powder, an alkaline electrolyte and a thickener.

The negative electrode can 4 is inserted into the opening end edge of the positive electrode can 2 so that the negative electrode 3 is contained. In the negative electrode case 4, a folded portion 4a and a folded bottom portion 4b are formed, and an open edge end of the folded portion 4a is folded back along an outer peripheral surface in a U-shape in cross section. At the folded portion 4a, the negative electrode can 4 is in close contact with the inner peripheral surface of the opening end edge of the positive electrode can 2 through the gasket 6, thereby achieving airtight sealing.

The current collector layer 9 is arranged inside by first forming a 3-layer clad material consisting of the nickel layer 7, the stainless steel layer 8 and the current collector layer 9 made of copper into a cup shape by press-forming, and then forming a tin-plated layer on the thus press-formed clad material by electroless plating of tin or the like. After the tin-plated layer is formed, it is subjected to a heat treatment at the melting point of tin (232 ℃ C.) or higher. When the tin-plated layer is subjected to a heat treatment at the melting point of tin (232 c) or higher, the copper layer is not exposed because pinholes or cracks existing in the tin-plated layer are filled, thereby preventing the generation of hydrogen gas.

Further, when the tin plating layer is provided only in the inner face area of the negative electrode case, the leakage resistance characteristic is improved, which is preferable. The term "inner face area" used herein is defined as an area of the inner portion (the side in contact with the electrolyte) of the negative electrode can 4, and the face more inside than the folded bottom portion 4b. The tin-plated layer is not formed on the folded portion 4a and the folded bottom portion 4b which are in contact with the gasket, preventing the electrolyte from creeping up by creeping phenomenon, thereby improving the leakage resistance characteristic. This is because the alkaline electrolyte is more likely to creep up on the tin-plated layer 10 than on the current collector layer 9.

By covering unnecessary portions (the folded portion 4a and the folded bottom portion 4b folded back into a U-shaped cross section along the outer peripheral surface) with a tape of gummed paper or the like, a tin-plated layer can be formed only in the inner region using electroless plating of tin or the like, and then, the tin-plated layer thus formed can be subjected to heat treatment.

In another case, the three-layer coating material is press-formed into a cup shape with the current collector layer 9 disposed inside, a tin-plated layer is formed by using electroless plating, and then, unnecessary portions are removed or peeled off by etching using acid or the like, the tin-plated layer may be formed only in the inner face area of the cup, and thereafter, the tin-plated layer thus formed may be subjected to heat treatment.

It is preferable that the thickness of the tin plating layer 10 is between 0.05 μm and 5 μm. In the case where the thickness thereof is less than 0.05 μm, since it takes a long time to perform the heat treatment and the negative electrode can is deformed, the case is not preferable. Further, since it takes a long time to form the plating layer, the case is not suitable.

As for the heat treatment atmosphere of the tin-plated layer 10, the oxygen concentration is preferably 0.01% to 1%. This is because it is considered that, with the heat treatment atmosphere of the tin-plated layer 10 of the negative electrode can, the surface oxidation of the tin-plated layer can be suppressed by making the oxygen concentration as low as in the atmosphere. When the tin-plated layer 10 is subjected to heat treatment in an atmosphere in which the oxygen concentration exceeds 1%, there is a risk of causing a problem in discharge characteristics due to an increase in contact resistance caused by oxidation of the tin surface. Further, when the oxygen concentration is less than 0.01%, not only hardly any significant effect is exerted on the surface resistance of the tin-plated layer 10, but also it takes a longer time and additional cost to maintain the atmosphere, and therefore, no particular advantage is produced at such a low level of oxygen concentration as described above.

As for the alkaline electrolyte, it is preferable that sodium hydroxide is in the range of 15% to 30% by weight, or potassium hydroxide is in the range of 1% to 15% by weight. When the ratio of potassium hydroxide in the alkaline electrolytic solution is less than 1% by weight, improvement in discharge characteristics due to excellent conductivity of the potassium hydroxide aqueous solution is small as compared with that of the sodium hydroxide aqueous solution, which is not preferable. Further, when the ratio of potassium hydroxide by weight is more than 15%, since the aqueous potassium hydroxide solution has a higher wettability with copper than the aqueous sodium hydroxide solution, the leakage resistance characteristics of the battery may be deteriorated, which is not preferable. Sodium hydroxide and potassium hydroxide may be used as the electrolyte individually or in combination.

Further, by bringing the peripheral portion 6b of the projecting portion 6a of the gasket 6 on the center side into contact with the inner face of the negative electrode case 4, or bringing the gap between the peripheral portion 6b of the projecting portion 6a of the gasket 6 on the center side and the inner face of the negative electrode case 4 to 0.05mm or less, the peripheral portion 6b of the projecting portion 6a of the gasket on the center side does not become a support for the negative electrode case 3, and thus, the contact between the negative electrode and the positive electrode in the battery is not hindered, which is preferable.

As the positive electrode active material used in the present invention, silver oxide, manganese dioxide, synthetic oxides, and nickel hydroxide; however, the present invention is not limited to these.

Example 1

A battery having a configuration as shown in fig. 1 was prepared as example 1. The negative electrode case 4 having the folded portion 4a and the folded bottom portion 4b was formed by press-molding a three-layer clad material having a thickness of 0.2mm composed of a nickel layer 7, a stainless steel layer 8 made of SUS304, and a current collector layer 9 made of copper. This negative electrode can 4 was subjected to etching by a mixed aqueous solution of sulfuric acid and hydrogen peroxide, washed with water, immersed in a shaking electroless plating solution, washed with hot water, washed with water, and then dried, thereby forming a 0.3 μm-thick tin plating layer on the entire area of the copper surface of the negative electrode can 4. Thereafter, after the inner face area 11 of the negative electrode can was masked with a chlorosulfonated polyethylene rubber stopper, and unnecessary portions of the tin plated layer of the folded portion 4a and the folded bottom portion 4b on the inner face, the main component of which was an oxide on the copper substrate, were peeled and removed by dipping into a peeling solution of a tin plate, and then, the resulting negative electrode can was subjected to a heat treatment at 232 ℃ in an atmosphere having an oxygen concentration of 1% or less, thereby producing a negative electrode can 4.

On the other hand, an alkaline electrolyte containing 22% by weight of sodium hydroxide and 9% by weight of potassium hydroxide is poured into the positive electrode can 2, and then a disk-shaped sheet of the positive electrode 1 is inserted therein, thereby allowing the positive electrode 1 to absorb the alkaline electrolyte.

Next, a separator 5 pressed in a circular shape from a three-layer structure consisting of a nonwoven fabric, cellophane, and a graft copolymerized polyethylene film was placed on the sheet of the positive electrode 1. Then, the separator 5 was impregnated with an alkaline electrolyte solution containing 22% by weight of sodium hydroxide and 9% by weight of potassium hydroxide, and the alkaline electrolyte solution was added dropwise.

Next, the gel-like negative electrode 3 composed of mercury-free zinc alloy powder containing aluminum, indium, and bismuth, zinc oxide, a thickener, sodium hydroxide, potassium hydroxide, and water is placed on the separator 5. The negative electrode can 4 is inserted into the open end edge of the positive electrode can 2 such that it wraps the negative electrode 3 with the annular seal 6 made of nylon 66 coated with an asphalt and epoxy type sealant interposed therebetween. The opening end edge of the positive electrode can 2 is hermetically sealed by caulking. This results in the desired alkaline cell. On this occasion, the peripheral portion 6b of the protruding portion 6a of the gasket 6 on the center side is allowed to contact with the inner face of the negative electrode can 4.

Example 2

In example 2, the heat treatment temperature of the tin plating layer was set to 250 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Example 3

In example 3, the clearance between the peripheral portion 6b of the protruding portion 6a of the gasket 6 on the center side and the inner face of the negative electrode case was allowed to be 0.05 mm. The heat treatment temperature of the tin-plated layer was set to 240 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Example 4

In example 4, the distance between the peripheral portion 6b of the protruding portion 6a of the gasket 6 on the center side and the inner face of the negative electrode case was allowed to be 0.07 mm. The heat treatment temperature of the tin-plated layer was set to 240 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Example 5

In example 5, the alkaline electrolyte was allowed to be a mixed solution containing 15% by weight of sodium hydroxide and 15% by weight of potassium hydroxide. The heat treatment temperature of the tin-plated layer was set to 240 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Example 6

In example 6, the alkaline electrolyte was allowed to be a mixed solution containing 30% by weight of sodium hydroxide and 1% by weight of potassium hydroxide. The heat treatment temperature of the tin-plated layer was set to 240 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Example 7

In example 7, the alkaline electrolyte was allowed to be a mixed solution containing 30% by weight of sodium hydroxide and 15% by weight of potassium hydroxide. The heat treatment temperature of the tin-plated layer was set to 240 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Example 8

In example 8, the alkaline electrolyte was allowed to be a mixed solution containing 30% by weight of sodium hydroxide and 0.5% by weight of potassium hydroxide. The heat treatment temperature of the tin-plated layer was set to 240 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Example 9

In example 9, the alkaline electrolyte was allowed to be a mixed solution containing 15% by weight of sodium hydroxide and 20% by weight of potassium hydroxide. The heat treatment temperature of the tin-plated layer was set to 240 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

Comparative example 1

In comparative example 1, an alkaline battery was prepared by using a negative electrode can, in which a tin plating layer having a thickness of 0.1 μm was formed on the negative electrode can 4 by ordinary electroless plating. The tin-plated layer is not heat-treated. Other conditions were the same as in example 1.

Comparative example 2

In comparative example 2, the tin plating layer was heat-treated at 210 ℃. Other conditions for preparing the alkaline battery were the same as in example 1.

210 cells were prepared for each of examples 1 to 9 and comparative examples 1 and 2. The evaluation results of the leak occurrence ratio after storage for 120 days and storage for 140 days are shown in table 1, from 100 batteries among the batteries thus prepared in each of examples 1 to 9 and comparative examples 1 and 2, stored under a severe environment of 40 ℃ and 90% RH. In addition, the evaluation results of the discharge capacity [ mAh ] at the terminal voltage of 1.2V after constant discharge of 30k Ω after 100 days of storage from among the batteries thus prepared in each of examples 1 to 9 and comparative examples 1 and 2 at 60 ℃ and 0% RH are shown in table 1. Incidentally, in each cell, the initial discharge capacity was about 28 mAh. Finally, the results of evaluating 10 batteries from the batteries thus prepared in each of examples 1 to 9 and comparative examples 1 and 2 with respect to the closed circuit voltage [ V ] in an environment of-10 ℃ at a load resistance of 2k Ω after 5 seconds under the initial condition (depth of discharge: 0%) are shown in table 1.

First, when examples 1 and 2 and comparative examples 1 and 2 were compared with each other on the basis of table 1, it was found that the leakage resistance characteristics and the charge holding characteristics can be improved by forming a tin-plated layer using electroless plating and then heating it at a melting point (232 ℃) or higher. In examples 1 and 2, there was no leakage at all after 120 days and 140 days.

By contrast, in comparative example 1, 3% exhibited leakage after 120 days and 10% exhibited leakage after 140 days; however, in comparative example 2, 2% exhibited leakage after 120 days and 8% exhibited leakage after 140 days.

In examples 1 and 2, it is considered that, since the tin-plated layer is subjected to heat treatment at the melting point temperature or higher, defects such as pin holes or cracks are completely repaired, and the copper layer is entirely wrapped up, so that the generation of hydrogen gas can be prevented. Thus, a high leakage resistance is obtained. In comparative example 1, in contrast, since the tin-plated layer was not subjected to the heat treatment, defects such as pin holes or cracks remained, and thus the current collector (copper) layer was exposed. For this reason, it is considered that the zinc powder or the like comes into contact with the copper layer, hydrogen gas is generated, the internal pressure increases, and then, leakage occurs. Further, it is considered that, although comparative example 2 was subjected to the heat treatment, the treatment temperature was relatively low, and thus, defects such as pin holes or cracks were not repaired, and as a result, the current collector layer was exposed.

Next, when a comparison is made among examples 1, 3 and 4 on the basis of table 1, no leakage occurred at one point in examples 1 and 3. When example 4 was compared with comparative example 1, although the leakage of example 4 occurred at a low rate, about 3% thereof appeared after storage for 140 days, for example. In the alkaline battery, when the gap between the outer peripheral portion 6b of the protruding portion 6a of the gasket 6 on the center side and the inner face of the negative electrode case is 0.05mm or less, the leakage resistance characteristic and the capacity retention characteristic are excellent. This is because the zinc powder of the negative electrode can be prevented from entering the gap between the gasket and the negative electrode case when sealing the battery by bringing the peripheral portion 6b of the protruding portion 6a of the gasket 6 on the center side and the inner face of the negative electrode case 4 into contact with each other or making the gap therebetween smaller than 0.05mm or less. When zinc powder enters between the seal and the negative electrode can, the zinc powder contacts the current collector layer containing copper, which has a low hydrogen overpotential, causing hydrogen gas to be generated. Further, as long as the gap between the outer peripheral portion 6b of the protruding portion 6a of the gasket 6 on the center side and the inner face of the negative electrode case is 0.05mm or less, a certain degree of error generated at the time of assembling the negative electrode case and the gasket or a certain degree of error of the formation position of the tin plating layer can be tolerated. In particular, even when the current collector layer is exposed to some extent due to variation in the end of the tin plating layer, since zinc powder does not enter the gap between the gasket and the negative electrode can, the generation of hydrogen gas is prevented.

When a comparison is made between examples 5 to 7 on the basis of table 1, it is found that good closed circuit voltage characteristics can be obtained by making the alkaline electrolyte a water solution in which the amount of sodium hydroxide is between 15% and 30% by weight and the amount of potassium hydroxide is between 1% and 15% by weight. In addition, there was no leakage at all in examples 5 to 7. In order to obtain good closed circuit voltage characteristics, an amount of sodium hydroxide added in the range of 15 to 30% by weight is suitable.

On the other hand, although example 8 did not leak and was better than example 1, the closed circuit voltage was lower than that of the other examples. This is because the amount of potassium hydroxide contained in the electrolyte solution is considered to be small. The conductivity of the aqueous solution of potassium hydroxide is excellent as compared with that of the aqueous solution of sodium hydroxide. For this reason, the amount of potassium hydroxide contained in example 8 was small, and it is considered that the closed circuit voltage was lowered. For this reason, in the case of carefully taking into consideration the closed circuit voltage characteristic, it is preferable that the amount of potassium hydroxide contained in the alkaline electrolyte is 1% by weight or more.

In example 9, leakage occurred after 140 days of storage. This is because the amount of potassium hydroxide contained in the alkaline electrolyte is large. Since the aqueous potassium hydroxide solution has a higher wettability to copper than the aqueous sodium hydroxide solution, when the amount of potassium hydroxide is large, a creeping phenomenon occurs, thereby causing leakage. In order to improve the leakage resistance characteristics, it is particularly preferable that the amount of potassium hydroxide contained by weight is 15% or less.

In addition, as for the plating layer for the negative electrode case, not only tin, but also at least one metal or alloy of indium (melting point: 156.6 ℃ C.) and bismuth (melting point: 271.4 ℃ C.) and an alloy thereof is allowed as a metal or alloy having a higher hydrogen overpotential than copper.

According to the invention, sinceThe tin-plated layer 10 can be formed without defects such as pinholes, cracks and contamination due to impurities within the negative electrode can 4, and hydrogen gas (H) can be suppressed₂) Or hydrogen gas is generated by bringing zinc as a negative electrode active material into contact with the current collector layer 9 of the negative electrode can 4, corrosion of zinc can also be suppressed, and similarly, the leakage resistance characteristics can be obtained by the creep phenomenon of the alkaline electrolyte. According to the present invention, a good alkaline battery can be obtained without using mercury.

As for the method for forming the tin film, not only wet methods such as electroless plating method and electrolytic plating method but also dry methods such as PVD (physical vapor deposition) method and CVD (chemical vapor deposition) method are permissible.

Further, the present invention is not limited to such examples and comparative examples as described above. It is to be understood that various changes, modifications and alterations may be made to the present invention without departing from the scope and spirit of the present invention.

Description of the figures

1. Positive electrode

2. Positive electrode shell

3. Negative electrode

4. Negative electrode casing

4a. folded part

4b. folding bottom

5. Partition board

6. Sealing gasket

Projection on the center side

Peripheral part 6b

7. Nickel layer

8. Stainless steel layer

9. Current collector layer

10. Tin coating

11. Inner surface area

Claims (8)

1. An alkaline battery comprising: a positive electrode; a negative electrode containing zinc alloy powder; a separator separating the positive electrode from the negative electrode; an alkaline electrolyte; a positive electrode case that houses the positive electrode, a negative electrode case that houses the negative electrode, the negative electrode case having a tin-plated layer that is heat-treated at a tin melting point of 232 ℃ or higher and being in contact with the negative electrode through the tin-plated layer; and a gasket interposed between the positive electrode can and the negative electrode can.

2. The alkaline cell of claim 1 wherein the positive electrode comprises silver oxide or manganese dioxide.

3. The alkaline cell according to claim 1, wherein the tin-plated layer is a tin-plated layer that is heat-treated in an atmosphere having an oxygen concentration of 1% or less.

4. The alkaline cell of claim 1, wherein said tin-plated layer is formed on an inner face area of said negative electrode can.

5. The alkaline cell of claim 1, wherein 15% to 30% by weight sodium hydroxide, or 1% to 15% by weight potassium hydroxide is present in the alkaline electrolyte.

6. The alkaline cell as claimed in claim 1, wherein the peripheral portion of the protruding portion of the seal gasket on the center side is in contact with the inner face of the negative electrode casing or has a gap of 0.05mm or less from the inner face of the negative electrode casing.

7. The alkaline cell of claim 1, wherein said tin-plated layer is a tin-plated layer formed by electroless plating.

8. A method for producing an alkaline cell comprising:

a first step of forming a tin-plated layer on a surface of a negative electrode case facing a negative electrode such that the tin-plated layer is in contact with the negative electrode and the negative electrode case is electrically connected to the negative electrode through the tin-plated layer;

a second step of subjecting the tin-plated layer to heat treatment at a melting point of tin of 232 ℃ or higher; and

third, a negative electrode case and a positive electrode case containing a positive electrode, a negative electrode, a separator, and an alkaline electrolyte are filled so that a sealing gasket is interposed between the negative electrode case and the positive electrode case to achieve airtight sealing.