JP2000299089A - Square alkaline secondary battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a square alkaline secondary battery which allows permanently displaying on a container without corroding the container, and prevents the swelling of a positive electrode. SOLUTION: This square alkaline secondary battery has a rectangular tube- like metal container 1 with a bottom, and an electrode group stored in the container 1 and having a structure wherein a positive electrode and negative electrode are alternately laminated through a separator. Unevenness for displaying information is formed, by pressing, on a container side face facing the outermost layer of the electrode group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a prismatic alkaline secondary battery and a method for producing the same.

[0002]

2. Description of the Related Art With the recent development of electronic equipment, the demand for batteries as a driving source thereof has been increasing. Among these batteries, alkaline secondary batteries such as nickel-hydrogen secondary batteries and nickel-cadmium secondary batteries are widely used as power sources for personal computers and mobile phones.
Cylindrical and prismatic alkaline secondary batteries are known. The prismatic alkaline secondary battery has a structure in which a positive electrode containing nickel hydroxide as an active material and a negative electrode are alternately stacked via a separator, and an alkaline electrolyte is contained in a bottomed rectangular cylindrical container. Having.

[0003] In an alkaline secondary battery used for a long period of time, it is expected that there will be a problem in the performance of a product and a complaint will be generated by a user. For this reason, in a prismatic alkaline secondary battery, a production lot (Lot) and a battery type are displayed on a container or an outer tube covering the container. For example, when a user makes a complaint, a history at the time of battery manufacture is checked from the manufacturing lot and the battery type displayed for the battery in question, and a countermeasure is found from this history.
That is, the production lot and the battery type are important information for examining the history at the time of battery production.

In this prismatic alkaline secondary battery, when the container is not covered with an outer tube, the production lot and the battery type are printed on the surface of the container by an ink jet method, a stamp method, or the like, or the surface of the container is irradiated with a laser. It is displayed by shaving.

However, according to the method of printing on the surface of the container, there is a problem that the display is easily lost during use. On the other hand, according to the method of shaving the container surface with a laser,
When the container is made of, for example, steel whose surface is nickel-plated, since the surface plating layer is peeled off by the laser and the steel is exposed, there is a possibility that this portion is corroded and the sealing property is impaired. This method is also expensive in terms of equipment.

Incidentally, the alkaline secondary battery has a property that the positive electrode swells during overcharge and as the charge / discharge cycle progresses. Since the container of the cylindrical alkaline secondary battery has a bottomed cylindrical shape, it has a high shape retention against internal stress, and is hardly deformed even when the positive electrode swells. For this reason,
Swelling of the positive electrode is suppressed by the container. On the other hand, since the container of the prismatic alkaline secondary battery has a bottomed rectangular cylindrical shape, it expands when an internal stress such as swelling of the positive electrode is applied. Therefore, the prismatic alkaline secondary battery has a small effect of suppressing the swelling of the positive electrode by the container, and therefore the degree of swelling of the positive electrode is larger than that of the cylindrical secondary battery. When the positive electrode swells, voids increase in the positive electrode, so that the electrolytic solution in the separator moves there, and the electrolytic solution holding amount of the separator decreases. As a result, the secondary battery has a problem that the charge and discharge cycle life is short because the internal resistance increases as the charge and discharge cycle progresses. In addition, the deformation of the container due to the swelling causes a problem that the battery dimensions deviate from the standard values and cannot be incorporated into the electronic device.

[0007] In view of the above, Patent Publication No. 2619
No. 624 describes a method for manufacturing a prismatic alkaline battery in which a container is pressed in the direction in which the electrode group is stacked, so that the side surface of the container is dented to press the electrode group. JP-A-5-13054 discloses an electrode plate of a laminated electrode group in a prismatic secondary battery in which an electrode group formed by laminating an anode plate, a separator and a cathode plate is housed in an outer can. A rectangular secondary battery is disclosed in which a wide surface of the outer can, which is a surface parallel to the above, is curved in a direction toward the inside of the battery with respect to a peripheral portion at a central portion.

[0008]

SUMMARY OF THE INVENTION The present invention is capable of providing a permanent display on a container without corroding the container,
Another object of the present invention is to provide a prismatic alkaline secondary battery in which swelling of the positive electrode is suppressed and a method for producing the same.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a metal container having a bottomed rectangular cylindrical shape, and an electrode group housed in the container and having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween. Wherein the information is displayed by irregularities formed by pressing on the side of the container facing the outermost layer of the electrode group.

The present invention also provides an electrode gasket having a structure in which a positive electrode and a negative electrode are alternately laminated with a separator interposed therebetween, and an insulating gasket provided at an opening of a bottomed rectangular cylindrical metal container containing an alkaline electrolyte. And a step of caulking and fixing the sealing member through, and a step of displaying information on the container by pressing a side surface of the container facing the outermost layer of the electrode group to form a concave portion. This is a method for manufacturing a prismatic alkaline secondary battery.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A prismatic alkaline secondary battery according to the present invention will be described below with reference to FIGS.

FIG. 1 is a perspective view showing a prismatic alkaline rechargeable battery according to the present invention, and FIG. 2 is a sectional view of a principal part of the prismatic alkaline rechargeable battery of FIG.

A metal container 1 having a rectangular shape with a bottom and also serving as a negative electrode terminal has a bent portion 1a formed by bending an upper end of an opening inward, and an inward projecting portion formed at a lower end of the opening. And a stepped portion 1b having a predetermined shape. Electrode group 2
Is manufactured by alternately laminating the positive electrode 3 and the negative electrode 4 with the separator 5 interposed therebetween such that the outermost layer becomes the negative electrode. The electrode group 2 is housed in the container 1 such that the lamination direction is orthogonal to the longitudinal direction of the container 1. The outermost negative electrode 3 of the electrode group 5 is in contact with the inner surface of the container 1. On the side surface of the container facing the outermost layer of the electrode group 5, "IIHII" and a concave portion 6 formed by pressing are described. The alkaline electrolyte is contained in the container 1. The sealing member 7 having a positive electrode terminal and an explosion-proof function includes a rectangular sealing plate 9 having a gas vent hole 8 formed therein, and a cap-shaped positive terminal disposed on the sealing plate 9 so as to cover the gas vent hole 8. And a rubber safety valve 11 disposed in a space surrounded by the sealing plate 9 and the positive electrode terminal 10 so as to close the gas vent hole 8. The positive electrode terminal 10 has a plurality of gas vent holes (not shown). A bottomed rectangular cylindrical insulating gasket 12 having an opening at the bottom is disposed in a compressed state between the opening of the container 1 and the sealing plate 9, and the sealing member 7 is caulked to the opening of the container 1. It is fixed. One end of the positive electrode lead 13 is connected to the positive electrode 3,
The other end is connected to the lower surface of the sealing plate 9.

Hereinafter, the positive electrode 3, the negative electrode 4, the separator 5, the alkaline electrolyte and the container 1 will be described.

1) Positive electrode 3 This positive electrode 3 contains nickel hydroxide.

For the positive electrode, for example, a paste containing nickel hydroxide powder as a main component, a conductive agent, a binder and water is prepared, and the paste is filled in a current collector, which is dried and pressed. It is produced by doing.

As the nickel hydroxide powder, for example, non-eutectic nickel hydroxide powder or nickel hydroxide powder in which zinc and / or cobalt are eutectic with metallic nickel can be used.

Examples of the conductive material include cobalt compounds such as cobalt monoxide, dicobalt trioxide, and cobalt hydroxide, and metallic cobalt. Further, a composite form having these cobalt or cobalt compounds on the surface of the nickel hydroxide powder may be used.

Examples of the binder include polytetrafluoroethylene, carboxymethylcellulose, sodium polyacrylate, polyvinyl alcohol and the like.

Examples of the current collector include those having a mesh-like, sponge-like, fiber-like, or felt-like porous structure made of a metal such as nickel or stainless steel, or a nickel-plated resin. it can.

2) Negative electrode 4 This negative electrode 4 contains a hydrogen storage alloy.

The negative electrode is prepared by, for example, kneading a hydrogen storage alloy powder with a conductive agent, a binder and water to prepare a paste, filling the paste into a conductive substrate, drying the paste, and then molding. Manufactured.

Such a hydrogen storage alloy negative electrode is a cadmium negative electrode.
The capacity of the secondary battery can be improved
Preferred. The hydrogen storage alloy is particularly restricted.
Instead of hydrogen generated electrochemically in the electrolyte
Can occlude and easily release the stored hydrogen during discharge
Anything can be used. For example, LaNi_Five, MmNi_Five
(Mm is misch metal), LmNi_Five(Lm is La
Including at least one selected from rare earth elements)
Al, Mn, Co, Ti, Cu,
Multi-element system substituted by elements such as Zn, Zr, Cr, B
Or TiNi-based or TiFe-based
Can be. In particular, the general formula LmNi_wCo _xMn_yAl
_z(The total value of the atomic ratios w, y, and z is 5.00 ≦ w + x + y
+ Z ≦ 5.5)
This is preferable because the charge / discharge cycle life can be improved.

Examples of the conductive agent include carbon black and graphite.

Examples of the binder include polyacrylic acid salts such as sodium polyacrylate and potassium polyacrylate, fluorine resins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CM).
C) and the like.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, a nickel net, and a nickel plate, and a three-dimensional substrate such as a felt-like porous metal or a sponge-like porous metal. Can be mentioned.

The negative electrode 4 may be a material containing a cadmium compound such as metal cadmium or cadmium hydroxide, in addition to a material containing a hydrogen storage alloy as described above.

3) Separator 5 Examples of the separator 5 include a nonwoven fabric made of a polyamide fiber and a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, an aqueous solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH)
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

5) Container 1 This container 1 can be formed, for example, from a steel plate having a surface plated with nickel.

The depth of the concave portion 6 formed by pressing on the side of the container facing the outermost layer of the electrode group 2 is set to a value corresponding to 0.5 to 10% of the width orthogonal to the longitudinal direction of the container. Is preferred. This is due to the following reasons. The depth of the recess is set at 0. 0 of the width orthogonal to the longitudinal direction of the container.
If it is less than 5%, it may be difficult to read the display. On the other hand, when the depth of the concave portion exceeds 10% of the width orthogonal to the longitudinal direction of the container, the degree of compression of the electrode group by the concave portion increases, so that the battery reaction may occur unevenly in the electrode group. The separator may be locally crushed, the distance between the positive electrode and the negative electrode may be reduced, and the internal short circuit occurrence rate may increase. A more preferable range of the depth of the concave portion is 1 to 6%.

In each of the container side faces facing the outermost layer of the electrode group 2, it is preferable that the total area of the concave portions is set to a value corresponding to 2 to 70% of the area of the container side faces. This is due to the following reasons. If the total area is less than 2%, it may be difficult to sufficiently suppress the swelling of the positive electrode. On the other hand, if the total area exceeds 70%, the display may be difficult to read. A more preferable range of the total area is 5 to 50%.

In FIG. 1 described above, an example has been described in which the character information is recessed. However, pressing may be performed so that the character information is formed as a projection and the other portions are formed as a recess.

Also, in FIG. 1 described above, an example in which five characters are formed near the center of the side surface of the container has been described, but the display position is not particularly limited as long as it is the side surface of the container facing the outermost layer of the electrode group. However, any position may be used as long as it is suitable for the display purpose and the swelling of the positive electrode can be suppressed.

Further, not only characters but also symbols and figures can be displayed on the side of the container as needed.

Furthermore, the number of characters, symbols, and figures is not particularly limited, and can be changed according to the purpose. For example, there may be a case where only one character, symbol or graphic is required, or a case where ten or more characters, symbols or graphic are required.

Next, a method of manufacturing the prismatic alkaline secondary battery according to the present invention will be described.

(First Step) An insulating gasket is placed at the opening of a metal container having a bottomed rectangular cylindrical shape containing an electrode group having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween and an alkaline electrolyte. The sealing member is swaged and fixed.

As the positive electrode, the negative electrode, the separator and the alkaline electrolyte, the same ones as described above can be used. Further, the container can be formed from the same material as described above.

Here, caulking means a sealing method comprising a step of reducing the diameter of the opening of the container and a step of bending the opening inward. For example, after reducing the diameter of the opening of the container and bending the opening inward,
Caulking can be performed by reducing the diameter of the opening.

(Second step) By pressing the side of the container facing the outermost layer of the electrode group to form a concave portion, target information is displayed on the container.

The depth of the recess is 0.5 to 1 of the width orthogonal to the longitudinal direction of the container for the same reason as described above.
It is preferable to set the value to 0%. A more preferable range of the depth of the concave portion is 1 to 6%.

In each of the container side surfaces facing the outermost layer of the electrode group 2, the total area of the recess is set to a value corresponding to 2 to 70% of the area of the container side surfaces for the same reason as described above. Is preferred. A more preferable range of the total area is 5 to 50%.

According to the present invention described above, a rectangular cylindrical metal container having a bottom and an electrode group housed in the container and having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween. In the provided prismatic alkaline secondary battery, by displaying information in the unevenness formed by pressing on the container side facing the outermost layer of the electrode group, it is possible to avoid disappearance due to external effects such as friction, An indication can be permanently displayed on the surface of the container. Further, it is possible to prevent the corrosion of the container that occurs when the concave portion is formed by shaving the container surface with a laser or the like.

Further, in the secondary battery, the concave portion can prevent the positive electrode from swelling at the time of overcharging and during the progress of the charge / discharge cycle. as a result,
(I) Since the movement of the electrolyte solution in the separator to the positive electrode can be suppressed, the charge / discharge cycle life of the secondary battery can be improved. Also, (ii) the container can be kept from swelling, so that the standard dimensions can be maintained.

According to the method of manufacturing a prismatic alkaline secondary battery according to the present invention, an electrode group having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween, and a bottomed rectangular cylindrical shape containing an alkaline electrolyte. After caulking and fixing the sealing member to the opening of the metal container via an insulating gasket, pressing the side surface of the container facing the outermost layer of the electrode group to form a recess, thereby displaying information on the container. Thus, in addition to the above-described effects of permanent display and suppression of swelling of the positive electrode, it is possible to correct an outwardly curved surface by swaging.

That is, in the prismatic alkaline secondary battery, the electrode group is usually housed in the container such that the laminating direction of the electrode group is orthogonal to the longitudinal direction of the container. The side surface along the longitudinal direction of the container is more easily deformed than the side surface orthogonal to the longitudinal direction. For example, after reducing the diameter of the opening of the container, when the upper end of the opening is crimped inward by crimping the sealing member to the opening of the container via an insulating gasket, in the longitudinal direction of the container during the bending process The sides along it curve outward. As a result, the positive electrode is likely to swell, and a long life may not be obtained. After the caulking and fixing step as in the present invention, information is displayed on the container by pressing a side surface along the longitudinal direction of the container to form a concave portion, so that outward bending can be corrected. In addition, the swelling of the positive electrode can be sufficiently suppressed.

[0048]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Negative Electrode> Using a commercially available lanthanum-enriched misch metal Mm and Ni, Co, Mn, and Al, a hydrogen occlusion having a composition of MMMi _3.6 Co _0.8 Mn _0.4 Al _0.2 was performed by a high frequency furnace. An alloy was made. The hydrogen storage alloy was mechanically pulverized and passed through a 200-mesh sieve. 0.4 part by weight of sodium polyacrylate, 0.1 part by weight of carboxymethyl cellulose (CMC), dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60 wt.
%) 1.5 parts by weight and carbon powder 0.
By mixing 8 parts by weight with 55 parts by weight of water,
A paste was prepared. This paste was applied to a punched metal, dried, and then pressed to form a paste-type negative electrode.

<Preparation of Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 7.5 parts by weight of cobalt hydroxide powder was mixed with 0.3 parts by weight of carboxymethylcellulose and Dispersion of fluoroethylene (specific gravity 1.5, solid content 60w
(t%) was added, and 30 parts by weight of pure water was added thereto and mixed to prepare a paste. Subsequently, this paste was filled in a nickel-plated foamed metal substrate, dried, and then subjected to pressure molding to produce a paste-type positive electrode.

<Separator> A nonwoven fabric made of long fibers having an average diameter of 3 μm, a basis weight of 42 g / m ² , and a thickness of 0.18 mm was prepared from a polypropylene resin by a melt blow method. After immersing this nonwoven fabric in an aqueous solution of acrylic acid, the acrylic acid monomer is graft-polymerized by irradiating ultraviolet rays, and after washing to remove unreacted acrylic acid,
By drying, -COOH is used as an ion exchange group.
A nonwoven fabric mainly composed of a polypropylene fiber having a group was produced.

Next, an electrode group was prepared by alternately stacking the negative electrode and the positive electrode such that the outermost layer became the negative electrode with the separator interposed therebetween. The electrode is formed in a steel container having a bottomed rectangular cylindrical shape having a widened opening and an inwardly protruding step formed at a lower end of the opening, and having a nickel-plated surface. The groups were stored such that the stacking direction was orthogonal to the longitudinal direction of the container. An alkaline electrolyte composed of 7N KOH and 1N LiOH was injected into the container. After placing a positive electrode terminal and a sealing member having an explosion-proof function on the step of the container via an insulating gasket, the opening of the container is reduced in diameter, and the opening is bent inward to open the container. A square nickel-metal hydride secondary battery having a height of 47 mm, a width along the longitudinal direction of 17 mm, and a width (thickness) perpendicular to the longitudinal direction of 5.5 mm is obtained by caulking and fixing the sealing member to the portion via an insulating gasket. Manufactured.

Next, a region facing the outermost layer of the electrode group on the side surface of the container of the prismatic nickel-metal hydride secondary battery is subjected to press working with a flat plate on which a projection “IIHII” is formed, respectively. A concave portion was formed on each side surface and indicated as “IIHII”. The depth of the recess is 0.
1 mm, 1.8% of the width orthogonal to the longitudinal direction of the container
Was equivalent to Further, the total area of the concave portion on each side surface is 30% of the container side surface facing the outermost layer of the electrode group.
%.

(Example 2) A square nickel-metal hydride was formed in the same manner as in Example 1 except that the depth of the recess was set to 0.9% (0.05 mm) of the width orthogonal to the longitudinal direction of the container. A secondary battery was manufactured.

(Example 3) A square nickel-metal hydride was prepared in the same manner as in Example 1 except that the depth of the recess was 3.6% (0.2 mm) of the width orthogonal to the longitudinal direction of the container. A secondary battery was manufactured.

(Example 4) Square nickel-metal hydride was prepared in the same manner as in Example 1 except that the depth of the recess was set to 5.5% (0.3 mm) of the width orthogonal to the longitudinal direction of the container. A secondary battery was manufactured.

(Example 5) A square nickel-metal hydride was formed in the same manner as in Example 1 except that the depth of the concave portion was 7.3% (0.4 mm) of the width orthogonal to the longitudinal direction of the container. A secondary battery was manufactured.

Example 6 A square nickel-metal hydride was manufactured in the same manner as in Example 1 except that the total area of the recesses on each side was 10% of the side of the container facing the outermost layer of the electrode group. A secondary battery was manufactured.

(Comparative Example 1) A prismatic nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1 except that the ink jet method indicated "IIHII" instead of the recess formed by press working.

The container surfaces of the obtained rectangular nickel-metal hydride secondary batteries of Examples 1 to 6 and Comparative Example 1 were washed with organic solvents of ethyl alcohol and acetone. Table 1 shows the results.

[0061]

[Table 1]

As is clear from Table 1, the secondary batteries of Examples 1 to 6 provided with the containers in which the target information was displayed in the recesses formed by the press working were displayed by ethyl alcohol washing and acetone washing. It turns out that it does not disappear. On the other hand, it can be seen that the display of the secondary battery of Comparative Example 1 including the container in which the target information is displayed by the inkjet printing disappears by the ethyl alcohol washing and the acetone washing.

Comparative Example 2 A prismatic nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1 except that “IIHII” was displayed by laser irradiation instead of press working.

Twenty rechargeable batteries of Examples 1 to 6 and Comparative Example 2 were prepared, and the number of batteries that corroded in the container when stored for 7 days in air having a humidity of 93% at 60 ° C. And the results are shown in Table 2 below.

[0065]

[Table 2]

As is evident from Table 2, the secondary batteries of Examples 1 to 6 provided with the containers in which the target information was displayed by the concave portions formed by the press working, had the number of the cells corroded in the containers. It turns out that there is none. On the other hand, it can be seen that the secondary battery of Comparative Example 2 including the container in which the target information is displayed by the laser irradiation has eight cells in which the container has been corroded.

Further, the secondary batteries of Examples 1 to 6 and Comparative Example 1 were each subjected to a discharge current of 1 CmA in an atmosphere of 25 ° C.
After charging at ΔV (10 mV), the charge / discharge cycle of discharging at 1 CmA until the battery voltage reached 1.0 V was defined as one cycle, and this charge / discharge cycle was repeated. At this time, the discharge capacity was calculated from the time required for the battery voltage to reach 1.0 V at 1 CmA in each cycle.

FIG. 3 shows the results of the discharge capacity transition of the charge / discharge cycle characteristic test. The discharge capacity ratio on the vertical axis in FIG.
6 shows the discharge capacity of the secondary batteries of Comparative Examples 1 to 6 and subsequent cycles. The cycle number ratio on the horizontal axis in FIG. 3 is defined as 100, where the number of cycles at which the discharge capacity of the secondary battery of Example 1 reaches 80% of the discharge capacity in the first cycle is 100.
9 shows the number of cycles of the secondary batteries of Examples 2 to 6 and Comparative Example 1.

As is apparent from FIG. 3, the secondary batteries of Examples 1 to 6 provided with the container in which the target information was displayed in the recesses formed by the press working, display the target information by ink jet printing. It can be seen that the charge / discharge cycle life is superior to that of the secondary battery of Comparative Example 1 including the sealed container. This is because the concave portions formed on the container surfaces of the secondary batteries of Examples 1 to 6 suppress swelling of the container due to swelling of the positive electrode during cycle progress, and suppress the depletion of the electrolyte in the separator. Because it is.

Therefore, the change in the thickness of the container during the above-described charge / discharge cycle test was measured, and the results are shown in FIG. The container thickness change amount on the vertical axis in FIG. 4 represents the container thickness change amount in each cycle when the initial container thickness of each of Examples 1 to 6 and Comparative Example 1 is set to zero.
The horizontal axis in FIG. 4 is the number of cycles.

As is clear from FIG. 4, the secondary batteries of Examples 1 to 6 have a smaller change in the thickness of the outer can with the progress of the cycle than the secondary battery of Comparative Example 1.

[0072]

As described above in detail, according to the present invention, a long-life rectangular alkali having a container in which target information is permanently displayed without causing corrosion, and in which swelling of the positive electrode is suppressed. A secondary battery and a method for manufacturing the secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a prismatic alkaline secondary battery according to the present invention.

FIG. 2 is a cross-sectional view of a principal part of the prismatic alkaline secondary battery of FIG. 1 along the line AA.

FIG. 3 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity ratio in the secondary batteries of Examples 1 to 6 and Comparative Example 1.

FIG. 4 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the amount of change in container thickness in the secondary batteries of Examples 1 to 6 and Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 1a ... Bending part, 1b ... Step part, 6 ... Recessed part, 9 ... Sealing plate, 12 ... Insulating gasket.

Claims (2)

[Claims] 1. A prismatic alkaline secondary battery comprising: a bottomed rectangular cylindrical metal container; and an electrode group housed in the container and having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween. 3. The prismatic alkaline secondary battery according to claim 1, wherein information is displayed by unevenness formed by pressing on a side surface of the container facing the outermost layer of the electrode group. 2. An electrode group having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween, and an opening of a metal container having a bottomed rectangular cylindrical shape in which an alkaline electrolyte is accommodated via an insulating gasket. A step of caulking and fixing a member, and a step of displaying information on the container by pressing a side surface of the container facing the outermost layer of the electrode group to form a concave portion, wherein Battery manufacturing method.