JP2001006723A - Alkaline secondary battery and manufacture of alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery having a high capacity and improved in charge/discharge cycle life. SOLUTION: This alkaline secondary battery is equipped with a group of electrodes made up by spirally winding positive electrodes 2 and negative electrodes 4 with separators 3 interposed there between so that the outermost circumference is formed of a negative electrode 4. The ratio of the thickness of the positive electrode 2 to that of the negative electrode 4 is 2 to 2.5, and an angle θN made by a wind-beginning end 4a of the negative electrode 4 with a wind-terminating end 4b thereof is 0 to 30 deg. while an angle θP made by the wind-beginning end 4a of the negative electrode 4 with a wind-terminating end 2b of the positive electrodes 2 is 330 to 350 deg. (where, the angles are each an angle increasing from the wind-beginning end 4a in the winding direction).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery and a method for manufacturing an alkaline secondary battery.

[0002]

2. Description of the Related Art Alkaline secondary batteries such as nickel cadmium secondary batteries and nickel hydrogen secondary batteries, nickel zinc secondary batteries and lithium ion secondary batteries are known as batteries used in portable electronic equipment. ing. As a cylindrical nickel-metal hydride secondary battery which is an example of an alkaline secondary battery, an electrode group in which a positive electrode containing nickel hydroxide and a negative electrode containing a hydrogen storage alloy are spirally wound via a separator, and an alkaline electrolyte Is known that has a structure in which a container is housed in a bottomed cylindrical container. The outermost periphery of the electrode group is a negative electrode, which is in electrical contact with the container also serving as a negative electrode terminal.

In this nickel-metal hydride secondary battery, the capacity regulating electrode is a positive electrode, and the outermost periphery of the electrode group is a negative electrode, so that the positive electrode is thicker than the negative electrode.
Since the capacity of the positive electrode has been increased due to the recent demand for higher capacity, the thickness ratio between the positive electrode and the negative electrode tends to increase.

[0004]

However, when the difference in thickness between the positive electrode and the negative electrode increases, it is difficult to wind the positive electrode, the negative electrode, and the separator so that the cross-sectional shape of the spiral electrode group becomes circular. Problem arises. When an electrode group having an elliptical cross-sectional shape is housed in a bottomed cylindrical container, the electrode group is non-uniformly pressed from the container, so that a portion where adhesion between the positive electrode, the separator and the negative electrode is low is generated. As a result, the charge / discharge reaction occurs non-uniformly in the electrode group, so that the deterioration of the electrode group is accelerated and the charge / discharge cycle life is shortened.

An object of the present invention is to provide an alkaline secondary battery having a high capacity and an improved charge / discharge cycle life.

Another object of the present invention is to provide a method of manufacturing an alkaline secondary battery in which a positive electrode and a negative electrode can be easily wound and the yield can be improved.

[0007]

According to the present invention, there is provided an alkaline secondary battery comprising an electrode group in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween such that the outermost periphery is a negative electrode. In the above, the thickness ratio of the positive electrode to the negative electrode is 2 to 2.5, and in the electrode group, the angle between the winding start end of the negative electrode and the winding end end of the negative electrode is 0 to 30 °. And the angle between the winding start end of the negative electrode and the winding end end of the positive electrode is 330 to 350 ° (however, each of the angles is from the winding start end of the negative electrode in the winding direction). (The angle becomes larger).

According to the method of manufacturing an alkaline secondary battery according to the present invention, a separator is sandwiched between two semi-cylindrical core materials, and a positive electrode and a negative electrode are spirally wound around the separator while the separator is interposed therebetween. In the method for manufacturing an alkaline secondary battery including the electrode group described above and a cylindrical container having a bottom in which the electrode group is stored, the diameter of the core is 20 to 30% of the inner diameter of the container. It is a feature that it is.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (cylindrical alkaline secondary battery) according to the present invention will be described with reference to FIG.

An electrode group 5 formed by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a cylindrical container 1 having a bottom. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular first sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 1. The ring-shaped insulating gasket 8 is
Is arranged between the periphery of the container and the inner surface of the upper opening of the container 1,
The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking to reduce the diameter of the upper opening inward. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. Rubber safety valve 1
1 is arranged so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 so that a protrusion of the positive electrode terminal 10 is provided on the holding plate 1.
2 so as to protrude from the holes. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

As shown in FIG. 2, the electrode group 5 includes an angle θ _N between the winding end 4b of the negative electrode and the winding start end 4a of the negative electrode 4 (where the angle θ _N is Negative electrode 4
Is an angle that increases from the winding start end 4a in the winding direction) to 0 ° to 30 °. Also,
The winding end 2b of the positive electrode forms an angle θ _P with the winding start 4a of the negative electrode 4 (where the angle θ _P increases in the winding direction from the winding start 4a of the negative electrode 4). (The angle) is 330 to 350 °.

The angle θ _N is defined in the above-described range for the following reason. The angle θ _N
0 °, that is the winding end to the winding start portion 4a of the negative electrode and an end portion 4b or the same position, or when the angle theta _N exceeds 30 °, the thickness ratio 2 for the negative electrode of the positive electrode
When the value is 2.5, the shape of the cross section of the electrode group becomes elliptical.
If the angle θ _N exceeds 30 °, the winding end of the positive electrode and the winding end of the negative electrode may be too far apart, making it difficult to smoothly store the electrode group in the container. . A more preferable range of the angle theta _N is 10 to 20
゜.

The angle θ _P is defined in the above-described range for the following reason. The angle θ _P
Is smaller than 330 °, the length of the positive electrode is shortened and the reaction area of the positive electrode is reduced, so that the high-current discharge characteristics of the secondary battery are reduced. On the other hand, if the angle theta _P is greater than 350 °, the thickness ratio negative electrode of the positive electrode 2 to 2.
When it is 5, the shape of the cross section of the electrode group becomes elliptical. A more preferable range of the angle theta _P is ° 335-345.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described.

1) Positive electrode 2 This positive electrode 2 contains nickel hydroxide.

The positive electrode 2 is prepared by, for example, kneading nickel hydroxide powder, a conductive agent and a binder in the presence of water to prepare a paste, filling the conductive substrate with the paste, drying, and rolling. It is manufactured by performing molding.

As the nickel hydroxide powder, for example, a powder composed of nickel hydroxide or a nickel hydroxide powder in which zinc and cobalt are eutectic can be used. The latter positive electrode containing nickel hydroxide powder can improve charge efficiency and charge / discharge cycle characteristics in a high temperature state.

As the conductive agent, at least one selected from a cobalt compound and metallic cobalt can be used. Examples of the cobalt compound include cobalt monoxide and cobalt hydroxide.
Also, instead of adding the conductive agent to the paste,
The surface of the nickel hydroxide powder may be coated with at least one selected from a cobalt compound and metallic cobalt, and this may be added to the paste.

Examples of the binder include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylates (eg, sodium polyacrylate, potassium potassium acrylate), acrylic Copolymer of acid and vinyl alcohol, copolymer of acrylate and vinyl alcohol, water-soluble cellulose derivative (for example, methyl cellulose (MC),
One or more selected from carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC)), polyacrylamide (PA), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO) and the like can be used.

Examples of the conductive substrate include a two-dimensional substrate such as a punching metal and an expanded metal, a fibrous metal porous body (non-plated type) caused by chattering vibration, a sponge-like porous metal body of a plated type and a felt. A three-dimensional substrate such as a porous metal body can be used.

The thickness of the positive electrode is 2 to 2 times the thickness of the negative electrode.
It is preferable to make the size equivalent to 2.5 times. If the thickness ratio of the positive electrode to the negative electrode is less than twice, it may be difficult to increase the capacity of the secondary battery. On the other hand, if the thickness ratio exceeds 2.5 times, the facing area between the positive electrode and the negative electrode decreases, so that the high current discharge characteristics and the internal pressure characteristics of the secondary battery may be reduced. A more preferable range of the thickness ratio is 2.1 to 2.4 times.

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

The negative electrode 4 is prepared by, for example, kneading a hydrogen storage alloy powder, a conductive material and a binder together with pure water to prepare a paste, applying the paste to a conductive substrate, drying the paste, and then rolling and forming the paste. It is manufactured by doing.

The hydrogen storage alloy is not particularly limited, as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ , MmNi
₅ (Mm is Misch metal enriched in Ce), LmNi ₅
(Lm is La-enriched misch metal), and part of Ni of these alloys is Al, Mn, Co, Ti, Cu, Zn, Z
multi-elements substituted with elements such as r, Cr, B,
Alternatively, TiNi-based and TiFe-based materials can be used. In particular, the general formula _{LmNi w Co x Mn y Al z} ( atomic ratio w, x, y, the total value of z is 5.00 ≦ w + x + y +
a hydrogen storage alloy having a composition represented by z ≦ 5.50) or a general formula AB _x (where A is Ti and / or Zr, and B is Mn, Ni, V, Co, Cr, A
and at least one element selected from the group consisting of 1, Fe, Cu, Mo, La, Ce, Pr, and Nd, and x is 1.8 ≦ x ≦
It is preferable to use a hydrogen storage alloy represented by the following formula (2.5), wherein the main component of the alloy phase is a C14 or C15 Laves phase.

Examples of the conductive material include carbon black and graphite.

As the binder, one or more selected from the polymers described above for the positive electrode can be used.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal porous body. it can.

3) Separator 3 As the separator 3, a non-woven fabric made of a polyamide fiber or a non-woven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group can be used.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, potassium hydroxide (KOH) alone or sodium hydroxide (Na)
OH) and lithium hydroxide (LiOH), or an aqueous solution having a composition to which both are added.

Hereinafter, a method for manufacturing an alkaline secondary battery according to the present invention will be described.

In the manufacturing method according to the present invention, an electrode group is manufactured by the method described below. First, as shown in FIG.
The band-shaped separator 22 is composed of two semi-cylindrical cores 21a and 21b.
And sandwich the core. The diameter R of the core is a size corresponding to 20 to 30% of the inner diameter of the bottomed cylindrical container in which the electrode group is stored. Next, a positive electrode and a negative electrode are wound around this core in a spiral shape so that the outermost periphery becomes a negative electrode while the separator is interposed therebetween, thereby producing the electrode group.

After the two cores are removed from the obtained electrode group, the electrode group and the alkaline electrolyte are housed in a cylindrical container having a bottom, and the container is sealed and the like to assemble an alkaline secondary battery. .

As the positive electrode, the negative electrode, the separator, and the alkaline electrolyte, the same ones as described in the alkaline secondary battery described above can be used.

The two cores can be made of, for example, iron, nickel, or the like. In particular, it is preferable to form the main body from iron and apply nickel plating to the surface.

The reason for defining the diameter R within the above range is as follows. When the diameter R is less than 20% of the inner diameter of the container, it is difficult to wind the positive electrode and the negative electrode, so that the positive electrode and the negative electrode are easily cracked, and the occurrence rate of internal short circuit increases. Also, if the winding is forcibly attempted, the core may be broken during the winding. Such a problem occurs more remarkably when the flexibility of the positive electrode and the negative electrode is reduced by increasing the capacity. On the other hand, when the diameter R exceeds 30% of the inner diameter of the container, the volume of the electrode group decreases. The diameter R is more preferably set to 22 to 27% of the inner diameter of the container.

The above-described alkaline secondary battery according to the present invention may be manufactured by the method according to the present invention.

The alkaline secondary battery according to the present invention described in detail above includes an electrode group in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween so that the outermost periphery becomes a negative electrode. The thickness ratio of the negative electrode to the winding end of the negative electrode and the winding end of the negative electrode in the electrode group is 0 to 30 °, and the winding start of the negative electrode. The angle between the part and the winding end of the positive electrode is 330 to 350 ° (however, each of the angles is an angle that increases in the winding direction from the winding start end of the negative electrode). It is assumed that. According to such a secondary battery, the thickness ratio of the positive electrode to the negative electrode is 2 to
When the ratio is 2.5, the shape of the cross section of the electrode group can be made substantially a perfect circle. When such an electrode group is housed in a bottomed cylindrical container, the electrode group is uniformly compressed from the container, so that a charge / discharge reaction can be uniformly generated in the electrode group, and as the charge / discharge cycle progresses, Deterioration of the electrode group can be suppressed. As a result, it is possible to increase the capacity while maintaining excellent charge / discharge cycle life.

The production method according to the present invention is also directed to an electrode group in which a separator is sandwiched between two semi-cylindrical core members, and a positive electrode and a negative electrode are spirally wound around the separator with the separator interposed therebetween. And a bottomed cylindrical container in which the electrode group is housed, wherein the diameter of the core is 20 to 30% of the inner diameter of the container. It is characterized by doing. That is, when the capacity of an alkaline secondary battery is increased, the thickness of the positive electrode increases, and the density of the positive and negative electrodes increases, so that the flexibility of the positive and negative electrodes tends to decrease. By defining the diameter of the core in the above-described range, even if the flexibility of the positive and negative electrodes is low, it can be easily wound,
The yield in manufacturing the electrode group can be improved.
As a result, a high capacity alkaline secondary battery can be manufactured with a high yield.

[0039]

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

(Examples 1-3 and Comparative Examples 1-2) <Preparation of Negative Electrode> The composition was LmNi _4.0 Co _0.3 Mn _0.1 Al
0.5 part by weight of sodium polyacrylate to 100 parts by weight of the hydrogen storage alloy powder represented by _0.3, carboxymethylcellulose (CMC) 0.12 parts by weight, dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 6
0% by weight) and 1.0 part by weight of carbon black as a conductive material.
A paste was prepared by mixing with 30 parts by weight of water. These pastes were applied to a punched metal as a conductive substrate, dried, and pressed to produce a negative electrode.

<Preparation of Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 parts of carboxymethyl cellulose (CMC).
A paste was prepared by adding 0.5 parts by weight of a polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60% by weight) in terms of solid content and mixing with 45 parts by weight of pure water. . Subsequently, the paste was filled in a foamed nickel substrate, dried, and then rolled by roller pressing to produce a positive electrode. The thickness ratio of the obtained positive electrode to the negative electrode was 2.25.

Next, a separator made of a nonwoven fabric made of polyamide fiber was interposed between the negative electrode and the positive electrode, and spirally wound to produce five types of electrode groups. In the five types of electrode groups, the outermost periphery is a negative electrode, and an angle θ _N formed between the winding start end of the negative electrode and the winding end end of the negative electrode (where the angle θ _N is the winding start end of the negative electrode) And the angle θ _P between the winding start end of the negative electrode and the winding end end of the positive electrode (however, the angle θ _P is the winding start end of the negative electrode). Is an angle that increases from the part in the winding direction) to the values shown in Table 1 below.

After storing such an electrode group in a cylindrical container having a bottom, an electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide is stored, and sealing is performed, as shown in FIG. 1 described above. Structure, theoretical capacity is 1700m
With Ah, a sealed cylindrical nickel-metal hydride secondary battery of 4 / 5A size was assembled.

The obtained secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were charged at a rate of 1.0 C for 90 minutes and discharged at a rate of 1.0 C to 1.0 V (charge / discharge cycle). A pause of 30 minutes is provided between charging and discharging), and the change in the discharge capacity retention ratio is shown in FIG. The discharge capacity retention rate of each secondary battery was calculated based on the discharge capacity in the first cycle.

[0045]

[Table 1]

As is clear from FIG. 4, the secondary batteries of Examples 1 to 3 can suppress a decrease in the discharge capacity retention ratio as compared with the secondary batteries of Comparative Examples 1 and 2.

(Examples 4 to 6 and Comparative Examples 3 and 4) An angle θ _N formed between the winding start end of the negative electrode and the winding end end of the negative electrode, and the winding start end of the negative electrode and the positive electrode A sealed cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Examples 1 and 2 described above, except that the angle θ _P formed with the end of winding was set to a value shown in Table 2 below.

With respect to the obtained secondary batteries of Examples 4 to 6 and Comparative Examples 3 and 4, the battery was charged at a rate of 1.0 C for 90 minutes, and then discharged to 1.0 V at a rate of 1.0 C. The capacity was measured and used as a reference capacity. Next, each secondary battery was charged at a rate of 1.0 C for 90 minutes, and then charged at a rate of 3.0 C.
The discharge capacity at the time of discharging to 1.0 V at the rate of C was measured, the maintenance ratio of the obtained discharge capacity to the reference capacity was calculated, and the results are also shown in Table 2 below.

[0049]

[Table 2]

As is evident from Table 2, the secondary batteries of Examples 4 to 6 have higher discharge capacities when discharged with a large current than the secondary batteries of Comparative Examples 3 and 4.

(Examples 7 to 9 and Comparative Examples 5 to 6) <Preparation of Negative Electrode> The composition was LmNi _4.0 Co _0.3 Mn _0.1 Al.
0.5 part by weight of sodium polyacrylate to 100 parts by weight of the hydrogen storage alloy powder represented by _0.3, carboxymethylcellulose (CMC) 0.12 parts by weight, dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 6
0% by weight) and 1.0 part by weight of carbon black as a conductive material.
A paste was prepared by mixing with 30 parts by weight of water. These pastes were applied to a punched metal as a conductive substrate, dried, and pressed to produce a negative electrode.

<Preparation of Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 parts of carboxymethyl cellulose (CMC).
A paste was prepared by adding 0.5 parts by weight of a polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60% by weight) in terms of solid content and mixing with 45 parts by weight of pure water. . Subsequently, the paste was filled in a foamed nickel substrate, dried, and then rolled by roller pressing to produce a positive electrode. The thickness ratio of the obtained positive electrode to the negative electrode was 2.25.

Two iron core members each having a semi-cylindrical shape and nickel plating on the surface were prepared. A band-shaped separator made of a nonwoven fabric made of polyamide was sandwiched between the two core materials, and five types of winding cores having different diameters R were prepared. The ratio of the diameter R of each core to the inner diameter of the bottomed cylindrical container is shown in Table 3 below. An electrode group was produced by spirally winding the above-described positive electrode and negative electrode around each core with the separator interposed therebetween.

After removing the two core members from the obtained electrode group, the electrode group was housed in a cylindrical container having a bottom.
Subsequently, an alkaline electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide was accommodated in the container, and the container was sealed, for example, to have the structure shown in FIG. 1 described above, with a theoretical capacity of 1700 mAh and a capacity of 4700 mAh. A sealed cylindrical nickel-metal hydride secondary battery having a size of / 5 A was assembled.

The secondary batteries of Examples 7 to 9 and Comparative Examples 5 to 6 were subjected to charge / discharge cycles under the same conditions as described above, and the change in the discharge capacity retention ratio is shown in FIG. The discharge capacity retention rate of each secondary battery was calculated based on the discharge capacity in the first cycle.

For the secondary batteries of Examples 7 to 9 and Comparative Examples 5 to 6, the number of defective electrodes when 1,000 electrode groups were produced was measured, and the results are also shown in Table 3 below. .

[0057]

[Table 3]

As is apparent from FIG. 5, the secondary batteries of Examples 7 to 9 can suppress a decrease in the discharge capacity retention ratio as compared with the secondary batteries of Comparative Examples 5 and 6. On the other hand, as is evident from Table 3, the secondary batteries of Examples 7 to 9 can reduce the number of insulation failures during the production of the electrode group as compared with the secondary batteries of Comparative Example 5. In addition, the cycle life of the secondary battery of Comparative Example 6 was inferior because the volume ratio of the core in the electrode group was high, so that the pressure received from the container of the electrode group was higher than an appropriate value, and the internal pressure characteristics were This is probably due to the decline.

[0059]

As described in detail above, according to the present invention,
A high capacity and long life alkaline secondary battery can be provided. Further, according to the present invention, it is possible to provide a method for manufacturing an alkaline secondary battery in which the positive electrode and the negative electrode can be easily wound and the yield is improved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an alkaline secondary battery according to the present invention.

FIG. 2 is a sectional view showing a main part of an electrode group incorporated in the alkaline secondary battery of FIG. 1;

FIG. 3 is a plan view for explaining a method of manufacturing an alkaline secondary battery according to the present invention.

FIG. 4 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity retention ratio in the cylindrical nickel-metal hydride secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2.

FIG. 5 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity retention ratio in the cylindrical nickel-metal hydride secondary batteries of Examples 7 to 9 and Comparative Examples 5 to 6.

[Explanation of symbols]

 2 ... Positive electrode, 2b ... End winding end of positive electrode 3 ... Separator, 4 ... Negative electrode, 4a ... Start winding end of negative electrode 4b ... End winding end of negative electrode.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Dr. Suzuki Inventor 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation F-term (reference) 5H028 AA07 BB08 CC13 HH00 HH01 HH05

Claims (2)

[Claims] 1. An alkaline secondary battery comprising an electrode group in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween so that the outermost periphery is a negative electrode, wherein the thickness ratio of the positive electrode to the negative electrode is 2 The electrode group, the angle between the winding start end of the negative electrode and the winding end end of the negative electrode is 0 to 30 °, and the winding start end of the negative electrode and the positive electrode An alkali secondary, wherein an angle between the winding end and the winding end is 330 to 350 ° (wherein each angle is an angle that increases in a winding direction from the winding start end of the negative electrode). battery. 2. An electrode group in which a separator is sandwiched between two semi-cylindrical core members, and a positive electrode and a negative electrode are wound around the separator in a spiral shape with the separator interposed therebetween, and the electrode group is housed therein. The diameter of the core is 20 to 30% of the inner diameter of the container, wherein the diameter of the core is 20 to 30% of the inner diameter of the container. Battery manufacturing method.