JP2000100467A - Flat battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent battery capacity drop and defects by internal short- circuiting caused by the break of an electrode or the peeling and drop of an active material layer occurring when an electrode group with an oval cross section is constituted of the band-like electrode formed with the active material layer by applying a paste on both faces or one face of a core made of a metal foil or via electrolytical deposition. SOLUTION: A stripe-like recess 41b with a prescribed width centering on a folding line is formed in advance on an active material layer at least on the inside face of a fold section 41a at least on the innermost periphery near the core section of one band-like positive electrode 41. The positive electrode 41 and one band-like negative electrode are folded and wound via a separator to form an electrode group with an oval cross section. The width of the stripe- like recess 41b is preferably set to the range of 0.5-3.0 mm on the right and left respectively centering on the folding line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin flat battery in which an electrode group having an oval cross section is formed by winding one strip-shaped positive electrode plate and one strip-shaped negative electrode plate via a separator. . In particular, it is an object of the present invention to perform a preliminary processing on a folded portion of an electrode plate to eliminate any failure accident due to breakage of the electrode plate and peeling or falling off of the active material layer when the electrode group is formed.

[0002]

2. Description of the Related Art In recent years, as portable devices such as portable telephones, notebook personal computers, and camcorders have become smaller, lighter, and thinner, the progress of small secondary batteries as power sources for driving the devices has been remarkable. is there. Initially, conventional types of lead / acid and nickel / cadmium have been used, and recently, new types of nickel / metal hydride and lithium / ion based systems capable of higher energy density have been put into practical use.

In a small sealed lead-acid battery, a plurality of positive plates and negative plates are alternately stacked with a separator interposed therebetween.
An electrode group formed by connecting polar plates having the same polarity is housed in a Morroblock-type plastic battery case for 3 cells or 6 cells, and is formed in series, and then a sealed rectangular battery is generally used. is there.

A nickel-cadmium battery and a nickel-cadmium battery
In a metal hydride-based battery, a cylindrical battery in which a band-shaped positive electrode plate and a negative electrode plate are wound via a separator, and a coil-shaped electrode group is housed and sealed in a metal battery container. Or, a positive electrode plate and a negative electrode plate are alternately stacked via a separator, and an electrode group formed by connecting electrode plates of the same polarity is housed in a metal battery container to form a prismatic battery, which has a predetermined voltage. A plurality of cells are connected in series or in parallel so as to have a capacity, and an integrated battery pack is used.

[0005] In a lithium ion secondary battery, a cylindrical battery has basically the same configuration as a nickel-cadmium type or a nickel / metal hydride type. On the other hand, in a flat battery having a rectangular or oval thin cross section, which is regarded as important for reducing the thickness of the device and reducing the dead space of the power supply unit, the positive electrode, the negative electrode plate, and the separator are provided separately. Is extremely thin, so that each of the strip-shaped positive and negative plates is wound through a separator so as to be folded, and a group of electrodes configured to have an oval cross section is housed, and an electrolytic solution is injected. A battery of a method of sealing after impregnation is employed.

In order to further reduce the thickness or the capacity of the flat type battery of this type, the core material of the electrode plate and the separator are made as thin as possible, or the core portion of the electrode group and the separator of the outermost peripheral portion are formed. A method of reducing the amount of use or increasing the pressure applied to the electrode group to reduce the thickness of the electrode group and inserting and storing it in the battery container is adopted.

[0007]

In order to construct such an electrode group with high productivity, the first step is to form a core by winding the core with the separator sandwiched between the cores. Then, one strip-shaped positive electrode plate and one strip-shaped negative electrode plate are wound in a coil shape with a separator interposed therebetween, and the outer periphery thereof is wrapped with an extra separator and fixed to form an electrode group having an elliptical cross section. Constitute. Next, as a second step, the electrode group is pressed while being held between a pair of flat plates parallel to the long axis of the electrode group having an elliptical cross section, and deformed to form a cross section as shown in FIG. A step of forming an oval electrode group is employed. FIG. 1 is an enlarged view of a cross section of a main part of an electrode group 1 of a thin flat lithium ion secondary battery. In FIG. 1, one strip-shaped positive electrode plate 11 and one negative electrode plate 1
2 are wound so as to be folded to form an electrode group 1. The electrode group 1 is configured by first winding the positive electrode plate 11 and the negative electrode plate 12 via the separator 13 so that one end of the separator 13 surrounds the folded core 13a. The separator 13 wraps the outer periphery of the electrode group 1, and the other end 13b of the separator tightly fixes the electrode group 1 by a heat welding method or the like.

In the final stage of pressing and deforming in the second stage for forming this electrode group, the innermost folded portion 11a of the positive electrode plate 11 near the core 13a and the next folded portion 11a 'and At the innermost folded portion 12a of the negative electrode plate 12 and the next folded portion 12a ', the core material of the electrode plate may be broken and the electrode plate may be broken, resulting in a reduction in cell capacity. Was. Also, even if the electrode plate does not break, the active material layer peels off from the core material, and small pieces of the active material layer fall off, which breaks the separator, causing an internal short circuit between the positive and negative electrodes, and using an organic electrolyte. It also caused the reliability of the lithium-ion secondary battery to deteriorate. Therefore, it is extremely important to eliminate breakage of these electrode plates and exfoliation and falling off of the active material layer. In such a failure accident, the packing density of the active material layer is relatively higher than that of the negative electrode plate, and the tensile strength and the reverse bending strength of the core material of the electrode plate are relatively higher than that of the copper foil of the core material for the negative electrode plate. It often occurred on the positive electrode plate using a low aluminum foil, and tended to concentrate on the innermost folded portion near the core.

FIG. 2 is a plan view showing a folded portion of the band-shaped positive electrode plate in the case where an electrode group having an oval cross section is formed at the final stage. In FIG. 2, in the innermost folded portion 11 a near the core portion of the positive electrode plate 11, breakage and peeling and falling off of the active material layer easily occur. In the folded portion 11a 'next to the innermost folded portion 11a, breakage of the positive electrode plate and peeling or falling off of the active material layer may occur rarely. Further, in the next folded portion 11a ″ (corresponding to the outer periphery of the innermost folded portion 11a), no breakage of the positive electrode plate and no accident of peeling or falling off of the active material layer were observed.

Reference numeral 11b denotes an aluminum positive electrode lead tab, on which an insulating tape 11c is adhered.

FIG. 3 is an enlarged sectional view of only the core portion and the outer peripheral portion of the electrode group having an oval cross section. In FIG. 3, a negative electrode plate 12 adjacent to a core 13a made of a separator 13 separating a positive electrode plate 11 and a negative electrode plate 12 has an active material mainly composed of a carbon material on both surfaces of a core material 12d made of copper foil. Material layer 1
2e and 12f are applied. At the innermost bent portion of the negative electrode plate, it was found that the active material layer 12e 'on the inner surface rarely peeled off or fell off. In contrast to this negative electrode plate, the positive electrode plate 11 is a core material 11d made of aluminum foil.
Active material layers 11e and 11f mainly composed of lithium cobalt oxide (LiCoO ₂ ) are applied to both surfaces of the substrate. The positive electrode plate 11 is the innermost negative electrode plate 1
In the first bent portion, the outer active material layer 11e 'and the outer active material layer 11f' on the inner surface are often peeled off and fall off, but the core material 11d is broken at the folded portion. As a result, the positive electrode plate 11 may be broken.

In order to prevent the above-described breakage of the electrode plate and the occurrence of peeling-off of the active material layer, the thickness of the core material of the electrode plate or the winding core of the electrode group composed of the separator is increased. It is possible to increase the radius of curvature of the folded portion of the electrode plate, or to remove the active material layer in the vicinity of the folded portion of the electrode plate in advance, but in any case, it is necessary to reduce the battery capacity. Therefore, it could not be said to be an appropriate means for a new type of battery aiming for higher energy density.

On the other hand, Japanese Unexamined Patent Publication No.
No. 5 and JP-A-5-41211,
In a foamed electrode plate in which an active material is filled in a sponge-like nickel sheet or a paste-type electrode plate in which an active material paste is applied to a core material and dried, a coil is formed by forming a groove parallel to a direction perpendicular to the winding direction. A cylindrical battery constituting an electrode group is disclosed. However, breakage of the electrode plate and peeling / falling of the active material layer when forming an oval electrode group having a band-shaped positive / negative plate and separator using a foil core material for a thin flat battery There has been no proposal for an effective means for suppressing a defective accident caused by the above.

[0014]

SUMMARY OF THE INVENTION The present invention relates to a strip-shaped electrode plate in which an active material layer is formed by applying a paste on both sides or one side of a core material made of a metal foil, or by electrolytic deposition. Wherein the active material layer on at least the inner side surface of at least the innermost folded portion near the core of one strip-shaped positive electrode plate has a streak-shaped recess having a predetermined width centered on the fold line. Is formed in advance, and a flat battery including an electrode group formed by winding this positive electrode plate and one band-shaped negative electrode plate through a separator so as to fold it.

By adopting such a configuration, it is possible to completely suppress breakage of the electrode plate and peeling-off and falling off of the active material layer, which have conventionally occurred when an electrode group having an oval cross section is formed. Thus, the reliability of flat batteries, particularly flat lithium-ion secondary batteries, can be dramatically improved without any decrease in the quality of the battery and no internal short circuit failure.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings and tables by way of examples.

Example 1 50 parts by weight of lithium cobalt oxide (LiCoO ₂ ) powder as a positive electrode material, 1.5 parts by weight of acetylene black as a conductive agent, and 50 wt.
A 7% by weight polytetrafluoroethylene (PTFE) dispersion solution and 41.5 parts by weight of a 1 wt% aqueous solution of ammonium carboxymethyl cellulose as a thickener are added and kneaded to prepare a paste for a positive electrode. Thickness 2
A positive electrode paste was applied to both sides of a core material made of 0 μm aluminum foil using a die coater to a thickness of 0.35 mm, dried, and then heated to 200 to 300 ° C.
Sinter between the PTFE particles of the binder. Thereafter, roll pressing was performed until the thickness of the electrode plate became 0.18 mm, and the electrode plate was cut into a predetermined size to obtain a belt-shaped positive electrode plate. As shown in FIGS. 4 and 5, the positive electrode plate 41 has a core material 4 made of aluminum foil.
Active material layers 41f and 41f 'are applied to both surfaces of 1e. Of the innermost folded portion 41a near the core portion of the positive electrode plate 41, the next folded portion 41a ', and the next folded portion 41a "(the outer folded portion of the innermost folded portion 41a). , 41a and 41a ', each having a width of 1.0 mm (total width W2.0 mm) on the left and right sides with respect to the folding lines of the folding portions indicated by 41a and 41a'.
1b and 41b 'were formed on the active material layer 41f on the inner surface of the folded portion. The depth D of these streaks is 0.05
mm, the thickness of the active material layer of the positive electrode plate was 0.08 mm.
Equivalent to 5%. The streak-shaped concave portion is formed of a V-shaped streak having a cross section at an angle 41 h of 60 °, and the pitch P between the streaks is 0.
At 75 mm, the angle A of these streaks 41 g with respect to the folding line was set to 45 °. These streak-shaped concave portions 41b
And 41b 'are formed by forming streaky projections having a pitch, angle and height determined by knurling on the outer periphery of a roller having a thickness of 2.0 mm, and forming a predetermined folded portion of the belt-shaped positive electrode plate. A method was employed in which this roller was rotated and pressed on the active material layer. A positive electrode plate having these streak-shaped recesses is provided with aluminum lead tabs 4.
1c was welded, and an insulating tape 41d was applied thereon to cover.

On the other hand, styrene-
A negative electrode paste prepared by adding and kneading 5 parts by weight of a binder solution made of a butadiene copolymer is applied to both surfaces of a core material made of a copper foil having a thickness of 10 μm using a die coater, and dried, Roll pressing was performed until the thickness became 0.15 mm, and the resultant was cut into a predetermined size to obtain a strip-shaped negative electrode plate. A lead tab made of nickel was welded to the negative electrode plate, and an insulating tape was stuck thereon to cover.

As the separator, a polyethylene microporous membrane having a thickness of 27 μm was used.

In the first stage, one end of the separator is sandwiched between slits 62 of a core 61 having an elliptical cross section (see FIG. 6) provided with a slit in the short axis, and the core is rotated to rotate the core. A separator is wound around the outer periphery of the core member, and one positive electrode plate and one negative electrode plate are wound via the separator to form an electrode group having an elliptical cross section. The outer periphery of the electrode group is wrapped with a separator, and the other end of the separator is fixed by a heat welding method to bind the electrode group.

In this state, the electrode group is extracted from the core member,
This electrode group is pressed and deformed at a pressure of 50 kgf / cm ² while being sandwiched between a pair of flat plates parallel to the long axis of the electrode group, to form an electrode group having an oval cross section. Thereafter, the electrode group is inserted into a nickel-plated steel battery container having an oval cross section, and then the positive electrode tab is laser-welded to the aluminum positive terminal of the lid. Further, the negative electrode tab is connected to a nickel-plated steel frame previously fixed to the upper edge of the battery container by resistance welding. After that, add a predetermined amount of organic electrolyte
After impregnation, the gap between the lid and the upper edge of the cell container was sealed by a laser welding method to complete a flat battery.

As the organic electrolyte, anhydrous lithium phosphofluoride (LiPF ₆ ) was dissolved in a mixed solvent of 30 vol% ethylene carbonate, 50 vol% diethyl carbonate, and 20 vol% methyl propionate to a concentration of 1 mol / l. Using.

(Example 2) A positive electrode plate and a negative electrode plate were prepared in the same manner as in Example 1, and streak-shaped concave portions were formed in advance on both surfaces of the innermost folded portion near the core. These streak-like concave portions are each 2.0 mm wide (4.0 mm in total width) and 0.02 mm in depth with respect to the folding line of the folding portion.
And 25.0% of the thickness of the active material layer of the positive electrode plate being 0.08 mm.
And a thickness of 0.07 mm of the active material layer of the negative electrode plate.
It corresponds to 8.6%. The streak-shaped recess has a V-shaped streak having a cross section at an angle of 100 °, and the pitch between the streaks is 2.0.
mm, the angle of these streaks to the fold line is 90 °
I tried to be.

For comparison, as shown in Examples 1 and 2 according to the present invention, the active material layer on the inner surface of the innermost folded portion near the core of the positive electrode plate is also provided. A positive and negative electrode plate of a conventional example in which streak-shaped recesses were not formed in advance on the active material layers on both surfaces of the innermost folded portion near the core of the negative electrode plate was separately prepared. A flat battery was manufactured in the same manner as in Example 1 using the positive electrode plate and the negative electrode plate of Example 2 and the conventional example. The separator, electrolyte composition, and battery assembly conditions of these batteries were exactly the same as in Example 1.

Each of the first, second and prior art examples
Table 1 shows the results obtained by examining and comparing the 00 cells with respect to the reduction in battery capacity due to the breakage of the electrode plate and the peeling / falling of the active material layer when forming the electrode group, and the failure rate of internal short circuit.

[0026]

[Table 1]

In the first embodiment, an example is shown in which a streak-shaped concave portion is formed in the active material layer on the innermost periphery and the inner surface of the next folded portion, which is close to the core of the positive electrode plate. The case where the streak-shaped recess was formed only in the active material layer on the inner surface of the innermost folded portion near the core of the plate was also examined. At the same prototype cell size of 1000 cells, the defect rate was also zero. Further, in the second embodiment, both the positive and negative plates have an example in which streaky recesses are formed in the active material layers on both surfaces of the innermost folded portion near the core, respectively. We confirmed that it worked.

Therefore, it can be said that it is an essential condition of the present invention that at least the streaks are formed in the active material layer on the inner surface of the innermost folded portion near the core portion of the positive electrode plate made of aluminum foil as a core material. .

In order to secure higher reliability compared to the prior art, in the positive electrode plate, not only the active material layer in the innermost folded portion near the core portion but also the next folded portion. The active material layer on at least the inner surface of the negative electrode plate is also formed with streak-shaped concave portions, and further, the innermost peripheral portion near the core portion of the negative electrode plate and the active material layer on at least the inner surface of the next folded portion have streaky concave portions. It is desirable to form.

It is rather ineffective to press the entire surface of the concave portions formed in the active material layers on the inner surface or both surfaces of the folded portion of the positive and negative electrode plates. Probably, the density of the active material layer in that portion becomes too high, so that the active material layer is easily peeled off from the core material or the core material is easily broken when the electrode plate is folded.

Also, when the pitch between the streaks of the streak-shaped recess is extremely reduced, it is not as effective as when the entire surface is pressed. Further, it can be easily understood that the streaky recess parallel to the folding line cannot provide an effect when the pitch is increased.

It is appropriate that the angle of the V-shaped cross section of the streak-shaped concave portion is not less than 30 ° and not more than 120 °. The depth of the streak-shaped concave portion has no effect even if it is too shallow with respect to the thickness of the active material layer on one side of the core material. On the contrary, it is not effective. The depth of the streak-shaped recess is selected from a range of 20% to 70% of the thickness of the active material layer.

The width of the streak-shaped concave portion is 0.5 mm or more and 3.0 mm or less on each side of the folding line (total width 1.
(0 to 6.0 mm) is appropriate, and the pitch between the streaks is selected from the range of 0.5 mm or more and 5.0 mm or less.

The shape, depth, and pitch of the V-shaped streak can be observed with an optical microscope by immersing the electrode plate in an epoxy resin, curing after degassing, cutting and polishing.

In the embodiment according to the present invention, a battery container having an oval cross section is used, but a battery container having a rectangular cross section is selected in order to increase the amount of electrolyte. Further, in order to seal the space between the battery container and the lid, not only laser welding as in the embodiment but also a method of caulking via a gasket may be used.

In the embodiments, the lithium ion secondary battery using the positive electrode plate using LiCoO ₂ as an active material has been described, but the present invention is not limited to this positive electrode active material. The present invention can be similarly applied to a positive electrode plate using a lithium-containing composite oxide such as lithium nickelate (LiNiO ₂ ) or spinel type lithium manganate (LiMn ₂ O ₄ ) as an active material. It goes without saying that the present invention can be applied not only to a lithium ion secondary battery using an organic electrolyte, but also to a primary battery and a secondary battery using a non-aqueous electrolyte such as a polymer electrolyte. Further, for example, in a nickel-cadmium-based or nickel-metal hydride-based material, the active material layer may be coated with a paste or electrolytically deposited on both or one side of a core material made of nickel foil or nickel-plated steel foil. The present invention can be similarly applied to a strip-shaped electrode plate formed by the above method.

Prior to forming an electrode group having an oval cross section according to the present invention, in the embodiment, one positive electrode plate and one negative electrode plate are wound via a first-stage separator to form an elliptical cross section. In forming the electrode group, a core element having an elliptical cross section shown in FIG. 6 was used, but the slit 72 shown in FIG. 7 was used.
It is extremely effective to use the winding core 71 having a rhombus-shaped cross section. This is advantageous not only in that the winding can be accurately performed without spinning during winding, but also that a dense electrode group can be formed without generating useless voids in the core.

[0038]

As described above in detail, according to the present invention, an active material layer is formed by applying a paste on both sides or one side of a core material made of a metal foil, or by electrolytic deposition. Battery capacity due to the conventional breakage of the electrode plate and the peeling and falling off of the active material layer when forming an electrode group with an oval cross section by winding the strip-shaped positive electrode plate and the negative electrode plate so as to be folded through a separator In this case, the reliability of various types of flat batteries can be drastically improved by eliminating the occurrence of failures due to the deterioration of the battery and the internal short circuit.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view of a main part of an electrode group of a flat type lithium ion secondary battery.

FIG. 2 is a plan view showing a folded portion of a belt-shaped positive electrode plate when an electrode group having an oval cross section is formed.

FIG. 3 is an enlarged sectional view of only a core portion and an outer peripheral portion of an electrode group having an oval cross section.

FIG. 4 is a view showing an innermost folded portion of the belt-shaped positive electrode plate and an active material layer on the inner surface of the next folded portion according to the present invention.
FIG. 4 is a plan view showing an example of a state in which streak-shaped concave portions having a predetermined pitch centered on a folding line have a predetermined width and are formed in advance.

FIG. 5 is an enlarged sectional view showing an example of a streak-shaped concave portion formed in advance in a folded portion of a positive electrode plate according to the present invention.

FIG. 6 is a cross-sectional view showing an example of a core member for forming an electrode group having an elliptical cross section prior to forming an electrode group having an oval cross section according to the present invention.

FIG. 7 is a cross-sectional view showing another example of a core for forming an electrode group having an elliptical cross section in the present invention.

[Explanation of symbols]

 41 Positive electrode plate 41a Innermost folded portion 41a 'Next folded portion 41b Streaked recess 41b' Streaked recess

Claims (18)

[Claims] 1. A streak-shaped concave portion having a predetermined width centered on a fold line is formed in advance on at least an inner surface of at least an inner surface of a fold portion closest to a core portion of one strip-shaped positive electrode plate. A flat battery including an electrode group having an oval cross section formed by folding the positive electrode plate and one strip-shaped negative electrode plate via a separator. 2. The flat battery according to claim 1, wherein the width of the streak-shaped recess is in the range of 0.5 mm or more and 3.0 mm or less on each of the left and right sides of the folding line. 3. The depth of the streak-like concave portion is 20 times the thickness of the active material layer.
2. The flat battery according to claim 1, wherein the range is not less than 70% and not more than 70%. 4. The flat battery according to claim 1, wherein the cross section of the streak-shaped concave portion in a range of 30 ° or more and 120 ° or less is formed by a V-shaped streak. 5. The pitch between the streaks of the streak-shaped recess is 0.
The flat battery according to claim 1, wherein the flat battery has a range of 5 mm or more and 5.0 mm or less. 6. The flat battery according to claim 1, wherein the streaky recess formed in the folded portion is formed not only in the positive electrode plate but also in the negative electrode plate. 7. A belt-shaped electrode plate in which an active material layer is formed by applying a paste or electrolytically depositing a paste on both sides or one side of a core material made of a metal foil.
2. The flat battery according to 1. 8. A lithium cobaltate, lithium nickelate, or lithium cobaltate on both sides or one side of a core material made of aluminum foil.
The flat type according to claim 1, comprising a positive electrode plate on which an active material layer mainly composed of a lithium-containing composite oxide such as spinel-type lithium manganate is formed, and a non-aqueous electrolyte composed of an organic electrolyte, a polymer electrolyte, or the like. battery. 9. A stripe-shaped concave portion having a predetermined width centering on a fold line is formed in advance on at least the active material layer on at least the inner side surface of at least the innermost fold portion near the core portion of one strip-shaped positive electrode plate. Then, the positive electrode plate and one strip-shaped negative electrode plate are wound through a separator to form an electrode group having an elliptical cross section, and the electrode group is formed by the length of the electrode group having an elliptical cross section. An electrode group having an oval cross section obtained by being pressed and deformed while being sandwiched between a pair of flat plates parallel to the axis is housed in a battery container, and is sealed after pouring and impregnating with an electrolytic solution. A method for manufacturing a flat battery. 10. The method for manufacturing a flat battery according to claim 9, wherein the width of the streak-shaped concave portion is in the range of 0.5 mm or more and 3.0 mm or less on each of the left and right sides of the folding line. 11. The depth of the streak-shaped recess is 2 times the thickness of the active material layer.
The method for manufacturing a flat battery according to claim 9, wherein the range is 0% or more and 70% or less. 12. The streak-shaped recess has a cross section in the range of 30 ° or more and 120 ° or less formed by V-shaped streaks.
3. The method for producing a flat battery according to claim 1. 13. The pitch between the streaks of the streak-shaped concave portion is in a range of 0.5 mm or more and 5.0 mm or less.
3. The method for producing a flat battery according to claim 1. 14. The method of manufacturing a flat battery according to claim 9, wherein the streaked recess formed in the folded portion is formed not only in the positive electrode plate but also in the negative electrode plate. 15. A strip-shaped electrode plate in which an active material layer is formed by applying a paste or electrolytically depositing a paste on both surfaces or one surface of a core material made of a metal foil.
3. The method for producing a flat battery according to claim 1. 16. A lithium cobaltate, a lithium nickelate, and a core material made of aluminum foil on both sides or one side thereof.
The flat type according to claim 9, comprising a positive electrode plate on which an active material layer mainly composed of a lithium-containing composite oxide such as spinel-type lithium manganate is formed, and a non-aqueous electrolyte made of an organic electrolyte, a polymer electrolyte, or the like. Battery manufacturing method. 17. A pressure is applied to the outer periphery of a disk having a predetermined thickness while rotating a roller having a stripe-shaped projection formed thereon to form a stripe-shaped depression in advance on the active material layer of the folded portion of the strip-shaped electrode plate. The method for manufacturing a flat battery according to claim 9. 18. The electrode group according to claim 9, wherein one strip-shaped positive electrode plate and one strip-shaped negative electrode plate are wound via a separator by using a core member having a rhombic cross section to first form an electrode group having an elliptical cross section. Method for manufacturing a flat battery.