JP2021082448A - Manufacturing method for battery - Google Patents

Abstract

To provide a technique of manufacturing a battery with improved sealing property.SOLUTION: A manufacturing method for a battery including an electrode body, a laminate outer package, and a current collector terminal that is partially led out from the outer package includes a step of heat sealing an outer periphery of the outer package while disposing the electrode body so that the electrode body is housed in the outer package and disposing the current collector terminal so that at least a part is led out from the outer package. The heat sealing is performed by a heat sealing device that applies a predetermined heat quantity to the periphery while having the outer periphery held from both sides. In the heat sealing, in order to make the heat quantity obtained by drawing heat from the current collector terminal in a direction of the electrode body in the heat quantity applied to a region of the held periphery that faces the current collector terminal and the heat quantity applied to a non-facing region of not facing the current collector terminal substantially the same, the heat quantity applied from the heat sealing device is made different between these regions.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for manufacturing a battery. More specifically, the present invention relates to a method for manufacturing a battery including a laminated exterior body.

In recent years, the applications of batteries have been expanding more and more. In particular, secondary batteries such as lithium ion secondary batteries and sodium ion secondary batteries are used not only for so-called portable power sources such as personal computers and mobile terminals, but also in recent years. It is preferably used as a power source for driving a vehicle. In particular, lithium-ion secondary batteries, which are lightweight and have high energy density, are preferable as high-output power sources for driving vehicles such as electric vehicles (EV), plug-in hybrid vehicles (PHV), and hybrid vehicles (HV), and will continue to be used in the future. Demand is expected to grow.

As a general configuration of a battery for the above-mentioned applications, for example, an electrode body including a positive electrode, a negative electrode, and a separator may be housed inside an exterior body and sealed. In recent years, there has been an increasing demand for miniaturization of batteries, and batteries equipped with an exterior body made of a laminated film are being energetically developed. Such a laminated film has, for example, a multilayer structure as described in Patent Document 1. For example, a three-layered laminated film in which resin layers are laminated on both sides of a metal layer is typically used as an exterior body of a battery.

Japanese Unexamined Patent Publication No. 2005-116228

When producing a battery having an outer body made of a laminated film, for example, an electrode body is housed inside the outer body, a peripheral edge portion (opening) is sandwiched between a pair of welding heads, and heat welding is performed to seal the outer body. In the peripheral portion of the peripheral portion to be heat-welded, the portion including the lead-out portion of the current collecting terminal connected to the electrode body, the amount of heat applied from the welding head at the time of heat welding is transmitted through the current collecting terminal and escapes to, for example, the electrode body. (So-called heat drawing), the amount of heat applied to the portion is reduced as a result (that is, the amount of heat drawing is large), and heat welding may be insufficient. In order to secure a sufficient amount of heat for heat welding in the relevant portion, for example, if the welding temperature is raised, the amount of heat applied to the region other than the current collector terminal lead-out portion in the same portion becomes excessive, and the resin layer of the laminated film melts more than necessary. There is a risk of Excessive melting of the resin layer causes the metal layer to be exposed. Exposure of the metal layer due to excessive melting of the resin layer is not preferable because it may cause a short circuit due to contact with the current collector terminal and the electrode body.

In Patent Document 1 described above, in order to suppress excessive heat escape (heat drawing) via the current collector terminal during heat welding, heat welding is performed with a portion other than the current collector terminal outlet portion sandwiched between heat insulating materials. Is disclosed to do. Patent Document 1 describes that since the temperature is lowered in the portion where the heat insulating material is arranged, an excessive amount of heat is not applied to the portion and the resin layer is less likely to melt.
However, since the amount of heat applied from the welding head is accumulated in the heat insulating material, if the heat welding of the laminated film is continuously performed, the effect of preventing the heat melting of the resin layer by the heat insulating material may be reduced. Further, since the heat insulating material has a certain thickness, for example, a large pressure is applied to the edge of the heat insulating material as compared with other parts, causing damage to the laminated film and causing the above-mentioned short circuit. ..

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to highly suppress the occurrence of heat welding defects when sealing the laminated exterior body, and to remarkably improve the airtightness. It is to provide a technique for manufacturing a battery.

The present inventor pays attention to heat drawing in the lead-out portion of the positive and negative electrode current collecting terminals (that is, the region facing the positive and negative electrode current collecting terminals in the peripheral edge of the laminated exterior body) when sealing the peripheral edge portion of the laminated exterior body. did.
Then, in the peripheral portion of the laminated exterior body, the amount of heat after heat is drawn from the current collecting terminal in the region facing the positive and negative electrode current collecting terminals toward the electrode body does not face the positive and negative electrode current collecting terminals. We have found that by performing heat welding so that the amount of heat applied to the non-opposing region is almost the same, it is possible to highly suppress the occurrence of defects that may occur in the heat welding of the laminated exterior body, and have completed the present invention. It was.
That is, the method for manufacturing a battery disclosed here includes an electrode body having a layer that functions as a positive electrode, a negative electrode, and a separator, a laminated exterior body that houses the electrode body in a sealed state, the positive electrode, and the positive electrode and the above. A method for manufacturing a battery including a positive electrode current collecting terminal for external connection and a negative electrode current collecting terminal which are connected to the negative electrode, respectively, and a positive electrode current collecting terminal which is partially led out from the laminated exterior body to the outside. Is.
The positive electrode body is arranged so as to be housed inside the laminated outer body, and the positive and negative electrode current collecting terminals are arranged so that at least a part of the electrode body is led out to the outside of the laminated outer body. This includes a step of heat-welding and sealing the peripheral edge of the laminated outer body in this state.
The heat welding is performed by a heat sealing device that sandwiches the peripheral edge portion from both sides and applies a predetermined amount of heat to the peripheral edge portion.
Here, the amount of heat applied to the region of the sandwiched peripheral edge portion facing the positive / negative electrode current collecting terminal, the amount of heat after being heat-drawn from the current collecting terminal toward the electrode body, and the positive / negative electrode current collection. The heat welding is performed by making the amount of heat applied from the heat sealing device different between the facing region and the non-opposing region so that the amount of heat applied to the non-opposing region not facing the terminal is substantially the same. It is characterized by performing.

The manufacturing method having such a configuration remarkably suppresses the occurrence of defects that may occur when the amount of heat applied to the facing region from the heat sealing device during heat welding of the laminated exterior body escapes to the electrode body side, and the sealing is good. It is possible to provide a battery having a property.

It is a top view which shows typically the structure of the battery manufactured by the manufacturing method of the battery which concerns on one Embodiment. FIG. 2 is a sectional view taken along line II-II showing the structure of the battery in FIG. It is a process drawing which shows typically the manufacturing method of the battery which concerns on one Embodiment. It is a schematic diagram which shows the welding process of the laminated exterior body in the manufacturing method of the battery which concerns on one Embodiment. (A) is a perspective view explaining a welding process. (B) is a front view which shows the welding part in a welding process. (C) is a sectional view taken along the line CC of FIG. 4 (B). (D) is a cross-sectional view taken along the line DD of FIG. 4 (B). (E) is a cross-sectional view taken along the line CC of FIG. 4 (B) in the modified example 1. It is CC sectional view of FIG. 4 (B) in the modification 2. FIG.

Hereinafter, typical embodiments in the present disclosure will be described in detail with reference to the drawings. Matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art.
In the following drawings, members and parts that perform the same action are described with the same reference numerals. Further, the dimensional relations (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relations. In this specification, the numerical ranges A to B indicate A or more and B or less.
Hereinafter, as an application target of the present invention, details will be given while exemplifying a method for manufacturing a lithium ion secondary battery (hereinafter, also simply referred to as “battery”) having a structure in which a laminated electrode body is housed in an outer body made of a laminated film. Explain to. However, it is not intended to limit the battery manufacturing method according to the present disclosure to those described in the following embodiments.

<Overall configuration of battery>
First, the configuration of the battery manufactured by the battery manufacturing method disclosed here will be described with reference to FIG. FIG. 1 is a plan view schematically showing a structure of a battery manufactured by the method for manufacturing a battery according to an embodiment.
As shown in FIG. 1, the battery 1 roughly includes, for example, an electrode body 20, a positive electrode current collecting terminal 42 and a negative electrode current collecting terminal 44 for external connection, and a laminated exterior body 30. The electrode body 20 is housed inside the laminated exterior body 30 in a state where the peripheral edge portion is heat-welded (heat-sealed). A part of the positive electrode current collecting terminal 42 and the negative electrode current collecting terminal 44 is led out from the inside of the laminated exterior body 30 to the outside, and the positive electrode current collecting terminal lead-out unit 32 and the negative electrode current collecting terminal lead-out unit are led out to the laminated outer body 30. 34 is formed. In FIG. 1, the positive electrode current collecting terminal lead-out unit 32 and the negative electrode current collector terminal lead-out unit 34 are formed at both end portions facing each other in the X direction.

<Electrode body>
Although detailed illustration is omitted, the electrode body 20 has, for example, a positive electrode, a negative electrode, and a layer that functions as a separator. For example, when the electrode body 20 is a laminated electrode body, the positive electrode is, for example, a rectangular sheet-shaped positive electrode current collector and a positive electrode mixture layer coated on the surface (one side or both sides) of the positive electrode body. It can be a positive electrode sheet having and. Further, the negative electrode may be, for example, a negative electrode sheet having a rectangular sheet-shaped negative electrode current collector and a negative electrode mixture layer coated on the surface (one side or both sides) of the negative electrode current collector. Both the positive electrode sheet and the negative electrode sheet have a current collector exposed portion on which a mixture layer is not formed at one end in the long side direction (X direction) of the sheet. The electrode body 20 is formed by alternately stacking a positive electrode and a negative electrode with a layer that functions as a separator interposed therebetween. At this time, for example, the electrode sheets are laminated so that the exposed portion of the positive electrode current collector protrudes from one end in the X direction and the exposed portion of the negative electrode current collector protrudes from the other end in the X direction. In the electrode body 20, for example, the central portion in the X direction is the core portion in which the electrode mixture layers are laminated, and the both end portions in the X direction are the regions in which the current collector exposed portions (current collectors) are laminated. .. In the region where the current collectors are stacked, the current collectors are collected in the stacking direction to form a current collector terminal joint for external connection. The positive electrode current collecting terminal 42 is joined to the positive electrode current collecting terminal joint, and the negative electrode current collecting terminal 44 is joined to the negative electrode current collecting terminal joint.

The layer that functions as the separator may be a separator made of a porous body, for example, when the battery 1 is a so-called non-aqueous electrolyte lithium ion secondary battery that includes a non-aqueous electrolyte as an electrolyte. Further, for example, when the battery 1 is a so-called all-solid-state lithium ion secondary battery including a powdery solid electrolyte as an electrolyte, it may be a solid electrolyte layer.
The detailed structure of the electrode body 20 is not particularly limited as long as the current collecting terminal joint is formed as described above and the current collecting terminals of the same electrode are joined there. The members and materials (for example, current collector foil, mixture layer, separator, solid electrolyte layer, etc.) constituting the electrode body 20 are particularly limited to those typically used for this type of lithium ion secondary battery. Since it can be used without any problem and does not characterize the present invention, detailed description thereof will be omitted.

<Laminate exterior>
The laminated exterior body 30 is made of a laminated film. The laminate film constituting the laminate exterior body 30 may be the same as that conventionally known, and is not particularly limited. Typically, the laminated exterior body 30 may be, for example, a laminated film having a multilayer structure. The specific configuration of the laminated exterior body 30 will be described with reference to FIG. FIG. 2 is a sectional view taken along line II-II showing the structure of the battery in FIG.
As shown in FIG. 2, the laminated exterior body 30 has, for example, a three-layer structure, and has a sealant layer 36a, a gas barrier layer 36b, and a protective layer 36c from the side closer to the electrode body 20, and is configured by being laminated in this order. Has been done.

-Sealant layer-
The sealant layer 36a is the innermost layer of the exterior body 30, and is located on the side closest to the electrode body 20. The sealant layer 36a is a layer for enabling heat welding of the exterior body 30, and is made of, for example, a thermoplastic resin. Examples of the thermoplastic resin include polyolefins such as polyethylene (PE) and polypropylene (PP); polyesters such as polyethylene terephthalate (PET); crystalline resins such as polystyrene, polyvinyl chloride and the like; and non-crystalline resins. Be done.

-Gas barrier layer-
The gas barrier layer 36b is a layer that blocks the movement of gas inside and outside the battery 1. For example, the gas barrier layer 36b can prevent the gas generated inside the battery 1 from flowing out and the air, moisture, and the like from the outside of the battery 1 from flowing into the inside.
The gas barrier layer 36b is made of, for example, a metal material. Examples of the metal material include aluminum, iron, stainless steel and the like. Among them, as the constituent material of the gas barrier layer 36b, for example, an aluminum foil and an aluminum vapor deposition layer are preferable.

-Protective layer-
The protective layer 36c is located on the outer surface side of the gas barrier layer 36b, and may be, for example, the outermost layer of the laminated exterior body 30. The protection 36c is, for example, a layer for improving the durability of the laminated exterior body 30. Examples of the constituent material include polyester such as PET and polyamide.

The layer structure of the laminated exterior body 30 is not particularly limited, and may be, for example, four or more layers (4 to 10 layers). For example, in the stacking direction (Z direction) of each of the above layers, an adhesive layer for adhering them may be formed between the layers as described above. Further, a print layer or the like may be provided as the outermost layer.

<Current collector terminal>
The current collecting terminal is a plate-shaped conductive member. For example, the positive electrode current collector terminal 42 is joined to the positive electrode current collector 22, and at least a part of the positive electrode current collector terminal 42 is drawn out from the inside of the laminated exterior body 30 (positive electrode current collector terminal lead-out unit 32). Although not shown in FIG. 2, the negative electrode current collector terminal is joined to the negative electrode current collector, and at least a part of the negative electrode current collector terminal is drawn out from the inside of the laminated exterior body 30 (negative electrode current collector terminal lead-out unit). ).

<Battery manufacturing>
Next, the method of manufacturing the battery disclosed here will be described with reference to FIG. FIG. 3 is a process diagram schematically showing a method for manufacturing a battery according to an embodiment.
As shown in the figure, the battery manufacturing method disclosed here includes an electrode body preparation step S10, a current collecting terminal mounting step S20, an exterior body accommodating step S30, and a sealing step S40.
<Electrode body preparation process>
The electrode body preparation step S10 is a step of constructing an electrode body as a power generation element of the battery. Since the method for constructing the electrode body may be the same as the conventional one and does not characterize the present invention, detailed description thereof will be omitted.

<Current collector terminal mounting process>
The current collector terminal mounting step S20 is a step of joining the current collector terminals of the same electrode to the current collector terminal joint portion of the electrode body prepared in step S10. As the means for joining the current collecting terminal to the current collecting terminal joining portion, conventionally known joining means such as ultrasonic welding, laser welding, and resistance welding can be used without particular limitation.

<Exterior body storage process>
The exterior body accommodating step S30 is a step of accommodating the electrode body to which the current collecting terminals are bonded in the step S20 in the laminated exterior body. In step S30, the electrode body and the laminated outer body are overlapped and arranged so that the electrode body is housed inside the laminated outer body. At this time, the electrode body is arranged so that the current collecting terminal is in a state where at least a part thereof is led out to the outside of the laminated exterior body.
The electrode body and the laminated outer body may be, for example, superposed in the order of the laminated outer body, the electrode body, and the laminated outer body. For example, the electrode body may be sandwiched between two laminated films (exterior bodies), or the electrode body may be inserted into a bag-shaped laminated outer body.

<Sealing process>
The sealing step S40 is a step of heat welding and sealing the peripheral edge of the laminated exterior body in which the electrode body is housed in the step S30. For example, in the sandwiching direction of the electrode body, the peripheral edge portion of the laminated exterior body is sandwiched between the heating portions of the heat sealing device (also referred to as "heat sealer") from both sides, and a predetermined amount of heat is applied to the peripheral edge portion to laminate. Seal the peripheral edge of the exterior body.
Hereinafter, step S40 in the present invention will be described with reference to FIG. The following description describes the welding in the vicinity of the positive electrode current collecting terminal outlet, but the same applies to the welding in the vicinity of the negative electrode current collector terminal outlet. Note that FIG. 4 is a schematic view showing a welding process of the laminated exterior body in the method for manufacturing a battery according to the embodiment. (A) is a perspective view explaining a welding process. (B) is a front view which shows the welding part in a welding process. (C) is a sectional view taken along the line CC of FIG. 4 (B). (D) is a cross-sectional view taken along the line DD of FIG. 4 (B). (E) is a cross-sectional view taken along the line CC of FIG. 4 (B) in the modified example 1.

<Heat sealing device>
As the heat-sealing device used in the battery manufacturing method disclosed herein, a general heat-sealing device can be used, and the description of the overall configuration thereof will be omitted. In the following, only the heating portion, which is the main body for performing heat welding by sandwiching the laminated outer body, will be described in the heat sealing device.
For example, it is preferable that the amount of heat applied from the heat sealing device is set to be different between the region facing the current collecting terminal and the non-opposing region not facing each other in the peripheral edge portion of the laminated exterior body. It is preferable that the amount of heat applied in the opposite region after being heat-drawn from the current collecting terminal toward the electrode body is substantially the same as the amount of heat applied in the non-opposing region.
Specifically, as shown in FIGS. 4A and 4B, for example, the heating unit 10 has a region R1 that sandwiches the facing region 30a and a region R2 that sandwiches the non-facing region 30b. For example, the amount of heat applied from the region R1 to the opposite region 30a and the amount of heat applied from the region R2 to the non-opposite region 30b may be configured to be different from each other. For example, the amount of heat applied to the non-opposing region 30b is preferably relatively small. Here, the facing region 30a is a region facing the positive electrode current collecting terminal 42 in the laminated exterior body 30. The non-opposing region 30b is a region of the laminated exterior body 30 that does not face the positive electrode current collecting terminal 42.

<Structure of heating part>
For example, in the region R2, the cross-sectional area where heat is conducted during welding may be made smaller than the cross-sectional area in the region R1. Then, since the thermal resistance value in the region R2 becomes relatively large, the amount of heat applied from the region R2 to the laminated exterior body 30 (non-opposing region 30b) becomes relatively small. As a result, excessive thermal melting of the laminated exterior body 30 (non-opposing region 30b) sandwiched between the regions R2 can be remarkably suppressed.
As a method of relatively reducing the cross-sectional area in the region R2, for example, as shown in the drawing, providing a plurality of holes 12 in the region R2 can be mentioned.
The shape of the hole 12 is not particularly limited, but for example, the planar shape may be a shape including an arc such as a perfect circle or an ellipse, a substantially polygonal shape, or the like. The hole 12 is preferably a through hole, for example, and may be substantially parallel to the wide surface of the battery 1 so that the angle with respect to the wide surface is less than 10 degrees (FIG. 4 (C)). The hole 12 may be a recess, for example, and in that case, the depth in the X direction (that is, the horizontal plane direction of the laminated exterior body 30) in FIG. 4C is not particularly limited.
The number of holes 12 is not particularly limited, but may be 1, 2, 3, 4, and 5 or more, and may be 30, 25, 20, and 10 or less, for example.
The diameter of the hole 12 is not particularly limited.

The planar shape and cross-sectional shape of the region R1 are not particularly limited as long as the cross-sectional area in the region is relatively large. For example, as shown in FIG. 4D, it is preferable not to form the above-mentioned hole 12 in the region R1. When forming holes in the region R1, it is preferable that the number of holes, the size of the holes, and the like are smaller than, for example, the region R2.

<Effect>
For a battery provided with a conventional laminated exterior body, when heat welding the facing regions as described above in the laminated outer body, the amount of heat applied to the laminated outer body from the heat sealing device is applied to, for example, the electrode body side via the current collecting terminal. By escaping, there was a risk that the heat welding of the opposite region would be insufficient. This causes the inflow of air from the outside to the inside of the laminated exterior, the outflow of the electrolytic solution from the inside to the outside of the laminated exterior, and the outflow of gas generated in the process of the battery reaction, so that the battery is used properly. Therefore, it was an issue that needed to be resolved immediately. On the other hand, when the amount of heat applied from the heating portion is increased in order to suppress welding failure due to heat escape, the resin layer of the laminated outer body is excessively melted by the amount of heat in the non-opposing region, resulting in the above-mentioned problems. In addition to the occurrence, for example, the metal layer (gas barrier layer) in the laminated outer body may be exposed, and the metal layer and the electrode body may be short-circuited.
In the present invention, in the heat sealing device used for heat welding of a laminated exterior body, the cross-sectional area where heat is conducted in the non-opposing region is made smaller than the cross-sectional area in the facing region. As a result, even if the amount of heat during heat welding is increased in consideration of heat escape from the current collecting terminal to the electrode body, an excessive amount of heat is applied to the laminated outer body in the non-opposing region from the heat sealing device. Is suppressed, and the occurrence of the above-mentioned problems can be prevented. According to the battery manufacturing method disclosed here, the airtightness of the laminated exterior body due to welding is improved in the facing region, and the thermal melting of the resin layer is suppressed in the non-opposing region, so that the airtightness of the laminated exterior body is remarkable. It is possible to provide an improved battery.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above.
<Modification example 1>
For example, as shown in FIG. 4 (E), the hole 12 may be formed so that the angle with respect to the wide surface of the battery is 10 degrees or more. In this case, the air warmed at the time of welding flows to the U side in the Z direction (that is, the sandwiching direction of the laminated outer body 30 with respect to the heating portion 10) through the holes 12, thereby heating the laminated outer body from the region R2. The amount can be reduced efficiently.
<Modification 2>
For example, the cross-sectional shape of the region R2 can be a shape as shown in FIG. For example, in the X direction (that is, in the horizontal plane direction of the laminated exterior body 30), the width L2 of a part of the heating portion 10 may be smaller than the width L1 of the contact portion with the laminated exterior body 30. The width L1 of the contact portion with the laminated exterior body 30 is preferably the same in both the region R1 and the region R2.

<Modification example 3>
In the above embodiment, the case where the present invention is applied to a laminated electrode body has been described, but a long positive electrode sheet and a long negative electrode sheet are alternately laminated with a separator interposed therebetween and wound in the winding axis direction. It may be applied to a wound electrode body having a rotated structure.

<Modification example 4>
In the above embodiment, the positive electrode current collecting terminal lead-out unit 32 and the negative electrode current collector terminal lead-out unit 34 are formed at both end portions facing each other in the X direction (see FIG. 1), but the positive electrode current collector terminal lead-out unit 32 And the negative electrode current collecting terminal lead-out unit 34 may be formed on the same side, for example. In this case, for example, the two current collecting terminal outlets are formed so as not to overlap in the short side direction (Y direction) of the electrode body 20.

1 Battery 10 Heating part 12 Hole 20 Electrode body 22 Positive electrode current collector 30 Laminated exterior body 30a Opposing area 30b Non-opposing area 32 Positive current collecting terminal lead-out part 34 Negative-negative current collecting terminal lead-out part 36a Sealant layer 36b Gas barrier layer 36c Protective layer 42 Positive electrode current collecting terminal 44 Negative electrode current collecting terminal S10 Electrode body preparation step S20 Current collecting terminal mounting step S30 Exterior body accommodating step S40 Sealing step R1 region R2 region L1, L2 Width X, Y, Z, U directions

Claims (1)

An electrode body having a layer that functions as a positive electrode, a negative electrode, and a separator, and
A laminated exterior body that houses the electrode body in a sealed state, and
Positive and negative electrode current collecting terminals for external connection and negative electrode current collecting terminals that are connected to the positive electrode and the negative electrode, respectively, and a part of which is led out from the laminated exterior body to the outside.
Is a method of manufacturing a battery equipped with
The positive electrode body is arranged so as to be housed inside the laminated outer body, and the positive and negative electrode current collecting terminals are arranged so that at least a part of the electrode body is led out to the outside of the laminated outer body. In this state, the step of heat-welding and sealing the peripheral edge of the laminated outer body is included.
The heat welding is performed by a heat sealing device that sandwiches the peripheral edge portion from both sides and applies a predetermined amount of heat to the peripheral edge portion.
Here, the amount of heat applied to the region of the sandwiched peripheral edge portion facing the positive and negative electrode current collecting terminals, the amount of heat after being heat-pulled from the current collecting terminal toward the electrode body, and the positive and negative electrode current collection. The heat welding is performed by making the amount of heat applied from the heat sealing device different between the facing region and the non-opposing region so that the amount of heat applied to the non-opposing region not facing the terminal is substantially the same. A manufacturing method characterized by performing.

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