Sealing method

Abstract

To provide a sealing method that can more reliably seal a battery's electrolyte filling port by welding a sealant to the port.SOLUTION: In a method of welding a sealant 33 to a liquid filling port for injecting electrolyte into a battery, at the time of sealing, a sealant is welded by pressing a heating element 40 against each divided area of the sealant.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a method of welding a sealing material arranged to cover a liquid injection port of a battery.

Background Art

[0002] In the manufacture of a lithium-ion battery, there is a step of injecting an electrolytic solution from a provided liquid injection port and then sealing the liquid injection port by welding a sealing material.

[0003] Patent Document 1 discloses that in a welding step, a hot plate welding apparatus including a hot plate body having a heat generating portion disposed therein and a thin plate-shaped cover plate made of a rigid body having high thermal conductivity detachably attached to the hot plate body is used. The first resin portion and the second resin portion are brought into contact with the melting surface of the cover plate, respectively. When the first resin portion and the second resin portion are heated and melted by a preset melting amount, respectively, the first resin portion and the second resin portion are separated from the melting surface of the cover plate, and then the first resin portion and the second resin portion are brought into pressure contact with each other. Here, a form in which the heating element is composed of one member is shown.

[0004] Further, Patent Document 2 discloses that heat welding of an opening of a laminated exterior body is performed by aligning a current collecting terminal with a recess of a press plate. Here, it is shown that one press plate is used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When the member forming the liquid injection port is rectangular, particularly when it is formed long in one direction, there is a high possibility that distortion such as warping occurs along the longitudinal direction of the member forming the liquid injection port. In welding using a heating element composed of a single member, there is a possibility that the sealing material cannot be sufficiently welded to the member.

[0007] Therefore, an object of the present disclosure is to provide a method for welding a sealing material that can perform sealing more reliably when welding and sealing the liquid injection port of a battery.

Means for Solving the Problems

[0008] The present application discloses a method for welding a sealing material to a liquid injection port for injecting an electrolyte into a battery. When sealing, the sealing material is welded by pressing a heating element against each divided region of the sealing material.

[0009] A plurality of heating elements may be arranged along the surface of the sealing material.

[0010] The heating element may be movable along the surface of the sealing material.

[0011] The gap between adjacent heating elements can be an integral multiple of the interval of the liquid injection ports.

[0012] The heating element may be rotatable about an axis.

[0013] The heating element may be biased by an elastic body.

[0014] After the heating element contacts the sealing body, the heating element may be pushed into the direction of the sealing body by a predetermined distance.

[0015] The width of the heating element may be configured to be larger than the width of the frame forming the liquid injection port to which the sealing material is welded.

Effect of the Invention

[0016] According to the present disclosure, even if the injection port has a shape that is long in at least one direction, by welding with a plurality of heating elements, the sealing material can be appropriately welded to the injection port.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0018] 1. Structure of the Secondary Battery First, the structure of the secondary battery 10 according to one form manufactured by the manufacturing method of the secondary battery to which the welding method of the sealing material of the present disclosure is applied will be described with reference to the drawings. The directions of the three-dimensional orthogonal coordinate system are also shown in the drawings. Here, the xy plane is the horizontal plane, the z-axis direction is the vertical direction, and the larger z is, the upper side is.

[0019] FIG. 1 is a schematic external perspective view for explaining the structure of the secondary battery 10. In this form, the secondary battery 10 is a bipolar lithium-ion secondary battery. Thus, the secondary battery 10 has a plurality of metal conductive plates 11 and power storage modules 12, respectively, and these are alternately stacked and electrically connected to form a series connection. The secondary battery 10 is typically used for batteries such as hybrid vehicles and electric vehicles. In addition, both ends in the stacking direction (the z-axis direction in FIG. 1) of the stack are made of conductive plates 11. A positive electrode terminal (not shown) is connected to the conductive plate 11 at one end in the stacking direction, and a negative electrode terminal (not shown) is connected to the conductive plate 11 at the other end in the stacking direction.

[0020] The power storage module 12 is a flat single battery as a whole, having front and back surfaces and side surfaces 12a forming a thickness.

[0021] 1.1. Internal Structure of Power Storage Module FIG. 2 shows a cross-sectional view schematically showing the internal structure of one power storage module 12. The power storage module 12 includes an electrode stack in which a plurality of bipolar electrodes 13 are stacked, a plurality of sealing bodies 20 provided on each bipolar electrode 13, and a liquid injection portion 30 (see FIG. 1) which is a portion for injecting an electrolytic solution. The plurality of bipolar electrodes 13 are stacked along the thickness direction (the z-axis direction, the thickness direction in the flat plate shape), and the sealing bodies 20 are arranged on each bipolar electrode 13.

[0022] 1.1.1. Electrode Stack [Bipolar Electrode] Hereinafter, in the description of each member, there may be descriptions of "upper surface" and "lower surface". In FIG. 2, the "upper surface" means the side larger in the z direction, and the "lower surface" means the side smaller in the z direction. This is for convenience of description, but the "upper surface" can be rephrased as "first surface" and the "lower surface" as "second surface". The bipolar electrode 13 includes a current collector foil 14, a positive electrode active material layer 15 (first active material layer) provided on the lower surface of the current collector foil 14, a negative electrode active material layer 16 (second active material layer) provided on the upper surface of the current collector foil 14, and a separator 17.

[0023] The current collector foil 14 is a foil-shaped conductive member, and for example, a metal foil is used. It does not have to be a single-layer metal foil, and it may be a clad foil or a laminated foil in which different metal foils are laminated. The type of metal is not particularly limited, and for example, a foil in which an aluminum foil and a copper foil are laminated so that the upper surface is an aluminum layer and the lower surface is a copper layer can be mentioned. Other metals include titanium, nickel, stainless steel (for example, SUS304, SUS301, etc. defined in JIS G 4305:2015), steel (for example, cold-rolled steel sheet (SPCC, etc.) defined in JIS G 3141:2005), and the like.

[0024] The positive electrode active material layer 15 constitutes the positive electrode of the bipolar electrode 13, and in this embodiment, it is disposed on the lower surface of the current collector foil 14 via an adhesive layer such as acetylene black. The positive electrode active material layer 15 can contain a positive electrode active material, a conductive assistant, and a binder. Examples of the positive electrode active material include composite oxides, metal lithium, sulfur, and the like. The composition of the composite oxide includes, for example, at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. Examples of the composite oxide include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, LiNiMnCoO2, and the like. The binder serves to tie the active material or the conductive assistant to the surface of the current collector foil 14 and maintain the conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide-based resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, acrylic resins containing monomer units such as acrylic acid and methacrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester crosslinked bodies, starch-acrylic acid graft polymers, and the like. These binders can be used alone or in combination. Examples of the conductive assistant include acetylene black, carbon black, graphite, and the like.

[0025] The negative electrode active material layer 16 constitutes the negative electrode of the bipolar electrode 13 and is disposed on the upper surface of the current collector foil 14 in this embodiment. The negative electrode active material layer 16 can contain a negative electrode active material, a conductive assistant, and a binder. The conductive assistant and the binder can be considered in the same manner as the positive electrode active material layer 15. Examples of the negative electrode active material include carbon such as graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, and soft carbon, metal compounds, elements capable of alloying with lithium or compounds of the elements, boron-added carbon, and the like. Examples of the elements capable of alloying with lithium include silicon and tin.

[0026] The separator 17 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains a liquid electrolyte, and is disposed on the upper surface of the negative electrode active material layer 16 in this embodiment. Examples of the material constituting the separator 17 include polypropylene, polyethylene, polyolefin, polyester, and the like. The separator 17 may have a single-layer structure or a multilayer structure. Examples of the electrolyte absorbed and retained by the separator 17 include a liquid electrolyte (electrolyte solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. When the separator 17 is impregnated with the electrolyte, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. Further, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used as the non-aqueous solvent.

[0027] The current collector foil 14, the positive electrode active material layer 15, the negative electrode active material layer 16, and the separator 17 are configured to have different sizes in plan view. More specifically, the current collector foil 14 is the largest, followed by the separator 17, then the negative electrode active material layer 16, and the positive electrode active material layer 17 is the smallest. As can be seen from FIG. 2, the current collector foil 14, the positive electrode active material layer 15, the negative electrode active material layer 16, and the separator 17 are arranged with their centers aligned in plan view, and the difference in size is manifested in the degree of edge protrusion (overhang). Therefore, the edge of the current collector foil 14 protrudes the most, and the edges of the separator 14, the negative electrode active material layer 16, and the positive electrode active material layer 15 protrude in this order from the outside to the inside.

[0028] To form the positive electrode active material layer 15 and the negative electrode active material layer 16 on the current collector foil 14, conventionally known methods such as the roll coating method, die coating method, dip coating method, doctor blade method, spray coating method, curtain coating method, etc. are used. Specifically, an active material, a solvent, and, if necessary, a binder and a conductive aid are mixed to produce a slurry-like composition for forming the active material layer, and after applying the composition for forming the active material layer to the upper and lower surfaces of the current collector foil 14, it is dried. The solvent is, for example, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, or water.

[0029] [Laminated Structure of Electrode Stack] In the electrode stack, the bipolar electrodes 13 adjacent to each other in the stacking direction (z-axis direction) are stacked such that the positive electrode active material layer 15 of one bipolar electrode 13 overlaps with the separator 17 of the other bipolar electrode 13.

[0030] In addition, at the stacking direction ends of the electrode stack formed by the bipolar electrodes 13, the positive terminal electrode 18 is provided at the upper end and the negative terminal electrode 19 is provided at the lower end. The positive terminal electrode 18 has the current collector foil 14 and the positive electrode active material layer 15 provided on the lower surface of the current collector foil 14. The positive electrode active material layer 15 is stacked on the adjacent bipolar electrode 13, and the current collector foil 14 is stacked on its upper surface. The negative terminal electrode 19 has a current collector foil 14, a negative electrode active material layer 16 provided on the upper surface of the current collector foil 14, and a separator 17 laminated on the upper surface thereof. The separator 17 is laminated on the adjacent bipolar electrode 13, the negative electrode active material layer 16 is laminated on the lower surface thereof, and the current collector foil 14 is further laminated on the lower surface thereof. The positive terminal electrode 18 and the negative terminal electrode 19 are each laminated on a conductive plate 11 adjacent to the current collector foil 14.

[0031] 1.1.2. Sealing body The sealing body 20 is a member that seals the bipolar electrode 13 by being disposed at the outer peripheral end of the bipolar electrode 13. Accordingly, the sealing body 20 also seals between the bipolar electrodes 13 adjacent in the stacking direction. In this embodiment, the sealing body 20 has a first seal member 21, a second seal member 22, and a spacer 23.

[0032] [First seal member] The first seal member 21 is a frame-shaped member, and this is disposed along the outer peripheral end (outer edge) of the bipolar electrode 13. Specifically, as can be seen from FIG. 2, the first seal member 21 is disposed and joined between the upper surface of the current collector foil 14 and the lower surface of the separator 17 at the outer peripheral end of the bipolar electrode 13, so that the negative electrode active material layer 16 is disposed within its frame. In this embodiment, a predetermined interval is provided between the inner edge of the first seal member 21 and the negative electrode active material layer 16 to form a space S. On the other hand, the outer edge of the first seal member 21 is configured such that the first seal member 21 protrudes outside the current collector foil 14.

[0033] The first seal member 21 has electrical insulation properties and can be made of a known material, for example, a resin material having electrolyte resistance such as acid-modified polyethylene (acid-modified PE), acid-modified polypropylene (acid-modified PP), polyethylene, or polypropylene.

[0034] [Second seal member] The second seal member 22 is a frame-shaped member, which is arranged along the outer peripheral end portion (outer edge) of the bipolar electrode 13. Specifically, as can be seen from FIG. 2, the second seal member 22 is arranged and joined between the lower surface of the current collector foil 14 and the upper surface of the spacer 23 at the outer peripheral end portion of the bipolar electrode 13, and in combination with the spacer 23, the positive electrode active material layer 15 is arranged within its frame. In this embodiment, a predetermined interval is provided between the inner edge of the second seal member 22 and the positive electrode active material layer 15 to form a space S. On the other hand, the outer edge of the second seal member 22 is configured such that the second seal member 22 protrudes outside the current collector foil 14, and the upper surface of the second seal member 22 and the lower surface of the first seal member 21 are joined. The material of the second seal member 22 can be considered in the same way as that of the first seal member 21.

[0035] [Spacer] The spacer 23 is a frame-shaped member, which is arranged along the outer peripheral end portion of the bipolar electrode 13. Specifically, as can be seen from FIG. 2, the spacer 23, in combination with the second seal member 22, is arranged and joined between the lower surface of the second seal member 22 and the upper surface of the separator 17 of the adjacent bipolar electrode 13 at the outer peripheral end portion of the bipolar electrode 13, and the positive electrode active material layer 15 is arranged within its frame. In this embodiment, the inner edge of the spacer member 23 is arranged at a distance from the positive electrode active material layer 15. On the other hand, the outer edge of the spacer 23 protrudes outside the separator 17, and its lower surface is joined to the upper surface of the first seal member 21 of the adjacent sealing body 20. The material of the spacer 23 can be considered in the same way as that of the first seal member 21.

[0036] 1.1.3. Liquid injection part The liquid injection part 30 is formed on a part of the side surface 12a of the power storage module 12, and is a part for injecting (liquid injection) the electrolytic solution into the power storage module 12. Fig. 3 shows an exploded perspective view (with the sealing material 33 separated and shown) of a part of the part where the liquid injection part 30 is arranged on the side surface 12a of one power storage module 12 out of those in Fig. 1, with focus on one power storage module 12. Fig. 4 shows a cross-sectional view taken along the line A-A parallel to the x-axis in Fig. 3.

[0037] In this embodiment, the liquid injection part 30 has a through hole 31, a liquid injection port forming frame 32, and a sealing material 33.

[0038] [Through hole] The through hole 31 is formed on the side surface 12a of the power storage module 12, and is a hole that penetrates the sealing body 30 and communicates the space S with the outside. For example, one through hole 31 can be provided for one bipolar electrode 13, and in that case, the number of through holes 13 corresponding to the number of bipolar electrodes 13 provided is formed. Since the plurality of bipolar electrodes 13 are laminated as described above and the positions in the z direction in Fig. 3 are different, the position of the through hole 31 in the z-axis direction is also changed according to the position of the bipolar electrode 13.

[0039] In this embodiment, each through hole 31 is a horizontally long slit with a long side extending in the direction of going around the side surface 12a. Although this shape is not particularly limited, since the shape of the space S communicated with the through hole 31 is small in the lamination direction of the bipolar electrodes 13 (z-axis direction in Fig. 3) and large in the plane direction (xy plane direction in Fig. 3) due to its nature, the electrolytic solution can be efficiently injected by making the through hole 31 into a slit.

[0040] [Liquid injection port forming frame] The liquid injection port forming frame 32 is a frame-shaped member disposed on the side surface 12a. The liquid injection port forming frame 32 is disposed so as to surround the outer opening of each through hole 31. As a result, a recess 32a surrounded by the liquid injection port forming frame 32 with the side surface 12a having the through hole 31 as the bottom is formed by the thickness of the liquid injection port forming frame 32 (the size in the y-axis direction in FIG. 3). Further, the surface 32b of the liquid injection port forming frame 32 on the side opposite to the side in contact with the side surface 12a becomes a welding surface with the sealing material 33.

[0041] In this embodiment, the liquid injection port forming frame 32 has a rectangular outer frame 32c that forms its outer shape, and the inside of the outer frame 32c is partitioned by partition walls 32d to form each recess 32a. The outer frame 32c is a rectangular frame body along the x-z plane and has a shape that extends long in the x-axis direction with respect to the z-axis direction. Also, each recess 32a partitioned by the partition wall 32d is also long in the x-axis direction with respect to the z-axis direction.

[0042] [Sealing material] The sealing material 33 is a sheet-shaped member, is covered on the liquid injection port forming frame 32 so as to cover the recess 32a (liquid injection port) formed by the liquid injection port forming frame 32, and is adhered to the surface 32b. Thereby, it is possible to prevent the injected electrolytic solution from leaking from the secondary battery 10. The sealing material 33 is a sheet formed of a resin such as a polypropylene resin or a polyethylene resin. Thereby, the thermal adhesiveness can be enhanced.

[0043] 2. Manufacturing method of secondary battery The secondary battery 10 has a liquid injection step, a first charging step, a high-temperature aging step, and a sealing step. Here, the sealing method of the liquid injection port of the present disclosure is included in the sealing step. This will be described in detail below.

[0044] 2.1. Liquid injection step In the liquid injection process, an electrolytic solution is injected into the bipolar electrode 13. In the liquid injection process, for example, the secondary battery 10 before liquid injection (the sealing material 33 is not adhered) is placed in a chamber, and a liquid supply device is connected to an injection port forming frame 32 that functions as an injection port. Vacuum pumping is performed on the bipolar electrode 13 by a vacuum pump through a vacuum suction pipe with a valve arranged in the liquid supply device opened, the valve is closed, and the inside of the chamber is kept in a depressurized state. In this state, the valve of the liquid supply pipe is opened, and the electrolytic solution is sent into the bipolar electrode 13 through the recess 32a and the through hole 31, and the electrolytic solution is injected into the bipolar electrode 13.

[0045] 2.2. First charging process In the first charging process, the first charge is performed. The conditions of the first charging process are not particularly limited and are as known.

[0046] 2.3. High-temperature aging process Next, the high-temperature aging process is performed. The high-temperature aging process is as known. For example, the secondary battery 10 is conditioned by a procedure such as leaving it standing at 65°C for 15 hours.

[0047] 2.2. Sealing process In the sealing process, the sealing material 33 is placed over the recess 32a (injection port) formed by the injection port forming frame 32 to cover it, and the sealing material 33 is welded to the surface 32b of the injection port forming frame 32. More specifically, it is as follows.

[0048] FIG. 5 schematically shows a first form of the welding method in the sealing process. FIG. 5 is a view of the injection port forming frame 32 and the sealing material 33 seen from the direction indicated by arrow B in FIG. 3 (i.e., from above). As can be seen from FIG. 5, in the sealing process of the first form, a plurality of heating elements 40 are arranged at predetermined intervals along the x-axis (the longitudinal direction of the outer frame 32c), and these are pressed against the sealing material 33 covering the injection port forming frame 32 as shown in FIG. 5(a) (pressed in the y-axis direction), and the sealing material 33 is welded to the injection port forming frame 32 at the portion where the heating element 40 is pressed. Next, as shown in FIG. 5(b), the heating element 40 is moved along the surface of the sealing material 33 in the x-axis direction to sequentially weld the sealing material 33 to the liquid injection port forming frame 32, and all the portions to be welded are welded.

[0049] FIG. 6 shows a diagram for explaining a second form of the welding method in the sealing process. FIG. 6 is a view from the same perspective as FIG. 3. In the second form of the welding method, heating elements 40 are assigned to each of a plurality of sealing regions P, Q,... (only two sealing regions are shown in FIG. 6, but actually more sealing regions are arranged in the x-axis direction.) arranged in the x-axis direction, and welding is performed by pressing each heating element 40 against each sealing region. In this second form, the size of the heating element 40 is determined so that the sealing region can be sealed only by pressing the heating element 40 without moving it in the x-axis direction. Therefore, in the second form, the number of sealing regions is the same as the number of heating elements 40.

[0050] In the third form of the welding method in the sealing process, welding is performed while sequentially moving a plurality of sealing regions P, Q,... with one heating element 40. That is, for example, after one heating element 40 welds the sealing region P, it moves and welds the sealing region Q. It is not necessarily required to weld all the sealing regions with one heating element 40, but even when a plurality of heating elements 40 are provided, each heating element 40 sequentially seals two or more sealing regions. Therefore, in the third form, the number of heating elements 40 is less than the number of sealing regions.

[0051] According to the welding method as described above, even if there are distortions such as warping or bending in the liquid injection port forming frame 32, the sealing material 33 can be more reliably welded to the liquid injection port forming frame 32 to perform sealing. Although described exaggeratedly in Fig. 5, the surface (surface 32b) of the liquid injection port forming frame 32 on the side welded to the sealing material 33 is not necessarily flat. Particularly when the longitudinal direction (x-axis direction in this embodiment) is large, this is prominent, and for example, it is often curved as shown in Fig. 5. On the other hand, according to the sealing process including the welding method of each of the above embodiments, since the heating element 40 is welded while moving along the surface of the sealing material 33, or each region is welded by a plurality of non-moving heating elements 40, the sealing material 33 can be more reliably welded to the liquid injection port forming frame 32 for sealing.

[0052] Here, the gap between adjacent heating elements 40 is preferably an integral multiple of the interval of the liquid injection ports. Also, the width of the heating element 40 can be made larger than the width of the frame forming the liquid injection port (the interval between the partition walls 32d in contact with both sides in the x-axis direction of the concave portion 32a. The size in the D' and x-axis directions in Fig. 4). According to this, one or more frames forming the liquid injection port can be welded by a single heating element 40, and the certainty of welding the sealing material 33 to the liquid injection port forming frame 32 can be enhanced.

[0053] Furthermore, for the heating element 40, at least one of the following configuration of Modification Example 1 to Modification Example 3 can also be applied. Figs. 7 show diagrams for explanation. Each of the diagrams shown in Fig. 7 is an enlarged view focusing on two heating elements 40 in Fig. 5(a).

[0054] In Fig. 7(a), the heating element 40 is rotatable about an axis E parallel to the z-axis. According to this, even if there is a portion with a large inclination on the joint surface between the liquid injection port forming frame 32 and the heating element 40, the heating element 40 rotates to follow the inclination, and the certainty of welding the sealing material 33 to the liquid injection port forming frame 32 can be enhanced.

[0055] In Fig. 7(b), the heating element 40 is biased in the pressing direction (y-axis direction) of the sealing material 33 by an elastic body 41. According to this, even if there is a portion with large unevenness on the joint surface between the liquid injection port forming frame 32 and the sealing material 33, the heating element 40 can always maintain a state of pressing the sealing material 33 with a predetermined pressure, and the certainty of welding the sealing material 33 to the liquid injection port forming frame 32 can be enhanced.

[0056] FIG. 7(c) is configured such that the heating element 40, which is a rod-shaped member, can be pushed into the sealing material 33 in the pressing direction (y-axis direction) of the rod 42. According to this, even if there is a portion with large irregularities on the joint surface between the liquid injection port forming frame 32 and the sealing material 33, the plurality of heating elements 40 can be individually moved in the y-axis direction. Using this, after first pressing the heating element 40 against the sealing material 33, each heating element 40 further moves to press corresponding to the irregularities of the joint surface, and it is possible to always maintain a state where the sealing material 33 is pressed with a predetermined pushing amount, thereby enhancing the certainty of welding the sealing material 33 to the liquid injection port forming frame 32.

Description of Reference Numerals

[0057] 10... secondary battery, 11... conductive plate, 12... power storage module, 13... bipolar electrode, 20... sealing portion, 30... liquid injection portion, 31... through hole, 32... liquid injection port forming frame, 33... sealing material, 40... heating element

Claims

1. A method of welding a sealing material to a liquid injection port for injecting an electrolytic solution into a battery, wherein during the sealing, the sealing material is welded by pressing a heating element against each divided region of the sealing material. A method for sealing a liquid injection port.

2. The method for sealing a liquid injection port according to claim 1, wherein a plurality of the heating elements are arranged along the surface of the sealing material.

3. The method for sealing a liquid injection port according to claim 1, wherein the heating element is movable along the surface of the sealing material.

4. The method for sealing a liquid injection port according to claim 1, wherein the gap between adjacent heating elements is an integral multiple of the interval of the liquid injection ports.

5. The method for sealing a liquid injection port according to claim 1, wherein the heating element is rotatable about an axis.

6. The method for sealing a liquid injection port according to claim 1, wherein the heating element is biased by an elastic body.

7. The method for sealing a liquid injection port according to claim 1, wherein after the heating element contacts the sealing body, the heating element is pushed into the direction of the sealing body by a predetermined distance.

8. The method for sealing a liquid injection port according to claim 1, wherein the width of the heating element is larger than the width of the frame forming the liquid injection port to which the sealing material is welded.

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