Secondary battery manufacturing method and secondary battery

Abstract

To provide a secondary battery manufacturing method that suppresses insufficient sealing in product when the liquid pouring mouth of a battery is sealed by fusing a sealant.SOLUTION: The secondary battery manufacturing method includes: a liquid injection step for injecting an electrolytic solution to an electrode from a pouring mouth surrounded with a cylindrical member; a sealing step for fusing a transparent resin film to the cylindrical member to seal an opening of the cylindrical member; and an inspection step for inspecting a fused state between the cylindrical member and the resin film and detecting the presence of an unfused region by a visual method, or by a method for processing an image acquired by imaging the resin film fused to the cylindrical member and identifying an unconnected section.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a secondary battery and a secondary battery.

Background Art

[0002] In the manufacture of lithium-ion batteries, there is a step of injecting an electrolyte 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 bipolar lithium-ion battery, a plurality of cells are sealed adjacent to each other within a single liquid injection frame. Here, in the prior art including Patent Document 1, due to resistance to the electrolyte, a sheet in which an aluminum foil is laminated with a resin (aluminum laminate sheet) is conventionally used for lithium-ion batteries.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is important that the sealing is performed reliably. If there are bubbles (voids) etc. on the sealing surface (welded part) and the sealing is insufficient, the electrolytes of different cells may mix. This may cause a short circuit, which may lead to heat generation and ignition.

[0006] Therefore, an object of the present disclosure is to provide a method for manufacturing a secondary battery capable of suppressing the occurrence of insufficient sealing in a product in the sealing obtained by welding a sealing material to a liquid injection port of a battery. Further, such a secondary battery is provided.

Means for Solving the Problems

[0007] From the perspective of cost reduction, the sealing is performed by welding as described above. However, the generation of bubbles due to welding can be sudden, and inspections are required each time. In contrast, the inventor conceived that improving the ease of inspection can suppress the occurrence of products with insufficient sealing, and embodied this idea.

[0008] The present application discloses a method for manufacturing a secondary battery having electrodes, the method including: a liquid injection step of injecting an electrolytic solution into the electrodes through a liquid injection port surrounded by a cylindrical member; a sealing step of welding a resin film that is transparent to the cylindrical member to seal the opening of the cylindrical member; and an inspection step of inspecting the welding state between the cylindrical member and the resin film to detect the presence or absence of an unsealed area by visually inspecting or by image processing of an image obtained by photographing the resin film welded to the cylindrical member to identify an unbonded portion. Note that the "cylindrical member" surrounding the liquid injection port may be simply referred to as a "liquid injection frame".

[0009] The cylindrical member may be configured to contain polyethylene, and the resin film may have a polyethylene layer.

[0010] The resin film may have a polyvinyl alcohol layer, and the layer on the cylindrical member side may be a polyethylene layer.

[0011] In the sealing step, the resin film may be welded to the cylindrical member by pressing a heating body against the resin film.

[0012] In the sealing step, after bringing the resin film into contact with the cylindrical member, a laser having a wavelength absorbed by the cylindrical member and the resin film may be irradiated along the cylindrical member from the resin film side to perform welding.

[0013] In the inspection step, the detection may be performed by irradiating polarized light onto the welding surface between the cylindrical member and the resin film and receiving the reflected light.

[0014] This application discloses a secondary battery having a liquid injection port for injecting an electrolytic solution into an electrode, a cylindrical member formed so as to surround the liquid injection port, and a transparent resin film covering the opening of the cylindrical member.

[0015] In the above secondary battery, the cylindrical member may contain polyethylene, and the resin film may be configured to have a polyethylene layer.

[0016] In the above secondary battery, the resin film may have a polyvinyl alcohol layer, and the layer on the side of the cylindrical member may be a polyethylene layer.

Advantages of the Invention

[0017] According to the present disclosure, it is possible to easily check the presence or absence of defects in the joining of the cylindrical member and the film for sealing, such as voids, and it is possible to suppress the occurrence of a secondary battery with insufficient sealing as a product.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0019] 1. Structure of the Secondary Battery First, the structure of the secondary battery 10 according to one example of the present disclosure will be described with reference to the drawings. The drawings also show the directions of the three-dimensional orthogonal coordinate system. Here, the xy plane is the horizontal plane, the z-axis direction is the vertical direction, and the larger one in the z-axis direction is the upper side.

[0020] FIG. 1 is a schematic external perspective view for explaining the structure of the secondary battery 10. In this embodiment, 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 of hybrid vehicles, electric vehicles, etc. In addition, both ends in the stacking direction (the z-axis direction in FIG. 1) of the stacking are 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.

[0021] 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.

[0022] 1.1. Internal Structure of the Power Storage Module FIG. 2 shows a cross-sectional view schematically showing the internal structure focusing on one power storage module 12. The power storage module 12 includes an electrode laminate formed by stacking a plurality of bipolar electrodes 13, a plurality of sealing bodies 20 provided on each bipolar electrode 13, and a liquid injection part 30 (see FIG. 1) which is a part 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.

[0023] 1.1.1. Electrode Laminate [Bipolar Electrode] In the following descriptions of each component, there may be descriptions of "upper surface" and "lower surface". However, in FIG. 2, the "upper surface" means the larger side in the z-axis direction, and the "lower surface" means the smaller side in the z-axis direction. For convenience, such descriptions are used, but the "upper surface" can be rephrased as the "first surface", and the "lower surface" can be rephrased as the "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.

[0024] The current collector foil 14 is a foil-shaped conductive member, and for example, a metal foil is used. It is not necessary 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. 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 (such as SUS304, SUS316, SUS301, etc. defined in JIS G 4305:2015), steel (such as cold-rolled steel sheets (SPCC, etc.) defined in JIS G 3141:2005), and the like.

[0025] 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 include a positive electrode active material, a conductive auxiliary agent, and a binder. Examples of the positive electrode active material include composite oxides, metal lithium, and sulfur. 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 fasten the active material or the conductive aid 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 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 cross-linked bodies, starch-acrylic acid graft polymers, and the like. These binders can be used alone or in combination. Examples of the conductive aid include acetylene black, carbon black, graphite, and the like.

[0026] 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 aid, and a binder. The conductive aid 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 such elements, boron-added carbon, and the like. Examples of the elements capable of alloying with lithium include silicon and tin.

[0027] 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. The electrolyte absorbed and held by the separator 17 includes, for example, 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, LiN(CF3SO2)2, etc. can be used as the electrolyte salt. Further, as the non-aqueous solvent, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, ethers, etc. can be used.

[0028] 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 appears 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 inside.

[0029] 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 a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, a 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 an active material layer, and the composition for forming the active material layer is applied to the upper and lower surfaces of the current collector foil 14 and then dried. The solvent is, for example, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, water.

[0030] [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.

[0031] In addition, at the end of the electrode laminate in the stacking direction by the bipolar electrode 13, a positive terminal electrode 18 is provided at the upper end thereof, and a negative terminal electrode 19 is provided at the lower end thereof. The positive terminal electrode 18 has a current collector foil 14 and a 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 laminated on the adjacent bipolar electrode 13, and the current collector foil 14 is laminated on the upper surface thereof. 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 the conductive plate 11 adjacent to the current collector foil 14.

[0032] 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 adjacent bipolar electrodes 13 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.

[0033] [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.

[0034] The first sealing member 21 has electrical insulation and can be made of a resin material with electrolyte resistance, such as acid-modified polyethylene (acid-modified PE), acid-modified polypropylene (acid-modified PP), polyethylene, or polypropylene, which are well-known materials.

[0035] [Second Sealing Member] The second sealing member 22 is a frame-shaped member, which is arranged along the outer peripheral end (outer edge) of the bipolar electrode 13. Specifically, as can be seen from FIG. 2, the second sealing 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 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 sealing 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 sealing member 22 is configured such that the second sealing member 22 protrudes outside the current collector foil 14, and the upper surface of the second sealing member 22 is joined to the lower surface of the first sealing member 21. The material of the second sealing member 22 can be considered in the same way as that of the first sealing member 21.

[0036] [Spacer] The spacer 23 is a frame-shaped member, which is arranged along the outer peripheral end of the bipolar electrode 13. Specifically, as can be seen from FIG. 2, the spacer 23, in combination with the second sealing member 22, is arranged and joined between the lower surface of the second sealing member 22 and the upper surface of the separator 17 of the adjacent bipolar electrode 13 at the outer peripheral end 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 sealing 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 sealing member 21.

[0037] 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 (filling) the electrolytic solution into the power storage module 12. Fig. 3 shows an exploded perspective view (displayed with the resin film 33 separated) of a part of the part of the side surface 12a where the liquid injection part 30 is arranged among those in Fig. 1, focusing on one power storage module 12. Fig. 4 shows a cross-sectional view (the resin film 33 is not separated) along the line A-A parallel to the x-axis among those in Fig. 3.

[0038] In this embodiment, the liquid injection part 30 has a liquid injection port 31, a liquid injection frame 32, and a resin film 33.

[0039] [Liquid injection port] The liquid injection port 31 is formed on the side surface 12a of the power storage module 12, and is an opening formed on the side surface 12a side among the holes (not shown) that penetrate the sealing body 30 and communicate the space S with the outside. One liquid injection port 31 (through hole) can be provided for example for one bipolar electrode 13, and in that case, the number of liquid injection ports 31 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-axis direction in Fig. 3 are different, the position of the liquid injection port 31 in the z-axis direction is also changed according to the position of the bipolar electrode 13.

[0040] In this embodiment, each liquid injection port 31 (through hole) 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 liquid injection port 31 (through hole) is small in the lamination direction of the bipolar electrodes 13 (z-axis direction in Fig. 3) and large in the plane direction (x-y plane direction in Fig. 3) due to its nature, the electrolytic solution can be efficiently injected by making the liquid injection port 31 (through hole) into a slit.

[0041] [Liquid injection frame] The liquid injection frame 32 is a cylindrical member and is arranged on the side surface 12a. The liquid injection frame 32 is arranged so as to surround each liquid injection port 31. As a result, a recess 32a having an opening surrounded by the liquid injection frame 32 with the thickness of the liquid injection frame 32 (the size in the y-axis direction in FIG. 3) having the side surface 12a with the liquid injection port 31 as the bottom is formed. Further, the surface 32b of the liquid injection frame 32 on the side opposite to the side contacting the side surface 12a becomes a welding surface with the resin film 33.

[0042] In this embodiment, the liquid injection frame 32 has a rectangular outer frame 32c forming its outer shape, and the inside of the outer frame 32c is partitioned by partition walls 32d to form respective recesses 32a. The outer frame 32c is a frame body made of a rectangular cylindrical member 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.

[0043] The material constituting the liquid injection frame 32 is not particularly limited, but it is preferably made of resin, and among them, it is preferably made of polyethylene.

[0044] [Resin film] The resin film 33 is a sealing material made of sheet-shaped resin, is covered on the liquid injection frame 32 so as to cover the recess 32a formed by the liquid injection frame 32, and is welded to the surface 32b. Thereby, it is possible to prevent the injected electrolytic solution from leaking from the secondary battery 10.

[0045] The resin film 33 is transparent. As a result, as will be described later, the state of the welding surface between the liquid injection frame and the resin film can be visually obtained with high accuracy. Here, "transparent" means a property in which the light transmittance is high and the other side can be seen through the resin film. At this time, the resin film only needs to be transparent, and it may be colorless or colored.

[0046] The resin film 33 is made of resin and only needs to be transparent, and its layer structure is not particularly limited. However, it preferably has a layer made of at least one of polyvinyl alcohol and polyethylene. Since polyvinyl alcohol can suppress the permeability of the electrolytic solution to a low level, it has high barrier properties while ensuring transparency. According to the inventor's tests, when a resin film made of polyvinyl alcohol is welded to the injection frame by pressing with a heating body (heating temperature 145°C, pressing time 10 seconds, pressing amount 0.1 mm), the permeation amount per 1 m 2 per day was 0.1 ml in terms of conversion. This was approximately 1 / 200 of the permeation amount with respect to polyethylene.

[0047] On the other hand, polyethylene has excellent weldability when the injection frame is made of polyethylene. From such a perspective, it is more preferable to use a resin film having a two-layer structure in which the layer on the injection frame side is made of polyethylene and a layer made of polyvinyl alcohol is laminated on the layer. However, it is also possible to ensure the weldability (thermal adhesiveness) of polyvinyl alcohol itself with the injection frame (polyethylene), and the resin film 33 may be composed of a single layer of polyvinyl alcohol.

[0048] In addition, since the resin film 33 is composed only of a resin material, it has high flexibility. After sealing, as can be seen from FIG. 4, it is recessed at the center of the recess 32a (because vacuum suction is performed during liquid injection as described later). Therefore, the volume (capacity) of the recess 32a sealed with the resin film 33 can be reduced, the excess electrolytic solution accumulated here can be reduced, or the amount of the electrolytic solution that should originally enter the bipolar electrode 13 and accumulates in the recess 32a can be reduced.

[0049] 2. Manufacturing method of secondary battery The secondary battery 10 can be manufactured, for example, by the manufacturing method S10 as shown in the flow in FIG. 5. As can be seen from FIG. 5, the manufacturing method S10 of the secondary battery includes a liquid injection step S11, a first charging step S12, a high-temperature aging step S13, a sealing step S14, and an inspection step S15. Details will be described below.

[0050] 2.1. Liquid injection process In the liquid injection process S11, an electrolytic solution is injected into the bipolar electrode 13. In the liquid injection process S11, for example, the secondary battery 10 before liquid injection (the resin film 33 is not welded) is placed in the chamber, and a liquid supply device is connected to the liquid injection frame 32. The valve arranged in the liquid supply device is opened, and the inside of the bipolar electrode 13 is evacuated by a vacuum pump through a vacuum evacuation pipe. The valve is closed, and the inside of the chamber is kept in a reduced pressure state. In this state, the valve of the liquid supply pipe is opened, and the electrolytic solution is sent from the recess 32a and the liquid injection port 31 through the through hole into the bipolar electrode 13, and the electrolytic solution is injected into the bipolar electrode 13.

[0051] 2.2. First charging process In the first charging process S12, the first charging is performed. The conditions of the first charging process are not particularly limited and are as known.

[0052] 2.3. High-temperature aging process Next, the high-temperature aging process S13 is performed. The process of high-temperature aging is as known. For example, the secondary battery 10 is conditioned by a procedure such as standing still at 65 °C for 15 hours.

[0053] 2.4. Sealing process In the sealing process S14, the resin film 33 is placed over the injection frame 32 so as to cover the recess 32a formed by the injection frame 32, and the resin film 33 is welded to the surface 32b of the injection frame 32. More specifically, it is as follows.

[0054] FIG. 6 schematically shows a sealing method according to one exemplary embodiment in the sealing process S14. FIG. 6 is a view of the injection frame 32 and the resin film 33 seen from the direction indicated by the arrow B in FIG. 3 (that is, from above). As can be seen from FIG. 6, in the sealing step S14 in this example, the heating element 40 is pressed against the resin film 33 covering the liquid injection frame 32 (pressed in the y-axis direction), and the liquid injection frame 32 and the resin film 33 are welded at the portion sandwiched between the liquid injection frame 32 and the heating element 40. The specific welding conditions are not particularly limited, and the temperature of the heating element 40, the pressing time, and the pressing amount can be set as required. According to the welding method of this example, the welding cost can be kept low.

[0055] In addition, as a sealing step according to another embodiment, the use of a laser can be mentioned. More specifically, after bringing the resin film 33 into contact with the liquid injection frame 32, a laser is irradiated along the liquid injection frame 32 from the resin film 33 side to melt and bond the interface between the resin film 33 and the liquid injection frame 32. The laser used here is not particularly limited, but a laser having a wavelength absorbed by the liquid injection frame and the resin film can be mentioned. According to the welding method of this example, heating of the resin film other than the welded portion can be suppressed, and damage to the resin film can be minimized.

[0056] 2.5. Inspection process In the inspection step S15, the welding state of the welded portion between the liquid injection frame 32 and the resin film 33 obtained in the sealing step S14 is inspected to detect the presence or absence of an un-welded region. Here, the welding state to be inspected is to detect an un-welded region (which may be described as an "unjoined region") at least at the portion where the liquid injection frame 32 and the resin film 33 should be welded. The unjoined region is a portion where bubbles are present or a region larger than the bubbles where welding has not occurred. FIG. 7 shows an example of the unjoined region R by a dotted line. The existence of such an unbonded region increases the possibility of mixing of electrolytes of different cells as described above, which may cause a short circuit and lead to heat generation and ignition. Therefore, in the inspection step S15, an unbonded region exceeding a predetermined level is detected and excluded, and the sealing step S14 is performed again to solve the problem. The predetermined level may be determined based on thresholds such as the total area of the unbonded regions, the number of unbonded regions, and the maximum area of a single unbonded region, which are determined in advance by prior tests or the like.

[0057] In the present disclosure, since the transparent resin film 33 is used as the sealing material, after the sealing step S14, the bonding surface can be visually recognized through the transparent film 33, so that the unbonded region can be easily detected.

[0058] Specific methods for recognizing the unbonded region include a visual method or a method of identifying the unbonded region by image processing of an image obtained by photographing a resin film welded to a cylindrical member (injection frame). Examples of methods for obtaining an image for image processing include photographing with a camera. At that time, polarized light may be irradiated as illumination, and the reflected light may be imaged by the camera through a polarization lens to obtain an image with a desired phase. More specifically, as shown by the arrow C in FIG. 4, the polarized light reaches the bonding surface without being reflected on the surface of the transparent film 33, and the reflected light D whose phase has changed due to diffuse reflection on the bonding surface is photographed by the camera through the polarization lens to obtain an image passing through components other than the specular reflection component. According to this, even in a situation where it is difficult to see the bonding surface due to specular reflection occurring in the transparent film 33, the situation of the bonding surface can be clearly obtained.

[0059] As described above, according to the present disclosure, it is possible to easily check the presence or absence of defects in the bonding between a cylindrical member (injection frame) and a film for sealing, such as voids, and suppress the production of a secondary battery with insufficient sealing as a product.

Explanation of Reference Numerals

[0060] 10... Secondary battery, 11... Current collector plate, 12... Power storage module, 13... Bipolar electrode, 20... Sealing portion, 30... Liquid injection portion, 31... Liquid injection port, 32... Liquid injection frame (cylindrical member), 33... Resin film, 40... Heating element

Claims

1. A method for manufacturing a secondary battery having an electrode, comprising: a liquid injection step of injecting an electrolytic solution into the electrode from a liquid injection port surrounded by a cylindrical member; a sealing step of sealing the opening of the cylindrical member by welding a resin film that is transparent to the cylindrical member; an inspection step of inspecting the welding state between the cylindrical member and the resin film to detect the presence or absence of an un-welded region by a method of visual inspection or by image processing of an image obtained by photographing the resin film welded to the cylindrical member to identify an un-bonded portion; A method for manufacturing a secondary battery.

2. The method for manufacturing a secondary battery according to claim 1, wherein the cylindrical member contains polyethylene and the resin film has a polyethylene layer.

3. The method for manufacturing a secondary battery according to claim 2, wherein the resin film has a polyvinyl alcohol layer and the layer on the side of the cylindrical member is the polyethylene layer.

4. The method for manufacturing a secondary battery according to claim 1 or 2, wherein in the sealing step, the resin film is welded to the cylindrical member by pressing a heating body against the resin film.

5. The method for manufacturing a secondary battery according to claim 1 or 2, wherein in the sealing step, after bringing the resin film into contact with the cylindrical member, a laser having a wavelength absorbed by the cylindrical member and the resin film is irradiated along the cylindrical member from the resin film side to perform the welding.

6. The method for manufacturing a secondary battery according to claim 1 or 2, wherein in the inspection step, the detection is performed by irradiating polarized light onto the welding surface between the cylindrical member and the resin film and receiving the reflected light.

7. A liquid injection port for injecting an electrolytic solution into an electrode; a cylindrical member formed so as to surround the liquid injection port; a transparent resin film covering the opening of the cylindrical member; A secondary battery.

8. The secondary battery according to claim 7, wherein the cylindrical member contains polyethylene and the resin film has a polyethylene layer.

9. The secondary battery according to claim 7, wherein the resin film has a polyvinyl alcohol layer and the layer on the side of the cylindrical member is the polyethylene layer.

Images