Secondary battery manufacturing method and its use

Abstract

To provide a technique that can suppress the size variations of secondary batteries.SOLUTION: A manufacturing method disclosed herein includes: a battery case assembling step of assembling a battery case 10 that houses an electrode body 20 at an inside thereof; a case deforming step at which a gas is injected to the inside of the battery case 10 having been assembled to deform the battery case 10; a liquid injecting step of injecting an electrolytic solution to the inside of the battery case 10; and a sealing step of sealing the battery case 10 on which the liquid injection has been performed. In the case deforming step, an expansion surface 14a is formed on a first side wall 14, and an area of a high expansion area EA where the expansion amount from a reference part 14c is equal to or more than 1 / 2 of a maximum expansion width H is set to be equal to or more than 1 / 3 of the total area of the expansion surface 14a. By doing this, a whole plastic deformation due to an expansion from the inside is induced onto the first side wall 14, so that the size variations of secondary batteries 1 after manufacturing can be suppressed.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The technology disclosed herein relates to a method for manufacturing a secondary battery, a secondary battery, and a battery pack. [Background technology]

[0002] Secondary batteries such as lithium ion secondary batteries are widely used in various fields. For example, the secondary battery has a configuration in which an electrode body and an electrolyte are accommodated in a battery case. At this time, most of the electrolyte permeates the inside of the electrode body. In addition, the battery case of the secondary battery is provided with an electrolyte injection hole for injecting the electrolyte. This electrolyte injection hole is sealed with a sealing member after the electrolyte is injected.

[0003] Patent Document 1 (International Publication No. WO 2018 / 155506) describes a battery module including a plurality of secondary batteries of this type. Specifically, the battery module described in Patent Document 1 includes a plurality of battery cells (secondary batteries) that are stacked and compressed in one direction, and a spacer that is sandwiched between the plurality of battery cells facing the side surfaces of the battery cells, and has a plurality of pressure adjustment parts that are discretely arranged and structurally deformed to press against the side surfaces of the battery cells. This makes it possible to absorb the accumulation of dimensional errors of the battery cells and keep them within a specified dimension. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 155506 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology of absorbing dimensional variations with spacers as described in Patent Document 1 has a limit to the range of dimensional variations that can be absorbed. For this reason, in recent years, there has been a demand for technology that can easily suppress the dimensional variations themselves of secondary batteries. The technology disclosed herein has been made to solve such problems, and aims to provide a technology that can suppress the dimensional variations of secondary batteries. [Means for solving the problem]

[0006] In order to achieve the above object, the technology disclosed herein provides a method for manufacturing a secondary battery having the following configuration (hereinafter, also simply referred to as a "manufacturing method").

[0007] The manufacturing method disclosed herein is a method for manufacturing a secondary battery including an electrode assembly including a positive electrode and a negative electrode, an electrolyte, and a battery case that contains the electrode assembly and the electrolyte. The battery case includes an exterior body including a bottom that is a long rectangular plate-like member, a pair of first side walls extending upward from the long side of the bottom, a pair of second side walls extending upward from the short side of the bottom, an upper opening surrounded by the upper ends of the first side walls and the second side walls, and a sealing plate that seals the upper opening and has an electrolyte injection hole. The manufacturing method disclosed herein includes the following steps: a battery case assembling step of assembling a battery case by sealing the upper opening with a sealing plate in a state in which the electrode assembly is placed inside the exterior body; a case deformation step of injecting gas into the assembled battery case through the electrolyte injection hole to deform the battery case; an electrolyte injection step of injecting electrolyte into the deformed battery case through the electrolyte injection hole; and a sealing step of sealing the electrolyte injection hole of the battery case after electrolyte injection. In the manufacturing method disclosed herein, in the case deformation process, an expansion surface is formed on at least one of a pair of first side walls, with the central portion of the first side wall protruding toward a first direction away from the electrode body, and an apex portion, which is the portion protruding the most from the electrode body in the first direction, and a reference portion, which is the portion protruding the least, are formed within the surface of the expansion surface, and when the protrusion amount from the reference portion to the apex in the first direction is defined as the maximum expansion width H, the area in a front view of the high expansion region, which is a region where the protrusion amount from the reference portion is 1 / 2 or more of the maximum expansion width H, is 1 / 3 or more of the total area of ​​the expansion surface.

[0008] In the manufacturing method disclosed herein, a case deformation step is carried out in which gas is injected into the assembled battery case to deform the battery case. As a result, overall deformation due to expansion from the inside occurs in the first side wall of the battery case, so that dimensional variations in the secondary battery after manufacture can be suppressed. Furthermore, the case deformation step of the manufacturing method disclosed herein is controlled so that the area of ​​the high expansion region where the protrusion amount from the reference surface is equal to or greater than a certain amount is equal to or greater than 1 / 3 of the total area of ​​the expansion surface. As a result, the expansion of the first side exceeds the elastic range and becomes plastic deformation, so that dimensional variations due to shrinkage after the case deformation step can be prevented. [Brief description of the drawings]

[0009] [Figure 1] 1 is a perspective view illustrating a schematic appearance of a secondary battery according to an embodiment; [Diagram 2] 2 is a vertical sectional view showing a schematic internal structure of the secondary battery shown in FIG. [Diagram 3] 1 is a front view showing a schematic external appearance of a secondary battery according to an embodiment; [Figure 4] 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 4 is a cross-sectional view of FIG. [Figure 6] 1 is a flowchart illustrating a manufacturing method according to an embodiment. [Figure 7] FIG. 11 is a perspective view illustrating the connection between the sealing plate and the electrode body in the battery case assembly process. [Figure 8] 5 is a vertical cross-sectional view illustrating gas injection into the battery case during the case deformation process. FIG. [Figure 9] FIG. 4 is a vertical cross-sectional view illustrating the injection of an electrolyte in a liquid injection step. [Figure 10] 1 is a perspective view showing a schematic external appearance of a battery pack according to an embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the technology disclosed herein will be described in detail with reference to the drawings. Note that matters other than those specifically mentioned in this specification and necessary for implementing the technology disclosed herein can be understood as design matters of a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. In addition, in the following drawings, members and parts that perform the same function are described with the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

[0011] In this specification, the term "secondary battery" refers to a general electric storage device that can repeatedly be charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode via an electrolyte. Such "secondary batteries" include so-called storage batteries such as lithium ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, as well as capacitors such as electric double layer capacitors. In other words, the manufacturing method disclosed herein is not limited to a method for manufacturing a specific type of battery, and can be widely applied to the manufacture of general electric storage devices in which an electrode body and an electrolyte are housed in a battery case.

[0012] 1. Structure of secondary batteries First, the structure of the secondary battery according to this embodiment will be described. FIG. 1 is a perspective view showing the external appearance of the secondary battery according to this embodiment. FIG. 2 is a longitudinal sectional view showing the internal structure of the secondary battery shown in FIG. 1. FIG. 3 is a front view showing the external appearance of the secondary battery according to this embodiment. FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3. FIG. 5 is a sectional view taken along the line VV in FIG. 3. In addition, the symbol X in FIGS. 1 to 5 indicates the width direction, the symbol Y indicates the depth direction, and the symbol Z indicates the height direction. Furthermore, the symbols L, R, F, Rr, U, and D indicate the left, right, front, rear, upper, and lower, respectively. However, these directions are determined for the convenience of explanation, and are not intended to limit the installation mode of the secondary battery during use or manufacture.

[0013] 1 and 2, the secondary battery 1 according to this embodiment includes a battery case 10, an electrode assembly 20, and an electrolyte 30. Each member constituting the secondary battery 1 will be specifically described below.

[0014] (1) Battery case The battery case 10 in this embodiment is a box-shaped container having an internal space 10a. The internal space 10a of the battery case 10 accommodates an electrode assembly 20 and an electrolyte 30. As shown in Figs. 1 and 2, the secondary battery 1 according to this embodiment includes a flat rectangular parallelepiped battery case 10. The battery case 10 is preferably a metal member having a certain level of strength or more. Examples of materials for the battery case 10 include aluminum and aluminum alloys. Although it is not intended to limit the technology disclosed herein, the internal volume of the battery case 10 may be 500 cm3 or more. 3 More than 1000cm is preferable. 3 The above is more preferable. Since such a large-capacity secondary battery 1 requires a large amount of electrolyte 30, the effects of the technology disclosed herein are more preferably exhibited. The upper limit of the internal volume of the battery case 10 is not particularly limited, and is not limited to 3000 cm. 3 Less than 1500cm is also acceptable. 3 The technology disclosed herein can be applied to a distance of 300 cm or less. 3 Less than (typically 150cm 3 This can also be applied to small batteries (see below).

[0015] Moreover, the battery case 10 in this embodiment includes an exterior body 12 and a sealing plate 17. Each of the members will be described below.

[0016] (a) Exterior body The exterior body 12 is a flat box-shaped body with an open top. Specifically, the exterior body 12 includes a bottom 13 that is a long rectangular plate-like member, a pair of first side walls 14 extending upward U from a long side 13a (side along the width direction X) of the bottom 13, a pair of second side walls 15 extending upward U from a short side 13b (side along the depth direction Y) of the bottom 13, and a top opening 16 surrounded by the upper ends of the first side walls 14 and the second side walls 15. In other words, the first side walls 14 are side walls with a relatively large area. On the other hand, the second side walls 15 are side walls with a relatively small area. In the battery case 10 having the exterior body 12 with such a configuration, the first side walls 14 are preferentially deformed (expanded) when the internal pressure increases. This makes it possible to easily control the deformation position and deformation amount in the case deformation step S20 described below, and therefore makes it possible to appropriately suppress dimensional variations in the secondary battery 1.

[0017] In addition, the specific dimensions of the exterior body 12 can be appropriately changed as long as the effect of the technology disclosed herein is not significantly impaired. For example, the height (dimension in the height direction Z) of the first side wall 14 is preferably 5 cm or more, more preferably 8 cm or more. The width (dimension in the width direction X) of the first side wall 14 is preferably 20 cm or more, more preferably 25 cm or more. In this way, by forming the first side wall 14 having a certain height and width (i.e., area) or more, the first side wall 14 becomes easier to deform in the case deformation step S20. On the other hand, the upper limit of the height and width of the first side wall 14 is not particularly limited. For example, the height of the first side wall 14 may be 12 cm or less, or 10 cm or less. The width of the first side wall 14 may be 35 cm or less, or 30 cm or less. The aspect ratio (ratio of height to width) of the first side wall 14 is preferably 2 or more, more preferably 3 or more. This makes it easier to deform the first side wall 14. On the other hand, the upper limit of the aspect ratio of the first side wall 14 is not particularly limited, and may be 8 or less, or 5 or less.

[0018] Moreover, the width (dimension in the depth direction Y) of the second side wall 15 is preferably 5 cm or less, and more preferably 4 cm or less. In this way, by narrowing the width of the second side wall 15, deformation of the second side wall 15 can be suitably suppressed. On the other hand, the lower limit of the width of the second side wall 15 is not particularly limited, and may be 1 cm or more, or 3 cm or more. The height (dimension in the height direction Z) of the second side wall 15 is set to the same height as the first side wall 14.

[0019] Moreover, the thickness (dimension in the depth direction Y) of the first side wall 14 is preferably 3 mm or less, more preferably 2 mm or less, and even more preferably 1.5 mm or less. This makes it easier to deform the first side wall 14. On the other hand, from the viewpoint of ensuring the strength of the battery case 10, the thickness of the first side wall 14 is preferably 0.15 mm or more, and more preferably 0.2 mm or more. On the other hand, it is preferable that the bottom 13 and the second side wall 15 are thicker than the first side wall 14. This makes it easier to deform the first side wall 14. The specific thickness of the bottom 13 is preferably 0.5 mm or more, and more preferably 1 mm or more. This makes it possible to suitably suppress the deformation of the bottom 13. On the other hand, in consideration of the weight and material cost of the secondary battery 1, the thickness of the bottom 13 is preferably 4 mm or less, more preferably 3 mm or less, and even more preferably 2.5 mm or less. The thickness (dimension in the width direction X) of the second side wall 15 is preferably 0.15 mm or more, and more preferably 0.2 mm or more, which can suppress deformation of the second side wall 15. On the other hand, in consideration of the weight and material costs of the secondary battery 1, the thickness of the second side wall 15 is preferably 3 mm or less, more preferably 2 mm or less, and even more preferably 1.5 mm or less.

[0020] (b) Sealing plate The sealing plate 17 is a plate-like member that seals the upper opening 16 of the exterior body 12. The sealing plate 17 is provided with an electrolyte injection hole 17a for injecting the electrolyte 30 into the battery case 10. In the secondary battery 1 after manufacture, the electrolyte injection hole 17a is sealed with a sealing member 18. The sealing plate 17 is also preferably thicker than the first side wall 14. This can suppress deformation of the sealing plate 17 in the case deformation step S20. Specifically, the thickness of the sealing plate 17 is preferably 1 mm or more, and more preferably 1.5 mm or more. On the other hand, in consideration of the weight and material cost of the secondary battery 1, the thickness of the sealing plate 17 is preferably 5 mm or less, and more preferably 4 mm or less.

[0021] Further, the sealing plate 17 in this embodiment is formed with a gas exhaust valve 17b. The gas exhaust valve 17b is a thin-walled portion formed to be thinner than other portions of the sealing plate 17. This gas exhaust valve 17b breaks open when the internal pressure of the battery case 10 rises suddenly due to the generation of decomposition gas or the like. This can prevent excessive deformation of the secondary battery 1 during charging and discharging. The thickness of the gas exhaust valve 17b is preferably 0.5 mm or less, more preferably 0.3 mm or less. This allows the gas exhaust valve 17b to operate appropriately when the internal pressure rises during charging and discharging. On the other hand, the lower limit of the thickness of the gas exhaust valve 17b is preferably 0.05 mm or more, more preferably 0.1 mm or more. This can suppress malfunction of the gas exhaust valve 17b in the case deformation step S20.

[0022] A pair of electrode terminals 40 are attached to the sealing plate 17. Each electrode terminal 40 is a structure combining a plurality of conductive members and extends along the height direction Z. A current collecting member 40a constituting the lower end of the electrode terminal 40 is connected to the electrode body 20 inside the battery case 10. As shown in FIG. 4, in this embodiment, each of the pair of electrode terminals 40 has a plurality of current collecting members 40a (three in FIG. 4). Meanwhile, an external terminal 40b constituting the upper end of the electrode terminal 40 is exposed to the outside of the battery case 10. The structure of the electrode terminal 40 can be a structure that can be adopted in a general secondary battery without any particular restrictions, and the technology disclosed herein is not limited thereto, so detailed description will be omitted.

[0023] (2) Electrode body As described above, the electrode body 20 is housed inside the battery case 10. As shown in Fig. 4, in this embodiment, a plurality of electrode bodies 20 (three in Fig. 4) are housed inside the battery case 10. However, the number of electrode bodies 20 is not particularly limited and may be one. Although not shown in the figure, an insulating sheet is disposed between the electrode body 20 and the exterior body 12. This can prevent electrical conduction between the electrode body 20 and the battery case 10.

[0024] The electrode body 20 includes a positive electrode and a negative electrode. The electrode body 20 in this embodiment is a flat wound electrode body. Specifically, the electrode body 20 is formed by winding a laminate formed by stacking long sheet-like positive electrodes and negative electrodes with a separator interposed therebetween. Note that the materials of each member (positive electrode, negative electrode, separator, etc.) constituting the electrode body 20 can be materials that can be used in general secondary batteries without particular restrictions, and detailed explanations are omitted since they do not limit the technology disclosed herein. In addition, the electrode body 20 is housed in the battery case 10 so that its winding axis is along the long side 13a of the bottom 13 of the exterior body 12. Therefore, in the secondary battery 1 according to this embodiment, the flat surface 20a of the electrode body 20 and the first side wall 14 of the exterior body 12 face each other.

[0025] The dimensions of the electrode body 20 are not particularly limited, and are appropriately adjusted in consideration of the relationship between battery performance and production efficiency. Specifically, when the electrode body 20 is made smaller, the excess space in the battery case 10 (internal volume of the battery case - volume of the electrode body) increases, and the amount of liquid injected at one time in the liquid injection step S30 described below can be increased. This contributes to improving production efficiency. From this perspective, the dimensions of the electrode body 20 are set to a value that satisfies the requirement that the excess space in the battery case 10 is 50 cm 3 or more (more preferably 100 cm 3 More preferably, 150 cm 3 On the other hand, if the electrode body 20 is made larger, the battery performance such as the battery capacity can be improved. From this viewpoint, the dimensions of the electrode body 20 are set so that the surplus space in the battery case 10 is 250 cm or more. 3 Less than or equal to 200 cm 3 Less than 170cm, more preferably 3 In the manufacturing method disclosed herein, the battery case 10 is expanded in the case deformation step S20. This increases the internal capacity of the battery case 10, so that the surplus space within the battery case 10 immediately after the battery case assembly step S10 is set to 170 cm 3 High production efficiency can be achieved even in the following cases.

[0026] (3) Electrolyte The electrolyte 30 is accommodated in the battery case 10 together with the electrode assembly 20. Specifically, the electrolyte 30 permeates the inside of the electrode assembly 20 (between the positive and negative electrodes). A part of the electrolyte 30 may be present outside the electrode assembly 20 (between the electrode assembly 20 and the battery case 10) as excess electrolyte 32. This allows the excess electrolyte 32 to be supplied to the inside of the electrode assembly 20 when the electrolyte 30 is decomposed inside the electrode assembly 20. Note that the components of the electrolyte 30 can be any components that can be used in general secondary batteries without any particular restrictions, and detailed description thereof will be omitted since they do not limit the technology disclosed herein.

[0027] (4) Shape of the first side wall Here, in this embodiment, the battery case 10 is expanded in a case deformation step S20 described later. Therefore, as shown in Figs. 3 and 4, in the manufactured secondary battery 1, an expansion surface 14a is formed on a first side wall 14 of the battery case 10. This expansion surface 14a is the first side wall 14 whose central portion protrudes in a first direction (outward in the depth direction Y in Fig. 3) away from the electrode body 20. As will be described in detail later, by causing such expansion deformation during the manufacturing process, dimensional variation of the manufactured secondary battery 1 can be suppressed.

[0028] In the plane of the expansive surface 14a, a top portion 14b is formed, which is a portion that protrudes the most from the electrode body 20 (typically the flat surface 20a of the electrode body 20) in the first direction (depth direction Y). Meanwhile, in the plane of the expansive surface 14a, a reference portion 14c is also formed, which is a portion that protrudes the least from the electrode body 20 in the first direction. As shown by the dashed line in FIG. 3, the reference portion 14c in this embodiment is formed on the outer periphery of the first side wall 14. Since the outer periphery of the first side wall 14 is connected to any one of the bottom 13, the second side wall 15, and the sealing plate 17, expansion deformation due to an increase in internal pressure is unlikely to occur. Therefore, in the secondary battery 1 after manufacture, the reference portion 14c is likely to be formed on the outer periphery of the first side wall 14. Meanwhile, in the secondary battery 1 according to this embodiment, the top portion 14b is formed near the center of the first side wall 14. The vicinity of the center of the first side wall 14 is the part farthest from the outer circumferential edge, and therefore is prone to expansion and deformation due to an increase in internal pressure. For this reason, in the manufactured secondary battery 1, the apex 14b is likely to be formed near the center of the first side wall 14.

[0029] In this specification, the amount of protrusion from the reference portion 14c to the top portion 14b in the first direction (depth direction Y) is referred to as the "maximum expansion width H" (see Figs. 4 and 5). This maximum expansion width H is preferably 1.2 mm or more, more preferably 1.3 mm or more, even more preferably 1.4 mm or more, and particularly preferably 1.5 mm or more. This allows the battery case 10 to be appropriately plastically deformed, and therefore the dimensional variation due to contraction of the battery case 10 can be more suitably prevented. Meanwhile, the maximum expansion width H is preferably 2.0 mm or less, more preferably 1.9 mm or less, even more preferably 1.8 mm or less, and particularly preferably 1.7 mm or less. This allows the strength of the battery case 10 to be suppressed from being reduced due to excessive deformation.

[0030] In this specification, the region where the protrusion amount from the reference portion 14c is 1 / 2 or more of the maximum expansion width H is referred to as the "high expansion region EA". As will be described in detail later, in the manufacturing method according to this embodiment, the first side wall 14 of the battery case 10 is caused to deform overall due to expansion from the inside. Therefore, in the secondary battery 1 after manufacturing, as shown by the dotted line in FIG. 3, the high expansion region EA is formed to be substantially elliptical in front view. The apex 14b, which is the most expanded part, is formed near the center of the high expansion region EA. The aspect ratio of the high expansion region EA is preferably 1.5 or more, more preferably 1.6 or more, even more preferably 1.8 or more, and particularly preferably 2 or more. This allows the battery case 10 to be appropriately plastically deformed. On the other hand, the upper limit of the aspect ratio of the high expansion region EA is not particularly limited, and may be 5 or less, 4 or less, or 3 or less. In this specification, the aspect ratio of the high expansion region EA is the ratio of the long axis length to the short axis length of the high expansion region EA.

[0031] 2. Manufacturing method of secondary batteries Next, a method for manufacturing the secondary battery 1 having the above configuration will be described. Fig. 6 is a flow chart for explaining the manufacturing method according to this embodiment. Fig. 7 is a perspective view for explaining the connection between the sealing plate and the electrode body in the battery case assembly process. Fig. 8 is a perspective view for explaining the injection of gas into the battery case in the case deformation process. Fig. 9 is a perspective view for explaining the injection of electrolyte in the electrolyte injection process.

[0032] 6, the manufacturing method according to this embodiment includes at least a battery case assembly step S10, a case deformation step S20, a liquid injection step S30, and a sealing step S40. Each step will be described below.

[0033] (1) Battery case assembly process S10 In this step, the upper opening 16 is sealed with the sealing plate 17 while the electrode body 20 is disposed inside the exterior body 12, and the battery case 10 is assembled. An example of a specific procedure of this step is as follows. First, as shown in FIG. 7, the current collecting member 40a of the electrode terminal 40 is connected to each of the multiple electrode bodies 20. This integrates the sealing plate 17 and the electrode body 20. In this state, the electrode body 20 is inserted into the interior of the exterior body 12 from the upper opening 16. Then, the electrode body 20 and the sealing plate 17 are further lowered, so that the upper opening 16 of the exterior body 12 is closed with the sealing plate 17. Next, the upper ends of the first side wall 14 and the second side wall 15 of the exterior body 12 are joined to the outer periphery of the sealing plate 17. This constructs a battery case 10 in which the electrode body 20 is accommodated in the internal space 10a. Note that, for joining the sealing plate 17 to the exterior body 12, a conventionally known joining means can be used without any particular restrictions. A suitable example of such a joining means is laser welding.

[0034] Here, the exterior body 12 and the sealing plate 17 supplied to this process usually have dimensional variations due to manufacturing tolerances. In addition, the exterior body 12 and the sealing plate 17 may be slightly deformed due to external force or heat when assembling various components in this process. For this reason, the battery case 10 constructed in this process has dimensional variations of a certain level or more. If the dimensional variations of the battery case 10 become too large, the binding pressure during construction of the battery pack becomes non-uniform, which may cause a decrease in battery performance.

[0035] (2) Case deformation process S20 In the manufacturing method according to the present embodiment, a case deformation step S20 is performed to eliminate the dimensional variation of the battery case 10. In this case deformation step S20, gas is injected into the assembled battery case 10 through the electrolyte injection hole 17a to deform the battery case 10. As a result, the first side wall 14 of the battery case 10 expands to form the expansion surface 14a. As an example, a gas supply means G as shown in FIG. 8 is used in this step. The gas supply means G includes a supply port G1 and a gas generation source G2. The supply port G1 is configured so as to be able to seal the inside of the battery case 10 when attached to the electrolyte injection hole 17a. Meanwhile, various devices (such as a compressor or a gas cylinder) that generate high-pressure gas are used for the gas generation source G2. Then, in this step, the supply port G1 is attached to the electrolyte injection hole 17a, and the gas generation source G2 is operated. As a result, the case internal pressure increases, and the first side wall 14 is expanded and deformed overall. This allows the battery cases 10 to be deformed to a degree that exceeds the dimensional variation that occurs in the battery case assembly step S10, thereby allowing the secondary batteries 1 to have a uniform shape after production.

[0036] However, according to the study of the present inventor, if the amount of deformation in this step is too small, the amount of deformation of the first side wall 14 cannot exceed the elastic range, and the battery case 10 may shrink after the end of this step. In this case, the battery case 10 returns to the shape before gas injection, so that the dimensional variation of the battery case 10 before gas injection remains. In contrast, in the manufacturing method according to the present embodiment, the amount of deformation of the battery case 10 in the case deformation step S20 is controlled as follows so that the expansion of the first side wall 14 exceeds the elastic range and becomes plastic deformation. The control of the amount of deformation in the case deformation step S20 described below can be performed, for example, by detecting the shape of the battery case 10 after injecting a predetermined amount of gas into the battery case 10 and adjusting the amount of gas injection based on the detection result. If the detected amount of deformation of the battery case 10 satisfies the desired range, it is not necessary to adjust the amount of gas injection.

[0037] Specifically, in the manufacturing method according to the present embodiment, the area of ​​the high expansion region EA in a front view (see FIG. 3) is set to be 1 / 3 or more of the total area of ​​the expansion surface 14a. When the high expansion region EA is deformed to form a certain amount of high expansion region EA in this way, the expansion of the first side wall 14 exceeds the elastic range and becomes plastic deformation. This can prevent dimensional variations due to contraction of the battery case 10 after this process. It is more preferable that the ratio of the area of ​​the high expansion region EA to the total area of ​​the expansion surface 14a is 1 / 2 or more. This can more suitably cause plastic deformation of the first side wall 14. On the other hand, the upper limit of the ratio of the area of ​​the high expansion region EA to the total area of ​​the expansion surface 14a is not particularly limited, and may be 4 / 5 or less, 3 / 4 or less, or 2 / 3 or less.

[0038] The deformation amount in the case deformation step S20 is preferably set so that the inclination angle θ1 of the expansion surface 14a along the height direction Z is equal to or greater than a certain value. This allows the plastic deformation of the first side wall 14 to occur more appropriately. Specifically, FIG. 4 is a cross-sectional view along the up-down direction (height direction Z) passing through the center of the long side direction (width direction X) of the first side wall 14 in FIG. 3. When checking FIG. 4, it is preferable that the inclination angle θ1 of the expansion surface 14a in the region 1 cm downward from the lower surface 17c of the sealing plate 17 is 3° or more (more preferably 4° or more, even more preferably 5° or more, and particularly preferably 6° or more). By expanding the first side wall 14 so as to generate such an inclination angle θ1, the contraction of the battery case 10 after the case deformation step S20 can be more preferably prevented. On the other hand, from the viewpoint of suppressing a decrease in the strength of the battery case 10 due to excessive deformation, the upper limit value of the inclination angle θ1 is preferably 10° or less, more preferably 9° or less, more preferably 8° or less, and more preferably 7° or less.

[0039] Similarly, the deformation amount in the case deformation step S20 is preferably set so that the inclination angle θ2 of the expansion surface 14a along the width direction X is equal to or greater than a certain value. This allows the plastic deformation of the first side wall 14 to occur more appropriately. Specifically, FIG. 5 is a cross-sectional view along the long side direction (width direction X) passing through the center of the up-down direction (height direction Z) of the first side wall 14 in FIG. 3. When checking FIG. 5, it is preferable that the inclination angle θ2 of the expansion surface 14a in the region 2.3 mm inward from the boundary between the first side wall 14 and the second side wall 15 is 0.5° or more (more preferably 1° or more, even more preferably 1.5° or more, and particularly preferably 2° or more). By expanding the first side wall 14 so as to generate such an inclination angle θ2, the contraction of the battery case 10 after the case deformation step S20 can be more appropriately prevented. On the other hand, from the viewpoint of preventing a decrease in strength of the battery case 10 due to excessive deformation, the upper limit of the inclination angle θ2 is preferably 5° or less, more preferably 4.5° or less, more preferably 4° or less, and more preferably 3.5° or less.

[0040] In addition, the internal volume of the battery case 10 after the case deformation step S20 is increased. This increases the amount of electrolyte injected at one time in the electrolyte injection step S30, which will be described later, and contributes to a significant improvement in manufacturing efficiency. Considering the increase in the amount of electrolyte injected at this step S30, the increase in internal volume is about 40 cm 3 More than 70cm (preferably 3 More preferably, 100 cm 3 It is preferable to carry out the expansion so that the internal volume is increased by 200 cm or more. This contributes to a significant improvement in manufacturing efficiency. Furthermore, when such a large expansion is caused, plastic deformation of the battery case 10 is likely to occur, and dimensional variations after manufacturing can be suitably suppressed. On the other hand, it is preferable that the increase in the internal volume is set within a range that can prevent damage to the battery case 10 (gas release valve 17b, the joint between the sealing plate 17 and the exterior body 12, etc.). Specifically, the upper limit of the increase in the internal volume is set to 200 cm. 3 Less than 150cm is preferable. 3 Less than 120cm is preferable. 3 The following are particularly preferred:

[0041] The pressure of the gas supplied to the battery case 10 is preferably 0.03 MPa or more, more preferably 0.05 MPa or more, and particularly preferably 0.10 MPa or more. This allows the battery case 10 to be appropriately plastically deformed. On the other hand, the upper limit of the gas pressure is preferably 0.20 MPa or less, more preferably 0.15 MPa or less, and particularly preferably 0.12 MPa or less. This allows the battery case 10 to be prevented from being damaged. In addition, the gas supply time is preferably 5 seconds or more, more preferably 10 seconds or more, and even more preferably 12 seconds or more. This allows the battery case 10 to be appropriately plastically deformed. On the other hand, from the viewpoint of shortening the manufacturing time, the gas supply time is preferably 30 seconds or less, and more preferably 20 seconds or less. However, these gas pressures and supply times are appropriately changed depending on the strength and content of the battery case 10, and do not limit the technology disclosed herein. A person generally skilled in the art can easily analyze the gas supply conditions under which the area of ​​the high expansion region EA is equal to or greater than 1 / 3 of the total area of ​​the expansion surface 14a by performing multiple preliminary tests. The gas used in this step is not particularly limited as long as it does not significantly impair the performance of the secondary battery 1 after manufacture. Examples of such gases include air, helium gas, nitrogen gas, and argon gas. In addition, from the viewpoint of suppressing performance degradation due to the inclusion of moisture, it is preferable to perform a drying process on the gas before supplying it to the battery case 10.

[0042] When the flat battery case 10 described above is used, the first side wall 14, which has a relatively large area, expands preferentially, so that the position and amount of deformation in this process can be managed. According to an experiment conducted by the present inventor, it has been confirmed that the apex 14b is formed in a portion of the expanding surface 14a after deformation slightly above the central portion in the height direction Z. Specifically, when the height dimension of the first side wall 14 is 100%, the expanding surface 14a is formed with the apex 14b located within a range of 50.5% to 52.5% (for example, at a position of about 51%) from the lower end of the first side wall 14. It has also been confirmed that when the flat battery case 10 is expanded, the second side wall 15, which has a relatively small area, is slightly recessed toward the inside of the battery case 10.

[0043] (3) Liquid injection process S30 In this step, the electrolyte 30 is injected into the deformed battery case 10 through the electrolyte injection hole 17a. As an example, in this step, the electrolyte 30 is injected according to the following procedure. First, as shown in FIG. 9, the injection nozzle P is inserted into the electrolyte injection hole 17a. Then, the electrolyte 30 is injected into the battery case 10 from the injection nozzle P. At this time, the electrolyte 30 is injected in a plurality of times while permeating the inside of the electrode body 20 so that the electrolyte 30 does not spurt out from the electrolyte injection hole 17a. At this time, if the battery case 10 is expanded in the case deformation step S20, the amount of electrolyte that can be supplied in one injection increases. As a result, the number of injections of the electrolyte 30 in this step is reduced, which can contribute to a significant improvement in manufacturing efficiency.

[0044] In addition, in the liquid injection step S30, a decompression process may be performed to reduce the pressure inside the battery case 10. As a result, the inside of the electrode body 20 (between the positive and negative electrodes) becomes negative pressure. When the electrolyte solution 30 is injected in this state, the electrolyte solution 30 is sucked into the inside of the electrode body 20, which has become negative pressure. This can shorten the time required for the electrolyte solution 30 to penetrate. Note that the decompression process in the manufacturing method according to this embodiment is performed in a state in which the battery case 10 is accommodated in a decompression chamber D as shown in FIG. 9. This can prevent the battery case 10 from shrinking due to the pressure difference between the inside and outside of the battery case 10, and can prevent dimensional variations from occurring in the battery case 10 after the liquid injection step S30.

[0045] The internal pressure of the battery case 10 during the decompression treatment is preferably -50 kPa or less, more preferably -80 kPa or less. This allows the permeation time of the electrolyte solution 30 to be suitably shortened. On the other hand, when the inside of the decompression chamber D is decompressed, the lower limit of the pressure during the decompression treatment is not particularly limited as long as the decompression chamber D is not damaged. For example, the lower limit of the pressure inside the decompression chamber D may be -100 kPa or more. The decompression treatment is not essential in the liquid injection step S30. For example, when an electrode body (such as a laminated electrode body) into which the electrolyte solution easily permeates is used, the electrolyte solution may be injected under an atmospheric pressure environment without the decompression treatment.

[0046] (4) Sealing process S40 In this step, the electrolyte injection hole 17a of the battery case 10 after injection is sealed. This results in the secondary battery 1 (see FIG. 1) in which the electrode body 20 and electrolyte 30 are accommodated in the sealed battery case 10. The sealing member 18 for sealing the electrolyte injection hole 17a is not limited to the technology disclosed herein, and any conventionally known member can be used without particular restriction. An example of the sealing member 18 is a blind rivet. In addition, after sealing the electrolyte injection hole 17a with the sealing member 18, the sealing member 18 may be welded to the battery case 10 (sealing plate 17). This allows the sealing member 18 to be fixed more firmly.

[0047] (5) Summary As described above, in the manufacturing method according to the present embodiment, a case deformation step S20 is performed in which gas is injected into the assembled battery case 10 to deform the battery case 10. As a result, an overall deformation due to expansion from the inside occurs in the first side wall 14 of the battery case 10, so that dimensional variations in the secondary battery 1 after manufacture can be suppressed. Furthermore, in the case deformation step S20 in this embodiment, gas is injected into the battery case 10 so that the area of ​​the high expansion region EA is ⅓ or more of the total area of ​​the expansion surface 14a. As a result, the expansion of the first side wall 14 exceeds the elastic range and becomes plastic deformation, so that dimensional variations due to contraction after the case deformation step S20 can be prevented.

[0048] 3. Battery pack Next, the manufacturing method according to this embodiment can contribute to improving the performance of a battery pack 100 including a plurality of secondary batteries. Fig. 10 is a perspective view showing a typical appearance of the battery pack according to this embodiment. A specific description will be given below with reference to Fig. 10.

[0049] As shown in FIG. 10, the battery pack 100 according to this embodiment includes a plurality of cells 110. The cells 110 are arranged such that the first side walls 14 (see FIG. 1) of the battery case 10 face each other. A spacer 120 is disposed between two adjacent cells 110. The cells 110 are sandwiched between a pair of restraining plates 130. The pair of restraining plates 130 are connected by a bridging member 140 extending along the arrangement direction (depth direction Y in FIG. 10). As a result, each cell 110 is restrained at a predetermined restraining pressure. The battery pack 100 shown in FIG. 10 includes a connecting member 150 that electrically connects the cells 110 to each other. The connecting member 150 connects the electrode terminals 40 of the adjacent cells 110. As a result, the battery pack 100 including the cells 110 can be used as one battery unit.

[0050] In the battery pack 100 according to the present embodiment, the secondary battery 1 having the above configuration is used for 90% or more of the cells 110. In other words, 90% or more of the cells 110 in the present embodiment are secondary batteries 1 in which the expansion surface 14a is formed on the first side wall 14, and the area of ​​the high expansion area EA of the expansion surface 14a is 1 / 3 or more of the total area of ​​the expansion surface 14a. This allows the cells 110 constituting the battery pack 100 to have the same shape, so that a uniform binding pressure can be applied to each of the cells 110. As a result, the battery pack 100 according to the present embodiment can exhibit high performance as a whole battery unit. Note that, according to the manufacturing method according to the present embodiment, the secondary battery 1 having the above configuration can be used for all (100%) of the cells 110 constituting the battery pack 100. Since there is almost no dimensional variation between the cells 110, the battery pack 100 can exhibit particularly high battery performance. Moreover, the technology disclosed herein is particularly suitable for application to a battery pack 100 having 20 or more cells 110 (more preferably 40 or more, even more preferably 60 or more, and particularly preferably 80 or more). According to the technology disclosed herein, even in a battery pack 100 having a very large number of cells 110, the cells 110 can easily have the same shape.

[0051] 4. Other embodiments An embodiment of the manufacturing method disclosed herein has been described above. Note that the manufacturing method disclosed herein is not limited to the above embodiment, and various aspects can be modified as appropriate. An example of an aspect that can be modified from the above embodiment will be described below.

[0052] (1) Drying process The manufacturing method disclosed herein may include steps other than the four steps S10 to S40 shown in FIG. 6. For example, a drying step for drying the electrode body in the battery case may be performed after the battery case assembly step S10 is performed and before the electrolyte injection step S30 is started. This can prevent performance degradation (capacity reduction, output reduction, etc.) caused by moisture entering the electrode body. In the drying step, it is preferable to perform heating while reducing the pressure inside the battery case. This can efficiently remove moisture inside the electrode body. For example, the heating temperature in the drying step is preferably 80° C. or higher, more preferably 90° C. or higher, and particularly preferably 100° C. or higher. This can suitably remove moisture inside the electrode body. In addition, the heating temperature is preferably 200° C. or lower, more preferably 150° C. or lower, and particularly preferably 120° C. or lower. This can suppress deterioration of resin members (separator, insulating film, etc.). In addition, the pressure inside the battery case during the drying step is preferably reduced to -6 Pa to -10 Pa. This allows the evaporated water to be easily removed.

[0053] As described above, the drying step can be performed without any particular restrictions as long as it is performed after the battery case assembly step S10 is performed and before the electrolyte injection step S30 is started. In consideration of maintaining the shape of the battery case 10, the drying step is preferably performed before the case deforming step S20. Specifically, in the drying step, a pressure drop due to a decompression process and a pressure increase due to evaporation of water may occur, which may cause deformation of the battery case 10. In contrast, if the case deforming step S20 is performed after the drying step, deformation that exceeds the dimensional variation caused in the drying step can be caused in the battery case 10, and the shape of the battery case 10 can be easily made uniform.

[0054] (2) Initial charging process In the manufacturing method disclosed herein, an initial charging step may be performed between the injection step S30 and the sealing step S40. In this initial charging step, an external charging device is connected to the electrode terminal 40 with the electrolyte injection hole 17a open, and charging is performed up to a predetermined voltage at room temperature (for example, about 20°C to 30°C). As a result, a part of the electrolyte 30 decomposes and a large amount of decomposition gas is generated. By performing this initial charging before the sealing step S40, it is possible to prevent the gas release valve from operating during the initial charging. In addition, if the initial charging is performed after the sealing step S40, the first side wall 14 of the battery case 10 may further expand due to an increase in internal pressure caused by the generation of decomposition gas. Since there is an individual difference in the amount of gas generated at this time, performing the initial charging with the electrolyte injection hole 17a sealed may cause dimensional variations in the secondary battery 1 after production. From this viewpoint as well, it is preferable to perform the initial charging step before the sealing step S40 in which the electrolyte injection hole 17a is sealed. The charging conditions in the initial charging step are not particularly limited and can be changed as appropriate according to the specifications of the target (secondary battery). In addition, when the initial charging step is performed, it is preferable to perform a decompression process before performing the sealing step S40. This allows the decomposition gas generated in the initial charging step to be more appropriately exhausted.

[0055] (3)Leak inspection process In the manufacturing method disclosed herein, it is preferable to perform a leak inspection process after the case deformation process S20 is performed and before the sealing process S40 is started (preferably immediately after the case deformation process S20). This makes it possible to detect damage to the battery case (such as the gas exhaust valve and the joint between the sealing plate and the exterior body) caused by the case deformation process S20. An example of a specific procedure for the leak inspection process is as follows. In the leak inspection process, first, a test gas for leak inspection (e.g., helium gas) is filled into the battery case. Then, an inspection device that detects the test gas is used to inspect leakage of the test gas from inside the battery case. This makes it possible to inspect the presence or absence of damage to the battery case and the location of the damage. Note that the leak inspection process can also be included in the case deformation process S20 described above. Specifically, the case deformation process S20 may use the test gas as the gas to be injected into the battery case, and may deform the battery case while inspecting leakage of the test gas with the inspection device. This makes it possible to expand the battery case while checking the presence or absence of damage.

[0056] (4) Target for forming the expansive surface As shown in FIG. 4 and FIG. 5, in the secondary battery 1 according to the above embodiment, the expansion surface 14a is formed on both of the pair of first side walls 14. However, the expansion surface in the technology disclosed herein may be formed on only one of the pair of first side walls. For example, in the case deformation step S20, if gas is injected into the battery case while a plate-shaped deformation restricting member is pressed against one of the first side walls, the expansion surface can be formed on only one of the pair of first side walls. According to this aspect, it is possible to cause appropriate plastic deformation in the first side wall to be deformed while suppressing an increase in the dimension of the battery case in the depth direction Y. On the other hand, in consideration of the improvement in manufacturing efficiency due to the increase in the internal volume of the battery case 10, it is preferable to form the expansion surface 14a on both of the first side walls 14 as in the above embodiment.

[0057] The embodiments of the technology disclosed herein have been described above. However, the above description is merely an example and does not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples exemplified in the above description.

[0058] That is, the technology disclosed herein encompasses the technologies described in the following [Item 1] to [Item 8].

[0059] [Item 1] A method for manufacturing a secondary battery including an electrode assembly including a positive electrode and a negative electrode, an electrolyte, and a battery case that accommodates the electrode assembly and the electrolyte, comprising: The battery case is an exterior body including a bottom portion which is a long rectangular plate-like member, a pair of first side walls which extend upward from a long side of the bottom portion, a pair of second side walls which extend upward from a short side of the bottom portion, and an upper surface opening which is surrounded by upper ends of the first side walls and the second side walls; a sealing plate that seals the upper opening and has an electrolyte injection hole; Including, Here, the steps are as follows: a battery case assembling step of assembling the battery case by sealing the top opening with the sealing plate in a state where the electrode body is disposed inside the exterior body; a case deformation step of injecting a gas into the assembled battery case through the electrolyte injection hole to deform the battery case; a liquid injection step of injecting the electrolyte into the deformed interior of the battery case through the electrolyte injection hole; a sealing step of sealing the electrolyte injection hole of the battery case after the electrolyte injection; Inclusive of In the case deformation process, At least one of the pair of first side walls has an expansive surface formed thereon, the expansive surface protruding in a first direction in which a central portion of the first side wall is separated from the electrode body; Within the expansive surface, a top portion that is a portion that protrudes the most from the electrode body in the first direction and a reference portion that is a portion that protrudes the least in the first direction are formed, and A method for manufacturing a secondary battery, wherein when a protrusion amount from the reference portion to the top in the first direction is defined as a maximum expansion width H, an area of ​​a high expansion region, which is a region whose protrusion amount from the reference portion is 1 / 2 or more of the maximum expansion width H, in a front view is 1 / 3 or more of the total area of ​​the expansion surface.

[0060] [Item 2] 2. The manufacturing method according to item 1, wherein the first side wall has a height of 5 cm or more and a width of 20 cm or more.

[0061] [Item 3] 3. The manufacturing method according to item 1 or 2, wherein the case deformation step is controlled so that an aspect ratio of the high expansion region in a front view is 2 or more.

[0062] [Item 4] 4. The manufacturing method according to any one of items 1 to 3, wherein the case deforming step is controlled so that an inclination angle of the expansive surface in a region 1 cm downward from the underside of the sealing plate in a cross section along the up-down direction passing through a center in a long side direction of the first side wall is 5° or more.

[0063] [Item 5] 5. The manufacturing method according to any one of items 1 to 4, wherein the case deformation step is controlled so that an inclination angle of the expansive surface in a region extending 2.3 mm inward from a boundary between the first side wall and the second side wall is 1° or more in a cross section along a long side direction passing through a center in a vertical direction of the first side wall.

[0064] [Item 6] An electrode assembly including a positive electrode and a negative electrode; An electrolyte; a battery case that accommodates the electrode assembly and the electrolyte; A secondary battery comprising: The battery case is an exterior body including a bottom portion which is a long rectangular plate-like member, a pair of first side walls which extend upward from a long side of the bottom portion, a pair of second side walls which extend upward from a short side of the bottom portion, and an upper surface opening which is surrounded by upper ends of the first side walls and the second side walls; a sealing plate that seals the top opening; Including, At least one of the pair of first side walls has an expansive surface formed thereon, the expansive surface protruding in a first direction in which a central portion of the first side wall is separated from the electrode body; Within the expansive surface, a top portion that is a portion that protrudes the most from the electrode body in the first direction and a reference portion that is a portion that protrudes the least in the first direction are formed, and A secondary battery, wherein when the protrusion amount from the reference portion to the top in the first direction is defined as a maximum expansion width H, the area of ​​a high expansion region in a front view, which is a region in which the protrusion amount from the reference portion is 1 / 2 or more of the maximum expansion width H, is 1 / 3 or more of the total area of ​​the expansion surface.

[0065] [Item 7] 7. The secondary battery according to item 6, wherein the first side wall has a height of 5 cm or more and a width of 20 cm or more.

[0066] [Item 8] 8. The secondary battery according to item 6 or 7, wherein the high expansion region has an aspect ratio of 2 or more when viewed from the front.

[0067] [Item 9] 9. The secondary battery according to any one of items 6 to 8, wherein in a cross section along the up-down direction passing through a center in the long side direction of the first side wall, an inclination angle of the expansive surface in a region extending 1 cm downward from the lower surface of the sealing plate is 5° or more.

[0068] [Item 10] 10. The secondary battery according to any one of items 6 to 9, wherein in a cross section along a long side direction passing through a center in a vertical direction of the first side wall, an inclination angle of the expansive surface in a region extending 2.3 mm inward from a boundary between the first side wall and the second side wall is 1° or more.

[0069] [Item 11] A plurality of batteries; a connection member that electrically connects each of the plurality of unit cells; Equipped with 11. A battery pack, in which 90% or more of the plurality of single cells are the secondary battery according to any one of items 6 to 10. [Explanation of symbols]

[0070] 1 Secondary battery 10 Battery case 10a Internal space 12 Exterior body 13 Bottom 14 First side wall 14a Expansion surface 14b Top 14c Reference section 15 Second side wall 16 Top opening 17 Sealing plate 17a Electrolyte injection hole 17b Gas exhaust valve 18 Sealing member 20 Electrode body 30 Electrolyte 32 Excess electrolyte 40 electrode terminal 40a Current collecting member 40b External terminal EA high expansion area H Maximum expansion width

Claims

1. A method for manufacturing a secondary battery including an electrode assembly including a positive electrode and a negative electrode, an electrolyte, and a battery case that accommodates the electrode assembly and the electrolyte, comprising: The battery case is an exterior body including a bottom portion which is a long rectangular plate-like member, a pair of first side walls which extend upward from a long side of the bottom portion, a pair of second side walls which extend upward from a short side of the bottom portion, and an upper surface opening which is surrounded by upper ends of the first side walls and the second side walls; a sealing plate that seals the upper opening and has an electrolyte injection hole; Including, Here, the steps are as follows: a battery case assembling step of assembling the battery case by sealing the top opening with the sealing plate in a state where the electrode body is disposed inside the exterior body; a case deformation step of injecting a gas into the assembled battery case through the electrolyte injection hole to plastically deform the battery case; a liquid injection step of injecting the electrolyte into the inside of the battery case after the plastic deformation through the electrolyte injection hole; a sealing step of sealing the electrolyte injection hole of the battery case after the electrolyte injection; Inclusive of In the case deformation process, At least one of the pair of first side walls is formed with an expansive surface that protrudes in a first direction in which a central portion of the first side wall is separated from the electrode body, A top portion, which is a portion that protrudes the most from the electrode body in the first direction, and a reference portion, which is a portion that protrudes the least from the electrode body in the first direction, are formed within the expansive surface; and A method for manufacturing a secondary battery, wherein when a protrusion amount from the reference portion to the top in the first direction is defined as a maximum expansion width H, an area of ​​a high expansion region, which is a region whose protrusion amount from the reference portion is equal to or more than 1 / 2 of the maximum expansion width H, in a front view is equal to or more than 1 / 3 of the total area of ​​the expansion surface.

2. The method of claim 1 , wherein the first side wall has a height of at least 5 cm and a width of at least 20 cm.

3. The manufacturing method according to claim 1 or 2, wherein the case deformation step is controlled so that an aspect ratio of the high expansion region in a front view is 2 or more.

4. 3. The manufacturing method according to claim 1, wherein the case deformation step is controlled so that an inclination angle of the expansion surface in a region extending 1 cm downward from the underside of the sealing plate in a cross section along a vertical direction passing through a center of a long side direction of the first side wall is 5° or more.

5. 3. The manufacturing method according to claim 1, wherein the case deformation process is controlled so that an inclination angle of the expansion surface in a region extending 2.3 mm inward from a boundary between the first side wall and the second side wall in a cross section along a long side direction passing through a vertical center of the first side wall is 1° or more.

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