Secondary battery and method for manufacturing a secondary battery

Abstract

The goal is to increase the voltage resistance of secondary batteries while also making them smaller. [Solution] A secondary battery comprising a resin cell case 20 consisting of a box-shaped case body 30 having an opening and a lid 40, wherein the case body 30 has a boss portion 36 having a through portion 38 that penetrates the lid 40 and a head having an outer diameter larger than the through portion 38, the lid 40 has a boss hole 41 through which the boss portion 36 penetrates, the boss hole 41 has a seat portion 42 in which the head is housed on the outside of the lid 40, and a sealing material 28 is provided between the head and the seat portion 42, and the exposed joint portion 27 between the lid 40 and the case body 30 is welded to be airtight. Thus, mechanical strength and airtightness are ensured by different configurations. Despite being small and made of resin, it can withstand high internal pressure on its own.

Description

TECHNICAL FIELD

[0001] The present invention relates to a secondary battery and a method for manufacturing the secondary battery, and more particularly, to a secondary battery provided with a miniaturized resin cell case and a method for manufacturing the secondary battery.

BACKGROUND ART

[0002] Conventionally, in secondary batteries for driving electric vehicles and hybrid vehicles, a large number of secondary battery cells are used in combination to obtain a high voltage. At this time, in order to suppress expansion and contraction of the battery cells, a plurality of high-strength metal plate-shaped secondary battery cells are stacked and assembled into a battery module using a restraint or the like. Such a battery module is housed in a case and mounted on a vehicle as a driving battery pack.

[0003] However, such a battery module requires a separate restraint or the like in addition to the battery cells, so additional components are necessary. This reduces the energy density of the battery pack. In addition, a metal cell case leads to an increase in weight. Furthermore, there are problems such as an increase in manufacturing cost.

[0004] Accordingly, Cell-to-Pack, in which battery cells are directly used as a battery pack, has been proposed. For such secondary batteries, lightweight resin cells are desirable. In addition, despite being made of resin, high airtightness and high strength to withstand increases in internal pressure and the like are required. Moreover, compact cells are desirable.

[0005] Therefore, Patent Document 1 describes the following invention. Figure 21 is a diagram showing a conventional resin energy storage cell. As shown in Figure 21, a rectangular element is fabricated in which a pair of polarizable electrodes 102a and 102b face each other via a separator 103. This element is impregnated with an electrolyte and housed in a rectangular case 104 and a top cover 105. A gasket 106 placed between the case 104 and the top cover 105 is sealed by heat crimping. A pair of terminals 107a and 107b are joined to the case 104 and the top cover 105 to fabricate an energy storage cell 101. After covering this energy storage cell 101 in a rectangular shape with an outer resin 108, the pair of terminals 107a and 107b are bent along the circumferential surface of the outer resin 108 and placed on the mounting surface, thereby enabling the arrangement of a large-area element in a small mounting area and achieving miniaturization and high capacity. Furthermore, high sealing performance can be obtained by sealing the gasket 106 between the case 104 and the top cover 105 by heat crimping, and then covering the energy storage cell 101 with the outer resin 108. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-66687 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the invention disclosed in Patent Document 1, the case 104 housing the pair of polarizing electrodes 102a and 102b has a gasket 106 joined by heat crimping to increase pressure resistance, and is further covered with an outer resin 108 to improve airtightness. For this reason, it could not be said that it was sufficiently miniaturized.

[0008] The problem that the present invention aims to solve with a secondary battery and a method for manufacturing a secondary battery is to increase the voltage resistance and make it more compact. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a secondary battery comprising a cell case made of thermoplastic resin, which consists of a box-shaped case body having an opening and a lid that seals the opening, wherein the case body has a boss portion having a through portion that penetrates the lid and a head portion having a larger outer diameter than the through portion that is continuous with the through portion and exposed to the outside of the cell case, the lid has a boss hole through which the boss portion penetrates, the boss hole has a seat portion that accommodates the head portion of the boss portion on the outside of the lid, and a sealing material is provided between the head portion and the seat portion to airtightly seal the head portion and the seat portion, and the exposed joint between the lid and the case body is welded together so as to be airtight.

[0010] The head has a tapered portion whose outer diameter increases toward the outside of the cell case, and the boss hole may have a seat portion corresponding to the tapered shape of the head. The head portion has a large-diameter section that is continuous with the tapered section and has an outer diameter larger than the maximum outer diameter of the tapered section, and the seat portion may have a shape corresponding to the shape of the head portion.

[0011] The boss portion is positioned on the periphery of the head and has a projection that protrudes from the periphery toward the interior of the cell case, the seat portion of the lid has a projection housing portion which is a space corresponding to the shape of the projection, and the sealing material may be positioned between the projection and the lid to airtightly seal the projection and the lid.

[0012] The protruding portion of the head may have a winding portion at its end facing inward towards the cell case, which protrudes in an annular shape in the direction of the central axis of the boss portion, and the protruding portion housing portion may have a winding portion housing portion which is a space corresponding to the shape of the winding portion of the head.

[0013] The upper end of the head may be positioned in the same plane as the lid. Alternatively, the upper end of the head may be covered by the lid. Furthermore, the present invention relates to a method for manufacturing a secondary battery comprising a resin cell case consisting of a box-shaped case body having an opening and a lid that seals the opening, wherein the case body has a boss portion that penetrates the lid, the lid has a boss hole through which the boss portion penetrates and a seat portion on the outside of the lid with an inner diameter larger than the inner diameter of the boss hole, and is provided with a sealing material that is placed on the seat portion to provide an airtight seal, the lid is assembled to the case body by passing the boss portion through the boss hole, the tip of the boss portion protruding from the boss hole is heat-crimped, and the seat portion is filled with molten resin via the sealing material to form a head with an outer diameter larger than the outer diameter of the shaft portion, and the exposed joint between the lid and the case body is welded to provide an airtight seal.

[0014] The exposed joint between the lid and the case body may be sealed by hermetically welding using a laser welding machine. The seat portion has a tapered portion forming part that has a tapered shape in which its outer diameter increases toward the outside of the cell case, and by heat crimping, a tapered portion that has a tapered shape in which its outer diameter increases toward the outside of the cell case in accordance with the shape of the seat portion may be formed on the head portion.

[0015] The seat portion may be continuous with the tapered portion and have a large-diameter portion forming portion with an outer diameter larger than the maximum outer diameter of the tapered portion, and the large-diameter portion corresponding to the shape of the seat portion may be formed on the head by the heat crimping.

[0016] The seat portion is positioned around the periphery of the head portion and has a projection-forming portion which is a space corresponding to the shape of a projection that protrudes from the periphery toward the interior of the cell case. The projection corresponding to the shape of the seat portion may be formed on the head portion by heat crimping.

[0017] The protruding portion forming part of the seat portion may have an end portion in the inward direction of the cell case that protrudes in an annular shape in the direction of the central axis of the boss portion, and a rolled portion corresponding to the shape of the seat portion may be formed on the head by heat crimping.

[0018] By the thermal caulking, the upper end of the head portion may be formed to be arranged on the same plane as the lid. Alternatively, a protrusion may be provided around the boss hole of the lid, and an embedded portion may be formed by the thermal caulking such that the upper end of the head portion is covered with the lid.

[0019] The boss portion may be arranged on the end face of the wall of the case body on the opening side. Alternatively, the boss portion may be provided offset from the end face of the wall of the case body on the opening side toward the inner side of the case body.

[0020] In this case, the base end portion of the boss portion may have a base portion that is continuous from the bottom face of the case body opposite to the opening side. Further, the size of the boss portion can be changed according to the load, in accordance with the interval at which the boss portions are arranged.

[0021] Further, the exposed joint portion between the lid and the case body is hermetically welded by irradiating laser light from the lid side with a laser welder, and the welding trajectory of the laser welder can be a continuous trajectory at the peripheral edge of the end face of the wall of the case body on the opening side. Effects of the Invention

[0022] According to the secondary battery and the method for manufacturing the secondary battery of the present invention, there is an effect that the pressure resistance can be increased and the size can be further reduced. Brief Description of the Drawings

[0023] [Figure 1] It is a perspective view of the battery cell of the present embodiment. [Figure 2] It is a schematic diagram for explaining the shape of the battery cell of the present embodiment with the lid removed. [Figure 3] It is an exploded perspective view of the battery cell of the present embodiment. [Figure 4] It is a cross-sectional view of the IV-IV portion in FIG. 1. [Figure 5] This is a partially enlarged view of Figure 4. [Figure 6] This is a partial cross-sectional view of section IV-IV in Figure 1, showing the relationship between the boss portion and the boss hole before heat crimping. [Figure 7] This is a partial cross-sectional view of section IV-IV in Figure 1, showing the relationship between the boss portion and the boss hole during heat riveting. [Figure 8] This is a partial cross-sectional view of section IV-IV in Figure 1, showing the sealing of the case body and lid after heat crimping. [Figure 9] This is a partial cross-sectional view of the IV-IV portion of the boss section in Figure 1, which does not have a shaft. [Figure 10] This is a partial cross-sectional view of section IV-IV in Figure 1, showing an example of a head having a large diameter section without a tapered portion. [Figure 11] This is a partial cross-sectional view of section IV-IV in Figure 1, showing an example of a head having a tapered section and a large-diameter section. [Figure 12] This is a partial cross-sectional view of section IV-IV in Figure 1, showing an example of a head having a protruding portion. [Figure 13] This is a partial cross-sectional view of section IV-IV in Figure 1, showing another example of a head with a protrusion. [Figure 14] This is a partial cross-sectional view of section IV-IV in Figure 1, showing an example of a head with a winding portion. [Figure 15] (a) A partial cross-sectional view of section IV-IV in Figure 1 after the boss section has been heat-crimped. (b) A diagram showing the formation of the embedded section from state a. [Figure 16] This is a perspective view of a battery cell according to the second embodiment. [Figure 17] This is a perspective view of the main body case with the lid removed in the battery cell of the second embodiment. [Figure 18] This is a perspective view of the lid of the second embodiment. [Figure 19] This is a view of the main body case of the second embodiment with the lid removed, as seen from the thickness direction Z. [Figure 20] This is a partial cross-sectional view of section IV-IV in Figure 1, showing the conventional joint between the lid and the case body. [Figure 21]This diagram shows a conventional energy storage cell. [Modes for carrying out the invention]

[0024] (Summary of the first embodiment) Figure 1 is a perspective view of the battery cell 1 of the first embodiment. As described in the background art, this embodiment is a technology that can be suitably used in CTP (Cell-to-Pack) where the battery cell 1 of a secondary battery is used directly as a battery pack. In such a CTP, a battery module using restraints is not constructed.

[0025] Furthermore, instead of the conventional metal case, a resin cell case 20 is used to reduce weight. Therefore, the battery cell 1 itself needs to have increased mechanical strength against increased internal pressure, while also maintaining airtightness.

[0026] Furthermore, the reason for adopting CTP is the volume per unit area [Ah / m³] 3 Since one of the objectives is to increase the strength of the cell case 20, increasing the volume of the battery cell 1 more than necessary to improve the strength of the cell case 20 would contradict the objective.

[0027] Figure 20 is a partial cross-sectional view of section IV-IV in Figure 1, showing the joint between the conventional lid 40 and the case body 30. Conventionally, the joint 27 between the lid 40 and the case body 30 is in contact at the joint surface 27a. This joint surface 27a was welded from the outside using a laser welding machine 80. However, the welded surface of this joint surface 27a ensures both mechanical jointing of the lid 40 and the case body 30 and airtightness to withstand internal pressure. Conventionally, multiple battery cells 1 were stacked and restrained with a restraining device. Therefore, expansion of the battery cells 1 was suppressed. As a result, the stress that would try to peel off the joint surface 27a was also suppressed. However, in the CTP described above, the battery cell 1 must withstand such internal pressure on its own. However, if the structure of the cell case is enlarged and strengthened to withstand such internal pressure, the volume of the battery cell 1 increases. For this reason, it is difficult to solve the above problems with welding only at the ends as in the conventional method.

[0028] Figure 5 is a partially enlarged view of Figure 4 of the battery cell 1 of this embodiment. For detailed information on the configuration of the boss portion 36 and the joint portion 27, please refer to Figure 8. As shown in Figure 5, the battery cell 1 of this embodiment addresses mechanical strength and airtightness in two separate ways. Specifically, the battery cell 1, which is a lithium-ion secondary battery, comprises a thermoplastic resin cell case 20 consisting of a box-shaped case body 30 having an opening 39 and a lid 40 that seals the opening 39. The case body 30 has a boss portion 36 having a through portion (shaft portion) 38 that penetrates the lid 40 and a head portion 37. The lid 40 has a boss hole 41 through which the boss portion 36 penetrates. The boss hole 41 has a seat portion 42 that accommodates the head portion 37 of the boss portion 36 on the outside of the lid 40. Between the head portion 37 and the seat portion 42, there is a sealing material 28 that airtightly seals the head portion 37 and the seat portion 42. With this configuration, the lid 40 is fixed to the case body 30 with high strength. Meanwhile, the exposed joint 27 between the lid 40 and the case body 30 is welded using a laser welding machine 80 to ensure an airtight seal. This configuration ensures airtightness by sealing without any gaps.

[0029] In Figure 8, the laser welding machine 80 irradiates the lid 40 from above (upwards in the drawing) with laser light 81. However, it is not limited to this, and the case body 30 may also be irradiated from the side (leftwards in the drawing). This allows the boss portion 36 and boss hole 41 to be positioned further outwards from the case body 30 and lid 40. In this case, the head portion 37 of the boss portion 36 and the joint portion 27 may overlap in the vertical direction (Z-axis direction). With such a configuration, a larger space can be provided for housing the electrode body.

[0030] In this way, by ensuring mechanical strength and airtightness through different configurations, the battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0031] (Configuration of the first embodiment) The secondary battery and method for manufacturing the secondary battery of the present invention will be described below with reference to Figures 1 to 15, using a lithium-ion secondary battery cell 1 and an embodiment of its manufacturing method as an example. However, the present invention is not intended to be understood in a limited way by each embodiment.

[0032] First, we will describe the battery cell 1 of the lithium-ion secondary battery of this embodiment, which is an example of a secondary battery to which the present invention is applied. For the purpose of clarifying the description of the invention, the following descriptions and drawings may be omitted, simplified, or schematic as appropriate. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations have been omitted where necessary.

[0033] <Battery cell 1> The following describes the battery cell 1. The orientation in which the battery cell 1 is used is not limited. Therefore, in this description, for the sake of convenience, as shown in Figure 1, the top surface 34 of the cell case 20 of the battery cell 1, which has the external positive electrode terminal 50 and the external negative electrode terminal 52, will be described as being vertically upward. The longitudinal direction of the cell case 20 of the battery cell 1 is defined as the width direction X. The direction of the short side of the cell case 20 is defined as the length direction (height direction, downward) Y. The thickness direction of the cell case 20, which is perpendicular to the width direction X and the length direction Y, is defined as the thickness direction Z.

[0034] The battery cell 1 shown in Figure 1 is a rechargeable secondary battery that uses a non-aqueous electrolyte as its electrolyte. A lithium-ion secondary battery is a secondary battery that charges and discharges by the movement of lithium ions, which are charge carriers, between the positive electrode and the negative electrode.

[0035] Figure 3 is an exploded perspective view of the battery cell 1 of this embodiment. As shown in Figure 3, the battery cell 1 has wound electrode bodies 10, 11, a cell case 20, and a non-aqueous electrolyte (not shown). In this embodiment, the battery cell 1 houses two electrode bodies 10, 11 side by side in the width direction X of the cell case 20 within a single cell case 20. The battery cell 1 of this embodiment is composed of two electrode bodies 10, 11 connected in series. However, in this invention, the number of electrode bodies housed in a single cell case 20 is not particularly limited and may be one or three or more. Note that in Figure 1, the cell case 20 and components other than the electrode bodies 10, 11 housed within the cell case 20 are not shown.

[0036] <Electrode body 10, 11> Electrode bodies 10 and 11 are electrode bodies formed into a flat shape by winding a positive electrode plate and a negative electrode plate with a separator in between. Electrode bodies 10 and 11 are formed by laminating a long positive electrode plate and a long negative electrode plate with two long sheet-like separators in between. They are wound around a winding axis parallel to the Y-axis direction, which is perpendicular to the longitudinal direction of the positive electrode sheet and the negative electrode sheet, and then press-formed into a flat shape. In the following description, since electrode body 10 and electrode body 11 have the same configuration, the description of electrode body 10 may be omitted by describing electrode body 11.

[0037] The positive electrode plate comprising the positive electrode includes a positive electrode composite material layer formed on at least one surface of the positive electrode current collector. From the viewpoint of improving battery performance, it is preferable that the positive electrode composite material layer be formed on both sides of the positive electrode current collector. Any material that can be used in lithium-ion secondary batteries can be used for each component constituting the positive electrode plate without particular limitations.

[0038] As the positive electrode current collector, for example, a metal foil made of a metal mainly composed of aluminum can be used. The positive electrode active material layer contains a positive electrode active material capable of reversibly intercepting and releasing lithium ions, which are charge carriers. As the positive electrode active material, for example, lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxide can be used. The positive electrode active material layer may also contain optional components other than the positive electrode active material. Examples of optional components other than the positive electrode active material include conductive materials, binders, and various additives. As conductive materials, for example, graphite, acetylene black (AB), carbon materials such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) can be used. As a binder, for example, polyvinylidene fluoride (PVdF) can be used.

[0039] The negative electrode plate comprising the negative electrode comprises a negative composite material layer formed on at least one surface of a long negative electrode current collector. From the viewpoint of improving battery performance, it is preferable that the negative electrode composite material layer be formed on both sides of the negative electrode current collector. Any material that can be used in lithium-ion secondary batteries can be used for each component constituting the negative electrode plate without particular limitations. As the negative electrode current collector, for example, a metal foil formed of a metal mainly composed of copper can be used. The negative electrode active material layer contains a negative electrode active material capable of reversibly adsorbing and releasing charge carriers. As the negative electrode active material, for example, a carbon material such as graphite can be used. The negative electrode composite material layer may contain optional components other than the negative electrode active material. Examples of optional components other than the negative electrode active material include binders, dispersants, and various additives. As a binder, for example, rubbers such as styrene-butadiene rubber (SBR) can be used. As a dispersant, for example, celluloses such as carboxymethylcellulose (CMC) can be used.

[0040] A separator is provided between the positive and negative electrode plates to insulate them from each other. The separator holds a non-aqueous electrolyte. Any separator that can be used in lithium-ion secondary batteries can be used without particular limitations. As the separator, a porous sheet made of olefin resins such as polyethylene (PE) and polypropylene (PP), or resins such as cellulose can be used. The separator may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure with PP layers laminated on both sides of a PE layer). In addition, a heat-resistant layer (HRL) may be formed on the surface of the separator.

[0041] <Cell Case 20> As shown in Figures 1-3, the cell case 20 is a housing that encloses the electrode bodies 10 and 11 together with the non-aqueous electrolyte. The cell case 20 has a rectangular parallelepiped shape that is flattened in the thickness direction Z. The cell case 20 is molded using an insulating resin. By using an insulating resin, such as polyphenylene sulfide (PPS), as the material for the cell case 20, it is possible to easily form a housing with a complex shape that is lightweight and has high insulating properties, compared to using a metal as the material. However, it is not limited to resin.

[0042] As shown in Figure 3, in the battery cell 1 according to this embodiment, the cell case 20 has a case body 30 and a lid 40. The case body 30 is a box-shaped member with a rectangular parallelepiped shape that is flattened in the thickness direction Z. When arranged in the orientation shown in Figure 1, the faces constituting the rectangular parallelepiped have the following relationships. The case body 30 has a side portion 31, a top portion 34, a bottom portion 35, a first end portion 32, and a second end portion 33. The side portion 31 faces the lid 40 in the thickness direction Z of the cell case 20. The first end portion 32 and the second end portion 33 face each other left and right in the width direction X of the cell case 20. The top portion 34 and the bottom portion 35 face each other in the length direction Y of the cell case 20.

[0043] The lid 40 is a roughly rectangular plate-like member attached to the case body 30 so as to close the opening of the case body 30. The lid 40 seals the case body 30 which houses the electrode bodies 10 and 11. As will be described in detail later, the lid 40 is fixed to the opening 39 of the case body 30 by a boss portion 36 and is welded at the joint portion 27. This seals the cell case 20 airtight.

[0044] <Nonaqueous electrolyte> Non-aqueous electrolytes not shown in the diagram can be any non-aqueous electrolyte that can be used in lithium-ion secondary batteries without particular limitations. The non-aqueous electrolyte is a composition containing a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, aprotic solvents such as carbonates, esters, and ethers can be used. Among aprotic solvents, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be suitably used as non-aqueous solvents. Such non-aqueous solvents can be used individually or in appropriate combinations of two or more. As the supporting salt, lithium salts such as LiPF6, LiBF4, and LiClO4 can be suitably used. The electrolyte may contain additives as needed.

[0045] Figure 2 is a schematic diagram illustrating the shape of the battery cell 1 according to this embodiment with the lid 40 removed. Figure 2 illustrates the state in which the electrode bodies 10 and 11 are housed in the respective storage compartments 21 and 22, and the lid 40 is placed over the case body 30 to which the insulating cover 60 is attached. In the battery cell 1 according to this embodiment, each electrode body 10 and 11 is housed in the respective storage compartments 21 and 22. Then, a non-aqueous electrolyte is injected into each storage compartment 21 and 22 to impregnate each electrode body 10 and 11 with the non-aqueous electrolyte. After that, the lid 40 is attached to the case body 30 so as to cover the first storage compartment 21 and the second storage compartment 22.

[0046] In Figures 1-3, an example is shown in which one lid 40 is provided for two storage compartments 21 and 22. However, the lid 40 may be prepared as a separate component for each storage compartment 21 and 22. By providing a lid 40 for each storage compartment 21 and 22 in this way, it becomes easier to weld the lid 40, and it becomes possible to adjust the pressure applied to each electrode body 10 and 11 by changing the shape of the lid 40 according to the variations in each electrode body 10 and 11.

[0047] <External positive terminal 50, external negative terminal 52, etc.> As shown in Figure 3, in the battery cell 1 according to this embodiment, the case body 30 has an external positive electrode terminal 50 and an external negative electrode terminal 52 that are insert-molded. The case body 30 also has storage sections 21 and 22 for housing the electrode bodies 10 and 11.

[0048] The positive electrode of the electrode body 10 is connected to the external positive electrode terminal 50. The external positive electrode terminal 50, to which the positive electrode of the electrode body 10 is connected, is made of a metal mainly composed of aluminum, for example. The negative electrode of the electrode body 11 is connected to the external negative electrode terminal 52. The external negative electrode terminal 52, to which the negative electrode of the electrode body 11 is connected, is made of a metal mainly composed of copper, for example.

[0049] The insulating cover 60 is provided so as to cover the intermediate terminal (not shown) on the top surface 34. The positive electrode tab group 10a of the electrode body 10 is connected to the external positive electrode terminal 50. The negative electrode tab group 10b of the electrode body 10 is connected to the intermediate negative electrode terminal (not shown) which is covered by the insulating cover 60. In this storage state, the positive electrode tab group 10a of the electrode body 11 is connected to the intermediate positive electrode terminal (not shown). The negative electrode tab group 10b of the electrode body 11 is connected to the external negative electrode terminal 52.

[0050] In the battery cell 1 manufactured in this manner, the external positive electrode terminal 50 and the external negative electrode terminal 52 are arranged in a straight line on the same plane. Therefore, the current path in the battery cell 1 passes through the electrode bodies 10 and 11 that are close to the terminal arrangement surface, and is formed in a path with little meandering relative to the terminal arrangement surface. As a result, the battery cell 1 according to Embodiment 1 can reduce the resistance value as a battery.

[0051] The flattened electrode bodies 10 and 11 are provided with curved portions 12 and 13 made of laminated material with curved outer surfaces at both ends in the width direction X. The electrode bodies 10 and 11 also have flat portions 14 and 15 made of laminated material with flat outer surfaces that connect the curved portions 12 and 13. The flat portions 14 and 15 face each other in the thickness direction Z of the electrode bodies 10 and 11.

[0052] As shown in Figure 3, such electrode bodies 10 and 11 have a flat surface 17 formed from an XY plane at the upper end in the thickness direction Z, and a flat surface 16 formed from an XY plane at the lower end in the thickness direction Z. Flat surfaces 16 and 17 face each other in the thickness direction Z. Flat surfaces 16 and 17 have a substantially rectangular shape.

[0053] The electrode bodies 10 and 11 have end faces 18 at the electrode-side ends in the longitudinal direction Y. The end opposite to the end face 18 in the longitudinal direction Y has an end face 19. The end faces 18 and 19 are laminated surfaces in which the positive electrode plate, negative electrode plate, and separator are stacked, and are open to the outside of the electrode bodies 10 and 11.

[0054] The electrode bodies 10 and 11 are housed in the storage sections 21 and 22 with their winding axes oriented parallel to the length direction Y of the cell case 20. The electrode bodies 10 and 11 housed in the storage sections 21 and 22 have curved portions 12 and 13 positioned on both sides in the width direction X of the cell case 20, and flat portions 14 and 15 positioned on both sides in the thickness direction Z of the cell case 20.

[0055] The cell case 20 has four opposing surfaces 23a, 24a, 25a, and 26a that face the flat surfaces 16 and 17 of the electrode bodies 10 and 11. The opposing surfaces 23a, 24a and the opposing surfaces 25a and 26a face each other in the thickness direction Z of the cell case 20.

[0056] In the battery cell 1 of this embodiment, the case body 30 includes an opposing surface 23a facing the flat surface 16 of the electrode body 10, and an opposing surface 24a facing the flat surface 16 of the electrode body 11. The lid 40 includes an opposing surface 25a facing the flat surface 17 of the electrode body 10, and an opposing surface 26a facing the flat surface 17 of the electrode body 11.

[0057] The opposing surfaces 23a and 24a are the inner surfaces of the first opposing portions 23 and 24 of the side portion 31 that face the flat portion 14. The opposing surfaces 25a and 26a are the inner surfaces of the second opposing portions 25 and 26 of the side portion 31 that face the flat portion 15. The opposing surfaces 23a, 24a, 25a, and 26a face the storage portions 21 and 22.

[0058] <Pressure change in battery cell 1> Figure 4 is a cross-sectional view along the line IV-IV in Figure 1. In Figure 4, the structure of the electrode body 10 housed in the cell case 20 is the same as the structure of the electrode body 11 housed in the cell case 20 shown in Figure 3. Here, we will explain the problems that may occur during charging and discharging of the battery cell 1, using the structure of the electrode body 11 housed in the cell case 20 as an example. As the battery cell 1 is charged and discharged, the electrode body 11 sealed inside the cell case 20 expands and contracts. In addition, gas is generated from the electrode body 11. When the battery cell 1 is charged and discharged, the electrode body 11 inside the cell case 20 expands and contracts in the thickness direction Z due to the intercalation and release of lithium ions. In addition, gas is generated by various reactions, and the internal pressure increases with the rise in temperature.

[0059] In battery cell 1, expansion of the electrode body 11 inside the cell case 20 and the generation of gas from the electrode body 11 create a pressure F[N] that pushes the cell case 20 from the inside outward in the thickness direction Z. Then, a reaction force F'[N] acts on the electrode body 11, which holds the non-aqueous electrolyte, counteracting the pressure F[N]. As a result, the electrolyte is pushed out from the end faces 18 and 19 to the outside of the electrode body 11, causing the non-aqueous electrolyte to leak out of the electrode body 11.

[0060] Non-aqueous electrolyte leaking from the electrode body 11 flows down the opposing surfaces 24a and 26a and accumulates at the bottom of the cell case 20. Furthermore, the electrolyte accumulated at the bottom of the cell case 20 permeates into the electrode body 11 from the end surface 19. In this way, the electrolyte leaking from the electrode body 11 is reabsorbed into the electrode body 11 via the end surface 19.

[0061] However, the pressure F[N] generated by the expansion of the electrode body 11 increases with repeated charging and discharging, and therefore the reaction force F'[N] that opposes the pressure F[N] also increases. For this reason, if the electrolyte only penetrates into the electrode body 11 from the end face 19 during charging and discharging, uneven salt concentration in the electrolyte held in the electrode body 11 may occur, or electrolyte depletion may occur. If uneven salt concentration in the electrolyte held in the electrode body 11 occurs, or electrolyte depletion occurs, there is a risk that the internal resistance of the battery cell 1 will increase, leading to a decrease in battery performance.

[0062] (Method for manufacturing a lithium-ion secondary battery according to the first embodiment) The manufacturing method of the lithium-ion secondary battery of this embodiment is characterized by the method of joining the case body 30 and the lid 40 of the cell case 20. Other steps in the manufacturing method of secondary batteries, including lithium-ion secondary batteries, can be performed using well-known methods. Therefore, the explanation of those steps will be omitted, and the method of joining the case body 30 and the lid 40 in the cell case 20, which is a characteristic of the manufacturing method of the lithium-ion secondary battery of this embodiment, will be described in detail below.

[0063] <Assembly and application of sealant 28> As shown in Figures 1 and 2, the case body 30 is provided with numerous (more than 30 in Figure 2) cylindrical boss portions 36 facing the lid 40 for penetrating the lid 40. In this embodiment, the boss portions 36 are arranged on the end faces of the walls (32, 33, 34, 35) of the case body 30 on the opening 39 side. In this embodiment, as a simplified example for illustrative purposes, the boss portions 36 are provided at equal intervals, in a single row, and of the same size around the two storage compartments 21 and 22 that house the two electrode bodies 10 and 11 of the opening 39. It should be noted that the present invention is not limited to this embodiment, and various configurations can be adopted by those skilled in the art to meet the required pressure resistance and airtightness, in addition to the configuration of the case body 30 and lid 40.

[0064] The lid 40 is provided with a boss hole 41 through which the boss portion 36 passes, at a position corresponding to the boss portion 36. Figure 6 is a partial cross-sectional view of section IV-IV in Figure 1, showing the relationship between the boss portion 36 and the boss hole 41 before heat crimping. Figure 7 is a partial cross-sectional view of section IV-IV in Figure 1, showing the relationship between the boss portion 36 and the boss hole 41 during heat crimping. Figure 8 is a partial cross-sectional view of section IV-IV in Figure 1, showing the sealing of the case body 30 and the lid 40 after heat crimping. The method of joining the case body 30 and the lid 40 in this embodiment will be described in detail below with reference to Figures 6 to 8.

[0065] As shown in Figure 6, the numerous boss portions 36 of the case body 30 are inserted into the corresponding boss holes 41 of the lid 40 for assembly. The boss portions 36 are inserted into the boss holes 41 until they stop. Prior to this assembly, a sealant 28 is applied to the seat portion 42 of the boss hole 41 of the lid 40. The sealant 28 is a liquid liquid gasket that hardens by heat crimping. For example, ThreeBond® 1170H from ThreeBond Corporation can be used.

[0066] As shown in Figure 8, the joint surface 27a, which is the laser welding surface, is then welded by the heat of the laser beam 81. At this time, a gap is intentionally left between the inner surface 40b of the lid 40 that is to be heat-crimped and the base end 37h of the boss portion 36 of the case body 30, taking into account the tolerances between the lid 40 and the case body 30. Therefore, after inserting a number of boss portions 36 into the boss holes 41 and performing heat crimping, there may be a gap between the base end 37h of the boss portion 36 of the case body 30. Even if there is a gap here, the joint 27 is welded by laser welding, so the airtightness of the cell case 20 is ensured.

[0067] <Heat crimping> Figure 7 is a partial cross-sectional view of the section IV-IV in Figure 1, showing the relationship between the boss portion 36 and the boss hole 41 during heat scribing. In this embodiment, heat scribing is performed using a heat scribing machine 70. The heat scribing machine 70 can be appropriately selected considering the heat resistance of the sealing material 28, the effect on heat, etc. In this embodiment, since a counter electrode cannot be installed inside the case body 30, the impulse heater 72, consisting of a sheath heater, is used to instantaneously heat the case to 350°C in about 10 seconds using an impulse method. The heated head 71 is brought into contact with the top of the boss portion 36, and pressure is applied in the direction of the arrow to melt it. After melting, the head 71 is used to press the tip portion 37g of the boss portion 36, and the molten resin is filled into the tapered portion forming portion 42a of the seat portion 42 to form a tapered portion 37c on the head portion 37. At this time, the sealing material 28 is between the molten resin and the seat portion 42, sealing them airtight. Furthermore, the tip 37g of the formed head 37 is shaped to be flush with the outer surface 40a of the lid 40. In this way, the tip 37g of the head 37 is formed by heat crimping so that it is positioned on the same plane as the outer surface 40a of the lid 40. After shaping, it is immediately cooled with an air nozzle 73. At this time, the sealing material 28 also solidifies, ensuring a secure seal.

[0068] <Sealing of the case body 30 and lid 40> Figure 8 is a partial cross-sectional view of section IV-IV in Figure 1, showing the sealing of the case body 30 and the lid 40 after heat crimping. As shown in Figure 1, the joint 27 between the lid 40 and the case body 30 is exposed around the lid 40 of the cell case 20. This externally visible joint 27 is welded to the lid 40 by laser welding to create an airtight seal. In Figure 8, although it is depicted schematically, in reality, the laser irradiation is performed at a position sufficiently far from the boss portion 36 so as not to affect the boss portion 36. Therefore, the joint 27 is welded completely airtight without any gaps.

[0069] Through the processes described above, mechanical strength and airtightness are ensured by different configurations. As a result, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0070] (Examples) The following describes an example of this embodiment. <Example 1> Example 1 is a battery cell 1 of the lithium-ion secondary battery described in the manufacturing method of the lithium-ion secondary battery of this embodiment shown in Figures 6 to 8 above.

[0071] The boss hole 41 in Example 1 has a tapered portion forming portion 42a of the seat portion 42 that corresponds to the tapered shape of the head portion 37. By heat crimping, the head portion 37 is formed into a tapered portion 37c, which has a tapered shape in which its outer diameter expands toward the outside of the cell case 20.

[0072] The tip 37g of the head 37 is positioned on the same plane as the outer surface 40a of the lid 40. Furthermore, the sealing material 28 provides an airtight seal between the tapered portion 37c and the seat portion 42. Because Example 1 has this configuration, the tapered portion 37c of the boss portion 36 can withstand the stress that would cause the lid 40 to detach from the case body 30. Therefore, strong stress is not applied to the joint 27 that is welded by laser welding.

[0073] Furthermore, the tapered portion 37c of the boss portion 36 is positioned so as not to overlap with the joint portion 27 and the lid 40 in the XY direction (left-right direction in Figure 7). This prevents the load and heat generated when the tapered portion 37c is formed from affecting the joint portion 27, resulting in a more airtight seal.

[0074] As described above, mechanical strength and airtightness are ensured through different configurations. Therefore, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0075] <Example 2> Figure 9 is a partial cross-sectional view of the IV-IV portion of the boss portion 36 in Figure 1, which has almost no through portion 38, which is a cylindrical shaft portion. Embodiment 2 differs from Embodiment 1 in that the boss portion 36 has almost no through portion 38, which is a cylindrical shaft portion, and is composed entirely of a tapered portion 37c.

[0076] With this shape, compared to Example 1, the lid 40 can withstand greater stress due to the wide area of ​​the tapered portion 37c, preventing it from separating from the case body 30. Therefore, strong stress does not concentrate at the joint 27 welded by laser welding.

[0077] As described above, mechanical strength and airtightness are ensured through different configurations. Therefore, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0078] <Example 3> Figure 10 is a partial cross-sectional view of the IV-IV portion of Figure 1, showing an example of the head 37 without the tapered portion 37c. Embodiment 3 lacks the tapered portion 37c. The boss portion 36 has a large-diameter portion 37d, which is a disc-shaped flange portion provided from the end of the cylindrical through portion (shaft portion) 38.

[0079] The lid 40 has a large-diameter portion forming section 42b that forms the shape of the large-diameter portion 37d. Since the large-diameter portion forming section 42b has a horizontal surface, the sealing material 28 can be applied stably. When resin is filled into the large-diameter portion forming section 42b by heat crimping, the large-diameter portion 37d is formed.

[0080] As described above, mechanical strength and airtightness are ensured through different configurations. Therefore, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0081] <Example 4> Figure 11 is a partial cross-sectional view of section IV-IV of Figure 1, showing an example of a head 37 having a tapered portion 37c and a large-diameter portion 37d. The seat portion 42 has a tapered portion forming portion 42a that forms the tapered portion 37c and a large-diameter portion forming portion 42b that is continuous therewith and forms the shape of a large-diameter portion 37d with an outer diameter larger than the maximum outer diameter of the tapered portion 37c. Liquid sealant 28 can be stably applied to the horizontal large-diameter portion forming portion 42b. When resin is filled into the tapered portion forming portion 42a and the large-diameter portion forming portion 42b by heat crimping, the tapered portion 37c and the large-diameter portion 37d are formed in the head 37.

[0082] As described above, mechanical strength and airtightness are ensured through different configurations. Therefore, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0083] <Example 5> Figure 12 is a partial cross-sectional view of section IV-IV of Figure 1, showing an example of a head portion 37 having a protruding portion 37e. The cylindrical through portion 38 and the large-diameter portion 37d are common to Embodiment 4. In Embodiment 5, the boss portion 36 is positioned on the periphery of the large-diameter portion 37d and has a protruding portion 37e that protrudes from the periphery toward the interior of the cell case 20. The protruding portion 37e is generally cylindrical in shape, and its base end is tapered to stabilize the boss portion 36.

[0084] The seat portion 42 of the lid 40 is provided with a large-diameter portion forming portion 42b for forming the shape of the large-diameter portion 37d, as well as a protrusion portion forming portion 42c for forming the shape of the protrusion portion 37e. A sealing material 28 is applied in advance to the radially outer end of the protrusion portion forming portion 42c. When resin is filled into the large-diameter portion forming portion 42b and the protrusion portion forming portion 42c by heat crimping, the large-diameter portion 37d and the protrusion portion 37e are formed on the head portion 37 of the boss portion 36. At this time, the protrusion portion forming portion 42c becomes the protrusion portion housing portion 42d, which is a space for housing the protrusion portion 37e. The gap between the protrusion portion 37e and the protrusion portion housing portion 42d is airtightly sealed by the sealing material 28.

[0085] <Example 6> Figure 13 is a partial cross-sectional view of section IV-IV of Figure 1, showing another example of a head portion 37 having a projection 37e. In Example 5, the projection 37e was generally cylindrical, but in Example 6, the radial cross-sectional shape of the projection 37e near the center is triangular. The outer surface away from the center is a cylindrical surface parallel to the central axis. On the other hand, the inner surface near the center has a tapered shape from the large-diameter portion 37d at the tip towards the base.

[0086] Furthermore, the sealing material 28 is applied to the central side of the protruding portion 42c of the seat portion 42. Applying it in this way allows for more even application than in Example 5. As described above, mechanical strength and airtightness are ensured through different configurations. Therefore, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0087] <Example 7> Figure 14 is a partial cross-sectional view of the section IV-IV in Figure 1, showing an example of a head 37 having a winding portion 37f. Embodiment 7 has a winding portion 37f in addition to the configuration of the large-diameter portion 37d and the protruding portion 37e of Embodiment 5. The winding portion 37f is the portion of the protruding portion 37e of the head 37 in which its lower end in the direction of the inside of the cell case 20 protrudes in an annular shape in the direction of the central axis of the boss portion 36.

[0088] The seat portion 42 of the lid 40 includes a large-diameter portion forming portion 42b, a protruding portion forming portion 42c, and a winding portion forming portion 42e. A sealing material 28 is applied in advance to the horizontal end faces of the protruding portion forming portion 42c and the winding portion forming portion 42e on the inside side of the cell case 20. When resin is filled into the large-diameter portion forming portion 42b, the protruding portion forming portion 42c, and the winding portion forming portion 42e by heat crimping, the large-diameter portion 37d, the protruding portion 37e, and the winding portion 37f are formed. The protruding portion forming portion 42c and the winding portion forming portion 42e become the protruding portion housing portion 42d and the winding portion housing portion 42f, which house the protruding portion 37e and the winding portion 37f. The gaps between the protruding portion 37e and the protruding portion housing portion 42d, and between the winding portion 37f and the winding portion housing portion 42f are airtightly sealed by the sealing material 28.

[0089] The winding portion 37f winds up a part of the lid 40, thereby increasing its mechanical strength and improving its airtightness. As described above, mechanical strength and airtightness are ensured through different configurations. Therefore, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0090] <Example 8> In Examples 1 to 7, the head portion 37 of the boss portion 36 was exposed, but in Example 8, the tip portion 37g of the head portion 37 is covered by the lid 40.

[0091] Figure 15(a) is a partial cross-sectional view of the IV-IV section of Figure 1 after the boss portion 36 has been heat-crimped. First, the boss portion 36 is heat-crimped using the same procedure as in Example 1 shown in Figures 6-8 to reach the state shown in Figure 15(a).

[0092] This figure shows the formation of the embedded portion 42g from the state shown in Figure 15(b)a. The lid 40 has an embedded portion 42g, which is a protrusion made of resin integral with the lid 40, around the boss hole 41. This embedded portion 42g is then deformed again by heat using the heat crimping machine 70 so that the upper end of the head 37 is covered.

[0093] Since the boss portion 36 is completely covered with resin in this way, airtightness can be firmly maintained. In the case of Example 7, sealing with the sealing material 28 is unnecessary. As described above, mechanical strength and airtightness are ensured through different configurations. Therefore, battery cell 1, despite being small and made of resin, functions as a battery pack that can withstand high internal pressure on its own.

[0094] (Effects of the first embodiment) (1-1) Mechanical strength and airtightness are ensured by different configurations. As a result, despite being small and made of resin, it functions as a battery pack that can withstand high internal pressure with a single battery cell 1. This has the effect of increasing the pressure resistance of the secondary battery and making it smaller.

[0095] (1-2) The case body 30 is provided with a boss portion 36 having a through portion 38 that penetrates the lid 40 and a head portion 37 that is continuous with the through portion 38 and exposed to the outside of the cell case 20, having a larger outer diameter than the through portion 38. The lid 40 is provided with a boss hole 41 through which the boss portion 36 penetrates. The boss hole 41 has a seat portion 42 that accommodates the head portion 37 of the boss portion 36 on the outside of the lid 40. As a result, the lid 40 is firmly fixed to the case body 30 by the boss portion 36, and has the effect of having mechanical strength to withstand the expansion of the electrode bodies 10, 11, etc.

[0096] (1-3) A sealing material 28 is provided between the head portion 37 and the seat portion 42 to airtightly seal the head portion 37 and the seat portion 42. This has the effect of maintaining an airtight state at the boss portion 36.

[0097] (1-4) The exposed joint 27 between the lid 40 and the case body 30 is welded together by laser welding so as to be airtight and without gaps. This has the effect of making the cell case 20 highly airtight due to the welding.

[0098] (1-5) In Example 1, the tapered portion 37c is provided, which has the effect of making heat crimping easier. (1-6) In Example 2, the area of ​​the tapered portion 37c is large, which has the effect of improving airtightness.

[0099] (1-7) In Example 3, the large-diameter portion forming portion 42b has a horizontal surface, which has the effect of allowing the sealing material 28 to be applied stably. (1-8) In Example 4, the tapered portion 37c is provided, which has the effect of making heat crimping easy, and the large diameter portion forming portion 42b has a horizontal surface, which has the effect of allowing the sealing material 28 to be applied stably.

[0100] (1-9) In Examples 5 and 6, the presence of the protruding portion 37e has the effect of allowing the lid 40 to be more firmly fixed to the case body 30. (1-10) In Example 7, since the retractable portion 37f is present, the lid 40 can be more firmly fixed to the case body 30.

[0101] (1-11) In Example 8, the embedded portion 42g completely seals the boss portion 36, which has the effect of making it airtight. Therefore, there is also the effect that the sealing material 28 is not required.

[0102] (1-12) In Examples 1 to 7, the surface of the boss portion 36 is shaped to be flat, which has the effect of preventing wasted space when a large number of battery cells 1 are combined. (Second embodiment) The second embodiment differs from the first embodiment in its configuration, particularly in the arrangement of the boss portion 36. Below, only the configurations that differ from the first embodiment will be described; other configurations will not be explained.

[0103] <Arrangement of boss section 36> Figure 16 is a perspective view of the battery cell 1 of the second embodiment. As shown in Figure 1, in the first embodiment, the boss portions 36 were arranged in a single row at equal intervals along the length direction Y around the perimeter of the lid 40 and in the center in the width direction X.

[0104] On the other hand, as shown in Figure 16, in the second embodiment, the spacing around the lid 40 is different. Also, the size of the boss portion 36 is different, with a large boss portion 36a and a small boss portion 36b (collectively referred to as "boss portion 36"). Furthermore, it differs in that the small boss portions 36b are arranged in two rows along the length direction Y at the center in the width direction X.

[0105] Figure 18 is a perspective view of the lid 40 of the second embodiment. In the lid 40 as well, large boss holes 41a and small boss holes 41b are drilled in accordance with the positions of large boss portion 36a and small boss portion 36b. In the lid 40 of the second embodiment, various shapes of recesses are formed to reduce weight and improve strength, and the boss portions 36 can be arranged to accommodate such complex shapes.

[0106] <Structure of boss section 36> Figure 17 is a perspective view of the case body 30 with the lid 40 removed in the completed battery cell 1 of the second embodiment. Therefore, the head portion 37 is already formed on the large boss portion 36a and the small boss portion 36b. As shown in Figure 16, the configuration as seen from the outside is different, but as shown in Figure 17, the internal configuration of the case body 30 is also different. In the first embodiment, the boss portion 36 was provided on the joining surface 27a, which is the end face on the opening 39 side (lid 40 side) of the wall (partition wall 29, first end face portion 32, second end face portion 33, top surface portion 34, bottom surface portion 35) of the case body 30, as shown in Figure 3.

[0107] On the other hand, in the second embodiment, the boss portion 36 is provided offset inward from the joint surface 27a, which is the end face on the opening 39 side of the wall (29, 32, 33, 34, 35) of the case body 30.

[0108] The boss portion 36 includes a base portion 36c. The base portion 36c is a continuous portion from the opposing surfaces 23a and 24a, which are the bottom surfaces of the case body 30 opposite to the opening 39 side. The base portion 36c protrudes inward from the first end surface 32, the second end surface 33, the top surface 34, the bottom surface 35, and the partition wall 29 of the case body 30. The degree of offset can range from a portion of the wall (29, 32, 33, 34, 35) protruding inward to being completely separated from the wall.

[0109] Furthermore, the opposing portions 23 and 24, which are the side walls forming the bottom of the storage sections 21 and 22 in the thickness direction Z, are continuous with the through portion 38 and the head portion 37. For this reason, the large boss portion 36a and the small boss portion 36b are positioned at an offset location from the walls of the case body 30 (first end face portion 32, second end face portion 33, top surface portion 34, bottom surface portion 35, partition wall 29). In other words, the base portion 36c of the boss portion 36, which is continuous with the opposing portion 23 that is on the bottom surface of the storage section 21, the through portion 38, and the head portion 37 are heat-crimped to the lid 40. In other words, the structure is continuous from the opposing portion 23 to the lid 40. For this reason, high rigidity can be maintained in the thickness direction Z.

[0110] <Formation of laser welding line 27b> Figure 19 is a view of the case body 30 with the lid 40 removed in the second embodiment, viewed from the thickness direction Z. The exposed joint 27 between the lid 40 and the case body 30 is airtightly welded by irradiating it with laser light 81 from the lid 40 side using a laser welding machine 80. At the same time, the laser welding line 27b, which is the welding trajectory of the laser welding machine 80, forms a continuous trajectory at the periphery of the joint surface 27a, which is the end face on the opening 39 side of the wall (29, 32, 33, 34, 35) of the case body 30. Because the boss portion 36 is offset inward, the boss portion 36 is not positioned at the periphery of the joint surface 27a of the case body 30. In addition, the boss portions 36 of the partition wall 29 are offset towards the storage sections 21 and 22, respectively, and are arranged in two rows. The center of the joint surface 27a of the partition wall 29 in the width direction X forms a continuous surface along the length direction Y. Therefore, as shown in Figure 19, the laser welding lines 27b on the partition wall 29 and the other walls (32, 33, 34, 35) can be formed in a continuous "figure eight" shape. As a result, a straight and seamless laser welding line 27b can be formed, and high airtightness can be maintained.

[0111] Furthermore, since a sufficient distance can be maintained between the boss portion 36 and the laser welding at the joint surface 27a, the thermal crimping of the boss portion 36 and the laser welding at the joint surface 27a do not affect each other. <Arrangement of boss portion 36 in exhaust port 35a> As shown in Figure 17, the bottom surface 35 of the case body 30 in the second embodiment has two exhaust ports 35a. The exhaust ports 35a are outlets that release gas to reduce the internal pressure when the internal pressure of the battery cell 1 increases. For this reason, the area of ​​these exhaust ports 35a needs to be open. Therefore, in the second embodiment, the boss portion 36 is not located in the area of ​​these exhaust ports 35a. As a result, gas can be smoothly exhausted from the exhaust ports 35a.

[0112] <Boss section large 36a and boss section small 36b> The boss portion 36 changes its size according to the load and the spacing at which it is arranged. As described above, in the second embodiment, the boss portion 36 is not provided in the exhaust port 35a. However, the boss portion 36 cannot support the load in the exhaust port 35a. Therefore, in the second embodiment, the boss portions 36 other than those flanking the exhaust port 35a are small boss portions 36b, while the boss portion 36 flanking the exhaust port 35a is a large boss portion 36a. Since the large boss portion 36a can withstand a larger load than the small boss portion 36b, it can also support the load applied to the exhaust port 35a. As a result, it is possible to eliminate any part of the cell case 20 where the load-bearing capacity is weak.

[0113] In the second embodiment, the boss portion 36 was described as having two sizes, a large boss portion 36a and a small boss portion 36b. However, it is also possible to configure it with three or more sizes depending on the degree of load.

[0114] <Arrangement of boss portion 36 in bulkhead 29> The battery cell 1 of the second embodiment has the same two housing sections 21 and 22 as the battery cell 1 of the first embodiment, and these are separated by a partition wall 29. Therefore, the laser welding line 27b can be formed using this partition wall 29. To ensure strength and airtightness, it is preferable that the laser welding line 27b on the partition wall 29 is continuous without gaps with the laser welding line 27b arranged on the periphery of the case body 30. For this reason, the boss section 36 of the second embodiment is provided so as to be offset from the figure-eight shaped laser welding line 27b. In this case, it is also conceivable that it be offset to either side in the width direction X.

[0115] However, in the second embodiment, boss portions 36 were arranged on both sides of the laser welding line 27b provided in the partition wall 29. This ensured balanced and sufficient strength. Furthermore, complete isolation between the storage section 21 and the storage section 22 could be achieved.

[0116] (Effects of the second embodiment) (2-1) The spacing, size, and arrangement of the bosses 36 are optimized so that the load on each part is evenly distributed. As a result, the cell case 20 of the battery cell 1 can optimally accommodate the load on each part. This has the effect of being able to sufficiently withstand the expansion of the electrode bodies 10 and 11 and the increase in internal pressure due to gas generation with a minimal configuration.

[0117] On the other hand, eliminating parts with excessive pressure resistance has the effect of achieving overall miniaturization and weight reduction. (2-2) The boss portion 36 is offset and protrudes inward from the first end face portion 32, the second end face portion 33, the top portion 34, the bottom portion 35, and the partition wall 29 of the case body 30. However, because it has a base portion 36c, the boss portion 36 has a base portion 36c that is continuous with the opposing portion 23 that is on the bottom surface of the storage portion 21, a through portion 38, and a head portion 37 which are heat-crimped to the lid 40. In other words, it has a continuous structure from the opposing portion 23 to the lid 40. This has the effect of maintaining high rigidity in the thickness direction Z.

[0118] (2-3) A laser welding line 27b is formed in the shape of an eight. This allows for the formation of a straight and seamless laser welding line 27b, which has the effect of maintaining high airtightness. In addition, because it is sufficiently far away from the boss portion 36, the thermal crimping of the boss portion 36 and the laser welding at the joint surface 27a do not affect each other.

[0119] (2-4) In the second embodiment, the boss portion 36 is not located in the exhaust port 35a. This has the effect of allowing for smooth exhaust from the exhaust port 35a.

[0120] (2-5) The large boss portion 36a can withstand a greater load than the small boss portion 36b, and can therefore also bear the load applied to the exhaust port 35a. This has the effect of eliminating any part of the cell case 20 that is weak in terms of load resistance.

[0121] (2-6) In the second embodiment, two rows of bosses 36 are arranged on both sides of the laser welding line 27b provided in the partition wall 29. This has the effect of ensuring a balanced and sufficient strength.

[0122] (Another example) In this embodiment, the invention has been described using Examples 1 to 8, but these are illustrative examples and do not limit the present invention.

[0123] In this embodiment, the boss portion 36 is heat-crimped first, followed by laser welding of the joint portion 27. However, the joint portion 27 may be laser-welded first, followed by heat-crimping of the boss portion 36.

[0124] In this embodiment, the joint 27 is welded using a laser welding machine 80, but it may also be welded using ultrasonic waves or electrical resistance heat. Furthermore, it can also be sealed with an adhesive or the like. The configurations in the first embodiment and each of the embodiments, as well as in the second embodiment, can be combined with each other as long as there is no impediment. For example, each of the embodiments in the first embodiment can be implemented in the second embodiment.

[0125] In the first embodiment, for the sake of simplicity, the boss portions 36 are shown in Figure 1 as being provided at equal intervals along the perimeter of the lid 40 of the cell case 20, and also in a single row at equal intervals along the central partition wall 29. However, the arrangement of the boss portions 36 is not limited to this. The spacing can be wider or narrower depending on the required strength. Also, the size of each boss portion 36 is not uniform, but can be larger or smaller depending on the required strength. Furthermore, the arrangement of the boss portions 36 is not limited to one row, but may be two or more rows. Also, they may not be arranged linearly, but in a zigzag pattern. In the second embodiment, an example of a specific embodiment was illustrated, but of course, the present invention is not limited to such specific examples.

[0126] Furthermore, each boss portion 36 can be configured as shown in Examples 1 to 7, and different configurations may be used depending on the location and size. ○In this embodiment, the secondary battery is exemplified as having two electrode bodies 10 and 11 housed in two storage compartments 21 and 22, but it may also be configured to house a single electrode body or to house three or more electrode bodies.

[0127] In this embodiment, the two storage compartments 21 and 22 are sealed with one lid 40, but each storage compartment 21 and 22 may be sealed individually with two lids 40. In this embodiment, the battery cell 1 has a partition between the two storage compartments 21 and 22 for insulation, and the cell case 20 is made of resin. However, if the battery cell 1 consists only of a single cell, the cell case 20 can also be made of metal.

[0128] ○In this embodiment, the battery cell 1 is exemplified as a CTP (Cell-to-Pack) lithium-ion battery cell 1 that constitutes a battery pack for vehicle propulsion. However, the secondary battery of the present invention is not limited in terms of its structure, composition, shape, etc. In this embodiment, the electrode bodies 10 and 11 are exemplified as wound-type electrode bodies 10 and 11 using a wound body, but it can also be applied to laminated electrode bodies in which multiple rectangular positive electrode plates and negative electrode plates are stacked with separators in between. Furthermore, it can be implemented in other non-aqueous electrolyte secondary batteries, etc. It may also be applied to alkaline secondary batteries such as nickel-metal hydride secondary batteries.

[0129] ○The drawings are provided for understanding the invention, but may not accurately reflect an actual secondary battery due to omissions, exaggerations, or schematics, and do not limit the present invention. ○The numerical values, numerical ranges, compositions, etc., in this embodiment are illustrative and do not limit the present invention. They can be appropriately optimized and implemented by those skilled in the art.

[0130] ○The present invention can be implemented by those skilled in the art with additions, deletions, and modifications, without departing from the scope of the claims. [Explanation of symbols]

[0131] 1…Battery cell (rechargeable battery, lithium-ion rechargeable battery) 10, 11...electrode body 12, 13... curved section 14, 15...Flat area 16, 17...Flat surface 18, 19...end face 20... Cell case 21, 22... Storage compartments 23, 24, 25, 26... Opposing section (side wall) 23a, 24a, 25a, 26a...Opposing surface 27…Joint part 27a...joint surface 27b... Laser welding line 28...Sealant 29…Bulkhead 30…Case body 31…Side part 32...First end face 33...Second end face 34...Top section 35…Bottom part 36... Boss section 36a... Boss Department 36b... Boss section small 36c...Base part 37...Head 37c...Tapered section 37d...Large diameter section 37e…Protrusion 37f...winding section 37g...Tip 37h…Proximal end 38…Through section (shaft section) 39…Opening 40…Lid 40a…Outer surface 40b…Inner surface 41... Boss Hole 41a...Large boss hole 41b... Small boss hole 42... Seat part 42a...Tapered section 42b...Large diameter section forming part 42c...Protrusion forming part 42d... Protruding part housing 42e...Wrap-around section forming section 42f... Winding section housing section 42g…implanted portion 43…recess 50…External positive terminal 52...External negative terminal 60... Insulating cover 70... Heat crimping machine 71... Head 72... Impulse heater 73...Air nozzle 80… Laser welding machine 81… Laser light X...Width direction (longest direction) Y...Length direction Z...Thickness direction

Claims

1. A secondary battery comprising a cell case made of thermoplastic resin, which consists of a box-shaped case body having an opening and a lid that seals the opening, The case body comprises a boss portion having a through portion that penetrates the lid and a head portion that is continuous with the through portion and exposed to the outside of the cell case, having a larger outer diameter than the through portion. The lid is provided with a boss hole through which the boss portion passes, The boss hole has a seat portion on the outside of the lid into which the head portion of the boss portion is housed. A sealing material is provided between the head portion and the seat portion to airtightly seal the head portion and the seat portion. A secondary battery characterized in that the exposed joint between the lid and the case body is welded together in such a way that it is airtightly sealed.

2. The head portion has a tapered shape in which its outer diameter increases towards the outside of the cell case. The secondary battery according to claim 1, characterized in that the boss hole has the seat portion corresponding to the tapered shape of the head.

3. The head portion has a large-diameter portion that is continuous with the tapered portion and has an outer diameter larger than the maximum outer diameter of the tapered portion. The secondary battery according to claim 2, characterized in that the seat portion has a shape corresponding to the shape of the head.

4. The boss portion is positioned on the periphery of the head and has a projection that protrudes from the periphery toward the interior of the cell case. The seat portion of the lid has a protrusion housing portion which is a space corresponding to the shape of the protrusion, The secondary battery according to claim 1, characterized in that the sealing material is disposed between the protruding portion and the lid so as to airtightly seal the protruding portion and the lid.

5. The protruding portion of the head has a winding portion at its end in the direction toward the inside of the cell case that protrudes in an annular shape in the direction of the central axis of the boss portion. The secondary battery according to claim 4, characterized in that the protruding portion housing portion has a winding portion housing portion which is a space corresponding to the shape of the winding portion of the head.

6. The secondary battery according to any one of claims 1 to 5, characterized in that the upper end of the head is arranged in the same plane as the lid.

7. The secondary battery according to any one of claims 1 to 5, characterized in that the upper end of the head is covered by the lid.

8. A method for manufacturing a secondary battery comprising a resin cell case consisting of a box-shaped case body having an opening and a lid that seals the opening, The case body has a boss portion that penetrates the lid, The lid has a boss hole through which the boss portion passes, and a seat portion on the outside of the lid with an inner diameter larger than the inner diameter of the boss hole. The seat portion is provided with a sealing material that is arranged to provide an airtight seal, The boss portion is passed through the boss hole, and the lid is assembled to the case body. The tip of the boss portion protruding from the boss hole is heat-crimped, and the seat portion is filled with molten resin via the sealing material, thereby forming a head portion with an outer diameter larger than the outer diameter of the shaft portion. A method for manufacturing a secondary battery, characterized by welding the exposed joint between the lid and the case body so as to be airtightly sealed.

9. The method for manufacturing a secondary battery according to claim 8, characterized in that the exposed joint between the lid and the case body is sealed by hermetically welding with a laser welding machine.

10. The seat portion has a tapered portion forming part, which has a tapered shape in which its outer diameter increases toward the outside of the cell case. The method for manufacturing a secondary battery according to claim 8, characterized in that the heat crimping process forms a tapered portion on the head, which has a tapered shape in which its outer diameter expands toward the outside of the cell case in accordance with the shape of the seat portion.

11. The seat portion is continuous with the tapered portion and has a large-diameter portion forming portion whose outer diameter is larger than the maximum outer diameter of the tapered portion. The method for manufacturing a secondary battery according to claim 10, characterized in that a large-diameter portion corresponding to the shape of the seat portion is formed on the head portion by the heat crimping.

12. The seat portion is positioned around the periphery of the head portion and has a projection-forming portion which is a space corresponding to the shape of a projection that protrudes from the periphery toward the interior of the cell case. The method for manufacturing a secondary battery according to claim 8, characterized in that the protrusion corresponding to the shape of the seat portion is formed on the head portion by the heat crimping.

13. The protruding portion forming part of the seat has a winding portion forming part at its end in the direction of the cell case, which protrudes in an annular shape in the direction of the central axis of the boss portion. The method for manufacturing a secondary battery according to claim 12, characterized in that a winding portion corresponding to the shape of the seat portion is formed on the head by the heat crimping.

14. A method for manufacturing a secondary battery according to any one of claims 8 to 13, characterized in that the upper end of the head is formed by the heat crimping so that it is arranged in the same plane as the lid.

15. The lid has a projection around the boss hole, A method for manufacturing a secondary battery according to any one of claims 8 to 13, characterized in that the upper end of the head is covered by the lid by the heat crimping method, thereby forming an embedded portion.

16. The secondary battery according to claim 1, characterized in that the boss portion is arranged on the end face of the wall of the case body on the opening side.

17. The secondary battery according to claim 1, characterized in that the boss portion is provided offset inward from the end face of the wall of the case body on the opening side of the case body.

18. The secondary battery according to claim 17, characterized in that the base end of the boss portion has a base portion that is continuous with the bottom surface of the case body opposite to the opening side.

19. The secondary battery according to claim 17, characterized in that the size of the boss portion is changed according to the load and according to the spacing between them.

20. The secondary battery according to claim 17, characterized in that the exposed joint between the lid and the case body is airtightly welded by irradiating laser light from the lid side with a laser welding machine, and the welding trajectory of the laser welding machine is a continuous trajectory at the peripheral edge of the end face on the opening side of the wall of the case body.

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