Secondary batteries

Abstract

To provide a secondary battery that is stably held when assembled into a battery module.SOLUTION: A secondary battery according to this disclosure includes a bottomed square cylindrical outer can having an opening, a power generation element housed in the outer can, a long plate-shaped sealing plate whose peripheral edge is welded to the opening over the entire circumference and seals the opening, a pair of external terminals for electrical connection to external equipment, which are electrically connected to the power generation element and are attached to the sealing plate by penetrating the sealing plate, and a plurality of insulators attached to at least the outer surface side of the sealing plate to electrically insulate the pair of external terminals and the sealing plate. The outer surface of the sealing plate has exposed regions not covered by the plurality of insulators at both longitudinal ends of the sealing plate. At least one of the two exposed areas has a flat area surrounded by grooves either continuously or discretely in the central part of the exposed area.SELECTED DRAWING: Figure 4

Description

【Technical Field】 【0001】 The present disclosure relates to secondary batteries. 【Background Art】 【0002】 Lithium secondary batteries using non-aqueous electrolytes (hereinafter also referred to as "secondary batteries") are used for in-vehicle applications, information and communication technologies (e.g., personal computers, smartphones, etc.), and power storage. When a large amount of power supply is required (e.g., when secondary batteries are used for in-vehicle applications), a plurality of secondary batteries are used in the form of a battery module. A battery module refers to a battery that joins a plurality of secondary batteries using mounting components to form one module. 【0003】 Patent Document 1 discloses a rectangular secondary battery 100. As shown in FIG. 11, the secondary battery 100 includes a rectangular box-shaped battery case body 110 having an opening 111 (hereinafter also referred to as "outer can 110"), an electrode body (not shown) housed inside the outer can 110, a long plate-shaped battery case lid 120 closing the opening 111 (hereinafter also referred to as "sealing plate 120"), a positive electrode terminal member 130 and a negative electrode terminal member 140 extending outside the secondary battery 100, and a plurality of insulating members 150. The plurality of insulating members 150 are interposed between the battery case lid 120 and each of the positive electrode terminal member 130 and the negative electrode terminal member 140. The peripheral edge P120 of the sealing plate 120 is welded to the opening 111 over the entire circumference of the peripheral edge P120. 【0004】 The positive electrode terminal member 130 includes a positive electrode connection member (not shown) electrically connected to the electrode body, a positive electrode external terminal member 131 electrically connected to the positive electrode connection member, and a positive electrode fastening bolt 132 electrically connected to the positive electrode external terminal member 131. The positive electrode connection member has a caulking portion 133. The caulking portion 133 indicates a disk-shaped portion whose diameter is expanded by pressing. The caulking portion 133 and the sealing plate 120 support the positive electrode external terminal member 131 and the insulating member 150 in a sandwiched state. 【0005】 The negative electrode terminal member 140 includes a negative electrode connecting member (not shown) electrically connected to the electrode body, a negative electrode external terminal member 141 electrically connected to the negative electrode connecting member, and a negative electrode fastening bolt 142 electrically connected to the negative electrode external terminal member 141. The negative electrode connecting member has a crimping portion 143. The crimping portion 143 is a disc-shaped portion that is expanded in diameter by pressing. The crimping portion 143 and the sealing plate 120 support the negative electrode external terminal member 141 and the insulating member 150 while sandwiching them. [Prior art documents] [Patent Documents] 【0006】 [Patent Document 1] Japanese Patent Publication No. 2015-111573 [Overview of the Initiative] [Problems that the invention aims to solve] 【0007】 In recent years, with the increasing demand for smaller battery modules, there has been a need to further reduce the dimensional tolerances of the components that make up the battery module, thereby saving space and lowering costs. Ensuring high precision in the external dimensions of secondary batteries has also become crucial. 【0008】 From the viewpoint of ensuring the external shape of the secondary battery, it is preferable that the portion of the outer surface of the sealing plate used during the assembly of the secondary battery (for example, the portion of the sealing plate 120 that comes into contact with the assembly jig when the sealing plate 120 with the electrode body attached is pressed against the assembly jig to house the electrode body inside the outer casing 110) and the portion of the outer surface of the sealing plate used for assembling the battery module (for example, the portion of the sealing plate 120 that comes into contact with the mounting parts) are the same. Furthermore, in order to prevent warping of the sealing plate, it is preferable that the aforementioned portion is at both ends of the outer surface of the sealing plate in the longitudinal direction of the sealing plate (exposed area SA shown in Figure 11). 【0009】 However, soft metals (such as aluminum) are often used as the material for the sealing plate. Therefore, the outer surface of the sealing plate used during the assembly of the secondary battery may be prone to distortion due to the load applied to the sealing plate during the assembly of the secondary battery. For example, when forming the crimped portion 133, a large load is likely to be applied to the area of ​​the sealing plate 120 where the crimped portion 133 is located. Therefore, the material in this area is likely to flow towards the peripheral edge P120 of the sealing plate 120 due to the load. As a result, the top surface of the exposed area SA may be distorted. In addition, when welding the peripheral edge P120 of the sealing plate 120 to the opening 111, the top surface of the exposed area SA may be distorted due to the heat of welding. 【0010】 As a result, when multiple secondary batteries are used in the form of a battery module, there is a risk that the secondary batteries may wobble relative to the mounting components. Therefore, there is a need for secondary batteries that suppress the occurrence of wobbling relative to the mounting components of the battery module when assembled into the battery module. In other words, there is a need for secondary batteries that are stably held when assembled into a battery module. 【0011】 This disclosure is made in light of the circumstances described above. One embodiment of this disclosure aims to solve the problem of providing a secondary battery that is stably held when assembled into a battery module. [Means for solving the problem] 【0012】 The following embodiments are included as means for solving the above problems. <1> A secondary battery according to a first aspect of the present disclosure comprises a bottomed rectangular tubular outer casing having an opening; a power generation element housed in the outer casing; a long plate-shaped sealing plate whose periphery is welded to the opening around its entire circumference to seal the opening; a pair of external terminals for electrically connecting to external equipment, which are electrically connected to the power generation element and are attached to the sealing plate through the sealing plate; and a plurality of insulators attached at least to the outer surface of the sealing plate to electrically insulate the pair of external terminals and the sealing plate, wherein the outer surface of the sealing plate has exposed areas at both ends in the longitudinal direction of the sealing plate that are not covered by the plurality of insulators, and at least one of the two exposed areas has a flat area in the central part of the exposed area that is continuously or discretely surrounded by grooves. 【0013】 In this disclosure, "power generation element" refers to a unit of the main component of a rechargeable secondary battery that supplies electrical energy through insertion and desorption reactions of metal ions, or oxidation and reduction reactions of lithium, which occur between a positive electrode and a negative electrode via an electrolyte. "Flat region continuously surrounded by grooves" indicates that the periphery of the flat region is surrounded by grooves. "Flat region discretely surrounded by grooves" indicates that the groove has multiple groove sections, and the periphery of the flat region is surrounded by multiple groove sections that are scattered apart from each other. "Flat region" refers to a planar region on which no grooves have been processed. 【0014】 In the secondary battery of the first embodiment, at least one of the two exposed regions has a flat region in the central part of the exposed region that is continuously or discretely surrounded by grooves. In other words, grooves are interposed between the flat region of the exposed region and the peripheral region located on the peripheral side with respect to the grooves that continuously or discretely surround the flat region. Therefore, the flat region is less likely to be distorted by the load applied to the sealing plate during the assembly of the secondary battery. Specifically, when forming the external terminals by crimping, a large load is likely to be applied to the region of the peripheral region of the sealing plate where the external terminals are located. However, because grooves are interposed between the peripheral region and the flat region, the material of the peripheral region is less likely to escape into the flat region. In other words, plastic flow from the outer surface of the peripheral region to the outer surface of the flat region due to crimping is less likely to occur. As a result, the outer surface of the flat region is less likely to be distorted by crimping. Furthermore, when welding the periphery of the sealing plate to the opening of the outer can, a groove is interposed between the periphery region and the flat region, so the flat region is less affected by the heat of welding. In other words, plastic flow from the outer surface of the periphery region to the outer surface of the flat region due to the heat of welding is less likely to occur. As a result, the outer surface of the flat region is less likely to be distorted by the heat of welding. As a result, the outer surface of the flat region is more likely to maintain its state before the secondary battery is assembled. Therefore, when the secondary battery of this disclosure is assembled into a battery module, the occurrence of fluctuations of the secondary battery relative to the mounting parts of the battery module is suppressed. In other words, the secondary battery of this disclosure is held stably. 【0015】 <2> A secondary battery according to a second aspect of the present disclosure has a groove comprising a pair of first grooves formed along the longitudinal direction of the sealing plate and a pair of second grooves formed along the short direction of the sealing plate, <1> This is a secondary battery as described in [the document]. 【0016】 In the second embodiment, the area of ​​the flat region can be made larger than in the case where the groove does not have a pair of first grooves and a pair of second grooves. As a result, the workability of assembling the secondary battery in the second embodiment is improved. 【0017】 <3> A secondary battery according to a third aspect of the present disclosure, wherein the outer surface of the sealing plate has a concave surface recessed with respect to the position of the flat region, the concave surface including a covering region covered by the insulator and a first groove of the pair of first grooves located on the central side of the sealing plate in the longitudinal direction of the sealing plate, <2> This is a secondary battery as described in [the document]. 【0018】 In the third embodiment, the length of the secondary battery in the thickness direction of the sealing plate is shorter than in the case where the outer surface of the sealing plate does not have a concave surface. Therefore, the secondary battery of the third embodiment can achieve a smaller battery module. 【0019】 <4> A secondary battery according to a fourth aspect of the present disclosure, wherein the length of the first groove located on the longitudinal central side of the sealing plate with respect to the flat region is longer than the length of the first groove located on the opposite side from the central side with respect to the flat region. <3> This is a secondary battery as described in [the document]. 【0020】 In the fourth embodiment, the length of the secondary battery in the thickness direction of the sealing plate is shorter than in the case where the length of the first groove located on the central side of the sealing plate with respect to the flat area is not longer than the length of the first groove located on the opposite side of the sealing plate with respect to the flat area. Therefore, the secondary battery of the fourth embodiment can achieve further miniaturization of the battery module. 【0021】 <5> A secondary battery according to a fifth aspect of the present disclosure further comprises a peripheral region located on the peripheral side of the sealing plate relative to the groove, wherein at least one of the two exposed regions is located on the peripheral side of the sealing plate relative to the groove, and the flat region and the peripheral region are located in the same plane. <1> ~ <4> It is a rechargeable battery as described in one of the following documents. 【0022】 In the fifth embodiment, when assembling the battery module, even if the mounting component comes into contact with the peripheral region of the exposed region when pressing the mounting component against the flat region, the outer surface of the flat region is less likely to be damaged than when the flat region and the peripheral region are not on the same plane. As a result, the secondary battery is held more stably when assembled into the battery module. [Effects of the Invention] 【0023】 According to the present disclosure, a secondary battery that is stably held when assembled to a battery module is provided. 【Brief Description of the Drawings】 【0024】 [Figure 1] FIG. 1 is a perspective view showing the appearance of a secondary battery according to the first embodiment. [Figure 2] FIG. 2 is an exploded perspective view of the secondary battery according to the first embodiment. [Figure 3] FIG. 3 is an exploded perspective view of a pair of external terminals, a sealing plate, and a plurality of insulators in the first embodiment. [Figure 4] FIG. 4 is a top view of the secondary battery according to the first embodiment. [Figure 5] FIG. 5 is a cross-sectional view taken along line C5-C5 of FIG. 4. [Figure 6] FIG. 6 is an exploded perspective view of a battery module using the secondary battery according to the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view taken along line C7-C7 of FIG. 7. [Figure 8] FIG. 8 is a top view of the secondary battery according to the second embodiment. [Figure 9] FIG. 9 is a cross-sectional view taken along line C9-C9 of FIG. 8. [Figure 10] FIG. 10 is a top view of the secondary battery according to the third embodiment. [Figure 11] FIG. 11 is a top view of a conventional secondary battery. 【Modes for Carrying Out the Invention】 【0025】 In the present disclosure, the numerical range indicated by “~” means a range including the numerical values described before and after “~” as the minimum value and the maximum value, respectively. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. 【0026】 Embodiments of the secondary battery of this disclosure will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and will not be repeated in the description. 【0027】 (1) First Embodiment As shown in Figures 1 to 3, the secondary battery 1A according to the first embodiment comprises a long plate-shaped sealing plate 10A, a bottomed rectangular tubular outer casing 20, a power generation element 30, a pair of external terminals 40, a plurality of insulators 50, and an insulating pouch 60 (see Figure 2). The sealing plate 10A is fixed to the outer casing 20. The power generation element 30 is housed in the insulating pouch 60 and then housed in the outer casing 20. The pair of external terminals 40 are electrically connected to the power generation element 30 and are fixed to the sealing plate 10A via the plurality of insulators 50. 【0028】 In the first embodiment, the side on which the sealing plate 10A of the secondary battery 1A is positioned is defined as the positive Z-axis direction (hereinafter also referred to as the "upper side"), and the opposite side is defined as the negative Z-axis direction (hereinafter also referred to as the "lower side"). One side of the longitudinal direction of the sealing plate 10A is defined as the positive X-axis direction (hereinafter also referred to as the "right side"), and the opposite side is defined as the negative X-axis direction (hereinafter also referred to as the "left side"). One side of the short direction of the sealing plate 10A is defined as the positive Y-axis direction (hereinafter also referred to as the "front side"), and the opposite side is defined as the negative Y-axis direction (hereinafter also referred to as the "rear side"). The X-axis, Y-axis, and Z-axis are all orthogonal to each other. Note that these orientations do not limit the orientation of the secondary battery of this disclosure when it is used. 【0029】 The secondary battery 1A is a rectangular lithium secondary battery using a non-aqueous electrolyte. Specifically, the secondary battery 1A supplies electrical energy through lithium ion insertion and deinsertion reactions that occur between the positive and negative electrodes. The size of the secondary battery 1A is not particularly limited. The length L1 (see Figure 1) in the vertical direction (Z-axis direction) of the secondary battery 1A is, for example, 6 cm to 7 cm. The length L2 (see Figure 1) in the horizontal direction (X-axis direction) of the secondary battery 1A is, for example, 11 cm to 14 cm. The length L3 (see Figure 1) in the front-to-back direction (Y-axis direction) of the secondary battery 1A is, for example, 1 cm to 1.5 cm. Applications of the secondary battery 1A include, for example, automotive applications, information and communication technology (e.g., personal computers, smartphones, etc.), and energy storage. Multiple secondary batteries 1A are preferably used in the form of a battery module. 【0030】 (1.1) Outer can The outer casing 20 houses the power generation element 30. The outer casing 20 has an opening 21 that is open on the top. As shown in Figure 2, the shape of the opening 21 from above is approximately rectangular. The longitudinal direction of the opening 21 is along the X-axis. The short direction of the opening 21 is along the Y-axis. The material of the outer casing 20 is metal (e.g., aluminum, copper, iron, or alloys thereof). 【0031】 (1.2) Sealing plate The sealing plate 10A seals the opening 21 of the outer container 20. The shape of the sealing plate 10A is a long plate, as shown in Figure 3. The periphery P10 of the sealing plate 10A is welded to the outer container 20. More specifically, the entire circumference of the periphery P10 of the sealing plate 10A is welded to the opening 21 of the outer container 20 by an energy beam. The energy beam includes laser beams and electron beams. 【0032】 The sealing plate 10A has a pair of through holes 11, a safety valve 12, a liquid injection hole 13, and a liquid injection plug 14. One of the pair of through holes 11 is located at the right end of the sealing plate 10A. The other of the pair of through holes 11 is located at the left end of the sealing plate 10A. The safety valve 12 is located in the center of the sealing plate 10A in the left-right direction. The liquid injection hole 13 is located between one of the pair of through holes 11 and the safety valve 12 in the left-right direction. The liquid injection plug 14 is attached to the liquid injection hole 13. The pair of through holes 11 are used to fix the pair of external terminals 40 to the sealing plate 10A. The safety valve 12 releases the gas inside the outer can 20 to the outside when the internal pressure of the outer can 20 reaches a predetermined pressure. The liquid injection hole 13 is used when injecting the non-aqueous electrolyte into the outer can. The liquid injection plug 14 seals the liquid injection hole 13. The material of the sealing plate 10A is metal (for example, aluminum, copper, iron, or alloys thereof). 【0033】 (1.3) Power generation elements The power generation element 30 comprises a flattened wound electrode body and a non-aqueous electrolyte. The wound electrode body has a positive electrode sheet, a negative electrode sheet, and a separator sheet, and the positive electrode sheet and the negative electrode sheet are stacked on top of each other via the separator sheet and wound around a winding axis. 【0034】 The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer supported on both sides of the positive electrode current collector. The positive electrode current collector is a metal foil (e.g., aluminum foil). The positive electrode active material layer contains a positive electrode active material and a positive electrode binder. The positive electrode active material is a material capable of intercalating and releasing lithium ions (e.g., LiNiO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The positive electrode binder is a fluororesin (e.g., polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, etc.) or polyvinyl acetate. The positive electrode active material layer may optionally contain conductive additives (e.g., acetylene black), thickeners, surfactants, dispersants, wetting agents, defoamers, etc. 【0035】 The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer supported on both sides of the negative electrode current collector. The negative electrode current collector may be copper foil or the like. The negative electrode active material layer contains a negative electrode active material and a negative electrode binder. The negative electrode active material is a substance capable of intercalating and releasing lithium ions (e.g., carbon materials (e.g., natural graphite, artificial graphite, etc.)). Examples include fluororesins (e.g., polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, etc.) and polyvinyl acetate. The positive electrode active material layer may optionally contain conductive additives (e.g., acetylene black), thickeners, surfactants, dispersants, wetting agents, defoamers, etc. 【0036】 A separator may be, for example, a porous resin plate. The material of the resin plate may be resin (e.g., polyethylene, polypropylene, etc.). 【0037】 Non-aqueous electrolytes contain an electrolyte and a non-aqueous solvent. Examples of electrolytes include lithium salts containing fluorine (e.g., lithium hexafluoride phosphate, lithium tetrafluoride borate, etc.) and lithium salts not containing fluorine (e.g., lithium perchlorate, lithium aluminate tetrachloride, etc.). Examples of non-aqueous solvents include cyclic carbonates (e.g., ethylene carbonate, etc.) and chain carbonates (e.g., dimethyl carbonate, ethyl methyl carbonate, etc.). Non-aqueous electrolytes may further contain additives (e.g., lithium bisoxalate borate, etc.). 【0038】 (1.4) External terminals A pair of external terminals 40 electrically connect the power generation element 30 to external equipment (not shown). One of the pair of external terminals 40 is a positive terminal, and the other is a negative terminal. The positive terminal is electrically connected to the positive current collector included in the power generation element 30. The negative terminal is electrically connected to the negative current collector included in the power generation element 30. 【0039】 Each of the pair of external terminals 40 has a current collection terminal 41, a terminal plate 42, and a bolt 43, as shown in Figure 3. The current collection terminal 41, terminal plate 42, and bolt 43 are fixed together to the sealing plate 10A by sandwiching the sealing plate 10A. 【0040】 The current collector terminal 41 has a shape that extends in the vertical direction. The lower end 411 of the current collector terminal 41 is located below the sealing plate 10A (i.e., inside the outer casing 20) and is electrically connected to the power generation element 30. The upper end 412 of the current collector terminal 41 protrudes upward from the outer surface S (upper main surface) of the sealing plate 10A through the through hole 11. 【0041】 The terminal plate 42 has a shape that extends in the left-right direction. The terminal plate 42 and the bolt 43 are located above the sealing plate 10A. One end of the terminal plate 42 in the left-right direction is electrically connected to the current collection terminal 41. Specifically, the upper end 412 of the current collection terminal 41 passes through one end of the terminal plate 42, and the tip of the upper end 412 is crimped (expanded in diameter). The other end of the terminal plate 42 in the left-right direction is electrically connected to the bolt 43. Specifically, the bolt 43 passes through the other end of the terminal plate 42 in the left-right direction. 【0042】 The materials of the current collection terminal 41, terminal plate 42, and bolt 43 are metals (for example, aluminum, copper, iron, or alloys thereof). 【0043】 (1.5) Insulator Multiple insulators 50 electrically insulate the sealing plate 10A from the pair of external terminals 40. As shown in Figure 3, the multiple insulators 50 include two gaskets 51 and two insulators 52. The gaskets 51 are located on the underside of the sealing plate 10A and are sandwiched and fixed between the sealing plate 10A and the current collector terminal 41. The insulators 52 are located on the upper side of the sealing plate 10A and are sandwiched and fixed between the sealing plate 10A and the terminal plate 42 and bolt 43. The gaskets 51 and insulators 52 are molded from resin. 【0044】 (1.6) Insulating packaging The insulating bag 60 electrically insulates the power generation element 30 from the sealing plate 10A and the outer container 20. The insulating bag 60 houses the power generation element 30. A portion of the insulating bag 60 may be welded to the power generation element 30. The insulating bag 60 is made of resin (for example, polyethylene, polypropylene, etc.). 【0045】 (1.7)Exposed area As shown in Figure 4, the outer surface S of the sealing plate 10A has exposed regions SA at both ends in the left-right direction that are not covered by the multiple insulators 50. Each of the two exposed regions SA has a flat region SA1, a groove SA2, and a peripheral region SA3. The groove SA2 surrounds the flat region SA1. The peripheral region SA3 surrounds the groove SA2. 【0046】 The flat region SA1 is continuously surrounded by the groove SA2 in the central part of the exposed region SA. The shape of the flat region SA1 when viewed from the top to the bottom is rectangular. The length L4 (see Figure 4) of the flat region SA1 in the left-right direction is, for example, 0.5 cm to 0.8 cm. The length L5 (see Figure 4) of the flat region SA1 in the front-back direction is, for example, 0.8 cm to 1.1 cm. 【0047】 The shape of groove SA2 when viewed from the top to the bottom is rectangular. Groove SA2 has a pair of first grooves SA21 formed along the longitudinal direction (left-right direction) of the sealing plate 10A, and a pair of second grooves SA22 formed along the short direction (front-back direction) of the sealing plate 10A. The pair of first grooves SA21 and the pair of second grooves SA22 constitute one annular groove. The cross-sectional shape of groove SA2 is rectangular, as shown in Figure 5. The length L7 in the front-back direction of the first grooves SA21 (see Figure 4) is, for example, 0.02 cm to 0.08 cm. The length L8 in the left-right direction of the second grooves SA22 (see Figure 4) is, for example, 0.02 cm to 0.08 cm. Lengths L7 and L8 may be the same or different. The vertical length L9 (see Figure 5) of the first groove SA21 and the second groove SA22 is, for example, 0.01 cm to 0.04 cm. 【0048】 It is preferable that the groove SA2 is formed by press-forming an unpressed sealing plate that does not have the groove SA2 formed therein. The structure of the unpressed sealing plate is the same as that of the sealing plate 10A, except that it does not have the groove SA2. When the unpressed sealing plate is press-formed using a mold, the area of ​​the unpressed sealing plate corresponding to the groove SA2 is crushed. In other words, the metal filling rate in the mold increases. As a result, the flatness of the flat region SA1 improves. Furthermore, as the metal filling rate increases, the metal density of the flat region SA1 increases. In other words, the hardness of the flat region SA1 improves. As a result, when assembling the secondary battery 1A, the outer surface S of the flat region SA1 is less likely to deform. 【0049】 The peripheral region SA3 is located on the peripheral P10 side of the sealing plate 10A relative to the groove SA2. The flat region SA1 and the peripheral region SA3 are located on the same plane. 【0050】 (1.8) Usage Multiple secondary batteries 1A are preferably used in a battery module 2, as shown in Figure 6. The battery module 2 comprises multiple secondary batteries 1A and multiple mounting parts 90. In the battery module 2, the secondary batteries 1A and the mounting parts 90 are stacked alternately along the front-rear direction. The mounting parts 90 are substantially plate-shaped. In the battery module 2, the mounting parts 90 have a pair of contact parts 91 that physically contact each of a pair of flat regions SA1 of the secondary batteries 1A, and a main body part 92. The mounting parts 90 are molded resin bodies. 【0051】 (1.9) Effects As explained with reference to Figures 1 to 7, the secondary battery 1A comprises an outer casing 20, a power generation element 30, a sealing plate 10A, a pair of external terminals 40, and a plurality of insulators 50. The outer surface S of the sealing plate 10A has exposed regions SA at both ends in the longitudinal direction of the sealing plate 10A. The two exposed regions SA have a flat region SA1 in the center of the exposed regions SA that is continuously surrounded by a groove SA2. In other words, in the secondary battery 1A, a groove SA2 is interposed between the flat region SA1 and the peripheral region SA3. Therefore, the flat region SA1 is less likely to be distorted by the load applied to the sealing plate 10A during the assembly of the secondary battery 1A. Specifically, when the current collection terminal 41 and the terminal plate 42 are integrated by crimping the tip of the upper end 412, a large load is likely to be applied to the region of the peripheral region SA3 of the sealing plate 10A where the terminal plate 42 is located. However, because a groove is interposed between the peripheral region SA3 and the flat region SA1, the material of the peripheral region SA3 is less likely to escape into the flat region SA1. In other words, plastic flow from the outer surface S of the peripheral region SA3 to the outer surface S of the flat region SA1 due to the crimping process is less likely to occur. As a result, the outer surface S of the flat region SA1 is less likely to be distorted by the crimping process. Furthermore, when welding the peripheral edge P10 of the sealing plate 10A to the opening 21 of the outer can 20, a groove SA2 is interposed between the peripheral region SA3 and the flat region SA1, so the flat region SA1 is less affected by the heat of welding. In other words, plastic flow from the outer surface S of the peripheral region SA3 to the outer surface S of the flat region SA1 due to the heat of welding is unlikely to occur. As a result, the outer surface S of the flat region SA1 is less likely to be distorted by the heat of welding. As a result, the outer surface S of the flat region SA1 is more likely to maintain its state before assembly of the secondary battery 1A during assembly of the secondary battery 1A. Therefore, when the secondary battery 1A is assembled into the battery module 2, the occurrence of fluctuations of the secondary battery 1A relative to the mounting parts 90 of the battery module 2 is suppressed. In other words, the secondary battery 1A is held stably. 【0052】 As explained with reference to Figures 1 to 7, in secondary battery 1A, groove SA2 has a pair of first grooves SA21 and a pair of second grooves SA22. As a result, the area of ​​the flat region SA1 can be made larger than when the groove SA2 does not have a pair of first grooves SA21 and a pair of second grooves SA22. This improves the workability of assembling the secondary battery 1A. 【0053】 As explained with reference to Figures 1 to 7, in secondary battery 1A, the two exposed regions SA further have a peripheral region SA3, and the flat region SA1 and the peripheral region SA3 are located on the same plane. As a result, when assembling the battery module 2, even if the mounting component 90 comes into contact with the peripheral region SA3 of the exposed region SA when the contact portion 91 of the mounting component 90 is pressed against the flat region SA1, the outer surface S of the flat region SA1 is less likely to be damaged than when the flat region SA1 and the peripheral region SA3 are not on the same plane. As a result, the secondary battery 1A is held more stably when assembled into the battery module 2. 【0054】 (2) Second Embodiment The secondary battery 1B according to the second embodiment is similar to the secondary battery 1A according to the first embodiment, except that the outer surface of the sealing plate has a concave surface. The secondary battery 1B comprises a long plate-shaped sealing plate 10B, an outer casing 20, a power generation element 30, a pair of external terminals 40, a plurality of insulators 50, and an insulating bag 60. The sealing plate 10B has a pair of through holes 11, a safety valve 12, a liquid injection hole 13, and a liquid injection plug 14. 【0055】 (2.1)Exposed area As shown in Figure 8, the outer surface S of the sealing plate 10B has exposed regions SA at both ends in the left-right direction. Each of the two exposed regions SA has a flat region SA1, a groove SA2B, and a peripheral region SA3. The groove SA2B surrounds the flat region SA1. The peripheral region SA3 is located on the peripheral P10 side of the sealing plate 10B relative to the groove SA2B. 【0056】 The groove SA2B has a pair of first grooves SA21 formed along the longitudinal direction (left-right direction) of the sealing plate 10B, and a third groove SA23 and a fourth groove SA24 formed along the short direction (front-back direction) of the sealing plate 10B. The third groove SA23 is located on the central side of the sealing plate 10B in the longitudinal direction (left-right direction) of the third groove SA23 and the fourth groove SA24. The fourth groove SA24 is located on the opposite side of the sealing plate 10B from the central side in the longitudinal direction (left-right direction) of the third groove SA23 and the fourth groove SA24. The cross-sectional shape of the third groove SA23 and the fourth groove SA24 is rectangular, as shown in Figure 9. The length L10 of the third groove SA23 relative to the flat region SA1 (see Figure 9) is longer than the length L9 of the fourth groove SA24 relative to the flat region SA1 (see Figure 9). 【0057】 (2.2) Concave As shown in Figure 8, the outer surface S of the sealing plate 10B has a pair of concave surfaces SB located towards the center in the longitudinal direction (left-right direction) relative to the two exposed regions SA. The concave surfaces SB are recessed in the vertical direction relative to the position of the flat region SA1. The concave surfaces SB include the covering region SB1 and the third groove SA23. The covering region SB1 is covered by the insulator 52. 【0058】 (2.3) Effects As described with reference to Figures 8 and 9, the secondary battery 1B comprises an outer casing 20, a power generation element 30, a sealing plate 10B, a pair of external terminals 40, and a plurality of insulators 50. The outer surface S of the sealing plate 10B has exposed regions SA at both ends in the longitudinal direction of the sealing plate 10B. The two exposed regions SA have a flat region SA1 in the center of the exposed regions SA that is continuously surrounded by a groove SA2. This ensures that the secondary battery 1B is stably held when assembled into the battery module 2. 【0059】 As explained with reference to Figures 8 and 9, in the secondary battery 1B, the outer surface of the sealing plate 10B has a concave surface SB, and the concave surface SB includes a covering area SB1 and a third groove SA23. As a result, the length of the secondary battery 1B in the thickness direction (vertical direction) of the sealing plate 10B is shorter than when the outer surface S of the sealing plate 10B does not have a concave surface SB. Therefore, the secondary battery 1B enables a smaller battery module 2. 【0060】 As explained with reference to Figures 8 and 9, in secondary battery 1B, the length L10 of the third groove SA23 relative to the flat region SA1 is longer than the length L9 of the fourth groove S24 relative to the flat region SA1. As a result, in the thickness direction (vertical direction) of the sealing plate 10B, the length of the secondary battery 1B is shorter than when the length L10 is not greater than the length L9. Therefore, the secondary battery 1B enables further miniaturization of the battery module 2. 【0061】 (3) Third Embodiment The secondary battery 1C according to the third embodiment is similar to the secondary battery 1A according to the first embodiment, except that the flat region is not continuously surrounded by grooves. As shown in Figure 10, the secondary battery 1C comprises a long plate-shaped sealing plate 10C, an outer casing 20, a power generation element 30, a pair of external terminals 40, a plurality of insulators 50, and an insulating bag 60. The sealing plate 10C has a pair of through holes 11, a safety valve 12, a liquid injection hole 13, and a liquid injection plug 14. 【0062】 (3.1)Exposed area The outer surface S of the sealing plate 10C has exposed regions SA at both ends in the left-right direction. Each of the two exposed regions SA has a flat region SA1, a groove SA2C, and a peripheral region SA3. The groove SA2C surrounds the flat region SA1. The peripheral region SA3 surrounds the groove SA2C. 【0063】 The flat region SA1 is discretely surrounded by grooves SA2C in the central part of the exposed region SA. The groove SA2C has a pair of fifth grooves SA25 formed along the longitudinal direction (left-right direction) of the sealing plate 10C, and a pair of second grooves SA26 formed along the short direction (front-back direction) of the sealing plate 10C. The pair of fifth grooves SA25 and the pair of second grooves SA26 do not constitute a single annular groove. The peripheral region SA3 is located on the peripheral P10 side of the sealing plate 10C relative to the groove SA2C. The flat region SA1 and the peripheral region SA3 are located on the same plane. 【0064】 (3.2) Effects As explained with reference to Figure 10, the secondary battery 1C comprises an outer casing 20, a power generation element 30, a sealing plate 10C, a pair of external terminals 40, and a plurality of insulators 50. The outer surface S of the sealing plate 10C has exposed regions SA at both ends in the longitudinal direction of the sealing plate 10C. The two exposed regions SA have a flat region SA1 discretely surrounded by grooves SA2C in the center of the exposed regions SA. This ensures that the secondary battery 1C is stably held when assembled into the battery module 2. 【0065】 Embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention. The drawings schematically show each component in order to facilitate understanding, and the thickness, length, number, etc. of each component shown may differ from the actual dimensions due to the convenience of drawing creation. Furthermore, the material, shape, dimensions, etc. of each component shown in the above embodiments are examples and are not particularly limited, and various modifications are possible without substantially departing from the effects of the present invention. 【0066】 (4) Variations In the first to third embodiments, the groove has a pair of first grooves formed along the longitudinal direction of the sealing plate and a pair of second grooves formed along the short direction of the sealing plate, but it is not necessary to have the first grooves and second grooves. The shape of the groove when viewed from the top to the bottom may be circular, polygonal (for example, triangular, pentagonal, hexagonal, etc.), or irregular in shape. 【0067】 In the second embodiment, the length of the flat region of the first groove located on the longitudinal central side of the sealing plate is longer than the length of the flat region of the first groove located on the opposite side from the central side, but it does not have to be longer than the length of the flat region of the first groove located on the opposite side from the central side. 【0068】 In the first to third embodiments, the flat region and the peripheral region are located on the same plane, but the flat region and the peripheral region do not necessarily have to be located on the same plane. 【0069】 In the first to third embodiments, the secondary battery is a lithium secondary battery using a non-aqueous electrolyte, but it may also be a lithium secondary battery using a solid electrolyte or gel electrolyte, a magnesium ion secondary battery, or a sodium ion secondary battery. 【0070】 In the first to third embodiments, the secondary battery is provided with an insulating bag, but it is not required to have an insulating bag. If the secondary battery is not provided with an insulating bag, an insulating film may be attached to the inner wall of the outer casing. 【0071】 In the first to third embodiments, the power generation element includes a wound electrode body, but a laminated electrode body may be provided instead of the wound electrode body. In the laminated electrode body, each of the positive electrode sheet, separator sheet, and negative electrode sheet has a single-sheet shape, and these sheets are laminated in this order. 【0072】 In the first to third embodiments, the cross-sectional shape of the groove is rectangular, but it may also be U-shaped, V-shaped, semicircular, or semi-elliptical.

Claims

[Claim 1] A bottomed rectangular tubular outer can with an opening, The power generation element housed in the aforementioned outer casing, A long plate-shaped sealing plate whose periphery is welded to the opening all around, and which seals the opening, A pair of external terminals for electrically connecting to external equipment are electrically connected to the power generation element and are attached to the sealing plate by penetrating the sealing plate, A plurality of insulators attached to at least the outer surface of the sealing plate to electrically insulate the pair of external terminals and the sealing plate, Equipped with, The outer surface of the sealing plate has exposed areas at both ends in the longitudinal direction of the sealing plate that are not covered by the plurality of insulators. At least one of the two exposed regions has a flat region in the central part of the exposed region that is continuously or discretely surrounded by grooves, The groove, A pair of first grooves formed along the longitudinal direction of the sealing plate, A pair of second grooves formed along the shorter direction of the sealing plate, It has, A secondary battery in which the groove surrounds only the flat region. [Claim 2] A bottomed rectangular tubular outer can having an opening, The power generation element housed in the aforementioned outer casing, A long plate-shaped sealing plate whose periphery is welded to the opening all around, and which seals the opening, A pair of external terminals for electrically connecting to external equipment are electrically connected to the power generation element and are attached to the sealing plate by penetrating the sealing plate, A plurality of insulators attached to at least the outer surface of the sealing plate to electrically insulate the pair of external terminals and the sealing plate, Equipped with, The outer surface of the sealing plate has exposed areas at both ends in the longitudinal direction of the sealing plate that are not covered by the plurality of insulators. At least one of the two exposed regions has a flat region in the central part of the exposed region that is continuously or discretely surrounded by grooves, The groove, A pair of first grooves formed along the longitudinal direction of the sealing plate, A pair of second grooves formed along the shorter direction of the sealing plate, It has, The outer surface of the sealing plate has a concave surface that is recessed relative to the position of the flat region, The aforementioned concave surface, The covering region covered by the insulator, Of the pair of second grooves, a third groove indicates the second groove located on the central side of the sealing plate in the longitudinal direction of the sealing plate, Rechargeable batteries, including those mentioned above. [Claim 3] The secondary battery according to claim 2, wherein when the secondary battery is cut in a plane perpendicular to the short direction, the length of the third groove located on the central side in the longitudinal direction of the sealing plate with respect to the outer surface of the flat area is longer than the length of the fourth groove indicating the second groove located on the opposite side from the central side with respect to the outer surface of the flat area.

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